Initial revision

1 files changed, 6013 insertions, 0 deletions

diff --git a/generic/tclIO.c b/generic/tclIO.c
new file mode 100644
index 0000000..73ff65f
--- /dev/null
+++ b/generic/tclIO.c
@@ -0,0 +1,6013 @@
+/* 
+ * 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) 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.
+ *
+ * SCCS: @(#) tclIO.c 1.272 97/10/22 10:27:53
+ */
+
+#include	"tclInt.h"
+#include	"tclPort.h"
+
+/*
+ * Make sure that both EAGAIN and EWOULDBLOCK are defined. This does not
+ * compile on systems where neither is defined. We want both defined so
+ * that we can test safely for both. In the code we still have to test for
+ * both because there may be systems on which both are defined and have
+ * different values.
+ */
+
+#if ((!defined(EWOULDBLOCK)) && (defined(EAGAIN)))
+#   define EWOULDBLOCK EAGAIN
+#endif
+#if ((!defined(EAGAIN)) && (defined(EWOULDBLOCK)))
+#   define EAGAIN EWOULDBLOCK
+#endif
+#if ((!defined(EAGAIN)) && (!defined(EWOULDBLOCK)))
+    error one of EWOULDBLOCK or EAGAIN must be defined
+#endif
+
+/*
+ * The following structure encapsulates the state for a background channel
+ * copy.  Note that the data buffer for the copy will be appended to this
+ * structure.
+ */
+
+typedef struct CopyState {
+    struct Channel *readPtr;	/* Pointer to input channel. */
+    struct Channel *writePtr;	/* Pointer to output channel. */
+    int readFlags;		/* Original read channel flags. */
+    int writeFlags;		/* Original write channel flags. */
+    int toRead;			/* Number of bytes to copy, or -1. */
+    int total;			/* Total bytes transferred (written). */
+    Tcl_Interp *interp;		/* Interp that started the copy. */
+    Tcl_Obj *cmdPtr;		/* Command to be invoked at completion. */
+    int bufSize;		/* Size of appended buffer. */
+    char buffer[1];		/* Copy buffer, this must be the last
+				 * field. */
+} CopyState;
+
+/*
+ * struct ChannelBuffer:
+ *
+ * Buffers data being sent to or from a channel.
+ */
+
+typedef struct ChannelBuffer {
+    int nextAdded;		/* The next position into which a character
+                                 * will be put in the buffer. */
+    int nextRemoved;		/* Position of next byte to be removed
+                                 * from the buffer. */
+    int bufSize;		/* How big is the buffer? */
+    struct ChannelBuffer *nextPtr;
+    				/* Next buffer in chain. */
+    char buf[4];		/* Placeholder for real buffer. The real
+                                 * buffer occuppies this space + bufSize-4
+                                 * bytes. This must be the last field in
+                                 * the structure. */
+} ChannelBuffer;
+
+#define CHANNELBUFFER_HEADER_SIZE	(sizeof(ChannelBuffer) - 4)
+
+/*
+ * The following defines the *default* buffer size for channels.
+ */
+
+#define CHANNELBUFFER_DEFAULT_SIZE	(1024 * 4)
+
+/*
+ * Structure to record a close callback. One such record exists for
+ * each close callback registered for a channel.
+ */
+
+typedef struct CloseCallback {
+    Tcl_CloseProc *proc;		/* The procedure to call. */
+    ClientData clientData;		/* Arbitrary one-word data to pass
+                                         * to the callback. */
+    struct CloseCallback *nextPtr;	/* For chaining close callbacks. */
+} CloseCallback;
+
+/*
+ * The following structure describes the information saved from a call to
+ * "fileevent". This is used later when the event being waited for to
+ * invoke the saved script in the interpreter designed in this record.
+ */
+
+typedef struct EventScriptRecord {
+    struct Channel *chanPtr;	/* The channel for which this script is
+                                 * registered. This is used only when an
+                                 * error occurs during evaluation of the
+                                 * script, to delete the handler. */
+    char *script;		/* Script to invoke. */
+    Tcl_Interp *interp;		/* In what interpreter to invoke script? */
+    int mask;			/* Events must overlap current mask for the
+                                 * stored script to be invoked. */
+    struct EventScriptRecord *nextPtr;
+    				/* Next in chain of records. */
+} EventScriptRecord;
+
+/*
+ * struct Channel:
+ *
+ * One of these structures is allocated for each open channel. It contains data
+ * specific to the channel but which belongs to the generic part of the Tcl
+ * channel mechanism, and it points at an instance specific (and type
+ * specific) * instance data, and at a channel type structure.
+ */
+
+typedef struct Channel {
+    char *channelName;		/* The name of the channel instance in Tcl
+                                 * commands. Storage is owned by the generic IO
+                                 * code,  is dynamically allocated. */
+    int	flags;			/* ORed combination of the flags defined
+                                 * below. */
+    Tcl_EolTranslation inputTranslation;
+				/* What translation to apply for end of line
+                                 * sequences on input? */    
+    Tcl_EolTranslation outputTranslation;
+    				/* What translation to use for generating
+                                 * end of line sequences in output? */
+    int inEofChar;		/* If nonzero, use this as a signal of EOF
+                                 * on input. */
+    int outEofChar;             /* If nonzero, append this to the channel
+                                 * when it is closed if it is open for
+                                 * writing. */
+    int unreportedError;	/* Non-zero if an error report was deferred
+                                 * because it happened in the background. The
+                                 * value is the POSIX error code. */
+    ClientData instanceData;	/* Instance specific data. */
+    Tcl_ChannelType *typePtr;	/* Pointer to channel type structure. */
+    int refCount;		/* How many interpreters hold references to
+                                 * this IO channel? */
+    CloseCallback *closeCbPtr;	/* Callbacks registered to be called when the
+                                 * channel is closed. */
+    ChannelBuffer *curOutPtr;	/* Current output buffer being filled. */
+    ChannelBuffer *outQueueHead;/* Points at first buffer in output queue. */
+    ChannelBuffer *outQueueTail;/* Points at last buffer in output queue. */
+
+    ChannelBuffer *saveInBufPtr;/* Buffer saved for input queue - eliminates
+                                 * need to allocate a new buffer for "gets"
+                                 * that crosses buffer boundaries. */
+    ChannelBuffer *inQueueHead;	/* Points at first buffer in input queue. */
+    ChannelBuffer *inQueueTail;	/* Points at last buffer in input queue. */
+
+    struct ChannelHandler *chPtr;/* List of channel handlers registered
+                                  * for this channel. */
+    int interestMask;		/* Mask of all events this channel has
+                                 * handlers for. */
+    struct Channel *nextChanPtr;/* Next in list of channels currently open. */
+    EventScriptRecord *scriptRecordPtr;
+    				/* Chain of all scripts registered for
+                                 * event handlers ("fileevent") on this
+                                 * channel. */
+    int bufSize;		/* What size buffers to allocate? */
+    Tcl_TimerToken timer;	/* Handle to wakeup timer for this channel. */
+    CopyState *csPtr;		/* State of background copy, or NULL. */
+} Channel;
+    
+/*
+ * Values for the flags field in Channel. Any ORed combination of the
+ * following flags can be stored in the field. These flags record various
+ * options and state bits about the channel. In addition to the flags below,
+ * the channel can also have TCL_READABLE (1<<1) and TCL_WRITABLE (1<<2) set.
+ */
+
+#define CHANNEL_NONBLOCKING	(1<<3)	/* Channel is currently in
+					 * nonblocking mode. */
+#define CHANNEL_LINEBUFFERED	(1<<4)	/* Output to the channel must be
+					 * flushed after every newline. */
+#define CHANNEL_UNBUFFERED	(1<<5)	/* Output to the channel must always
+					 * be flushed immediately. */
+#define BUFFER_READY		(1<<6)	/* Current output buffer (the
+					 * curOutPtr field in the
+                                         * channel structure) should be
+                                         * output as soon as possible even
+                                         * though it may not be full. */
+#define BG_FLUSH_SCHEDULED	(1<<7)	/* A background flush of the
+					 * queued output buffers has been
+                                         * scheduled. */
+#define CHANNEL_CLOSED		(1<<8)	/* Channel has been closed. No
+					 * further Tcl-level IO on the
+                                         * channel is allowed. */
+#define CHANNEL_EOF		(1<<9)	/* EOF occurred on this channel.
+					 * This bit is cleared before every
+                                         * input operation. */
+#define CHANNEL_STICKY_EOF	(1<<10)	/* EOF occurred on this channel because
+					 * we saw the input eofChar. This bit
+                                         * prevents clearing of the EOF bit
+                                         * before every input operation. */
+#define CHANNEL_BLOCKED	(1<<11)	/* EWOULDBLOCK or EAGAIN occurred
+					 * on this channel. This bit is
+                                         * cleared before every input or
+                                         * output operation. */
+#define INPUT_SAW_CR		(1<<12)	/* Channel is in CRLF eol input
+					 * translation mode and the last
+                                         * byte seen was a "\r". */
+#define CHANNEL_DEAD		(1<<13)	/* The channel has been closed by
+					 * the exit handler (on exit) but
+                                         * not deallocated. When any IO
+                                         * operation sees this flag on a
+                                         * channel, it does not call driver
+                                         * level functions to avoid referring
+                                         * to deallocated data. */
+#define CHANNEL_GETS_BLOCKED	(1<<14)	/* The last input operation was a gets
+					 * that failed to get a comlete line.
+					 * When set, file events will not be
+					 * delivered for buffered data unless
+					 * an EOL is present. */
+
+/*
+ * For each channel handler registered in a call to Tcl_CreateChannelHandler,
+ * there is one record of the following type. All of records for a specific
+ * channel are chained together in a singly linked list which is stored in
+ * the channel structure.
+ */
+
+typedef struct ChannelHandler {
+    Channel *chanPtr;		/* The channel structure for this channel. */
+    int mask;			/* Mask of desired events. */
+    Tcl_ChannelProc *proc;	/* Procedure to call in the type of
+                                 * Tcl_CreateChannelHandler. */
+    ClientData clientData;	/* Argument to pass to procedure. */
+    struct ChannelHandler *nextPtr;
+    				/* Next one in list of registered handlers. */
+} ChannelHandler;
+
+/*
+ * This structure keeps track of the current ChannelHandler being invoked in
+ * the current invocation of ChannelHandlerEventProc. There is a potential
+ * problem if a ChannelHandler is deleted while it is the current one, since
+ * ChannelHandlerEventProc needs to look at the nextPtr field. To handle this
+ * problem, structures of the type below indicate the next handler to be
+ * processed for any (recursively nested) dispatches in progress. The
+ * nextHandlerPtr field is updated if the handler being pointed to is deleted.
+ * The nextPtr field is used to chain together all recursive invocations, so
+ * that Tcl_DeleteChannelHandler can find all the recursively nested
+ * invocations of ChannelHandlerEventProc and compare the handler being
+ * deleted against the NEXT handler to be invoked in that invocation; when it
+ * finds such a situation, Tcl_DeleteChannelHandler updates the nextHandlerPtr
+ * field of the structure to the next handler.
+ */
+
+typedef struct NextChannelHandler {
+    ChannelHandler *nextHandlerPtr;	/* The next handler to be invoked in
+                                         * this invocation. */
+    struct NextChannelHandler *nestedHandlerPtr;
+					/* Next nested invocation of
+                                         * ChannelHandlerEventProc. */
+} NextChannelHandler;
+
+/*
+ * This variable holds the list of nested ChannelHandlerEventProc invocations.
+ */
+
+static NextChannelHandler *nestedHandlerPtr = (NextChannelHandler *) NULL;
+
+/*
+ * List of all channels currently open.
+ */
+
+static Channel *firstChanPtr = (Channel *) NULL;
+
+/*
+ * Has a channel exit handler been created yet?
+ */
+
+static int channelExitHandlerCreated = 0;
+
+/*
+ * The following structure describes the event that is added to the Tcl
+ * event queue by the channel handler check procedure.
+ */
+
+typedef struct ChannelHandlerEvent {
+    Tcl_Event header;		/* Standard header for all events. */
+    Channel *chanPtr;		/* The channel that is ready. */
+    int readyMask;		/* Events that have occurred. */
+} ChannelHandlerEvent;
+
+/*
+ * Static variables to hold channels for stdin, stdout and stderr.
+ */
+
+static Tcl_Channel stdinChannel = NULL;
+static int stdinInitialized = 0;
+static Tcl_Channel stdoutChannel = NULL;
+static int stdoutInitialized = 0;
+static Tcl_Channel stderrChannel = NULL;
+static int stderrInitialized = 0;
+
+/*
+ * Static functions in this file:
+ */
+
+static void		ChannelEventScriptInvoker _ANSI_ARGS_((
+			    ClientData clientData, int flags));
+static void		ChannelTimerProc _ANSI_ARGS_((
+			    ClientData clientData));
+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		CloseChannelsOnExit _ANSI_ARGS_((ClientData data));
+static int		CopyAndTranslateBuffer _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, char *script));
+static void		DeleteChannelTable _ANSI_ARGS_((
+			    ClientData clientData, Tcl_Interp *interp));
+static void		DeleteScriptRecord _ANSI_ARGS_((Tcl_Interp *interp,
+        		    Channel *chanPtr, int mask));
+static void		DiscardInputQueued _ANSI_ARGS_((
+			    Channel *chanPtr, int discardSavedBuffers));
+static void		DiscardOutputQueued _ANSI_ARGS_((
+    			    Channel *chanPtr));
+static int		DoRead _ANSI_ARGS_((Channel *chanPtr, char *srcPtr,
+			    int slen));
+static int		DoWrite _ANSI_ARGS_((Channel *chanPtr, char *srcPtr,
+			    int slen));
+static int		FlushChannel _ANSI_ARGS_((Tcl_Interp *interp,
+                            Channel *chanPtr, int calledFromAsyncFlush));
+static Tcl_HashTable	*GetChannelTable _ANSI_ARGS_((Tcl_Interp *interp));
+static int		GetEOL _ANSI_ARGS_((Channel *chanPtr));
+static int		GetInput _ANSI_ARGS_((Channel *chanPtr));
+static void		RecycleBuffer _ANSI_ARGS_((Channel *chanPtr,
+		            ChannelBuffer *bufPtr, int mustDiscard));
+static int		ScanBufferForEOL _ANSI_ARGS_((Channel *chanPtr,
+                            ChannelBuffer *bufPtr,
+                            Tcl_EolTranslation translation, int eofChar,
+		            int *bytesToEOLPtr, int *crSeenPtr));
+static int		ScanInputForEOL _ANSI_ARGS_((Channel *chanPtr,
+		            int *bytesQueuedPtr));
+static int		SetBlockMode _ANSI_ARGS_((Tcl_Interp *interp,
+		            Channel *chanPtr, int mode));
+static void		StopCopy _ANSI_ARGS_((CopyState *csPtr));
+static void		UpdateInterest _ANSI_ARGS_((Channel *chanPtr));
+static int		CheckForDeadChannel _ANSI_ARGS_((Tcl_Interp *interp,
+							Channel *chan));
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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. */
+{
+    int result = 0;
+    if (chanPtr->typePtr->blockModeProc != NULL) {
+	result = (chanPtr->typePtr->blockModeProc) (chanPtr->instanceData,
+		mode);
+    }
+    if (result != 0) {
+	Tcl_SetErrno(result);
+	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) {
+	chanPtr->flags &= (~(CHANNEL_NONBLOCKING | BG_FLUSH_SCHEDULED));
+    } else {
+	chanPtr->flags |= CHANNEL_NONBLOCKING;
+    }
+    return TCL_OK;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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. */
+{
+    switch (type) {
+	case TCL_STDIN:
+            stdinInitialized = 1;
+	    stdinChannel = channel;
+	    break;
+	case TCL_STDOUT:
+	    stdoutInitialized = 1;
+	    stdoutChannel = channel;
+	    break;
+	case TCL_STDERR:
+	    stderrInitialized = 1;
+	    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;
+
+    /*
+     * If the channels were not created yet, create them now and
+     * store them in the static variables.  Note that we need to set
+     * stdinInitialized before calling TclGetDefaultStdChannel in order
+     * to avoid recursive loops when TclGetDefaultStdChannel calls
+     * Tcl_CreateChannel.
