Merge commit '9966985d896629eede849a84f18e406d1164a16c' as 'tcl8.6'

1 files changed, 1441 insertions, 0 deletions

diff --git a/tcl8.6/generic/tclIOGT.c b/tcl8.6/generic/tclIOGT.c
new file mode 100644
index 0000000..7f61def
--- /dev/null
+++ b/tcl8.6/generic/tclIOGT.c
@@ -0,0 +1,1441 @@
+/*
+ * tclIOGT.c --
+ *
+ *	Implements a generic transformation exposing the underlying API at the
+ *	script level. Contributed by Andreas Kupries.
+ *
+ * Copyright (c) 2000 Ajuba Solutions
+ * Copyright (c) 1999-2000 Andreas Kupries (a.kupries@westend.com)
+ *
+ * See the file "license.terms" for information on usage and redistribution of
+ * this file, and for a DISCLAIMER OF ALL WARRANTIES.
+ */
+
+#include "tclInt.h"
+#include "tclIO.h"
+
+/*
+ * Forward declarations of internal procedures. First the driver procedures of
+ * the transformation.
+ */
+
+static int		TransformBlockModeProc(ClientData instanceData,
+			    int mode);
+static int		TransformCloseProc(ClientData instanceData,
+			    Tcl_Interp *interp);
+static int		TransformInputProc(ClientData instanceData, char *buf,
+			    int toRead, int *errorCodePtr);
+static int		TransformOutputProc(ClientData instanceData,
+			    const char *buf, int toWrite, int *errorCodePtr);
+static int		TransformSeekProc(ClientData instanceData, long offset,
+			    int mode, int *errorCodePtr);
+static int		TransformSetOptionProc(ClientData instanceData,
+			    Tcl_Interp *interp, const char *optionName,
+			    const char *value);
+static int		TransformGetOptionProc(ClientData instanceData,
+			    Tcl_Interp *interp, const char *optionName,
+			    Tcl_DString *dsPtr);
+static void		TransformWatchProc(ClientData instanceData, int mask);
+static int		TransformGetFileHandleProc(ClientData instanceData,
+			    int direction, ClientData *handlePtr);
+static int		TransformNotifyProc(ClientData instanceData, int mask);
+static Tcl_WideInt	TransformWideSeekProc(ClientData instanceData,
+			    Tcl_WideInt offset, int mode, int *errorCodePtr);
+
+/*
+ * Forward declarations of internal procedures. Secondly the procedures for
+ * handling and generating fileeevents.
+ */
+
+static void		TransformChannelHandlerTimer(ClientData clientData);
+
+/*
+ * Forward declarations of internal procedures. Third, helper procedures
+ * encapsulating essential tasks.
+ */
+
+typedef struct TransformChannelData TransformChannelData;
+
+static int		ExecuteCallback(TransformChannelData *ctrl,
+			    Tcl_Interp *interp, unsigned char *op,
+			    unsigned char *buf, int bufLen, int transmit,
+			    int preserve);
+
+/*
+ * Action codes to give to 'ExecuteCallback' (argument 'transmit'), telling
+ * the procedure what to do with the result of the script it calls.
+ */
+
+#define TRANSMIT_DONT	0	/* No transfer to do. */
+#define TRANSMIT_DOWN	1	/* Transfer to the underlying channel. */
+#define TRANSMIT_SELF	2	/* Transfer into our channel. */
+#define TRANSMIT_IBUF	3	/* Transfer to internal input buffer. */
+#define TRANSMIT_NUM	4	/* Transfer number to 'maxRead'. */
+
+/*
+ * Codes for 'preserve' of 'ExecuteCallback'.
+ */
+
+#define P_PRESERVE	1
+#define P_NO_PRESERVE	0
+
+/*
+ * Strings for the action codes delivered to the script implementing a
+ * transformation. Argument 'op' of 'ExecuteCallback'.
+ */
+
+#define A_CREATE_WRITE	(UCHARP("create/write"))
+#define A_DELETE_WRITE	(UCHARP("delete/write"))
+#define A_FLUSH_WRITE	(UCHARP("flush/write"))
+#define A_WRITE		(UCHARP("write"))
+
+#define A_CREATE_READ	(UCHARP("create/read"))
+#define A_DELETE_READ	(UCHARP("delete/read"))
+#define A_FLUSH_READ	(UCHARP("flush/read"))
+#define A_READ		(UCHARP("read"))
+
+#define A_QUERY_MAXREAD	(UCHARP("query/maxRead"))
+#define A_CLEAR_READ	(UCHARP("clear/read"))
+
+/*
+ * Management of a simple buffer.
