tclio.c

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    ClientData	     instanceData; /* Instance specific data for the new
				    * channel. */
    int		     mask;	   /* TCL_READABLE & TCL_WRITABLE to indicate
				    * if the channel is readable, writable. */
    Tcl_Channel	     prevChan;	   /* The channel structure to replace */
{
    ThreadSpecificData	*tsdPtr = TCL_TSD_INIT(&dataKey);
    Channel		*chanPtr, *prevChanPtr;
    ChannelState	*statePtr;

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

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

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

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

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     *	RW|   | + | + | +  |	superceded one !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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    chanPtr = statePtr->topChanPtr;

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

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

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

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

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

	    statePtr->csPtr = csPtr;
	}

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

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

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

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

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

	    DiscardInputQueued (statePtr, 0);
	}

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

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

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

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

	chanPtr->typePtr	= NULL;
	/*
	 * AK: Tcl_NotifyChannel may hold a reference to this block of memory
	 */
	Tcl_EventuallyFree((ClientData) chanPtr, TCL_DYNAMIC);
	UpdateInterest(downChanPtr);

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

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

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

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

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

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

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

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

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

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

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

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

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