+     */
+
+    switch (type) {
+	case TCL_STDIN:
+	    if (!stdinInitialized) {
+		stdinChannel = TclGetDefaultStdChannel(TCL_STDIN);
+		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 (stdinChannel != (Tcl_Channel) NULL) {
+                    (void) Tcl_RegisterChannel((Tcl_Interp *) NULL,
+                            stdinChannel);
+                }
+	    }
+	    channel = stdinChannel;
+	    break;
+	case TCL_STDOUT:
+	    if (!stdoutInitialized) {
+		stdoutChannel = TclGetDefaultStdChannel(TCL_STDOUT);
+		stdoutInitialized = 1;
+
+                /*
+                 * Artificially bump the refcount to ensure that the channel
+                 * is only closed on exit.
+                 *
+                 * NOTE: Must only do this if stdoutChannel is not NULL. It
+                 * can be NULL in situations where Tcl is unable to connect
+                 * to the standard output.
+                 */
+
+                if (stdoutChannel != (Tcl_Channel) NULL) {
+                    (void) Tcl_RegisterChannel((Tcl_Interp *) NULL,
+                            stdoutChannel);
+                }
+	    }
+	    channel = stdoutChannel;
+	    break;
+	case TCL_STDERR:
+	    if (!stderrInitialized) {
+		stderrChannel = TclGetDefaultStdChannel(TCL_STDERR);
+		stderrInitialized = 1;
+
+                /*
+                 * Artificially bump the refcount to ensure that the channel
+                 * is only closed on exit.
+                 *
+                 * NOTE: Must only do this if stderrChannel is not NULL. It
+                 * can be NULL in situations where Tcl is unable to connect
+                 * to the standard error.
+                 */
+
+                if (stderrChannel != (Tcl_Channel) NULL) {
+                    (void) Tcl_RegisterChannel((Tcl_Interp *) NULL,
+                            stderrChannel);
+                }
+	    }
+	    channel = 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. */
+{
+    Channel *chanPtr;
+    CloseCallback *cbPtr;
+
+    chanPtr = (Channel *) chan;
+
+    cbPtr = (CloseCallback *) ckalloc((unsigned) sizeof(CloseCallback));
+    cbPtr->proc = proc;
+    cbPtr->clientData = clientData;
+
+    cbPtr->nextPtr = chanPtr->closeCbPtr;
+    chanPtr->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. */
+{
+    Channel *chanPtr;
+    CloseCallback *cbPtr, *cbPrevPtr;
+
+    chanPtr = (Channel *) chan;
+    for (cbPtr = chanPtr->closeCbPtr, cbPrevPtr = (CloseCallback *) NULL;
+             cbPtr != (CloseCallback *) NULL;
+             cbPtr = cbPtr->nextPtr) {
+        if ((cbPtr->proc == proc) && (cbPtr->clientData == clientData)) {
+            if (cbPrevPtr == (CloseCallback *) NULL) {
+                chanPtr->closeCbPtr = cbPtr->nextPtr;
+            }
+            ckfree((char *) cbPtr);
+            break;
+        } else {
+            cbPrevPtr = cbPtr;
+        }
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * CloseChannelsOnExit --
+ *
+ *	Closes all the existing channels, on exit. This	routine is called
+ *	during exit processing.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	Closes all channels.
+ *
+ *----------------------------------------------------------------------
+ */
+
+	/* ARGSUSED */
+static void
+CloseChannelsOnExit(clientData)
+    ClientData clientData;		/* NULL - unused. */
+{
+    Channel *chanPtr;			/* Iterates over open channels. */
+    Channel *nextChanPtr;		/* Iterates over open channels. */
+
+
+    for (chanPtr = firstChanPtr; chanPtr != (Channel *) NULL;
+             chanPtr = nextChanPtr) {
+        nextChanPtr = chanPtr->nextChanPtr;
+
+        /*
+         * 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 *) stdinChannel) ||
+                (chanPtr == (Channel *) stdoutChannel) ||
+                (chanPtr == (Channel *) stderrChannel)) {
+
+            /*
+             * Decrement the refcount which was earlier artificially bumped
+             * up to keep the channel from being closed.
+             */
+
+            chanPtr->refCount--;
+        }
+
+        if (chanPtr->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.
+             */
+            
+            (chanPtr->typePtr->closeProc) (chanPtr->instanceData,
+                    (Tcl_Interp *) NULL);
+
+            /*
+             * 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;
+            chanPtr->flags |= CHANNEL_DEAD;
+        }
+    }
+
+    /*
+     * Reinitialize all the variables to the initial state:
+     */
+    
+    firstChanPtr = (Channel *) NULL;
+    nestedHandlerPtr = (NextChannelHandler *) NULL;
+    channelExitHandlerCreated = 0;
+    stdinChannel = NULL;
+    stdinInitialized = 0;
+    stdoutChannel = NULL;
+    stdoutInitialized = 0;
+    stderrChannel = NULL;
+    stderrInitialized = 0;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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. */
+    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);
+
+        /*
+         * Remove any fileevents registered in this interpreter.
+         */
+        
+        for (sPtr = chanPtr->scriptRecordPtr,
+                 prevPtr = (EventScriptRecord *) NULL;
+                 sPtr != (EventScriptRecord *) NULL;
+                 sPtr = nextPtr) {
+            nextPtr = sPtr->nextPtr;
+            if (sPtr->interp == interp) {
+                if (prevPtr == (EventScriptRecord *) NULL) {
+                    chanPtr->scriptRecordPtr = nextPtr;
+                } else {
+                    prevPtr->nextPtr = nextPtr;
+                }
+
+                Tcl_DeleteChannelHandler((Tcl_Channel) chanPtr,
+                        ChannelEventScriptInvoker, (ClientData) sPtr);
+
+		ckfree(sPtr->script);
+                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);
+        chanPtr->refCount--;
+        if (chanPtr->refCount <= 0) {
+            if (!(chanPtr->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;
+{
+    Channel *chanPtr = (Channel *) chan;
+    
+    if ((chan == stdinChannel) && (stdinInitialized)) {
+        if (chanPtr->refCount < 2) {
+            chanPtr->refCount = 0;
+            stdinChannel = NULL;
+            return;
+        }
+    } else if ((chan == stdoutChannel) && (stdoutInitialized)) {
+        if (chanPtr->refCount < 2) {
+            chanPtr->refCount = 0;
+            stdoutChannel = NULL;
+            return;
+        }
+    } else if ((chan == stderrChannel) && (stderrInitialized)) {
+        if (chanPtr->refCount < 2) {
+            chanPtr->refCount = 0;
+            stderrChannel = NULL;
+            return;
+        }
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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.
+ *
+ * Results:
+ *	A standard Tcl result.
+ *
+ * Side effects:
+ *	Deletes the hash entry for a channel associated with an interpreter.
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+Tcl_UnregisterChannel(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. */
+
+    chanPtr = (Channel *) chan;
+    
+    if (interp != (Tcl_Interp *) NULL) {
+        hTblPtr = (Tcl_HashTable *) Tcl_GetAssocData(interp, "tclIO", NULL);
+        if (hTblPtr == (Tcl_HashTable *) NULL) {
+            return TCL_OK;
+        }
+        hPtr = Tcl_FindHashEntry(hTblPtr, chanPtr->channelName);
+        if (hPtr == (Tcl_HashEntry *) NULL) {
+            return TCL_OK;
+        }
+        if ((Channel *) Tcl_GetHashValue(hPtr) != chanPtr) {
+            return TCL_OK;
+        }
+        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);
+    }
+
+    chanPtr->refCount--;
+    
+    /*
+     * 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 (chanPtr->refCount <= 0) {
+
+        /*
+         * Ensure that if there is another buffer, it gets flushed
+         * whether or not we are doing a background flush.
+         */
+
+        if ((chanPtr->curOutPtr != NULL) &&
+                (chanPtr->curOutPtr->nextAdded >
+                        chanPtr->curOutPtr->nextRemoved)) {
+            chanPtr->flags |= BUFFER_READY;
+        }
+        chanPtr->flags |= CHANNEL_CLOSED;
+        if (!(chanPtr->flags & BG_FLUSH_SCHEDULED)) {
+            if (Tcl_Close(interp, chan) != TCL_OK) {
+                return TCL_ERROR;
+            }
+        }
+    }
+    return TCL_OK;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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. */
+
+    chanPtr = (Channel *) chan;
+
+    if (chanPtr->channelName == (char *) NULL) {
+        panic("Tcl_RegisterChannel: channel without name");
+    }
+    if (interp != (Tcl_Interp *) NULL) {
+        hTblPtr = GetChannelTable(interp);
+        hPtr = Tcl_CreateHashEntry(hTblPtr, chanPtr->channelName, &new);
+        if (new == 0) {
+            if (chan == (Tcl_Channel) Tcl_GetHashValue(hPtr)) {
+                return;
+            }
+            panic("Tcl_RegisterChannel: duplicate channel names");
+        }
+        Tcl_SetHashValue(hPtr, (ClientData) chanPtr);
+    }
+    chanPtr->refCount++;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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->result
+ *	contains an error message. It also returns, in modePtr, the
+ *	modes in which the channel is opened.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+Tcl_Channel
+Tcl_GetChannel(interp, chanName, modePtr)
+    Tcl_Interp *interp;		/* Interpreter in which to find or create
+                                 * the channel. */
+    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. */
+    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->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;
+    }
+
+    chanPtr = (Channel *) Tcl_GetHashValue(hPtr);
+    if (modePtr != NULL) {
+        *modePtr = (chanPtr->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. */
+    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. */
+
+    chanPtr = (Channel *) ckalloc((unsigned) sizeof(Channel));
+    
+    if (chanName != (char *) NULL) {
+        chanPtr->channelName = ckalloc((unsigned) (strlen(chanName) + 1));
+        strcpy(chanPtr->channelName, chanName);
+    } else {
+        panic("Tcl_CreateChannel: NULL channel name");
+    }
+
+    chanPtr->flags = mask;
+
+    /*
+     * 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.
+     */
+
+    chanPtr->inputTranslation = TCL_TRANSLATE_AUTO;
+    chanPtr->outputTranslation = TCL_PLATFORM_TRANSLATION;
+    chanPtr->inEofChar = 0;
+    chanPtr->outEofChar = 0;
+
+    chanPtr->unreportedError = 0;
+    chanPtr->instanceData = instanceData;
+    chanPtr->typePtr = typePtr;
+    chanPtr->refCount = 0;
+    chanPtr->closeCbPtr = (CloseCallback *) NULL;
+    chanPtr->curOutPtr = (ChannelBuffer *) NULL;
+    chanPtr->outQueueHead = (ChannelBuffer *) NULL;
+    chanPtr->outQueueTail = (ChannelBuffer *) NULL;
+    chanPtr->saveInBufPtr = (ChannelBuffer *) NULL;
+    chanPtr->inQueueHead = (ChannelBuffer *) NULL;
+    chanPtr->inQueueTail = (ChannelBuffer *) NULL;
+    chanPtr->chPtr = (ChannelHandler *) NULL;
+    chanPtr->interestMask = 0;
+    chanPtr->scriptRecordPtr = (EventScriptRecord *) NULL;
+    chanPtr->bufSize = CHANNELBUFFER_DEFAULT_SIZE;
+    chanPtr->timer = NULL;
+    chanPtr->csPtr = 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.
+     */
+
+    chanPtr->nextChanPtr = firstChanPtr;
+    firstChanPtr = chanPtr;
+
+    if (!channelExitHandlerCreated) {
+        channelExitHandlerCreated = 1;
+        Tcl_CreateExitHandler(CloseChannelsOnExit, (ClientData) NULL);
+    }
+    
+    /*
+     * Install this channel in the first empty standard channel slot, if
+     * the channel was previously closed explicitly.
+     */
+
+    if ((stdinChannel == NULL) && (stdinInitialized == 1)) {
+	Tcl_SetStdChannel((Tcl_Channel)chanPtr, TCL_STDIN);
+        Tcl_RegisterChannel((Tcl_Interp *) NULL, (Tcl_Channel) chanPtr);
+    } else if ((stdoutChannel == NULL) && (stdoutInitialized == 1)) {
+	Tcl_SetStdChannel((Tcl_Channel)chanPtr, TCL_STDOUT);
+        Tcl_RegisterChannel((Tcl_Interp *) NULL, (Tcl_Channel) chanPtr);
+    } else if ((stderrChannel == NULL) && (stderrInitialized == 1)) {
+	Tcl_SetStdChannel((Tcl_Channel)chanPtr, TCL_STDERR);
+        Tcl_RegisterChannel((Tcl_Interp *) NULL, (Tcl_Channel) chanPtr);
+    } 
+    return (Tcl_Channel) chanPtr;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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. */
+{
+    Channel *chanPtr;		/* The actual channel. */
+
+    chanPtr = (Channel *) chan;
+    return (chanPtr->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.
+ *
+ *----------------------------------------------------------------------
+ */
+
+char *
+Tcl_GetChannelName(chan)
+    Tcl_Channel chan;		/* The channel for which to return the name. */
+{
+    Channel *chanPtr;		/* The actual channel. */
+
+    chanPtr = (Channel *) chan;
+    return chanPtr->channelName;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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;		/* The actual channel. */
+
+    chanPtr = (Channel *) chan;
+    return chanPtr->typePtr;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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;
+    result = (chanPtr->typePtr->getHandleProc)(chanPtr->instanceData,
+	    direction, &handle);
+    if (handlePtr) {
+	*handlePtr = handle;
+    }
+    return result;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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;		/* The actual channel. */
+
+    chanPtr = (Channel *) chan;
+    return chanPtr->instanceData;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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(chanPtr, bufPtr, mustDiscard)
+    Channel *chanPtr;		/* Channel for 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 for the input queue if the channel is readable.
+     */
+    
+    if (chanPtr->flags & TCL_READABLE) {
+        if (chanPtr->inQueueHead == (ChannelBuffer *) NULL) {
+            chanPtr->inQueueHead = bufPtr;
+            chanPtr->inQueueTail = bufPtr;
+            goto keepit;
+        }
+        if (chanPtr->saveInBufPtr == (ChannelBuffer *) NULL) {
+            chanPtr->saveInBufPtr = bufPtr;
+            goto keepit;
+        }
+    }
+
+    /*
+     * Only save buffers for the output queue if the channel is writable.
+     */
+
+    if (chanPtr->flags & TCL_WRITABLE) {
+        if (chanPtr->curOutPtr == (ChannelBuffer *) NULL) {
+            chanPtr->curOutPtr = bufPtr;
+            goto keepit;
+        }
+    }
+
+    /*
+     * If we reached this code we return the buffer to the OS.
+     */
+
+    ckfree((char *) bufPtr);
+    return;
+
+keepit:
+    bufPtr->nextRemoved = 0;
+    bufPtr->nextAdded = 0;
+    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(chanPtr)
+    Channel *chanPtr;		/* The channel for which to discard output. */
+{
+    ChannelBuffer *bufPtr;
+    
+    while (chanPtr->outQueueHead != (ChannelBuffer *) NULL) {
+        bufPtr = chanPtr->outQueueHead;
+        chanPtr->outQueueHead = bufPtr->nextPtr;
+        RecycleBuffer(chanPtr, bufPtr, 0);
+    }
+    chanPtr->outQueueHead = (ChannelBuffer *) NULL;
+    chanPtr->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, chanPtr)
+    Tcl_Interp *interp;		/* For error reporting (can be NULL) */
+    Channel    *chanPtr;	/* The channel to check. */
+{
+    if (chanPtr->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. */
+{
+    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;			/* Stores POSIX error codes from
+                                         * channel driver operations. */
+    errorCode = 0;
+
+    /*
+     * 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,chanPtr)) 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 (((chanPtr->curOutPtr != (ChannelBuffer *) NULL) &&
+                (chanPtr->curOutPtr->nextAdded == chanPtr->curOutPtr->bufSize))
+                || ((chanPtr->flags & BUFFER_READY) &&
+                        (chanPtr->outQueueHead == (ChannelBuffer *) NULL))) {
+            chanPtr->flags &= (~(BUFFER_READY));
+            chanPtr->curOutPtr->nextPtr = (ChannelBuffer *) NULL;
+            if (chanPtr->outQueueHead == (ChannelBuffer *) NULL) {
+                chanPtr->outQueueHead = chanPtr->curOutPtr;
+            } else {
+                chanPtr->outQueueTail->nextPtr = chanPtr->curOutPtr;
+            }
+            chanPtr->outQueueTail = chanPtr->curOutPtr;
+            chanPtr->curOutPtr = (ChannelBuffer *) NULL;
+        }
+        bufPtr = chanPtr->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) &&
+                (chanPtr->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)) {
+		if (chanPtr->flags & CHANNEL_NONBLOCKING) {
+		    if (!(chanPtr->flags & BG_FLUSH_SCHEDULED)) {
+			chanPtr->flags |= BG_FLUSH_SCHEDULED;
+			UpdateInterest(chanPtr);
+                    }
+                    errorCode = 0;
+                    break;
+		} else {
+		    panic("Blocking channel driver did not block on output");
+                }
+            }
+
+            /*
+             * Decide whether to report the error upwards or defer it.
