/* 
 * tclIO.c --
 *
 *	This file provides the generic portions (those that are the same on
 *	all platforms and for all channel types) of Tcl's IO facilities.
 *
 * Copyright (c) 1998-2000 Ajuba Solutions
 * Copyright (c) 1995-1997 Sun Microsystems, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution
 * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 *
 * RCS: @(#) $Id: tclIO.c,v 1.81 2004/11/30 19:34:47 dgp Exp $
 */

#include "tclInt.h"
#include "tclIO.h"
#include <assert.h>


/*
 * All static variables used in this file are collected into a single
 * instance of the following structure.  For multi-threaded implementations,
 * there is one instance of this structure for each thread.
 *
 * Notice that different structures with the same name appear in other
 * files.  The structure defined below is used in this file only.
 */

typedef struct ThreadSpecificData {
    /*
     * This variable holds the list of nested ChannelHandlerEventProc 
     * invocations.
     */
    NextChannelHandler *nestedHandlerPtr;

    /*
     * List of all channels currently open, indexed by ChannelState,
     * as only one ChannelState exists per set of stacked channels.
     */
    ChannelState *firstCSPtr;

#ifdef oldcode
    /*
     * Has a channel exit handler been created yet?
     */
    int channelExitHandlerCreated;

    /*
     * Has the channel event source been created and registered with the
     * notifier?
     */
    int channelEventSourceCreated;
#endif

    /*
     * Static variables to hold channels for stdin, stdout and stderr.
     */
    Tcl_Channel stdinChannel;
    int stdinInitialized;
    Tcl_Channel stdoutChannel;
    int stdoutInitialized;
    Tcl_Channel stderrChannel;
    int stderrInitialized;

} ThreadSpecificData;

static Tcl_ThreadDataKey dataKey;

/*
 * Static functions in this file:
 */

static ChannelBuffer *	AllocChannelBuffer _ANSI_ARGS_((int length));
static void		ChannelTimerProc _ANSI_ARGS_((
			    ClientData clientData));
static int		CheckChannelErrors _ANSI_ARGS_((ChannelState *statePtr,
			    int direction));
static int		CheckFlush _ANSI_ARGS_((Channel *chanPtr,
			    ChannelBuffer *bufPtr, int newlineFlag));
static int		CheckForDeadChannel _ANSI_ARGS_((Tcl_Interp *interp,
			    ChannelState *statePtr));
static void		CheckForStdChannelsBeingClosed _ANSI_ARGS_((
			    Tcl_Channel chan));
static void		CleanupChannelHandlers _ANSI_ARGS_((
			    Tcl_Interp *interp, Channel *chanPtr));
static int		CloseChannel _ANSI_ARGS_((Tcl_Interp *interp,
			    Channel *chanPtr, int errorCode));
static void		CommonGetsCleanup _ANSI_ARGS_((Channel *chanPtr,
			    Tcl_Encoding encoding));
static int		CopyAndTranslateBuffer _ANSI_ARGS_((
			    ChannelState *statePtr, char *result, int space));
static int		CopyBuffer _ANSI_ARGS_((Channel *chanPtr,
			    char *result, int space));
static int		CopyData _ANSI_ARGS_((CopyState *csPtr, int mask));
static void		CopyEventProc _ANSI_ARGS_((ClientData clientData,
			    int mask));
static void		CreateScriptRecord _ANSI_ARGS_((Tcl_Interp *interp,
			    Channel *chanPtr, int mask, Tcl_Obj *scriptPtr));
static void		DeleteChannelTable _ANSI_ARGS_((
			    ClientData clientData, Tcl_Interp *interp));
static void		DeleteScriptRecord _ANSI_ARGS_((Tcl_Interp *interp,
			    Channel *chanPtr, int mask));
static int		DetachChannel _ANSI_ARGS_((Tcl_Interp *interp,
			    Tcl_Channel chan));
static void		DiscardInputQueued _ANSI_ARGS_((ChannelState *statePtr,
			    int discardSavedBuffers));
static void		DiscardOutputQueued _ANSI_ARGS_((
			    ChannelState *chanPtr));
static int		DoRead _ANSI_ARGS_((Channel *chanPtr, char *srcPtr,
			    int slen));
static int		DoWrite _ANSI_ARGS_((Channel *chanPtr, CONST char *src,
			    int srcLen));
static int		DoReadChars _ANSI_ARGS_((Channel *chan,
			    Tcl_Obj *objPtr, int toRead, int appendFlag));
static int		DoWriteChars _ANSI_ARGS_((Channel *chan,
			    CONST char *src, int len));
static int		FilterInputBytes _ANSI_ARGS_((Channel *chanPtr,
			    GetsState *statePtr));
static int		FlushChannel _ANSI_ARGS_((Tcl_Interp *interp,
			    Channel *chanPtr, int calledFromAsyncFlush));
static Tcl_HashTable *	GetChannelTable _ANSI_ARGS_((Tcl_Interp *interp));
static int		GetInput _ANSI_ARGS_((Channel *chanPtr));
static int		HaveVersion _ANSI_ARGS_((Tcl_ChannelType *typePtr,
			    Tcl_ChannelTypeVersion minimumVersion));
static void		PeekAhead _ANSI_ARGS_((Channel *chanPtr,
			    char **dstEndPtr, GetsState *gsPtr));
static int		ReadBytes _ANSI_ARGS_((ChannelState *statePtr,
			    Tcl_Obj *objPtr, int charsLeft, int *offsetPtr));
static int		ReadChars _ANSI_ARGS_((ChannelState *statePtr,
			    Tcl_Obj *objPtr, int charsLeft,
			    int *offsetPtr, int *factorPtr));
static void		RecycleBuffer _ANSI_ARGS_((ChannelState *statePtr,
			    ChannelBuffer *bufPtr, int mustDiscard));
static int		StackSetBlockMode _ANSI_ARGS_((Channel *chanPtr,
			    int mode));
static int		SetBlockMode _ANSI_ARGS_((Tcl_Interp *interp,
			    Channel *chanPtr, int mode));
static void		StopCopy _ANSI_ARGS_((CopyState *csPtr));
static int		TranslateInputEOL _ANSI_ARGS_((ChannelState *statePtr,
			    char *dst, CONST char *src,
			    int *dstLenPtr, int *srcLenPtr));
static int		TranslateOutputEOL _ANSI_ARGS_((ChannelState *statePtr,
			    char *dst, CONST char *src,
			    int *dstLenPtr, int *srcLenPtr));
static void		UpdateInterest _ANSI_ARGS_((Channel *chanPtr));
static int		WriteBytes _ANSI_ARGS_((Channel *chanPtr,
			    CONST char *src, int srcLen));
static int		WriteChars _ANSI_ARGS_((Channel *chanPtr,
			    CONST char *src, int srcLen));

/*
 *---------------------------------------------------------------------------
 *
 * TclInitIOSubsystem --
 *
 *	Initialize all resources used by this subsystem on a per-process
 *	basis.  
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Depends on the memory subsystems.
 *
 *---------------------------------------------------------------------------
 */

void
TclInitIOSubsystem()
{
    /*
     * By fetching thread local storage we take care of
     * allocating it for each thread.
     */
    (void) TCL_TSD_INIT(&dataKey);
}   

/*
 *-------------------------------------------------------------------------
 *
 * TclFinalizeIOSubsystem --
 *
 *	Releases all resources used by this subsystem on a per-process 
 *	basis.  Closes all extant channels that have not already been 
 *	closed because they were not owned by any interp.  
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Depends on encoding and memory subsystems.
 *
 *-------------------------------------------------------------------------
 */

	/* ARGSUSED */
void
TclFinalizeIOSubsystem()
{
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
    Channel *chanPtr;			/* Iterates over open channels. */
    ChannelState *nextCSPtr;		/* Iterates over open channels. */
    ChannelState *statePtr;		/* state of channel stack */

    for (statePtr = tsdPtr->firstCSPtr; statePtr != (ChannelState *) NULL;
	    statePtr = nextCSPtr) {
	chanPtr = statePtr->topChanPtr;
	nextCSPtr = statePtr->nextCSPtr;

	/*
	 * Set the channel back into blocking mode to ensure that we wait
	 * for all data to flush out.
	 */

	(void) Tcl_SetChannelOption(NULL, (Tcl_Channel) chanPtr,
		"-blocking", "on");

	if ((chanPtr == (Channel *) tsdPtr->stdinChannel) ||
		(chanPtr == (Channel *) tsdPtr->stdoutChannel) ||
		(chanPtr == (Channel *) tsdPtr->stderrChannel)) {

	    /*
	     * Decrement the refcount which was earlier artificially bumped
	     * up to keep the channel from being closed.
	     */

	    statePtr->refCount--;
	}

	if (statePtr->refCount <= 0) {

	    /*
	     * Close it only if the refcount indicates that the channel is not
	     * referenced from any interpreter. If it is, that interpreter will
	     * close the channel when it gets destroyed.
	     */

	    (void) Tcl_Close((Tcl_Interp *) NULL, (Tcl_Channel) chanPtr);

	} else {

	    /*
	     * The refcount is greater than zero, so flush the channel.
	     */

	    Tcl_Flush((Tcl_Channel) chanPtr);

	    /*
	     * Call the device driver to actually close the underlying
	     * device for this channel.
	     */

	    if (chanPtr->typePtr->closeProc != TCL_CLOSE2PROC) {
		(chanPtr->typePtr->closeProc)(chanPtr->instanceData,
			(Tcl_Interp *) NULL);
	    } else {
		(chanPtr->typePtr->close2Proc)(chanPtr->instanceData,
			(Tcl_Interp *) NULL, 0);
	    }

	    /*
	     * Finally, we clean up the fields in the channel data structure
	     * since all of them have been deleted already. We mark the
	     * channel with CHANNEL_DEAD to prevent any further IO operations
	     * on it.
	     */

	    chanPtr->instanceData = (ClientData) NULL;
	    statePtr->flags |= CHANNEL_DEAD;
	}
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_SetStdChannel --
 *
 *	This function is used to change the channels that are used
 *	for stdin/stdout/stderr in new interpreters.
 *
 * Results:
 *	None
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_SetStdChannel(channel, type)
    Tcl_Channel channel;
    int type;			/* One of TCL_STDIN, TCL_STDOUT, TCL_STDERR. */
{
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
    switch (type) {
	case TCL_STDIN:
	    tsdPtr->stdinInitialized = 1;
	    tsdPtr->stdinChannel = channel;
	    break;
	case TCL_STDOUT:
	    tsdPtr->stdoutInitialized = 1;
	    tsdPtr->stdoutChannel = channel;
	    break;
	case TCL_STDERR:
	    tsdPtr->stderrInitialized = 1;
	    tsdPtr->stderrChannel = channel;
	    break;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetStdChannel --
 *
 *	Returns the specified standard channel.
 *
 * Results:
 *	Returns the specified standard channel, or NULL.
 *
 * Side effects:
 *	May cause the creation of a standard channel and the underlying
 *	file.
 *
 *----------------------------------------------------------------------
 */

Tcl_Channel
Tcl_GetStdChannel(type)
    int type;			/* One of TCL_STDIN, TCL_STDOUT, TCL_STDERR. */
{
    Tcl_Channel channel = NULL;
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

    /*
     * If the channels were not created yet, create them now and
     * store them in the static variables. 
     */

    switch (type) {
	case TCL_STDIN:
	    if (!tsdPtr->stdinInitialized) {
		tsdPtr->stdinChannel = TclpGetDefaultStdChannel(TCL_STDIN);
		tsdPtr->stdinInitialized = 1;

		/*
		 * Artificially bump the refcount to ensure that the channel
		 * is only closed on exit.
		 *
		 * NOTE: Must only do this if stdinChannel is not NULL. It
		 * can be NULL in situations where Tcl is unable to connect
		 * to the standard input.
		 */

		if (tsdPtr->stdinChannel != (Tcl_Channel) NULL) {
		    (void) Tcl_RegisterChannel((Tcl_Interp *) NULL,
			    tsdPtr->stdinChannel);
		}
	    }
	    channel = tsdPtr->stdinChannel;
	    break;
	case TCL_STDOUT:
	    if (!tsdPtr->stdoutInitialized) {
		tsdPtr->stdoutChannel = TclpGetDefaultStdChannel(TCL_STDOUT);
		tsdPtr->stdoutInitialized = 1;
		if (tsdPtr->stdoutChannel != (Tcl_Channel) NULL) {
		    (void) Tcl_RegisterChannel((Tcl_Interp *) NULL,
			    tsdPtr->stdoutChannel);
		}
	    }
	    channel = tsdPtr->stdoutChannel;
	    break;
	case TCL_STDERR:
	    if (!tsdPtr->stderrInitialized) {
		tsdPtr->stderrChannel = TclpGetDefaultStdChannel(TCL_STDERR);
		tsdPtr->stderrInitialized = 1;
		if (tsdPtr->stderrChannel != (Tcl_Channel) NULL) {
		    (void) Tcl_RegisterChannel((Tcl_Interp *) NULL,
			    tsdPtr->stderrChannel);
		}
	    }
	    channel = tsdPtr->stderrChannel;
	    break;
    }
    return channel;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_CreateCloseHandler
 *
 *	Creates a close callback which will be called when the channel is
 *	closed.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Causes the callback to be called in the future when the channel
 *	will be closed.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_CreateCloseHandler(chan, proc, clientData)
    Tcl_Channel chan;		/* The channel for which to create the
				 * close callback. */
    Tcl_CloseProc *proc;	/* The callback routine to call when the
				 * channel will be closed. */
    ClientData clientData;	/* Arbitrary data to pass to the
				 * close callback. */
{
    ChannelState *statePtr;
    CloseCallback *cbPtr;

    statePtr = ((Channel *) chan)->state;

    cbPtr = (CloseCallback *) ckalloc((unsigned) sizeof(CloseCallback));
    cbPtr->proc = proc;
    cbPtr->clientData = clientData;

    cbPtr->nextPtr = statePtr->closeCbPtr;
    statePtr->closeCbPtr = cbPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_DeleteCloseHandler --
 *
 *	Removes a callback that would have been called on closing
 *	the channel. If there is no matching callback then this
 *	function has no effect.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The callback will not be called in the future when the channel
 *	is eventually closed.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_DeleteCloseHandler(chan, proc, clientData)
    Tcl_Channel chan;		/* The channel for which to cancel the
				 * close callback. */
    Tcl_CloseProc *proc;	/* The procedure for the callback to
				 * remove. */
    ClientData clientData;	/* The callback data for the callback
				 * to remove. */
{
    ChannelState *statePtr;
    CloseCallback *cbPtr, *cbPrevPtr;

    statePtr = ((Channel *) chan)->state;
    for (cbPtr = statePtr->closeCbPtr, cbPrevPtr = (CloseCallback *) NULL;
	    cbPtr != (CloseCallback *) NULL;
	    cbPtr = cbPtr->nextPtr) {
	if ((cbPtr->proc == proc) && (cbPtr->clientData == clientData)) {
	    if (cbPrevPtr == (CloseCallback *) NULL) {
		statePtr->closeCbPtr = cbPtr->nextPtr;
	    }
	    ckfree((char *) cbPtr);
	    break;
	} else {
	    cbPrevPtr = cbPtr;
	}
    }
}

/*
 *----------------------------------------------------------------------
 *
 * GetChannelTable --
 *
 *	Gets and potentially initializes the channel table for an
 *	interpreter. If it is initializing the table it also inserts
 *	channels for stdin, stdout and stderr if the interpreter is
 *	trusted.
 *
 * Results:
 *	A pointer to the hash table created, for use by the caller.
 *
 * Side effects:
 *	Initializes the channel table for an interpreter. May create
 *	channels for stdin, stdout and stderr.
 *
 *----------------------------------------------------------------------
 */

static Tcl_HashTable *
GetChannelTable(interp)
    Tcl_Interp *interp;
{
    Tcl_HashTable *hTblPtr;	/* Hash table of channels. */
    Tcl_Channel stdinChan, stdoutChan, stderrChan;

    hTblPtr = (Tcl_HashTable *) Tcl_GetAssocData(interp, "tclIO", NULL);
    if (hTblPtr == (Tcl_HashTable *) NULL) {
	hTblPtr = (Tcl_HashTable *) ckalloc((unsigned) sizeof(Tcl_HashTable));
	Tcl_InitHashTable(hTblPtr, TCL_STRING_KEYS);

	(void) Tcl_SetAssocData(interp, "tclIO",
		(Tcl_InterpDeleteProc *) DeleteChannelTable,
		(ClientData) hTblPtr);

	/*
	 * If the interpreter is trusted (not "safe"), insert channels
	 * for stdin, stdout and stderr (possibly creating them in the
	 * process).
	 */

	if (Tcl_IsSafe(interp) == 0) {
	    stdinChan = Tcl_GetStdChannel(TCL_STDIN);
	    if (stdinChan != NULL) {
		Tcl_RegisterChannel(interp, stdinChan);
	    }
	    stdoutChan = Tcl_GetStdChannel(TCL_STDOUT);
	    if (stdoutChan != NULL) {
		Tcl_RegisterChannel(interp, stdoutChan);
	    }
	    stderrChan = Tcl_GetStdChannel(TCL_STDERR);
	    if (stderrChan != NULL) {
		Tcl_RegisterChannel(interp, stderrChan);
	    }
	}
    }
    return hTblPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * DeleteChannelTable --
 *
 *	Deletes the channel table for an interpreter, closing any open
 *	channels whose refcount reaches zero. This procedure is invoked
 *	when an interpreter is deleted, via the AssocData cleanup
 *	mechanism.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Deletes the hash table of channels. May close channels. May flush
 *	output on closed channels. Removes any channeEvent handlers that were
 *	registered in this interpreter.
 *
 *----------------------------------------------------------------------
 */

static void
DeleteChannelTable(clientData, interp)
    ClientData clientData;	/* The per-interpreter data structure. */
    Tcl_Interp *interp;		/* The interpreter being deleted. */
{
    Tcl_HashTable *hTblPtr;	/* The hash table. */
    Tcl_HashSearch hSearch;	/* Search variable. */
    Tcl_HashEntry *hPtr;	/* Search variable. */
    Channel *chanPtr;		/* Channel being deleted. */
    ChannelState *statePtr;	/* State of Channel being deleted. */
    EventScriptRecord *sPtr, *prevPtr, *nextPtr;
    				/* Variables to loop over all channel events
				 * registered, to delete the ones that refer
				 * to the interpreter being deleted. */

    /*
     * Delete all the registered channels - this will close channels whose
     * refcount reaches zero.
     */

    hTblPtr = (Tcl_HashTable *) clientData;
    for (hPtr = Tcl_FirstHashEntry(hTblPtr, &hSearch);
	    hPtr != (Tcl_HashEntry *) NULL;
	    hPtr = Tcl_FirstHashEntry(hTblPtr, &hSearch)) {

	chanPtr = (Channel *) Tcl_GetHashValue(hPtr);
	statePtr = chanPtr->state;

	/*
	 * Remove any fileevents registered in this interpreter.
	 */

	for (sPtr = statePtr->scriptRecordPtr,
		prevPtr = (EventScriptRecord *) NULL;
		sPtr != (EventScriptRecord *) NULL;
		sPtr = nextPtr) {
	    nextPtr = sPtr->nextPtr;
	    if (sPtr->interp == interp) {
		if (prevPtr == (EventScriptRecord *) NULL) {
		    statePtr->scriptRecordPtr = nextPtr;
		} else {
		    prevPtr->nextPtr = nextPtr;
		}

		Tcl_DeleteChannelHandler((Tcl_Channel) chanPtr,
			TclChannelEventScriptInvoker, (ClientData) sPtr);

		TclDecrRefCount(sPtr->scriptPtr);
		ckfree((char *) sPtr);
	    } else {
		prevPtr = sPtr;
	    }
	}

	/*
	 * Cannot call Tcl_UnregisterChannel because that procedure calls
	 * Tcl_GetAssocData to get the channel table, which might already
	 * be inaccessible from the interpreter structure. Instead, we
	 * emulate the behavior of Tcl_UnregisterChannel directly here.
	 */

	Tcl_DeleteHashEntry(hPtr);
	statePtr->refCount--;
	if (statePtr->refCount <= 0) {
	    if (!(statePtr->flags & BG_FLUSH_SCHEDULED)) {
		(void) Tcl_Close(interp, (Tcl_Channel) chanPtr);
	    }
	}
    }
    Tcl_DeleteHashTable(hTblPtr);
    ckfree((char *) hTblPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * CheckForStdChannelsBeingClosed --
 *
 *	Perform special handling for standard channels being closed. When
 *	given a standard channel, if the refcount is now 1, it means that
 *	the last reference to the standard channel is being explicitly
 *	closed. Now bump the refcount artificially down to 0, to ensure the
 *	normal handling of channels being closed will occur. Also reset the
 *	static pointer to the channel to NULL, to avoid dangling references.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Manipulates the refcount on standard channels. May smash the global
 *	static pointer to a standard channel.
 *
 *----------------------------------------------------------------------
 */

static void
CheckForStdChannelsBeingClosed(chan)
    Tcl_Channel chan;
{
    ChannelState *statePtr = ((Channel *) chan)->state;
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

    if ((chan == tsdPtr->stdinChannel) && (tsdPtr->stdinInitialized)) {
	if (statePtr->refCount < 2) {
	    statePtr->refCount = 0;
	    tsdPtr->stdinChannel = NULL;
	    return;
	}
    } else if ((chan == tsdPtr->stdoutChannel)
	    && (tsdPtr->stdoutInitialized)) {
	if (statePtr->refCount < 2) {
	    statePtr->refCount = 0;
	    tsdPtr->stdoutChannel = NULL;
	    return;
	}
    } else if ((chan == tsdPtr->stderrChannel)
	    && (tsdPtr->stderrInitialized)) {
	if (statePtr->refCount < 2) {
	    statePtr->refCount = 0;
	    tsdPtr->stderrChannel = NULL;
	    return;
	}
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_IsStandardChannel --
 *
 *	Test if the given channel is a standard channel.  No attempt
 *	is made to check if the channel or the standard channels
 *	are initialized or otherwise valid.
 *
 * Results:
 *	Returns 1 if true, 0 if false.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

int 
Tcl_IsStandardChannel(chan)
    Tcl_Channel chan;		/* Channel to check. */
{
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

    if ((chan == tsdPtr->stdinChannel) 
	    || (chan == tsdPtr->stdoutChannel)
	    || (chan == tsdPtr->stderrChannel)) {
	return 1;
    } else {
	return 0;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_RegisterChannel --
 *
 *	Adds an already-open channel to the channel table of an interpreter.
 *	If the interpreter passed as argument is NULL, it only increments
 *	the channel refCount.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	May increment the reference count of a channel.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_RegisterChannel(interp, chan)
    Tcl_Interp *interp;		/* Interpreter in which to add the channel. */
    Tcl_Channel chan;		/* The channel to add to this interpreter
				 * channel table. */
{
    Tcl_HashTable *hTblPtr;	/* Hash table of channels. */
    Tcl_HashEntry *hPtr;	/* Search variable. */
    int new;			/* Is the hash entry new or does it exist? */
    Channel *chanPtr;		/* The actual channel. */
    ChannelState *statePtr;	/* State of the actual channel. */

    /*
     * Always (un)register bottom-most channel in the stack.  This makes
     * management of the channel list easier because no manipulation is
     * necessary during (un)stack operation.
     */

    chanPtr = ((Channel *) chan)->state->bottomChanPtr;
    statePtr = chanPtr->state;

    if (statePtr->channelName == (CONST char *) NULL) {
	Tcl_Panic("Tcl_RegisterChannel: channel without name");
    }
    if (interp != (Tcl_Interp *) NULL) {
	hTblPtr = GetChannelTable(interp);
	hPtr = Tcl_CreateHashEntry(hTblPtr, statePtr->channelName, &new);
	if (new == 0) {
	    if (chan == (Tcl_Channel) Tcl_GetHashValue(hPtr)) {
		return;
	    }

	    Tcl_Panic("Tcl_RegisterChannel: duplicate channel names");
	}
	Tcl_SetHashValue(hPtr, (ClientData) chanPtr);
    }
    statePtr->refCount++;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_UnregisterChannel --
 *
 *	Deletes the hash entry for a channel associated with an interpreter.
 *	If the interpreter given as argument is NULL, it only decrements the
 *	reference count.  (This all happens in the Tcl_DetachChannel helper
 *	function).
 *	
 *	Finally, if the reference count of the channel drops to zero,
 *	it is deleted.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	Calls Tcl_DetachChannel which deletes the hash entry for a channel 
 *	associated with an interpreter.
 *	
 *	May delete the channel, which can have a variety of consequences,
 *	especially if we are forced to close the channel.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_UnregisterChannel(interp, chan)
    Tcl_Interp *interp;		/* Interpreter in which channel is defined. */
    Tcl_Channel chan;		/* Channel to delete. */
{
    ChannelState *statePtr;	/* State of the real channel. */

    statePtr = ((Channel *) chan)->state->bottomChanPtr->state;

    if (statePtr->flags & CHANNEL_INCLOSE) {
	if (interp != (Tcl_Interp *) NULL) {
	    Tcl_AppendResult(interp, "Illegal recursive call to close ",
		    "through close-handler of channel", (char *) NULL);
	}
	return TCL_ERROR;
    }

    if (DetachChannel(interp, chan) != TCL_OK) {
	return TCL_OK;
    }

    statePtr = ((Channel *) chan)->state->bottomChanPtr->state;

    /*
     * Perform special handling for standard channels being closed. If the
     * refCount is now 1 it means that the last reference to the standard
     * channel is being explicitly closed, so bump the refCount down
     * artificially to 0. This will ensure that the channel is actually
     * closed, below. Also set the static pointer to NULL for the channel.
     */

    CheckForStdChannelsBeingClosed(chan);

    /*
     * If the refCount reached zero, close the actual channel.
     */

    if (statePtr->refCount <= 0) {

	/*
	 * Ensure that if there is another buffer, it gets flushed
	 * whether or not we are doing a background flush.
	 */

	if ((statePtr->curOutPtr != NULL) &&
		(statePtr->curOutPtr->nextAdded >
			statePtr->curOutPtr->nextRemoved)) {
	    statePtr->flags |= BUFFER_READY;
	}
	Tcl_Preserve((ClientData)statePtr);
	if (!(statePtr->flags & BG_FLUSH_SCHEDULED)) {
	    /* We don't want to re-enter Tcl_Close */
	    if (!(statePtr->flags & CHANNEL_CLOSED)) {
		if (Tcl_Close(interp, chan) != TCL_OK) {
		    statePtr->flags |= CHANNEL_CLOSED;
		    Tcl_Release((ClientData)statePtr);
		    return TCL_ERROR;
		}
	    }
	}
	statePtr->flags |= CHANNEL_CLOSED;
	Tcl_Release((ClientData)statePtr);
    }
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_DetachChannel --
 *
 *	Deletes the hash entry for a channel associated with an interpreter.
 *	If the interpreter given as argument is NULL, it only decrements the
 *	reference count.  Even if the ref count drops to zero, the 
 *	channel is NOT closed or cleaned up.  This allows a channel to
 *	be detached from an interpreter and left in the same state it
 *	was in when it was originally returned by 'Tcl_OpenFileChannel',
 *	for example.
 *	
 *	This function cannot be used on the standard channels, and
 *	will return TCL_ERROR if that is attempted.
 *	
 *	This function should only be necessary for special purposes
 *	in which you need to generate a pristine channel from one
 *	that has already been used.  All ordinary purposes will almost
 *	always want to use Tcl_UnregisterChannel instead.
 *	
 *	Provided the channel is not attached to any other interpreter,
 *	it can then be closed with Tcl_Close, rather than with 
 *	Tcl_UnregisterChannel.
 *
 * Results:
 *	A standard Tcl result.  If the channel is not currently registered
 *	with the given interpreter, TCL_ERROR is returned, otherwise
 *	TCL_OK.  However no error messages are left in the interp's result.
 *
 * Side effects:
 *	Deletes the hash entry for a channel associated with an 
 *	interpreter.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_DetachChannel(interp, chan)
    Tcl_Interp *interp;		/* Interpreter in which channel is defined. */
    Tcl_Channel chan;		/* Channel to delete. */
{
    if (Tcl_IsStandardChannel(chan)) {
	return TCL_ERROR;
    }

    return DetachChannel(interp, chan);
}

/*
 *----------------------------------------------------------------------
 *
 * DetachChannel --
 *
 *	Deletes the hash entry for a channel associated with an interpreter.
 *	If the interpreter given as argument is NULL, it only decrements the
 *	reference count.  Even if the ref count drops to zero, the 
 *	channel is NOT closed or cleaned up.  This allows a channel to
 *	be detached from an interpreter and left in the same state it
 *	was in when it was originally returned by 'Tcl_OpenFileChannel',
 *	for example.
 *
 * Results:
 *	A standard Tcl result.  If the channel is not currently registered
 *	with the given interpreter, TCL_ERROR is returned, otherwise
 *	TCL_OK.  However no error messages are left in the interp's result.
 *
 * Side effects:
 *	Deletes the hash entry for a channel associated with an 
 *	interpreter.
 *
 *----------------------------------------------------------------------
 */

static int
DetachChannel(interp, chan)
    Tcl_Interp *interp;		/* Interpreter in which channel is defined. */
    Tcl_Channel chan;		/* Channel to delete. */
{
    Tcl_HashTable *hTblPtr;	/* Hash table of channels. */
    Tcl_HashEntry *hPtr;	/* Search variable. */
    Channel *chanPtr;		/* The real IO channel. */
    ChannelState *statePtr;	/* State of the real channel. */

    /*
     * Always (un)register bottom-most channel in the stack.  This makes
     * management of the channel list easier because no manipulation is
     * necessary during (un)stack operation.
     */

    chanPtr = ((Channel *) chan)->state->bottomChanPtr;
    statePtr = chanPtr->state;

    if (interp != (Tcl_Interp *) NULL) {
	hTblPtr = (Tcl_HashTable *) Tcl_GetAssocData(interp, "tclIO", NULL);
	if (hTblPtr == (Tcl_HashTable *) NULL) {
	    return TCL_ERROR;
	}
	hPtr = Tcl_FindHashEntry(hTblPtr, statePtr->channelName);
	if (hPtr == (Tcl_HashEntry *) NULL) {
	    return TCL_ERROR;
	}
	if ((Channel *) Tcl_GetHashValue(hPtr) != chanPtr) {
	    return TCL_ERROR;
	}
	Tcl_DeleteHashEntry(hPtr);

	/*
	 * Remove channel handlers that refer to this interpreter, so that they
	 * will not be present if the actual close is delayed and more events
	 * happen on the channel. This may occur if the channel is shared
	 * between several interpreters, or if the channel has async
	 * flushing active.
	 */

	CleanupChannelHandlers(interp, chanPtr);
    }

    statePtr->refCount--;

    return TCL_OK;
}

/*
 *---------------------------------------------------------------------------
 *
 * Tcl_GetChannel --
 *
 *	Finds an existing Tcl_Channel structure by name in a given
 *	interpreter. This function is public because it is used by
 *	channel-type-specific functions.
 *
 * Results:
 *	A Tcl_Channel or NULL on failure. If failed, interp's result
 *	object contains an error message.  *modePtr is filled with the
 *	modes in which the channel was opened.
 *
 * Side effects:
 *	None.
 *
 *---------------------------------------------------------------------------
 */

Tcl_Channel
Tcl_GetChannel(interp, chanName, modePtr)
    Tcl_Interp *interp;		/* Interpreter in which to find or create
				 * the channel. */
    CONST char *chanName;	/* The name of the channel. */
    int *modePtr;		/* Where to store the mode in which the
				 * channel was opened? Will contain an ORed
				 * combination of TCL_READABLE and
				 * TCL_WRITABLE, if non-NULL. */
{
    Channel *chanPtr;		/* The actual channel. */
    Tcl_HashTable *hTblPtr;	/* Hash table of channels. */
    Tcl_HashEntry *hPtr;	/* Search variable. */
    CONST char *name;		/* Translated name. */

    /*
     * Substitute "stdin", etc.  Note that even though we immediately
     * find the channel using Tcl_GetStdChannel, we still need to look
     * it up in the specified interpreter to ensure that it is present
     * in the channel table.  Otherwise, safe interpreters would always
     * have access to the standard channels.
     */

    name = chanName;
    if ((chanName[0] == 's') && (chanName[1] == 't')) {
	chanPtr = NULL;
	if (strcmp(chanName, "stdin") == 0) {
	    chanPtr = (Channel *) Tcl_GetStdChannel(TCL_STDIN);
	} else if (strcmp(chanName, "stdout") == 0) {
	    chanPtr = (Channel *) Tcl_GetStdChannel(TCL_STDOUT);
	} else if (strcmp(chanName, "stderr") == 0) {
	    chanPtr = (Channel *) Tcl_GetStdChannel(TCL_STDERR);
	}
	if (chanPtr != NULL) {
	    name = chanPtr->state->channelName;
	}
    }

    hTblPtr = GetChannelTable(interp);
    hPtr = Tcl_FindHashEntry(hTblPtr, name);
    if (hPtr == (Tcl_HashEntry *) NULL) {
	Tcl_AppendResult(interp, "can not find channel named \"",
		chanName, "\"", (char *) NULL);
	return NULL;
    }

    /*
     * Always return bottom-most channel in the stack.  This one lives
     * the longest - other channels may go away unnoticed.
     * The other APIs compensate where necessary to retrieve the
     * topmost channel again.
     */

    chanPtr = (Channel *) Tcl_GetHashValue(hPtr);
    chanPtr = chanPtr->state->bottomChanPtr;
    if (modePtr != NULL) {
	*modePtr = (chanPtr->state->flags & (TCL_READABLE|TCL_WRITABLE));
    }

    return (Tcl_Channel) chanPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_CreateChannel --
 *
 *	Creates a new entry in the hash table for a Tcl_Channel
 *	record.
 *
 * Results:
 *	Returns the new Tcl_Channel.
 *
 * Side effects:
 *	Creates a new Tcl_Channel instance and inserts it into the
 *	hash table.
 *
 *----------------------------------------------------------------------
 */

Tcl_Channel
Tcl_CreateChannel(typePtr, chanName, instanceData, mask)
    Tcl_ChannelType *typePtr;	/* The channel type record. */
    CONST char *chanName;	/* Name of channel to record. */
    ClientData instanceData;	/* Instance specific data. */
    int mask;			/* TCL_READABLE & TCL_WRITABLE to indicate
				 * if the channel is readable, writable. */
{
    Channel *chanPtr;		/* The channel structure newly created. */
    ChannelState *statePtr;	/* The stack-level independent state info
				 * for the channel. */
    CONST char *name;
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

    /*
     * With the change of the Tcl_ChannelType structure to use a version in
     * 8.3.2+, we have to make sure that our assumption that the structure
     * remains a binary compatible size is true.
     *
     * If this assertion fails on some system, then it can be removed
     * only if the user recompiles code with older channel drivers in
     * the new system as well.
     */

    assert(sizeof(Tcl_ChannelTypeVersion) == sizeof(Tcl_DriverBlockModeProc*));

