path: root/generic/tclIOCmd.c

/* 
 * tclIOCmd.c --
 *
 *	Contains the definitions of most of the Tcl commands relating to IO.
 *
 * Copyright (c) 1995-1997 Sun Microsystems, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution
 * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 *
 * RCS: @(#) $Id: tclIOCmd.c,v 1.27 2005/06/07 10:05:00 dkf Exp $
 */

#include "tclInt.h"

/*
 * Callback structure for accept callback in a TCP server.
 */

typedef struct AcceptCallback {
    char *script;			/* Script to invoke. */
    Tcl_Interp *interp;			/* Interpreter in which to run it. */
} AcceptCallback;

/*
 * Static functions for this file:
 */

static void	AcceptCallbackProc _ANSI_ARGS_((ClientData callbackData,
	            Tcl_Channel chan, char *address, int port));
static void	RegisterTcpServerInterpCleanup _ANSI_ARGS_((Tcl_Interp *interp,
	            AcceptCallback *acceptCallbackPtr));
static void	TcpAcceptCallbacksDeleteProc _ANSI_ARGS_((
		    ClientData clientData, Tcl_Interp *interp));
static void	TcpServerCloseProc _ANSI_ARGS_((ClientData callbackData));
static void	UnregisterTcpServerInterpCleanupProc _ANSI_ARGS_((
		    Tcl_Interp *interp, AcceptCallback *acceptCallbackPtr));

/*
 *----------------------------------------------------------------------
 *
 * Tcl_PutsObjCmd --
 *
 *	This procedure is invoked to process the "puts" Tcl command.
 *	See the user documentation for details on what it does.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	Produces output on a channel.
 *
 *----------------------------------------------------------------------
 */

	/* ARGSUSED */
int
Tcl_PutsObjCmd(dummy, interp, objc, objv)
    ClientData dummy;		/* Not used. */
    Tcl_Interp *interp;		/* Current interpreter. */
    int objc;			/* Number of arguments. */
    Tcl_Obj *CONST objv[];	/* Argument objects. */
{
    Tcl_Channel chan;			/* The channel to puts on. */
    Tcl_Obj *string;			/* String to write. */
    int newline;			/* Add a newline at end? */
    char *channelId;			/* Name of channel for puts. */
    int result;				/* Result of puts operation. */
    int mode;				/* Mode in which channel is opened. */

    switch (objc) {
    case 2: /* puts $x */
	string = objv[1];
	newline = 1;
	channelId = "stdout";
	break;

    case 3: /* puts -nonewline $x  or  puts $chan $x */ 
	if (strcmp(Tcl_GetString(objv[1]), "-nonewline") == 0) {
	    newline = 0;
	    channelId = "stdout";
	} else {
	    newline = 1;
	    channelId = Tcl_GetString(objv[1]);
	}
	string = objv[2];
	break;

    case 4: /* puts -nonewline $chan $x  or  puts $chan $x nonewline */
	if (strcmp(Tcl_GetString(objv[1]), "-nonewline") == 0) {
	    channelId = Tcl_GetString(objv[2]);
	    string = objv[3];
	} else {
	    /*
	     * The code below provides backwards compatibility with an
	     * old form of the command that is no longer recommended
	     * or documented.
	     */

	    char *arg;
	    int length;

	    arg = Tcl_GetStringFromObj(objv[3], &length);
	    if ((length != 9) || (strncmp(arg, "nonewline", (size_t) length) != 0)) {
		Tcl_AppendResult(interp, "bad argument \"", arg,
				 "\": should be \"nonewline\"",
				 (char *) NULL);
		return TCL_ERROR;
	    }
	    channelId = Tcl_GetString(objv[1]);
	    string = objv[2];
	}
	newline = 0;
	break;

    default: /* puts  or  puts some bad number of arguments... */
	Tcl_WrongNumArgs(interp, 1, objv, "?-nonewline? ?channelId? string");
	return TCL_ERROR;
    }

    chan = Tcl_GetChannel(interp, channelId, &mode);
    if (chan == (Tcl_Channel) NULL) {
        return TCL_ERROR;
    }
    if ((mode & TCL_WRITABLE) == 0) {
	Tcl_AppendResult(interp, "channel \"", channelId,
                "\" wasn't opened for writing", (char *) NULL);
        return TCL_ERROR;
    }

    result = Tcl_WriteObj(chan, string);
    if (result < 0) {
        goto error;
    }
    if (newline != 0) {
        result = Tcl_WriteChars(chan, "\n", 1);
        if (result < 0) {
            goto error;
        }
    }
    return TCL_OK;

    error:
    Tcl_AppendResult(interp, "error writing \"", channelId, "\": ",
	    Tcl_PosixError(interp), (char *) NULL);
    return TCL_ERROR;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_FlushObjCmd --
 *
 *	This procedure is called to process the Tcl "flush" command.
 *	See the user documentation for details on what it does.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	May cause output to appear on the specified channel.
 *
 *----------------------------------------------------------------------
 */

	/* ARGSUSED */
int
Tcl_FlushObjCmd(dummy, interp, objc, objv)
    ClientData dummy;		/* Not used. */
    Tcl_Interp *interp;		/* Current interpreter. */
    int objc;			/* Number of arguments. */
    Tcl_Obj *CONST objv[];	/* Argument objects. */
{
    Tcl_Channel chan;			/* The channel to flush on. */
    char *channelId;
    int mode;

    if (objc != 2) {
	Tcl_WrongNumArgs(interp, 1, objv, "channelId");
	return TCL_ERROR;
    }
    channelId = Tcl_GetString(objv[1]);
    chan = Tcl_GetChannel(interp, channelId, &mode);
    if (chan == (Tcl_Channel) NULL) {
	return TCL_ERROR;
    }
    if ((mode & TCL_WRITABLE) == 0) {
	Tcl_AppendResult(interp, "channel \"", channelId,
		"\" wasn't opened for writing", (char *) NULL);
        return TCL_ERROR;
    }
    
    if (Tcl_Flush(chan) != TCL_OK) {
	Tcl_AppendResult(interp, "error flushing \"", channelId, "\": ",
		Tcl_PosixError(interp), (char *) NULL);
	return TCL_ERROR;
    }
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetsObjCmd --
 *
 *	This procedure is called to process the Tcl "gets" command.
 *	See the user documentation for details on what it does.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	May consume input from channel.
 *
 *----------------------------------------------------------------------
 */