+ */
+
+typedef struct ResultBuffer ResultBuffer;
+
+static inline void	ResultClear(ResultBuffer *r);
+static inline void	ResultInit(ResultBuffer *r);
+static inline int	ResultEmpty(ResultBuffer *r);
+static inline int	ResultCopy(ResultBuffer *r, unsigned char *buf,
+			    size_t toRead);
+static inline void	ResultAdd(ResultBuffer *r, unsigned char *buf,
+			    size_t toWrite);
+
+/*
+ * This structure describes the channel type structure for Tcl-based
+ * transformations.
+ */
+
+static const Tcl_ChannelType transformChannelType = {
+    "transform",		/* Type name. */
+    TCL_CHANNEL_VERSION_5,	/* v5 channel */
+    TransformCloseProc,		/* Close proc. */
+    TransformInputProc,		/* Input proc. */
+    TransformOutputProc,	/* Output proc. */
+    TransformSeekProc,		/* Seek proc. */
+    TransformSetOptionProc,	/* Set option proc. */
+    TransformGetOptionProc,	/* Get option proc. */
+    TransformWatchProc,		/* Initialize notifier. */
+    TransformGetFileHandleProc,	/* Get OS handles out of channel. */
+    NULL,			/* close2proc */
+    TransformBlockModeProc,	/* Set blocking/nonblocking mode.*/
+    NULL,			/* Flush proc. */
+    TransformNotifyProc,	/* Handling of events bubbling up. */
+    TransformWideSeekProc,	/* Wide seek proc. */
+    NULL,			/* Thread action. */
+    NULL			/* Truncate. */
+};
+
+/*
+ * Possible values for 'flags' field in control structure, see below.
+ */
+
+#define CHANNEL_ASYNC (1<<0)	/* Non-blocking mode. */
+
+/*
+ * Definition of the structure containing the information about the internal
+ * input buffer.
+ */
+
+struct ResultBuffer {
+    unsigned char *buf;		/* Reference to the buffer area. */
+    size_t allocated;		/* Allocated size of the buffer area. */
+    size_t used;		/* Number of bytes in the buffer, no more than
+				 * number allocated. */
+};
+
+/*
+ * Additional bytes to allocate during buffer expansion.
+ */
+
+#define INCREMENT	512
+
+/*
+ * Number of milliseconds to wait before firing an event to flush out
+ * information waiting in buffers (fileevent support).
+ */
+
+#define FLUSH_DELAY	5
+
+/*
+ * Convenience macro to make some casts easier to use.
+ */
+
+#define UCHARP(x)	((unsigned char *) (x))
+
+/*
+ * Definition of a structure used by all transformations generated here to
+ * maintain their local state.
+ */
+
+struct TransformChannelData {
+    /*
+     * General section. Data to integrate the transformation into the channel
+     * system.
+     */
+
+    Tcl_Channel self;		/* Our own Channel handle. */
+    int readIsFlushed;		/* Flag to note whether in.flushProc was
+				 * called or not. */
+    int eofPending;		/* Flag: EOF seen down, not raised up */
+    int flags;			/* Currently CHANNEL_ASYNC or zero. */
+    int watchMask;		/* Current watch/event/interest mask. */
+    int mode;			/* Mode of parent channel, OR'ed combination
+				 * of TCL_READABLE, TCL_WRITABLE. */
+    Tcl_TimerToken timer;	/* Timer for automatic flushing of information
+				 * sitting in an internal buffer. Required for
+				 * full fileevent support. */
+
+    /*
+     * Transformation specific data.
+     */
+
+    int maxRead;		/* Maximum allowed number of bytes to read, as
+				 * given to us by the Tcl script implementing
+				 * the transformation. */
+    Tcl_Interp *interp;		/* Reference to the interpreter which created
+				 * the transformation. Used to execute the
+				 * code below. */
+    Tcl_Obj *command;		/* Tcl code to execute for a buffer */
+    ResultBuffer result;	/* Internal buffer used to store the result of
+				 * a transformation of incoming data. Also
+				 * serves as buffer of all data not yet
+				 * consumed by the reader. */
+    int refCount;
+};
+
+static void
+PreserveData(
+    TransformChannelData *dataPtr)
+{
+    dataPtr->refCount++;
+}
+
+static void
+ReleaseData(
+    TransformChannelData *dataPtr)
+{
+    if (--dataPtr->refCount) {
+	return;
+    }
+    ResultClear(&dataPtr->result);
+    Tcl_DecrRefCount(dataPtr->command);
+    ckfree(dataPtr);
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TclChannelTransform --
+ *
+ *	Implements the Tcl "testchannel transform" debugging command. This is
+ *	part of the testing environment. This sets up a tcl script (cmdObjPtr)
+ *	to be used as a transform on the channel.