    /*
     * JH: We could subsequently memset these to 0 to avoid the
     * numerous assignments to 0/NULL below.
     */

    chanPtr = (Channel *) ckalloc((unsigned) sizeof(Channel));
    statePtr = (ChannelState *) ckalloc((unsigned) sizeof(ChannelState));
    chanPtr->state = statePtr;

    chanPtr->instanceData = instanceData;
    chanPtr->typePtr = typePtr;

    /*
     * Set all the bits that are part of the stack-independent state
     * information for the channel.
     */

    if (chanName != (char *) NULL) {
	char *tmp = ckalloc((unsigned) (strlen(chanName) + 1));
	statePtr->channelName = tmp;
	strcpy(tmp, chanName);
    } else {
	Tcl_Panic("Tcl_CreateChannel: NULL channel name");
    }

    statePtr->flags = mask;

    /*
     * Set the channel to system default encoding.
     */

    statePtr->encoding = NULL;
    name = Tcl_GetEncodingName(NULL);
    if (strcmp(name, "binary") != 0) {
    	statePtr->encoding = Tcl_GetEncoding(NULL, name);
    }
    statePtr->inputEncodingState	= NULL;
    statePtr->inputEncodingFlags	= TCL_ENCODING_START;
    statePtr->outputEncodingState	= NULL;
    statePtr->outputEncodingFlags	= TCL_ENCODING_START;

    /*
     * Set the channel up initially in AUTO input translation mode to
     * accept "\n", "\r" and "\r\n". Output translation mode is set to
     * a platform specific default value. The eofChar is set to 0 for both
     * input and output, so that Tcl does not look for an in-file EOF
     * indicator (e.g. ^Z) and does not append an EOF indicator to files.
     */

    statePtr->inputTranslation	= TCL_TRANSLATE_AUTO;
    statePtr->outputTranslation	= TCL_PLATFORM_TRANSLATION;
    statePtr->inEofChar		= 0;
    statePtr->outEofChar	= 0;

    statePtr->unreportedError	= 0;
    statePtr->refCount		= 0;
    statePtr->closeCbPtr	= (CloseCallback *) NULL;
    statePtr->curOutPtr		= (ChannelBuffer *) NULL;
    statePtr->outQueueHead	= (ChannelBuffer *) NULL;
    statePtr->outQueueTail	= (ChannelBuffer *) NULL;
    statePtr->saveInBufPtr	= (ChannelBuffer *) NULL;
    statePtr->inQueueHead	= (ChannelBuffer *) NULL;
    statePtr->inQueueTail	= (ChannelBuffer *) NULL;
    statePtr->chPtr		= (ChannelHandler *) NULL;
    statePtr->interestMask	= 0;
    statePtr->scriptRecordPtr	= (EventScriptRecord *) NULL;
    statePtr->bufSize		= CHANNELBUFFER_DEFAULT_SIZE;
    statePtr->timer		= NULL;
    statePtr->csPtr		= NULL;

    statePtr->outputStage	= NULL;
    if ((statePtr->encoding != NULL) && (statePtr->flags & TCL_WRITABLE)) {
	statePtr->outputStage = (char *)
		ckalloc((unsigned) (statePtr->bufSize + 2));
    }

    /*
     * As we are creating the channel, it is obviously the top for now
     */

    statePtr->topChanPtr	= chanPtr;
    statePtr->bottomChanPtr	= chanPtr;
    chanPtr->downChanPtr	= (Channel *) NULL;
    chanPtr->upChanPtr		= (Channel *) NULL;
    chanPtr->inQueueHead	= (ChannelBuffer *) NULL;
    chanPtr->inQueueTail	= (ChannelBuffer *) NULL;

    /*
     * Link the channel into the list of all channels; create an on-exit
     * handler if there is not one already, to close off all the channels
     * in the list on exit.
     *
     * JH: Could call Tcl_SpliceChannel, but need to avoid NULL check.
     */

    statePtr->nextCSPtr = tsdPtr->firstCSPtr;
    tsdPtr->firstCSPtr = statePtr;

    /*
     * TIP #10. Mark the current thread as the one managing the new
     *		channel. Note: 'Tcl_GetCurrentThread' returns sensible
     *		values even for a non-threaded core.
     */

    statePtr->managingThread = Tcl_GetCurrentThread();

    /*
     * Install this channel in the first empty standard channel slot, if
     * the channel was previously closed explicitly.
     */

    if ((tsdPtr->stdinChannel == NULL) &&
	    (tsdPtr->stdinInitialized == 1)) {
	Tcl_SetStdChannel((Tcl_Channel) chanPtr, TCL_STDIN);
	Tcl_RegisterChannel((Tcl_Interp *) NULL, (Tcl_Channel) chanPtr);
    } else if ((tsdPtr->stdoutChannel == NULL) &&
	    (tsdPtr->stdoutInitialized == 1)) {
	Tcl_SetStdChannel((Tcl_Channel) chanPtr, TCL_STDOUT);
	Tcl_RegisterChannel((Tcl_Interp *) NULL, (Tcl_Channel) chanPtr);
    } else if ((tsdPtr->stderrChannel == NULL) &&
	    (tsdPtr->stderrInitialized == 1)) {
	Tcl_SetStdChannel((Tcl_Channel) chanPtr, TCL_STDERR);
	Tcl_RegisterChannel((Tcl_Interp *) NULL, (Tcl_Channel) chanPtr);
    } 
    return (Tcl_Channel) chanPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_StackChannel --
 *
 *	Replaces an entry in the hash table for a Tcl_Channel
 *	record. The replacement is a new channel with same name,
 *	it supercedes the replaced channel. Input and output of
 *	the superceded channel is now going through the newly
 *	created channel and allows the arbitrary filtering/manipulation
 *	of the dataflow.
 *
 *	Andreas Kupries <a.kupries@westend.com>, 12/13/1998
 *	"Trf-Patch for filtering channels"
 *
 * Results:
 *	Returns the new Tcl_Channel, which actually contains the
 *	saved information about prevChan.
 *
 * Side effects:
 *    A new channel structure is allocated and linked below
 *    the existing channel.  The channel operations and client
 *    data of the existing channel are copied down to the newly
 *    created channel, and the current channel has its operations
 *    replaced by the new typePtr.
 *
 *----------------------------------------------------------------------
 */

Tcl_Channel
Tcl_StackChannel(interp, typePtr, instanceData, mask, prevChan)
    Tcl_Interp *interp;		/* The interpreter we are working in */
    Tcl_ChannelType *typePtr;	/* The channel type record for the new
				 * channel. */
    ClientData instanceData;	/* Instance specific data for the new
				 * channel. */
    int mask;			/* TCL_READABLE & TCL_WRITABLE to indicate
				 * if the channel is readable, writable. */
    Tcl_Channel prevChan;	/* The channel structure to replace */
{
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
    Channel *chanPtr, *prevChanPtr;
    ChannelState *statePtr;

    /*
     * Find the given channel in the list of all channels.
     * If we don't find it, then it was never registered correctly.
     *
     * This operation should occur at the top of a channel stack.
     */

    statePtr = (ChannelState *) tsdPtr->firstCSPtr;
    prevChanPtr = ((Channel *) prevChan)->state->topChanPtr;

    while (statePtr->topChanPtr != prevChanPtr) {
	statePtr = statePtr->nextCSPtr;
    }

    if (statePtr == NULL) {
	Tcl_AppendResult(interp, "couldn't find state for channel \"",
		Tcl_GetChannelName(prevChan), "\"", (char *) NULL);
	return (Tcl_Channel) NULL;
    }

    /*
     * Here we check if the given "mask" matches the "flags"
     * of the already existing channel.
     *
     *	  | - | R | W | RW |
     *	--+---+---+---+----+	<=>  0 != (chan->mask & prevChan->mask)
     *	- |   |   |   |    |
     *	R |   | + |   | +  |	The superceding channel is allowed to
     *	W |   |   | + | +  |	restrict the capabilities of the
     *	RW|   | + | + | +  |	superceded one !
     *	--+---+---+---+----+
     */

    if ((mask & (statePtr->flags & (TCL_READABLE | TCL_WRITABLE))) == 0) {
	Tcl_AppendResult(interp,
		"reading and writing both disallowed for channel \"",
		Tcl_GetChannelName(prevChan), "\"", (char *) NULL);
	return (Tcl_Channel) NULL;
    }

    /*
     * Flush the buffers. This ensures that any data still in them
     * at this time is not handled by the new transformation. Restrict
     * this to writable channels. Take care to hide a possible bg-copy
     * in progress from Tcl_Flush and the CheckForChannelErrors inside.
     */

    if ((mask & TCL_WRITABLE) != 0) {
	CopyState *csPtr;

	csPtr = statePtr->csPtr;
	statePtr->csPtr = (CopyState *) NULL;

	if (Tcl_Flush((Tcl_Channel) prevChanPtr) != TCL_OK) {
	    statePtr->csPtr = csPtr;
	    Tcl_AppendResult(interp, "could not flush channel \"",
		    Tcl_GetChannelName(prevChan), "\"", (char *) NULL);
	    return (Tcl_Channel) NULL;
	}

	statePtr->csPtr = csPtr;
    }
    /*
     * Discard any input in the buffers. They are not yet read by the
     * user of the channel, so they have to go through the new
     * transformation before reading. As the buffers contain the
     * untransformed form their contents are not only useless but actually
     * distorts our view of the system.
     *
     * To preserve the information without having to read them again and
     * to avoid problems with the location in the channel (seeking might
     * be impossible) we move the buffers from the common state structure
     * into the channel itself. We use the buffers in the channel below
     * the new transformation to hold the data. In the future this allows
     * us to write transformations which pre-read data and push the unused
     * part back when they are going away.
     */

    if (((mask & TCL_READABLE) != 0) &&
	    (statePtr->inQueueHead != (ChannelBuffer *) NULL)) {
	/*
	 * Remark: It is possible that the channel buffers contain
	 * data from some earlier push-backs.
	 */

	statePtr->inQueueTail->nextPtr = prevChanPtr->inQueueHead;
	prevChanPtr->inQueueHead = statePtr->inQueueHead;

	if (prevChanPtr->inQueueTail == (ChannelBuffer *) NULL) {
	    prevChanPtr->inQueueTail = statePtr->inQueueTail;
	}

	statePtr->inQueueHead = (ChannelBuffer *) NULL;
	statePtr->inQueueTail = (ChannelBuffer *) NULL;
    }

    chanPtr = (Channel *) ckalloc((unsigned) sizeof(Channel));

    /*
     * Save some of the current state into the new structure,
     * reinitialize the parts which will stay with the transformation.
     *
     * Remarks:
     */

    chanPtr->state		= statePtr;
    chanPtr->instanceData	= instanceData;
    chanPtr->typePtr		= typePtr;
    chanPtr->downChanPtr	= prevChanPtr;
    chanPtr->upChanPtr		= (Channel *) NULL;
    chanPtr->inQueueHead	= (ChannelBuffer *) NULL;
    chanPtr->inQueueTail	= (ChannelBuffer *) NULL;

    /*
     * Place new block at the head of a possibly existing list of previously
     * stacked channels.
     */

    prevChanPtr->upChanPtr	= chanPtr;
    statePtr->topChanPtr	= chanPtr;

    return (Tcl_Channel) chanPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_UnstackChannel --
 *
 *	Unstacks an entry in the hash table for a Tcl_Channel
 *	record. This is the reverse to 'Tcl_StackChannel'.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	If TCL_ERROR is returned, the posix error code will be set
 *	with Tcl_SetErrno.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_UnstackChannel(interp, chan)
    Tcl_Interp *interp; /* The interpreter we are working in */
    Tcl_Channel chan;   /* The channel to unstack */
{
    Channel *chanPtr = (Channel *) chan;
    ChannelState *statePtr = chanPtr->state;
    int result = 0;

    /*
     * This operation should occur at the top of a channel stack.
     */

    chanPtr = statePtr->topChanPtr;

    if (chanPtr->downChanPtr != (Channel *) NULL) {
	/*
	 * Instead of manipulating the per-thread / per-interp list/hashtable
	 * of registered channels we wind down the state of the transformation,
	 * and then restore the state of underlying channel into the old
	 * structure.
	 */

	Channel *downChanPtr = chanPtr->downChanPtr;

	/*
	 * Flush the buffers. This ensures that any data still in them
	 * at this time _is_ handled by the transformation we are unstacking
	 * right now. Restrict this to writable channels. Take care to hide
	 * a possible bg-copy in progress from Tcl_Flush and the
	 * CheckForChannelErrors inside.
	 */

	if (statePtr->flags & TCL_WRITABLE) {
	    CopyState *csPtr;

	    csPtr = statePtr->csPtr;
	    statePtr->csPtr = (CopyState *) NULL;

	    if (Tcl_Flush((Tcl_Channel) chanPtr) != TCL_OK) {
		statePtr->csPtr = csPtr;
		Tcl_AppendResult(interp, "could not flush channel \"",
			Tcl_GetChannelName((Tcl_Channel) chanPtr), "\"",
			(char *) NULL);
		return TCL_ERROR;
	    }

	    statePtr->csPtr = csPtr;
	}

	/*
	 * Anything in the input queue and the push-back buffers of
	 * the transformation going away is transformed data, but not
	 * yet read. As unstacking means that the caller does not want
	 * to see transformed data any more we have to discard these
	 * bytes. To avoid writing an analogue to 'DiscardInputQueued'
	 * we move the information in the push back buffers to the
	 * input queue and then call 'DiscardInputQueued' on that.
	 */

	if (((statePtr->flags & TCL_READABLE) != 0) &&
		((statePtr->inQueueHead != (ChannelBuffer *) NULL) ||
		(chanPtr->inQueueHead  != (ChannelBuffer *) NULL))) {

	    if ((statePtr->inQueueHead != (ChannelBuffer *) NULL) &&
		    (chanPtr->inQueueHead  != (ChannelBuffer *) NULL)) {
		statePtr->inQueueTail->nextPtr = chanPtr->inQueueHead;
		statePtr->inQueueTail = chanPtr->inQueueTail;
		statePtr->inQueueHead = statePtr->inQueueTail;

	    } else if (chanPtr->inQueueHead != (ChannelBuffer *) NULL) {
		statePtr->inQueueHead = chanPtr->inQueueHead;
		statePtr->inQueueTail = chanPtr->inQueueTail;
	    }

	    chanPtr->inQueueHead = (ChannelBuffer *) NULL;
	    chanPtr->inQueueTail = (ChannelBuffer *) NULL;

	    DiscardInputQueued(statePtr, 0);
	}

	statePtr->topChanPtr = downChanPtr;
	downChanPtr->upChanPtr = (Channel *) NULL;

	/*
	 * Leave this link intact for closeproc
	 *  chanPtr->downChanPtr = (Channel *) NULL;
	 */

	/*
	 * Close and free the channel driver state.
	 */

	if (chanPtr->typePtr->closeProc != TCL_CLOSE2PROC) {
	    result = (chanPtr->typePtr->closeProc)(chanPtr->instanceData,
		    interp);
	} else {
	    result = (chanPtr->typePtr->close2Proc)(chanPtr->instanceData,
		    interp, 0);
	}

	chanPtr->typePtr = NULL;

	/*
	 * AK: Tcl_NotifyChannel may hold a reference to this block of memory
	 */

	Tcl_EventuallyFree((ClientData) chanPtr, TCL_DYNAMIC);
	UpdateInterest(downChanPtr);

	if (result != 0) {
	    Tcl_SetErrno(result);
	    return TCL_ERROR;
	}
    } else {
	/*
	 * This channel does not cover another one.
	 * Simply do a close, if necessary.
	 */

	if (statePtr->refCount <= 0) {
	    if (Tcl_Close(interp, chan) != TCL_OK) {
		return TCL_ERROR;
	    }
	}
    }

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetStackedChannel --
 *
 *	Determines whether the specified channel is stacked upon another.
 *
 * Results:
 *	NULL if the channel is not stacked upon another one, or a reference
 *	to the channel it is stacked upon. This reference can be used in
 *	queries, but modification is not allowed.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

Tcl_Channel
Tcl_GetStackedChannel(chan)
    Tcl_Channel chan;
{
    Channel *chanPtr = (Channel *) chan;	/* The actual channel. */

    return (Tcl_Channel) chanPtr->downChanPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetTopChannel --
 *
 *	Returns the top channel of a channel stack.
 *
 * Results:
 *	NULL if the channel is not stacked upon another one, or a reference
 *	to the channel it is stacked upon. This reference can be used in
 *	queries, but modification is not allowed.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

Tcl_Channel
Tcl_GetTopChannel(chan)
    Tcl_Channel chan;
{
    Channel *chanPtr = (Channel *) chan;	/* The actual channel. */

    return (Tcl_Channel) chanPtr->state->topChanPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetChannelInstanceData --
 *
 *	Returns the client data associated with a channel.
 *
 * Results:
 *	The client data.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

ClientData
Tcl_GetChannelInstanceData(chan)
    Tcl_Channel chan;		/* Channel for which to return client data. */
{
    Channel *chanPtr = (Channel *) chan;	/* The actual channel. */

    return chanPtr->instanceData;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetChannelThread --
 *
 *	Given a channel structure, returns the thread managing it.
 *	TIP #10
 *
 * Results:
 *	Returns the id of the thread managing the channel.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

Tcl_ThreadId
Tcl_GetChannelThread(chan)
    Tcl_Channel chan;		/* The channel to return managing thread for. */
{
    Channel *chanPtr = (Channel *) chan;	/* The actual channel. */

    return chanPtr->state->managingThread;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetChannelType --
 *
 *	Given a channel structure, returns the channel type structure.
 *
 * Results:
 *	Returns a pointer to the channel type structure.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

Tcl_ChannelType *
Tcl_GetChannelType(chan)
    Tcl_Channel chan;		/* The channel to return type for. */
{
    Channel *chanPtr = (Channel *) chan;	/* The actual channel. */

    return chanPtr->typePtr;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetChannelMode --
 *
 *	Computes a mask indicating whether the channel is open for
 *	reading and writing.
 *
 * Results:
 *	An OR-ed combination of TCL_READABLE and TCL_WRITABLE.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_GetChannelMode(chan)
    Tcl_Channel chan;		/* The channel for which the mode is
				 * being computed. */
{
    ChannelState *statePtr = ((Channel *) chan)->state;
					/* State of actual channel. */

    return (statePtr->flags & (TCL_READABLE | TCL_WRITABLE));
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetChannelName --
 *
 *	Returns the string identifying the channel name.
 *
 * Results:
 *	The string containing the channel name. This memory is
 *	owned by the generic layer and should not be modified by
 *	the caller.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

CONST char *
Tcl_GetChannelName(chan)
    Tcl_Channel chan;		/* The channel for which to return the name. */
{
    ChannelState *statePtr;	/* State of actual channel. */

    statePtr = ((Channel *) chan)->state;
    return statePtr->channelName;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetChannelHandle --
 *
 *	Returns an OS handle associated with a channel.
 *
 * Results:
 *	Returns TCL_OK and places the handle in handlePtr, or returns
 *	TCL_ERROR on failure.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_GetChannelHandle(chan, direction, handlePtr)
    Tcl_Channel chan;		/* The channel to get file from. */
    int direction;		/* TCL_WRITABLE or TCL_READABLE. */
    ClientData *handlePtr;	/* Where to store handle */
{
    Channel *chanPtr;		/* The actual channel. */
    ClientData handle;
    int result;

    chanPtr = ((Channel *) chan)->state->bottomChanPtr;
    result = (chanPtr->typePtr->getHandleProc)(chanPtr->instanceData,
	    direction, &handle);
    if (handlePtr) {
	*handlePtr = handle;
    }
    return result;
}

/*
 *---------------------------------------------------------------------------
 *
 * AllocChannelBuffer --
 *
 *	A channel buffer has BUFFER_PADDING bytes extra at beginning to
 *	hold any bytes of a native-encoding character that got split by
 *	the end of the previous buffer and need to be moved to the
 *	beginning of the next buffer to make a contiguous string so it
 *	can be converted to UTF-8.
 *
 *	A channel buffer has BUFFER_PADDING bytes extra at the end to
 *	hold any bytes of a native-encoding character (generated from a
 *	UTF-8 character) that overflow past the end of the buffer and
 *	need to be moved to the next buffer.
 *
 * Results:
 *	A newly allocated channel buffer.
 *
 * Side effects:
 *	None.
 *
 *---------------------------------------------------------------------------
 */

static ChannelBuffer *
AllocChannelBuffer(length)
    int length;			/* Desired length of channel buffer. */
{
    ChannelBuffer *bufPtr;
    int n;

    n = length + CHANNELBUFFER_HEADER_SIZE + BUFFER_PADDING + BUFFER_PADDING;
    bufPtr = (ChannelBuffer *) ckalloc((unsigned) n);
    bufPtr->nextAdded	= BUFFER_PADDING;
    bufPtr->nextRemoved	= BUFFER_PADDING;
    bufPtr->bufLength	= length + BUFFER_PADDING;
    bufPtr->nextPtr	= (ChannelBuffer *) NULL;
    return bufPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * RecycleBuffer --
 *
 *	Helper function to recycle input and output buffers. Ensures
 *	that two input buffers are saved (one in the input queue and
 *	another in the saveInBufPtr field) and that curOutPtr is set
 *	to a buffer. Only if these conditions are met is the buffer
 *	freed to the OS.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	May free a buffer to the OS.
 *
 *----------------------------------------------------------------------
 */

static void
RecycleBuffer(statePtr, bufPtr, mustDiscard)
    ChannelState *statePtr;	/* ChannelState in which to recycle buffers. */
    ChannelBuffer *bufPtr;	/* The buffer to recycle. */
    int mustDiscard;		/* If nonzero, free the buffer to the
				 * OS, always. */
{
    /*
     * Do we have to free the buffer to the OS?
     */

    if (mustDiscard) {
	ckfree((char *) bufPtr);
	return;
    }

    /*
     * Only save buffers which are at least as big as the requested
     * buffersize for the channel. This is to honor dynamic changes
     * of the buffersize made by the user.
     */

    if ((bufPtr->bufLength - BUFFER_PADDING) < statePtr->bufSize) {
	ckfree((char *) bufPtr);
	return;
    }

    /*
     * Only save buffers for the input queue if the channel is readable.
     */

    if (statePtr->flags & TCL_READABLE) {
	if (statePtr->inQueueHead == (ChannelBuffer *) NULL) {
	    statePtr->inQueueHead = bufPtr;
	    statePtr->inQueueTail = bufPtr;
	    goto keepit;
	}
	if (statePtr->saveInBufPtr == (ChannelBuffer *) NULL) {
	    statePtr->saveInBufPtr = bufPtr;
	    goto keepit;
	}
    }

    /*
     * Only save buffers for the output queue if the channel is writable.
     */

    if (statePtr->flags & TCL_WRITABLE) {
	if (statePtr->curOutPtr == (ChannelBuffer *) NULL) {
	    statePtr->curOutPtr = bufPtr;
	    goto keepit;
	}
    }

    /*
     * If we reached this code we return the buffer to the OS.
     */

    ckfree((char *) bufPtr);
    return;

    keepit:
    bufPtr->nextRemoved = BUFFER_PADDING;
    bufPtr->nextAdded = BUFFER_PADDING;
    bufPtr->nextPtr = (ChannelBuffer *) NULL;
}

/*
 *----------------------------------------------------------------------
 *
 * DiscardOutputQueued --
 *
 *	Discards all output queued in the output queue of a channel.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Recycles buffers.
 *
 *----------------------------------------------------------------------
 */

static void
DiscardOutputQueued(statePtr)
    ChannelState *statePtr;	/* ChannelState for which to discard output. */
{
    ChannelBuffer *bufPtr;

    while (statePtr->outQueueHead != (ChannelBuffer *) NULL) {
	bufPtr = statePtr->outQueueHead;
	statePtr->outQueueHead = bufPtr->nextPtr;
	RecycleBuffer(statePtr, bufPtr, 0);
    }
    statePtr->outQueueHead = (ChannelBuffer *) NULL;
    statePtr->outQueueTail = (ChannelBuffer *) NULL;
}

/*
 *----------------------------------------------------------------------
 *
 * CheckForDeadChannel --
 *
 *	This function checks is a given channel is Dead.
 *	(A channel that has been closed but not yet deallocated.)
 *
 * Results:
 *	True (1) if channel is Dead, False (0) if channel is Ok
 *
 * Side effects:
 *	None
 *
 *----------------------------------------------------------------------
 */

static int
CheckForDeadChannel(interp, statePtr)
    Tcl_Interp *interp;		/* For error reporting (can be NULL) */
    ChannelState *statePtr;	/* The channel state to check. */
{
    if (statePtr->flags & CHANNEL_DEAD) {
	Tcl_SetErrno(EINVAL);
	if (interp) {
	    Tcl_AppendResult(interp,
		    "unable to access channel: invalid channel",
		    (char *) NULL);   
	}
	return 1;
    }
    return 0;
}

/*
 *----------------------------------------------------------------------
 *
 * FlushChannel --
 *
 *	This function flushes as much of the queued output as is possible
 *	now. If calledFromAsyncFlush is nonzero, it is being called in an
 *	event handler to flush channel output asynchronously.
 *
 * Results:
 *	0 if successful, else the error code that was returned by the
 *	channel type operation.
 *
 * Side effects:
 *	May produce output on a channel. May block indefinitely if the
 *	channel is synchronous. May schedule an async flush on the channel.
 *	May recycle memory for buffers in the output queue.
 *
 *----------------------------------------------------------------------
 */

static int
FlushChannel(interp, chanPtr, calledFromAsyncFlush)
    Tcl_Interp *interp;			/* For error reporting during close. */
    Channel *chanPtr;			/* The channel to flush on. */
    int calledFromAsyncFlush;		/* If nonzero then we are being
					 * called from an asynchronous
					 * flush callback. */
{
    ChannelState *statePtr = chanPtr->state;
					/* State of the channel stack. */
    ChannelBuffer *bufPtr;		/* Iterates over buffered output
					 * queue. */
    int toWrite;			/* Amount of output data in current
					 * buffer available to be written. */
    int written;			/* Amount of output data actually
					 * written in current round. */
    int errorCode = 0;			/* Stores POSIX error codes from
					 * channel driver operations. */
    int wroteSome = 0;			/* Set to one if any data was
					 * written to the driver. */

    /*
     * Prevent writing on a dead channel -- a channel that has been closed
     * but not yet deallocated. This can occur if the exit handler for the
     * channel deallocation runs before all channels are deregistered in
     * all interpreters.
     */

    if (CheckForDeadChannel(interp, statePtr)) {
	return -1;
    }

    /*
     * Loop over the queued buffers and attempt to flush as
     * much as possible of the queued output to the channel.
     */

    while (1) {

	/*
	 * If the queue is empty and there is a ready current buffer, OR if
	 * the current buffer is full, then move the current buffer to the
	 * queue.
	 */

	if (((statePtr->curOutPtr != (ChannelBuffer *) NULL) &&
		(statePtr->curOutPtr->nextAdded == statePtr->curOutPtr->bufLength))
		|| ((statePtr->flags & BUFFER_READY) &&
			(statePtr->outQueueHead == (ChannelBuffer *) NULL))) {
	    statePtr->flags &= (~(BUFFER_READY));
	    statePtr->curOutPtr->nextPtr = (ChannelBuffer *) NULL;
	    if (statePtr->outQueueHead == (ChannelBuffer *) NULL) {
		statePtr->outQueueHead = statePtr->curOutPtr;
	    } else {
		statePtr->outQueueTail->nextPtr = statePtr->curOutPtr;
	    }
	    statePtr->outQueueTail = statePtr->curOutPtr;
	    statePtr->curOutPtr = (ChannelBuffer *) NULL;
	}
	bufPtr = statePtr->outQueueHead;

	/*
	 * If we are not being called from an async flush and an async
	 * flush is active, we just return without producing any output.
	 */

	if ((!calledFromAsyncFlush) &&
		(statePtr->flags & BG_FLUSH_SCHEDULED)) {
	    return 0;
	}

	/*
	 * If the output queue is still empty, break out of the while loop.
	 */

	if (bufPtr == (ChannelBuffer *) NULL) {
	    break;	/* Out of the "while (1)". */
	}

	/*
	 * Produce the output on the channel.
	 */

	toWrite = bufPtr->nextAdded - bufPtr->nextRemoved;
	written = (chanPtr->typePtr->outputProc) (chanPtr->instanceData,
		bufPtr->buf + bufPtr->nextRemoved, toWrite,
		&errorCode);

	/*
	 * If the write failed completely attempt to start the asynchronous
	 * flush mechanism and break out of this loop - do not attempt to
	 * write any more output at this time.
	 */

	if (written < 0) {

	    /*
	     * If the last attempt to write was interrupted, simply retry.
	     */

	    if (errorCode == EINTR) {
		errorCode = 0;
		continue;
	    }

	    /*
	     * If the channel is non-blocking and we would have blocked,
	     * start a background flushing handler and break out of the loop.
	     */

	    if ((errorCode == EWOULDBLOCK) || (errorCode == EAGAIN)) {
		/*
		 * This used to check for CHANNEL_NONBLOCKING, and panic
		 * if the channel was blocking.	 However, it appears
		 * that setting stdin to -blocking 0 has some effect on
		 * the stdout when it's a tty channel (dup'ed underneath)
		 */

		if (!(statePtr->flags & BG_FLUSH_SCHEDULED)) {
		    statePtr->flags |= BG_FLUSH_SCHEDULED;
		    UpdateInterest(chanPtr);
		}
		errorCode = 0;
		break;
	    }

	    /*
	     * Decide whether to report the error upwards or defer it.
	     */

	    if (calledFromAsyncFlush) {
		if (statePtr->unreportedError == 0) {
		    statePtr->unreportedError = errorCode;
		}
	    } else {
		Tcl_SetErrno(errorCode);
		if (interp != NULL) {

		    /*
		     * Casting away CONST here is safe because the
		     * TCL_VOLATILE flag guarantees CONST treatment
		     * of the Posix error string.
		     */

		    Tcl_SetResult(interp,
			    (char *) Tcl_PosixError(interp), TCL_VOLATILE);
		}
	    }

	    /*
	     * When we get an error we throw away all the output
	     * currently queued.
	     */

	    DiscardOutputQueued(statePtr);
	    continue;
	} else {
	    wroteSome = 1;
	}

	bufPtr->nextRemoved += written;

	/*
	 * If this buffer is now empty, recycle it.
	 */

	if (bufPtr->nextRemoved == bufPtr->nextAdded) {
	    statePtr->outQueueHead = bufPtr->nextPtr;
	    if (statePtr->outQueueHead == (ChannelBuffer *) NULL) {
		statePtr->outQueueTail = (ChannelBuffer *) NULL;
	    }
	    RecycleBuffer(statePtr, bufPtr, 0);
	}
    }	/* Closes "while (1)". */

    /*
     * If we wrote some data while flushing in the background, we are done.
     * We can't finish the background flush until we run out of data and
     * the channel becomes writable again.  This ensures that all of the
     * pending data has been flushed at the system level.
     */

    if (statePtr->flags & BG_FLUSH_SCHEDULED) {
	if (wroteSome) {
	    return errorCode;
	} else if (statePtr->outQueueHead == (ChannelBuffer *) NULL) {
	    statePtr->flags &= (~(BG_FLUSH_SCHEDULED));
	    (chanPtr->typePtr->watchProc)(chanPtr->instanceData,
		    statePtr->interestMask);
	}
    }

    /*
     * If the channel is flagged as closed, delete it when the refCount
     * drops to zero, the output queue is empty and there is no output
     * in the current output buffer.
     */

    if ((statePtr->flags & CHANNEL_CLOSED) && (statePtr->refCount <= 0) &&
	    (statePtr->outQueueHead == (ChannelBuffer *) NULL) &&
	    ((statePtr->curOutPtr == (ChannelBuffer *) NULL) ||
	    (statePtr->curOutPtr->nextAdded ==
		    statePtr->curOutPtr->nextRemoved))) {
	return CloseChannel(interp, chanPtr, errorCode);
    }
    return errorCode;
}

/*
 *----------------------------------------------------------------------
 *
 * CloseChannel --
 *
 *	Utility procedure to close a channel and free associated resources.
 *
 *	If the channel was stacked, then the it will copy the necessary
 *	elements of the NEXT channel into the TOP channel, in essence
 *	unstacking the channel.  The NEXT channel will then be freed.
 *
 *	If the channel was not stacked, then we will free all the bits
 *	for the TOP channel, including the data structure itself.
 *
 * Results:
 *	1 if the channel was stacked, 0 otherwise.
 *
 * Side effects:
 *	May close the actual channel; may free memory.
 *	May change the value of errno.
 *
 *----------------------------------------------------------------------
 */

static int
CloseChannel(interp, chanPtr, errorCode)
    Tcl_Interp *interp;			/* For error reporting. */
    Channel *chanPtr;			/* The channel to close. */
    int errorCode;			/* Status of operation so far. */
{
    int result = 0;			/* Of calling driver close
					 * operation. */
    ChannelState *statePtr;		/* state of the channel stack. */
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

    if (chanPtr == NULL) {
	return result;
    }
    statePtr = chanPtr->state;

    /*
     * No more input can be consumed so discard any leftover input.
     */

    DiscardInputQueued(statePtr, 1);

    /*
     * Discard a leftover buffer in the current output buffer field.
     */

    if (statePtr->curOutPtr != (ChannelBuffer *) NULL) {
	ckfree((char *) statePtr->curOutPtr);
	statePtr->curOutPtr = (ChannelBuffer *) NULL;
    }

    /*
     * The caller guarantees that there are no more buffers
     * queued for output.
     */

    if (statePtr->outQueueHead != (ChannelBuffer *) NULL) {
	Tcl_Panic("TclFlush, closed channel: queued output left");
    }

    /*
     * If the EOF character is set in the channel, append that to the
     * output device.
     */

    if ((statePtr->outEofChar != 0) && (statePtr->flags & TCL_WRITABLE)) {
	int dummy;
	char c = (char) statePtr->outEofChar;

	(chanPtr->typePtr->outputProc) (chanPtr->instanceData, &c, 1, &dummy);
    }

    /*
     * Remove this channel from of the list of all channels.
     */

    Tcl_CutChannel((Tcl_Channel) chanPtr);

    /*
     * Close and free the channel driver state.
     */

    if (chanPtr->typePtr->closeProc != TCL_CLOSE2PROC) {
	result = (chanPtr->typePtr->closeProc)(chanPtr->instanceData, interp);
    } else {
	result = (chanPtr->typePtr->close2Proc)(chanPtr->instanceData,
		interp, 0);
    }

    /*
     * Some resources can be cleared only if the bottom channel
     * in a stack is closed. All the other channels in the stack
     * are not allowed to remove.
     */

    if (chanPtr == statePtr->bottomChanPtr) {
	if (statePtr->channelName != (char *) NULL) {
	    ckfree((char *) statePtr->channelName);
	    statePtr->channelName = NULL;
	}