	/* ARGSUSED */
int
Tcl_GetsObjCmd(dummy, interp, objc, objv)
    ClientData dummy;		/* Not used. */
    Tcl_Interp *interp;		/* Current interpreter. */
    int objc;			/* Number of arguments. */
    Tcl_Obj *CONST objv[];	/* Argument objects. */
{
    Tcl_Channel chan;			/* The channel to read from. */
    int lineLen;			/* Length of line just read. */
    int mode;				/* Mode in which channel is opened. */
    char *name;
    Tcl_Obj *linePtr;

    if ((objc != 2) && (objc != 3)) {
	Tcl_WrongNumArgs(interp, 1, objv, "channelId ?varName?");
	return TCL_ERROR;
    }
    name = Tcl_GetString(objv[1]);
    chan = Tcl_GetChannel(interp, name, &mode);
    if (chan == (Tcl_Channel) NULL) {
	return TCL_ERROR;
    }
    if ((mode & TCL_READABLE) == 0) {
	Tcl_AppendResult(interp, "channel \"", name,
		"\" wasn't opened for reading", (char *) NULL);
        return TCL_ERROR;
    }

    linePtr = Tcl_NewObj();

    lineLen = Tcl_GetsObj(chan, linePtr);
    if (lineLen < 0) {
        if (!Tcl_Eof(chan) && !Tcl_InputBlocked(chan)) {
	    Tcl_DecrRefCount(linePtr);
	    Tcl_ResetResult(interp);
	    Tcl_AppendResult(interp, "error reading \"", name, "\": ",
		    Tcl_PosixError(interp), (char *) NULL);
            return TCL_ERROR;
        }
        lineLen = -1;
    }
    if (objc == 3) {
	if (Tcl_ObjSetVar2(interp, objv[2], NULL, linePtr,
		TCL_LEAVE_ERR_MSG) == NULL) {
	    Tcl_DecrRefCount(linePtr);
            return TCL_ERROR;
        }
	Tcl_SetObjResult(interp, Tcl_NewIntObj(lineLen));
        return TCL_OK;
    } else {
	Tcl_SetObjResult(interp, linePtr);
    }
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ReadObjCmd --
 *
 *	This procedure is invoked to process the Tcl "read" command.
 *	See the user documentation for details on what it does.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	May consume input from channel.
 *
 *----------------------------------------------------------------------
 */

	/* ARGSUSED */
int
Tcl_ReadObjCmd(dummy, interp, objc, objv)
    ClientData dummy;		/* Not used. */
    Tcl_Interp *interp;		/* Current interpreter. */
    int objc;			/* Number of arguments. */
    Tcl_Obj *CONST objv[];	/* Argument objects. */
{
    Tcl_Channel chan;		/* The channel to read from. */
    int newline, i;		/* Discard newline at end? */
    int toRead;			/* How many bytes to read? */
    int charactersRead;		/* How many characters were read? */
    int mode;			/* Mode in which channel is opened. */
    char *name;
    Tcl_Obj *resultPtr;

    if ((objc != 2) && (objc != 3)) {
	Interp *iPtr;

      argerror:
	iPtr = (Interp *) interp;
	Tcl_WrongNumArgs(interp, 1, objv, "channelId ?numChars?");
	/*
	 * Do not append directly; that makes ensembles using this
	 * command as a subcommand produce the wrong message.
	 */
	iPtr->flags |= INTERP_ALTERNATE_WRONG_ARGS;
	Tcl_WrongNumArgs(interp, 1, objv, "?-nonewline? channelId");
	iPtr->flags &= ~INTERP_ALTERNATE_WRONG_ARGS;
	return TCL_ERROR;
    }

    i = 1;
    newline = 0;
    if (strcmp(Tcl_GetString(objv[1]), "-nonewline") == 0) {
	newline = 1;
	i++;
    }

    if (i == objc) {
        goto argerror;
    }

    name = Tcl_GetString(objv[i]);
    chan = Tcl_GetChannel(interp, name, &mode);
    if (chan == (Tcl_Channel) NULL) {
	return TCL_ERROR;
    }
    if ((mode & TCL_READABLE) == 0) {
	Tcl_AppendResult(interp, "channel \"", name, 
                "\" wasn't opened for reading", (char *) NULL);
        return TCL_ERROR;
    }
    i++;	/* Consumed channel name. */

    /*
     * Compute how many bytes to read, and see whether the final
     * newline should be dropped.
     */

    toRead = -1;
    if (i < objc) {
	char *arg;
	
	arg = Tcl_GetString(objv[i]);
	if (isdigit(UCHAR(arg[0]))) { /* INTL: digit */
	    if (Tcl_GetIntFromObj(interp, objv[i], &toRead) != TCL_OK) {
                return TCL_ERROR;
	    }
	} else if (strcmp(arg, "nonewline") == 0) {
	    newline = 1;
	} else {
	    Tcl_AppendResult(interp, "bad argument \"", arg,
		    "\": should be \"nonewline\"", (char *) NULL);
	    return TCL_ERROR;
        }
    }

    resultPtr = Tcl_NewObj();
    Tcl_IncrRefCount(resultPtr);
    charactersRead = Tcl_ReadChars(chan, resultPtr, toRead, 0);
    if (charactersRead < 0) {
	Tcl_ResetResult(interp);
	Tcl_AppendResult(interp, "error reading \"", name, "\": ",
		Tcl_PosixError(interp), (char *) NULL);
	Tcl_DecrRefCount(resultPtr);
	return TCL_ERROR;
    }
    