+             */
+
+            if (calledFromAsyncFlush) {
+                if (chanPtr->unreportedError == 0) {
+                    chanPtr->unreportedError = errorCode;
+                }
+            } else {
+                Tcl_SetErrno(errorCode);
+		if (interp != NULL) {
+		    Tcl_SetResult(interp,
+			    Tcl_PosixError(interp), TCL_VOLATILE);
+		}
+            }
+
+            /*
+             * When we get an error we throw away all the output
+             * currently queued.
+             */
+
+            DiscardOutputQueued(chanPtr);
+            continue;
+        }
+
+        bufPtr->nextRemoved += written;
+
+        /*
+         * If this buffer is now empty, recycle it.
+         */
+
+        if (bufPtr->nextRemoved == bufPtr->nextAdded) {
+            chanPtr->outQueueHead = bufPtr->nextPtr;
+            if (chanPtr->outQueueHead == (ChannelBuffer *) NULL) {
+                chanPtr->outQueueTail = (ChannelBuffer *) NULL;
+            }
+            RecycleBuffer(chanPtr, bufPtr, 0);
+        }
+    }	/* Closes "while (1)". */
+    
+    /*
+     * If the queue became empty and we have the asynchronous flushing
+     * mechanism active, cancel the asynchronous flushing.
+     */
+
+    if ((chanPtr->outQueueHead == (ChannelBuffer *) NULL) &&
+            (chanPtr->flags & BG_FLUSH_SCHEDULED)) {
+        chanPtr->flags &= (~(BG_FLUSH_SCHEDULED));
+	(chanPtr->typePtr->watchProc)(chanPtr->instanceData,
+		chanPtr->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 ((chanPtr->flags & CHANNEL_CLOSED) && (chanPtr->refCount <= 0) &&
+            (chanPtr->outQueueHead == (ChannelBuffer *) NULL) &&
+            ((chanPtr->curOutPtr == (ChannelBuffer *) NULL) ||
+                    (chanPtr->curOutPtr->nextAdded ==
+                            chanPtr->curOutPtr->nextRemoved))) {
+        return CloseChannel(interp, chanPtr, errorCode);
+    }
+    return errorCode;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * CloseChannel --
+ *
+ *	Utility procedure to close a channel and free its associated
+ *	resources.
+ *
+ * Results:
+ *	0 on success or a POSIX error code if the operation failed.
+ *
+ * Side effects:
+ *	May close the actual channel; may free memory.
+ *
+ *----------------------------------------------------------------------
+ */
+
+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. */
+    Channel *prevChanPtr;		/* Preceding channel in list of
+                                         * all channels - used to splice a
+                                         * channel out of the list on close. */
+        
+    if (chanPtr == NULL) {
+        return result;
+    }
+    
+    /*
+     * No more input can be consumed so discard any leftover input.
+     */
+
+    DiscardInputQueued(chanPtr, 1);
+
+    /*
+     * Discard a leftover buffer in the current output buffer field.
+     */
+
+    if (chanPtr->curOutPtr != (ChannelBuffer *) NULL) {
+        ckfree((char *) chanPtr->curOutPtr);
+        chanPtr->curOutPtr = (ChannelBuffer *) NULL;
+    }
+    
+    /*
+     * The caller guarantees that there are no more buffers
+     * queued for output.
+     */
+
+    if (chanPtr->outQueueHead != (ChannelBuffer *) NULL) {
+        panic("TclFlush, closed channel: queued output left");
+    }
+
+    /*
+     * If the EOF character is set in the channel, append that to the
+     * output device.
+     */
+
+    if ((chanPtr->outEofChar != 0) && (chanPtr->flags & TCL_WRITABLE)) {
+        int dummy;
+        char c;
+
+        c = (char) chanPtr->outEofChar;
+        (chanPtr->typePtr->outputProc) (chanPtr->instanceData, &c, 1, &dummy);
+    }
+
+    /*
+     * Remove TCL_READABLE and TCL_WRITABLE from chanPtr->flags, so
+     * that close callbacks can not do input or output (assuming they
+     * squirreled the channel away in their clientData). This also
+     * prevents infinite loops if the callback calls any C API that
+     * could call FlushChannel.
+     */
+
+    chanPtr->flags &= (~(TCL_READABLE|TCL_WRITABLE));
+        
+    /*
+     * Splice this channel out of the list of all channels.
+     */
+
+    if (chanPtr == firstChanPtr) {
+        firstChanPtr = chanPtr->nextChanPtr;
+    } else {
+        for (prevChanPtr = firstChanPtr;
+                 (prevChanPtr != (Channel *) NULL) &&
+                     (prevChanPtr->nextChanPtr != chanPtr);
+                 prevChanPtr = prevChanPtr->nextChanPtr) {
+            /* Empty loop body. */
+        }
+        if (prevChanPtr == (Channel *) NULL) {
+            panic("FlushChannel: damaged channel list");
+        }
+        prevChanPtr->nextChanPtr = chanPtr->nextChanPtr;
+    }
+
+    /*
+     * OK, close the channel itself.
+     */
+        
+    result = (chanPtr->typePtr->closeProc) (chanPtr->instanceData, interp);
+    
+    if (chanPtr->channelName != (char *) NULL) {
+        ckfree(chanPtr->channelName);
+    }
+    
+    /*
+     * If we are being called synchronously, report either
+     * any latent error on the channel or the current error.
+     */
+        
+    if (chanPtr->unreportedError != 0) {
+        errorCode = chanPtr->unreportedError;
+    }
+    if (errorCode == 0) {
+        errorCode = result;
+        if (errorCode != 0) {
+            Tcl_SetErrno(errorCode);
+        }
+    }
+
+    /*
+     * Cancel any outstanding timer.
+     */
+
+    Tcl_DeleteTimerHandler(chanPtr->timer);
+
+    /*
+     * Mark the channel as deleted by clearing the type structure.
+     */
+
+    chanPtr->typePtr = NULL;
+
+    Tcl_EventuallyFree((ClientData) chanPtr, TCL_DYNAMIC);
+
+    return errorCode;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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. */
+{
+    ChannelHandler *chPtr, *chNext;	/* Iterate over channel handlers. */
+    CloseCallback *cbPtr;		/* Iterate over close callbacks
+                                         * for this channel. */
+    EventScriptRecord *ePtr, *eNextPtr;	/* Iterate over eventscript records. */
+    Channel *chanPtr;			/* The real IO channel. */
+    int result;				/* Of calling FlushChannel. */
+    NextChannelHandler *nhPtr;
+
+    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);
+
+    chanPtr = (Channel *) chan;
+    if (chanPtr->refCount > 0) {
+        panic("called Tcl_Close on channel with refCount > 0");
+    }
+
+    /*
+     * Remove any references to channel handlers for this channel that
+     * may be about to be invoked.
+     */
+
+    for (nhPtr = 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 = chanPtr->chPtr;
+             chPtr != (ChannelHandler *) NULL;
+             chPtr = chNext) {
+        chNext = chPtr->nextPtr;
+        ckfree((char *) chPtr);
+    }
+    chanPtr->chPtr = (ChannelHandler *) NULL;
+    
+    
+    /*
+     * Cancel any pending copy operation.
+     */
+
+    StopCopy(chanPtr->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.
+     */
+        
+    chanPtr->interestMask = 0;
+    
+    /*
+     * Remove any EventScript records for this channel.
+     */
+
+    for (ePtr = chanPtr->scriptRecordPtr;
+             ePtr != (EventScriptRecord *) NULL;
+             ePtr = eNextPtr) {
+        eNextPtr = ePtr->nextPtr;
+	ckfree(ePtr->script);
+        ckfree((char *) ePtr);
+    }
+    chanPtr->scriptRecordPtr = (EventScriptRecord *) NULL;
+        
+    /*
+     * Invoke the registered close callbacks and delete their records.
+     */
+
+    while (chanPtr->closeCbPtr != (CloseCallback *) NULL) {
+        cbPtr = chanPtr->closeCbPtr;
+        chanPtr->closeCbPtr = cbPtr->nextPtr;
+        (cbPtr->proc) (cbPtr->clientData);
+        ckfree((char *) cbPtr);
+    }
+
+    /*
+     * Ensure that the last output buffer will be flushed.
+     */
+    
+    if ((chanPtr->curOutPtr != (ChannelBuffer *) NULL) &&
+           (chanPtr->curOutPtr->nextAdded > chanPtr->curOutPtr->nextRemoved)) {
+        chanPtr->flags |= BUFFER_READY;
+    }
+
+    /*
+     * 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.
+     */
+    
+    chanPtr->flags |= CHANNEL_CLOSED;
+    result = FlushChannel(interp, chanPtr, 0);
+    if (result != 0) {
+        return TCL_ERROR;
+    }
+
+    return TCL_OK;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * Tcl_Write --
+ *
+ *	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.
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+Tcl_Write(chan, srcPtr, slen)
+    Tcl_Channel chan;			/* The channel to buffer output for. */
+    char *srcPtr;			/* Output to buffer. */
+    int slen;				/* Its length. Negative means
+                                         * the output is null terminated
+                                         * and we must compute its length. */
+{
+    Channel *chanPtr = (Channel *) chan;
+
+    /*
+     * Check for unreported error.
+     */
+
+    if (chanPtr->unreportedError != 0) {
+        Tcl_SetErrno(chanPtr->unreportedError);
+        chanPtr->unreportedError = 0;
+        return -1;
+    }
+    
+    /*
+     * If the channel is not open for writing punt.
+     */
+
+    if (!(chanPtr->flags & TCL_WRITABLE)) {
+        Tcl_SetErrno(EACCES);
+        return -1;
+    }
+    
+    /*
+     * If the channel is in the middle of a background copy, fail.
+     */
+
+    if (chanPtr->csPtr) {
+	Tcl_SetErrno(EBUSY);
+	return -1;
+    }
+
+    /*
+     * If length passed is negative, assume that the output is null terminated
+     * and compute its length.
+     */
+    
+    if (slen < 0) {
+        slen = strlen(srcPtr);
+    }
+
+    return DoWrite(chanPtr, srcPtr, slen);
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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, srcPtr, slen)
+    Channel *chanPtr;			/* The channel to buffer output for. */
+    char *srcPtr;			/* Data to write. */
+    int slen;				/* Number of bytes to write. */
+{
+    ChannelBuffer *outBufPtr;		/* Current output buffer. */
+    int foundNewline;			/* Did we find a newline in output? */
+    char *dPtr, *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 (slen > 0) {
+        
+        /*
+         * Make sure there is a current output buffer to accept output.
+         */
+
+        if (chanPtr->curOutPtr == (ChannelBuffer *) NULL) {
+            chanPtr->curOutPtr = (ChannelBuffer *) ckalloc((unsigned)
+                    (CHANNELBUFFER_HEADER_SIZE + chanPtr->bufSize));
+            chanPtr->curOutPtr->nextAdded = 0;
+            chanPtr->curOutPtr->nextRemoved = 0;
+            chanPtr->curOutPtr->bufSize = chanPtr->bufSize;
+            chanPtr->curOutPtr->nextPtr = (ChannelBuffer *) NULL;
+        }
+
+        outBufPtr = chanPtr->curOutPtr;
+
+        destCopied = outBufPtr->bufSize - outBufPtr->nextAdded;
+        if (destCopied > slen) {
+            destCopied = slen;
+        }
+        
+        destPtr = outBufPtr->buf + outBufPtr->nextAdded;
+        switch (chanPtr->outputTranslation) {
+            case TCL_TRANSLATE_LF:
+                srcCopied = destCopied;
+                memcpy((VOID *) destPtr, (VOID *) srcPtr, (size_t) destCopied);
+                break;
+            case TCL_TRANSLATE_CR:
+                srcCopied = destCopied;
+                memcpy((VOID *) destPtr, (VOID *) srcPtr, (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 = srcPtr;
+                     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:
+                panic("Tcl_Write: AUTO output translation mode not supported");
+            default:
+                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 (!(chanPtr->flags & BUFFER_READY)) {
+            if (outBufPtr->nextAdded == outBufPtr->bufSize) {
+                chanPtr->flags |= BUFFER_READY;
+            } else if (chanPtr->flags & CHANNEL_LINEBUFFERED) {
+                for (sPtr = srcPtr, i = 0, foundNewline = 0;
+                         (i < srcCopied) && (!foundNewline);
+                         i++, sPtr++) {
+                    if (*sPtr == '\n') {
+                        foundNewline = 1;
+                        break;
+                    }
+                }
+                if (foundNewline) {
+                    chanPtr->flags |= BUFFER_READY;
+                }
+            } else if (chanPtr->flags & CHANNEL_UNBUFFERED) {
+                chanPtr->flags |= BUFFER_READY;
+            }
+        }
+        
+        totalDestCopied += srcCopied;
+        srcPtr += srcCopied;
+        slen -= srcCopied;
+
+        if (chanPtr->flags & BUFFER_READY) {
+            if (FlushChannel(NULL, chanPtr, 0) != 0) {
+                return -1;
+            }
+        }
+    } /* Closes "while" */
+
+    return totalDestCopied;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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;			/* The actual channel. */
+
+    chanPtr = (Channel *) chan;
+
+    /*
+     * Check for unreported error.
+     */
+
+    if (chanPtr->unreportedError != 0) {
+        Tcl_SetErrno(chanPtr->unreportedError);
+        chanPtr->unreportedError = 0;
+        return TCL_ERROR;
+    }
+
+    /*
+     * If the channel is not open for writing punt.
+     */
+
+    if (!(chanPtr->flags & TCL_WRITABLE)) {
+        Tcl_SetErrno(EACCES);
+        return TCL_ERROR;
+    }
+    
+    /*
+     * If the channel is in the middle of a background copy, fail.
+     */
+
+    if (chanPtr->csPtr) {
+	Tcl_SetErrno(EBUSY);
+	return -1;
+    }
+
+    /*
+     * Force current output buffer to be output also.
+     */
+    
+    if ((chanPtr->curOutPtr != (ChannelBuffer *) NULL) &&
+            (chanPtr->curOutPtr->nextAdded > 0)) {
+        chanPtr->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(chanPtr, discardSavedBuffers)
+    Channel *chanPtr;		/* 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 = chanPtr->inQueueHead;
+    chanPtr->inQueueHead = (ChannelBuffer *) NULL;
+    chanPtr->inQueueTail = (ChannelBuffer *) NULL;
+    for (; bufPtr != (ChannelBuffer *) NULL; bufPtr = nxtPtr) {
+        nxtPtr = bufPtr->nextPtr;
+        RecycleBuffer(chanPtr, bufPtr, discardSavedBuffers);
+    }
+
+    /*
+     * If discardSavedBuffers is nonzero, must also discard any previously
+     * saved buffer in the saveInBufPtr field.
+     */
+    
+    if (discardSavedBuffers) {
+        if (chanPtr->saveInBufPtr != (ChannelBuffer *) NULL) {
+            ckfree((char *) chanPtr->saveInBufPtr);
+            chanPtr->saveInBufPtr = (ChannelBuffer *) NULL;
+        }
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * GetInput --
+ *
+ *	Reads input data from a device or file into an input buffer.