	Tcl_FreeEncoding(statePtr->encoding);
	if (statePtr->outputStage != NULL) {
	    ckfree((char *) statePtr->outputStage);
	    statePtr->outputStage = (char *) NULL;
	}
    }

    /*
     * If we are being called synchronously, report either
     * any latent error on the channel or the current error.
     */

    if (statePtr->unreportedError != 0) {
	errorCode = statePtr->unreportedError;
    }
    if (errorCode == 0) {
	errorCode = result;
	if (errorCode != 0) {
	    Tcl_SetErrno(errorCode);
	}
    }

    /*
     * Cancel any outstanding timer.
     */

    Tcl_DeleteTimerHandler(statePtr->timer);

    /*
     * Mark the channel as deleted by clearing the type structure.
     */

    if (chanPtr->downChanPtr != (Channel *) NULL) {
	Channel *downChanPtr = chanPtr->downChanPtr;

	statePtr->nextCSPtr	= tsdPtr->firstCSPtr;
	tsdPtr->firstCSPtr	= statePtr;

	statePtr->topChanPtr	= downChanPtr;
	downChanPtr->upChanPtr	= (Channel *) NULL;
	chanPtr->typePtr	= NULL;

	Tcl_EventuallyFree((ClientData) chanPtr, TCL_DYNAMIC);
	return Tcl_Close(interp, (Tcl_Channel) downChanPtr);
    }

    /*
     * There is only the TOP Channel, so we free the remaining
     * pointers we have and then ourselves.  Since this is the
     * last of the channels in the stack, make sure to free the
     * ChannelState structure associated with it.  We use
     * Tcl_EventuallyFree to allow for any last
     */

    chanPtr->typePtr = NULL;

    Tcl_EventuallyFree((ClientData) statePtr, TCL_DYNAMIC);
    Tcl_EventuallyFree((ClientData) chanPtr, TCL_DYNAMIC);

    return errorCode;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_CutChannel --
 *
 *	Removes a channel from the (thread-)global list of all channels
 *	(in that thread).  This is actually the statePtr for the stack
 *	of channel.
 *
 * Results:
 *	Nothing.
 *
 * Side effects:
 *	Resets the field 'nextCSPtr' of the specified channel state to NULL.
 *
 * NOTE:
 *	The channel to splice out of the list must not be referenced
 *	in any interpreter. This is something this procedure cannot
 *	check (despite the refcount) because the caller usually wants
 *	fiddle with the channel (like transfering it to a different
 *	thread) and thus keeps the refcount artifically high to prevent
 *	its destruction.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_CutChannel(chan)
    Tcl_Channel chan;			/* The channel being removed. Must
					 * not be referenced in any
					 * interpreter. */
{
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
    ChannelState *prevCSPtr;		/* Preceding channel state in list of
					 * all states - used to splice a
					 * channel out of the list on close. */
    ChannelState *statePtr = ((Channel *) chan)->state;
					/* state of the channel stack. */

    /*
     * Remove this channel from of the list of all channels
     * (in the current thread).
     */

    if (tsdPtr->firstCSPtr && (statePtr == tsdPtr->firstCSPtr)) {
	tsdPtr->firstCSPtr = statePtr->nextCSPtr;
    } else {
	for (prevCSPtr = tsdPtr->firstCSPtr;
		prevCSPtr && (prevCSPtr->nextCSPtr != statePtr);
		prevCSPtr = prevCSPtr->nextCSPtr) {
	    /* Empty loop body. */
	}
	if (prevCSPtr == (ChannelState *) NULL) {
	    Tcl_Panic("FlushChannel: damaged channel list");
	}
	prevCSPtr->nextCSPtr = statePtr->nextCSPtr;
    }

    statePtr->nextCSPtr = (ChannelState *) NULL;

    TclpCutFileChannel(chan);
    TclpCutSockChannel(chan);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_SpliceChannel --
 *
 *	Adds a channel to the (thread-)global list of all channels
 *	(in that thread). Expects that the field 'nextChanPtr' in
 *	the channel is set to NULL.
 *
 * Results:
 *	Nothing.
 *
 * Side effects:
 *	Nothing.
 *
 * NOTE:
 *	The channel to add to the list must not be referenced in any
 *	interpreter. This is something this procedure cannot check
 *	(despite the refcount) because the caller usually wants figgle
 *	with the channel (like transfering it to a different thread)
 *	and thus keeps the refcount artifically high to prevent its
 *	destruction.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_SpliceChannel(chan)
    Tcl_Channel chan;			/* The channel being added. Must
					 * not be referenced in any
					 * interpreter. */
{
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
    ChannelState *statePtr = ((Channel *) chan)->state;

    if (statePtr->nextCSPtr != (ChannelState *) NULL) {
	Tcl_Panic("Tcl_SpliceChannel: trying to add channel used in different list");
    }

    statePtr->nextCSPtr = tsdPtr->firstCSPtr;
    tsdPtr->firstCSPtr = statePtr;

    /*
     * TIP #10. Mark the current thread as the new one managing this
     *		channel. Note: 'Tcl_GetCurrentThread' returns sensible
     *		values even for a non-threaded core.
     */

    statePtr->managingThread = Tcl_GetCurrentThread();

    TclpSpliceFileChannel(chan);
    TclpSpliceSockChannel(chan);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_Close --
 *
 *	Closes a channel.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	Closes the channel if this is the last reference.
 *
 * NOTE:
 *	Tcl_Close removes the channel as far as the user is concerned.
 *	However, it may continue to exist for a while longer if it has
 *	a background flush scheduled. The device itself is eventually
 *	closed and the channel record removed, in CloseChannel, above.
 *
 *----------------------------------------------------------------------
 */

	/* ARGSUSED */
int
Tcl_Close(interp, chan)
    Tcl_Interp *interp;			/* Interpreter for errors. */
    Tcl_Channel chan;			/* The channel being closed. Must
					 * not be referenced in any
					 * interpreter. */
{
    CloseCallback *cbPtr;		/* Iterate over close callbacks
					 * for this channel. */
    Channel *chanPtr;			/* The real IO channel. */
    ChannelState *statePtr;		/* State of real IO channel. */
    int result;				/* Of calling FlushChannel. */

    if (chan == (Tcl_Channel) NULL) {
	return TCL_OK;
    }

    /*
     * Perform special handling for standard channels being closed. If the
     * refCount is now 1 it means that the last reference to the standard
     * channel is being explicitly closed, so bump the refCount down
     * artificially to 0. This will ensure that the channel is actually
     * closed, below. Also set the static pointer to NULL for the channel.
     */

    CheckForStdChannelsBeingClosed(chan);

    /*
     * This operation should occur at the top of a channel stack.
     */

    chanPtr = (Channel *) chan;
    statePtr = chanPtr->state;
    chanPtr = statePtr->topChanPtr;

    if (statePtr->refCount > 0) {
	Tcl_Panic("called Tcl_Close on channel with refCount > 0");
    }

    if (statePtr->flags & CHANNEL_INCLOSE) {
	Tcl_AppendResult(interp, "Illegal recursive call to close ",
		"through close-handler of channel", (char *) NULL);
	return TCL_ERROR;
    }
    statePtr->flags |= CHANNEL_INCLOSE;

    /*
     * When the channel has an escape sequence driven encoding such as
     * iso2022, the terminated escape sequence must write to the buffer.
     */
    if ((statePtr->encoding != NULL) && (statePtr->curOutPtr != NULL)
	    && (CheckChannelErrors(statePtr, TCL_WRITABLE) == 0)) {
	statePtr->outputEncodingFlags |= TCL_ENCODING_END;
	WriteChars(chanPtr, "", 0);
    }

    Tcl_ClearChannelHandlers(chan);

    /*
     * Invoke the registered close callbacks and delete their records.
     */

    while (statePtr->closeCbPtr != (CloseCallback *) NULL) {
	cbPtr = statePtr->closeCbPtr;
	statePtr->closeCbPtr = cbPtr->nextPtr;
	(cbPtr->proc) (cbPtr->clientData);
	ckfree((char *) cbPtr);
    }

    statePtr->flags &= ~CHANNEL_INCLOSE;

    /*
     * Ensure that the last output buffer will be flushed.
     */

    if ((statePtr->curOutPtr != (ChannelBuffer *) NULL) &&
	    (statePtr->curOutPtr->nextAdded > statePtr->curOutPtr->nextRemoved)) {
	statePtr->flags |= BUFFER_READY;
    }

    /*
     * If this channel supports it, close the read side, since we don't need it
     * anymore and this will help avoid deadlocks on some channel types.
     */

    if (chanPtr->typePtr->closeProc == TCL_CLOSE2PROC) {
	result = (chanPtr->typePtr->close2Proc)(chanPtr->instanceData, interp,
		TCL_CLOSE_READ);
    } else {
	result = 0;
    }

    /*
     * The call to FlushChannel will flush any queued output and invoke
     * the close function of the channel driver, or it will set up the
     * channel to be flushed and closed asynchronously.
     */

    statePtr->flags |= CHANNEL_CLOSED;
    if ((FlushChannel(interp, chanPtr, 0) != 0) || (result != 0)) {
	return TCL_ERROR;
    }
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ClearChannelHandlers --
 *
 *	Removes all channel handlers and event scripts from the channel,
 *	cancels all background copies involving the channel and any interest
 *	in events.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	See above. Deallocates memory.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_ClearChannelHandlers(channel)
    Tcl_Channel channel;
{
    ChannelHandler *chPtr, *chNext;	/* Iterate over channel handlers. */
    EventScriptRecord *ePtr, *eNextPtr;	/* Iterate over eventscript records. */
    Channel *chanPtr;			/* The real IO channel. */
    ChannelState *statePtr;		/* State of real IO channel. */
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
    NextChannelHandler *nhPtr;

    /*
     * This operation should occur at the top of a channel stack.
     */

    chanPtr = (Channel *) channel;
    statePtr = chanPtr->state;
    chanPtr = statePtr->topChanPtr;

    /*
     * Remove any references to channel handlers for this channel that
     * may be about to be invoked.
     */

    for (nhPtr = tsdPtr->nestedHandlerPtr;
	    nhPtr != (NextChannelHandler *) NULL;
	    nhPtr = nhPtr->nestedHandlerPtr) {
	if (nhPtr->nextHandlerPtr &&
		(nhPtr->nextHandlerPtr->chanPtr == chanPtr)) {
	    nhPtr->nextHandlerPtr = NULL;
	}
    }

    /*
     * Remove all the channel handler records attached to the channel
     * itself.
     */

    for (chPtr = statePtr->chPtr;
	    chPtr != (ChannelHandler *) NULL;
	    chPtr = chNext) {
	chNext = chPtr->nextPtr;
	ckfree((char *) chPtr);
    }
    statePtr->chPtr = (ChannelHandler *) NULL;

    /*
     * Cancel any pending copy operation.
     */

    StopCopy(statePtr->csPtr);

    /*
     * Must set the interest mask now to 0, otherwise infinite loops
     * will occur if Tcl_DoOneEvent is called before the channel is
     * finally deleted in FlushChannel. This can happen if the channel
     * has a background flush active.
     */

    statePtr->interestMask = 0;

    /*
     * Remove any EventScript records for this channel.
     */

    for (ePtr = statePtr->scriptRecordPtr;
	    ePtr != (EventScriptRecord *) NULL;
	    ePtr = eNextPtr) {
	eNextPtr = ePtr->nextPtr;
	TclDecrRefCount(ePtr->scriptPtr);
	ckfree((char *) ePtr);
    }
    statePtr->scriptRecordPtr = (EventScriptRecord *) NULL;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_Write --
 *
 *	Puts a sequence of bytes into an output buffer, may queue the
 *	buffer for output if it gets full, and also remembers whether the
 *	current buffer is ready e.g. if it contains a newline and we are in
 *	line buffering mode. Compensates stacking, i.e. will redirect the
 *	data from the specified channel to the topmost channel in a stack.
 *
 *	No encoding conversions are applied to the bytes being read.
 *
 * Results:
 *	The number of bytes written or -1 in case of error. If -1,
 *	Tcl_GetErrno will return the error code.
 *
 * Side effects:
 *	May buffer up output and may cause output to be produced on the
 *	channel.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_Write(chan, src, srcLen)
    Tcl_Channel chan;			/* The channel to buffer output for. */
    CONST char *src;			/* Data to queue in output buffer. */
    int srcLen;				/* Length of data in bytes, or < 0 for
					 * strlen(). */
{
    /*
     * Always use the topmost channel of the stack
     */

    Channel *chanPtr;
    ChannelState *statePtr;	/* state info for channel */

    statePtr = ((Channel *) chan)->state;
    chanPtr = statePtr->topChanPtr;

    if (CheckChannelErrors(statePtr, TCL_WRITABLE) != 0) {
	return -1;
    }

    if (srcLen < 0) {
	srcLen = strlen(src);
    }
    return DoWrite(chanPtr, src, srcLen);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_WriteRaw --
 *
 *	Puts a sequence of bytes into an output buffer, may queue the
 *	buffer for output if it gets full, and also remembers whether the
 *	current buffer is ready e.g. if it contains a newline and we are in
 *	line buffering mode. Writes directly to the driver of the channel,
 *	does not compensate for stacking.
 *
 *	No encoding conversions are applied to the bytes being read.
 *
 * Results:
 *	The number of bytes written or -1 in case of error. If -1,
 *	Tcl_GetErrno will return the error code.
 *
 * Side effects:
 *	May buffer up output and may cause output to be produced on the
 *	channel.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_WriteRaw(chan, src, srcLen)
    Tcl_Channel chan;			/* The channel to buffer output for. */
    CONST char *src;			/* Data to queue in output buffer. */
    int srcLen;				/* Length of data in bytes, or < 0 for
					 * strlen(). */
{
    Channel *chanPtr = ((Channel *) chan);
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    int errorCode, written;

    if (CheckChannelErrors(statePtr, TCL_WRITABLE | CHANNEL_RAW_MODE) != 0) {
	return -1;
    }

    if (srcLen < 0) {
	srcLen = strlen(src);
    }

    /*
     * Go immediately to the driver, do all the error handling by ourselves.
     * The code was stolen from 'FlushChannel'.
     */

    written = (chanPtr->typePtr->outputProc) (chanPtr->instanceData,
	    src, srcLen, &errorCode);

    if (written < 0) {
	Tcl_SetErrno(errorCode);
    }

    return written;
}

/*
 *---------------------------------------------------------------------------
 *
 * Tcl_WriteChars --
 *
 *	Takes a sequence of UTF-8 characters and converts them for output
 *	using the channel's current encoding, may queue the buffer for
 *	output if it gets full, and also remembers whether the current
 *	buffer is ready e.g. if it contains a newline and we are in
 *	line buffering mode. Compensates stacking, i.e. will redirect the
 *	data from the specified channel to the topmost channel in a stack.
 *
 * Results:
 *	The number of bytes written or -1 in case of error. If -1,
 *	Tcl_GetErrno will return the error code.
 *
 * Side effects:
 *	May buffer up output and may cause output to be produced on the
 *	channel.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_WriteChars(chan, src, len)
    Tcl_Channel chan;		/* The channel to buffer output for. */
    CONST char *src;		/* UTF-8 characters to queue in output buffer. */
    int len;			/* Length of string in bytes, or < 0 for 
				 * strlen(). */
{
    ChannelState *statePtr;	/* state info for channel */

    statePtr = ((Channel *) chan)->state;

    if (CheckChannelErrors(statePtr, TCL_WRITABLE) != 0) {
	return -1;
    }

    return DoWriteChars((Channel *) chan, src, len);
}

/*
 *---------------------------------------------------------------------------
 *
 * DoWriteChars --
 *
 *	Takes a sequence of UTF-8 characters and converts them for output
 *	using the channel's current encoding, may queue the buffer for
 *	output if it gets full, and also remembers whether the current
 *	buffer is ready e.g. if it contains a newline and we are in
 *	line buffering mode. Compensates stacking, i.e. will redirect the
 *	data from the specified channel to the topmost channel in a stack.
 *
 * Results:
 *	The number of bytes written or -1 in case of error. If -1,
 *	Tcl_GetErrno will return the error code.
 *
 * Side effects:
 *	May buffer up output and may cause output to be produced on the
 *	channel.
 *
 *----------------------------------------------------------------------
 */

static int
DoWriteChars(chanPtr, src, len)
    Channel *chanPtr;		/* The channel to buffer output for. */
    CONST char *src;		/* UTF-8 characters to queue in output buffer. */
    int len;			/* Length of string in bytes, or < 0 for 
				 * strlen(). */
{
    /*
     * Always use the topmost channel of the stack
     */

    ChannelState *statePtr;	/* state info for channel */

    statePtr = chanPtr->state;
    chanPtr = statePtr->topChanPtr;

    if (len < 0) {
	len = strlen(src);
    }
    if (statePtr->encoding == NULL) {
	/*
	 * Inefficient way to convert UTF-8 to byte-array, but the  
	 * code parallels the way it is done for objects.
	 */

	Tcl_Obj *objPtr;
	int result;

	objPtr = Tcl_NewStringObj(src, len);
	src = (char *) Tcl_GetByteArrayFromObj(objPtr, &len);
	result = WriteBytes(chanPtr, src, len);
	TclDecrRefCount(objPtr);
	return result;
    }
    return WriteChars(chanPtr, src, len);
}

/*
 *---------------------------------------------------------------------------
 *
 * Tcl_WriteObj --
 *
 *	Takes the Tcl object and queues its contents for output.  If the 
 *	encoding of the channel is NULL, takes the byte-array representation 
 *	of the object and queues those bytes for output.  Otherwise, takes 
 *	the characters in the UTF-8 (string) representation of the object 
 *	and converts them for output using the channel's current encoding.  
 *	May flush internal buffers to output if one becomes full or is ready 
 *	for some other reason, e.g. if it contains a newline and the channel 
 *	is in line buffering mode.
 *
 * Results:
 *	The number of bytes written or -1 in case of error. If -1, 
 *	Tcl_GetErrno() will return the error code.
 *
 * Side effects:
 *	May buffer up output and may cause output to be produced on the
 *	channel.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_WriteObj(chan, objPtr)
    Tcl_Channel chan;		/* The channel to buffer output for. */
    Tcl_Obj *objPtr;		/* The object to write. */
{
    /*
     * Always use the topmost channel of the stack
     */
    Channel *chanPtr;
    ChannelState *statePtr;	/* state info for channel */
    char *src;
    int srcLen;

    statePtr = ((Channel *) chan)->state;
    chanPtr = statePtr->topChanPtr;

    if (CheckChannelErrors(statePtr, TCL_WRITABLE) != 0) {
	return -1;
    }
    if (statePtr->encoding == NULL) {
	src = (char *) Tcl_GetByteArrayFromObj(objPtr, &srcLen);
	return WriteBytes(chanPtr, src, srcLen);
    } else {
	src = Tcl_GetStringFromObj(objPtr, &srcLen);
	return WriteChars(chanPtr, src, srcLen);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * WriteBytes --
 *
 *	Write a sequence of bytes into an output buffer, may queue the
 *	buffer for output if it gets full, and also remembers whether the
 *	current buffer is ready e.g. if it contains a newline and we are in
 *	line buffering mode.
 *
 * Results:
 *	The number of bytes written or -1 in case of error. If -1,
 *	Tcl_GetErrno will return the error code.
 *
 * Side effects:
 *	May buffer up output and may cause output to be produced on the
 *	channel.
 *
 *----------------------------------------------------------------------
 */

static int
WriteBytes(chanPtr, src, srcLen)
    Channel *chanPtr;		/* The channel to buffer output for. */
    CONST char *src;		/* Bytes to write. */
    int srcLen;			/* Number of bytes to write. */
{
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    ChannelBuffer *bufPtr;
    char *dst;
    int dstMax, sawLF, savedLF, total, dstLen, toWrite;

    total = 0;
    sawLF = 0;
    savedLF = 0;

    /*
     * Loop over all bytes in src, storing them in output buffer with
     * proper EOL translation.
     */

    while (srcLen + savedLF > 0) {
	bufPtr = statePtr->curOutPtr;
	if (bufPtr == NULL) {
	    bufPtr = AllocChannelBuffer(statePtr->bufSize);
	    statePtr->curOutPtr = bufPtr;
	}
	dst = bufPtr->buf + bufPtr->nextAdded;
	dstMax = bufPtr->bufLength - bufPtr->nextAdded;
	dstLen = dstMax;

	toWrite = dstLen;
	if (toWrite > srcLen) {
	    toWrite = srcLen;
	}

	if (savedLF) {
	    /*
	     * A '\n' was left over from last call to TranslateOutputEOL()
	     * and we need to store it in this buffer.  If the channel is
	     * line-based, we will need to flush it.
	     */

	    *dst++ = '\n';
	    dstLen--;
	    sawLF++;
	}
	if (TranslateOutputEOL(statePtr, dst, src, &dstLen, &toWrite)) {
	    sawLF++;
	}
	dstLen += savedLF;
	savedLF = 0;

	if (dstLen > dstMax) {
	    savedLF = 1;
	    dstLen = dstMax;
	}
	bufPtr->nextAdded += dstLen;
	if (CheckFlush(chanPtr, bufPtr, sawLF) != 0) {
	    return -1;
	}
	total += dstLen;
	src += toWrite;
	srcLen -= toWrite;
	sawLF = 0;
    }
    return total;
}

/*
 *----------------------------------------------------------------------
 *
 * WriteChars --
 *
 *	Convert UTF-8 bytes to the channel's external encoding and
 *	write the produced bytes into an output buffer, may queue the 
 *	buffer for output if it gets full, and also remembers whether the
 *	current buffer is ready e.g. if it contains a newline and we are in
 *	line buffering mode.
 *
 * Results:
 *	The number of bytes written or -1 in case of error. If -1,
 *	Tcl_GetErrno will return the error code.
 *
 * Side effects:
 *	May buffer up output and may cause output to be produced on the
 *	channel.
 *
 *----------------------------------------------------------------------
 */

static int
WriteChars(chanPtr, src, srcLen)
    Channel *chanPtr;		/* The channel to buffer output for. */
    CONST char *src;		/* UTF-8 string to write. */
    int srcLen;			/* Length of UTF-8 string in bytes. */
{
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    ChannelBuffer *bufPtr;
    char *dst, *stage;
    int saved, savedLF, sawLF, total, dstLen, stageMax, dstWrote;
    int stageLen, toWrite, stageRead, endEncoding, result;
    int consumedSomething;
    Tcl_Encoding encoding;
    char safe[BUFFER_PADDING];

    total = 0;
    sawLF = 0;
    savedLF = 0;
    saved = 0;
    encoding = statePtr->encoding;

    /*
     * Write the terminated escape sequence even if srcLen is 0.
     */

    endEncoding = ((statePtr->outputEncodingFlags & TCL_ENCODING_END) != 0);

    /*
     * Loop over all UTF-8 characters in src, storing them in staging buffer
     * with proper EOL translation.
     */

    consumedSomething = 1;
    while (consumedSomething && (srcLen + savedLF + endEncoding > 0)) {
	consumedSomething = 0;
	stage = statePtr->outputStage;
	stageMax = statePtr->bufSize;
	stageLen = stageMax;

	toWrite = stageLen;
	if (toWrite > srcLen) {
	    toWrite = srcLen;
	}

	if (savedLF) {
	    /*
	     * A '\n' was left over from last call to TranslateOutputEOL()
	     * and we need to store it in the staging buffer.  If the
	     * channel is line-based, we will need to flush the output
	     * buffer (after translating the staging buffer).
	     */

	    *stage++ = '\n';
	    stageLen--;
	    sawLF++;
	}
	if (TranslateOutputEOL(statePtr, stage, src, &stageLen, &toWrite)) {
	    sawLF++;
	}

	stage -= savedLF;
	stageLen += savedLF;
	savedLF = 0;

	if (stageLen > stageMax) {
	    savedLF = 1;
	    stageLen = stageMax;
	}
	src += toWrite;
	srcLen -= toWrite;

	/*
	 * Loop over all UTF-8 characters in staging buffer, converting them
	 * to external encoding, storing them in output buffer.
	 */

	while (stageLen + saved + endEncoding > 0) {
	    bufPtr = statePtr->curOutPtr;
	    if (bufPtr == NULL) {
		bufPtr = AllocChannelBuffer(statePtr->bufSize);
		statePtr->curOutPtr = bufPtr;
	    }
	    dst = bufPtr->buf + bufPtr->nextAdded;
	    dstLen = bufPtr->bufLength - bufPtr->nextAdded;

	    if (saved != 0) {
		/*
		 * Here's some translated bytes left over from the last
		 * buffer that we need to stick at the beginning of this
		 * buffer.
		 */

		memcpy((VOID *) dst, (VOID *) safe, (size_t) saved);
		bufPtr->nextAdded += saved;
		dst += saved;
		dstLen -= saved;
		saved = 0;
	    }

	    result = Tcl_UtfToExternal(NULL, encoding, stage, stageLen,
		    statePtr->outputEncodingFlags,
		    &statePtr->outputEncodingState, dst,
		    dstLen + BUFFER_PADDING, &stageRead, &dstWrote, NULL);

	    /* Fix for SF #506297, reported by Martin Forssen
	     * <ruric@users.sourceforge.net>.
	     *
	     * The encoding chosen in the script exposing the bug writes out
	     * three intro characters when TCL_ENCODING_START is set, but does
	     * not consume any input as TCL_ENCODING_END is cleared. As some
	     * output was generated the enclosing loop calls UtfToExternal
	     * again, again with START set. Three more characters in the out
	     * and still no use of input ... To break this infinite loop we
	     * remove TCL_ENCODING_START from the set of flags after the first
	     * call (no condition is required, the later calls remove an unset
	     * flag, which is a no-op). This causes the subsequent calls to
	     * UtfToExternal to consume and convert the actual input.
	     */

	    statePtr->outputEncodingFlags &= ~TCL_ENCODING_START;

	    /*
	     * The following code must be executed only when result is not 0.
	     */

	    if ((result != 0) && ((stageRead + dstWrote) == 0)) {
		/*
		 * We have an incomplete UTF-8 character at the end of the
		 * staging buffer.  It will get moved to the beginning of the
		 * staging buffer followed by more bytes from src.
		 */

		src -= stageLen;
		srcLen += stageLen;
		stageLen = 0;
		savedLF = 0;
		break;
	    }
	    bufPtr->nextAdded += dstWrote;
	    if (bufPtr->nextAdded > bufPtr->bufLength) {
		/*
		 * When translating from UTF-8 to external encoding, we
		 * allowed the translation to produce a character that
		 * crossed the end of the output buffer, so that we would
		 * get a completely full buffer before flushing it.  The
		 * extra bytes will be moved to the beginning of the next
		 * buffer.
		 */

		saved = bufPtr->nextAdded - bufPtr->bufLength;
		memcpy((VOID *) safe, (VOID *) (dst + dstLen), (size_t) saved);
		bufPtr->nextAdded = bufPtr->bufLength;
	    }
	    if (CheckFlush(chanPtr, bufPtr, sawLF) != 0) {
		return -1;
	    }

	    total += dstWrote;
	    stage += stageRead;
	    stageLen -= stageRead;
	    sawLF = 0;

	    consumedSomething = 1;

	    /*
	     * If all translated characters are written to the buffer,
	     * endEncoding is set to 0 because the escape sequence may be
	     * output.
	     */

	    if ((stageLen + saved == 0) && (result == 0)) {
		endEncoding = 0;
	    }
	}
    }

    /* If nothing was written and it happened because there was no progress
     * in the UTF conversion, we throw an error.
     */

    if (!consumedSomething && (total == 0)) {
	Tcl_SetErrno(EINVAL);
	return -1;
    }
    return total;
}

/*
 *---------------------------------------------------------------------------
 *
 * TranslateOutputEOL --
 *
 *	Helper function for WriteBytes() and WriteChars().  Converts the
 *	'\n' characters in the source buffer into the appropriate EOL
 *	form specified by the output translation mode.
 *
 *	EOL translation stops either when the source buffer is empty
 *	or the output buffer is full.
 *
 *	When converting to CRLF mode and there is only 1 byte left in
 *	the output buffer, this routine stores the '\r' in the last
 *	byte and then stores the '\n' in the byte just past the end of the 
 *	buffer.  The caller is responsible for passing in a buffer that
 *	is large enough to hold the extra byte.
 *
 * Results:
 *	The return value is 1 if a '\n' was translated from the source
 *	buffer, or 0 otherwise -- this can be used by the caller to
 *	decide to flush a line-based channel even though the channel
 *	buffer is not full.
 *
 *	*dstLenPtr is filled with how many bytes of the output buffer
 *	were used.  As mentioned above, this can be one more that
 *	the output buffer's specified length if a CRLF was stored.
 *
 *	*srcLenPtr is filled with how many bytes of the source buffer
 *	were consumed.  
 *
 * Side effects:
 *	It may be obvious, but bears mentioning that when converting
 *	in CRLF mode (which requires two bytes of storage in the output
 *	buffer), the number of bytes consumed from the source buffer
 *	will be less than the number of bytes stored in the output buffer.
 *
 *---------------------------------------------------------------------------
 */

static int
TranslateOutputEOL(statePtr, dst, src, dstLenPtr, srcLenPtr)
    ChannelState *statePtr;	/* Channel being read, for translation and
				 * buffering modes. */
    char *dst;			/* Output buffer filled with UTF-8 chars by
				 * applying appropriate EOL translation to
				 * source characters. */
    CONST char *src;		/* Source UTF-8 characters. */
    int *dstLenPtr;		/* On entry, the maximum length of output
				 * buffer in bytes.  On exit, the number of
				 * bytes actually used in output buffer. */
    int *srcLenPtr;		/* On entry, the length of source buffer.
				 * On exit, the number of bytes read from
				 * the source buffer. */
{
    char *dstEnd;
    int srcLen, newlineFound;

    newlineFound = 0;
    srcLen = *srcLenPtr;

    switch (statePtr->outputTranslation) {
	case TCL_TRANSLATE_LF: {
	    for (dstEnd = dst + srcLen; dst < dstEnd; ) {
		if (*src == '\n') {
		    newlineFound = 1;
		}
		*dst++ = *src++;
	    }
	    *dstLenPtr = srcLen;
	    break;
	}
	case TCL_TRANSLATE_CR: {
	    for (dstEnd = dst + srcLen; dst < dstEnd;) {
		if (*src == '\n') {
		    *dst++ = '\r';
		    newlineFound = 1;
		    src++;
		} else {
		    *dst++ = *src++;
		}
	    }
	    *dstLenPtr = srcLen;
	    break;
	}
	case TCL_TRANSLATE_CRLF: {
	    /*
	     * Since this causes the number of bytes to grow, we
	     * start off trying to put 'srcLen' bytes into the
	     * output buffer, but allow it to store more bytes, as
	     * long as there's still source bytes and room in the
	     * output buffer.
	     */

	    char *dstStart, *dstMax;
	    CONST char *srcStart;

	    dstStart = dst;
	    dstMax = dst + *dstLenPtr;

	    srcStart = src;

	    if (srcLen < *dstLenPtr) {
		dstEnd = dst + srcLen;
	    } else {
		dstEnd = dst + *dstLenPtr;
	    }
	    while (dst < dstEnd) {
		if (*src == '\n') {
		    if (dstEnd < dstMax) {
			dstEnd++;
		    }
		    *dst++ = '\r';
		    newlineFound = 1;
		}
		*dst++ = *src++;
	    }
	    *srcLenPtr = src - srcStart;
	    *dstLenPtr = dst - dstStart;
	    break;
	}
	default: {
	    break;
	}
    }
    return newlineFound;
}

/*
 *---------------------------------------------------------------------------
 *
 * CheckFlush --
 *
 *	Helper function for WriteBytes() and WriteChars().  If the
 *	channel buffer is ready to be flushed, flush it.
 *
 * Results:
 *	The return value is -1 if there was a problem flushing the
 *	channel buffer, or 0 otherwise.
 *
 * Side effects:
 *	The buffer will be recycled if it is flushed.
 *
 *---------------------------------------------------------------------------
 */

static int
CheckFlush(chanPtr, bufPtr, newlineFlag)
    Channel *chanPtr;		/* Channel being read, for buffering mode. */
    ChannelBuffer *bufPtr;	/* Channel buffer to possibly flush. */
    int newlineFlag;		/* Non-zero if a the channel buffer
				 * contains a newline. */
{
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    /*
     * The current buffer is ready for output:
     * 1. if it is full.
     * 2. if it contains a newline and this channel is line-buffered.
     * 3. if it contains any output and this channel is unbuffered.
     */

    if ((statePtr->flags & BUFFER_READY) == 0) {
	if (bufPtr->nextAdded == bufPtr->bufLength) {
	    statePtr->flags |= BUFFER_READY;
	} else if (statePtr->flags & CHANNEL_LINEBUFFERED) {
	    if (newlineFlag != 0) {
		statePtr->flags |= BUFFER_READY;
	    }
	} else if (statePtr->flags & CHANNEL_UNBUFFERED) {
	    statePtr->flags |= BUFFER_READY;
	}
    }
    if (statePtr->flags & BUFFER_READY) {
	if (FlushChannel(NULL, chanPtr, 0) != 0) {
	    return -1;
	}
    }
    return 0;
}

/*
 *---------------------------------------------------------------------------
 *
 * Tcl_Gets --
 *
 *	Reads a complete line of input from the channel into a Tcl_DString.
 *
 * Results:
 *	Length of line read (in characters) or -1 if error, EOF, or blocked.
 *	If -1, use Tcl_GetErrno() to retrieve the POSIX error code for the
 *	error or condition that occurred.
 *
 * Side effects:
 *	May flush output on the channel.  May cause input to be consumed
 *	from the channel.
 *
 *---------------------------------------------------------------------------
 */

int
Tcl_Gets(chan, lineRead)
    Tcl_Channel chan;		/* Channel from which to read. */
    Tcl_DString *lineRead;	/* The line read will be appended to this
				 * DString as UTF-8 characters.  The caller
				 * must have initialized it and is responsible
				 * for managing the storage. */
{
    Tcl_Obj *objPtr;
    int charsStored, length;
    char *string;

    TclNewObj(objPtr);
    charsStored = Tcl_GetsObj(chan, objPtr);
    if (charsStored > 0) {
	string = Tcl_GetStringFromObj(objPtr, &length);
	Tcl_DStringAppend(lineRead, string, length);
    }
    TclDecrRefCount(objPtr);
    return charsStored;
}