+ *
+ * Results:
+ *	A standard Tcl result.
+ *
+ * Side effects:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+	/* ARGSUSED */
+int
+TclChannelTransform(
+    Tcl_Interp *interp,		/* Interpreter for result. */
+    Tcl_Channel chan,		/* Channel to transform. */
+    Tcl_Obj *cmdObjPtr)		/* Script to use for transform. */
+{
+    Channel *chanPtr;		/* The actual channel. */
+    ChannelState *statePtr;	/* State info for channel. */
+    int mode;			/* Read/write mode of the channel. */
+    int objc;
+    TransformChannelData *dataPtr;
+    Tcl_DString ds;
+
+    if (chan == NULL) {
+	return TCL_ERROR;
+    }
+
+    if (TCL_OK != Tcl_ListObjLength(interp, cmdObjPtr, &objc)) {
+	Tcl_SetObjResult(interp,
+		Tcl_NewStringObj("-command value is not a list", -1));
+	return TCL_ERROR;
+    }
+
+    chanPtr = (Channel *) chan;
+    statePtr = chanPtr->state;
+    chanPtr = statePtr->topChanPtr;
+    chan = (Tcl_Channel) chanPtr;
+    mode = (statePtr->flags & (TCL_READABLE|TCL_WRITABLE));
+
+    /*
+     * Now initialize the transformation state and stack it upon the specified
+     * channel. One of the necessary things to do is to retrieve the blocking
+     * regime of the underlying channel and to use the same for us too.
+     */
+
+    dataPtr = ckalloc(sizeof(TransformChannelData));
+
+    dataPtr->refCount = 1;
+    Tcl_DStringInit(&ds);
+    Tcl_GetChannelOption(interp, chan, "-blocking", &ds);
+    dataPtr->readIsFlushed = 0;
+    dataPtr->eofPending = 0;
+    dataPtr->flags = 0;
+    if (ds.string[0] == '0') {
+	dataPtr->flags |= CHANNEL_ASYNC;
+    }
+    Tcl_DStringFree(&ds);
+
+    dataPtr->watchMask = 0;
+    dataPtr->mode = mode;
+    dataPtr->timer = NULL;
+    dataPtr->maxRead = 4096;	/* Initial value not relevant. */
+    dataPtr->interp = interp;
+    dataPtr->command = cmdObjPtr;
+    Tcl_IncrRefCount(dataPtr->command);
+
+    ResultInit(&dataPtr->result);
+
+    dataPtr->self = Tcl_StackChannel(interp, &transformChannelType, dataPtr,
+	    mode, chan);
+    if (dataPtr->self == NULL) {
+	Tcl_AppendPrintfToObj(Tcl_GetObjResult(interp),
+		"\nfailed to stack channel \"%s\"", Tcl_GetChannelName(chan));
+	ReleaseData(dataPtr);
+	return TCL_ERROR;
+    }
+    Tcl_Preserve(dataPtr->self);
+
+    /*
+     * At last initialize the transformation at the script level.
+     */
+
+    PreserveData(dataPtr);
+    if ((dataPtr->mode & TCL_WRITABLE) && ExecuteCallback(dataPtr, NULL,
+	    A_CREATE_WRITE, NULL, 0, TRANSMIT_DONT, P_NO_PRESERVE) != TCL_OK){
+	Tcl_UnstackChannel(interp, chan);
+	ReleaseData(dataPtr);
+	return TCL_ERROR;
+    }
+
+    if ((dataPtr->mode & TCL_READABLE) && ExecuteCallback(dataPtr, NULL,
+	    A_CREATE_READ, NULL, 0, TRANSMIT_DONT, P_NO_PRESERVE) != TCL_OK) {
+	ExecuteCallback(dataPtr, NULL, A_DELETE_WRITE, NULL, 0, TRANSMIT_DONT,
+		P_NO_PRESERVE);
+	Tcl_UnstackChannel(interp, chan);
+	ReleaseData(dataPtr);
+	return TCL_ERROR;
+    }
+
+    ReleaseData(dataPtr);
+    return TCL_OK;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * ExecuteCallback --
+ *
+ *	Executes the defined callback for buffer and operation.
+ *
+ * Side effects:
+ *	As of the executed tcl script.