    /*
     * If requested, remove the last newline in the channel if at EOF.
     */
    
    if ((charactersRead > 0) && (newline != 0)) {
	char *result;
	int length;

	result = Tcl_GetStringFromObj(resultPtr, &length);
	if (result[length - 1] == '\n') {
	    Tcl_SetObjLength(resultPtr, length - 1);
	}
    }
    Tcl_SetObjResult(interp, resultPtr);
    Tcl_DecrRefCount(resultPtr);
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_SeekObjCmd --
 *
 *	This procedure is invoked to process the Tcl "seek" command. See
 *	the user documentation for details on what it does.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	Moves the position of the access point on the specified channel.
 *	May flush queued output.
 *
 *----------------------------------------------------------------------
 */

	/* ARGSUSED */
int
Tcl_SeekObjCmd(clientData, interp, objc, objv)
    ClientData clientData;		/* Not used. */
    Tcl_Interp *interp;			/* Current interpreter. */
    int objc;				/* Number of arguments. */
    Tcl_Obj *CONST objv[];		/* Argument objects. */
{
    Tcl_Channel chan;			/* The channel to tell on. */
    Tcl_WideInt offset;			/* Where to seek? */
    int mode;				/* How to seek? */
    Tcl_WideInt result;			/* Of calling Tcl_Seek. */
    char *chanName;
    int optionIndex;
    static CONST char *originOptions[] = {
	"start", "current", "end", (char *) NULL
    };
    static int modeArray[] = {SEEK_SET, SEEK_CUR, SEEK_END};

    if ((objc != 3) && (objc != 4)) {
	Tcl_WrongNumArgs(interp, 1, objv, "channelId offset ?origin?");
	return TCL_ERROR;
    }
    chanName = Tcl_GetString(objv[1]);
    chan = Tcl_GetChannel(interp, chanName, NULL);
    if (chan == (Tcl_Channel) NULL) {
	return TCL_ERROR;
    }
    if (Tcl_GetWideIntFromObj(interp, objv[2], &offset) != TCL_OK) {
	return TCL_ERROR;
    }
    mode = SEEK_SET;
    if (objc == 4) {
	if (Tcl_GetIndexFromObj(interp, objv[3], originOptions, "origin", 0,
		&optionIndex) != TCL_OK) {
	    return TCL_ERROR;
	}
	mode = modeArray[optionIndex];
    }

    result = Tcl_Seek(chan, offset, mode);
    if (result == Tcl_LongAsWide(-1)) {
        Tcl_AppendResult(interp, "error during seek on \"", 
		chanName, "\": ", Tcl_PosixError(interp), (char *) NULL);
        return TCL_ERROR;
    }
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_TellObjCmd --
 *
 *	This procedure is invoked to process the Tcl "tell" command.
 *	See the user documentation for details on what it does.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

	/* ARGSUSED */
int
Tcl_TellObjCmd(clientData, interp, objc, objv)
    ClientData clientData;		/* Not used. */
    Tcl_Interp *interp;			/* Current interpreter. */
    int objc;				/* Number of arguments. */
    Tcl_Obj *CONST objv[];		/* Argument objects. */
{
    Tcl_Channel chan;			/* The channel to tell on. */
    char *chanName;

    if (objc != 2) {
	Tcl_WrongNumArgs(interp, 1, objv, "channelId");
	return TCL_ERROR;
    }
    /*
     * Try to find a channel with the right name and permissions in
     * the IO channel table of this interpreter.
     */
    
    chanName = Tcl_GetString(objv[1]);
    chan = Tcl_GetChannel(interp, chanName, NULL);
    if (chan == (Tcl_Channel) NULL) {
	return TCL_ERROR;
    }
    Tcl_SetObjResult(interp, Tcl_NewWideIntObj(Tcl_Tell(chan)));
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_CloseObjCmd --
 *
 *	This procedure is invoked to process the Tcl "close" command.
 *	See the user documentation for details on what it does.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	May discard queued input; may flush queued output.
 *
 *----------------------------------------------------------------------
 */

	/* ARGSUSED */
int
Tcl_CloseObjCmd(clientData, interp, objc, objv)
    ClientData clientData;	/* Not used. */
    Tcl_Interp *interp;		/* Current interpreter. */
    int objc;			/* Number of arguments. */
    Tcl_Obj *CONST objv[];	/* Argument objects. */
{
    Tcl_Channel chan;			/* The channel to close. */
    char *arg;

    if (objc != 2) {
	Tcl_WrongNumArgs(interp, 1, objv, "channelId");
	return TCL_ERROR;
    }

    arg = Tcl_GetString(objv[1]);
    chan = Tcl_GetChannel(interp, arg, NULL);
    if (chan == (Tcl_Channel) NULL) {
	return TCL_ERROR;
    }

    if (Tcl_UnregisterChannel(interp, chan) != TCL_OK) {
        /*
         * If there is an error message and it ends with a newline, remove
         * the newline. This is done for command pipeline channels where the
         * error output from the subprocesses is stored in interp's result.
         *
         * NOTE: This is likely to not have any effect on regular error
         * messages produced by drivers during the closing of a channel,
         * because the Tcl convention is that such error messages do not
         * have a terminating newline.
         */

	Tcl_Obj *resultPtr;
	char *string;
	int len;
	
	resultPtr = Tcl_GetObjResult(interp);
	if (Tcl_IsShared(resultPtr)) {
	    resultPtr = Tcl_DuplicateObj(resultPtr);
	    Tcl_SetObjResult(interp, resultPtr);
	}
	string = Tcl_GetStringFromObj(resultPtr, &len);
        if ((len > 0) && (string[len - 1] == '\n')) {
	    Tcl_SetObjLength(resultPtr, len - 1);
        }
        return TCL_ERROR;
    }

    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_FconfigureObjCmd --
 *
 *	This procedure is invoked to process the Tcl "fconfigure" command.
 *	See the user documentation for details on what it does.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	May modify the behavior of an IO channel.
 *
 *----------------------------------------------------------------------
 */