+ *
+ * Results:
+ *	A Posix error code or 0.
+ *
+ * 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. */
+
+    /*
+     * 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,chanPtr)) return EINVAL;
+
+    /*
+     * 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.
+     */
+
+    if ((chanPtr->inQueueTail != (ChannelBuffer *) NULL) &&
+           (chanPtr->inQueueTail->nextAdded < chanPtr->inQueueTail->bufSize)) {
+        bufPtr = chanPtr->inQueueTail;
+        toRead = bufPtr->bufSize - bufPtr->nextAdded;
+    } else {
+	if (chanPtr->saveInBufPtr != (ChannelBuffer *) NULL) {
+	    bufPtr = chanPtr->saveInBufPtr;
+	    chanPtr->saveInBufPtr = (ChannelBuffer *) NULL;
+	} else {
+	    bufPtr = (ChannelBuffer *) ckalloc(
+		((unsigned) CHANNELBUFFER_HEADER_SIZE + chanPtr->bufSize));
+	    bufPtr->bufSize = chanPtr->bufSize;
+	}
+	bufPtr->nextRemoved = 0;
+	bufPtr->nextAdded = 0;
+        toRead = bufPtr->bufSize;
+        if (chanPtr->inQueueTail == (ChannelBuffer *) NULL) {
+            chanPtr->inQueueHead = bufPtr;
+        } else {
+            chanPtr->inQueueTail->nextPtr = bufPtr;
+        }
+        chanPtr->inQueueTail = bufPtr;
+        bufPtr->nextPtr = (ChannelBuffer *) NULL;
+    }
+      
+    /*
+     * 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 (chanPtr->flags & CHANNEL_EOF) {
+	return 0;
+    }
+
+    nread = (chanPtr->typePtr->inputProc) (chanPtr->instanceData,
+	    bufPtr->buf + bufPtr->nextAdded, toRead, &result);
+
+    if (nread == 0) {
+	chanPtr->flags |= CHANNEL_EOF;
+    } else if (nread < 0) {
+	if ((result == EWOULDBLOCK) || (result == EAGAIN)) {
+	    chanPtr->flags |= CHANNEL_BLOCKED;
+	    result = EAGAIN;
+	    if (chanPtr->flags & CHANNEL_NONBLOCKING) {
+		Tcl_SetErrno(result);
+	    } else {
+		panic("Blocking channel driver did not block on input");
+	    }
+	} else {
+	    Tcl_SetErrno(result);
+	}
+	return result;
+    } else {
+	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) {
+	    chanPtr->flags |= CHANNEL_BLOCKED;
+	}
+    }
+    return 0;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * CopyAndTranslateBuffer --
+ *
+ *	Copy at most one buffer of input to the result space, doing
+ *	eol translations according to mode in effect currently.
+ *
+ * Results:
+ *	Number of characters (as opposed to bytes) copied. May return
+ *	zero if no input is available to be translated.
+ *
+ * Side effects:
+ *	Consumes buffered input. May deallocate one buffer.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+CopyAndTranslateBuffer(chanPtr, result, space)
+    Channel *chanPtr;		/* The 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? */
+{
+    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? */
+    ChannelBuffer *bufPtr;	/* The buffer from which to copy bytes. */
+    char curByte;		/* The byte we are currently translating. */
+    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 (chanPtr->inQueueHead == (ChannelBuffer *) NULL) {
+        return 0;
+    }
+    bufPtr = chanPtr->inQueueHead;
+    bytesInBuffer = bufPtr->nextAdded - bufPtr->nextRemoved;
+    if (bytesInBuffer < space) {
+        space = bytesInBuffer;
+    }
+    copied = 0;
+    switch (chanPtr->inputTranslation) {
+        case TCL_TRANSLATE_LF:
+
+            if (space == 0) {
+                return 0;
+            }
+            
+	    /*
+             * Copy the current chunk into the result buffer.
+             */
+
+            memcpy((VOID *) result,
+                    (VOID *)(bufPtr->buf + bufPtr->nextRemoved),
+                    (size_t) space);
+            bufPtr->nextRemoved += space;
+            copied = space;
+            break;
+
+        case TCL_TRANSLATE_CR:
+
+            if (space == 0) {
+                return 0;
+            }
+
+	    /*
+             * Copy the current chunk into the result buffer, then
+             * replace all \r with \n.
+             */
+
+            memcpy((VOID *) result,
+                    (VOID *)(bufPtr->buf + bufPtr->nextRemoved),
+                    (size_t) space);
+            bufPtr->nextRemoved += space;
+            for (copied = 0; copied < space; copied++) {
+                if (result[copied] == '\r') {
+                    result[copied] = '\n';
+                }
+            }
+            break;
+
+        case TCL_TRANSLATE_CRLF:
+
+            /*
+             * If there is a held-back "\r" at EOF, produce it now.
+             */
+            
+            if (space == 0) {
+                if ((chanPtr->flags & (INPUT_SAW_CR | CHANNEL_EOF)) ==
+                        (INPUT_SAW_CR | CHANNEL_EOF)) {
+                    result[0] = '\r';
+                    chanPtr->flags &= (~(INPUT_SAW_CR));
+                    return 1;
+                }
+                return 0;
+            }
+
+            /*
+             * Copy the current chunk and replace "\r\n" with "\n"
+             * (but not standalone "\r"!).
+             */
+
+            for (copied = 0;
+                     (copied < space) &&
+                         (bufPtr->nextRemoved < bufPtr->nextAdded);
+                     copied++) {
+                curByte = bufPtr->buf[bufPtr->nextRemoved];
+                bufPtr->nextRemoved++;
+                if (curByte == '\r') {
+                    if (chanPtr->flags & INPUT_SAW_CR) {
+                        result[copied] = '\r';
+                    } else {
+                        chanPtr->flags |= INPUT_SAW_CR;
+                        copied--;
+                    }
+                } else if (curByte == '\n') {
+                    chanPtr->flags &= (~(INPUT_SAW_CR));
+                    result[copied] = '\n';
+                } else {
+                    if (chanPtr->flags & INPUT_SAW_CR) {
+                        chanPtr->flags &= (~(INPUT_SAW_CR));
+                        result[copied] = '\r';
+                        bufPtr->nextRemoved--;
+                    } else {
+                        result[copied] = curByte;
+                    }
+                }
+            }
+            break;
+                
+        case TCL_TRANSLATE_AUTO:
+            
+            if (space == 0) {
+                return 0;
+            }
+
+            /*
+             * Loop over the current buffer, converting "\r" and "\r\n"
+             * to "\n".
+             */
+
+            for (copied = 0;
+                     (copied < space) &&
+                         (bufPtr->nextRemoved < bufPtr->nextAdded); ) {
+                curByte = bufPtr->buf[bufPtr->nextRemoved];
+                bufPtr->nextRemoved++;
+                if (curByte == '\r') {
+                    result[copied] = '\n';
+		    copied++;
+                    if (bufPtr->nextRemoved < bufPtr->nextAdded) {
+                        if (bufPtr->buf[bufPtr->nextRemoved] == '\n') {
+                            bufPtr->nextRemoved++;
+                        }
+                        chanPtr->flags &= (~(INPUT_SAW_CR));
+                    } else {
+                        chanPtr->flags |= INPUT_SAW_CR;
+                    }
+                } else {
+                    if (curByte == '\n') {
+                        if (!(chanPtr->flags & INPUT_SAW_CR)) {
+                            result[copied] = '\n';
+			    copied++;
+                        }
+                    } else {
+                        result[copied] = curByte;
+			copied++;
+                    }
+                    chanPtr->flags &= (~(INPUT_SAW_CR));
+                }
+            }
+            break;
+
+        default:
+            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 (chanPtr->inEofChar != 0) {
+        for (i = 0; i < copied; i++) {
+            if (result[i] == (char) chanPtr->inEofChar) {
+                break;
+            }
+        }
+        if (i < copied) {
+
+            /*
+             * Set sticky EOF so that no further input is presented
+             * to the caller.
+             */
+            
+            chanPtr->flags |= (CHANNEL_EOF | CHANNEL_STICKY_EOF);
+
+            /*
+             * Reset the start of valid data in the input buffer to the
+             * position of the eofChar, so that subsequent reads will
+             * encounter it immediately. First we set it to the position
+             * of the last byte consumed if all result bytes were the
+             * product of one input byte; since it is possible that "\r\n"
+             * contracted to "\n" in the result, we have to search back
+             * from that position until we find the eofChar, because it
+             * is possible that its actual position in the buffer is n
+             * bytes further back (n is the number of "\r\n" sequences
+             * that were contracted to "\n" in the result).
+             */
+                  
+            bufPtr->nextRemoved -= (copied - i);
+            while ((bufPtr->nextRemoved > 0) &&
+                    (bufPtr->buf[bufPtr->nextRemoved] !=
+                            (char) chanPtr->inEofChar)) {
+                bufPtr->nextRemoved--;
+            }
+            copied = i;
+        }
+    }
+
+    /*
+     * 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, 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;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * ScanBufferForEOL --
+ *
+ *	Scans one buffer for EOL according to the specified EOL
+ *	translation mode. If it sees the input eofChar for the channel
+ *	it stops also.
+ *
+ * Results:
+ *	TRUE if EOL is found, FALSE otherwise. Also sets output parameter
+ *	bytesToEOLPtr to the number of bytes so far to EOL, and crSeenPtr
+ *	to whether a "\r" was seen.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+ScanBufferForEOL(chanPtr, bufPtr, translation, eofChar, bytesToEOLPtr,
+                 crSeenPtr)
+    Channel *chanPtr;
+    ChannelBuffer *bufPtr;		/* Buffer to scan for EOL. */
+    Tcl_EolTranslation translation;	/* Translation mode to use. */
+    int eofChar;			/* EOF char to look for. */
+    int *bytesToEOLPtr;			/* Running counter. */
+    int *crSeenPtr;			/* Has "\r" been seen? */
+{
+    char *rPtr;				/* Iterates over input string. */
+    char *sPtr;				/* Where to stop search? */
+    int EOLFound;
+    int bytesToEOL;
+    
+    for (EOLFound = 0, rPtr = bufPtr->buf + bufPtr->nextRemoved,
+             sPtr = bufPtr->buf + bufPtr->nextAdded,
+             bytesToEOL = *bytesToEOLPtr;
+             (!EOLFound) && (rPtr < sPtr);
+             rPtr++) {
+        switch (translation) {
+            case TCL_TRANSLATE_AUTO:
+                if ((*rPtr == (char) eofChar) && (eofChar != 0)) {
+                    chanPtr->flags |= (CHANNEL_EOF | CHANNEL_STICKY_EOF);
+                    EOLFound = 1;
+                } else if (*rPtr == '\n') {
+
+		    /*
+                     * CopyAndTranslateBuffer wants to know the length
+                     * of the result, not the input. The input is one
+                     * larger because "\r\n" shrinks to "\n".
+                     */
+
+                    if (!(*crSeenPtr)) {
+                        bytesToEOL++;
+			EOLFound = 1;
+                    } else {
+
+			/*
+			 * This is a lf at the begining of a buffer
+			 * where the previous buffer ended in a cr.
+			 * Consume this lf because we've already emitted
+			 * the newline for this crlf sequence. ALSO, if
+                         * bytesToEOL is 0 (which means that we are at the
+                         * first character of the scan), unset the
+                         * INPUT_SAW_CR flag in the channel, because we
+                         * already handled it; leaving it set would cause
+                         * CopyAndTranslateBuffer to potentially consume
+                         * another lf if one follows the current byte.
+			 */
+
+			bufPtr->nextRemoved++;
+                        *crSeenPtr = 0;
+                        chanPtr->flags &= (~(INPUT_SAW_CR));
+		    }
+                } else if (*rPtr == '\r') {
+                    bytesToEOL++;
+                    EOLFound = 1;
+                } else {
+                    *crSeenPtr = 0;
+                    bytesToEOL++;
+                }
+                break;
+            case TCL_TRANSLATE_LF:
+                if ((*rPtr == (char) eofChar) && (eofChar != 0)) {
+                    chanPtr->flags |= (CHANNEL_EOF | CHANNEL_STICKY_EOF);
+                    EOLFound = 1;
+                } else {
+                    if (*rPtr == '\n') {
+                        EOLFound = 1;
+                    }
+                    bytesToEOL++;
+                }
+                break;
+            case TCL_TRANSLATE_CR:
+                if ((*rPtr == (char) eofChar) && (eofChar != 0)) {
+                    chanPtr->flags |= (CHANNEL_EOF | CHANNEL_STICKY_EOF);
+                    EOLFound = 1;
+                } else {
+                    if (*rPtr == '\r') {
+                        EOLFound = 1;
+                    }
+                    bytesToEOL++;
+                }
+                break;
+            case TCL_TRANSLATE_CRLF:
+                if ((*rPtr == (char) eofChar) && (eofChar != 0)) {
+                    chanPtr->flags |= (CHANNEL_EOF | CHANNEL_STICKY_EOF);
+                    EOLFound = 1;
+                } else if (*rPtr == '\n') {
+
+                    /*
+                     * CopyAndTranslateBuffer wants to know the length
+                     * of the result, not the input. The input is one
+                     * larger because crlf shrinks to lf.
+                     */
+
+                    if (*crSeenPtr) {
+                        EOLFound = 1;
+                    } else {
+                        bytesToEOL++;
+                    }
+                } else {
+                    if (*rPtr == '\r') {
+                        *crSeenPtr = 1;
+                    } else {
+                        *crSeenPtr = 0;
+                    }
+                    bytesToEOL++;
+                }
+                break;
+            default:
+                panic("unknown eol translation mode");
+        }
+    }
+
+    *bytesToEOLPtr = bytesToEOL;
+    return EOLFound;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * ScanInputForEOL --
+ *
+ *	Scans queued input for chanPtr for an end of line (according to the
+ *	current EOL translation mode) and returns the number of bytes
+ *	upto and including the end of line, or -1 if none was found.
+ *
+ * Results:
+ *	Count of bytes upto and including the end of line if one is present
+ *	or -1 if none was found. Also returns in an output parameter the
+ *	number of bytes queued if no end of line was found.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+ScanInputForEOL(chanPtr, bytesQueuedPtr)
+    Channel *chanPtr;	/* Channel for which to scan queued
+                                 * input for end of line. */
+    int *bytesQueuedPtr;	/* Where to store the number of bytes
+                                 * currently queued if no end of line
+                                 * was found. */
+{
+    ChannelBuffer *bufPtr;	/* Iterates over queued buffers. */
+    int bytesToEOL;		/* How many bytes to end of line? */
+    int EOLFound;		/* Did we find an end of line? */
+    int crSeen;			/* Did we see a "\r" in CRLF mode? */
+
+    *bytesQueuedPtr = 0;
+    bytesToEOL = 0;
+    EOLFound = 0;
+    for (bufPtr = chanPtr->inQueueHead,
+             crSeen = (chanPtr->flags & INPUT_SAW_CR) ? 1 : 0;
+            (!EOLFound) && (bufPtr != (ChannelBuffer *) NULL);
+            bufPtr = bufPtr->nextPtr) {
+        EOLFound = ScanBufferForEOL(chanPtr, bufPtr, chanPtr->inputTranslation,
+                chanPtr->inEofChar, &bytesToEOL, &crSeen);
+    }
+
+    if (EOLFound == 0) {
+        *bytesQueuedPtr = bytesToEOL;
+        return -1;
+    }
+    return bytesToEOL;        
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * GetEOL --
+ *
+ *	Accumulate input into the channel input buffer queue until an
+ *	end of line has been seen.
+ *
+ * Results:
+ *	Number of bytes buffered (at least 1) or -1 on failure.
+ *
+ * Side effects:
+ *	Consumes input from the channel.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+GetEOL(chanPtr)
+    Channel *chanPtr;	/* Channel to queue input on. */
+{
+    int bytesToEOL;		/* How many bytes in buffer up to and
+                                 * including the end of line? */
+    int bytesQueued;		/* How many bytes are queued currently
+                                 * in the input chain of the channel? */
+
+    /*
+     * Check for unreported error.