/*
 *---------------------------------------------------------------------------
 *
 * Tcl_GetsObj --
 *
 *	Accumulate input from the input channel until end-of-line or
 *	end-of-file has been seen.  Bytes read from the input channel
 *	are converted to UTF-8 using the encoding specified by the
 *	channel.
 *
 * Results:
 *	Number of characters accumulated in the object or -1 if error,
 *	blocked, or EOF.  If -1, use Tcl_GetErrno() to retrieve the
 *	POSIX error code for the error or condition that occurred.
 *
 * Side effects:
 *	Consumes input from the channel.
 *
 *	On reading EOF, leave channel pointing at EOF char.
 *	On reading EOL, leave channel pointing after EOL, but don't
 *	return EOL in dst buffer.
 *
 *---------------------------------------------------------------------------
 */

int
Tcl_GetsObj(chan, objPtr)
    Tcl_Channel chan;		/* Channel from which to read. */
    Tcl_Obj *objPtr;		/* The line read will be appended to this
				 * object as UTF-8 characters. */
{
    GetsState gs;
    Channel *chanPtr = (Channel *) chan;
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    ChannelBuffer *bufPtr;
    int inEofChar, skip, copiedTotal, oldLength, oldFlags, oldRemoved;
    Tcl_Encoding encoding;
    char *dst, *dstEnd, *eol, *eof;
    Tcl_EncodingState oldState;

    /*
     * This operation should occur at the top of a channel stack.
     */

    chanPtr = statePtr->topChanPtr;

    if (CheckChannelErrors(statePtr, TCL_READABLE) != 0) {
	copiedTotal = -1;
	goto done;
    }

    bufPtr = statePtr->inQueueHead;
    encoding = statePtr->encoding;

    /*
     * Preserved so we can restore the channel's state in case we don't
     * find a newline in the available input.
     */

    Tcl_GetStringFromObj(objPtr, &oldLength);
    oldFlags = statePtr->inputEncodingFlags;
    oldState = statePtr->inputEncodingState;
    oldRemoved = BUFFER_PADDING;
    if (bufPtr != NULL) {
	oldRemoved = bufPtr->nextRemoved;
    }

    /*
     * If there is no encoding, use "iso8859-1" -- Tcl_GetsObj() doesn't
     * produce ByteArray objects.  
     */

    if (encoding == NULL) {
	encoding = Tcl_GetEncoding(NULL, "iso8859-1");
    }

    /*
     * Object used by FilterInputBytes to keep track of how much data has
     * been consumed from the channel buffers.
     */

    gs.objPtr		= objPtr;
    gs.dstPtr		= &dst;
    gs.encoding		= encoding;
    gs.bufPtr		= bufPtr;
    gs.state		= oldState;
    gs.rawRead		= 0;
    gs.bytesWrote	= 0;
    gs.charsWrote	= 0;
    gs.totalChars	= 0;

    dst = objPtr->bytes + oldLength;
    dstEnd = dst;

    skip = 0;
    eof = NULL;
    inEofChar = statePtr->inEofChar;

    while (1) {
	if (dst >= dstEnd) {
	    if (FilterInputBytes(chanPtr, &gs) != 0) {
		goto restore;
	    }
	    dstEnd = dst + gs.bytesWrote;
	}

	/*
	 * Remember if EOF char is seen, then look for EOL anyhow, because
	 * the EOL might be before the EOF char.
	 */

	if (inEofChar != '\0') {
	    for (eol = dst; eol < dstEnd; eol++) {
		if (*eol == inEofChar) {
		    dstEnd = eol;
		    eof = eol;
		    break;
		}
	    }
	}

	/*
	 * On EOL, leave current file position pointing after the EOL, but
	 * don't store the EOL in the output string.
	 */

	switch (statePtr->inputTranslation) {
	    case TCL_TRANSLATE_LF: {
		for (eol = dst; eol < dstEnd; eol++) {
		    if (*eol == '\n') {
			skip = 1;
			goto goteol;
		    }
		}
		break;
	    }
	    case TCL_TRANSLATE_CR: {
		for (eol = dst; eol < dstEnd; eol++) {
		    if (*eol == '\r') {
			skip = 1;
			goto goteol;
		    }
		}
		break;
	    }
	    case TCL_TRANSLATE_CRLF: {
		for (eol = dst; eol < dstEnd; eol++) {
		    if (*eol == '\r') {
			eol++;

			/*
			 * If a CR is at the end of the buffer,
			 * then check for a LF at the begining
			 * of the next buffer.
			 */

			if (eol >= dstEnd) {
			    int offset;

			    offset = eol - objPtr->bytes;
			    dst = dstEnd;
			    if (FilterInputBytes(chanPtr, &gs) != 0) {
				goto restore;
			    }
			    dstEnd = dst + gs.bytesWrote;
			    eol = objPtr->bytes + offset;
			    if (eol >= dstEnd) {
				skip = 0;
				goto goteol;
			    }
			}
			if (*eol == '\n') {
			    eol--;
			    skip = 2;
			    goto goteol;
			}
		    }
		}
		break;
	    }
	    case TCL_TRANSLATE_AUTO: {
		eol = dst;
		skip = 1;
		if (statePtr->flags & INPUT_SAW_CR) {
		    statePtr->flags &= ~INPUT_SAW_CR;
		    if ((eol < dstEnd) && (*eol == '\n')) {
			/*
			 * Skip the raw bytes that make up the '\n'.
			 */

			char tmp[1 + TCL_UTF_MAX];
			int rawRead;

			bufPtr = gs.bufPtr;
			Tcl_ExternalToUtf(NULL, gs.encoding,
				bufPtr->buf + bufPtr->nextRemoved,
				gs.rawRead, statePtr->inputEncodingFlags,
				&gs.state, tmp, 1 + TCL_UTF_MAX, &rawRead,
				NULL, NULL);
			bufPtr->nextRemoved += rawRead;
			gs.rawRead -= rawRead;
			gs.bytesWrote--;
			gs.charsWrote--;
			memmove(dst, dst + 1, (size_t) (dstEnd - dst));
			dstEnd--;
		    }
		}
		for (eol = dst; eol < dstEnd; eol++) {
		    if (*eol == '\r') {
			eol++;
			if (eol == dstEnd) {
			    /*
			     * If buffer ended on \r, peek ahead to see if a
			     * \n is available.
			     */

			    int offset;

			    offset = eol - objPtr->bytes;
			    dst = dstEnd;
			    PeekAhead(chanPtr, &dstEnd, &gs);
			    eol = objPtr->bytes + offset;
			    if (eol >= dstEnd) {
				eol--;
				statePtr->flags |= INPUT_SAW_CR;
				goto goteol;
			    }
			}
			if (*eol == '\n') {
			    skip++;
			}
			eol--;
			goto goteol;
		    } else if (*eol == '\n') {
			goto goteol;
		    }
		}
	    }
	}
	if (eof != NULL) {
	    /*
	     * EOF character was seen.  On EOF, leave current file position
	     * pointing at the EOF character, but don't store the EOF
	     * character in the output string.
	     */

	    dstEnd = eof;
	    statePtr->flags |= (CHANNEL_EOF | CHANNEL_STICKY_EOF);
	    statePtr->inputEncodingFlags |= TCL_ENCODING_END;
	}
	if (statePtr->flags & CHANNEL_EOF) {
	    skip = 0;
	    eol = dstEnd;
	    if (eol == objPtr->bytes + oldLength) {
		/*
		 * If we didn't append any bytes before encountering EOF,
		 * caller needs to see -1.
		 */

		Tcl_SetObjLength(objPtr, oldLength);
		CommonGetsCleanup(chanPtr, encoding);
		copiedTotal = -1;
		goto done;
	    }
	    goto goteol;
	}
	dst = dstEnd;
    }

    /*
     * Found EOL or EOF, but the output buffer may now contain too many
     * UTF-8 characters.  We need to know how many raw bytes correspond to
     * the number of UTF-8 characters we want, plus how many raw bytes
     * correspond to the character(s) making up EOL (if any), so we can
     * remove the correct number of bytes from the channel buffer.
     */

    goteol:
    bufPtr = gs.bufPtr;
    statePtr->inputEncodingState = gs.state;
    Tcl_ExternalToUtf(NULL, gs.encoding, bufPtr->buf + bufPtr->nextRemoved,
	    gs.rawRead, statePtr->inputEncodingFlags,
	    &statePtr->inputEncodingState, dst,
	    eol - dst + skip + TCL_UTF_MAX, &gs.rawRead, NULL,
	    &gs.charsWrote);
    bufPtr->nextRemoved += gs.rawRead;

    /*
     * Recycle all the emptied buffers.
     */

    Tcl_SetObjLength(objPtr, eol - objPtr->bytes);
    CommonGetsCleanup(chanPtr, encoding);
    statePtr->flags &= ~CHANNEL_BLOCKED;
    copiedTotal = gs.totalChars + gs.charsWrote - skip;
    goto done;

    /*
     * Couldn't get a complete line.  This only happens if we get a error
     * reading from the channel or we are non-blocking and there wasn't
     * an EOL or EOF in the data available.
     */

    restore:
    bufPtr = statePtr->inQueueHead;
    bufPtr->nextRemoved = oldRemoved;

    for (bufPtr = bufPtr->nextPtr; bufPtr != NULL; bufPtr = bufPtr->nextPtr) {
	bufPtr->nextRemoved = BUFFER_PADDING;
    }
    CommonGetsCleanup(chanPtr, encoding);

    statePtr->inputEncodingState = oldState;
    statePtr->inputEncodingFlags = oldFlags;
    Tcl_SetObjLength(objPtr, oldLength);

    /*
     * We didn't get a complete line so we need to indicate to UpdateInterest
     * that the gets blocked.  It will wait for more data instead of firing
     * a timer, avoiding a busy wait.  This is where we are assuming that the
     * next operation is a gets.  No more file events will be delivered on 
     * this channel until new data arrives or some operation is performed
     * on the channel (e.g. gets, read, fconfigure) that changes the blocking
     * state.  Note that this means a file event will not be delivered even
     * though a read would be able to consume the buffered data.
     */

    statePtr->flags |= CHANNEL_NEED_MORE_DATA;
    copiedTotal = -1;

    done:
    /*
     * Update the notifier state so we don't block while there is still
     * data in the buffers.
     */

    UpdateInterest(chanPtr);
    return copiedTotal;
}

/*
 *---------------------------------------------------------------------------
 *
 * FilterInputBytes --
 *
 *	Helper function for Tcl_GetsObj.  Produces UTF-8 characters from
 *	raw bytes read from the channel.  
 *
 *	Consumes available bytes from channel buffers.  When channel
 *	buffers are exhausted, reads more bytes from channel device into
 *	a new channel buffer.  It is the caller's responsibility to
 *	free the channel buffers that have been exhausted.
 *
 * Results:
 *	The return value is -1 if there was an error reading from the
 *	channel, 0 otherwise.
 *
 * Side effects:
 *	Status object keeps track of how much data from channel buffers
 *	has been consumed and where UTF-8 bytes should be stored.
 *
 *---------------------------------------------------------------------------
 */

static int
FilterInputBytes(chanPtr, gsPtr)
    Channel *chanPtr;		/* Channel to read. */
    GetsState *gsPtr;		/* Current state of gets operation. */
{
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    ChannelBuffer *bufPtr;
    char *raw, *rawStart, *rawEnd;
    char *dst;
    int offset, toRead, dstNeeded, spaceLeft, result, rawLen, length;
    Tcl_Obj *objPtr;
#define ENCODING_LINESIZE   20	/* Lower bound on how many bytes to convert
				 * at a time.  Since we don't know a priori
				 * how many bytes of storage this many source
				 * bytes will use, we actually need at least
				 * ENCODING_LINESIZE * TCL_MAX_UTF bytes of
				 * room. */

    objPtr = gsPtr->objPtr;

    /*
     * Subtract the number of bytes that were removed from channel buffer
     * during last call.
     */

    bufPtr = gsPtr->bufPtr;
    if (bufPtr != NULL) {
	bufPtr->nextRemoved += gsPtr->rawRead;
	if (bufPtr->nextRemoved >= bufPtr->nextAdded) {
	    bufPtr = bufPtr->nextPtr;
	}
    }
    gsPtr->totalChars += gsPtr->charsWrote;

    if ((bufPtr == NULL) || (bufPtr->nextAdded == BUFFER_PADDING)) {
	/*
	 * All channel buffers were exhausted and the caller still hasn't
	 * seen EOL.  Need to read more bytes from the channel device.
	 * Side effect is to allocate another channel buffer.
	 */

	read:
	if (statePtr->flags & CHANNEL_BLOCKED) {
	    if (statePtr->flags & CHANNEL_NONBLOCKING) {
		gsPtr->charsWrote = 0;
		gsPtr->rawRead = 0;
		return -1;
	    }
	    statePtr->flags &= ~CHANNEL_BLOCKED;
	}
	if (GetInput(chanPtr) != 0) {
	    gsPtr->charsWrote = 0;
	    gsPtr->rawRead = 0;
	    return -1;
	}
	bufPtr = statePtr->inQueueTail;
	gsPtr->bufPtr = bufPtr;
    }

    /*
     * Convert some of the bytes from the channel buffer to UTF-8.  Space in
     * objPtr's string rep is used to hold the UTF-8 characters.  Grow the
     * string rep if we need more space.
     */

    rawStart = bufPtr->buf + bufPtr->nextRemoved;
    raw = rawStart;
    rawEnd = bufPtr->buf + bufPtr->nextAdded;
    rawLen = rawEnd - rawStart;

    dst = *gsPtr->dstPtr;
    offset = dst - objPtr->bytes;
    toRead = ENCODING_LINESIZE;
    if (toRead > rawLen) {
	toRead = rawLen;
    }
    dstNeeded = toRead * TCL_UTF_MAX + 1;
    spaceLeft = objPtr->length - offset - TCL_UTF_MAX - 1;
    if (dstNeeded > spaceLeft) {
	length = offset * 2;
	if (offset < dstNeeded) {
	    length = offset + dstNeeded;
	}
	length += TCL_UTF_MAX + 1;
	Tcl_SetObjLength(objPtr, length);
	spaceLeft = length - offset;
	dst = objPtr->bytes + offset;
	*gsPtr->dstPtr = dst;
    }
    gsPtr->state = statePtr->inputEncodingState;
    result = Tcl_ExternalToUtf(NULL, gsPtr->encoding, raw, rawLen,
	    statePtr->inputEncodingFlags, &statePtr->inputEncodingState,
	    dst, spaceLeft, &gsPtr->rawRead, &gsPtr->bytesWrote,
	    &gsPtr->charsWrote);

    /*
     * Make sure that if we go through 'gets', that we reset the
     * TCL_ENCODING_START flag still.  [Bug #523988]
     */

    statePtr->inputEncodingFlags &= ~TCL_ENCODING_START;

    if (result == TCL_CONVERT_MULTIBYTE) {
	/*
	 * The last few bytes in this channel buffer were the start of a
	 * multibyte sequence.  If this buffer was full, then move them to
	 * the next buffer so the bytes will be contiguous.  
	 */

	ChannelBuffer *nextPtr;
	int extra;

	nextPtr = bufPtr->nextPtr;
	if (bufPtr->nextAdded < bufPtr->bufLength) {
	    if (gsPtr->rawRead > 0) {
		/*
		 * Some raw bytes were converted to UTF-8.  Fall through,
		 * returning those UTF-8 characters because a EOL might be
		 * present in them.
		 */
	    } else if (statePtr->flags & CHANNEL_EOF) {
		/*
		 * There was a partial character followed by EOF on the
		 * device.  Fall through, returning that nothing was found.
		 */

		bufPtr->nextRemoved = bufPtr->nextAdded;
	    } else {
		/*
		 * There are no more cached raw bytes left.  See if we can
		 * get some more.
		 */

		goto read;
	    }
	} else {
	    if (nextPtr == NULL) {
		nextPtr = AllocChannelBuffer(statePtr->bufSize);
		bufPtr->nextPtr = nextPtr;
		statePtr->inQueueTail = nextPtr;
	    }
	    extra = rawLen - gsPtr->rawRead;
	    memcpy((VOID *) (nextPtr->buf + BUFFER_PADDING - extra),
		    (VOID *) (raw + gsPtr->rawRead), (size_t) extra);
	    nextPtr->nextRemoved -= extra;
	    bufPtr->nextAdded -= extra;
	}
    }

    gsPtr->bufPtr = bufPtr;
    return 0;
}

/*
 *---------------------------------------------------------------------------
 *
 * PeekAhead --
 *
 *	Helper function used by Tcl_GetsObj().  Called when we've seen a
 *	\r at the end of the UTF-8 string and want to look ahead one
 *	character to see if it is a \n.
 *
 * Results:
 *	*gsPtr->dstPtr is filled with a pointer to the start of the range of
 *	UTF-8 characters that were found by peeking and *dstEndPtr is filled
 *	with a pointer to the bytes just after the end of the range.
 *
 * Side effects:
 *	If no more raw bytes were available in one of the channel buffers,
 *	tries to perform a non-blocking read to get more bytes from the
 *	channel device.
 *
 *---------------------------------------------------------------------------
 */

static void
PeekAhead(chanPtr, dstEndPtr, gsPtr)
    Channel *chanPtr;		/* The channel to read. */
    char **dstEndPtr;		/* Filled with pointer to end of new range
				 * of UTF-8 characters. */
    GetsState *gsPtr;		/* Current state of gets operation. */
{
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    ChannelBuffer *bufPtr;
    Tcl_DriverBlockModeProc *blockModeProc;
    int bytesLeft;

    bufPtr = gsPtr->bufPtr;

    /*
     * If there's any more raw input that's still buffered, we'll peek into
     * that.  Otherwise, only get more data from the channel driver if it
     * looks like there might actually be more data.  The assumption is that
     * if the channel buffer is filled right up to the end, then there
     * might be more data to read.
     */

    blockModeProc = NULL;
    if (bufPtr->nextPtr == NULL) {
	bytesLeft = bufPtr->nextAdded - (bufPtr->nextRemoved + gsPtr->rawRead);
	if (bytesLeft == 0) {
	    if (bufPtr->nextAdded < bufPtr->bufLength) {
		/*
		 * Don't peek ahead if last read was short read.
		 */

		goto cleanup;
	    }
	    if ((statePtr->flags & CHANNEL_NONBLOCKING) == 0) {
		blockModeProc = Tcl_ChannelBlockModeProc(chanPtr->typePtr);
		if (blockModeProc == NULL) {
		    /*
		     * Don't peek ahead if cannot set non-blocking mode.
		     */

		    goto cleanup;
		}
		StackSetBlockMode(chanPtr, TCL_MODE_NONBLOCKING);
	    }
	}
    }
    if (FilterInputBytes(chanPtr, gsPtr) == 0) {
	*dstEndPtr = *gsPtr->dstPtr + gsPtr->bytesWrote;
    }
    if (blockModeProc != NULL) {
	StackSetBlockMode(chanPtr, TCL_MODE_BLOCKING);
    }
    return;

    cleanup:
    bufPtr->nextRemoved += gsPtr->rawRead;
    gsPtr->rawRead = 0;
    gsPtr->totalChars += gsPtr->charsWrote;
    gsPtr->bytesWrote = 0;
    gsPtr->charsWrote = 0;
}

/*
 *---------------------------------------------------------------------------
 *
 * CommonGetsCleanup --
 *
 *	Helper function for Tcl_GetsObj() to restore the channel after
 *	a "gets" operation.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Encoding may be freed.
 *
 *---------------------------------------------------------------------------
 */

static void
CommonGetsCleanup(chanPtr, encoding)
    Channel *chanPtr;
    Tcl_Encoding encoding;
{
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    ChannelBuffer *bufPtr, *nextPtr;

    bufPtr = statePtr->inQueueHead;
    for ( ; bufPtr != NULL; bufPtr = nextPtr) {
	nextPtr = bufPtr->nextPtr;
	if (bufPtr->nextRemoved < bufPtr->nextAdded) {
	    break;
	}
	RecycleBuffer(statePtr, bufPtr, 0);
    }
    statePtr->inQueueHead = bufPtr;
    if (bufPtr == NULL) {
	statePtr->inQueueTail = NULL;
    } else {
	/*
	 * If any multi-byte characters were split across channel buffer
	 * boundaries, the split-up bytes were moved to the next channel
	 * buffer by FilterInputBytes().  Move the bytes back to their
	 * original buffer because the caller could change the channel's
	 * encoding which could change the interpretation of whether those
	 * bytes really made up multi-byte characters after all.
	 */

	nextPtr = bufPtr->nextPtr;
	for ( ; nextPtr != NULL; nextPtr = bufPtr->nextPtr) {
	    int extra;

	    extra = bufPtr->bufLength - bufPtr->nextAdded;
	    if (extra > 0) {
		memcpy((VOID *) (bufPtr->buf + bufPtr->nextAdded),
			(VOID *) (nextPtr->buf + BUFFER_PADDING - extra),
			(size_t) extra);
		bufPtr->nextAdded += extra;
		nextPtr->nextRemoved = BUFFER_PADDING;
	    }
	    bufPtr = nextPtr;
	}
    }
    if (statePtr->encoding == NULL) {
	Tcl_FreeEncoding(encoding);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_Read --
 *
 *	Reads a given number of bytes from a channel.  EOL and EOF
 *	translation is done on the bytes being read, so the number
 *	of bytes consumed from the channel may not be equal to the
 *	number of bytes stored in the destination buffer.
 *
 *	No encoding conversions are applied to the bytes being read.
 *
 * Results:
 *	The number of bytes read, or -1 on error. Use Tcl_GetErrno()
 *	to retrieve the error code for the error that occurred.
 *
 * Side effects:
 *	May cause input to be buffered.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_Read(chan, dst, bytesToRead)
    Tcl_Channel chan;		/* The channel from which to read. */
    char *dst;			/* Where to store input read. */
    int bytesToRead;		/* Maximum number of bytes to read. */
{
    Channel *chanPtr = (Channel *) chan;		
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */

    /*
     * This operation should occur at the top of a channel stack.
     */

    chanPtr = statePtr->topChanPtr;

    if (CheckChannelErrors(statePtr, TCL_READABLE) != 0) {
	return -1;
    }

    return DoRead(chanPtr, dst, bytesToRead);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ReadRaw --
 *
 *	Reads a given number of bytes from a channel.  EOL and EOF
 *	translation is done on the bytes being read, so the number
 *	of bytes consumed from the channel may not be equal to the
 *	number of bytes stored in the destination buffer.
 *
 *	No encoding conversions are applied to the bytes being read.
 *
 * Results:
 *	The number of bytes read, or -1 on error. Use Tcl_GetErrno()
 *	to retrieve the error code for the error that occurred.
 *
 * Side effects:
 *	May cause input to be buffered.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_ReadRaw(chan, bufPtr, bytesToRead)
    Tcl_Channel chan;		/* The channel from which to read. */
    char *bufPtr;		/* Where to store input read. */
    int bytesToRead;		/* Maximum number of bytes to read. */
{
    Channel *chanPtr = (Channel *) chan;		
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    int nread, result;
    int copied, copiedNow;

    /*
     * The check below does too much because it will reject a call to this
     * function with a channel which is part of an 'fcopy'. But we have to
     * allow this here or else the chaining in the transformation drivers
     * will fail with 'file busy' error instead of retrieving and
     * transforming the data to copy.
     *
     * We let the check procedure now believe that there is no fcopy in
     * progress. A better solution than this might be an additional flag
     * argument to switch off specific checks.
     */

    if (CheckChannelErrors(statePtr, TCL_READABLE | CHANNEL_RAW_MODE) != 0) {
	return -1;
    }

    /*
     * Check for information in the push-back buffers. If there is
     * some, use it. Go to the driver only if there is none (anymore)
     * and the caller requests more bytes.
     */

    for (copied = 0; copied < bytesToRead; copied += copiedNow) {
	copiedNow = CopyBuffer(chanPtr, bufPtr + copied,
		bytesToRead - copied);
	if (copiedNow == 0) {
	    if (statePtr->flags & CHANNEL_EOF) {
		goto done;
	    }
	    if (statePtr->flags & CHANNEL_BLOCKED) {
		if (statePtr->flags & CHANNEL_NONBLOCKING) {
		    goto done;
		}
		statePtr->flags &= (~(CHANNEL_BLOCKED));
	    }

#ifdef TCL_IO_TRACK_OS_FOR_DRIVER_WITH_BAD_BLOCKING
	    /* [SF Tcl Bug 943274]. Better emulation of non-blocking
	     * channels for channels without BlockModeProc, by keeping
	     * track of true fileevents generated by the OS == Data
	     * waiting and reading if and only if we are sure to have
	     * data.
	     */

	    if ((statePtr->flags & CHANNEL_NONBLOCKING) &&
		    (Tcl_ChannelBlockModeProc(chanPtr->typePtr) == NULL) &&
		    !(statePtr->flags & CHANNEL_HAS_MORE_DATA)) {
		/*
		 * We bypass the driver, it would block, as no data is
		 * available
		 */
		nread = -1;
		result = EWOULDBLOCK;
	    } else {
#endif /* TCL_IO_TRACK_OS_FOR_DRIVER_WITH_BAD_BLOCKING */
		/*
		 * Now go to the driver to get as much as is possible to
		 * fill the remaining request. Do all the error handling
		 * by ourselves.  The code was stolen from 'GetInput' and
		 * slightly adapted (different return value here).
		 *
		 * The case of 'bytesToRead == 0' at this point cannot happen.
		 */

		nread = (chanPtr->typePtr->inputProc)(chanPtr->instanceData,
			bufPtr + copied, bytesToRead - copied, &result);
#ifdef TCL_IO_TRACK_OS_FOR_DRIVER_WITH_BAD_BLOCKING
	    }
#endif /* TCL_IO_TRACK_OS_FOR_DRIVER_WITH_BAD_BLOCKING */
	    if (nread > 0) {
		/*
		 * If we get a short read, signal up that we may be
		 * BLOCKED. We should avoid calling the driver because
		 * on some platforms we will block in the low level
		 * reading code even though the channel is set into
		 * nonblocking mode.
		 */

		if (nread < (bytesToRead - copied)) {
		    statePtr->flags |= CHANNEL_BLOCKED;
		}

#ifdef TCL_IO_TRACK_OS_FOR_DRIVER_WITH_BAD_BLOCKING
		if (nread <= (bytesToRead - copied)) {
		    /*
		     * [SF Tcl Bug 943274] We have read the available
		     * data, clear flag.
		     */

		    statePtr->flags &= ~CHANNEL_HAS_MORE_DATA;
		}
#endif /* TCL_IO_TRACK_OS_FOR_DRIVER_WITH_BAD_BLOCKING */
	    } else if (nread == 0) {
		statePtr->flags |= CHANNEL_EOF;
		statePtr->inputEncodingFlags |= TCL_ENCODING_END;
	    } else if (nread < 0) {
		if ((result == EWOULDBLOCK) || (result == EAGAIN)) {
		    if (copied > 0) {
			/*
			 * Information that was copied earlier has precedence
			 * over EAGAIN/WOULDBLOCK handling.
			 */

			return copied;
		    }

		    statePtr->flags |= CHANNEL_BLOCKED;
		    result = EAGAIN;
		}

		Tcl_SetErrno(result);
		return -1;
	    } 

	    return copied + nread;
	}
    }

done:
    return copied;
}

/*
 *---------------------------------------------------------------------------
 *
 * Tcl_ReadChars --
 *
 *	Reads from the channel until the requested number of characters
 *	have been seen, EOF is seen, or the channel would block.  EOL
 *	and EOF translation is done.  If reading binary data, the raw
 *	bytes are wrapped in a Tcl byte array object.  Otherwise, the raw
 *	bytes are converted to UTF-8 using the channel's current encoding
 *	and stored in a Tcl string object.
 *
 * Results:
 *	The number of characters read, or -1 on error. Use Tcl_GetErrno()
 *	to retrieve the error code for the error that occurred.
 *
 * Side effects:
 *	May cause input to be buffered.
 *
 *---------------------------------------------------------------------------
 */

int
Tcl_ReadChars(chan, objPtr, toRead, appendFlag)
    Tcl_Channel chan;		/* The channel to read. */
    Tcl_Obj *objPtr;		/* Input data is stored in this object. */
    int toRead;			/* Maximum number of characters to store,
				 * or -1 to read all available data (up to EOF
				 * or when channel blocks). */
    int appendFlag;		/* If non-zero, data read from the channel
				 * will be appended to the object.  Otherwise,
				 * the data will replace the existing contents
				 * of the object. */
{
    Channel *chanPtr = (Channel *) chan;
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */

    /*
     * This operation should occur at the top of a channel stack.
     */

    chanPtr = statePtr->topChanPtr;

    if (CheckChannelErrors(statePtr, TCL_READABLE) != 0) {
	/*
	 * Update the notifier state so we don't block while there is still
	 * data in the buffers.
	 */

	UpdateInterest(chanPtr);
	return -1;
    }

    return DoReadChars(chanPtr, objPtr, toRead, appendFlag);
}
/*
 *---------------------------------------------------------------------------
 *
 * DoReadChars --
 *
 *	Reads from the channel until the requested number of characters
 *	have been seen, EOF is seen, or the channel would block.  EOL
 *	and EOF translation is done.  If reading binary data, the raw
 *	bytes are wrapped in a Tcl byte array object.  Otherwise, the raw
 *	bytes are converted to UTF-8 using the channel's current encoding
 *	and stored in a Tcl string object.
 *
 * Results:
 *	The number of characters read, or -1 on error. Use Tcl_GetErrno()
 *	to retrieve the error code for the error that occurred.
 *
 * Side effects:
 *	May cause input to be buffered.
 *
 *---------------------------------------------------------------------------
 */

static int
DoReadChars(chanPtr, objPtr, toRead, appendFlag)
    Channel *chanPtr;		/* The channel to read. */
    Tcl_Obj *objPtr;		/* Input data is stored in this object. */
    int toRead;			/* Maximum number of characters to store,
				 * or -1 to read all available data (up to EOF
				 * or when channel blocks). */
    int appendFlag;		/* If non-zero, data read from the channel
				 * will be appended to the object.  Otherwise,
				 * the data will replace the existing contents
				 * of the object. */
{
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    ChannelBuffer *bufPtr;
    int offset, factor, copied, copiedNow, result;
    Tcl_Encoding encoding;
#define UTF_EXPANSION_FACTOR	1024

    /*
     * This operation should occur at the top of a channel stack.
     */

    chanPtr = statePtr->topChanPtr;
    encoding = statePtr->encoding;
    factor = UTF_EXPANSION_FACTOR;

    if (appendFlag == 0) {
	if (encoding == NULL) {
	    Tcl_SetByteArrayLength(objPtr, 0);
	} else {
	    Tcl_SetObjLength(objPtr, 0);
	    /* 
	     * We're going to access objPtr->bytes directly, so
	     * we must ensure that this is actually a string
	     * object (otherwise it might have been pure Unicode).
	     */

	    Tcl_GetString(objPtr);
	}
	offset = 0;
    } else {
	if (encoding == NULL) {
	    Tcl_GetByteArrayFromObj(objPtr, &offset);
	} else {
	    Tcl_GetStringFromObj(objPtr, &offset);
	}
    }

    for (copied = 0; (unsigned) toRead > 0; ) {
	copiedNow = -1;
	if (statePtr->inQueueHead != NULL) {
	    if (encoding == NULL) {
		copiedNow = ReadBytes(statePtr, objPtr, toRead, &offset);
	    } else {
		copiedNow = ReadChars(statePtr, objPtr, toRead, &offset,
			&factor);
	    }

	    /*
	     * If the current buffer is empty recycle it.
	     */

	    bufPtr = statePtr->inQueueHead;
	    if (bufPtr->nextRemoved == bufPtr->nextAdded) {
		ChannelBuffer *nextPtr;

		nextPtr = bufPtr->nextPtr;
		RecycleBuffer(statePtr, bufPtr, 0);
		statePtr->inQueueHead = nextPtr;
		if (nextPtr == NULL) {
		    statePtr->inQueueTail = NULL;
		}
	    }
	}
	if (copiedNow < 0) {
	    if (statePtr->flags & CHANNEL_EOF) {
		break;
	    }
	    if (statePtr->flags & CHANNEL_BLOCKED) {
		if (statePtr->flags & CHANNEL_NONBLOCKING) {
		    break;
		}
		statePtr->flags &= ~CHANNEL_BLOCKED;
	    }
	    result = GetInput(chanPtr);
	    if (result != 0) {
		if (result == EAGAIN) {
		    break;
		}
		copied = -1;
		goto done;
	    }
	} else {
	    copied += copiedNow;
	    toRead -= copiedNow;
	}
    }
    statePtr->flags &= ~CHANNEL_BLOCKED;
    if (encoding == NULL) {
	Tcl_SetByteArrayLength(objPtr, offset);
    } else {
	Tcl_SetObjLength(objPtr, offset);
    }

    done:
    /*
     * Update the notifier state so we don't block while there is still
     * data in the buffers.
     */

    UpdateInterest(chanPtr);
    return copied;
}
/*
 *---------------------------------------------------------------------------
 *
 * ReadBytes --
 *
 *	Reads from the channel until the requested number of bytes have
 *	been seen, EOF is seen, or the channel would block.  Bytes from
 *	the channel are stored in objPtr as a ByteArray object.  EOL
 *	and EOF translation are done.
 *
 *	'bytesToRead' can safely be a very large number because
 *	space is only allocated to hold data read from the channel
 *	as needed.
 *
 * Results:
 *	The return value is the number of bytes appended to the object
 *	and *offsetPtr is filled with the total number of bytes in the
 *	object (greater than the return value if there were already bytes
 *	in the object).
 *
 * Side effects:
 *	None.
 *
 *---------------------------------------------------------------------------
 */

static int
ReadBytes(statePtr, objPtr, bytesToRead, offsetPtr)
    ChannelState *statePtr;	/* State of the channel to read. */
    Tcl_Obj *objPtr;		/* Input data is appended to this ByteArray
				 * object.  Its length is how much space
				 * has been allocated to hold data, not how
				 * many bytes of data have been stored in the
				 * object. */
    int bytesToRead;		/* Maximum number of bytes to store,
				 * or < 0 to get all available bytes.
				 * Bytes are obtained from the first
				 * buffer in the queue -- even if this number
				 * is larger than the number of bytes
				 * available in the first buffer, only the
				 * bytes from the first buffer are
				 * returned. */
    int *offsetPtr;		/* On input, contains how many bytes of
				 * objPtr have been used to hold data.  On
				 * output, filled with how many bytes are now
				 * being used. */
{
    int toRead, srcLen, offset, length, srcRead, dstWrote;
    ChannelBuffer *bufPtr;
    char *src, *dst;

    offset = *offsetPtr;

    bufPtr = statePtr->inQueueHead; 
    src = bufPtr->buf + bufPtr->nextRemoved;
    srcLen = bufPtr->nextAdded - bufPtr->nextRemoved;

    toRead = bytesToRead;
    if ((unsigned) toRead > (unsigned) srcLen) {
	toRead = srcLen;
    }

    dst = (char *) Tcl_GetByteArrayFromObj(objPtr, &length);
    if (toRead > length - offset - 1) {
	/*
	 * Double the existing size of the object or make enough room to
	 * hold all the characters we may get from the source buffer,
	 * whichever is larger.
	 */

	length = offset * 2;
	if (offset < toRead) {
	    length = offset + toRead + 1;
	}
	dst = (char *) Tcl_SetByteArrayLength(objPtr, length);
    }
    dst += offset;

    if (statePtr->flags & INPUT_NEED_NL) {
	statePtr->flags &= ~INPUT_NEED_NL;
	if ((srcLen == 0) || (*src != '\n')) {
	    *dst = '\r';
	    *offsetPtr += 1;
	    return 1;
	}
	*dst++ = '\n';
	src++;
	srcLen--;
	toRead--;
    }

    srcRead = srcLen;
    dstWrote = toRead;
    if (TranslateInputEOL(statePtr, dst, src, &dstWrote, &srcRead) != 0) {
	if (dstWrote == 0) {
	    return -1;
	}
    }
    bufPtr->nextRemoved += srcRead;
    *offsetPtr += dstWrote;
    return dstWrote;
}