	/* ARGSUSED */
int
Tcl_FconfigureObjCmd(clientData, interp, objc, objv)
    ClientData clientData;		/* Not used. */
    Tcl_Interp *interp;			/* Current interpreter. */
    int objc;				/* Number of arguments. */
    Tcl_Obj *CONST objv[];		/* Argument objects. */
{
    char *chanName, *optionName, *valueName;
    Tcl_Channel chan;			/* The channel to set a mode on. */
    int i;				/* Iterate over arg-value pairs. */
    Tcl_DString ds;			/* DString to hold result of
                                         * calling Tcl_GetChannelOption. */

    if ((objc < 2) || (((objc % 2) == 1) && (objc != 3))) {
	Tcl_WrongNumArgs(interp, 1, objv,
		"channelId ?optionName? ?value? ?optionName value?...");
        return TCL_ERROR;
    }
    chanName = Tcl_GetString(objv[1]);
    chan = Tcl_GetChannel(interp, chanName, NULL);
    if (chan == (Tcl_Channel) NULL) {
        return TCL_ERROR;
    }
    if (objc == 2) {
        Tcl_DStringInit(&ds);
        if (Tcl_GetChannelOption(interp, chan, (char *) NULL, &ds) != TCL_OK) {
	    Tcl_DStringFree(&ds);
	    return TCL_ERROR;
        }
        Tcl_DStringResult(interp, &ds);
        return TCL_OK;
    }
    if (objc == 3) {
        Tcl_DStringInit(&ds);
	optionName = Tcl_GetString(objv[2]);
        if (Tcl_GetChannelOption(interp, chan, optionName, &ds) != TCL_OK) {
            Tcl_DStringFree(&ds);
            return TCL_ERROR;
        }
        Tcl_DStringResult(interp, &ds);
        return TCL_OK;
    }
    for (i = 3; i < objc; i += 2) {
	optionName = Tcl_GetString(objv[i-1]);
	valueName = Tcl_GetString(objv[i]);
        if (Tcl_SetChannelOption(interp, chan, optionName, valueName)
		!= TCL_OK) {
            return TCL_ERROR;
        }
    }
    return TCL_OK;
}

/*
 *---------------------------------------------------------------------------
 *
 * Tcl_EofObjCmd --
 *
 *	This procedure is invoked to process the Tcl "eof" command.
 *	See the user documentation for details on what it does.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	Sets interp's result to boolean true or false depending on whether
 *	the specified channel has an EOF condition.
 *
 *---------------------------------------------------------------------------
 */

	/* ARGSUSED */
int
Tcl_EofObjCmd(unused, interp, objc, objv)
    ClientData unused;		/* Not used. */
    Tcl_Interp *interp;		/* Current interpreter. */
    int objc;			/* Number of arguments. */
    Tcl_Obj *CONST objv[];	/* Argument objects. */
{
    Tcl_Channel chan;
    int dummy;
    char *arg;

    if (objc != 2) {
	Tcl_WrongNumArgs(interp, 1, objv, "channelId");
        return TCL_ERROR;
    }

    arg = Tcl_GetString(objv[1]);
    chan = Tcl_GetChannel(interp, arg, &dummy);
    if (chan == NULL) {
	return TCL_ERROR;
    }

    Tcl_SetObjResult(interp, Tcl_NewBooleanObj(Tcl_Eof(chan)));
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ExecObjCmd --
 *
 *	This procedure is invoked to process the "exec" Tcl command.
 *	See the user documentation for details on what it does.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	See the user documentation.
 *
 *----------------------------------------------------------------------
 */

	/* ARGSUSED */
int
Tcl_ExecObjCmd(dummy, interp, objc, objv)
    ClientData dummy;			/* Not used. */
    Tcl_Interp *interp;			/* Current interpreter. */
    int objc;				/* Number of arguments. */
    Tcl_Obj *CONST objv[];		/* Argument objects. */
{
    /*
     * This procedure generates an argv array for the string arguments. It
     * starts out with stack-allocated space but uses dynamically-allocated
     * storage if needed.
     */

#define NUM_ARGS 20
    Tcl_Obj *resultPtr;
    CONST char **argv;
    char *string;
    Tcl_Channel chan;
    CONST char *argStorage[NUM_ARGS];
    int argc, background, i, index, keepNewline, result, skip, length;
    static CONST char *options[] = {
	"-keepnewline",	"--",		NULL
    };
    enum options {
	EXEC_KEEPNEWLINE, EXEC_LAST
    };

    /*
     * Check for a leading "-keepnewline" argument.
     */

    keepNewline = 0;
    for (skip = 1; skip < objc; skip++) {
	string = Tcl_GetString(objv[skip]);
	if (string[0] != '-') {
	    break;
	}
	if (Tcl_GetIndexFromObj(interp, objv[skip], options, "switch",
		TCL_EXACT, &index) != TCL_OK) {
	    return TCL_ERROR;
	}
	if (index == EXEC_KEEPNEWLINE) {
	    keepNewline = 1;
	} else {
	    skip++;
	    break;
	}
    }
    if (objc <= skip) {
	Tcl_WrongNumArgs(interp, 1, objv, "?switches? arg ?arg ...?");
	return TCL_ERROR;
    }

    /*
     * See if the command is to be run in background.
     */

    background = 0;
    string = Tcl_GetString(objv[objc - 1]);
    if ((string[0] == '&') && (string[1] == '\0')) {
	objc--;
        background = 1;
    }

    /*
     * Create the string argument array "argv". Make sure argv is large
     * enough to hold the argc arguments plus 1 extra for the zero
     * end-of-argv word.
     */

    argv = argStorage;
    argc = objc - skip;
    if ((argc + 1) > sizeof(argv) / sizeof(argv[0])) {
	argv = (CONST char **) ckalloc((unsigned)(argc + 1) * sizeof(char *));
    }

    /*
     * Copy the string conversions of each (post option) object into the
     * argument vector.
     */

    for (i = 0; i < argc; i++) {
	argv[i] = Tcl_GetString(objv[i + skip]);
    }
    argv[argc] = NULL;
    chan = Tcl_OpenCommandChannel(interp, argc, argv,
            (background ? 0 : TCL_STDOUT | TCL_STDERR));

    /*
     * Free the argv array if malloc'ed storage was used.
     */

    if (argv != argStorage) {
	ckfree((char *)argv);
    }

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

    if (background) {
        /*
	 * Store the list of PIDs from the pipeline in interp's result and
	 * detach the PIDs (instead of waiting for them).
	 */