+     */
+
+    if (chanPtr->unreportedError != 0) {
+        Tcl_SetErrno(chanPtr->unreportedError);
+        chanPtr->unreportedError = 0;
+        return -1;
+    }
+
+    /*
+     * Punt if the channel is not opened for reading.
+     */
+
+    if (!(chanPtr->flags & TCL_READABLE)) {
+        Tcl_SetErrno(EACCES);
+        return -1;
+    }
+
+    /*
+     * If the channel is in the middle of a background copy, fail.
+     */
+
+    if (chanPtr->csPtr) {
+	Tcl_SetErrno(EBUSY);
+	return -1;
+    }
+
+    /*
+     * 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 (!(chanPtr->flags & CHANNEL_STICKY_EOF)) {
+        chanPtr->flags &= (~(CHANNEL_EOF));
+    }
+    chanPtr->flags &= (~(CHANNEL_BLOCKED | CHANNEL_GETS_BLOCKED));
+
+    while (1) {
+        bytesToEOL = ScanInputForEOL(chanPtr, &bytesQueued);
+        if (bytesToEOL > 0) {
+            chanPtr->flags &= (~(CHANNEL_BLOCKED));
+            return bytesToEOL;
+        }
+        if (chanPtr->flags & CHANNEL_EOF) {
+	    /*
+	     * Boundary case where cr was at the end of the previous buffer
+	     * and this buffer just has a newline.  At EOF our caller wants
+	     * to see -1 for the line length.
+	     */
+            return (bytesQueued == 0) ? -1 : bytesQueued ;
+        }
+        if (chanPtr->flags & CHANNEL_BLOCKED) {
+            if (chanPtr->flags & CHANNEL_NONBLOCKING) {
+		goto blocked;
+            }
+            chanPtr->flags &= (~(CHANNEL_BLOCKED));
+        }
+	if (GetInput(chanPtr) != 0) {
+	    goto blocked;
+        }
+    }
+
+    blocked:
+
+    /*
+     * 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.
+     */
+
+    chanPtr->flags |= CHANNEL_GETS_BLOCKED;
+    return -1;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * Tcl_Read --
+ *
+ *	Reads a given number of characters from a channel.
+ *
+ * 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_Read(chan, bufPtr, toRead)
+    Tcl_Channel chan;		/* The channel from which to read. */
+    char *bufPtr;		/* Where to store input read. */
+    int toRead;			/* Maximum number of characters to read. */
+{
+    Channel *chanPtr;		/* The real IO channel. */
+    
+    chanPtr = (Channel *) chan;
+
+    /*
+     * Check for unreported error.
+     */
+
+    if (chanPtr->unreportedError != 0) {
+        Tcl_SetErrno(chanPtr->unreportedError);
+        chanPtr->unreportedError = 0;
+        return -1;
+    }
+
+    /*
+     * Punt if the channel is not opened for reading.
+     */
+
+    if (!(chanPtr->flags & TCL_READABLE)) {
+        Tcl_SetErrno(EACCES);
+        return -1;
+    }
+    
+    /*
+     * If the channel is in the middle of a background copy, fail.
+     */
+
+    if (chanPtr->csPtr) {
+	Tcl_SetErrno(EBUSY);
+	return -1;
+    }
+
+    return DoRead(chanPtr, bufPtr, toRead);
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * DoRead --
+ *
+ *	Reads a given number of characters from a channel.
+ *
+ * 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 characters to read. */
+{
+    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 (!(chanPtr->flags & CHANNEL_STICKY_EOF)) {
+        chanPtr->flags &= (~(CHANNEL_EOF));
+    }
+    chanPtr->flags &= (~(CHANNEL_BLOCKED | CHANNEL_GETS_BLOCKED));
+    
+    for (copied = 0; copied < toRead; copied += copiedNow) {
+        copiedNow = CopyAndTranslateBuffer(chanPtr, bufPtr + copied,
+                toRead - copied);
+        if (copiedNow == 0) {
+            if (chanPtr->flags & CHANNEL_EOF) {
+                return copied;
+            }
+            if (chanPtr->flags & CHANNEL_BLOCKED) {
+                if (chanPtr->flags & CHANNEL_NONBLOCKING) {
+                    return copied;
+                }
+                chanPtr->flags &= (~(CHANNEL_BLOCKED));
+            }
+            result = GetInput(chanPtr);
+            if (result != 0) {
+                if (result == EAGAIN) {
+                    return copied;
+                }
+                return -1;
+            }
+        }
+    }
+    chanPtr->flags &= (~(CHANNEL_BLOCKED));
+    return copied;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * Tcl_Gets --
+ *
+ *	Reads a complete line of input from the channel into a
+ *	Tcl_DString.
+ *
+ * Results:
+ *	Length of line read 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 characters of the line read
+                                 * (excluding the terminating newline if
+                                 * present) will be appended to this
+                                 * DString. The caller must have initialized
+                                 * it and is responsible for managing the
+                                 * storage. */
+{
+    Channel *chanPtr;		/* The channel to read from. */
+    char *buf;			/* Points into DString where data
+                                 * will be stored. */
+    int offset;			/* Offset from start of DString at
+                                 * which to append the line just read. */
+    int copiedTotal;		/* Accumulates total length of input copied. */
+    int copiedNow;		/* How many bytes were copied from the
+                                 * current input buffer? */
+    int lineLen;		/* Length of line read, including the
+                                 * translated newline. If this is zero
+                                 * and neither EOF nor BLOCKED is set,
+                                 * the current line is empty. */
+    
+    chanPtr = (Channel *) chan;
+
+    lineLen = GetEOL(chanPtr);
+    if (lineLen < 0) {
+        return -1;
+    }
+    offset = Tcl_DStringLength(lineRead);
+    Tcl_DStringSetLength(lineRead, lineLen + offset);
+    buf = Tcl_DStringValue(lineRead) + offset;
+
+    for (copiedTotal = 0; copiedTotal < lineLen; copiedTotal += copiedNow) {
+        copiedNow = CopyAndTranslateBuffer(chanPtr, buf + copiedTotal,
+                lineLen - copiedTotal);
+    }
+    if ((copiedTotal > 0) && (buf[copiedTotal - 1] == '\n')) {
+        copiedTotal--;
+    }
+    Tcl_DStringSetLength(lineRead, copiedTotal + offset);
+    return copiedTotal;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * Tcl_GetsObj --
+ *
+ *	Reads a complete line of input from the channel into a
+ *	string object.
+ *
+ * Results:
+ *	Length of line read 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_GetsObj(chan, objPtr)
+    Tcl_Channel chan;		/* Channel from which to read. */
+    Tcl_Obj *objPtr;		/* The characters of the line read
+                                 * (excluding the terminating newline if
+                                 * present) will be appended to this
+                                 * object. The caller must have initialized
+                                 * it and is responsible for managing the
+                                 * storage. */
+{
+    Channel *chanPtr;		/* The channel to read from. */
+    char *buf;			/* Points into DString where data
+                                 * will be stored. */
+    int offset;			/* Offset from start of DString at
+                                 * which to append the line just read. */
+    int copiedTotal;		/* Accumulates total length of input copied. */
+    int copiedNow;		/* How many bytes were copied from the
+                                 * current input buffer? */
+    int lineLen;		/* Length of line read, including the
+                                 * translated newline. If this is zero
+                                 * and neither EOF nor BLOCKED is set,
+                                 * the current line is empty. */
+    
+    chanPtr = (Channel *) chan;
+
+    lineLen = GetEOL(chanPtr);
+    if (lineLen < 0) {
+        return -1;
+    }
+    (void) Tcl_GetStringFromObj(objPtr, &offset);
+    Tcl_SetObjLength(objPtr, lineLen + offset);
+    buf = Tcl_GetStringFromObj(objPtr, NULL) + offset;
+
+    for (copiedTotal = 0; copiedTotal < lineLen; copiedTotal += copiedNow) {
+        copiedNow = CopyAndTranslateBuffer(chanPtr, buf + copiedTotal,
+                lineLen - copiedTotal);
+    }
+    if ((copiedTotal > 0) && (buf[copiedTotal - 1] == '\n')) {
+        copiedTotal--;
+    }
+    Tcl_SetObjLength(objPtr, copiedTotal + offset);
+    return copiedTotal;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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. */
+    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. */
+    ChannelBuffer *bufPtr;	/* Buffer to contain the data. */
+    int i;
+
+    chanPtr = (Channel *) chan;
+
+    /*
+     * Check for unreported error.
+     */
+
+    if (chanPtr->unreportedError != 0) {
+        Tcl_SetErrno(chanPtr->unreportedError);
+        chanPtr->unreportedError = 0;
+        return -1;
+    }
+
+    /*
+     * Punt if the channel is not opened for reading.
+     */
+
+    if (!(chanPtr->flags & TCL_READABLE)) {
+        Tcl_SetErrno(EACCES);
+        return -1;
+    }
+
+    /*
+     * If the channel is in the middle of a background copy, fail.
+     */
+
+    if (chanPtr->csPtr) {
+	Tcl_SetErrno(EBUSY);
+	return -1;
+    }
+
+    /*
+     * 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 (chanPtr->flags & CHANNEL_STICKY_EOF) {
+        return len;
+    }
+    chanPtr->flags &= (~(CHANNEL_BLOCKED | CHANNEL_EOF));
+
+    bufPtr = (ChannelBuffer *) ckalloc((unsigned)
+            (CHANNELBUFFER_HEADER_SIZE + len));
+    for (i = 0; i < len; i++) {
+        bufPtr->buf[i] = str[i];
+    }
+    bufPtr->bufSize = len;
+    bufPtr->nextAdded = len;
+    bufPtr->nextRemoved = 0;
+
+    if (chanPtr->inQueueHead == (ChannelBuffer *) NULL) {
+        bufPtr->nextPtr = (ChannelBuffer *) NULL;
+        chanPtr->inQueueHead = bufPtr;
+        chanPtr->inQueueTail = bufPtr;
+    } else if (atEnd) {
+        bufPtr->nextPtr = (ChannelBuffer *) NULL;
+        chanPtr->inQueueTail->nextPtr = bufPtr;
+        chanPtr->inQueueTail = bufPtr;
+    } else {
+        bufPtr->nextPtr = chanPtr->inQueueHead;
+        chanPtr->inQueueHead = bufPtr;
+    }
+
+    return len;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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.
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+Tcl_Seek(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? */
+{
+    Channel *chanPtr;		/* The real IO channel. */
+    ChannelBuffer *bufPtr;
+    int inputBuffered, outputBuffered;
+    int result;			/* Of device driver operations. */
+    int 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. */
+
+    chanPtr = (Channel *) chan;
+
+    /*
+     * Check for unreported error.
+     */
+
+    if (chanPtr->unreportedError != 0) {
+        Tcl_SetErrno(chanPtr->unreportedError);
+        chanPtr->unreportedError = 0;
+        return -1;
+    }
+
+    /*
+     * Disallow seek on channels that are open for neither writing nor
+     * reading (e.g. socket server channels).
+     */
+
+    if (!(chanPtr->flags & (TCL_WRITABLE|TCL_READABLE))) {
+        Tcl_SetErrno(EACCES);
+        return -1;
+    }
+
+    /*
+     * If the channel is in the middle of a background copy, fail.
+     */
+
+    if (chanPtr->csPtr) {
+	Tcl_SetErrno(EBUSY);
+	return -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,chanPtr)) return -1;
+
+    /*
+     * 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 -1;
+    }
+
+    /*
+     * Compute how much input and output is buffered. If both input and
+     * output is buffered, cannot compute the current position.
+     */
+
+    for (bufPtr = chanPtr->inQueueHead, inputBuffered = 0;
+             bufPtr != (ChannelBuffer *) NULL;
+             bufPtr = bufPtr->nextPtr) {
+        inputBuffered += (bufPtr->nextAdded - bufPtr->nextRemoved);
+    }
+    for (bufPtr = chanPtr->outQueueHead, outputBuffered = 0;
+             bufPtr != (ChannelBuffer *) NULL;
+             bufPtr = bufPtr->nextPtr) {
+        outputBuffered += (bufPtr->nextAdded - bufPtr->nextRemoved);
+    }
+    if ((chanPtr->curOutPtr != (ChannelBuffer *) NULL) &&
+           (chanPtr->curOutPtr->nextAdded > chanPtr->curOutPtr->nextRemoved)) {
+        chanPtr->flags |= BUFFER_READY;
+        outputBuffered +=
+            (chanPtr->curOutPtr->nextAdded - chanPtr->curOutPtr->nextRemoved);
+    }
+
+    if ((inputBuffered != 0) && (outputBuffered != 0)) {
+        Tcl_SetErrno(EFAULT);
+        return -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(chanPtr, 0);
+
+    /*
+     * Reset EOF and BLOCKED flags. We invalidate them by moving the
+     * access point. Also clear CR related flags.
+     */
+
+    chanPtr->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 (chanPtr->flags & CHANNEL_NONBLOCKING) {
+        wasAsync = 1;
+        result = 0;
+        if (chanPtr->typePtr->blockModeProc != NULL) {
+            result = (chanPtr->typePtr->blockModeProc) (chanPtr->instanceData,
+                    TCL_MODE_BLOCKING);
+        }
+        if (result != 0) {
+            Tcl_SetErrno(result);
+            return -1;
+        }
+        chanPtr->flags &= (~(CHANNEL_NONBLOCKING));
+        if (chanPtr->flags & BG_FLUSH_SCHEDULED) {
+            chanPtr->flags &= (~(BG_FLUSH_SCHEDULED));
+        }
+    }
+    
+    /*
+     * 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.
+         */
+
+        curPos = (chanPtr->typePtr->seekProc) (chanPtr->instanceData,
+                (long) offset, mode, &result);
+        if (curPos == -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) {
+        chanPtr->flags |= CHANNEL_NONBLOCKING;
+        result = 0;
+        if (chanPtr->typePtr->blockModeProc != NULL) {
+            result = (chanPtr->typePtr->blockModeProc) (chanPtr->instanceData,
+                    TCL_MODE_NONBLOCKING);
+        }
+        if (result != 0) {
+            Tcl_SetErrno(result);
+            return -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.
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+Tcl_Tell(chan)
+    Tcl_Channel chan;			/* The channel to return pos for. */
+{
+    Channel *chanPtr;			/* The actual channel to tell on. */
+    ChannelBuffer *bufPtr;
+    int inputBuffered, outputBuffered;
+    int result;				/* Of calling device driver. */
+    int curPos;				/* Position on device. */
+
+    chanPtr = (Channel *) chan;
+
+    /*
+     * Check for unreported error.
+     */
+
+    if (chanPtr->unreportedError != 0) {
+        Tcl_SetErrno(chanPtr->unreportedError);
+        chanPtr->unreportedError = 0;
+        return -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,chanPtr)) return -1;
+
+    /*
+     * Disallow tell on channels that are open for neither
+     * writing nor reading (e.g. socket server channels).
+     */
+
+    if (!(chanPtr->flags & (TCL_WRITABLE|TCL_READABLE))) {
+        Tcl_SetErrno(EACCES);
+        return -1;
+    }
+
+    /*
+     * If the channel is in the middle of a background copy, fail.
+     */
+
+    if (chanPtr->csPtr) {
+	Tcl_SetErrno(EBUSY);
+	return -1;
+    }
+
+    /*
+     * 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 -1;
+    }
+
+    /*
+     * Compute how much input and output is buffered. If both input and
+     * output is buffered, cannot compute the current position.
+     */
+
+    for (bufPtr = chanPtr->inQueueHead, inputBuffered = 0;
+             bufPtr != (ChannelBuffer *) NULL;
+             bufPtr = bufPtr->nextPtr) {
+        inputBuffered += (bufPtr->nextAdded - bufPtr->nextRemoved);
+    }
+    for (bufPtr = chanPtr->outQueueHead, outputBuffered = 0;
+             bufPtr != (ChannelBuffer *) NULL;
+             bufPtr = bufPtr->nextPtr) {
+        outputBuffered += (bufPtr->nextAdded - bufPtr->nextRemoved);
+    }
+    if ((chanPtr->curOutPtr != (ChannelBuffer *) NULL) &&
+           (chanPtr->curOutPtr->nextAdded > chanPtr->curOutPtr->nextRemoved)) {
+        chanPtr->flags |= BUFFER_READY;
+        outputBuffered +=
+            (chanPtr->curOutPtr->nextAdded - chanPtr->curOutPtr->nextRemoved);
+    }
+
+    if ((inputBuffered != 0) && (outputBuffered != 0)) {
+        Tcl_SetErrno(EFAULT);
+        return -1;
+    }
+
+    /*
+     * Get the current position in the device and compute the position
+     * where the next character will be read or written.