/*
 *---------------------------------------------------------------------------
 *
 * ReadChars --
 *
 *	Reads from the channel until the requested number of UTF-8
 *	characters have been seen, EOF is seen, or the channel would
 *	block.  Raw bytes from the channel are converted to UTF-8
 *	and stored in objPtr.  EOL and EOF translation is done.
 *
 *	'charsToRead' can safely be a very large number because
 *	space is only allocated to hold data read from the channel
 *	as needed.
 *
 * Results:
 *	The return value is the number of characters appended to
 *	the object, *offsetPtr is filled with the number of bytes that
 *	were appended, and *factorPtr is filled with the expansion
 *	factor used to guess how many bytes of UTF-8 to allocate to
 *	hold N source bytes.
 *
 * Side effects:
 *	None.
 *
 *---------------------------------------------------------------------------
 */

static int
ReadChars(statePtr, objPtr, charsToRead, offsetPtr, factorPtr)
    ChannelState *statePtr;	/* State of channel to read. */
    Tcl_Obj *objPtr;		/* Input data is appended to this object.
				 * objPtr->length is how much space has been
				 * allocated to hold data, not how many bytes
				 * of data have been stored in the object. */
    int charsToRead;		/* Maximum number of characters to store,
				 * or -1 to get all available characters.
				 * Characters are obtained from the first
				 * buffer in the queue -- even if this number
				 * is larger than the number of characters
				 * available in the first buffer, only the
				 * characters from the first buffer are
				 * returned. */
    int *offsetPtr;		/* On input, contains how many bytes of
				 * objPtr have been used to hold data.  On
				 * output, filled with how many bytes are now
				 * being used. */
    int *factorPtr;		/* On input, contains a guess of how many
				 * bytes need to be allocated to hold the
				 * result of converting N source bytes to
				 * UTF-8.  On output, contains another guess
				 * based on the data seen so far. */
{
    int toRead, factor, offset, spaceLeft, length, srcLen, dstNeeded;
    int srcRead, dstWrote, numChars, dstRead;
    ChannelBuffer *bufPtr;
    char *src, *dst;
    Tcl_EncodingState oldState;

    factor = *factorPtr;
    offset = *offsetPtr;

    bufPtr = statePtr->inQueueHead; 
    src = bufPtr->buf + bufPtr->nextRemoved;
    srcLen = bufPtr->nextAdded - bufPtr->nextRemoved;

    toRead = charsToRead;
    if ((unsigned)toRead > (unsigned)srcLen) {
	toRead = srcLen;
    }

    /*
     * 'factor' is how much we guess that the bytes in the source buffer
     * will expand when converted to UTF-8 chars.  This guess comes from
     * analyzing how many characters were produced by the previous
     * pass.
     */

    dstNeeded = toRead * factor / UTF_EXPANSION_FACTOR;
    spaceLeft = objPtr->length - offset - TCL_UTF_MAX - 1;

    if (dstNeeded > spaceLeft) {
	/*
	 * Double the existing size of the object or make enough room to
	 * hold all the characters we want from the source buffer,
	 * whichever is larger.
	 */

	length = offset * 2;
	if (offset < dstNeeded) {
	    length = offset + dstNeeded;
	}
	spaceLeft = length - offset;
	length += TCL_UTF_MAX + 1;
	Tcl_SetObjLength(objPtr, length);
    }
    if (toRead == srcLen) {
	/*
	 * Want to convert the whole buffer in one pass.  If we have
	 * enough space, convert it using all available space in object
	 * rather than using the factor.
	 */

	dstNeeded = spaceLeft;
    }
    dst = objPtr->bytes + offset;

    oldState = statePtr->inputEncodingState;
    if (statePtr->flags & INPUT_NEED_NL) {
	/*
	 * We want a '\n' because the last character we saw was '\r'.
	 */

	statePtr->flags &= ~INPUT_NEED_NL;
	Tcl_ExternalToUtf(NULL, statePtr->encoding, src, srcLen,
		statePtr->inputEncodingFlags, &statePtr->inputEncodingState,
		dst, TCL_UTF_MAX + 1, &srcRead, &dstWrote, &numChars);
	if ((dstWrote > 0) && (*dst == '\n')) {
	    /*
	     * The next char was a '\n'.  Consume it and produce a '\n'.
	     */

	    bufPtr->nextRemoved += srcRead;
	} else {
	    /*
	     * The next char was not a '\n'.  Produce a '\r'.
	     */

	    *dst = '\r';
	}
	statePtr->inputEncodingFlags &= ~TCL_ENCODING_START;
	*offsetPtr += 1;
	return 1;
    }

    Tcl_ExternalToUtf(NULL, statePtr->encoding, src, srcLen,
	    statePtr->inputEncodingFlags, &statePtr->inputEncodingState, dst,
	    dstNeeded + TCL_UTF_MAX, &srcRead, &dstWrote, &numChars);
    if (srcRead == 0) {
	/*
	 * Not enough bytes in src buffer to make a complete char.  Copy
	 * the bytes to the next buffer to make a new contiguous string,
	 * then tell the caller to fill the buffer with more bytes.
	 */

	ChannelBuffer *nextPtr;

	nextPtr = bufPtr->nextPtr;
	if (nextPtr == NULL) {
	    if (srcLen > 0) {
		/*
		 * There isn't enough data in the buffers to complete the next
		 * character, so we need to wait for more data before the next
		 * file event can be delivered.
		 *
		 * SF #478856.
		 *
		 * The exception to this is if the input buffer was
		 * completely empty before we tried to convert its
		 * contents. Nothing in, nothing out, and no incomplete
		 * character data. The conversion before the current one
		 * was complete.
		 */

		statePtr->flags |= CHANNEL_NEED_MORE_DATA;
	    }
	    return -1;
	}
	nextPtr->nextRemoved -= srcLen;
	memcpy((VOID *) (nextPtr->buf + nextPtr->nextRemoved), (VOID *) src,
		(size_t) srcLen);
	RecycleBuffer(statePtr, bufPtr, 0);
	statePtr->inQueueHead = nextPtr;
	return ReadChars(statePtr, objPtr, charsToRead, offsetPtr, factorPtr);
    }

    dstRead = dstWrote;
    if (TranslateInputEOL(statePtr, dst, dst, &dstWrote, &dstRead) != 0) {
	/*
	 * Hit EOF char.  How many bytes of src correspond to where the
	 * EOF was located in dst? Run the conversion again with an
	 * output buffer just big enough to hold the data so we can
	 * get the correct value for srcRead.
	 */

	if (dstWrote == 0) {
	    return -1;
	}
	statePtr->inputEncodingState = oldState;
	Tcl_ExternalToUtf(NULL, statePtr->encoding, src, srcLen,
		statePtr->inputEncodingFlags, &statePtr->inputEncodingState,
		dst, dstRead + TCL_UTF_MAX, &srcRead, &dstWrote, &numChars);
	TranslateInputEOL(statePtr, dst, dst, &dstWrote, &dstRead);
    } 

    /*
     * The number of characters that we got may be less than the number
     * that we started with because "\r\n" sequences may have been
     * turned into just '\n' in dst.
     */

    numChars -= (dstRead - dstWrote);

    if ((unsigned) numChars > (unsigned) toRead) {
	/*
	 * Got too many chars.
	 */

	CONST char *eof;

	eof = Tcl_UtfAtIndex(dst, toRead);
	statePtr->inputEncodingState = oldState;
	Tcl_ExternalToUtf(NULL, statePtr->encoding, src, srcLen,
		statePtr->inputEncodingFlags, &statePtr->inputEncodingState,
		dst, eof - dst + TCL_UTF_MAX, &srcRead, &dstWrote, &numChars);
	dstRead = dstWrote;
	TranslateInputEOL(statePtr, dst, dst, &dstWrote, &dstRead);
	numChars -= (dstRead - dstWrote);
    }
    statePtr->inputEncodingFlags &= ~TCL_ENCODING_START;

    bufPtr->nextRemoved += srcRead;
    if (dstWrote > srcRead + 1) {
	*factorPtr = dstWrote * UTF_EXPANSION_FACTOR / srcRead;
    }
    *offsetPtr += dstWrote;
    return numChars;
}

/*
 *---------------------------------------------------------------------------
 *
 * TranslateInputEOL --
 *
 *	Perform input EOL and EOF translation on the source buffer,
 *	leaving the translated result in the destination buffer.  
 *
 * Results:
 *	The return value is 1 if the EOF character was found when copying
 *	bytes to the destination buffer, 0 otherwise.  
 *
 * Side effects:
 *	None.
 *
 *---------------------------------------------------------------------------
 */

static int
TranslateInputEOL(statePtr, dstStart, srcStart, dstLenPtr, srcLenPtr)
    ChannelState *statePtr;	/* Channel being read, for EOL translation
				 * and EOF character. */
    char *dstStart;		/* Output buffer filled with chars by
				 * applying appropriate EOL translation to
				 * source characters. */
    CONST char *srcStart;	/* Source characters. */
    int *dstLenPtr;		/* On entry, the maximum length of output
				 * buffer in bytes; must be <= *srcLenPtr.  On
				 * exit, the number of bytes actually used in
				 * output buffer. */
    int *srcLenPtr;		/* On entry, the length of source buffer.
				 * On exit, the number of bytes read from
				 * the source buffer. */
{
    int dstLen, srcLen, inEofChar;
    CONST char *eof;

    dstLen = *dstLenPtr;

    eof = NULL;
    inEofChar = statePtr->inEofChar;
    if (inEofChar != '\0') {
	/*
	 * Find EOF in translated buffer then compress out the EOL.  The
	 * source buffer may be much longer than the destination buffer --
	 * we only want to return EOF if the EOF has been copied to the
	 * destination buffer.
	 */

	CONST char *src, *srcMax;

	srcMax = srcStart + *srcLenPtr;
	for (src = srcStart; src < srcMax; src++) {
	    if (*src == inEofChar) {
		eof = src;
		srcLen = src - srcStart;
		if (srcLen < dstLen) {
		    dstLen = srcLen;
		}
		*srcLenPtr = srcLen;
		break;
	    }
	}
    }
    switch (statePtr->inputTranslation) {
	case TCL_TRANSLATE_LF: {
	    if (dstStart != srcStart) {
		memcpy((VOID *) dstStart, (VOID *) srcStart, (size_t) dstLen);
	    }
	    srcLen = dstLen;
	    break;
	}
	case TCL_TRANSLATE_CR: {
	    char *dst, *dstEnd;

	    if (dstStart != srcStart) {
		memcpy((VOID *) dstStart, (VOID *) srcStart, (size_t) dstLen);
	    }
	    dstEnd = dstStart + dstLen;
	    for (dst = dstStart; dst < dstEnd; dst++) {
		if (*dst == '\r') {
		    *dst = '\n';
		}
	    }
	    srcLen = dstLen;
	    break;
	}
	case TCL_TRANSLATE_CRLF: {
	    char *dst;
	    CONST char *src, *srcEnd, *srcMax;

	    dst = dstStart;
	    src = srcStart;
	    srcEnd = srcStart + dstLen;
	    srcMax = srcStart + *srcLenPtr;

	    for ( ; src < srcEnd; ) {
		if (*src == '\r') {
		    src++;
		    if (src >= srcMax) {
			statePtr->flags |= INPUT_NEED_NL;
		    } else if (*src == '\n') {
			*dst++ = *src++;
		    } else {
			*dst++ = '\r';
		    }
		} else {
		    *dst++ = *src++;
		}
	    }
	    srcLen = src - srcStart;
	    dstLen = dst - dstStart;
	    break;
	}
	case TCL_TRANSLATE_AUTO: {
	    char *dst;
	    CONST char *src, *srcEnd, *srcMax;

	    dst = dstStart;
	    src = srcStart;
	    srcEnd = srcStart + dstLen;
	    srcMax = srcStart + *srcLenPtr;

	    if ((statePtr->flags & INPUT_SAW_CR) && (src < srcMax)) {
		if (*src == '\n') {
		    src++;
		}
		statePtr->flags &= ~INPUT_SAW_CR;
	    }
	    for ( ; src < srcEnd; ) {
		if (*src == '\r') {
		    src++;
		    if (src >= srcMax) {
			statePtr->flags |= INPUT_SAW_CR;
		    } else if (*src == '\n') {
			if (srcEnd < srcMax) {
			    srcEnd++;
			}
			src++;
		    }
		    *dst++ = '\n';
		} else {
		    *dst++ = *src++;
		}
	    }
	    srcLen = src - srcStart;
	    dstLen = dst - dstStart;
	    break;
	}
	default: {		/* lint. */
	    return 0;
	}
    }
    *dstLenPtr = dstLen;

    if ((eof != NULL) && (srcStart + srcLen >= eof)) {
	/*
	 * EOF character was seen in EOL translated range.  Leave current
	 * file position pointing at the EOF character, but don't store the
	 * EOF character in the output string.
	 */

	statePtr->flags |= (CHANNEL_EOF | CHANNEL_STICKY_EOF);
	statePtr->inputEncodingFlags |= TCL_ENCODING_END;
	statePtr->flags &= ~(INPUT_SAW_CR | INPUT_NEED_NL);
	return 1;
    }

    *srcLenPtr = srcLen;
    return 0;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_Ungets --
 *
 *	Causes the supplied string to be added to the input queue of
 *	the channel, at either the head or tail of the queue.
 *
 * Results:
 *	The number of bytes stored in the channel, or -1 on error.
 *
 * Side effects:
 *	Adds input to the input queue of a channel.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_Ungets(chan, str, len, atEnd)
    Tcl_Channel chan;		/* The channel for which to add the input. */
    CONST char *str;		/* The input itself. */
    int len;			/* The length of the input. */
    int atEnd;			/* If non-zero, add at end of queue; otherwise
				 * add at head of queue. */    
{
    Channel *chanPtr;		/* The real IO channel. */
    ChannelState *statePtr;	/* State of actual channel. */
    ChannelBuffer *bufPtr;	/* Buffer to contain the data. */
    int i, flags;

    chanPtr = (Channel *) chan;
    statePtr = chanPtr->state;

    /*
     * This operation should occur at the top of a channel stack.
     */

    chanPtr = statePtr->topChanPtr;

    /*
     * CheckChannelErrors clears too many flag bits in this one case.
     */

    flags = statePtr->flags;
    if (CheckChannelErrors(statePtr, TCL_READABLE) != 0) {
	len = -1;
	goto done;
    }
    statePtr->flags = flags;

    /*
     * If we have encountered a sticky EOF, just punt without storing.
     * (sticky EOF is set if we have seen the input eofChar, to prevent
     * reading beyond the eofChar). Otherwise, clear the EOF flags, and
     * clear the BLOCKED bit. We want to discover these conditions anew
     * in each operation.
     */

    if (statePtr->flags & CHANNEL_STICKY_EOF) {
	goto done;
    }
    statePtr->flags &= (~(CHANNEL_BLOCKED | CHANNEL_EOF));

    bufPtr = AllocChannelBuffer(len);
    for (i = 0; i < len; i++) {
	bufPtr->buf[bufPtr->nextAdded++] = str[i];
    }

    if (statePtr->inQueueHead == (ChannelBuffer *) NULL) {
	bufPtr->nextPtr = (ChannelBuffer *) NULL;
	statePtr->inQueueHead = bufPtr;
	statePtr->inQueueTail = bufPtr;
    } else if (atEnd) {
	bufPtr->nextPtr = (ChannelBuffer *) NULL;
	statePtr->inQueueTail->nextPtr = bufPtr;
	statePtr->inQueueTail = bufPtr;
    } else {
	bufPtr->nextPtr = statePtr->inQueueHead;
	statePtr->inQueueHead = bufPtr;
    }

    done:
    /*
     * Update the notifier state so we don't block while there is still
     * data in the buffers.
     */

    UpdateInterest(chanPtr);
    return len;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_Flush --
 *
 *	Flushes output data on a channel.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	May flush output queued on this channel.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_Flush(chan)
    Tcl_Channel chan;			/* The Channel to flush. */
{
    int result;				/* Of calling FlushChannel. */
    Channel *chanPtr = (Channel *) chan;	/* The actual channel. */
    ChannelState *statePtr = chanPtr->state;	/* State of actual channel. */

    /*
     * This operation should occur at the top of a channel stack.
     */

    chanPtr = statePtr->topChanPtr;

    if (CheckChannelErrors(statePtr, TCL_WRITABLE) != 0) {
	return -1;
    }

    /*
     * Force current output buffer to be output also.
     */

    if ((statePtr->curOutPtr != NULL)
	    && (statePtr->curOutPtr->nextAdded >
		    statePtr->curOutPtr->nextRemoved)) {
	statePtr->flags |= BUFFER_READY;
    }

    result = FlushChannel(NULL, chanPtr, 0);
    if (result != 0) {
	return TCL_ERROR;
    }

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * DiscardInputQueued --
 *
 *	Discards any input read from the channel but not yet consumed
 *	by Tcl reading commands.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	May discard input from the channel. If discardLastBuffer is zero,
 *	leaves one buffer in place for back-filling.
 *
 *----------------------------------------------------------------------
 */

static void
DiscardInputQueued(statePtr, discardSavedBuffers)
    ChannelState *statePtr;	/* Channel on which to discard
				 * the queued input. */
    int discardSavedBuffers;	/* If non-zero, discard all buffers including
				 * last one. */
{
    ChannelBuffer *bufPtr, *nxtPtr;	/* Loop variables. */

    bufPtr = statePtr->inQueueHead;
    statePtr->inQueueHead = (ChannelBuffer *) NULL;
    statePtr->inQueueTail = (ChannelBuffer *) NULL;
    for (; bufPtr != (ChannelBuffer *) NULL; bufPtr = nxtPtr) {
	nxtPtr = bufPtr->nextPtr;
	RecycleBuffer(statePtr, bufPtr, discardSavedBuffers);
    }

    /*
     * If discardSavedBuffers is nonzero, must also discard any previously
     * saved buffer in the saveInBufPtr field.
     */

    if (discardSavedBuffers) {
	if (statePtr->saveInBufPtr != (ChannelBuffer *) NULL) {
	    ckfree((char *) statePtr->saveInBufPtr);
	    statePtr->saveInBufPtr = (ChannelBuffer *) NULL;
	}
    }
}

/*
 *---------------------------------------------------------------------------
 *
 * GetInput --
 *
 *	Reads input data from a device into a channel buffer.  
 *
 * Results:
 *	The return value is the Posix error code if an error occurred while
 *	reading from the file, or 0 otherwise.  
 *
 * Side effects:
 *	Reads from the underlying device.
 *
 *---------------------------------------------------------------------------
 */

static int
GetInput(chanPtr)
    Channel *chanPtr;		/* Channel to read input from. */
{
    int toRead;			/* How much to read? */
    int result;			/* Of calling driver. */
    int nread;			/* How much was read from channel? */
    ChannelBuffer *bufPtr;	/* New buffer to add to input queue. */
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */

    /*
     * Prevent reading from a dead channel -- a channel that has been closed
     * but not yet deallocated, which can happen if the exit handler for
     * channel cleanup has run but the channel is still registered in some
     * interpreter.
     */

    if (CheckForDeadChannel(NULL, statePtr)) {
	return EINVAL;
    }

    /*
     * First check for more buffers in the pushback area of the
     * topmost channel in the stack and use them. They can be the
     * result of a transformation which went away without reading all
     * the information placed in the area when it was stacked.
     *
     * Two possibilities for the state: No buffers in it, or a single
     * empty buffer. In the latter case we can recycle it now.
     */

    if (chanPtr->inQueueHead != (ChannelBuffer *) NULL) {
	if (statePtr->inQueueHead != (ChannelBuffer *) NULL) {
	    RecycleBuffer(statePtr, statePtr->inQueueHead, 0);
	    statePtr->inQueueHead = (ChannelBuffer *) NULL;
	}

	statePtr->inQueueHead = chanPtr->inQueueHead;
	statePtr->inQueueTail = chanPtr->inQueueTail;
	chanPtr->inQueueHead = (ChannelBuffer *) NULL;
	chanPtr->inQueueTail = (ChannelBuffer *) NULL;
	return 0;
    }

    /*
     * Nothing in the pushback area, fall back to the usual handling
     * (driver, etc.)
     */

    /*
     * See if we can fill an existing buffer. If we can, read only
     * as much as will fit in it. Otherwise allocate a new buffer,
     * add it to the input queue and attempt to fill it to the max.
     */

    bufPtr = statePtr->inQueueTail;
    if ((bufPtr != NULL) && (bufPtr->nextAdded < bufPtr->bufLength)) {
	toRead = bufPtr->bufLength - bufPtr->nextAdded;
    } else {
	bufPtr = statePtr->saveInBufPtr;
	statePtr->saveInBufPtr = NULL;

	/*
	 * Check the actual buffersize against the requested
	 * buffersize. Buffers which are smaller than requested are
	 * squashed. This is done to honor dynamic changes of the
	 * buffersize made by the user.
	 */

	if ((bufPtr != NULL)
		&& (bufPtr->bufLength - BUFFER_PADDING < statePtr->bufSize)) {
	    ckfree((char *) bufPtr);
	    bufPtr = NULL;
	}

	if (bufPtr == NULL) {
	    bufPtr = AllocChannelBuffer(statePtr->bufSize);
	}
	bufPtr->nextPtr = (ChannelBuffer *) NULL;

	/* SF #427196: Use the actual size of the buffer to determine
	 * the number of bytes to read from the channel and not the
	 * size for new buffers. They can be different if the
	 * buffersize was changed between reads.
	 *
	 * Note: This affects performance negatively if the buffersize
	 * was extended but this small buffer is reused for all
	 * subsequent reads. The system never uses buffers with the
	 * requested bigger size in that case. An adjunct patch could
	 * try and delete all unused buffers it encounters and which
	 * are smaller than the formally requested buffersize.
	 */

	toRead = bufPtr->bufLength - bufPtr->nextAdded;

	if (statePtr->inQueueTail == NULL) {
	    statePtr->inQueueHead = bufPtr;
	} else {
	    statePtr->inQueueTail->nextPtr = bufPtr;
	}
	statePtr->inQueueTail = bufPtr;
    }

    /*
     * If EOF is set, we should avoid calling the driver because on some
     * platforms it is impossible to read from a device after EOF.
     */

    if (statePtr->flags & CHANNEL_EOF) {
	return 0;
    }

#ifdef TCL_IO_TRACK_OS_FOR_DRIVER_WITH_BAD_BLOCKING
    /*
     * [SF Tcl Bug 943274]. Better emulation of non-blocking channels
     * for channels without BlockModeProc, by keeping track of true
     * fileevents generated by the OS == Data waiting and reading if
     * and only if we are sure to have data.
     */

    if ((statePtr->flags & CHANNEL_NONBLOCKING) &&
	    (Tcl_ChannelBlockModeProc(chanPtr->typePtr) == NULL) &&
	    !(statePtr->flags & CHANNEL_HAS_MORE_DATA)) {
	/*
	 * Bypass the driver, it would block, as no data is available
	 */

	nread = -1;
	result = EWOULDBLOCK;
    } else {
#endif /* TCL_IO_TRACK_OS_FOR_DRIVER_WITH_BAD_BLOCKING */
	nread = (chanPtr->typePtr->inputProc)(chanPtr->instanceData,
		bufPtr->buf + bufPtr->nextAdded, toRead, &result);
#ifdef TCL_IO_TRACK_OS_FOR_DRIVER_WITH_BAD_BLOCKING
    }
#endif /* TCL_IO_TRACK_OS_FOR_DRIVER_WITH_BAD_BLOCKING */

    if (nread > 0) {
	bufPtr->nextAdded += nread;

	/*
	 * If we get a short read, signal up that we may be BLOCKED. We
	 * should avoid calling the driver because on some platforms we
	 * will block in the low level reading code even though the
	 * channel is set into nonblocking mode.
	 */

	if (nread < toRead) {
	    statePtr->flags |= CHANNEL_BLOCKED;
	}

#ifdef TCL_IO_TRACK_OS_FOR_DRIVER_WITH_BAD_BLOCKING
	if (nread <= toRead) {
	    /*
	     * [SF Tcl Bug 943274] We have read the available data,
	     * clear flag.
	     */

	    statePtr->flags &= ~CHANNEL_HAS_MORE_DATA;
	}
#endif /* TCL_IO_TRACK_OS_FOR_DRIVER_WITH_BAD_BLOCKING */

    } else if (nread == 0) {
	statePtr->flags |= CHANNEL_EOF;
	statePtr->inputEncodingFlags |= TCL_ENCODING_END;
    } else if (nread < 0) {
	if ((result == EWOULDBLOCK) || (result == EAGAIN)) {
	    statePtr->flags |= CHANNEL_BLOCKED;
	    result = EAGAIN;
	}
	Tcl_SetErrno(result);
	return result;
    }
    return 0;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_Seek --
 *
 *	Implements seeking on Tcl Channels. This is a public function
 *	so that other C facilities may be implemented on top of it.
 *
 * Results:
 *	The new access point or -1 on error. If error, use Tcl_GetErrno()
 *	to retrieve the POSIX error code for the error that occurred.
 *
 * Side effects:
 *	May flush output on the channel. May discard queued input.
 *
 *----------------------------------------------------------------------
 */

Tcl_WideInt
Tcl_Seek(chan, offset, mode)
    Tcl_Channel chan;		/* The channel on which to seek. */
    Tcl_WideInt offset;		/* Offset to seek to. */
    int mode;			/* Relative to which location to seek? */
{
    Channel *chanPtr = (Channel *) chan;	/* The real IO channel. */
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    int inputBuffered, outputBuffered;
				/* # bytes held in buffers. */
    int result;			/* Of device driver operations. */
    Tcl_WideInt curPos;		/* Position on the device. */
    int wasAsync;		/* Was the channel nonblocking before the
				 * seek operation? If so, must restore to
				 * nonblocking mode after the seek. */

    if (CheckChannelErrors(statePtr, TCL_WRITABLE | TCL_READABLE) != 0) {
	return Tcl_LongAsWide(-1);
    }

    /*
     * Disallow seek on dead channels -- channels that have been closed but
     * not yet been deallocated. Such channels can be found if the exit
     * handler for channel cleanup has run but the channel is still
     * registered in an interpreter.
     */

    if (CheckForDeadChannel(NULL, statePtr)) {
	return Tcl_LongAsWide(-1);
    }

    /*
     * This operation should occur at the top of a channel stack.
     */

    chanPtr = statePtr->topChanPtr;

    /*
     * Disallow seek on channels whose type does not have a seek procedure
     * defined. This means that the channel does not support seeking.
     */

    if (chanPtr->typePtr->seekProc == (Tcl_DriverSeekProc *) NULL) {
	Tcl_SetErrno(EINVAL);
	return Tcl_LongAsWide(-1);
    }

    /*
     * Compute how much input and output is buffered. If both input and
     * output is buffered, cannot compute the current position.
     */

    inputBuffered = Tcl_InputBuffered(chan);
    outputBuffered = Tcl_OutputBuffered(chan);

    if ((inputBuffered != 0) && (outputBuffered != 0)) {
	Tcl_SetErrno(EFAULT);
	return Tcl_LongAsWide(-1);
    }

    /*
     * If we are seeking relative to the current position, compute the
     * corrected offset taking into account the amount of unread input.
     */

    if (mode == SEEK_CUR) {
	offset -= inputBuffered;
    }

    /*
     * Discard any queued input - this input should not be read after
     * the seek.
     */

    DiscardInputQueued(statePtr, 0);

    /*
     * Reset EOF and BLOCKED flags. We invalidate them by moving the
     * access point. Also clear CR related flags.
     */

    statePtr->flags &=
	~(CHANNEL_EOF | CHANNEL_STICKY_EOF | CHANNEL_BLOCKED | INPUT_SAW_CR);

    /*
     * If the channel is in asynchronous output mode, switch it back
     * to synchronous mode and cancel any async flush that may be
     * scheduled. After the flush, the channel will be put back into
     * asynchronous output mode.
     */

    wasAsync = 0;
    if (statePtr->flags & CHANNEL_NONBLOCKING) {
	wasAsync = 1;
	result = StackSetBlockMode(chanPtr, TCL_MODE_BLOCKING);
	if (result != 0) {
	    return Tcl_LongAsWide(-1);
	}
	statePtr->flags &= (~(CHANNEL_NONBLOCKING));
	if (statePtr->flags & BG_FLUSH_SCHEDULED) {
	    statePtr->flags &= (~(BG_FLUSH_SCHEDULED));
	}
    }

    /*
     * If there is data buffered in statePtr->curOutPtr then mark
     * the channel as ready to flush before invoking FlushChannel.
     */

    if ((statePtr->curOutPtr != (ChannelBuffer *) NULL) &&
	    (statePtr->curOutPtr->nextAdded >
		    statePtr->curOutPtr->nextRemoved)) {
	statePtr->flags |= BUFFER_READY;
    }

    /*
     * If the flush fails we cannot recover the original position. In
     * that case the seek is not attempted because we do not know where
     * the access position is - instead we return the error. FlushChannel
     * has already called Tcl_SetErrno() to report the error upwards.
     * If the flush succeeds we do the seek also.
     */

    if (FlushChannel(NULL, chanPtr, 0) != 0) {
	curPos = -1;
    } else {

	/*
	 * Now seek to the new position in the channel as requested by the
	 * caller.  Note that we prefer the wideSeekProc if that is
	 * available and non-NULL...
	 */

	if (HaveVersion(chanPtr->typePtr, TCL_CHANNEL_VERSION_3) &&
		chanPtr->typePtr->wideSeekProc != NULL) {
	    curPos = (chanPtr->typePtr->wideSeekProc) (chanPtr->instanceData,
		    offset, mode, &result);
	} else if (offset < Tcl_LongAsWide(LONG_MIN) ||
		offset > Tcl_LongAsWide(LONG_MAX)) {
	    result = EOVERFLOW;
	    curPos = Tcl_LongAsWide(-1);
	} else {
	    curPos = Tcl_LongAsWide((chanPtr->typePtr->seekProc) (
		    chanPtr->instanceData, Tcl_WideAsLong(offset), mode,
		    &result));
	}
	if (curPos == Tcl_LongAsWide(-1)) {
	    Tcl_SetErrno(result);
	}
    }

    /*
     * Restore to nonblocking mode if that was the previous behavior.
     *
     * NOTE: Even if there was an async flush active we do not restore
     * it now because we already flushed all the queued output, above.
     */

    if (wasAsync) {
	statePtr->flags |= CHANNEL_NONBLOCKING;
	result = StackSetBlockMode(chanPtr, TCL_MODE_NONBLOCKING);
	if (result != 0) {
	    return Tcl_LongAsWide(-1);
	}
    }

    return curPos;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_Tell --
 *
 *	Returns the position of the next character to be read/written on
 *	this channel.
 *
 * Results:
 *	A nonnegative integer on success, -1 on failure. If failed,
 *	use Tcl_GetErrno() to retrieve the POSIX error code for the
 *	error that occurred.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

Tcl_WideInt
Tcl_Tell(chan)
    Tcl_Channel chan;			/* The channel to return pos for. */
{
    Channel *chanPtr = (Channel *) chan;	/* The real IO channel. */
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    int inputBuffered, outputBuffered;	/* # bytes held in buffers. */
    int result;				/* Of calling device driver. */
    Tcl_WideInt curPos;			/* Position on device. */

    if (CheckChannelErrors(statePtr, TCL_WRITABLE | TCL_READABLE) != 0) {
	return Tcl_LongAsWide(-1);
    }

    /*
     * Disallow tell on dead channels -- channels that have been closed but
     * not yet been deallocated. Such channels can be found if the exit
     * handler for channel cleanup has run but the channel is still
     * registered in an interpreter.
     */

    if (CheckForDeadChannel(NULL, statePtr)) {
	return Tcl_LongAsWide(-1);
    }

    /*
     * This operation should occur at the top of a channel stack.
     */

    chanPtr = statePtr->topChanPtr;

    /*
     * Disallow tell on channels whose type does not have a seek procedure
     * defined. This means that the channel does not support seeking.
     */

    if (chanPtr->typePtr->seekProc == (Tcl_DriverSeekProc *) NULL) {
	Tcl_SetErrno(EINVAL);
	return Tcl_LongAsWide(-1);
    }

    /*
     * Compute how much input and output is buffered. If both input and
     * output is buffered, cannot compute the current position.
     */

    inputBuffered = Tcl_InputBuffered(chan);
    outputBuffered = Tcl_OutputBuffered(chan);

    if ((inputBuffered != 0) && (outputBuffered != 0)) {
	Tcl_SetErrno(EFAULT);
	return Tcl_LongAsWide(-1);
    }

    /*
     * Get the current position in the device and compute the position
     * where the next character will be read or written.  Note that we
     * prefer the wideSeekProc if that is available and non-NULL...
     */

    if (HaveVersion(chanPtr->typePtr, TCL_CHANNEL_VERSION_3) &&
	    chanPtr->typePtr->wideSeekProc != NULL) {
	curPos = (chanPtr->typePtr->wideSeekProc) (chanPtr->instanceData,
		Tcl_LongAsWide(0), SEEK_CUR, &result);
    } else {
	curPos = Tcl_LongAsWide((chanPtr->typePtr->seekProc) (
		chanPtr->instanceData, 0, SEEK_CUR, &result));
    }
    if (curPos == Tcl_LongAsWide(-1)) {
	Tcl_SetErrno(result);
	return Tcl_LongAsWide(-1);
    }
    if (inputBuffered != 0) {
	return curPos - inputBuffered;
    }
    return curPos + outputBuffered;
}

