*** tcl.h.orig	Fri Oct 23 23:21:39 1998
--- tcl.h	Sun Mar 14 16:31:36 1999
***************
*** 1547,1552 ****
--- 1547,1574 ----
  EXTERN void		Tcl_WrongNumArgs _ANSI_ARGS_((Tcl_Interp *interp,
  			    int objc, Tcl_Obj *CONST objv[], char *message));
  
+ /* Andreas Kupries <andreas_kupries@users.sourceforge.net>, 05/31/1997.
+  * "Trf-Patch for filtering channels"
+  *
+  * C-Level API for (un)stacking of channels. This allows the introduction
+  * of filtering channels with relatively little changes to the core.
+  * This patch was created in cooperation with Jan Nijtmans <nijtmans@wxs.nl>
+  * and is therefore part of his plus-patches too.
+  *
+  * It would have been possible to place the following definitions according
+  * to the alphabetical order used elsewhere in this file, but I decided
+  * against that to ease the maintenance of the patch across new tcl versions
+  * (patch usually has no problems to integrate the patch file for the last
+  * version into the new one).
+  */
+ 
+ EXTERN Tcl_Channel     Tcl_ReplaceChannel _ANSI_ARGS_ ((Tcl_Interp* interp,
+ 			    Tcl_ChannelType* typePtr, ClientData instanceData,
+ 			    int mask, Tcl_Channel prevChan));
+ 
+ EXTERN void            Tcl_UndoReplaceChannel _ANSI_ARGS_ ((Tcl_Interp* interp,
+ 			    Tcl_Channel chan));
+ 
  #endif /* RESOURCE_INCLUDED */
  
  #undef TCL_STORAGE_CLASS
*** tclIO.c.orig	Fri Oct 30 01:38:38 1998
--- tclIO.c	Sun Mar 14 16:35:19 1999
***************
*** 170,175 ****
--- 170,197 ----
      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. */
+ 
+ 
+   /* Andreas Kupries <andreas_kupries@users.sourceforge.net>, 05/31/1997.
+    * "Trf-Patch for filtering channels"
+    *
+    * The single change to the internal datastructures of the core. Every
+    * channel now maintains a reference to the channel he is stacked upon.
+    * This reference is NULL for normal channels. Only the two exported
+    * procedures (Tcl_ReplaceChannel and Tcl_UndoReplaceChannel, see at the
+    * end of 'tcl.h') use this field in a non-trivial way.
+    *
+    * Of the existing procedures the only following are affected by this
+    * change:
+    *
+    * - Tcl_RegisterChannel
+    * - Tcl_CreateChannel
+    * - CloseChannel
+    *
+    * The why is explained at the changed locations.
+    */
+   struct Channel* supercedes; /* Refers to channel this one was stacked upon */
+ 
  } Channel;
      
  /*
***************
*** 1067,1073 ****
              if (chan == (Tcl_Channel) Tcl_GetHashValue(hPtr)) {
                  return;
              }
!             panic("Tcl_RegisterChannel: duplicate channel names");
          }
          Tcl_SetHashValue(hPtr, (ClientData) chanPtr);
      }
--- 1089,1108 ----
              if (chan == (Tcl_Channel) Tcl_GetHashValue(hPtr)) {
                  return;
              }
! 	    /* Andreas Kupries <andreas_kupries@users.sourceforge.net>, 05/31/1997.
!  	     * "Trf-Patch for filtering channels"
!  	     *
!  	     * This is the change to 'Tcl_RegisterChannel'.
!  	     *
!  	     * Explanation:
!  	     *		The moment a channel is stacked upon another he
!  	     *		takes the identity of the channel he supercedes,
!  	     *		i.e. he gets the *same* name. Because of this we
!  	     *		cannot check for duplicate names anymore, they
!  	     *		have to be allowed now.
! 	     */
! 
!             /* panic("Tcl_RegisterChannel: duplicate channel names"); */
          }
          Tcl_SetHashValue(hPtr, (ClientData) chanPtr);
      }
***************
*** 1218,1223 ****
--- 1253,1272 ----
      chanPtr->timer = NULL;
      chanPtr->csPtr = NULL;
  