+     */
+
+    curPos = (chanPtr->typePtr->seekProc) (chanPtr->instanceData,
+            (long) 0, SEEK_CUR, &result);
+    if (curPos == -1) {
+        Tcl_SetErrno(result);
+        return -1;
+    }
+    if (inputBuffered != 0) {
+        return (curPos - inputBuffered);
+    }
+    return (curPos + outputBuffered);
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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? */
+{
+    Channel *chanPtr;		/* The real channel structure. */
+
+    chanPtr = (Channel *) chan;
+    return ((chanPtr->flags & CHANNEL_STICKY_EOF) ||
+            ((chanPtr->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? */
+{
+    Channel *chanPtr;		/* The real channel structure. */
+
+    chanPtr = (Channel *) chan;
+    return (chanPtr->flags & CHANNEL_BLOCKED) ? 1 : 0;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * Tcl_InputBuffered --
+ *
+ *	Returns the number of bytes of input currently buffered in the
+ *	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. */
+{
+    Channel *chanPtr;
+    int bytesBuffered;
+    ChannelBuffer *bufPtr;
+
+    chanPtr = (Channel *) chan;
+    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. */
+{
+    Channel *chanPtr;
+    
+    /*
+     * 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;
+    }
+
+    chanPtr = (Channel *) chan;
+    chanPtr->bufSize = sz;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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. */
+{
+    Channel *chanPtr;
+
+    chanPtr = (Channel *) chan;
+    return chanPtr->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)*/
+    char *optionName;			/* 'bad option' name */
+    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 eofchar translation";
+	char **argv;
+	int  argc, i;
+	Tcl_DString ds;
+
+	Tcl_DStringInit(&ds);
+	Tcl_DStringAppend(&ds, (char *) 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) {
+	    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. */
+    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;
+    int flags;
+
+    /*
+     * If we are in the middle of a background copy, use the saved flags.
+     */
+
+    if (chanPtr->csPtr) {
+	if (chanPtr == chanPtr->csPtr->readPtr) {
+	    flags = chanPtr->csPtr->readFlags;
+	} else {
+	    flags = chanPtr->csPtr->writeFlags;
+	}
+    } else {
+	flags = chanPtr->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,chanPtr)) return TCL_ERROR;
+
+    /*
+     * 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, chanPtr->bufSize);
+        Tcl_DStringAppendElement(dsPtr, optionVal);
+        if (len > 0) {
+            return TCL_OK;
+        }
+    }
+    if ((len == 0) ||
+            ((len > 1) && (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 (chanPtr->inEofChar == 0) {
+                Tcl_DStringAppendElement(dsPtr, "");
+            } else {
+                char buf[4];
+
+                sprintf(buf, "%c", chanPtr->inEofChar);
+                Tcl_DStringAppendElement(dsPtr, buf);
+            }
+        }
+        if (flags & TCL_WRITABLE) {
+            if (chanPtr->outEofChar == 0) {
+                Tcl_DStringAppendElement(dsPtr, "");
+            } else {
+                char buf[4];
+
+                sprintf(buf, "%c", chanPtr->outEofChar);
+                Tcl_DStringAppendElement(dsPtr, buf);
+            }
+        }
+        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 (chanPtr->inputTranslation == TCL_TRANSLATE_AUTO) {
+                Tcl_DStringAppendElement(dsPtr, "auto");
+            } else if (chanPtr->inputTranslation == TCL_TRANSLATE_CR) {
+                Tcl_DStringAppendElement(dsPtr, "cr");
+            } else if (chanPtr->inputTranslation == TCL_TRANSLATE_CRLF) {
+                Tcl_DStringAppendElement(dsPtr, "crlf");
+            } else {
+                Tcl_DStringAppendElement(dsPtr, "lf");
+            }
+        }
+        if (flags & TCL_WRITABLE) {
+            if (chanPtr->outputTranslation == TCL_TRANSLATE_AUTO) {
+                Tcl_DStringAppendElement(dsPtr, "auto");
+            } else if (chanPtr->outputTranslation == TCL_TRANSLATE_CR) {
+                Tcl_DStringAppendElement(dsPtr, "cr");
+            } else if (chanPtr->outputTranslation == TCL_TRANSLATE_CRLF) {
+                Tcl_DStringAppendElement(dsPtr, "crlf");
+            } else {
+                Tcl_DStringAppendElement(dsPtr, "lf");
+            }
+        }
+        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. Also sets interp->result on error 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. */
+    char *optionName;		/* Which option to set? */
+    char *newValue;		/* New value for option. */
+{
+    int newMode;		/* New (numeric) mode to sert. */
+    Channel *chanPtr;		/* The real IO channel. */
+    size_t len;			/* Length of optionName string. */
+    int argc;
+    char **argv;
+    
+    chanPtr = (Channel *) chan;
+
+    /*
+     * If the channel is in the middle of a background copy, fail.
+     */
+
+    if (chanPtr->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,chanPtr)) return TCL_ERROR;
+    
+    len = strlen(optionName);
+
+    if ((len > 2) && (optionName[1] == 'b') &&
+            (strncmp(optionName, "-blocking", len) == 0)) {
+        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);
+    }
+
+    if ((len > 7) && (optionName[1] == 'b') &&
+            (strncmp(optionName, "-buffering", len) == 0)) {
+        len = strlen(newValue);
+        if ((newValue[0] == 'f') && (strncmp(newValue, "full", len) == 0)) {
+            chanPtr->flags &=
+                (~(CHANNEL_UNBUFFERED|CHANNEL_LINEBUFFERED));
+        } else if ((newValue[0] == 'l') &&
+                (strncmp(newValue, "line", len) == 0)) {
+            chanPtr->flags &= (~(CHANNEL_UNBUFFERED));
+            chanPtr->flags |= CHANNEL_LINEBUFFERED;
+        } else if ((newValue[0] == 'n') &&
+                (strncmp(newValue, "none", len) == 0)) {
+            chanPtr->flags &= (~(CHANNEL_LINEBUFFERED));
+            chanPtr->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;
+    }
+
+    if ((len > 7) && (optionName[1] == 'b') &&
+            (strncmp(optionName, "-buffersize", len) == 0)) {
+        chanPtr->bufSize = atoi(newValue);
+        if ((chanPtr->bufSize < 10) || (chanPtr->bufSize > (1024 * 1024))) {
+            chanPtr->bufSize = CHANNELBUFFER_DEFAULT_SIZE;
+        }
+        return TCL_OK;
+    }
+    
+    if ((len > 1) && (optionName[1] == 'e') &&
+            (strncmp(optionName, "-eofchar", len) == 0)) {
+        if (Tcl_SplitList(interp, newValue, &argc, &argv) == TCL_ERROR) {
+            return TCL_ERROR;
+        }
+        if (argc == 0) {
+            chanPtr->inEofChar = 0;
+            chanPtr->outEofChar = 0;
+        } else if (argc == 1) {
+            if (chanPtr->flags & TCL_WRITABLE) {
+                chanPtr->outEofChar = (int) argv[0][0];
+            }
+            if (chanPtr->flags & TCL_READABLE) {
+                chanPtr->inEofChar = (int) argv[0][0];
+            }
+        } else if (argc != 2) {
+            if (interp) {
+                Tcl_AppendResult(interp,
+                        "bad value for -eofchar: should be a list of one or",
+                        " two elements", (char *) NULL);
+            }
+            ckfree((char *) argv);
+            return TCL_ERROR;
+        } else {
+            if (chanPtr->flags & TCL_READABLE) {
+                chanPtr->inEofChar = (int) argv[0][0];
+            }
+            if (chanPtr->flags & TCL_WRITABLE) {
+                chanPtr->outEofChar = (int) argv[1][0];
+            }
+        }
+        if (argv != (char **) NULL) {
+            ckfree((char *) argv);
+        }
+        return TCL_OK;
+    }
+
+    if ((len > 1) && (optionName[1] == 't') &&
+            (strncmp(optionName, "-translation", len) == 0)) {
+	char *readMode, *writeMode;
+
+        if (Tcl_SplitList(interp, newValue, &argc, &argv) == TCL_ERROR) {
+            return TCL_ERROR;
+        }
+
+        if (argc == 1) {
+	    readMode = (chanPtr->flags & TCL_READABLE) ? argv[0] : NULL;
+	    writeMode = (chanPtr->flags & TCL_WRITABLE) ? argv[0] : NULL;
+	} else if (argc == 2) {
+	    readMode = (chanPtr->flags & TCL_READABLE) ? argv[0] : NULL;
+	    writeMode = (chanPtr->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) {
+	    if (*readMode == '\0') {
+		newMode = chanPtr->inputTranslation;
+	    } else if (strcmp(readMode, "auto") == 0) {
+		newMode = TCL_TRANSLATE_AUTO;
+	    } else if (strcmp(readMode, "binary") == 0) {
+		chanPtr->inEofChar = 0;
+		newMode = TCL_TRANSLATE_LF;
+	    } else if (strcmp(readMode, "lf") == 0) {
+		newMode = TCL_TRANSLATE_LF;
+	    } else if (strcmp(readMode, "cr") == 0) {
+		newMode = TCL_TRANSLATE_CR;
+	    } else if (strcmp(readMode, "crlf") == 0) {
+		newMode = TCL_TRANSLATE_CRLF;
+	    } else if (strcmp(readMode, "platform") == 0) {
+		newMode = 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 (newMode != chanPtr->inputTranslation) {
+		chanPtr->inputTranslation = (Tcl_EolTranslation) newMode;
+		chanPtr->flags &= ~(INPUT_SAW_CR);
+		chanPtr->flags &= ~(CHANNEL_GETS_BLOCKED);
+		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(chanPtr->typePtr->typeName, "tcp") == 0) {
+		    chanPtr->outputTranslation = TCL_TRANSLATE_CRLF;
+		} else {
+		    chanPtr->outputTranslation = TCL_PLATFORM_TRANSLATION;
+		}
+	    } else if (strcmp(writeMode, "binary") == 0) {
+		chanPtr->outEofChar = 0;
+		chanPtr->outputTranslation = TCL_TRANSLATE_LF;
+	    } else if (strcmp(writeMode, "lf") == 0) {
+		chanPtr->outputTranslation = TCL_TRANSLATE_LF;
+	    } else if (strcmp(writeMode, "cr") == 0) {
+		chanPtr->outputTranslation = TCL_TRANSLATE_CR;
+	    } else if (strcmp(writeMode, "crlf") == 0) {
+		chanPtr->outputTranslation = TCL_TRANSLATE_CRLF;
+	    } else if (strcmp(writeMode, "platform") == 0) {
+		chanPtr->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;
+    }
+
+    if (chanPtr->typePtr->setOptionProc != (Tcl_DriverSetOptionProc *) NULL) {
+        return (chanPtr->typePtr->setOptionProc) (chanPtr->instanceData,
+                interp, optionName, newValue);
+    }
+    
+    return Tcl_BadChannelOption(interp, optionName, (char *) NULL);
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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;
+{
+    EventScriptRecord *sPtr, *prevPtr, *nextPtr;
+
+    /*
+     * Remove fileevent records on this channel that refer to the
+     * given interpreter.
+     */
+    
+    for (sPtr = chanPtr->scriptRecordPtr,
+             prevPtr = (EventScriptRecord *) NULL;
+             sPtr != (EventScriptRecord *) NULL;
+             sPtr = nextPtr) {
+        nextPtr = sPtr->nextPtr;
+        if (sPtr->interp == interp) {
+            if (prevPtr == (EventScriptRecord *) NULL) {
+                chanPtr->scriptRecordPtr = nextPtr;
+            } else {
+                prevPtr->nextPtr = nextPtr;
+            }
+
+            Tcl_DeleteChannelHandler((Tcl_Channel) chanPtr,
+                    ChannelEventScriptInvoker, (ClientData) sPtr);
+
+	    ckfree(sPtr->script);
+            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;
+    ChannelHandler *chPtr;
+    NextChannelHandler nh;
+
+    Tcl_Preserve((ClientData)chanPtr);
+
+    /*
+     * 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 ((chanPtr->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 = nestedHandlerPtr;
+    nestedHandlerPtr = &nh;
+    
+    for (chPtr = chanPtr->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.
+     */
+
+    if (chanPtr->typePtr != NULL) {
+	UpdateInterest(chanPtr);
+    }
+    Tcl_Release((ClientData)chanPtr);
+
+    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. */
+{
+    int mask = chanPtr->interestMask;
+
+    /*
+     * If there are flushed buffers waiting to be written, then
+     * we need to watch for the channel to become writable.
+     */
+
+    if (chanPtr->flags & BG_FLUSH_SCHEDULED) {
+	mask |= TCL_WRITABLE;
+    }
+
+    /*
+     * If there is data in the input queue, and we aren't blocked waiting for
+     * an EOL, 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 (!(chanPtr->flags & CHANNEL_GETS_BLOCKED)
+		&& (chanPtr->inQueueHead != (ChannelBuffer *) NULL)
+		&& (chanPtr->inQueueHead->nextRemoved <
+			chanPtr->inQueueHead->nextAdded)) {
+	    mask &= ~TCL_READABLE;
+	    if (!chanPtr->timer) {
+		chanPtr->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;
+
+    if (!(chanPtr->flags & CHANNEL_GETS_BLOCKED)
+	    && (chanPtr->interestMask & TCL_READABLE)
+	    && (chanPtr->inQueueHead != (ChannelBuffer *) NULL)
+	    && (chanPtr->inQueueHead->nextRemoved <
+		    chanPtr->inQueueHead->nextAdded)) {
+	/*
+	 * Restart the timer in case a channel handler reenters the
+	 * event loop before UpdateInterest gets called by Tcl_NotifyChannel.
+	 */
+
+	chanPtr->timer = Tcl_CreateTimerHandler(0, ChannelTimerProc,
+			(ClientData) chanPtr);
+	Tcl_NotifyChannel((Tcl_Channel)chanPtr, TCL_READABLE);
+ 
+   } else {
+	chanPtr->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;
+
+    chanPtr = (Channel *) chan;
+    
+    /*
+     * 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 = chanPtr->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 = chanPtr->chPtr;
+        chanPtr->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.
+     */
+    
+    chanPtr->interestMask = 0;
+    for (chPtr = chanPtr->chPtr;
+	 chPtr != (ChannelHandler *) NULL;
+	 chPtr = chPtr->nextPtr) {
+	chanPtr->interestMask |= chPtr->mask;
+    }
+
+    UpdateInterest(chanPtr);
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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. */
+    
+{
+    ChannelHandler *chPtr, *prevChPtr;
+    Channel *chanPtr;
+    NextChannelHandler *nhPtr;
+
+    chanPtr = (Channel *) chan;
+
+    /*
+     * Find the entry and the previous one in the list.
+     */
+
+    for (prevChPtr = (ChannelHandler *) NULL, chPtr = chanPtr->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 = 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) {
+        chanPtr->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_DeleteChanelHandler is called inside an event.