        TclGetAndDetachPids(interp, chan);
        if (Tcl_Close(interp, chan) != TCL_OK) {
	    return TCL_ERROR;
        }
	return TCL_OK;
    }

    resultPtr = Tcl_NewObj();
    if (Tcl_GetChannelHandle(chan, TCL_READABLE, NULL) == TCL_OK) {
	if (Tcl_ReadChars(chan, resultPtr, -1, 0) < 0) {
	    Tcl_ResetResult(interp);
	    Tcl_AppendResult(interp, "error reading output from command: ",
		    Tcl_PosixError(interp), (char *) NULL);
	    Tcl_DecrRefCount(resultPtr);
	    return TCL_ERROR;
	}
    }
    /*
     * If the process produced anything on stderr, it will have been
     * returned in the interpreter result.  It needs to be appended to
     * the result string.
     */

    result = Tcl_Close(interp, chan);
    Tcl_AppendObjToObj(resultPtr, Tcl_GetObjResult(interp));

    /*
     * If the last character of the result is a newline, then remove
     * the newline character.
     */
    
    if (keepNewline == 0) {
	string = Tcl_GetStringFromObj(resultPtr, &length);
	if ((length > 0) && (string[length - 1] == '\n')) {
	    Tcl_SetObjLength(resultPtr, length - 1);
	}
    }
    Tcl_SetObjResult(interp, resultPtr);

    return result;
}

/*
 *---------------------------------------------------------------------------
 *
 * Tcl_FblockedObjCmd --
 *
 *	This procedure is invoked to process the Tcl "fblocked" command.
 *	See the user documentation for details on what it does.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	Sets interp's result to boolean true or false depending on whether
 *	the preceeding input operation on the channel would have blocked.
 *
 *---------------------------------------------------------------------------
 */

	/* ARGSUSED */
int
Tcl_FblockedObjCmd(unused, interp, objc, objv)
    ClientData unused;		/* Not used. */
    Tcl_Interp *interp;		/* Current interpreter. */
    int objc;			/* Number of arguments. */
    Tcl_Obj *CONST objv[];	/* Argument objects. */
{
    Tcl_Channel chan;
    int mode;
    char *arg;

    if (objc != 2) {
	Tcl_WrongNumArgs(interp, 1, objv, "channelId");
        return TCL_ERROR;
    }

    arg = Tcl_GetString(objv[1]);
    chan = Tcl_GetChannel(interp, arg, &mode);
    if (chan == NULL) {
        return TCL_ERROR;
    }
    if ((mode & TCL_READABLE) == 0) {
	Tcl_AppendResult(interp, "channel \"",
		arg, "\" wasn't opened for reading", (char *) NULL);
        return TCL_ERROR;
    }
        
    Tcl_SetObjResult(interp, Tcl_NewBooleanObj(Tcl_InputBlocked(chan)));
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_OpenObjCmd --
 *
 *	This procedure is invoked to process the "open" Tcl command.
 *	See the user documentation for details on what it does.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	See the user documentation.
 *
 *----------------------------------------------------------------------
 */

	/* ARGSUSED */
int
Tcl_OpenObjCmd(notUsed, interp, objc, objv)
    ClientData notUsed;			/* Not used. */
    Tcl_Interp *interp;			/* Current interpreter. */
    int objc;				/* Number of arguments. */
    Tcl_Obj *CONST objv[];		/* Argument objects. */
{
    int pipeline, prot;
    char *modeString, *what;
    Tcl_Channel chan;

    if ((objc < 2) || (objc > 4)) {
	Tcl_WrongNumArgs(interp, 1, objv, "fileName ?access? ?permissions?");
	return TCL_ERROR;
    }
    prot = 0666;
    if (objc == 2) {
	modeString = "r";
    } else {
	modeString = Tcl_GetString(objv[2]);
	if (objc == 4) {
	    if (Tcl_GetIntFromObj(interp, objv[3], &prot) != TCL_OK) {
		return TCL_ERROR;
	    }
	}
    }

    pipeline = 0;
    what = Tcl_GetString(objv[1]);
    if (what[0] == '|') {
	pipeline = 1;
    }

    /*
     * Open the file or create a process pipeline.
     */

    if (!pipeline) {
        chan = Tcl_FSOpenFileChannel(interp, objv[1], modeString, prot);
    } else {
	int mode, seekFlag, cmdObjc, binary;
	CONST char **cmdArgv;

        if (Tcl_SplitList(interp, what+1, &cmdObjc, &cmdArgv) != TCL_OK) {
            return TCL_ERROR;
        }

        mode = TclGetOpenModeEx(interp, modeString, &seekFlag, &binary);
        if (mode == -1) {
	    chan = NULL;
        } else {
	    int flags = TCL_STDERR | TCL_ENFORCE_MODE;
	    switch (mode & (O_RDONLY | O_WRONLY | O_RDWR)) {
		case O_RDONLY:
		    flags |= TCL_STDOUT;
		    break;
		case O_WRONLY:
		    flags |= TCL_STDIN;
		    break;
		case O_RDWR:
		    flags |= (TCL_STDIN | TCL_STDOUT);
		    break;
		default:
		    Tcl_Panic("Tcl_OpenCmd: invalid mode value");
		    break;
	    }
	    chan = Tcl_OpenCommandChannel(interp, cmdObjc, cmdArgv, flags);
	    if (binary) {
		Tcl_SetChannelOption(interp, chan, "-translation", "binary");
	    }
	}
        ckfree((char *) cmdArgv);
    }
    if (chan == (Tcl_Channel) NULL) {
        return TCL_ERROR;
    }
    Tcl_RegisterChannel(interp, chan);
    Tcl_AppendResult(interp, Tcl_GetChannelName(chan), (char *) NULL);
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * TcpAcceptCallbacksDeleteProc --
 *
 *	Assocdata cleanup routine called when an interpreter is being
 *	deleted to set the interp field of all the accept callback records
 *	registered with	the interpreter to NULL. This will prevent the
 *	interpreter from being used in the future to eval accept scripts.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Deallocates memory and sets the interp field of all the accept
 *	callback records to NULL to prevent this interpreter from being
 *	used subsequently to eval accept scripts.
 *
 *----------------------------------------------------------------------
 */