/*
 *---------------------------------------------------------------------------
 *
 * Tcl_SeekOld, Tcl_TellOld --
 *
 *	Backward-compatability versions of the seek/tell interface that
 *	do not support 64-bit offsets.  This interface is not documented
 *	or expected to be supported indefinitely.
 *
 * Results:
 *	As for Tcl_Seek and Tcl_Tell respectively, except truncated to
 *	whatever value will fit in an 'int'.
 *
 * Side effects:
 *	As for Tcl_Seek and Tcl_Tell respectively.
 *
 *---------------------------------------------------------------------------
 */

int
Tcl_SeekOld(chan, offset, mode)
    Tcl_Channel chan;		/* The channel on which to seek. */
    int offset;			/* Offset to seek to. */
    int mode;			/* Relative to which location to seek? */
{
    Tcl_WideInt wOffset, wResult;

    wOffset = Tcl_LongAsWide((long)offset);
    wResult = Tcl_Seek(chan, wOffset, mode);
    return (int)Tcl_WideAsLong(wResult);
}

int
Tcl_TellOld(chan)
    Tcl_Channel chan;		/* The channel to return pos for. */
{
    Tcl_WideInt wResult;

    wResult = Tcl_Tell(chan);
    return (int)Tcl_WideAsLong(wResult);
}

/*
 *---------------------------------------------------------------------------
 *
 * CheckChannelErrors --
 *
 *	See if the channel is in an ready state and can perform the
 *	desired operation.
 *
 * Results:
 *	The return value is 0 if the channel is OK, otherwise the
 *	return value is -1 and errno is set to indicate the error.
 *
 * Side effects:
 *	May clear the EOF and/or BLOCKED bits if reading from channel.
 *
 *---------------------------------------------------------------------------
 */

static int
CheckChannelErrors(statePtr, flags)
    ChannelState *statePtr;	/* Channel to check. */
    int flags;			/* Test if channel supports desired operation:
				 * TCL_READABLE, TCL_WRITABLE.  Also indicates
				 * Raw read or write for special close
				 * processing */
{
    int direction = flags & (TCL_READABLE|TCL_WRITABLE);

    /*
     * Check for unreported error.
     */

    if (statePtr->unreportedError != 0) {
	Tcl_SetErrno(statePtr->unreportedError);
	statePtr->unreportedError = 0;
	return -1;
    }

    /*
     * Only the raw read and write operations are allowed during close
     * in order to drain data from stacked channels.
     */

    if ((statePtr->flags & CHANNEL_CLOSED) &&
	    ((flags & CHANNEL_RAW_MODE) == 0)) {
	Tcl_SetErrno(EACCES);
	return -1;
    }

    /*
     * Fail if the channel is not opened for desired operation.
     */

    if ((statePtr->flags & direction) == 0) {
	Tcl_SetErrno(EACCES);
	return -1;
    }

    /*
     * Fail if the channel is in the middle of a background copy.
     *
     * Don't do this tests for raw channels here or else the chaining in the
     * transformation drivers will fail with 'file busy' error instead of
     * retrieving and transforming the data to copy.
     */

    if ((statePtr->csPtr != NULL) && ((flags & CHANNEL_RAW_MODE) == 0)) {
	Tcl_SetErrno(EBUSY);
	return -1;
    }

    if (direction == TCL_READABLE) {
	/*
	 * If we have not encountered a sticky EOF, clear the EOF bit
	 * (sticky EOF is set if we have seen the input eofChar, to prevent
	 * reading beyond the eofChar). Also, always clear the BLOCKED bit.
	 * We want to discover these conditions anew in each operation.
	 */

	if ((statePtr->flags & CHANNEL_STICKY_EOF) == 0) {
	    statePtr->flags &= ~CHANNEL_EOF;
	}
	statePtr->flags &= ~(CHANNEL_BLOCKED | CHANNEL_NEED_MORE_DATA);
    }

    return 0;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_Eof --
 *
 *	Returns 1 if the channel is at EOF, 0 otherwise.
 *
 * Results:
 *	1 or 0, always.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_Eof(chan)
    Tcl_Channel chan;			/* Does this channel have EOF? */
{
    ChannelState *statePtr = ((Channel *) chan)->state;
					/* State of real channel structure. */

    return ((statePtr->flags & CHANNEL_STICKY_EOF) ||
	    ((statePtr->flags & CHANNEL_EOF) &&
	    (Tcl_InputBuffered(chan) == 0))) ? 1 : 0;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_InputBlocked --
 *
 *	Returns 1 if input is blocked on this channel, 0 otherwise.
 *
 * Results:
 *	0 or 1, always.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_InputBlocked(chan)
    Tcl_Channel chan;			/* Is this channel blocked? */
{
    ChannelState *statePtr = ((Channel *) chan)->state;
					/* State of real channel structure. */

    return (statePtr->flags & CHANNEL_BLOCKED) ? 1 : 0;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_InputBuffered --
 *
 *	Returns the number of bytes of input currently buffered in the
 *	common internal buffer of a channel.
 *
 * Results:
 *	The number of input bytes buffered, or zero if the channel is not
 *	open for reading.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_InputBuffered(chan)
    Tcl_Channel chan;			/* The channel to query. */
{
    ChannelState *statePtr = ((Channel *) chan)->state;
					/* State of real channel structure. */
    ChannelBuffer *bufPtr;
    int bytesBuffered;

    for (bytesBuffered = 0, bufPtr = statePtr->inQueueHead;
	    bufPtr != (ChannelBuffer *) NULL;
	    bufPtr = bufPtr->nextPtr) {
	bytesBuffered += (bufPtr->nextAdded - bufPtr->nextRemoved);
    }

    /*
     * Don't forget the bytes in the topmost pushback area.
     */

    for (bufPtr = statePtr->topChanPtr->inQueueHead;
	    bufPtr != (ChannelBuffer *) NULL;
	    bufPtr = bufPtr->nextPtr) {
	bytesBuffered += (bufPtr->nextAdded - bufPtr->nextRemoved);
    }

    return bytesBuffered;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_OutputBuffered --
 *
 *    Returns the number of bytes of output currently buffered in the
 *    common internal buffer of a channel.
 *
 * Results:
 *    The number of output bytes buffered, or zero if the channel is not
 *    open for writing.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_OutputBuffered(chan)
    Tcl_Channel chan;		/* The channel to query. */
{
    ChannelState *statePtr = ((Channel *) chan)->state;
				/* State of real channel structure. */
    ChannelBuffer *bufPtr;
    int bytesBuffered;

    for (bytesBuffered = 0, bufPtr = statePtr->outQueueHead;
	bufPtr != (ChannelBuffer *) NULL;
	bufPtr = bufPtr->nextPtr) {
	bytesBuffered += (bufPtr->nextAdded - bufPtr->nextRemoved);
    }
    if ((statePtr->curOutPtr != (ChannelBuffer *) NULL) &&
	(statePtr->curOutPtr->nextAdded > statePtr->curOutPtr->nextRemoved)) {
	bytesBuffered +=
	    (statePtr->curOutPtr->nextAdded - statePtr->curOutPtr->nextRemoved);
    }

    return bytesBuffered;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ChannelBuffered --
 *
 *	Returns the number of bytes of input currently buffered in the
 *	internal buffer (push back area) of a channel.
 *
 * Results:
 *	The number of input bytes buffered, or zero if the channel is not
 *	open for reading.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_ChannelBuffered(chan)
    Tcl_Channel chan;			/* The channel to query. */
{
    Channel *chanPtr = (Channel *) chan;
					/* real channel structure. */
    ChannelBuffer *bufPtr;
    int bytesBuffered;

    for (bytesBuffered = 0, bufPtr = chanPtr->inQueueHead;
	    bufPtr != (ChannelBuffer *) NULL;
	    bufPtr = bufPtr->nextPtr) {
	bytesBuffered += (bufPtr->nextAdded - bufPtr->nextRemoved);
    }

    return bytesBuffered;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_SetChannelBufferSize --
 *
 *	Sets the size of buffers to allocate to store input or output
 *	in the channel. The size must be between 10 bytes and 1 MByte.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Sets the size of buffers subsequently allocated for this channel.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_SetChannelBufferSize(chan, sz)
    Tcl_Channel chan;			/* The channel whose buffer size
					 * to set. */
    int sz;				/* The size to set. */
{
    ChannelState *statePtr;		/* State of real channel structure. */

    /*
     * If the buffer size is smaller than 10 bytes or larger than one MByte,
     * do not accept the requested size and leave the current buffer size.
     */

    if (sz < 10) {
	return;
    }
    if (sz > (1024 * 1024)) {
	return;
    }

    statePtr = ((Channel *) chan)->state;
    statePtr->bufSize = sz;

    if (statePtr->outputStage != NULL) {
	ckfree((char *) statePtr->outputStage);
	statePtr->outputStage = NULL;
    }
    if ((statePtr->encoding != NULL) && (statePtr->flags & TCL_WRITABLE)) {
	statePtr->outputStage = (char *)
	    ckalloc((unsigned) (statePtr->bufSize + 2));
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetChannelBufferSize --
 *
 *	Retrieves the size of buffers to allocate for this channel.
 *
 * Results:
 *	The size.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_GetChannelBufferSize(chan)
    Tcl_Channel chan;		/* The channel for which to find the
				 * buffer size. */
{
    ChannelState *statePtr = ((Channel *) chan)->state;
					/* State of real channel structure. */

    return statePtr->bufSize;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_BadChannelOption --
 *
 *	This procedure generates a "bad option" error message in an
 *	(optional) interpreter.  It is used by channel drivers when 
 *	a invalid Set/Get option is requested. Its purpose is to concatenate
 *	the generic options list to the specific ones and factorize
 *	the generic options error message string.
 *
 * Results:
 *	TCL_ERROR.
 *
 * Side effects:
 *	An error message is generated in interp's result object to
 *	indicate that a command was invoked with the a bad option
 *	The message has the form
 *		bad option "blah": should be one of 
 *		<...generic options...>+<...specific options...>
 *	"blah" is the optionName argument and "<specific options>"
 *	is a space separated list of specific option words.
 *	The function takes good care of inserting minus signs before
 *	each option, commas after, and an "or" before the last option.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_BadChannelOption(interp, optionName, optionList)
    Tcl_Interp *interp;			/* Current interpreter. (can be NULL)*/
    CONST char *optionName;		/* 'bad option' name */
    CONST char *optionList;		/* Specific options list to append 
					 * to the standard generic options.
					 * can be NULL for generic options 
					 * only. */
{
    if (interp) {
	CONST char *genericopt = 
	    "blocking buffering buffersize encoding eofchar translation";
	CONST char **argv;
	int  argc, i;
	Tcl_DString ds;

	Tcl_DStringInit(&ds);
	Tcl_DStringAppend(&ds, genericopt, -1);
	if (optionList && (*optionList)) {
	    Tcl_DStringAppend(&ds, " ", 1);
	    Tcl_DStringAppend(&ds, optionList, -1);
	}
	if (Tcl_SplitList(interp, Tcl_DStringValue(&ds), 
		&argc, &argv) != TCL_OK) {
	    Tcl_Panic("malformed option list in channel driver");
	}
	Tcl_ResetResult(interp);
	Tcl_AppendResult(interp, "bad option \"", optionName, 
		"\": should be one of ", (char *) NULL);
	argc--;
	for (i = 0; i < argc; i++) {
	    Tcl_AppendResult(interp, "-", argv[i], ", ", (char *) NULL);
	}
	Tcl_AppendResult(interp, "or -", argv[i], (char *) NULL);
	Tcl_DStringFree(&ds);
	ckfree((char *) argv);
    }
    Tcl_SetErrno(EINVAL);
    return TCL_ERROR;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetChannelOption --
 *
 *	Gets a mode associated with an IO channel. If the optionName arg
 *	is non NULL, retrieves the value of that option. If the optionName
 *	arg is NULL, retrieves a list of alternating option names and
 *	values for the given channel.
 *
 * Results:
 *	A standard Tcl result. Also sets the supplied DString to the
 *	string value of the option(s) returned.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_GetChannelOption(interp, chan, optionName, dsPtr)
    Tcl_Interp *interp;		/* For error reporting - can be NULL. */
    Tcl_Channel chan;		/* Channel on which to get option. */
    CONST char *optionName;	/* Option to get. */
    Tcl_DString *dsPtr;		/* Where to store value(s). */
{
    size_t len;			/* Length of optionName string. */
    char optionVal[128];	/* Buffer for sprintf. */
    Channel *chanPtr = (Channel *) chan;
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    int flags;

    /*
     * Disallow options on dead channels -- channels that have been closed but
     * not yet been deallocated. Such channels can be found if the exit
     * handler for channel cleanup has run but the channel is still
     * registered in an interpreter.
     */

    if (CheckForDeadChannel(interp, statePtr)) {
	return TCL_ERROR;
    }

    /*
     * This operation should occur at the top of a channel stack.
     */

    chanPtr = statePtr->topChanPtr;

    /*
     * If we are in the middle of a background copy, use the saved flags.
     */

    if (statePtr->csPtr) {
	if (chanPtr == statePtr->csPtr->readPtr) {
	    flags = statePtr->csPtr->readFlags;
	} else {
	    flags = statePtr->csPtr->writeFlags;
	}
    } else {
	flags = statePtr->flags;
    }

    /*
     * If the optionName is NULL it means that we want a list of all
     * options and values.
     */

    if (optionName == (char *) NULL) {
	len = 0;
    } else {
	len = strlen(optionName);
    }

    if ((len == 0) || ((len > 2) && (optionName[1] == 'b') &&
	    (strncmp(optionName, "-blocking", len) == 0))) {
	if (len == 0) {
	    Tcl_DStringAppendElement(dsPtr, "-blocking");
	}
	Tcl_DStringAppendElement(dsPtr,
		(flags & CHANNEL_NONBLOCKING) ? "0" : "1");
	if (len > 0) {
	    return TCL_OK;
	}
    }
    if ((len == 0) || ((len > 7) && (optionName[1] == 'b') &&
	    (strncmp(optionName, "-buffering", len) == 0))) {
	if (len == 0) {
	    Tcl_DStringAppendElement(dsPtr, "-buffering");
	}
	if (flags & CHANNEL_LINEBUFFERED) {
	    Tcl_DStringAppendElement(dsPtr, "line");
	} else if (flags & CHANNEL_UNBUFFERED) {
	    Tcl_DStringAppendElement(dsPtr, "none");
	} else {
	    Tcl_DStringAppendElement(dsPtr, "full");
	}
	if (len > 0) {
	    return TCL_OK;
	}
    }
    if ((len == 0) || ((len > 7) && (optionName[1] == 'b') &&
	    (strncmp(optionName, "-buffersize", len) == 0))) {
	if (len == 0) {
	    Tcl_DStringAppendElement(dsPtr, "-buffersize");
	}
	TclFormatInt(optionVal, statePtr->bufSize);
	Tcl_DStringAppendElement(dsPtr, optionVal);
	if (len > 0) {
	    return TCL_OK;
	}
    }
    if ((len == 0) || ((len > 2) && (optionName[1] == 'e') &&
	    (strncmp(optionName, "-encoding", len) == 0))) {
	if (len == 0) {
	    Tcl_DStringAppendElement(dsPtr, "-encoding");
	}
	if (statePtr->encoding == NULL) {
	    Tcl_DStringAppendElement(dsPtr, "binary");
	} else {
	    Tcl_DStringAppendElement(dsPtr,
		    Tcl_GetEncodingName(statePtr->encoding));
	}
	if (len > 0) {
	    return TCL_OK;
	}
    }
    if ((len == 0) || ((len > 2) && (optionName[1] == 'e') &&
	    (strncmp(optionName, "-eofchar", len) == 0))) {
	if (len == 0) {
	    Tcl_DStringAppendElement(dsPtr, "-eofchar");
	}
	if (((flags & (TCL_READABLE|TCL_WRITABLE)) ==
		(TCL_READABLE|TCL_WRITABLE)) && (len == 0)) {
	    Tcl_DStringStartSublist(dsPtr);
	}
	if (flags & TCL_READABLE) {
	    if (statePtr->inEofChar == 0) {
		Tcl_DStringAppendElement(dsPtr, "");
	    } else {
		char buf[4];

		sprintf(buf, "%c", statePtr->inEofChar);
		Tcl_DStringAppendElement(dsPtr, buf);
	    }
	}
	if (flags & TCL_WRITABLE) {
	    if (statePtr->outEofChar == 0) {
		Tcl_DStringAppendElement(dsPtr, "");
	    } else {
		char buf[4];

		sprintf(buf, "%c", statePtr->outEofChar);
		Tcl_DStringAppendElement(dsPtr, buf);
	    }
	}
	if (!(flags & (TCL_READABLE|TCL_WRITABLE))) {
	    /*
	     * Not readable or writable (e.g. server socket)
	     */

	    Tcl_DStringAppendElement(dsPtr, "");
	}
	if (((flags & (TCL_READABLE|TCL_WRITABLE)) ==
		(TCL_READABLE|TCL_WRITABLE)) && (len == 0)) {
	    Tcl_DStringEndSublist(dsPtr);
	}
	if (len > 0) {
	    return TCL_OK;
	}
    }
    if ((len == 0) || ((len > 1) && (optionName[1] == 't') &&
	    (strncmp(optionName, "-translation", len) == 0))) {
	if (len == 0) {
	    Tcl_DStringAppendElement(dsPtr, "-translation");
	}
	if (((flags & (TCL_READABLE|TCL_WRITABLE)) ==
		(TCL_READABLE|TCL_WRITABLE)) && (len == 0)) {
	    Tcl_DStringStartSublist(dsPtr);
	}
	if (flags & TCL_READABLE) {
	    if (statePtr->inputTranslation == TCL_TRANSLATE_AUTO) {
		Tcl_DStringAppendElement(dsPtr, "auto");
	    } else if (statePtr->inputTranslation == TCL_TRANSLATE_CR) {
		Tcl_DStringAppendElement(dsPtr, "cr");
	    } else if (statePtr->inputTranslation == TCL_TRANSLATE_CRLF) {
		Tcl_DStringAppendElement(dsPtr, "crlf");
	    } else {
		Tcl_DStringAppendElement(dsPtr, "lf");
	    }
	}
	if (flags & TCL_WRITABLE) {
	    if (statePtr->outputTranslation == TCL_TRANSLATE_AUTO) {
		Tcl_DStringAppendElement(dsPtr, "auto");
	    } else if (statePtr->outputTranslation == TCL_TRANSLATE_CR) {
		Tcl_DStringAppendElement(dsPtr, "cr");
	    } else if (statePtr->outputTranslation == TCL_TRANSLATE_CRLF) {
		Tcl_DStringAppendElement(dsPtr, "crlf");
	    } else {
		Tcl_DStringAppendElement(dsPtr, "lf");
	    }
	}
	if (!(flags & (TCL_READABLE|TCL_WRITABLE))) {
	    /*
	     * Not readable or writable (e.g. server socket)
	     */

	    Tcl_DStringAppendElement(dsPtr, "auto");
	}
	if (((flags & (TCL_READABLE|TCL_WRITABLE)) ==
		(TCL_READABLE|TCL_WRITABLE)) && (len == 0)) {
	    Tcl_DStringEndSublist(dsPtr);
	}
	if (len > 0) {
	    return TCL_OK;
	}
    }
    if (chanPtr->typePtr->getOptionProc != (Tcl_DriverGetOptionProc *) NULL) {
	/*
	 * let the driver specific handle additional options
	 * and result code and message.
	 */

	return (chanPtr->typePtr->getOptionProc) (chanPtr->instanceData,
		interp, optionName, dsPtr);
    } else {
	/*
	 * no driver specific options case.
	 */

	if (len == 0) {
	    return TCL_OK;
	}
	return Tcl_BadChannelOption(interp, optionName, NULL);
    }
}

/*
 *---------------------------------------------------------------------------
 *
 * Tcl_SetChannelOption --
 *
 *	Sets an option on a channel.
 *
 * Results:
 *	A standard Tcl result.  On error, sets interp's result object
 *	if interp is not NULL.
 *
 * Side effects:
 *	May modify an option on a device.
 *
 *---------------------------------------------------------------------------
 */

int
Tcl_SetChannelOption(interp, chan, optionName, newValue)
    Tcl_Interp *interp;		/* For error reporting - can be NULL. */
    Tcl_Channel chan;		/* Channel on which to set mode. */
    CONST char *optionName;	/* Which option to set? */
    CONST char *newValue;	/* New value for option. */
{
    Channel *chanPtr = (Channel *) chan;	/* The real IO channel. */
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    size_t len;			/* Length of optionName string. */
    int argc;
    CONST char **argv;

    /*
     * If the channel is in the middle of a background copy, fail.
     */

    if (statePtr->csPtr) {
	if (interp) {
	    Tcl_AppendResult(interp, "unable to set channel options: ",
		    "background copy in progress", (char *) NULL);
	}
	return TCL_ERROR;
    }

    /*
     * Disallow options on dead channels -- channels that have been closed but
     * not yet been deallocated. Such channels can be found if the exit
     * handler for channel cleanup has run but the channel is still
     * registered in an interpreter.
     */

    if (CheckForDeadChannel(NULL, statePtr)) {
	return TCL_ERROR;
    }

    /*
     * This operation should occur at the top of a channel stack.
     */

    chanPtr = statePtr->topChanPtr;

    len = strlen(optionName);

    if ((len > 2) && (optionName[1] == 'b') &&
	    (strncmp(optionName, "-blocking", len) == 0)) {
	int newMode;
	if (Tcl_GetBoolean(interp, newValue, &newMode) == TCL_ERROR) {
	    return TCL_ERROR;
	}
	if (newMode) {
	    newMode = TCL_MODE_BLOCKING;
	} else {
	    newMode = TCL_MODE_NONBLOCKING;
	}
	return SetBlockMode(interp, chanPtr, newMode);
    } else if ((len > 7) && (optionName[1] == 'b') &&
	    (strncmp(optionName, "-buffering", len) == 0)) {
	len = strlen(newValue);
	if ((newValue[0] == 'f') && (strncmp(newValue, "full", len) == 0)) {
	    statePtr->flags &=
		    (~(CHANNEL_UNBUFFERED|CHANNEL_LINEBUFFERED));
	} else if ((newValue[0] == 'l') &&
		(strncmp(newValue, "line", len) == 0)) {
	    statePtr->flags &= (~(CHANNEL_UNBUFFERED));
	    statePtr->flags |= CHANNEL_LINEBUFFERED;
	} else if ((newValue[0] == 'n') &&
		(strncmp(newValue, "none", len) == 0)) {
	    statePtr->flags &= (~(CHANNEL_LINEBUFFERED));
	    statePtr->flags |= CHANNEL_UNBUFFERED;
	} else {
	    if (interp) {
		Tcl_AppendResult(interp, "bad value for -buffering: ",
			"must be one of full, line, or none",
			(char *) NULL);
		return TCL_ERROR;
	    }
	}
	return TCL_OK;
    } else if ((len > 7) && (optionName[1] == 'b') &&
	    (strncmp(optionName, "-buffersize", len) == 0)) {
	int newBufferSize;
	if (Tcl_GetInt(interp, newValue, &newBufferSize) == TCL_ERROR) {
	    return TCL_ERROR;
	}
	Tcl_SetChannelBufferSize(chan, newBufferSize);
    } else if ((len > 2) && (optionName[1] == 'e') &&
	    (strncmp(optionName, "-encoding", len) == 0)) {
	Tcl_Encoding encoding;

	if ((newValue[0] == '\0') || (strcmp(newValue, "binary") == 0)) {
	    encoding = NULL;
	} else {
	    encoding = Tcl_GetEncoding(interp, newValue);
	    if (encoding == NULL) {
		return TCL_ERROR;
	    }
	}

	/*
	 * When the channel has an escape sequence driven encoding such as
	 * iso2022, the terminated escape sequence must write to the buffer.
	 */

	if ((statePtr->encoding != NULL) && (statePtr->curOutPtr != NULL)
		&& (CheckChannelErrors(statePtr, TCL_WRITABLE) == 0)) {
	    statePtr->outputEncodingFlags |= TCL_ENCODING_END;
	    WriteChars(chanPtr, "", 0);
	}
	Tcl_FreeEncoding(statePtr->encoding);
	statePtr->encoding = encoding;
	statePtr->inputEncodingState = NULL;
	statePtr->inputEncodingFlags = TCL_ENCODING_START;
	statePtr->outputEncodingState = NULL;
	statePtr->outputEncodingFlags = TCL_ENCODING_START;
	statePtr->flags &= ~CHANNEL_NEED_MORE_DATA;
	UpdateInterest(chanPtr);
    } else if ((len > 2) && (optionName[1] == 'e') &&
	    (strncmp(optionName, "-eofchar", len) == 0)) {
	if (Tcl_SplitList(interp, newValue, &argc, &argv) == TCL_ERROR) {
	    return TCL_ERROR;
	}
	if (argc == 0) {
	    statePtr->inEofChar = 0;
	    statePtr->outEofChar = 0;
	} else if (argc == 1) {
	    if (statePtr->flags & TCL_WRITABLE) {
		statePtr->outEofChar = (int) argv[0][0];
	    }
	    if (statePtr->flags & TCL_READABLE) {
		statePtr->inEofChar = (int) argv[0][0];
	    }
	} else if (argc != 2) {
	    if (interp) {
		Tcl_AppendResult(interp,
			"bad value for -eofchar: should be a list of zero,",
			" one, or two elements", (char *) NULL);
	    }
	    ckfree((char *) argv);
	    return TCL_ERROR;
	} else {
	    if (statePtr->flags & TCL_READABLE) {
		statePtr->inEofChar = (int) argv[0][0];
	    }
	    if (statePtr->flags & TCL_WRITABLE) {
		statePtr->outEofChar = (int) argv[1][0];
	    }
	}
	if (argv != NULL) {
	    ckfree((char *) argv);
	}

	/*
	 * [SF Tcl Bug 930851] Reset EOF and BLOCKED flags. Changing
	 * the character which signals eof can transform a current eof
	 * condition into a 'go ahead'. Ditto for blocked.
	 */

	statePtr->flags &=
		~(CHANNEL_EOF | CHANNEL_STICKY_EOF | CHANNEL_BLOCKED);

	return TCL_OK;
    } else if ((len > 1) && (optionName[1] == 't') &&
	    (strncmp(optionName, "-translation", len) == 0)) {
	CONST char *readMode, *writeMode;

	if (Tcl_SplitList(interp, newValue, &argc, &argv) == TCL_ERROR) {
	    return TCL_ERROR;
	}

	if (argc == 1) {
	    readMode = (statePtr->flags & TCL_READABLE) ? argv[0] : NULL;
	    writeMode = (statePtr->flags & TCL_WRITABLE) ? argv[0] : NULL;
	} else if (argc == 2) {
	    readMode = (statePtr->flags & TCL_READABLE) ? argv[0] : NULL;
	    writeMode = (statePtr->flags & TCL_WRITABLE) ? argv[1] : NULL;
	} else {
	    if (interp) {
		Tcl_AppendResult(interp,
			"bad value for -translation: must be a one or two",
			" element list", (char *) NULL);
	    }
	    ckfree((char *) argv);
	    return TCL_ERROR;
	}

	if (readMode) {
	    TclEolTranslation translation;
	    if (*readMode == '\0') {
		translation = statePtr->inputTranslation;
	    } else if (strcmp(readMode, "auto") == 0) {
		translation = TCL_TRANSLATE_AUTO;
	    } else if (strcmp(readMode, "binary") == 0) {
		translation = TCL_TRANSLATE_LF;
		statePtr->inEofChar = 0;
		Tcl_FreeEncoding(statePtr->encoding);		    
		statePtr->encoding = NULL;
	    } else if (strcmp(readMode, "lf") == 0) {
		translation = TCL_TRANSLATE_LF;
	    } else if (strcmp(readMode, "cr") == 0) {
		translation = TCL_TRANSLATE_CR;
	    } else if (strcmp(readMode, "crlf") == 0) {
		translation = TCL_TRANSLATE_CRLF;
	    } else if (strcmp(readMode, "platform") == 0) {
		translation = TCL_PLATFORM_TRANSLATION;
	    } else {
		if (interp) {
		    Tcl_AppendResult(interp,
			    "bad value for -translation: ",
			    "must be one of auto, binary, cr, lf, crlf,",
			    " or platform", (char *) NULL);
		}
		ckfree((char *) argv);
		return TCL_ERROR;
	    }

	    /*
	     * Reset the EOL flags since we need to look at any buffered
	     * data to see if the new translation mode allows us to
	     * complete the line.
	     */

	    if (translation != statePtr->inputTranslation) {
		statePtr->inputTranslation = translation;
		statePtr->flags &= ~(INPUT_SAW_CR);
		statePtr->flags &= ~(CHANNEL_NEED_MORE_DATA);
		UpdateInterest(chanPtr);
	    }
	}
	if (writeMode) {
	    if (*writeMode == '\0') {
		/* Do nothing. */
	    } else if (strcmp(writeMode, "auto") == 0) {
		/*
		 * This is a hack to get TCP sockets to produce output
		 * in CRLF mode if they are being set into AUTO mode.
		 * A better solution for achieving this effect will be
		 * coded later.
		 */

		if (strcmp(Tcl_ChannelName(chanPtr->typePtr), "tcp") == 0) {
		    statePtr->outputTranslation = TCL_TRANSLATE_CRLF;
		} else {
		    statePtr->outputTranslation = TCL_PLATFORM_TRANSLATION;
		}
	    } else if (strcmp(writeMode, "binary") == 0) {
		statePtr->outEofChar = 0;
		statePtr->outputTranslation = TCL_TRANSLATE_LF;
		Tcl_FreeEncoding(statePtr->encoding);		    
		statePtr->encoding = NULL;
	    } else if (strcmp(writeMode, "lf") == 0) {
		statePtr->outputTranslation = TCL_TRANSLATE_LF;
	    } else if (strcmp(writeMode, "cr") == 0) {
		statePtr->outputTranslation = TCL_TRANSLATE_CR;
	    } else if (strcmp(writeMode, "crlf") == 0) {
		statePtr->outputTranslation = TCL_TRANSLATE_CRLF;
	    } else if (strcmp(writeMode, "platform") == 0) {
		statePtr->outputTranslation = TCL_PLATFORM_TRANSLATION;
	    } else {
		if (interp) {
		    Tcl_AppendResult(interp,
			    "bad value for -translation: ",
			    "must be one of auto, binary, cr, lf, crlf,",
			    " or platform", (char *) NULL);
		}
		ckfree((char *) argv);
		return TCL_ERROR;
	    }
	}
	ckfree((char *) argv);		  
	return TCL_OK;
    } else if (chanPtr->typePtr->setOptionProc != NULL) {
	return (*chanPtr->typePtr->setOptionProc)(chanPtr->instanceData,
		interp, optionName, newValue);
    } else {
	return Tcl_BadChannelOption(interp, optionName, (char *) NULL);
    }

    /*
     * If bufsize changes, need to get rid of old utility buffer.
     */

    if (statePtr->saveInBufPtr != NULL) {
	RecycleBuffer(statePtr, statePtr->saveInBufPtr, 1);
	statePtr->saveInBufPtr = NULL;
    }
    if (statePtr->inQueueHead != NULL) {
	if ((statePtr->inQueueHead->nextPtr == NULL)
		&& (statePtr->inQueueHead->nextAdded ==
			statePtr->inQueueHead->nextRemoved)) {
	    RecycleBuffer(statePtr, statePtr->inQueueHead, 1);
	    statePtr->inQueueHead = NULL;
	    statePtr->inQueueTail = NULL;
	}
    }

    /*
     * If encoding or bufsize changes, need to update output staging buffer.
     */

    if (statePtr->outputStage != NULL) {
	ckfree((char *) statePtr->outputStage);
	statePtr->outputStage = NULL;
    }
    if ((statePtr->encoding != NULL) && (statePtr->flags & TCL_WRITABLE)) {
	statePtr->outputStage = (char *) 
	    ckalloc((unsigned) (statePtr->bufSize + 2));
    }
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * CleanupChannelHandlers --
 *
 *	Removes channel handlers that refer to the supplied interpreter,
 *	so that if the actual channel is not closed now, these handlers
 *	will not run on subsequent events on the channel. This would be
 *	erroneous, because the interpreter no longer has a reference to
 *	this channel.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Removes channel handlers.
 *
 *----------------------------------------------------------------------
 */

static void
CleanupChannelHandlers(interp, chanPtr)
    Tcl_Interp *interp;
    Channel *chanPtr;
{
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    EventScriptRecord *sPtr, *prevPtr, *nextPtr;

    /*
     * Remove fileevent records on this channel that refer to the
     * given interpreter.
     */

    for (sPtr = statePtr->scriptRecordPtr,
	    prevPtr = (EventScriptRecord *) NULL;
	    sPtr != (EventScriptRecord *) NULL;
	    sPtr = nextPtr) {
	nextPtr = sPtr->nextPtr;
	if (sPtr->interp == interp) {
	    if (prevPtr == (EventScriptRecord *) NULL) {
		statePtr->scriptRecordPtr = nextPtr;
	    } else {
		prevPtr->nextPtr = nextPtr;
	    }

	    Tcl_DeleteChannelHandler((Tcl_Channel) chanPtr,
		    TclChannelEventScriptInvoker, (ClientData) sPtr);

	    TclDecrRefCount(sPtr->scriptPtr);
	    ckfree((char *) sPtr);
	} else {
	    prevPtr = sPtr;
	}
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_NotifyChannel --
 *
 *	This procedure is called by a channel driver when a driver
 *	detects an event on a channel.  This procedure is responsible
 *	for actually handling the event by invoking any channel
 *	handler callbacks.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Whatever the channel handler callback procedure does.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_NotifyChannel(channel, mask)
    Tcl_Channel channel;	/* Channel that detected an event. */
    int mask;			/* OR'ed combination of TCL_READABLE,
				 * TCL_WRITABLE, or TCL_EXCEPTION: indicates
				 * which events were detected. */
{
    Channel *chanPtr = (Channel *) channel;
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    ChannelHandler *chPtr;
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
    NextChannelHandler nh;
    Channel *upChanPtr;
    Tcl_ChannelType *upTypePtr;

#ifdef TCL_IO_TRACK_OS_FOR_DRIVER_WITH_BAD_BLOCKING
    /* [SF Tcl Bug 943274]
     * For a non-blocking channel without blockmodeproc we keep track
     * of actual input coming from the OS so that we can do a credible
     * imitation of non-blocking behaviour.
     */

    if ((mask & TCL_READABLE) &&
	    (statePtr->flags & CHANNEL_NONBLOCKING) &&
	    (Tcl_ChannelBlockModeProc(chanPtr->typePtr) == NULL) &&
	    !(statePtr->flags & CHANNEL_TIMER_FEV)) {

	statePtr->flags |= CHANNEL_HAS_MORE_DATA;
    }
#endif /* TCL_IO_TRACK_OS_FOR_DRIVER_WITH_BAD_BLOCKING */

    /*
     * In contrast to the other API functions this procedure walks towards
     * the top of a stack and not down from it.
     *
     * The channel calling this procedure is the one who generated the event,
     * and thus does not take part in handling it. IOW, its HandlerProc is
     * not called, instead we begin with the channel above it.
     *
     * This behaviour also allows the transformation channels to
     * generate their own events and pass them upward.
     */

    while (mask && (chanPtr->upChanPtr != ((Channel *) NULL))) {
	Tcl_DriverHandlerProc *upHandlerProc;

	upChanPtr = chanPtr->upChanPtr;
	upTypePtr = upChanPtr->typePtr;
	upHandlerProc = Tcl_ChannelHandlerProc(upTypePtr);
	if (upHandlerProc != NULL) {
	    mask = (*upHandlerProc) (upChanPtr->instanceData, mask);
	}