+     */
+
+    chanPtr->interestMask = 0;
+    for (chPtr = chanPtr->chPtr;
+             chPtr != (ChannelHandler *) NULL;
+             chPtr = chPtr->nextPtr) {
+        chanPtr->interestMask |= chPtr->mask;
+    }
+
+    UpdateInterest(chanPtr);
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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. */
+{
+    EventScriptRecord *esPtr, *prevEsPtr;
+
+    for (esPtr = chanPtr->scriptRecordPtr,
+             prevEsPtr = (EventScriptRecord *) NULL;
+             esPtr != (EventScriptRecord *) NULL;
+             prevEsPtr = esPtr, esPtr = esPtr->nextPtr) {
+        if ((esPtr->interp == interp) && (esPtr->mask == mask)) {
+            if (esPtr == chanPtr->scriptRecordPtr) {
+                chanPtr->scriptRecordPtr = esPtr->nextPtr;
+            } else {
+                prevEsPtr->nextPtr = esPtr->nextPtr;
+            }
+
+            Tcl_DeleteChannelHandler((Tcl_Channel) chanPtr,
+                    ChannelEventScriptInvoker, (ClientData) esPtr);
+            
+	    ckfree(esPtr->script);
+            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, script)
+    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. */
+    char *script;			/* A copy of this script is stored
+                                         * in the newly created record. */
+{
+    EventScriptRecord *esPtr;
+
+    for (esPtr = chanPtr->scriptRecordPtr;
+             esPtr != (EventScriptRecord *) NULL;
+             esPtr = esPtr->nextPtr) {
+        if ((esPtr->interp == interp) && (esPtr->mask == mask)) {
+	    ckfree(esPtr->script);
+            esPtr->script = (char *) NULL;
+            break;
+        }
+    }
+    if (esPtr == (EventScriptRecord *) NULL) {
+        esPtr = (EventScriptRecord *) ckalloc((unsigned)
+                sizeof(EventScriptRecord));
+        Tcl_CreateChannelHandler((Tcl_Channel) chanPtr, mask,
+                ChannelEventScriptInvoker, (ClientData) esPtr);
+        esPtr->nextPtr = chanPtr->scriptRecordPtr;
+        chanPtr->scriptRecordPtr = esPtr;
+    }
+    esPtr->chanPtr = chanPtr;
+    esPtr->interp = interp;
+    esPtr->mask = mask;
+    esPtr->script = ckalloc((unsigned) (strlen(script) + 1));
+    strcpy(esPtr->script, script);
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * ChannelEventScriptInvoker --
+ *
+ *	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.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static void
+ChannelEventScriptInvoker(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. */
+    char *script;		/* Script to eval. */
+    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;
+    script = esPtr->script;
+
+    /*
+     * 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_GlobalEval(interp, script);
+
+    /*
+     * 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_FileEventCmd --
+ *
+ *	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_FileEventCmd(clientData, interp, argc, argv)
+    ClientData clientData;		/* Not used. */
+    Tcl_Interp *interp;			/* Interpreter in which the channel
+                                         * for which to create the handler
+                                         * is found. */
+    int argc;				/* Number of arguments. */
+    char **argv;			/* Argument strings. */
+{
+    Channel *chanPtr;			/* The channel to create
+                                         * the handler for. */
+    Tcl_Channel chan;			/* The opaque type for the channel. */
+    int c;				/* First char of mode argument. */
+    int mask;				/* Mask for events of interest. */
+    size_t length;			/* Length of mode argument. */
+
+    /*
+     * Parse arguments.
+     */
+
+    if ((argc != 3) && (argc != 4)) {
+	Tcl_AppendResult(interp, "wrong # args: must be \"", argv[0],
+		" channelId event ?script?", (char *) NULL);
+	return TCL_ERROR;
+    }
+    c = argv[2][0];
+    length = strlen(argv[2]);
+    if ((c == 'r') && (strncmp(argv[2], "readable", length) == 0)) {
+        mask = TCL_READABLE;
+    } else if ((c == 'w') && (strncmp(argv[2], "writable", length) == 0)) {
+        mask = TCL_WRITABLE;
+    } else {
+	Tcl_AppendResult(interp, "bad event name \"", argv[2],
+		"\": must be readable or writable", (char *) NULL);
+	return TCL_ERROR;
+    }
+    chan = Tcl_GetChannel(interp, argv[1], NULL);
+    if (chan == (Tcl_Channel) NULL) {
+        return TCL_ERROR;
+    }
+    
+    chanPtr = (Channel *) chan;
+    if ((chanPtr->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 (argc == 3) {
+	EventScriptRecord *esPtr;
+	for (esPtr = chanPtr->scriptRecordPtr;
+             esPtr != (EventScriptRecord *) NULL;
+             esPtr = esPtr->nextPtr) {
+	    if ((esPtr->interp == interp) && (esPtr->mask == mask)) {
+		Tcl_SetResult(interp, esPtr->script, TCL_STATIC);
+		break;
+	    }
+	}
+        return TCL_OK;
+    }
+
+    /*
+     * If we are supposed to delete a stored script, do so.
+     */
+
+    if (argv[3][0] == 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, argv[3]);
+    
+    return TCL_OK;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TclTestChannelCmd --
+ *
+ *	Implements the Tcl "testchannel" debugging command and its
+ *	subcommands. This is part of the testing environment but must be
+ *	in this file instead of tclTest.c because it needs access to the
+ *	fields of struct Channel.
+ *
+ * Results:
+ *	A standard Tcl result.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+	/* ARGSUSED */
+int
+TclTestChannelCmd(clientData, interp, argc, argv)
+    ClientData clientData;	/* Not used. */
+    Tcl_Interp *interp;		/* Interpreter for result. */
+    int argc;			/* Count of additional args. */
+    char **argv;		/* Additional arg strings. */
+{
+    char *cmdName;		/* Sub command. */
+    Tcl_HashTable *hTblPtr;	/* Hash table of channels. */
+    Tcl_HashSearch hSearch;	/* Search variable. */
+    Tcl_HashEntry *hPtr;	/* Search variable. */
+    Channel *chanPtr;		/* The actual channel. */
+    Tcl_Channel chan;		/* The opaque type. */
+    size_t len;			/* Length of subcommand string. */
+    int IOQueued;		/* How much IO is queued inside channel? */
+    ChannelBuffer *bufPtr;	/* For iterating over queued IO. */
+    char buf[128];		/* For sprintf. */
+    
+    if (argc < 2) {
+        Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
+                " subcommand ?additional args..?\"", (char *) NULL);
+        return TCL_ERROR;
+    }
+    cmdName = argv[1];
+    len = strlen(cmdName);
+
+    chanPtr = (Channel *) NULL;
+    if (argc > 2) {
+        chan = Tcl_GetChannel(interp, argv[2], NULL);
+        if (chan == (Tcl_Channel) NULL) {
+            return TCL_ERROR;
+        }
+        chanPtr = (Channel *) chan;
+    }
+    
+    if ((cmdName[0] == 'i') && (strncmp(cmdName, "info", len) == 0)) {
+        if (argc != 3) {
+            Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
+                    " info channelName\"", (char *) NULL);
+            return TCL_ERROR;
+        }
+        Tcl_AppendElement(interp, argv[2]);
+        Tcl_AppendElement(interp, chanPtr->typePtr->typeName);
+        if (chanPtr->flags & TCL_READABLE) {
+            Tcl_AppendElement(interp, "read");
+        } else {
+            Tcl_AppendElement(interp, "");
+        }
+        if (chanPtr->flags & TCL_WRITABLE) {
+            Tcl_AppendElement(interp, "write");
+        } else {
+            Tcl_AppendElement(interp, "");
+        }
+        if (chanPtr->flags & CHANNEL_NONBLOCKING) {
+            Tcl_AppendElement(interp, "nonblocking");
+        } else {
+            Tcl_AppendElement(interp, "blocking");
+        }
+        if (chanPtr->flags & CHANNEL_LINEBUFFERED) {
+            Tcl_AppendElement(interp, "line");
+        } else if (chanPtr->flags & CHANNEL_UNBUFFERED) {
+            Tcl_AppendElement(interp, "none");
+        } else {
+            Tcl_AppendElement(interp, "full");
+        }
+        if (chanPtr->flags & BG_FLUSH_SCHEDULED) {
+            Tcl_AppendElement(interp, "async_flush");
+        } else {
+            Tcl_AppendElement(interp, "");
+        }
+        if (chanPtr->flags & CHANNEL_EOF) {
+            Tcl_AppendElement(interp, "eof");
+        } else {
+            Tcl_AppendElement(interp, "");
+        }
+        if (chanPtr->flags & CHANNEL_BLOCKED) {
+            Tcl_AppendElement(interp, "blocked");
+        } else {
+            Tcl_AppendElement(interp, "unblocked");
+        }
+        if (chanPtr->inputTranslation == TCL_TRANSLATE_AUTO) {
+            Tcl_AppendElement(interp, "auto");
+            if (chanPtr->flags & INPUT_SAW_CR) {
+                Tcl_AppendElement(interp, "saw_cr");
+            } else {
+                Tcl_AppendElement(interp, "");
+            }
+        } else if (chanPtr->inputTranslation == TCL_TRANSLATE_LF) {
+            Tcl_AppendElement(interp, "lf");
+            Tcl_AppendElement(interp, "");
+        } else if (chanPtr->inputTranslation == TCL_TRANSLATE_CR) {
+            Tcl_AppendElement(interp, "cr");
+            Tcl_AppendElement(interp, "");
+        } else if (chanPtr->inputTranslation == TCL_TRANSLATE_CRLF) {
+            Tcl_AppendElement(interp, "crlf");
+            if (chanPtr->flags & INPUT_SAW_CR) {
+                Tcl_AppendElement(interp, "queued_cr");
+            } else {
+                Tcl_AppendElement(interp, "");
+            }
+        }
+        if (chanPtr->outputTranslation == TCL_TRANSLATE_AUTO) {
+            Tcl_AppendElement(interp, "auto");
+        } else if (chanPtr->outputTranslation == TCL_TRANSLATE_LF) {
+            Tcl_AppendElement(interp, "lf");
+        } else if (chanPtr->outputTranslation == TCL_TRANSLATE_CR) {
+            Tcl_AppendElement(interp, "cr");
+        } else if (chanPtr->outputTranslation == TCL_TRANSLATE_CRLF) {
+            Tcl_AppendElement(interp, "crlf");
+        }
+        for (IOQueued = 0, bufPtr = chanPtr->inQueueHead;
+                 bufPtr != (ChannelBuffer *) NULL;
+                 bufPtr = bufPtr->nextPtr) {
+            IOQueued += bufPtr->nextAdded - bufPtr->nextRemoved;
+        }
+        TclFormatInt(buf, IOQueued);
+        Tcl_AppendElement(interp, buf);
+        
+        IOQueued = 0;
+        if (chanPtr->curOutPtr != (ChannelBuffer *) NULL) {
+            IOQueued = chanPtr->curOutPtr->nextAdded -
+                chanPtr->curOutPtr->nextRemoved;
+        }
+        for (bufPtr = chanPtr->outQueueHead;
+                 bufPtr != (ChannelBuffer *) NULL;
+                 bufPtr = bufPtr->nextPtr) {
+            IOQueued += (bufPtr->nextAdded - bufPtr->nextRemoved);
+        }
+        TclFormatInt(buf, IOQueued);
+        Tcl_AppendElement(interp, buf);
+        
+        TclFormatInt(buf, Tcl_Tell((Tcl_Channel) chanPtr));
+        Tcl_AppendElement(interp, buf);
+
+        TclFormatInt(buf, chanPtr->refCount);
+        Tcl_AppendElement(interp, buf);
+
+        return TCL_OK;
+    }
+
+    if ((cmdName[0] == 'i') &&
+            (strncmp(cmdName, "inputbuffered", len) == 0)) {
+        if (argc != 3) {
+            Tcl_AppendResult(interp, "channel name required",
+                    (char *) NULL);
+            return TCL_ERROR;
+        }
+        
+        for (IOQueued = 0, bufPtr = chanPtr->inQueueHead;
+                 bufPtr != (ChannelBuffer *) NULL;
+                 bufPtr = bufPtr->nextPtr) {
+            IOQueued += bufPtr->nextAdded - bufPtr->nextRemoved;
+        }
+        sprintf(buf, "%d", IOQueued);
+        Tcl_AppendResult(interp, buf, (char *) NULL);
+        return TCL_OK;
+    }
+        
+    if ((cmdName[0] == 'm') && (strncmp(cmdName, "mode", len) == 0)) {
+        if (argc != 3) {
+            Tcl_AppendResult(interp, "channel name required",
+                    (char *) NULL);
+            return TCL_ERROR;
+        }
+        
+        if (chanPtr->flags & TCL_READABLE) {
+            Tcl_AppendElement(interp, "read");
+        } else {
+            Tcl_AppendElement(interp, "");
+        }
+        if (chanPtr->flags & TCL_WRITABLE) {
+            Tcl_AppendElement(interp, "write");
+        } else {
+            Tcl_AppendElement(interp, "");
+        }
+        return TCL_OK;
+    }
+    
+    if ((cmdName[0] == 'n') && (strncmp(cmdName, "name", len) == 0)) {
+        if (argc != 3) {
+            Tcl_AppendResult(interp, "channel name required",
+                    (char *) NULL);
+            return TCL_ERROR;
+        }
+        Tcl_AppendResult(interp, chanPtr->channelName, (char *) NULL);
+        return TCL_OK;
+    }
+    
+    if ((cmdName[0] == 'o') && (strncmp(cmdName, "open", len) == 0)) {
+        hTblPtr = (Tcl_HashTable *) Tcl_GetAssocData(interp, "tclIO", NULL);
+        if (hTblPtr == (Tcl_HashTable *) NULL) {
+            return TCL_OK;
+        }
+        for (hPtr = Tcl_FirstHashEntry(hTblPtr, &hSearch);
+                 hPtr != (Tcl_HashEntry *) NULL;
+                 hPtr = Tcl_NextHashEntry(&hSearch)) {
+            Tcl_AppendElement(interp, Tcl_GetHashKey(hTblPtr, hPtr));
+        }
+        return TCL_OK;
+    }
+
+    if ((cmdName[0] == 'o') &&
+            (strncmp(cmdName, "outputbuffered", len) == 0)) {
+        if (argc != 3) {
+            Tcl_AppendResult(interp, "channel name required",
+                    (char *) NULL);
+            return TCL_ERROR;
+        }
+        
+        IOQueued = 0;
+        if (chanPtr->curOutPtr != (ChannelBuffer *) NULL) {
+            IOQueued = chanPtr->curOutPtr->nextAdded -
+                chanPtr->curOutPtr->nextRemoved;
+        }
+        for (bufPtr = chanPtr->outQueueHead;
+                 bufPtr != (ChannelBuffer *) NULL;
+                 bufPtr = bufPtr->nextPtr) {
+            IOQueued += (bufPtr->nextAdded - bufPtr->nextRemoved);
+        }
+        sprintf(buf, "%d", IOQueued);
+        Tcl_AppendResult(interp, buf, (char *) NULL);
+        return TCL_OK;
+    }
+        
+    if ((cmdName[0] == 'q') &&
+            (strncmp(cmdName, "queuedcr", len) == 0)) {
+        if (argc != 3) {
+            Tcl_AppendResult(interp, "channel name required",
+                    (char *) NULL);
+            return TCL_ERROR;
+        }
+        
+        Tcl_AppendResult(interp,
+                (chanPtr->flags & INPUT_SAW_CR) ? "1" : "0",
+                (char *) NULL);
+        return TCL_OK;
+    }
+    
+    if ((cmdName[0] == 'r') && (strncmp(cmdName, "readable", len) == 0)) {
+        hTblPtr = (Tcl_HashTable *) Tcl_GetAssocData(interp, "tclIO", NULL);
+        if (hTblPtr == (Tcl_HashTable *) NULL) {
+            return TCL_OK;
+        }
+        for (hPtr = Tcl_FirstHashEntry(hTblPtr, &hSearch);
+                 hPtr != (Tcl_HashEntry *) NULL;
+                 hPtr = Tcl_NextHashEntry(&hSearch)) {
+            chanPtr = (Channel *) Tcl_GetHashValue(hPtr);
+            if (chanPtr->flags & TCL_READABLE) {
+                Tcl_AppendElement(interp, Tcl_GetHashKey(hTblPtr, hPtr));
+            }
+        }
+        return TCL_OK;
+    }
+
+    if ((cmdName[0] == 'r') && (strncmp(cmdName, "refcount", len) == 0)) {
+        if (argc != 3) {
+            Tcl_AppendResult(interp, "channel name required",
+                    (char *) NULL);
+            return TCL_ERROR;
+        }
+        
+        sprintf(buf, "%d", chanPtr->refCount);
+        Tcl_AppendResult(interp, buf, (char *) NULL);
+        return TCL_OK;
+    }
+    
+    if ((cmdName[0] == 't') && (strncmp(cmdName, "type", len) == 0)) {
+        if (argc != 3) {
+            Tcl_AppendResult(interp, "channel name required",
+                    (char *) NULL);
+            return TCL_ERROR;
+        }
+        Tcl_AppendResult(interp, chanPtr->typePtr->typeName, (char *) NULL);
+        return TCL_OK;
+    }
+    
+    if ((cmdName[0] == 'w') && (strncmp(cmdName, "writable", len) == 0)) {
+        hTblPtr = (Tcl_HashTable *) Tcl_GetAssocData(interp, "tclIO", NULL);
+        if (hTblPtr == (Tcl_HashTable *) NULL) {
+            return TCL_OK;
+        }
+        for (hPtr = Tcl_FirstHashEntry(hTblPtr, &hSearch);
+                 hPtr != (Tcl_HashEntry *) NULL;
+                 hPtr = Tcl_NextHashEntry(&hSearch)) {
+            chanPtr = (Channel *) Tcl_GetHashValue(hPtr);
+            if (chanPtr->flags & TCL_WRITABLE) {
+                Tcl_AppendElement(interp, Tcl_GetHashKey(hTblPtr, hPtr));
+            }
+        }
+        return TCL_OK;
+    }
+
+    Tcl_AppendResult(interp, "bad option \"", cmdName, "\": should be ",
+            "info, open, readable, or writable",
+            (char *) NULL);
+    return TCL_ERROR;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TclTestChannelEventCmd --
+ *
+ *	This procedure implements the "testchannelevent" command. It is
+ *	used to test the Tcl channel event mechanism. It is present in
+ *	this file instead of tclTest.c because it needs access to the
+ *	internal structure of the channel.