+     /* Andreas Kupries <andreas_kupries@users.sourceforge.net>, 05/31/1997.
+      * "Trf-Patch for filtering channels"
+      *
+      * This is the change to 'Tcl_CreateChannel'.
+      *
+      * Explanation:
+      *	It is of course necessary to initialize the new field
+      *	in the Channel structure. The chosen value indicates
+      *	that the created channel is a normal one, and not
+      *	stacked upon another.
+      */
+ 
+     chanPtr->supercedes = (Channel*) 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
***************
*** 1250,1255 ****
--- 1299,1490 ----
      return (Tcl_Channel) chanPtr;
  }
  
+ /* Andreas Kupries <andreas_kupries@users.sourceforge.net>, 05/31/1997.
+  * "Trf-Patch for filtering channels"
+  *
+  * The following two procedures are the new, exported ones. They
+  * - create a channel stacked upon an existing one and
+  * - pop a stacked channel off, thus revealing the superceded one.
+  *
+  * Please read the following completely.
+  */
+ /*
+  *----------------------------------------------------------------------
+  *
+  * Tcl_ReplaceChannel --
+  *
+  *	Replaces an entry in the hash table for a Tcl_Channel
+  *	record.
+  *
+  * Results:
+  *	Returns the new Tcl_Channel.
+  *
+  * Side effects:
+  *	Replaces a Tcl_Channel instance into the hash table.
+  *
+  *----------------------------------------------------------------------
+  */
+ 
+ Tcl_Channel
+ Tcl_ReplaceChannel(interp, typePtr, instanceData, mask, prevChan)
+     Tcl_Interp* interp; /* the interpreter we are working in */
+     Tcl_ChannelType *typePtr;	/* The channel type record. */
+     ClientData instanceData;	/* Instance specific data. */
+     int mask;			/* TCL_READABLE & TCL_WRITABLE to indicate
+                                  * if the channel is readable, writable. */
+     Tcl_Channel prevChan;	/* The channel structure that should
+ 				 * be replaced. */
+ {
+   Channel *chanPtr, *pt, *prevPt;
+ 
+   /*
+    * Replace the channel into the list of all channels;
+    */
+ 
+   prevPt = (Channel*) NULL;
+   pt     = (Channel*) firstChanPtr;
+ 
+   while (pt != (Channel *) prevChan) {
+     prevPt = pt;
+     pt     = pt->nextChanPtr;
+   }
+ 
+   if (!pt) {
+     return (Tcl_Channel) NULL;
+   }
+ 
+   /*
+    * Here we check if the "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 & Tcl_GetChannelMode (prevChan)) == 0) {
+     return (Tcl_Channel) NULL;
+   }
+ 
+ 
+   chanPtr = (Channel *) ckalloc((unsigned) sizeof(Channel));
+   chanPtr->flags = mask;
+ 
+   /*
+    * Set the channel up initially in no Input translation mode and
+    * no Output translation mode.
+    */
+ 
+   chanPtr->inputTranslation = TCL_TRANSLATE_LF;
+   chanPtr->outputTranslation = TCL_TRANSLATE_LF;
+   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;
+ 
+   chanPtr->supercedes = (Channel*) prevChan;
+ 
+   chanPtr->channelName = (char *) ckalloc (strlen(pt->channelName)+1);
+   strcpy (chanPtr->channelName, pt->channelName);
+ 
+   if (prevPt) {
+     prevPt->nextChanPtr = chanPtr;
+   } else {
+     firstChanPtr = chanPtr;
+   }
+ 
+   chanPtr->nextChanPtr = pt->nextChanPtr;
+   
+ 
+   Tcl_RegisterChannel (interp, (Tcl_Channel) chanPtr);
+ 
+   /* The superceded channel is effectively unregistered */
+   /*chanPtr->supercedes->refCount --;*/
+ 
+   return (Tcl_Channel) chanPtr;
+ }
+ 
+ /*
+  *----------------------------------------------------------------------