	/* ARGSUSED */
static void
TcpAcceptCallbacksDeleteProc(clientData, interp)
    ClientData clientData;	/* Data which was passed when the assocdata
                                 * was registered. */
    Tcl_Interp *interp;		/* Interpreter being deleted - not used. */
{
    Tcl_HashTable *hTblPtr;
    Tcl_HashEntry *hPtr;
    Tcl_HashSearch hSearch;
    AcceptCallback *acceptCallbackPtr;

    hTblPtr = (Tcl_HashTable *) clientData;
    for (hPtr = Tcl_FirstHashEntry(hTblPtr, &hSearch);
             hPtr != (Tcl_HashEntry *) NULL;
             hPtr = Tcl_NextHashEntry(&hSearch)) {
        acceptCallbackPtr = (AcceptCallback *) Tcl_GetHashValue(hPtr);
        acceptCallbackPtr->interp = (Tcl_Interp *) NULL;
    }
    Tcl_DeleteHashTable(hTblPtr);
    ckfree((char *) hTblPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * RegisterTcpServerInterpCleanup --
 *
 *	Registers an accept callback record to have its interp
 *	field set to NULL when the interpreter is deleted.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	When, in the future, the interpreter is deleted, the interp
 *	field of the accept callback data structure will be set to
 *	NULL. This will prevent attempts to eval the accept script
 *	in a deleted interpreter.
 *
 *----------------------------------------------------------------------
 */

static void
RegisterTcpServerInterpCleanup(interp, acceptCallbackPtr)
    Tcl_Interp *interp;		/* Interpreter for which we want to be
                                 * informed of deletion. */
    AcceptCallback *acceptCallbackPtr;
    				/* The accept callback record whose
                                 * interp field we want set to NULL when
                                 * the interpreter is deleted. */
{
    Tcl_HashTable *hTblPtr;	/* Hash table for accept callback
                                 * records to smash when the interpreter
                                 * will be deleted. */
    Tcl_HashEntry *hPtr;	/* Entry for this record. */
    int new;			/* Is the entry new? */

    hTblPtr = (Tcl_HashTable *) Tcl_GetAssocData(interp,
            "tclTCPAcceptCallbacks",
            NULL);
    if (hTblPtr == (Tcl_HashTable *) NULL) {
        hTblPtr = (Tcl_HashTable *) ckalloc((unsigned) sizeof(Tcl_HashTable));
        Tcl_InitHashTable(hTblPtr, TCL_ONE_WORD_KEYS);
        (void) Tcl_SetAssocData(interp, "tclTCPAcceptCallbacks",
                TcpAcceptCallbacksDeleteProc, (ClientData) hTblPtr);
    }
    hPtr = Tcl_CreateHashEntry(hTblPtr, (char *) acceptCallbackPtr, &new);
    if (!new) {
        Tcl_Panic("RegisterTcpServerCleanup: damaged accept record table");
    }
    Tcl_SetHashValue(hPtr, (ClientData) acceptCallbackPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * UnregisterTcpServerInterpCleanupProc --
 *
 *	Unregister a previously registered accept callback record. The
 *	interp field of this record will no longer be set to NULL in
 *	the future when the interpreter is deleted.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Prevents the interp field of the accept callback record from
 *	being set to NULL in the future when the interpreter is deleted.
 *
 *----------------------------------------------------------------------
 */

static void
UnregisterTcpServerInterpCleanupProc(interp, acceptCallbackPtr)
    Tcl_Interp *interp;		/* Interpreter in which the accept callback
                                 * record was registered. */
    AcceptCallback *acceptCallbackPtr;
    				/* The record for which to delete the
                                 * registration. */
{
    Tcl_HashTable *hTblPtr;
    Tcl_HashEntry *hPtr;

    hTblPtr = (Tcl_HashTable *) Tcl_GetAssocData(interp,
            "tclTCPAcceptCallbacks", NULL);
    if (hTblPtr == (Tcl_HashTable *) NULL) {
        return;
    }
    hPtr = Tcl_FindHashEntry(hTblPtr, (char *) acceptCallbackPtr);
    if (hPtr == (Tcl_HashEntry *) NULL) {
        return;
    }
    Tcl_DeleteHashEntry(hPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * AcceptCallbackProc --
 *
 *	This callback is invoked by the TCP channel driver when it
 *	accepts a new connection from a client on a server socket.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Whatever the script does.
 *
 *----------------------------------------------------------------------
 */

static void
AcceptCallbackProc(callbackData, chan, address, port)
    ClientData callbackData;		/* The data stored when the callback
                                         * was created in the call to
                                         * Tcl_OpenTcpServer. */
    Tcl_Channel chan;			/* Channel for the newly accepted
                                         * connection. */
    char *address;			/* Address of client that was
                                         * accepted. */
    int port;				/* Port of client that was accepted. */
{
    AcceptCallback *acceptCallbackPtr;
    Tcl_Interp *interp;
    char *script;
    char portBuf[TCL_INTEGER_SPACE];
    int result;

    acceptCallbackPtr = (AcceptCallback *) callbackData;

    /*
     * Check if the callback is still valid; the interpreter may have gone
     * away, this is signalled by setting the interp field of the callback
     * data to NULL.
     */
    
    if (acceptCallbackPtr->interp != (Tcl_Interp *) NULL) {

        script = acceptCallbackPtr->script;
        interp = acceptCallbackPtr->interp;
        
        Tcl_Preserve((ClientData) script);
        Tcl_Preserve((ClientData) interp);

	TclFormatInt(portBuf, port);
        Tcl_RegisterChannel(interp, chan);

        /*
         * Artificially bump the refcount to protect the channel from
         * being deleted while the script is being evaluated.
         */

        Tcl_RegisterChannel((Tcl_Interp *) NULL,  chan);
        
        result = Tcl_VarEval(interp, script, " ", Tcl_GetChannelName(chan),
                " ", address, " ", portBuf, (char *) NULL);
        if (result != TCL_OK) {
            Tcl_BackgroundError(interp);
	    Tcl_UnregisterChannel(interp, chan);
        }