	/* ELSE:
	 * Ignore transformations which are unable to handle the event
	 * coming from below. Assume that they don't change the mask and
	 * pass it on.
	 */

	chanPtr = upChanPtr;
    }

    channel = (Tcl_Channel) chanPtr;

    /*
     * Here we have either reached the top of the stack or the mask is
     * empty.  We break out of the procedure if it is the latter.
     */

    if (!mask) {
	return;
    }

    /*
     * We are now above the topmost channel in a stack and have events
     * left. Now call the channel handlers as usual.
     *
     * Preserve the channel struct in case the script closes it.
     */

    Tcl_Preserve((ClientData) channel);
    Tcl_Preserve((ClientData) statePtr);

    /*
     * If we are flushing in the background, be sure to call FlushChannel
     * for writable events.  Note that we have to discard the writable
     * event so we don't call any write handlers before the flush is
     * complete.
     */

    if ((statePtr->flags & BG_FLUSH_SCHEDULED) && (mask & TCL_WRITABLE)) {
	FlushChannel(NULL, chanPtr, 1);
	mask &= ~TCL_WRITABLE;
    }

    /*
     * Add this invocation to the list of recursive invocations of
     * ChannelHandlerEventProc.
     */

    nh.nextHandlerPtr = (ChannelHandler *) NULL;
    nh.nestedHandlerPtr = tsdPtr->nestedHandlerPtr;
    tsdPtr->nestedHandlerPtr = &nh;

    for (chPtr = statePtr->chPtr; chPtr != (ChannelHandler *) NULL; ) {
	/*
	 * If this channel handler is interested in any of the events that
	 * have occurred on the channel, invoke its procedure.
	 */

	if ((chPtr->mask & mask) != 0) {
	    nh.nextHandlerPtr = chPtr->nextPtr;
	    (*(chPtr->proc))(chPtr->clientData, mask);
	    chPtr = nh.nextHandlerPtr;
	} else {
	    chPtr = chPtr->nextPtr;
	}
    }

    /*
     * Update the notifier interest, since it may have changed after
     * invoking event handlers. Skip that if the channel was deleted
     * in the call to the channel handler.
     */

    if (chanPtr->typePtr != NULL) {
	UpdateInterest(chanPtr);
    }

    Tcl_Release((ClientData) statePtr);
    Tcl_Release((ClientData) channel);

    tsdPtr->nestedHandlerPtr = nh.nestedHandlerPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * UpdateInterest --
 *
 *	Arrange for the notifier to call us back at appropriate times
 *	based on the current state of the channel.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	May schedule a timer or driver handler.
 *
 *----------------------------------------------------------------------
 */

static void
UpdateInterest(chanPtr)
    Channel *chanPtr;		/* Channel to update. */
{
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    int mask = statePtr->interestMask;

    /*
     * If there are flushed buffers waiting to be written, then
     * we need to watch for the channel to become writable.
     */

    if (statePtr->flags & BG_FLUSH_SCHEDULED) {
	mask |= TCL_WRITABLE;
    }

    /*
     * If there is data in the input queue, and we aren't waiting for more
     * data, then we need to schedule a timer so we don't block in the
     * notifier.  Also, cancel the read interest so we don't get duplicate
     * events.
     */

    if (mask & TCL_READABLE) {
	if (!(statePtr->flags & CHANNEL_NEED_MORE_DATA)
		&& (statePtr->inQueueHead != (ChannelBuffer *) NULL)
		&& (statePtr->inQueueHead->nextRemoved <
			statePtr->inQueueHead->nextAdded)) {
	    mask &= ~TCL_READABLE;

	    /*
	     * Andreas Kupries, April 11, 2003
	     *
	     * Some operating systems (Solaris 2.6 and higher (but not
	     * Solaris 2.5, go figure)) generate READABLE and
	     * EXCEPTION events when select()'ing [*] on a plain file,
	     * even if EOF was not yet reached. This is a problem in
	     * the following situation:
	     *
	     * - An extension asks to get both READABLE and EXCEPTION
	     *   events.
	     * - It reads data into a buffer smaller than the buffer
	     *   used by Tcl itself.
	     * - It does not process all events in the event queue, but
	     *   only one, at least in some situations.
	     *
	     * In that case we can get into a situation where
	     *
	     * - Tcl drops READABLE here, because it has data in its own
	     *   buffers waiting to be read by the extension.
	     * - A READABLE event is syntesized via timer.
	     * - The OS still reports the EXCEPTION condition on the file.
	     * - And the extension gets the EXCPTION event first, and
	     *   handles this as EOF.
	     *
	     * End result ==> Premature end of reading from a file.
	     *
	     * The concrete example is 'Expect', and its [expect]
	     * command (and at the C-level, deep in the bowels of
	     * Expect, 'exp_get_next_event'. See marker 'SunOS' for
	     * commentary in that function too).
	     *
	     * [*] As the Tcl notifier does. See also for marker
	     * 'SunOS' in file 'exp_event.c' of Expect.
	     *
	     * Our solution here is to drop the interest in the
	     * EXCEPTION events too. This compiles on all platforms,
	     * and also passes the testsuite on all of them.
	     */

	    mask &= ~TCL_EXCEPTION;

	    if (!statePtr->timer) {
		statePtr->timer = Tcl_CreateTimerHandler(0, ChannelTimerProc,
			(ClientData) chanPtr);
	    }
	}
    }
    (chanPtr->typePtr->watchProc)(chanPtr->instanceData, mask);
}

/*
 *----------------------------------------------------------------------
 *
 * ChannelTimerProc --
 *
 *	Timer handler scheduled by UpdateInterest to monitor the
 *	channel buffers until they are empty.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	May invoke channel handlers.
 *
 *----------------------------------------------------------------------
 */

static void
ChannelTimerProc(clientData)
    ClientData clientData;
{
    Channel *chanPtr = (Channel *) clientData;
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */

    if (!(statePtr->flags & CHANNEL_NEED_MORE_DATA)
	    && (statePtr->interestMask & TCL_READABLE)
	    && (statePtr->inQueueHead != (ChannelBuffer *) NULL)
	    && (statePtr->inQueueHead->nextRemoved <
		    statePtr->inQueueHead->nextAdded)) {
	/*
	 * Restart the timer in case a channel handler reenters the
	 * event loop before UpdateInterest gets called by Tcl_NotifyChannel.
	 */

	statePtr->timer = Tcl_CreateTimerHandler(0, ChannelTimerProc,
		(ClientData) chanPtr);

#ifdef TCL_IO_TRACK_OS_FOR_DRIVER_WITH_BAD_BLOCKING
	/* Set the TIMER flag to notify the higher levels that the
	 * driver might have no data for us. We do this only if we are
	 * in non-blocking mode and the driver has no BlockModeProc
	 * because only then we really don't know if the driver will
	 * block or not. A similar test is done in "PeekAhead".
	 */

	if ((statePtr->flags & CHANNEL_NONBLOCKING) &&
	    (Tcl_ChannelBlockModeProc(chanPtr->typePtr) == NULL)) {
	    statePtr->flags |= CHANNEL_TIMER_FEV;
	}
#endif /* TCL_IO_TRACK_OS_FOR_DRIVER_WITH_BAD_BLOCKING */

	Tcl_Preserve((ClientData) statePtr);
	Tcl_NotifyChannel((Tcl_Channel)chanPtr, TCL_READABLE);

#ifdef TCL_IO_TRACK_OS_FOR_DRIVER_WITH_BAD_BLOCKING
	statePtr->flags &= ~CHANNEL_TIMER_FEV; 
#endif /* TCL_IO_TRACK_OS_FOR_DRIVER_WITH_BAD_BLOCKING */

	Tcl_Release((ClientData) statePtr);
    } else {
	statePtr->timer = NULL;
	UpdateInterest(chanPtr);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_CreateChannelHandler --
 *
 *	Arrange for a given procedure to be invoked whenever the
 *	channel indicated by the chanPtr arg becomes readable or
 *	writable.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	From now on, whenever the I/O channel given by chanPtr becomes
 *	ready in the way indicated by mask, proc will be invoked.
 *	See the manual entry for details on the calling sequence
 *	to proc.  If there is already an event handler for chan, proc
 *	and clientData, then the mask will be updated.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_CreateChannelHandler(chan, mask, proc, clientData)
    Tcl_Channel chan;		/* The channel to create the handler for. */
    int mask;			/* OR'ed combination of TCL_READABLE,
				 * TCL_WRITABLE, and TCL_EXCEPTION:
				 * indicates conditions under which
				 * proc should be called. Use 0 to
				 * disable a registered handler. */
    Tcl_ChannelProc *proc;	/* Procedure to call for each
				 * selected event. */
    ClientData clientData;	/* Arbitrary data to pass to proc. */
{
    ChannelHandler *chPtr;
    Channel *chanPtr = (Channel *) chan;
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */

    /*
     * Check whether this channel handler is not already registered. If
     * it is not, create a new record, else reuse existing record (smash
     * current values).
     */

    for (chPtr = statePtr->chPtr;
	    chPtr != (ChannelHandler *) NULL;
	    chPtr = chPtr->nextPtr) {
	if ((chPtr->chanPtr == chanPtr) && (chPtr->proc == proc) &&
		(chPtr->clientData == clientData)) {
	    break;
	}
    }
    if (chPtr == (ChannelHandler *) NULL) {
	chPtr = (ChannelHandler *) ckalloc((unsigned) sizeof(ChannelHandler));
	chPtr->mask = 0;
	chPtr->proc = proc;
	chPtr->clientData = clientData;
	chPtr->chanPtr = chanPtr;
	chPtr->nextPtr = statePtr->chPtr;
	statePtr->chPtr = chPtr;
    }

    /*
     * The remainder of the initialization below is done regardless of
     * whether or not this is a new record or a modification of an old
     * one.
     */

    chPtr->mask = mask;

    /*
     * Recompute the interest mask for the channel - this call may actually
     * be disabling an existing handler.
     */

    statePtr->interestMask = 0;
    for (chPtr = statePtr->chPtr;
	    chPtr != (ChannelHandler *) NULL;
	    chPtr = chPtr->nextPtr) {
	statePtr->interestMask |= chPtr->mask;
    }

    UpdateInterest(statePtr->topChanPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_DeleteChannelHandler --
 *
 *	Cancel a previously arranged callback arrangement for an IO
 *	channel.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	If a callback was previously registered for this chan, proc and
 *	 clientData , it is removed and the callback will no longer be called
 *	when the channel becomes ready for IO.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_DeleteChannelHandler(chan, proc, clientData)
    Tcl_Channel chan;		/* The channel for which to remove the
				 * callback. */
    Tcl_ChannelProc *proc;	/* The procedure in the callback to delete. */
    ClientData clientData;	/* The client data in the callback
				 * to delete. */
{
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
    ChannelHandler *chPtr, *prevChPtr;
    Channel *chanPtr = (Channel *) chan;
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    NextChannelHandler *nhPtr;

    /*
     * Find the entry and the previous one in the list.
     */

    for (prevChPtr = (ChannelHandler *) NULL, chPtr = statePtr->chPtr;
	    chPtr != (ChannelHandler *) NULL;
	    chPtr = chPtr->nextPtr) {
	if ((chPtr->chanPtr == chanPtr) && (chPtr->clientData == clientData)
		&& (chPtr->proc == proc)) {
	    break;
	}
	prevChPtr = chPtr;
    }

    /*
     * If not found, return without doing anything.
     */

    if (chPtr == (ChannelHandler *) NULL) {
	return;
    }

    /*
     * If ChannelHandlerEventProc is about to process this handler, tell it to
     * process the next one instead - we are going to delete *this* one.
     */

    for (nhPtr = tsdPtr->nestedHandlerPtr;
	    nhPtr != (NextChannelHandler *) NULL;
	    nhPtr = nhPtr->nestedHandlerPtr) {
	if (nhPtr->nextHandlerPtr == chPtr) {
	    nhPtr->nextHandlerPtr = chPtr->nextPtr;
	}
    }

    /*
     * Splice it out of the list of channel handlers.
     */

    if (prevChPtr == (ChannelHandler *) NULL) {
	statePtr->chPtr = chPtr->nextPtr;
    } else {
	prevChPtr->nextPtr = chPtr->nextPtr;
    }
    ckfree((char *) chPtr);

    /*
     * Recompute the interest list for the channel, so that infinite loops
     * will not result if Tcl_DeleteChannelHandler is called inside an
     * event.
     */

    statePtr->interestMask = 0;
    for (chPtr = statePtr->chPtr;
	    chPtr != (ChannelHandler *) NULL;
	    chPtr = chPtr->nextPtr) {
	statePtr->interestMask |= chPtr->mask;
    }

    UpdateInterest(statePtr->topChanPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * DeleteScriptRecord --
 *
 *	Delete a script record for this combination of channel, interp
 *	and mask.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Deletes a script record and cancels a channel event handler.
 *
 *----------------------------------------------------------------------
 */

static void
DeleteScriptRecord(interp, chanPtr, mask)
    Tcl_Interp *interp;		/* Interpreter in which script was to be
				 * executed. */
    Channel *chanPtr;		/* The channel for which to delete the
				 * script record (if any). */
    int mask;			/* Events in mask must exactly match mask
				 * of script to delete. */
{
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    EventScriptRecord *esPtr, *prevEsPtr;

    for (esPtr = statePtr->scriptRecordPtr,
	    prevEsPtr = (EventScriptRecord *) NULL;
	    esPtr != (EventScriptRecord *) NULL;
	    prevEsPtr = esPtr, esPtr = esPtr->nextPtr) {
	if ((esPtr->interp == interp) && (esPtr->mask == mask)) {
	    if (esPtr == statePtr->scriptRecordPtr) {
		statePtr->scriptRecordPtr = esPtr->nextPtr;
	    } else {
		prevEsPtr->nextPtr = esPtr->nextPtr;
	    }

	    Tcl_DeleteChannelHandler((Tcl_Channel) chanPtr,
		    TclChannelEventScriptInvoker, (ClientData) esPtr);

	    TclDecrRefCount(esPtr->scriptPtr);
	    ckfree((char *) esPtr);

	    break;
	}
    }
}

/*
 *----------------------------------------------------------------------
 *
 * CreateScriptRecord --
 *
 *	Creates a record to store a script to be executed when a specific
 *	event fires on a specific channel.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Causes the script to be stored for later execution.
 *
 *----------------------------------------------------------------------
 */

static void
CreateScriptRecord(interp, chanPtr, mask, scriptPtr)
    Tcl_Interp *interp;			/* Interpreter in which to execute
					 * the stored script. */
    Channel *chanPtr;			/* Channel for which script is to
					 * be stored. */
    int mask;				/* Set of events for which script
					 * will be invoked. */
    Tcl_Obj *scriptPtr;			/* Pointer to script object. */
{
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    EventScriptRecord *esPtr;

    for (esPtr = statePtr->scriptRecordPtr;
	    esPtr != (EventScriptRecord *) NULL;
	    esPtr = esPtr->nextPtr) {
	if ((esPtr->interp == interp) && (esPtr->mask == mask)) {
	    TclDecrRefCount(esPtr->scriptPtr);
	    esPtr->scriptPtr = (Tcl_Obj *) NULL;
	    break;
	}
    }
    if (esPtr == (EventScriptRecord *) NULL) {
	esPtr = (EventScriptRecord *)
		ckalloc((unsigned) sizeof(EventScriptRecord));
	Tcl_CreateChannelHandler((Tcl_Channel) chanPtr, mask,
		TclChannelEventScriptInvoker, (ClientData) esPtr);
	esPtr->nextPtr = statePtr->scriptRecordPtr;
	statePtr->scriptRecordPtr = esPtr;
    }
    esPtr->chanPtr = chanPtr;
    esPtr->interp = interp;
    esPtr->mask = mask;
    Tcl_IncrRefCount(scriptPtr);
    esPtr->scriptPtr = scriptPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * TclChannelEventScriptInvoker --
 *
 *	Invokes a script scheduled by "fileevent" for when the channel
 *	becomes ready for IO. This function is invoked by the channel
 *	handler which was created by the Tcl "fileevent" command.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Whatever the script does.
 *
 *----------------------------------------------------------------------
 */

void
TclChannelEventScriptInvoker(clientData, mask)
    ClientData clientData;	/* The script+interp record. */
    int mask;			/* Not used. */
{
    Tcl_Interp *interp;		/* Interpreter in which to eval the script. */
    Channel *chanPtr;		/* The channel for which this handler is
				 * registered. */
    EventScriptRecord *esPtr;	/* The event script + interpreter to eval it
				 * in. */
    int result;			/* Result of call to eval script. */

    esPtr	= (EventScriptRecord *) clientData;
    chanPtr	= esPtr->chanPtr;
    mask	= esPtr->mask;
    interp	= esPtr->interp;

    /*
     * We must preserve the interpreter so we can report errors on it
     * later.  Note that we do not need to preserve the channel because
     * that is done by Tcl_NotifyChannel before calling channel handlers.
     */

    Tcl_Preserve((ClientData) interp);
    result = Tcl_EvalObjEx(interp, esPtr->scriptPtr, TCL_EVAL_GLOBAL);

    /*
     * On error, cause a background error and remove the channel handler
     * and the script record.
     *
     * NOTE: Must delete channel handler before causing the background error
     * because the background error may want to reinstall the handler.
     */

    if (result != TCL_OK) {
	if (chanPtr->typePtr != NULL) {
	    DeleteScriptRecord(interp, chanPtr, mask);
	}
	Tcl_BackgroundError(interp);
    }
    Tcl_Release((ClientData) interp);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_FileEventObjCmd --
 *
 *	This procedure implements the "fileevent" Tcl command. See the
 *	user documentation for details on what it does. This command is
 *	based on the Tk command "fileevent" which in turn is based on work
 *	contributed by Mark Diekhans.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	May create a channel handler for the specified channel.
 *
 *----------------------------------------------------------------------
 */

	/* ARGSUSED */
int
Tcl_FileEventObjCmd(clientData, interp, objc, objv)
    ClientData clientData;		/* Not used. */
    Tcl_Interp *interp;			/* Interpreter in which the channel
					 * for which to create the handler
					 * is found. */
    int objc;				/* Number of arguments. */
    Tcl_Obj *CONST objv[];		/* Argument objects. */
{
    Channel *chanPtr;			/* The channel to create
					 * the handler for. */
    ChannelState *statePtr;		/* state info for channel */
    Tcl_Channel chan;			/* The opaque type for the channel. */
    char *chanName;
    int modeIndex;			/* Index of mode argument. */
    int mask;
    static CONST char *modeOptions[] = {"readable", "writable", NULL};
    static int maskArray[] = {TCL_READABLE, TCL_WRITABLE};

    if ((objc != 3) && (objc != 4)) {
	Tcl_WrongNumArgs(interp, 1, objv, "channelId event ?script?");
	return TCL_ERROR;
    }
    if (Tcl_GetIndexFromObj(interp, objv[2], modeOptions, "event name", 0,
	    &modeIndex) != TCL_OK) {
	return TCL_ERROR;
    }
    mask = maskArray[modeIndex];

    chanName = Tcl_GetString(objv[1]);
    chan = Tcl_GetChannel(interp, chanName, NULL);
    if (chan == (Tcl_Channel) NULL) {
	return TCL_ERROR;
    }
    chanPtr = (Channel *) chan;
    statePtr = chanPtr->state;
    if ((statePtr->flags & mask) == 0) {
	Tcl_AppendResult(interp, "channel is not ",
		(mask == TCL_READABLE) ? "readable" : "writable",
		(char *) NULL);
	return TCL_ERROR;
    }

    /*
     * If we are supposed to return the script, do so.
     */

    if (objc == 3) {
	EventScriptRecord *esPtr;
	for (esPtr = statePtr->scriptRecordPtr;
		esPtr != (EventScriptRecord *) NULL;
		esPtr = esPtr->nextPtr) {
	    if ((esPtr->interp == interp) && (esPtr->mask == mask)) {
		Tcl_SetObjResult(interp, esPtr->scriptPtr);
		break;
	    }
	}
	return TCL_OK;
    }

    /*
     * If we are supposed to delete a stored script, do so.
     */

    if (*(Tcl_GetString(objv[3])) == '\0') {
	DeleteScriptRecord(interp, chanPtr, mask);
	return TCL_OK;
    }

    /*
     * Make the script record that will link between the event and the
     * script to invoke. This also creates a channel event handler which
     * will evaluate the script in the supplied interpreter.
     */

    CreateScriptRecord(interp, chanPtr, mask, objv[3]);

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * TclCopyChannel --
 *
 *	This routine copies data from one channel to another, either
 *	synchronously or asynchronously.  If a command script is
 *	supplied, the operation runs in the background.  The script
 *	is invoked when the copy completes.  Otherwise the function
 *	waits until the copy is completed before returning.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	May schedule a background copy operation that causes both
 *	channels to be marked busy.
 *
 *----------------------------------------------------------------------
 */

int
TclCopyChannel(interp, inChan, outChan, toRead, cmdPtr)
    Tcl_Interp *interp;		/* Current interpreter. */
    Tcl_Channel inChan;		/* Channel to read from. */
    Tcl_Channel outChan;	/* Channel to write to. */
    int toRead;			/* Amount of data to copy, or -1 for all. */
    Tcl_Obj *cmdPtr;		/* Pointer to script to execute or NULL. */
{
    Channel *inPtr = (Channel *) inChan;
    Channel *outPtr = (Channel *) outChan;
    ChannelState *inStatePtr, *outStatePtr;
    int readFlags, writeFlags;
    CopyState *csPtr;
    int nonBlocking = (cmdPtr) ? CHANNEL_NONBLOCKING : 0;

    inStatePtr = inPtr->state;
    outStatePtr = outPtr->state;

    if (inStatePtr->csPtr) {
	Tcl_AppendResult(interp, "channel \"",
		Tcl_GetChannelName(inChan), "\" is busy", NULL);
	return TCL_ERROR;
    }
    if (outStatePtr->csPtr) {
	Tcl_AppendResult(interp, "channel \"",
		Tcl_GetChannelName(outChan), "\" is busy", NULL);
	return TCL_ERROR;
    }

    readFlags = inStatePtr->flags;
    writeFlags = outStatePtr->flags;

    /*
     * Set up the blocking mode appropriately.  Background copies need
     * non-blocking channels.  Foreground copies need blocking channels.
     * If there is an error, restore the old blocking mode.
     */

    if (nonBlocking != (readFlags & CHANNEL_NONBLOCKING)) {
	if (SetBlockMode(interp, inPtr,
		nonBlocking ? TCL_MODE_NONBLOCKING : TCL_MODE_BLOCKING)
		!= TCL_OK) {
	    return TCL_ERROR;
	}
    }	    
    if (inPtr != outPtr) {
	if (nonBlocking != (writeFlags & CHANNEL_NONBLOCKING)) {
	    if (SetBlockMode(NULL, outPtr,
		    nonBlocking ? TCL_MODE_NONBLOCKING : TCL_MODE_BLOCKING)
		    != TCL_OK) {
		if (nonBlocking != (readFlags & CHANNEL_NONBLOCKING)) {
		    SetBlockMode(NULL, inPtr,
			    (readFlags & CHANNEL_NONBLOCKING)
			    ? TCL_MODE_NONBLOCKING : TCL_MODE_BLOCKING);
		    return TCL_ERROR;
		}
	    }
	}
    }

    /*
     * Make sure the output side is unbuffered.
     */

    outStatePtr->flags = (outStatePtr->flags & ~(CHANNEL_LINEBUFFERED))
	| CHANNEL_UNBUFFERED;

    /*
     * Allocate a new CopyState to maintain info about the current copy in
     * progress.  This structure will be deallocated when the copy is
     * completed.
     */

    csPtr = (CopyState *) ckalloc(sizeof(CopyState) + inStatePtr->bufSize);
    csPtr->bufSize = inStatePtr->bufSize;
    csPtr->readPtr = inPtr;
    csPtr->writePtr = outPtr;
    csPtr->readFlags = readFlags;
    csPtr->writeFlags = writeFlags;
    csPtr->toRead = toRead;
    csPtr->total = 0;
    csPtr->interp = interp;
    if (cmdPtr) {
	Tcl_IncrRefCount(cmdPtr);
    }
    csPtr->cmdPtr = cmdPtr;
    inStatePtr->csPtr = csPtr;
    outStatePtr->csPtr = csPtr;

    /*
     * Start copying data between the channels.
     */

    return CopyData(csPtr, 0);
}

/*
 *----------------------------------------------------------------------
 *
 * CopyData --
 *
 *	This function implements the lowest level of the copying
 *	mechanism for TclCopyChannel.
 *
 * Results:
 *	Returns TCL_OK on success, else TCL_ERROR.
 *
 * Side effects:
 *	Moves data between channels, may create channel handlers.
 *
 *----------------------------------------------------------------------
 */

static int
CopyData(csPtr, mask)
    CopyState *csPtr;		/* State of copy operation. */
    int mask;			/* Current channel event flags. */
{
    Tcl_Interp *interp;
    Tcl_Obj *cmdPtr, *errObj = NULL, *bufObj = NULL;
    Tcl_Channel inChan, outChan;
    ChannelState *inStatePtr, *outStatePtr;
    int result = TCL_OK, size, total, sizeb;
    char *buffer;

    int inBinary, outBinary, sameEncoding; /* Encoding control */
    int underflow;	/* input underflow */

    inChan	= (Tcl_Channel) csPtr->readPtr;
    outChan	= (Tcl_Channel) csPtr->writePtr;
    inStatePtr	= csPtr->readPtr->state;
    outStatePtr	= csPtr->writePtr->state;
    interp	= csPtr->interp;
    cmdPtr	= csPtr->cmdPtr;

    /*
     * Copy the data the slow way, using the translation mechanism.
     *
     * Note: We have make sure that we use the topmost channel in a stack
     * for the copying. The caller uses Tcl_GetChannel to access it, and
     * thus gets the bottom of the stack.
     */

    inBinary = (inStatePtr->encoding == NULL);
    outBinary = (outStatePtr->encoding == NULL);
    sameEncoding = (inStatePtr->encoding == outStatePtr->encoding);

    if (!(inBinary || sameEncoding)) {
	TclNewObj(bufObj);
	Tcl_IncrRefCount(bufObj);
    }

    while (csPtr->toRead != 0) {
	/*
	 * Check for unreported background errors.
	 */

	if (inStatePtr->unreportedError != 0) {
	    Tcl_SetErrno(inStatePtr->unreportedError);
	    inStatePtr->unreportedError = 0;
	    goto readError;
	}
	if (outStatePtr->unreportedError != 0) {
	    Tcl_SetErrno(outStatePtr->unreportedError);
	    outStatePtr->unreportedError = 0;
	    goto writeError;
	}

	/*
	 * Read up to bufSize bytes.
	 */

	if ((csPtr->toRead == -1) || (csPtr->toRead > csPtr->bufSize)) {
	    sizeb = csPtr->bufSize;
	} else {
	    sizeb = csPtr->toRead;
	}

	if (inBinary || sameEncoding) {
	    size = DoRead(inStatePtr->topChanPtr, csPtr->buffer, sizeb);
	} else {
	    size = DoReadChars(inStatePtr->topChanPtr, bufObj, sizeb, 0 /* No append */);
	}
	underflow = (size >= 0) && (size < sizeb);	/* input underflow */

	if (size < 0) {
	    readError:
	    TclNewObj(errObj);
	    Tcl_AppendStringsToObj(errObj, "error reading \"",
		    Tcl_GetChannelName(inChan), "\": ",
		    Tcl_PosixError(interp), (char *) NULL);
	    break;
	} else if (underflow) {
	    /*
	     * We had an underflow on the read side.  If we are at EOF,
	     * then the copying is done, otherwise set up a channel
	     * handler to detect when the channel becomes readable again.
	     */

	    if ((size == 0) && Tcl_Eof(inChan)) {
		break;
	    }
	    if (! Tcl_Eof(inChan) && !(mask & TCL_READABLE)) {
		if (mask & TCL_WRITABLE) {
		    Tcl_DeleteChannelHandler(outChan, CopyEventProc,
			    (ClientData) csPtr);
		}
		Tcl_CreateChannelHandler(inChan, TCL_READABLE,
			CopyEventProc, (ClientData) csPtr);
	    }
	    if (size == 0) {
		if (bufObj != (Tcl_Obj *) NULL) {
		    TclDecrRefCount(bufObj);
		    bufObj = (Tcl_Obj *) NULL;
		}
		return TCL_OK;
	    }
	}

	/*
	 * Now write the buffer out.
	 */

	if (inBinary || sameEncoding) {
	    buffer = csPtr->buffer;
	    sizeb = size;
	} else {
	    buffer = Tcl_GetStringFromObj(bufObj, &sizeb);
	}

	if (outBinary || sameEncoding) {
	    sizeb = DoWrite(outStatePtr->topChanPtr, buffer, sizeb);
	} else {
	    sizeb = DoWriteChars(outStatePtr->topChanPtr, buffer, sizeb);
	}

	if (inBinary || sameEncoding) {
	    /* Both read and write counted bytes */
	    size = sizeb;
	} /* else : Read counted characters, write counted bytes, i.e. size != sizeb */

	if (sizeb < 0) {
	    writeError:
	    TclNewObj(errObj);
	    Tcl_AppendStringsToObj(errObj, "error writing \"",
		    Tcl_GetChannelName(outChan), "\": ",
		    Tcl_PosixError(interp), (char *) NULL);
	    break;
	}

	/*
	 * Update the current byte count.  Do it now so the count is
	 * valid before a return or break takes us out of the loop.
	 * The invariant at the top of the loop should be that 
	 * csPtr->toRead holds the number of bytes left to copy.
	 */

	if (csPtr->toRead != -1) {
	    csPtr->toRead -= size;
	}
	csPtr->total += size;

	/*
	 * Break loop if EOF && (size>0)
	 */

	if (Tcl_Eof(inChan)) {
	    break;
	}

	/*
	 * Check to see if the write is happening in the background.  If so,
	 * stop copying and wait for the channel to become writable again.
	 * After input underflow we already installed a readable handler
	 * therefore we don't need a writable handler.
	 */

	if (!underflow && (outStatePtr->flags & BG_FLUSH_SCHEDULED)) {
	    if (!(mask & TCL_WRITABLE)) {
		if (mask & TCL_READABLE) {
		    Tcl_DeleteChannelHandler(inChan, CopyEventProc,
			    (ClientData) csPtr);
		}
		Tcl_CreateChannelHandler(outChan, TCL_WRITABLE,
			CopyEventProc, (ClientData) csPtr);
	    }
	    if (bufObj != (Tcl_Obj *) NULL) {
		TclDecrRefCount(bufObj);
		bufObj = (Tcl_Obj *) NULL;
	    }
	    return TCL_OK;
	}

	/*
	 * For background copies, we only do one buffer per invocation so
	 * we don't starve the rest of the system.
	 */

	if (cmdPtr) {
	    /*
	     * The first time we enter this code, there won't be a
	     * channel handler established yet, so do it here.
	     */

	    if (mask == 0) {
		Tcl_CreateChannelHandler(outChan, TCL_WRITABLE,
			CopyEventProc, (ClientData) csPtr);
	    }
	    if (bufObj != (Tcl_Obj *) NULL) {
		TclDecrRefCount(bufObj);
		bufObj = (Tcl_Obj *) NULL;
	    }
	    return TCL_OK;
	}
    } /* while */

    if (bufObj != (Tcl_Obj *) NULL) {
	TclDecrRefCount(bufObj);
	bufObj = (Tcl_Obj *) NULL;
    }

    /*
     * Make the callback or return the number of bytes transferred.
     * The local total is used because StopCopy frees csPtr.
     */

    total = csPtr->total;
    if (cmdPtr) {
	/*
	 * Get a private copy of the command so we can mutate it
	 * by adding arguments.  Note that StopCopy frees our saved
	 * reference to the original command obj.
	 */

	cmdPtr = Tcl_DuplicateObj(cmdPtr);
	Tcl_IncrRefCount(cmdPtr);
	StopCopy(csPtr);
	Tcl_Preserve((ClientData) interp);

	Tcl_ListObjAppendElement(interp, cmdPtr, Tcl_NewIntObj(total));
	if (errObj) {
	    Tcl_ListObjAppendElement(interp, cmdPtr, errObj);
	}
	if (Tcl_EvalObjEx(interp, cmdPtr, TCL_EVAL_GLOBAL) != TCL_OK) {
	    Tcl_BackgroundError(interp);
	    result = TCL_ERROR;
	}
	TclDecrRefCount(cmdPtr);
	Tcl_Release((ClientData) interp);
    } else {
	StopCopy(csPtr);
	if (errObj) {
	    Tcl_SetObjResult(interp, errObj);
	    result = TCL_ERROR;
	} else {
	    Tcl_ResetResult(interp);
	    Tcl_SetObjResult(interp, Tcl_NewIntObj(total));
	}
    }
    return result;
}

/*
 *----------------------------------------------------------------------
 *
 * DoRead --
 *
 *	Reads a given number of bytes from a channel.
 *
 *	No encoding conversions are applied to the bytes being read.
 *
 * Results:
 *	The number of characters read, or -1 on error. Use Tcl_GetErrno()
 *	to retrieve the error code for the error that occurred.
 *
 * Side effects:
 *	May cause input to be buffered.
 *
 *----------------------------------------------------------------------
 */

static int
DoRead(chanPtr, bufPtr, toRead)
    Channel *chanPtr;		/* The channel from which to read. */
    char *bufPtr;		/* Where to store input read. */
    int toRead;			/* Maximum number of bytes to read. */
{
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    int copied;			/* How many characters were copied into
				 * the result string? */
    int copiedNow;		/* How many characters were copied from
				 * the current input buffer? */
    int result;			/* Of calling GetInput. */

    /*
     * If we have not encountered a sticky EOF, clear the EOF bit. Either
     * way clear the BLOCKED bit. We want to discover these anew during
     * each operation.
     */

    if (!(statePtr->flags & CHANNEL_STICKY_EOF)) {
	statePtr->flags &= ~CHANNEL_EOF;
    }
    statePtr->flags &= ~(CHANNEL_BLOCKED | CHANNEL_NEED_MORE_DATA);

    for (copied = 0; copied < toRead; copied += copiedNow) {
	copiedNow = CopyAndTranslateBuffer(statePtr, bufPtr + copied,
		toRead - copied);
	if (copiedNow == 0) {
	    if (statePtr->flags & CHANNEL_EOF) {
		goto done;
	    }
	    if (statePtr->flags & CHANNEL_BLOCKED) {
		if (statePtr->flags & CHANNEL_NONBLOCKING) {
		    goto done;
		}
		statePtr->flags &= (~(CHANNEL_BLOCKED));
	    }
	    result = GetInput(chanPtr);
	    if (result != 0) {
		if (result != EAGAIN) {
		    copied = -1;
		}
		goto done;
	    }
	}
    }

    statePtr->flags &= (~(CHANNEL_BLOCKED));

    done:
    /*
     * Update the notifier state so we don't block while there is still
     * data in the buffers.
     */