+ *
+ * Results:
+ *	A standard Tcl result.
+ *
+ * Side effects:
+ *	Creates, deletes and returns channel event handlers.
+ *
+ *----------------------------------------------------------------------
+ */
+
+	/* ARGSUSED */
+int
+TclTestChannelEventCmd(dummy, interp, argc, argv)
+    ClientData dummy;			/* Not used. */
+    Tcl_Interp *interp;			/* Current interpreter. */
+    int argc;				/* Number of arguments. */
+    char **argv;			/* Argument strings. */
+{
+    Channel *chanPtr;
+    EventScriptRecord *esPtr, *prevEsPtr, *nextEsPtr;
+    char *cmd;
+    int index, i, mask, len;
+
+    if ((argc < 3) || (argc > 5)) {
+        Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
+                " channelName cmd ?arg1? ?arg2?\"", (char *) NULL);
+        return TCL_ERROR;
+    }
+    chanPtr = (Channel *) Tcl_GetChannel(interp, argv[1], NULL);
+    if (chanPtr == (Channel *) NULL) {
+        return TCL_ERROR;
+    }
+    cmd = argv[2];
+    len = strlen(cmd);
+    if ((cmd[0] == 'a') && (strncmp(cmd, "add", (unsigned) len) == 0)) {
+        if (argc != 5) {
+            Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
+                    " channelName add eventSpec script\"", (char *) NULL);
+            return TCL_ERROR;
+        }
+        if (strcmp(argv[3], "readable") == 0) {
+            mask = TCL_READABLE;
+        } else if (strcmp(argv[3], "writable") == 0) {
+            mask = TCL_WRITABLE;
+        } else if (strcmp(argv[3], "none") == 0) {
+            mask = 0;
+	} else {
+            Tcl_AppendResult(interp, "bad event name \"", argv[3],
+                    "\": must be readable, writable, or none", (char *) NULL);
+            return TCL_ERROR;
+        }
+
+        esPtr = (EventScriptRecord *) ckalloc((unsigned)
+                sizeof(EventScriptRecord));
+        esPtr->nextPtr = chanPtr->scriptRecordPtr;
+        chanPtr->scriptRecordPtr = esPtr;
+        
+        esPtr->chanPtr = chanPtr;
+        esPtr->interp = interp;
+        esPtr->mask = mask;
+        esPtr->script = ckalloc((unsigned) (strlen(argv[4]) + 1));
+        strcpy(esPtr->script, argv[4]);
+
+        Tcl_CreateChannelHandler((Tcl_Channel) chanPtr, mask,
+                ChannelEventScriptInvoker, (ClientData) esPtr);
+        
+        return TCL_OK;
+    }
+
+    if ((cmd[0] == 'd') && (strncmp(cmd, "delete", (unsigned) len) == 0)) {
+        if (argc != 4) {
+            Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
+                    " channelName delete index\"", (char *) NULL);
+            return TCL_ERROR;
+        }
+        if (Tcl_GetInt(interp, argv[3], &index) == TCL_ERROR) {
+            return TCL_ERROR;
+        }
+        if (index < 0) {
+            Tcl_AppendResult(interp, "bad event index: ", argv[3],
+                    ": must be nonnegative", (char *) NULL);
+            return TCL_ERROR;
+        }
+        for (i = 0, esPtr = chanPtr->scriptRecordPtr;
+                 (i < index) && (esPtr != (EventScriptRecord *) NULL);
+                 i++, esPtr = esPtr->nextPtr) {
+	    /* Empty loop body. */
+        }
+        if (esPtr == (EventScriptRecord *) NULL) {
+            Tcl_AppendResult(interp, "bad event index ", argv[3],
+                    ": out of range", (char *) NULL);
+            return TCL_ERROR;
+        }
+        if (esPtr == chanPtr->scriptRecordPtr) {
+            chanPtr->scriptRecordPtr = esPtr->nextPtr;
+        } else {
+            for (prevEsPtr = chanPtr->scriptRecordPtr;
+                     (prevEsPtr != (EventScriptRecord *) NULL) &&
+                         (prevEsPtr->nextPtr != esPtr);
+                     prevEsPtr = prevEsPtr->nextPtr) {
+                /* Empty loop body. */
+            }
+            if (prevEsPtr == (EventScriptRecord *) NULL) {
+                panic("TclTestChannelEventCmd: damaged event script list");
+            }
+            prevEsPtr->nextPtr = esPtr->nextPtr;
+        }
+        Tcl_DeleteChannelHandler((Tcl_Channel) chanPtr,
+                ChannelEventScriptInvoker, (ClientData) esPtr);
+	ckfree(esPtr->script);
+        ckfree((char *) esPtr);
+
+        return TCL_OK;
+    }
+
+    if ((cmd[0] == 'l') && (strncmp(cmd, "list", (unsigned) len) == 0)) {
+        if (argc != 3) {
+            Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
+                    " channelName list\"", (char *) NULL);
+            return TCL_ERROR;
+        }
+        for (esPtr = chanPtr->scriptRecordPtr;
+                 esPtr != (EventScriptRecord *) NULL;
+                 esPtr = esPtr->nextPtr) {
+	    char *event;
+	    if (esPtr->mask) {
+		event = ((esPtr->mask == TCL_READABLE)
+			? "readable" : "writable");
+	    } else {
+		event = "none";
+	    }
+            Tcl_AppendElement(interp, event);
+            Tcl_AppendElement(interp, esPtr->script);
+        }
+        return TCL_OK;
+    }
+
+    if ((cmd[0] == 'r') && (strncmp(cmd, "removeall", (unsigned) len) == 0)) {
+        if (argc != 3) {
+            Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
+                    " channelName removeall\"", (char *) NULL);
+            return TCL_ERROR;
+        }
+        for (esPtr = chanPtr->scriptRecordPtr;
+                 esPtr != (EventScriptRecord *) NULL;
+                 esPtr = nextEsPtr) {
+            nextEsPtr = esPtr->nextPtr;
+            Tcl_DeleteChannelHandler((Tcl_Channel) chanPtr,
+                    ChannelEventScriptInvoker, (ClientData) esPtr);
+	    ckfree(esPtr->script);
+            ckfree((char *) esPtr);
+        }
+        chanPtr->scriptRecordPtr = (EventScriptRecord *) NULL;
+        return TCL_OK;
+    }
+
+    if  ((cmd[0] == 's') && (strncmp(cmd, "set", (unsigned) len) == 0)) {
+        if (argc != 5) {
+            Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
+                    " channelName delete index event\"", (char *) NULL);
+            return TCL_ERROR;
+        }
+        if (Tcl_GetInt(interp, argv[3], &index) == TCL_ERROR) {
+            return TCL_ERROR;
+        }
+        if (index < 0) {
+            Tcl_AppendResult(interp, "bad event index: ", argv[3],
+                    ": must be nonnegative", (char *) NULL);
+            return TCL_ERROR;
+        }
+        for (i = 0, esPtr = chanPtr->scriptRecordPtr;
+                 (i < index) && (esPtr != (EventScriptRecord *) NULL);
+                 i++, esPtr = esPtr->nextPtr) {
+	    /* Empty loop body. */
+        }
+        if (esPtr == (EventScriptRecord *) NULL) {
+            Tcl_AppendResult(interp, "bad event index ", argv[3],
+                    ": out of range", (char *) NULL);
+            return TCL_ERROR;
+        }
+
+        if (strcmp(argv[4], "readable") == 0) {
+            mask = TCL_READABLE;
+        } else if (strcmp(argv[4], "writable") == 0) {
+            mask = TCL_WRITABLE;
+        } else if (strcmp(argv[4], "none") == 0) {
+            mask = 0;
+	} else {
+            Tcl_AppendResult(interp, "bad event name \"", argv[4],
+                    "\": must be readable, writable, or none", (char *) NULL);
+            return TCL_ERROR;
+        }
+	esPtr->mask = mask;
+        Tcl_CreateChannelHandler((Tcl_Channel) chanPtr, mask,
+                ChannelEventScriptInvoker, (ClientData) esPtr);
+	return TCL_OK;
+    }    
+    Tcl_AppendResult(interp, "bad command ", cmd, ", must be one of ",
+            "add, delete, list, set, or removeall", (char *) NULL);
+    return TCL_ERROR;
+
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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;
+    int readFlags, writeFlags;
+    CopyState *csPtr;
+    int nonBlocking = (cmdPtr) ? CHANNEL_NONBLOCKING : 0;
+
+    if (inPtr->csPtr) {
+	Tcl_AppendStringsToObj(Tcl_GetObjResult(interp), "channel \"",
+		Tcl_GetChannelName(inChan), "\" is busy", NULL);
+	return TCL_ERROR;
+    }
+    if (outPtr->csPtr) {
+	Tcl_AppendStringsToObj(Tcl_GetObjResult(interp), "channel \"",
+		Tcl_GetChannelName(outChan), "\" is busy", NULL);
+	return TCL_ERROR;
+    }
+
+    readFlags = inPtr->flags;
+    writeFlags = outPtr->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_BLOCKING : TCL_MODE_NONBLOCKING)
+		    != 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.
+     */
+
+    outPtr->flags = (outPtr->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) + inPtr->bufSize);
+    csPtr->bufSize = inPtr->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;
+    inPtr->csPtr = csPtr;
+    outPtr->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;
+    Tcl_Channel inChan, outChan;
+    int result = TCL_OK;
+    int size;
+    int total;
+
+    inChan = (Tcl_Channel)csPtr->readPtr;
+    outChan = (Tcl_Channel)csPtr->writePtr;
+    interp = csPtr->interp;
+    cmdPtr = csPtr->cmdPtr;
+
+    /*
+     * Copy the data the slow way, using the translation mechanism.
+     */
+
+    while (csPtr->toRead != 0) {
+
+	/*
+	 * Check for unreported background errors.
+	 */
+
+	if (csPtr->readPtr->unreportedError != 0) {
+	    Tcl_SetErrno(csPtr->readPtr->unreportedError);
+	    csPtr->readPtr->unreportedError = 0;
+	    goto readError;
+	}
+	if (csPtr->writePtr->unreportedError != 0) {
+	    Tcl_SetErrno(csPtr->writePtr->unreportedError);
+	    csPtr->writePtr->unreportedError = 0;
+	    goto writeError;
+	}
+	
+	/*
+	 * Read up to bufSize bytes.
+	 */
+
+	if ((csPtr->toRead == -1)
+		|| (csPtr->toRead > csPtr->bufSize)) {
+	    size = csPtr->bufSize;
+	} else {
+	    size = csPtr->toRead;
+	}
+	size = DoRead(csPtr->readPtr, csPtr->buffer, size);
+
+	if (size < 0) {
+	    readError:
+	    errObj = Tcl_NewObj();
+	    Tcl_AppendStringsToObj(errObj, "error reading \"",
+		    Tcl_GetChannelName(inChan), "\": ",
+		    Tcl_PosixError(interp), (char *) NULL);
+	    break;
+	} else if (size == 0) {
+	    /*
+	     * 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 (Tcl_Eof(inChan)) {
+		break;
+	    } else if (!(mask & TCL_READABLE)) {
+		if (mask & TCL_WRITABLE) {
+		    Tcl_DeleteChannelHandler(outChan, CopyEventProc,
+			    (ClientData) csPtr);
+		}
+		Tcl_CreateChannelHandler(inChan, TCL_READABLE,
+			CopyEventProc, (ClientData) csPtr);
+	    }
+	    return TCL_OK;
+	}
+
+	/*
+	 * Now write the buffer out.
+	 */
+
+	size = DoWrite(csPtr->writePtr, csPtr->buffer, size);
+	if (size < 0) {
+	    writeError:
+	    errObj = Tcl_NewObj();
+	    Tcl_AppendStringsToObj(errObj, "error writing \"",
+		    Tcl_GetChannelName(outChan), "\": ",
+		    Tcl_PosixError(interp), (char *) NULL);
+	    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.
+	 */
+
+	if (csPtr->writePtr->flags & BG_FLUSH_SCHEDULED) {
+	    if (!(mask & TCL_WRITABLE)) {
+		if (mask & TCL_READABLE) {
+		    Tcl_DeleteChannelHandler(outChan, CopyEventProc,
+			    (ClientData) csPtr);
+		}
+		Tcl_CreateChannelHandler(outChan, TCL_WRITABLE,
+			CopyEventProc, (ClientData) csPtr);
+	    }
+	    return TCL_OK;
+	}
+
+	/*
+	 * Update the current byte count if we care.
+	 */
+
+	if (csPtr->toRead != -1) {
+	    csPtr->toRead -= size;
+	}
+	csPtr->total += size;
+
+	/*
+	 * 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);
+	    }
+	    return TCL_OK;
+	}
+    }
+
+    /*
+     * 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_GlobalEvalObj(interp, cmdPtr) != TCL_OK) {
+	    Tcl_BackgroundError(interp);
+	    result = TCL_ERROR;
+	}
+	Tcl_DecrRefCount(cmdPtr);
+	Tcl_Release((ClientData) interp);
+    } else {
+	StopCopy(csPtr);
+	if (errObj) {
+	    Tcl_SetObjResult(interp, errObj);
+	    result = TCL_ERROR;
+	} else {
+	    Tcl_ResetResult(interp);
+	    Tcl_SetIntObj(Tcl_GetObjResult(interp), total);
+	}
+    }
+    return result;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * 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 . */
+{
+    int nonBlocking;
+
+    if (!csPtr) {
+	return;
+    }
+
+    /*
+     * Restore the old blocking mode and output buffering mode.
+     */
+
+    nonBlocking = (csPtr->readFlags & CHANNEL_NONBLOCKING);
+    if (nonBlocking != (csPtr->readPtr->flags & CHANNEL_NONBLOCKING)) {
+	SetBlockMode(NULL, csPtr->readPtr,
+		nonBlocking ? TCL_MODE_NONBLOCKING : TCL_MODE_BLOCKING);
+    }
+    if (csPtr->writePtr != csPtr->writePtr) {
+	if (nonBlocking != (csPtr->writePtr->flags & CHANNEL_NONBLOCKING)) {
+	    SetBlockMode(NULL, csPtr->writePtr,
+		    nonBlocking ? TCL_MODE_NONBLOCKING : TCL_MODE_BLOCKING);
+	}
+    }
+    csPtr->writePtr->flags &= ~(CHANNEL_LINEBUFFERED | CHANNEL_UNBUFFERED);
+    csPtr->writePtr->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);
+	}
+        Tcl_DecrRefCount(csPtr->cmdPtr);
+    }
+    csPtr->readPtr->csPtr = NULL;
+    csPtr->writePtr->csPtr = NULL;
+    ckfree((char*) csPtr);
+}