+  *
+  * Tcl_UndoReplaceChannel --
+  *
+  *	Unstacks an entry in the hash table for a Tcl_Channel
+  *	record.
+  *
+  * Results:
+  *	Returns the old Tcl_Channel, i.e. the one which was stacked over.
+  *
+  * Side effects:
+  *	Replaces a Tcl_Channel instance into the hash table.
+  *
+  *----------------------------------------------------------------------
+  */
+ 
+ void
+ Tcl_UndoReplaceChannel (interp, chan)
+ Tcl_Interp* interp; /* The interpreter we are working in */
+ Tcl_Channel chan;   /* The channel to unstack */
+ {
+   Channel* chanPtr = (Channel*) chan;
+ 
+   if (chanPtr->supercedes != (Channel*) NULL) {
+     Tcl_HashTable *hTblPtr;	/* Hash table of channels. */
+     Tcl_HashEntry *hPtr;	/* Search variable. */
+     int new;			/* Is the hash entry new or does it exist? */
+ 
+     /*
+      * Insert the channel we were stacked upon back into
+      * the list of open channels. Place it back into the hashtable too.
+      * Correct 'refCount', as this actually unregisters 'chan'.
+      */
+ 
+     chanPtr->supercedes->nextChanPtr = firstChanPtr;
+     firstChanPtr                     = chanPtr->supercedes;
+ 
+     hTblPtr = GetChannelTable (interp);
+     hPtr    = Tcl_CreateHashEntry (hTblPtr, chanPtr->channelName, &new);
+ 
+     Tcl_SetHashValue(hPtr, (ClientData) chanPtr->supercedes);
+     chanPtr->refCount --;
+ 
+     /* The superceded channel is effectively registered again */
+     /*chanPtr->supercedes->refCount ++;*/
+   }
+ 
+   /*
+    * Disconnect the channels, then do a regular close upon the
+    * stacked one. This may cause flushing of data into the
+    * superceded channel (if 'chan' remembered its parent in itself).
+    */
+ 
+   chanPtr->supercedes = NULL;
+ 
+   if (chanPtr->refCount == 0) {
+     Tcl_Close (interp, chan);
+   }
+ }
+ 
  /*
   *----------------------------------------------------------------------
   *
***************
*** 1863,1868 ****
--- 2098,2138 ----
          if (errorCode != 0) {
              Tcl_SetErrno(errorCode);
          }
+     }
+ 
+     /* Andreas Kupries <andreas_kupries@users.sourceforge.net>, 05/31/1997.
+      * "Trf-Patch for filtering channels"
+      *
+      * This is the change to 'CloseChannel'.
+      *
+      * Explanation
+      *		Closing a filtering channel closes the one it
+      *		superceded too. This basically ripples through
+      *		the whole chain of filters until it reaches
+      *		the underlying normal channel.
+      *
+      *		This is done by reintegrating the superceded
+      *		channel into the (thread) global list of open
+      *		channels and then invoking a regular close.
+      *		There is no need to handle the complexities of
+      *		this process by ourselves.
+      *
+      *		*Note*
+      *		This has to be done after the call to the
+      *		'closeProc' of the filtering channel to allow
+      *		that one the flushing of internal buffers into
+      *		the underlying channel.
+      */
+ 
+     if (chanPtr->supercedes != (Channel*) NULL) {
+       /* Insert the channel we were stacked upon back into
+        * the list of open channels, then do a regular close.
+        */
+ 
+       chanPtr->supercedes->nextChanPtr = firstChanPtr;
+       firstChanPtr                     = chanPtr->supercedes;
+       chanPtr->supercedes->refCount --; /* is deregistered */
+       Tcl_Close (interp, (Tcl_Channel) chanPtr->supercedes);
      }
  
      /*