        /*
         * Decrement the artificially bumped refcount. After this it is
         * not safe anymore to use "chan", because it may now be deleted.
         */

        Tcl_UnregisterChannel((Tcl_Interp *) NULL, chan);
        
        Tcl_Release((ClientData) interp);
        Tcl_Release((ClientData) script);
    } else {

        /*
         * The interpreter has been deleted, so there is no useful
         * way to utilize the client socket - just close it.
         */

        Tcl_Close((Tcl_Interp *) NULL, chan);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TcpServerCloseProc --
 *
 *	This callback is called when the TCP server channel for which it
 *	was registered is being closed. It informs the interpreter in
 *	which the accept script is evaluated (if that interpreter still
 *	exists) that this channel no longer needs to be informed if the
 *	interpreter is deleted.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	In the future, if the interpreter is deleted this channel will
 *	no longer be informed.
 *
 *----------------------------------------------------------------------
 */

static void
TcpServerCloseProc(callbackData)
    ClientData callbackData;	/* The data passed in the call to
                                 * Tcl_CreateCloseHandler. */
{
    AcceptCallback *acceptCallbackPtr;
    				/* The actual data. */

    acceptCallbackPtr = (AcceptCallback *) callbackData;
    if (acceptCallbackPtr->interp != (Tcl_Interp *) NULL) {
        UnregisterTcpServerInterpCleanupProc(acceptCallbackPtr->interp,
                acceptCallbackPtr);
    }
    Tcl_EventuallyFree((ClientData) acceptCallbackPtr->script, TCL_DYNAMIC);
    ckfree((char *) acceptCallbackPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_SocketObjCmd --
 *
 *	This procedure is invoked to process the "socket" Tcl command.
 *	See the user documentation for details on what it does.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	Creates a socket based channel.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_SocketObjCmd(notUsed, interp, objc, objv)
    ClientData notUsed;			/* Not used. */
    Tcl_Interp *interp;			/* Current interpreter. */
    int objc;				/* Number of arguments. */
    Tcl_Obj *CONST objv[];		/* Argument objects. */
{
    static CONST char *socketOptions[] = {
	"-async", "-myaddr", "-myport","-server", (char *) NULL
    };
    enum socketOptions {
	SKT_ASYNC,      SKT_MYADDR,      SKT_MYPORT,      SKT_SERVER  
    };
    int optionIndex, a, server, port;
    char *arg, *copyScript, *host, *script;
    char *myaddr = NULL;
    int myport = 0;
    int async = 0;
    Tcl_Channel chan;
    AcceptCallback *acceptCallbackPtr;
    
    server = 0;
    script = NULL;

    if (TclpHasSockets(interp) != TCL_OK) {
	return TCL_ERROR;
    }

    for (a = 1; a < objc; a++) {
	arg = Tcl_GetString(objv[a]);
	if (arg[0] != '-') {
	    break;
	}
	if (Tcl_GetIndexFromObj(interp, objv[a], socketOptions,
		"option", TCL_EXACT, &optionIndex) != TCL_OK) {
	    return TCL_ERROR;
	}
	switch ((enum socketOptions) optionIndex) {
	    case SKT_ASYNC: {
                if (server == 1) {
                    Tcl_AppendResult(interp,
                            "cannot set -async option for server sockets",
                            (char *) NULL);
                    return TCL_ERROR;
                }
                async = 1;		
		break;
	    }
	    case SKT_MYADDR: {
		a++;
                if (a >= objc) {
		    Tcl_AppendResult(interp,
			    "no argument given for -myaddr option",
                            (char *) NULL);
		    return TCL_ERROR;
		}
                myaddr = Tcl_GetString(objv[a]);
		break;
	    }
	    case SKT_MYPORT: {
		char *myPortName;
		a++;
                if (a >= objc) {
		    Tcl_AppendResult(interp,
			    "no argument given for -myport option",
                            (char *) NULL);
		    return TCL_ERROR;
		}
		myPortName = Tcl_GetString(objv[a]);
		if (TclSockGetPort(interp, myPortName, "tcp", &myport)
			!= TCL_OK) {
		    return TCL_ERROR;
		}
		break;
	    }
	    case SKT_SERVER: {
                if (async == 1) {
                    Tcl_AppendResult(interp,
                            "cannot set -async option for server sockets",
                            (char *) NULL);
                    return TCL_ERROR;
                }
		server = 1;
		a++;
		if (a >= objc) {
		    Tcl_AppendResult(interp,
			    "no argument given for -server option",
                            (char *) NULL);
		    return TCL_ERROR;
		}
                script = Tcl_GetString(objv[a]);
		break;
	    }
	    default: {
		Tcl_Panic("Tcl_SocketObjCmd: bad option index to SocketOptions");
	    }
	}
    }
    if (server) {
        host = myaddr;		/* NULL implies INADDR_ANY */
	if (myport != 0) {
	    Tcl_AppendResult(interp, "Option -myport is not valid for servers",
		    NULL);
	    return TCL_ERROR;
	}
    } else if (a < objc) {
	host = Tcl_GetString(objv[a]);
	a++;
    } else {
wrongNumArgs:
	Tcl_AppendResult(interp, "wrong # args: should be either:\n",
		Tcl_GetString(objv[0]),
                " ?-myaddr addr? ?-myport myport? ?-async? host port\n",
		Tcl_GetString(objv[0]),
                " -server command ?-myaddr addr? port",
                (char *) NULL);
        return TCL_ERROR;
    }

    if (a == objc-1) {
	if (TclSockGetPort(interp, Tcl_GetString(objv[a]),
		"tcp", &port) != TCL_OK) {
	    return TCL_ERROR;
	}
    } else {
	goto wrongNumArgs;
    }

    if (server) {
        acceptCallbackPtr = (AcceptCallback *) ckalloc((unsigned)
                sizeof(AcceptCallback));
        copyScript = ckalloc((unsigned) strlen(script) + 1);
        strcpy(copyScript, script);
        acceptCallbackPtr->script = copyScript;
        acceptCallbackPtr->interp = interp;
        chan = Tcl_OpenTcpServer(interp, port, host, AcceptCallbackProc,
                (ClientData) acceptCallbackPtr);
        if (chan == (Tcl_Channel) NULL) {
            ckfree(copyScript);
            ckfree((char *) acceptCallbackPtr);
            return TCL_ERROR;
        }