    UpdateInterest(chanPtr);
    return copied;
}

/*
 *----------------------------------------------------------------------
 *
 * CopyAndTranslateBuffer --
 *
 *	Copy at most one buffer of input to the result space, doing
 *	eol translations according to mode in effect currently.
 *
 * Results:
 *	Number of bytes stored in the result buffer (as opposed to the
 *	number of bytes read from the channel).  May return
 *	zero if no input is available to be translated.
 *
 * Side effects:
 *	Consumes buffered input. May deallocate one buffer.
 *
 *----------------------------------------------------------------------
 */

static int
CopyAndTranslateBuffer(statePtr, result, space)
    ChannelState *statePtr;	/* Channel state from which to read input. */
    char *result;		/* Where to store the copied input. */
    int space;			/* How many bytes are available in result
				 * to store the copied input? */
{
    ChannelBuffer *bufPtr;	/* The buffer from which to copy bytes. */
    int bytesInBuffer;		/* How many bytes are available to be
				 * copied in the current input buffer? */
    int copied;			/* How many characters were already copied
				 * into the destination space? */
    int i;			/* Iterates over the copied input looking
				 * for the input eofChar. */

    /*
     * If there is no input at all, return zero. The invariant is that either
     * there is no buffer in the queue, or if the first buffer is empty, it
     * is also the last buffer (and thus there is no input in the queue).
     * Note also that if the buffer is empty, we leave it in the queue.
     */

    if (statePtr->inQueueHead == (ChannelBuffer *) NULL) {
	return 0;
    }
    bufPtr = statePtr->inQueueHead;
    bytesInBuffer = bufPtr->nextAdded - bufPtr->nextRemoved;

    copied = 0;
    switch (statePtr->inputTranslation) {
	case TCL_TRANSLATE_LF: {
	    if (bytesInBuffer == 0) {
		return 0;
	    }

	    /*
	     * Copy the current chunk into the result buffer.
	     */

	    if (bytesInBuffer < space) {
		space = bytesInBuffer;
	    }
	    memcpy((VOID *) result,
		    (VOID *) (bufPtr->buf + bufPtr->nextRemoved),
		    (size_t) space);
	    bufPtr->nextRemoved += space;
	    copied = space;
	    break;
	}
	case TCL_TRANSLATE_CR: {
	    char *end;

	    if (bytesInBuffer == 0) {
		return 0;
	    }

	    /*
	     * Copy the current chunk into the result buffer, then
	     * replace all \r with \n.
	     */

	    if (bytesInBuffer < space) {
		space = bytesInBuffer;
	    }
	    memcpy((VOID *) result,
		    (VOID *) (bufPtr->buf + bufPtr->nextRemoved),
		    (size_t) space);
	    bufPtr->nextRemoved += space;
	    copied = space;

	    for (end = result + copied; result < end; result++) {
		if (*result == '\r') {
		    *result = '\n';
		}
	    }
	    break;
	}
	case TCL_TRANSLATE_CRLF: {
	    char *src, *end, *dst;
	    int curByte;

	    /*
	     * If there is a held-back "\r" at EOF, produce it now.
	     */

	    if (bytesInBuffer == 0) {
		if ((statePtr->flags & (INPUT_SAW_CR | CHANNEL_EOF)) ==
			(INPUT_SAW_CR | CHANNEL_EOF)) {
		    result[0] = '\r';
		    statePtr->flags &= ~INPUT_SAW_CR;
		    return 1;
		}
		return 0;
	    }

	    /*
	     * Copy the current chunk and replace "\r\n" with "\n"
	     * (but not standalone "\r"!).
	     */

	    if (bytesInBuffer < space) {
		space = bytesInBuffer;
	    }
	    memcpy((VOID *) result,
		    (VOID *) (bufPtr->buf + bufPtr->nextRemoved),
		    (size_t) space);
	    bufPtr->nextRemoved += space;
	    copied = space;

	    end = result + copied;
	    dst = result;
	    for (src = result; src < end; src++) {
		curByte = *src;
		if (curByte == '\n') {
		    statePtr->flags &= ~INPUT_SAW_CR;
		} else if (statePtr->flags & INPUT_SAW_CR) {
		    statePtr->flags &= ~INPUT_SAW_CR;
		    *dst = '\r';
		    dst++;
		}
		if (curByte == '\r') {
		    statePtr->flags |= INPUT_SAW_CR;
		} else {
		    *dst = (char) curByte;
		    dst++;
		}
	    }
	    copied = dst - result;
	    break;
	}
	case TCL_TRANSLATE_AUTO: {
	    char *src, *end, *dst;
	    int curByte;

	    if (bytesInBuffer == 0) {
		return 0;
	    }

	    /*
	     * Loop over the current buffer, converting "\r" and "\r\n"
	     * to "\n".
	     */

	    if (bytesInBuffer < space) {
		space = bytesInBuffer;
	    }
	    memcpy((VOID *) result,
		    (VOID *) (bufPtr->buf + bufPtr->nextRemoved),
		    (size_t) space);
	    bufPtr->nextRemoved += space;
	    copied = space;

	    end = result + copied;
	    dst = result;
	    for (src = result; src < end; src++) {
		curByte = *src;
		if (curByte == '\r') {
		    statePtr->flags |= INPUT_SAW_CR;
		    *dst = '\n';
		    dst++;
		} else {
		    if ((curByte != '\n') || 
			    !(statePtr->flags & INPUT_SAW_CR)) {
			*dst = (char) curByte;
			dst++;
		    }
		    statePtr->flags &= ~INPUT_SAW_CR;
		}
	    }
	    copied = dst - result;
	    break;
	}
	default: {
	    Tcl_Panic("unknown eol translation mode");
	}
    }

    /*
     * If an in-stream EOF character is set for this channel, check that
     * the input we copied so far does not contain the EOF char.  If it does,
     * copy only up to and excluding that character.
     */

    if (statePtr->inEofChar != 0) {
	for (i = 0; i < copied; i++) {
	    if (result[i] == (char) statePtr->inEofChar) {
		/*
		 * Set sticky EOF so that no further input is presented
		 * to the caller.
		 */

		statePtr->flags |= (CHANNEL_EOF | CHANNEL_STICKY_EOF);
		statePtr->inputEncodingFlags |= TCL_ENCODING_END;
		copied = i;
		break;
	    }
	}
    }

    /*
     * If the current buffer is empty recycle it.
     */

    if (bufPtr->nextRemoved == bufPtr->nextAdded) {
	statePtr->inQueueHead = bufPtr->nextPtr;
	if (statePtr->inQueueHead == (ChannelBuffer *) NULL) {
	    statePtr->inQueueTail = (ChannelBuffer *) NULL;
	}
	RecycleBuffer(statePtr, bufPtr, 0);
    }

    /*
     * Return the number of characters copied into the result buffer.
     * This may be different from the number of bytes consumed, because
     * of EOL translations.
     */

    return copied;
}

/*
 *----------------------------------------------------------------------
 *
 * CopyBuffer --
 *
 *	Copy at most one buffer of input to the result space.
 *
 * Results:
 *	Number of bytes stored in the result buffer.  May return
 *	zero if no input is available.
 *
 * Side effects:
 *	Consumes buffered input. May deallocate one buffer.
 *
 *----------------------------------------------------------------------
 */

static int
CopyBuffer(chanPtr, result, space)
    Channel *chanPtr;		/* Channel from which to read input. */
    char *result;		/* Where to store the copied input. */
    int space;			/* How many bytes are available in result
				 * to store the copied input? */
{
    ChannelBuffer *bufPtr;	/* The buffer from which to copy bytes. */
    int bytesInBuffer;		/* How many bytes are available to be
				 * copied in the current input buffer? */
    int copied;			/* How many characters were already copied
				 * into the destination space? */

    /*
     * If there is no input at all, return zero. The invariant is that
     * either there is no buffer in the queue, or if the first buffer
     * is empty, it is also the last buffer (and thus there is no
     * input in the queue).  Note also that if the buffer is empty, we
     * don't leave it in the queue, but recycle it.
     */

    if (chanPtr->inQueueHead == (ChannelBuffer *) NULL) {
	return 0;
    }
    bufPtr = chanPtr->inQueueHead;
    bytesInBuffer = bufPtr->nextAdded - bufPtr->nextRemoved;

    copied = 0;

    if (bytesInBuffer == 0) {
	RecycleBuffer(chanPtr->state, bufPtr, 0);
	chanPtr->inQueueHead = (ChannelBuffer *) NULL;
	chanPtr->inQueueTail = (ChannelBuffer *) NULL;
	return 0;
    }

    /*
     * Copy the current chunk into the result buffer.
     */

    if (bytesInBuffer < space) {
	space = bytesInBuffer;
    }

    memcpy((VOID *) result,
	   (VOID *) (bufPtr->buf + bufPtr->nextRemoved),
	   (size_t) space);
    bufPtr->nextRemoved += space;
    copied = space;

    /*
     * We don't care about in-stream EOF characters here as the data
     * read here may still flow through one or more transformations,
     * i.e. is not in its final state yet.
     */

    /*
     * If the current buffer is empty recycle it.
     */

    if (bufPtr->nextRemoved == bufPtr->nextAdded) {
	chanPtr->inQueueHead = bufPtr->nextPtr;
	if (chanPtr->inQueueHead == (ChannelBuffer *) NULL) {
	    chanPtr->inQueueTail = (ChannelBuffer *) NULL;
	}
	RecycleBuffer(chanPtr->state, bufPtr, 0);
    }

    /*
     * Return the number of characters copied into the result buffer.
     */

    return copied;
}

/*
 *----------------------------------------------------------------------
 *
 * DoWrite --
 *
 *	Puts a sequence of characters into an output buffer, may queue the
 *	buffer for output if it gets full, and also remembers whether the
 *	current buffer is ready e.g. if it contains a newline and we are in
 *	line buffering mode.
 *
 * Results:
 *	The number of bytes written or -1 in case of error. If -1,
 *	Tcl_GetErrno will return the error code.
 *
 * Side effects:
 *	May buffer up output and may cause output to be produced on the
 *	channel.
 *
 *----------------------------------------------------------------------
 */

static int
DoWrite(chanPtr, src, srcLen)
    Channel *chanPtr;			/* The channel to buffer output for. */
    CONST char *src;			/* Data to write. */
    int srcLen;				/* Number of bytes to write. */
{
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    ChannelBuffer *outBufPtr;		/* Current output buffer. */
    int foundNewline;			/* Did we find a newline in output? */
    char *dPtr;
    CONST char *sPtr;			/* Search variables for newline. */
    int crsent;				/* In CRLF eol translation mode,
					 * remember the fact that a CR was
					 * output to the channel without
					 * its following NL. */
    int i;				/* Loop index for newline search. */
    int destCopied;			/* How many bytes were used in this
					 * destination buffer to hold the
					 * output? */
    int totalDestCopied;		/* How many bytes total were
					 * copied to the channel buffer? */
    int srcCopied;			/* How many bytes were copied from
					 * the source string? */
    char *destPtr;			/* Where in line to copy to? */

    /*
     * If we are in network (or windows) translation mode, record the fact
     * that we have not yet sent a CR to the channel.
     */

    crsent = 0;

    /*
     * Loop filling buffers and flushing them until all output has been
     * consumed.
     */

    srcCopied = 0;
    totalDestCopied = 0;

    while (srcLen > 0) {

	/*
	 * Make sure there is a current output buffer to accept output.
	 */

	if (statePtr->curOutPtr == (ChannelBuffer *) NULL) {
	    statePtr->curOutPtr = AllocChannelBuffer(statePtr->bufSize);
	}

	outBufPtr = statePtr->curOutPtr;

	destCopied = outBufPtr->bufLength - outBufPtr->nextAdded;
	if (destCopied > srcLen) {
	    destCopied = srcLen;
	}

	destPtr = outBufPtr->buf + outBufPtr->nextAdded;
	switch (statePtr->outputTranslation) {
	    case TCL_TRANSLATE_LF:
		srcCopied = destCopied;
		memcpy((VOID *) destPtr, (VOID *) src, (size_t) destCopied);
		break;
	    case TCL_TRANSLATE_CR:
		srcCopied = destCopied;
		memcpy((VOID *) destPtr, (VOID *) src, (size_t) destCopied);
		for (dPtr = destPtr; dPtr < destPtr + destCopied; dPtr++) {
		    if (*dPtr == '\n') {
			*dPtr = '\r';
		    }
		}
		break;
	    case TCL_TRANSLATE_CRLF:
		for (srcCopied = 0, dPtr = destPtr, sPtr = src;
		     dPtr < destPtr + destCopied;
		     dPtr++, sPtr++, srcCopied++) {
		    if (*sPtr == '\n') {
			if (crsent) {
			    *dPtr = '\n';
			    crsent = 0;
			} else {
			    *dPtr = '\r';
			    crsent = 1;
			    sPtr--, srcCopied--;
			}
		    } else {
			*dPtr = *sPtr;
		    }
		}
		break;
	    case TCL_TRANSLATE_AUTO:
		Tcl_Panic("Tcl_Write: AUTO output translation mode not supported");
	    default:
		Tcl_Panic("Tcl_Write: unknown output translation mode");
	}

	/*
	 * The current buffer is ready for output if it is full, or if it
	 * contains a newline and this channel is line-buffered, or if it
	 * contains any output and this channel is unbuffered.
	 */

	outBufPtr->nextAdded += destCopied;
	if (!(statePtr->flags & BUFFER_READY)) {
	    if (outBufPtr->nextAdded == outBufPtr->bufLength) {
		statePtr->flags |= BUFFER_READY;
	    } else if (statePtr->flags & CHANNEL_LINEBUFFERED) {
		for (sPtr = src, i = 0, foundNewline = 0;
			(i < srcCopied) && (!foundNewline);
			i++, sPtr++) {
		    if (*sPtr == '\n') {
			foundNewline = 1;
			break;
		    }
		}
		if (foundNewline) {
		    statePtr->flags |= BUFFER_READY;
		}
	    } else if (statePtr->flags & CHANNEL_UNBUFFERED) {
		statePtr->flags |= BUFFER_READY;
	    }
	}

	totalDestCopied += srcCopied;
	src += srcCopied;
	srcLen -= srcCopied;

	if (statePtr->flags & BUFFER_READY) {
	    if (FlushChannel(NULL, chanPtr, 0) != 0) {
		return -1;
	    }
	}
    } /* Closes "while" */

    return totalDestCopied;
}

/*
 *----------------------------------------------------------------------
 *
 * CopyEventProc --
 *
 *	This routine is invoked as a channel event handler for
 *	the background copy operation.  It is just a trivial wrapper
 *	around the CopyData routine.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

static void
CopyEventProc(clientData, mask)
    ClientData clientData;
    int mask;
{
    (void) CopyData((CopyState *)clientData, mask);
}

/*
 *----------------------------------------------------------------------
 *
 * StopCopy --
 *
 *	This routine halts a copy that is in progress.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Removes any pending channel handlers and restores the blocking
 *	and buffering modes of the channels.  The CopyState is freed.
 *
 *----------------------------------------------------------------------
 */

static void
StopCopy(csPtr)
    CopyState *csPtr;		/* State for bg copy to stop . */
{
    ChannelState *inStatePtr, *outStatePtr;
    int nonBlocking;

    if (!csPtr) {
	return;
    }

    inStatePtr = csPtr->readPtr->state;
    outStatePtr = csPtr->writePtr->state;

    /*
     * Restore the old blocking mode and output buffering mode.
     */

    nonBlocking = (csPtr->readFlags & CHANNEL_NONBLOCKING);
    if (nonBlocking != (inStatePtr->flags & CHANNEL_NONBLOCKING)) {
	SetBlockMode(NULL, csPtr->readPtr,
		nonBlocking ? TCL_MODE_NONBLOCKING : TCL_MODE_BLOCKING);
    }
    if (csPtr->readPtr != csPtr->writePtr) {
	nonBlocking = (csPtr->writeFlags & CHANNEL_NONBLOCKING);
	if (nonBlocking != (outStatePtr->flags & CHANNEL_NONBLOCKING)) {
	    SetBlockMode(NULL, csPtr->writePtr,
		    nonBlocking ? TCL_MODE_NONBLOCKING : TCL_MODE_BLOCKING);
	}
    }
    outStatePtr->flags &= ~(CHANNEL_LINEBUFFERED | CHANNEL_UNBUFFERED);
    outStatePtr->flags |=
	csPtr->writeFlags & (CHANNEL_LINEBUFFERED | CHANNEL_UNBUFFERED);

    if (csPtr->cmdPtr) {
	Tcl_DeleteChannelHandler((Tcl_Channel)csPtr->readPtr, CopyEventProc,
		(ClientData)csPtr);
	if (csPtr->readPtr != csPtr->writePtr) {
	    Tcl_DeleteChannelHandler((Tcl_Channel)csPtr->writePtr,
		    CopyEventProc, (ClientData)csPtr);
	}
	TclDecrRefCount(csPtr->cmdPtr);
    }
    inStatePtr->csPtr = NULL;
    outStatePtr->csPtr = NULL;
    ckfree((char *) csPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * StackSetBlockMode --
 *
 *	This function sets the blocking mode for a channel, iterating
 *	through each channel in a stack and updates the state flags.
 *
 * Results:
 *	0 if OK, result code from failed blockModeProc otherwise.
 *
 * Side effects:
 *	Modifies the blocking mode of the channel and possibly generates
 *	an error.
 *
 *----------------------------------------------------------------------
 */

static int
StackSetBlockMode(chanPtr, mode)
    Channel *chanPtr;		/* Channel to modify. */
    int mode;			/* One of TCL_MODE_BLOCKING or
				 * TCL_MODE_NONBLOCKING. */
{
    int result = 0;
    Tcl_DriverBlockModeProc *blockModeProc;

    /*
     * Start at the top of the channel stack
     */

    chanPtr = chanPtr->state->topChanPtr;
    while (chanPtr != (Channel *) NULL) {
	blockModeProc = Tcl_ChannelBlockModeProc(chanPtr->typePtr);
	if (blockModeProc != NULL) {
	    result = (*blockModeProc) (chanPtr->instanceData, mode);
	    if (result != 0) {
		Tcl_SetErrno(result);
		return result;
	    }
	}
	chanPtr = chanPtr->downChanPtr;
    }
    return 0;
}

/*
 *----------------------------------------------------------------------
 *
 * SetBlockMode --
 *
 *	This function sets the blocking mode for a channel and updates
 *	the state flags.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	Modifies the blocking mode of the channel and possibly generates
 *	an error.
 *
 *----------------------------------------------------------------------
 */

static int
SetBlockMode(interp, chanPtr, mode)
    Tcl_Interp *interp;		/* Interp for error reporting. */
    Channel *chanPtr;		/* Channel to modify. */
    int mode;			/* One of TCL_MODE_BLOCKING or
				 * TCL_MODE_NONBLOCKING. */
{
    ChannelState *statePtr = chanPtr->state;	/* state info for channel */
    int result = 0;

    result = StackSetBlockMode(chanPtr, mode);
    if (result != 0) {
	if (interp != (Tcl_Interp *) NULL) {
	    Tcl_AppendResult(interp, "error setting blocking mode: ",
		    Tcl_PosixError(interp), (char *) NULL);
	}
	return TCL_ERROR;
    }
    if (mode == TCL_MODE_BLOCKING) {
	statePtr->flags &= (~(CHANNEL_NONBLOCKING | BG_FLUSH_SCHEDULED));
    } else {
	statePtr->flags |= CHANNEL_NONBLOCKING;
    }
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetChannelNames --
 *
 *	Return the names of all open channels in the interp.
 *
 * Results:
 *	TCL_OK or TCL_ERROR.
 *
 * Side effects:
 *	Interp result modified with list of channel names.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_GetChannelNames(interp)
    Tcl_Interp *interp;		/* Interp for error reporting. */
{
    return Tcl_GetChannelNamesEx(interp, (char *) NULL);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetChannelNamesEx --
 *
 *	Return the names of open channels in the interp filtered
 *	filtered through a pattern.  If pattern is NULL, it returns
 *	all the open channels.
 *
 * Results:
 *	TCL_OK or TCL_ERROR.
 *
 * Side effects:
 *	Interp result modified with list of channel names.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_GetChannelNamesEx(interp, pattern)
    Tcl_Interp *interp;		/* Interp for error reporting. */
    CONST char *pattern;	/* pattern to filter on. */
{
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
    ChannelState *statePtr;
    CONST char *name;		/* name for channel */
    Tcl_Obj *resultPtr;		/* pointer to result object */
    Tcl_HashTable *hTblPtr;	/* Hash table of channels. */
    Tcl_HashEntry *hPtr;	/* Search variable. */
    Tcl_HashSearch hSearch;	/* Search variable. */

    if (interp == (Tcl_Interp *) NULL) {
	return TCL_OK;
    }

    /*
     * Get the channel table that stores the channels registered
     * for this interpreter.
     */

    hTblPtr = GetChannelTable(interp);
    TclNewObj(resultPtr);

    for (hPtr = Tcl_FirstHashEntry(hTblPtr, &hSearch);
	    hPtr != (Tcl_HashEntry *) NULL;
	    hPtr = Tcl_NextHashEntry(&hSearch)) {

	statePtr = ((Channel *) Tcl_GetHashValue(hPtr))->state;
	if (statePtr->topChanPtr == (Channel *) tsdPtr->stdinChannel) {
	    name = "stdin";
	} else if (statePtr->topChanPtr == (Channel *) tsdPtr->stdoutChannel) {
	    name = "stdout";
	} else if (statePtr->topChanPtr == (Channel *) tsdPtr->stderrChannel) {
	    name = "stderr";
	} else {
	    /*
	     * This is also stored in Tcl_GetHashKey(hTblPtr, hPtr),
	     * but it's simpler to just grab the name from the statePtr.
	     */

	    name = statePtr->channelName;
	}

	if (((pattern == NULL) || Tcl_StringMatch(name, pattern)) &&
		(Tcl_ListObjAppendElement(interp, resultPtr,
			Tcl_NewStringObj(name, -1)) != TCL_OK)) {
	    TclDecrRefCount(resultPtr);
	    return TCL_ERROR;
	}
    }
    Tcl_SetObjResult(interp, resultPtr);
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_IsChannelRegistered --
 *
 *	Checks whether the channel is associated with the interp.
 *	See also Tcl_RegisterChannel and Tcl_UnregisterChannel.
 *
 * Results:
 *	0 if the channel is not registered in the interpreter, 1 else.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_IsChannelRegistered(interp, chan)
     Tcl_Interp *interp;	/* The interp to query of the channel */
     Tcl_Channel chan;		/* The channel to check */
{
    Tcl_HashTable	*hTblPtr;	/* Hash table of channels. */
    Tcl_HashEntry	*hPtr;		/* Search variable. */
    Channel		*chanPtr;	/* The real IO channel. */
    ChannelState	*statePtr;	/* State of the real channel. */

    /*
     * Always check bottom-most channel in the stack.  This is the one
     * that gets registered.
     */

    chanPtr = ((Channel *) chan)->state->bottomChanPtr;
    statePtr = chanPtr->state;

    hTblPtr = (Tcl_HashTable *) Tcl_GetAssocData(interp, "tclIO", NULL);
    if (hTblPtr == (Tcl_HashTable *) NULL) {
	return 0;
    }
    hPtr = Tcl_FindHashEntry(hTblPtr, statePtr->channelName);
    if (hPtr == (Tcl_HashEntry *) NULL) {
	return 0;
    }
    if ((Channel *) Tcl_GetHashValue(hPtr) != chanPtr) {
	return 0;
    }

    return 1;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_IsChannelShared --
 *
 *	Checks whether the channel is shared by multiple interpreters.
 *
 * Results:
 *	A boolean value (0 = Not shared, 1 = Shared).
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_IsChannelShared(chan)
    Tcl_Channel chan;		/* The channel to query */
{
    ChannelState *statePtr = ((Channel *) chan)->state;
					/* State of real channel structure. */

    return ((statePtr->refCount > 1) ? 1 : 0);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_IsChannelExisting --
 *
 *	Checks whether a channel of the given name exists in the
 *	(thread)-global list of all channels.
 *	See Tcl_GetChannelNamesEx for function exposed at the Tcl level.
 *
 * Results:
 *	A boolean value (0 = Does not exist, 1 = Does exist).
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_IsChannelExisting(chanName)
    CONST char *chanName;	/* The name of the channel to look for. */
{
    ChannelState *statePtr;
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
    CONST char *name;
    int chanNameLen;

    chanNameLen = strlen(chanName);
    for (statePtr = tsdPtr->firstCSPtr;
	    statePtr != NULL;
	    statePtr = statePtr->nextCSPtr) {
	if (statePtr->topChanPtr == (Channel *) tsdPtr->stdinChannel) {
	    name = "stdin";
	} else if (statePtr->topChanPtr == (Channel *) tsdPtr->stdoutChannel) {
	    name = "stdout";
	} else if (statePtr->topChanPtr == (Channel *) tsdPtr->stderrChannel) {
	    name = "stderr";
	} else {
	    name = statePtr->channelName;
	}

	if ((*chanName == *name) &&
		(memcmp(name, chanName, (size_t) chanNameLen) == 0)) {
	    return 1;
	}
    }

    return 0;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ChannelName --
 *
 *	Return the name of the channel type.
 *
 * Results:
 *	A pointer the name of the channel type.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

CONST char *
Tcl_ChannelName(chanTypePtr)
    Tcl_ChannelType *chanTypePtr;	/* Pointer to channel type. */
{
    return chanTypePtr->typeName;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ChannelVersion --
 *
 *	Return the of version of the channel type.
 *
 * Results:
 *	One of the TCL_CHANNEL_VERSION_* constants from tcl.h
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

Tcl_ChannelTypeVersion
Tcl_ChannelVersion(chanTypePtr)
    Tcl_ChannelType *chanTypePtr;	/* Pointer to channel type. */
{
    if (chanTypePtr->version == TCL_CHANNEL_VERSION_2) {
	return TCL_CHANNEL_VERSION_2;
    } else if (chanTypePtr->version == TCL_CHANNEL_VERSION_3) {
	return TCL_CHANNEL_VERSION_3;
    } else {
	/*
	 * In <v2 channel versions, the version field is occupied
	 * by the Tcl_DriverBlockModeProc
	 */

	return TCL_CHANNEL_VERSION_1;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * HaveVersion --
 *
 *	Return whether a channel type is (at least) of a given version.
 *
 * Results:
 *	True if the minimum version is exceeded by the version actually
 *	present.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

static int
HaveVersion(chanTypePtr, minimumVersion)
    Tcl_ChannelType *chanTypePtr;
    Tcl_ChannelTypeVersion minimumVersion;
{
    Tcl_ChannelTypeVersion actualVersion = Tcl_ChannelVersion(chanTypePtr);

    return ((int)actualVersion) >= ((int)minimumVersion);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ChannelBlockModeProc --
 *
 *	Return the Tcl_DriverBlockModeProc of the channel type.
 *
 * Results:
 *	A pointer to the proc.
 *
 * Side effects:
 *	None.
 *
 *---------------------------------------------------------------------- */

Tcl_DriverBlockModeProc *
Tcl_ChannelBlockModeProc(chanTypePtr)
    Tcl_ChannelType *chanTypePtr;	/* Pointer to channel type. */
{
    if (HaveVersion(chanTypePtr, TCL_CHANNEL_VERSION_2)) {
	return chanTypePtr->blockModeProc;
    } else {
	/*
	 * The v1 structure had the blockModeProc in a different place.
	 */

	return (Tcl_DriverBlockModeProc *) (chanTypePtr->version);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ChannelCloseProc --
 *
 *	Return the Tcl_DriverCloseProc of the channel type.
 *
 * Results:
 *	A pointer to the proc.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

Tcl_DriverCloseProc *
Tcl_ChannelCloseProc(chanTypePtr)
    Tcl_ChannelType *chanTypePtr;	/* Pointer to channel type. */
{
    return chanTypePtr->closeProc;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ChannelClose2Proc --
 *
 *	Return the Tcl_DriverClose2Proc of the channel type.
 *
 * Results:
 *	A pointer to the proc.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

Tcl_DriverClose2Proc *
Tcl_ChannelClose2Proc(chanTypePtr)
    Tcl_ChannelType *chanTypePtr;	/* Pointer to channel type. */
{
    return chanTypePtr->close2Proc;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ChannelInputProc --
 *
 *	Return the Tcl_DriverInputProc of the channel type.
 *
 * Results:
 *	A pointer to the proc.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

Tcl_DriverInputProc *
Tcl_ChannelInputProc(chanTypePtr)
    Tcl_ChannelType *chanTypePtr;	/* Pointer to channel type. */
{
    return chanTypePtr->inputProc;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ChannelOutputProc --
 *
 *	Return the Tcl_DriverOutputProc of the channel type.
 *
 * Results:
 *	A pointer to the proc.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

Tcl_DriverOutputProc *
Tcl_ChannelOutputProc(chanTypePtr)
    Tcl_ChannelType *chanTypePtr;	/* Pointer to channel type. */
{
    return chanTypePtr->outputProc;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ChannelSeekProc --
 *
 *	Return the Tcl_DriverSeekProc of the channel type.
 *
 * Results:
 *	A pointer to the proc.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

Tcl_DriverSeekProc *
Tcl_ChannelSeekProc(chanTypePtr)
    Tcl_ChannelType *chanTypePtr;	/* Pointer to channel type. */
{
    return chanTypePtr->seekProc;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ChannelSetOptionProc --
 *
 *	Return the Tcl_DriverSetOptionProc of the channel type.
 *
 * Results:
 *	A pointer to the proc.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

Tcl_DriverSetOptionProc *
Tcl_ChannelSetOptionProc(chanTypePtr)
    Tcl_ChannelType *chanTypePtr;	/* Pointer to channel type. */
{
    return chanTypePtr->setOptionProc;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ChannelGetOptionProc --
 *
 *	Return the Tcl_DriverGetOptionProc of the channel type.
 *
 * Results:
 *	A pointer to the proc.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

Tcl_DriverGetOptionProc *
Tcl_ChannelGetOptionProc(chanTypePtr)
    Tcl_ChannelType *chanTypePtr;	/* Pointer to channel type. */
{
    return chanTypePtr->getOptionProc;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ChannelWatchProc --
 *
 *	Return the Tcl_DriverWatchProc of the channel type.
 *
 * Results:
 *	A pointer to the proc.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

Tcl_DriverWatchProc *
Tcl_ChannelWatchProc(chanTypePtr)
    Tcl_ChannelType *chanTypePtr;	/* Pointer to channel type. */
{
    return chanTypePtr->watchProc;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ChannelGetHandleProc --
 *
 *	Return the Tcl_DriverGetHandleProc of the channel type.
 *
 * Results:
 *	A pointer to the proc.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

Tcl_DriverGetHandleProc *
Tcl_ChannelGetHandleProc(chanTypePtr)
    Tcl_ChannelType *chanTypePtr;	/* Pointer to channel type. */
{
    return chanTypePtr->getHandleProc;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ChannelFlushProc --
 *
 *	Return the Tcl_DriverFlushProc of the channel type.
 *
 * Results:
 *	A pointer to the proc.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

Tcl_DriverFlushProc *
Tcl_ChannelFlushProc(chanTypePtr)
    Tcl_ChannelType *chanTypePtr;	/* Pointer to channel type. */
{
    if (HaveVersion(chanTypePtr, TCL_CHANNEL_VERSION_2)) {
	return chanTypePtr->flushProc;
    } else {
	return NULL;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ChannelHandlerProc --
 *
 *	Return the Tcl_DriverHandlerProc of the channel type.
 *
 * Results:
 *	A pointer to the proc.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

Tcl_DriverHandlerProc *
Tcl_ChannelHandlerProc(chanTypePtr)
    Tcl_ChannelType *chanTypePtr;	/* Pointer to channel type. */
{
    if (HaveVersion(chanTypePtr, TCL_CHANNEL_VERSION_2)) {
	return chanTypePtr->handlerProc;
    } else {
	return NULL;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ChannelWideSeekProc --
 *
 *	Return the Tcl_DriverWideSeekProc of the channel type.
 *
 * Results:
 *	A pointer to the proc.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

Tcl_DriverWideSeekProc *
Tcl_ChannelWideSeekProc(chanTypePtr)
    Tcl_ChannelType *chanTypePtr;	/* Pointer to channel type. */
{
    if (HaveVersion(chanTypePtr, TCL_CHANNEL_VERSION_3)) {
	return chanTypePtr->wideSeekProc;
    } else {
	return NULL;
    }
}

#if 0
/*
 * For future debugging work, a simple function to print the flags of
 * a channel in semi-readable form.
 */

static int
DumpFlags(str, flags)
     char *str;
     int flags;
{
    char buf[20];
    int i = 0;

    if (flags & TCL_READABLE)           buf[i++] = 'r'; else buf[i++]='_';
    if (flags & TCL_WRITABLE)           buf[i++] = 'w'; else buf[i++]='_';
    if (flags & CHANNEL_NONBLOCKING)    buf[i++] = 'n'; else buf[i++]='_';
    if (flags & CHANNEL_LINEBUFFERED)   buf[i++] = 'l'; else buf[i++]='_';
    if (flags & CHANNEL_UNBUFFERED)     buf[i++] = 'u'; else buf[i++]='_';
    if (flags & BUFFER_READY)           buf[i++] = 'R'; else buf[i++]='_';
    if (flags & BG_FLUSH_SCHEDULED)     buf[i++] = 'F'; else buf[i++]='_';
    if (flags & CHANNEL_CLOSED)         buf[i++] = 'c'; else buf[i++]='_';
    if (flags & CHANNEL_EOF)            buf[i++] = 'E'; else buf[i++]='_';
    if (flags & CHANNEL_STICKY_EOF)     buf[i++] = 'S'; else buf[i++]='_';
    if (flags & CHANNEL_BLOCKED)        buf[i++] = 'B'; else buf[i++]='_';
    if (flags & INPUT_SAW_CR)           buf[i++] = '/'; else buf[i++]='_';
    if (flags & INPUT_NEED_NL)          buf[i++] = '*'; else buf[i++]='_';
    if (flags & CHANNEL_DEAD)           buf[i++] = 'D'; else buf[i++]='_';
    if (flags & CHANNEL_RAW_MODE)       buf[i++] = 'R'; else buf[i++]='_';
#ifdef TCL_IO_TRACK_OS_FOR_DRIVER_WITH_BAD_BLOCKING
    if (flags & CHANNEL_TIMER_FEV)      buf[i++] = 'T'; else buf[i++]='_';
    if (flags & CHANNEL_HAS_MORE_DATA)  buf[i++] = 'H'; else buf[i++]='_';
#endif /* TCL_IO_TRACK_OS_FOR_DRIVER_WITH_BAD_BLOCKING */
    if (flags & CHANNEL_INCLOSE)        buf[i++] = 'x'; else buf[i++]='_';
    buf[i] ='\0';

    fprintf(stderr,"%s: %s\n", str, buf);
    return 0;
}
#endif