        /*
         * Register with the interpreter to let us know when the
         * interpreter is deleted (by having the callback set the
         * acceptCallbackPtr->interp field to NULL). This is to
         * avoid trying to eval the script in a deleted interpreter.
         */

        RegisterTcpServerInterpCleanup(interp, acceptCallbackPtr);
        
        /*
         * Register a close callback. This callback will inform the
         * interpreter (if it still exists) that this channel does not
         * need to be informed when the interpreter is deleted.
         */
        
        Tcl_CreateCloseHandler(chan, TcpServerCloseProc,
                (ClientData) acceptCallbackPtr);
    } else {
        chan = Tcl_OpenTcpClient(interp, port, host, myaddr, myport, async);
        if (chan == (Tcl_Channel) NULL) {
            return TCL_ERROR;
        }
    }
    Tcl_RegisterChannel(interp, chan);            
    Tcl_AppendResult(interp, Tcl_GetChannelName(chan), (char *) NULL);
    
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_FcopyObjCmd --
 *
 *	This procedure is invoked to process the "fcopy" Tcl command.
 *	See the user documentation for details on what it does.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	Moves data between two channels and possibly sets up a
 *	background copy handler.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_FcopyObjCmd(dummy, interp, objc, objv)
    ClientData dummy;		/* Not used. */
    Tcl_Interp *interp;		/* Current interpreter. */
    int objc;			/* Number of arguments. */
    Tcl_Obj *CONST objv[];	/* Argument objects. */
{
    Tcl_Channel inChan, outChan;
    char *arg;
    int mode, i;
    int toRead, index;
    Tcl_Obj *cmdPtr;
    static CONST char* switches[] = { "-size", "-command", NULL };
    enum { FcopySize, FcopyCommand };

    if ((objc < 3) || (objc > 7) || (objc == 4) || (objc == 6)) {
	Tcl_WrongNumArgs(interp, 1, objv,
		"input output ?-size size? ?-command callback?");
	return TCL_ERROR;
    }

    /*
     * Parse the channel arguments and verify that they are readable
     * or writable, as appropriate.
     */

    arg = Tcl_GetString(objv[1]);
    inChan = Tcl_GetChannel(interp, arg, &mode);
    if (inChan == (Tcl_Channel) NULL) {
	return TCL_ERROR;
    }
    if ((mode & TCL_READABLE) == 0) {
	Tcl_AppendResult(interp, "channel \"", arg, 
                "\" wasn't opened for reading", (char *) NULL);
        return TCL_ERROR;
    }
    arg = Tcl_GetString(objv[2]);
    outChan = Tcl_GetChannel(interp, arg, &mode);
    if (outChan == (Tcl_Channel) NULL) {
	return TCL_ERROR;
    }
    if ((mode & TCL_WRITABLE) == 0) {
	Tcl_AppendResult(interp, "channel \"", arg, 
                "\" wasn't opened for writing", (char *) NULL);
        return TCL_ERROR;
    }

    toRead = -1;
    cmdPtr = NULL;
    for (i = 3; i < objc; i += 2) {
	if (Tcl_GetIndexFromObj(interp, objv[i], switches, "switch", 0,
		(int *) &index) != TCL_OK) {
	    return TCL_ERROR;
	}
	switch (index) {
	    case FcopySize:
		if (Tcl_GetIntFromObj(interp, objv[i+1], &toRead) != TCL_OK) {
		    return TCL_ERROR;
		}
		break;
	    case FcopyCommand:
		cmdPtr = objv[i+1];
		break;
	}
    }

    return TclCopyChannel(interp, inChan, outChan, toRead, cmdPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ChanTruncateObjCmd --
 *
 *	This procedure is invoked to process the "chan truncate" Tcl command.
 *	See the user documentation for details on what it does.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	Truncates a channel (or rather a file underlying a channel).
 *
 *----------------------------------------------------------------------
 */

int
TclChanTruncateObjCmd(dummy, interp, objc, objv)
    ClientData dummy;		/* Not used. */
    Tcl_Interp *interp;		/* Current interpreter. */
    int objc;			/* Number of arguments. */
    Tcl_Obj *CONST objv[];	/* Argument objects. */
{
    Tcl_Channel chan;
    int mode;
    Tcl_WideInt length;
    char *chanName;

    if ((objc < 2) || (objc > 3)) {
	Tcl_WrongNumArgs(interp, 1, objv, "channelId ?length?");
	return TCL_ERROR;
    }
    chanName = TclGetString(objv[1]);
    chan = Tcl_GetChannel(interp, chanName, &mode);
    if (chan == NULL) {
	return TCL_ERROR;
    }

    if (objc == 3) {
	/*
	 * User is supplying an explicit length.
	 */
	if (Tcl_GetWideIntFromObj(interp, objv[2], &length) != TCL_OK) {
	    return TCL_ERROR;
	}
	if (length < 0) {
	    Tcl_AppendResult(interp,
		    "cannot truncate to negative length of file", NULL);
	    return TCL_ERROR;
	}
    } else {
	/*
	 * User wants to truncate to the current file position.
	 */
	length = Tcl_Tell(chan);
	if (length == Tcl_WideAsLong(-1)) {
	    Tcl_AppendResult(interp,
		    "could not determine current location in \"", chanName,
		    "\": ", Tcl_PosixError(interp), NULL);
	    return TCL_ERROR;
	}
    }

    if (Tcl_TruncateChannel(chan, length) != TCL_OK) {
	Tcl_AppendResult(interp, "error during truncate on \"", chanName,
		"\": ", Tcl_PosixError(interp), (char *) NULL);
	return TCL_ERROR;
    }

    return TCL_OK;
}