+ *
+ * Result:
+ *	A standard TCL error code. In case of an error a message is left in
+ *	the result area of the specified interpreter.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+ExecuteCallback(
+    TransformChannelData *dataPtr,
+				/* Transformation with the callback. */
+    Tcl_Interp *interp,		/* Current interpreter, possibly NULL. */
+    unsigned char *op,		/* Operation invoking the callback. */
+    unsigned char *buf,		/* Buffer to give to the script. */
+    int bufLen,			/* And its length. */
+    int transmit,		/* Flag, determines whether the result of the
+				 * callback is sent to the underlying channel
+				 * or not. */
+    int preserve)		/* Flag. If true the procedure will preserve
+				 * the result state of all accessed
+				 * interpreters. */
+{
+    Tcl_Obj *resObj;		/* See below, switch (transmit). */
+    int resLen;
+    unsigned char *resBuf;
+    Tcl_InterpState state = NULL;
+    int res = TCL_OK;
+    Tcl_Obj *command = TclListObjCopy(NULL, dataPtr->command);
+    Tcl_Interp *eval = dataPtr->interp;
+
+    Tcl_Preserve(eval);
+
+    /*
+     * Step 1, create the complete command to execute. Do this by appending
+     * operation and buffer to operate upon to a copy of the callback
+     * definition. We *cannot* create a list containing 3 objects and then use
+     * 'Tcl_EvalObjv', because the command may contain additional prefixed
+     * arguments. Feather's curried commands would come in handy here.
+     */
+
+    if (preserve == P_PRESERVE) {
+	state = Tcl_SaveInterpState(eval, res);
+    }
+
+    Tcl_IncrRefCount(command);
+    Tcl_ListObjAppendElement(NULL, command, Tcl_NewStringObj((char *) op, -1));
+
+    /*
+     * Use a byte-array to prevent the misinterpretation of binary data coming
+     * through as UTF while at the tcl level.
+     */
+
+    Tcl_ListObjAppendElement(NULL, command, Tcl_NewByteArrayObj(buf, bufLen));
+
+    /*
+     * Step 2, execute the command at the global level of the interpreter used
+     * to create the transformation. Destroy the command afterward. If an
+     * error occured and the current interpreter is defined and not equal to
+     * the interpreter for the callback, then copy the error message into
+     * current interpreter. Don't copy if in preservation mode.
+     */
+
+    res = Tcl_EvalObjEx(eval, command, TCL_EVAL_GLOBAL);
+    Tcl_DecrRefCount(command);
+    command = NULL;
+
+    if ((res != TCL_OK) && (interp != NULL) && (eval != interp)
+	    && (preserve == P_NO_PRESERVE)) {
+	Tcl_SetObjResult(interp, Tcl_GetObjResult(eval));
+	Tcl_Release(eval);
+	return res;
+    }
+
+    /*
+     * Step 3, transmit a possible conversion result to the underlying
+     * channel, or ourselves.
+     */
+
+    switch (transmit) {
+    case TRANSMIT_DONT:
+	/* nothing to do */
+	break;
+
+    case TRANSMIT_DOWN:
+	if (dataPtr->self == NULL) {
+	    break;
+	}
+	resObj = Tcl_GetObjResult(eval);
+	resBuf = Tcl_GetByteArrayFromObj(resObj, &resLen);
+	Tcl_WriteRaw(Tcl_GetStackedChannel(dataPtr->self), (char *) resBuf,
+		resLen);
+	break;
+
+    case TRANSMIT_SELF:
+	if (dataPtr->self == NULL) {
+	    break;
+	}
+	resObj = Tcl_GetObjResult(eval);
+	resBuf = Tcl_GetByteArrayFromObj(resObj, &resLen);
+	Tcl_WriteRaw(dataPtr->self, (char *) resBuf, resLen);
+	break;
+
+    case TRANSMIT_IBUF:
+	resObj = Tcl_GetObjResult(eval);
+	resBuf = Tcl_GetByteArrayFromObj(resObj, &resLen);
+	ResultAdd(&dataPtr->result, resBuf, resLen);
+	break;
+
+    case TRANSMIT_NUM:
+	/*
+	 * Interpret result as integer number.
+	 */
+
+	resObj = Tcl_GetObjResult(eval);
+	TclGetIntFromObj(eval, resObj, &dataPtr->maxRead);
+	break;
+    }
+
+    Tcl_ResetResult(eval);
+    if (preserve == P_PRESERVE) {
+	(void) Tcl_RestoreInterpState(eval, state);
+    }
+    Tcl_Release(eval);
+    return res;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TransformBlockModeProc --
+ *
+ *	Trap handler. Called by the generic IO system during option processing
+ *	to change the blocking mode of the channel.
+ *
+ * Side effects:
+ *	Forwards the request to the underlying channel.
+ *
+ * Result:
+ *	0 if successful, errno when failed.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+TransformBlockModeProc(
+    ClientData instanceData,	/* State of transformation. */
+    int mode)			/* New blocking mode. */
+{
+    TransformChannelData *dataPtr = instanceData;
+
+    if (mode == TCL_MODE_NONBLOCKING) {
+	dataPtr->flags |= CHANNEL_ASYNC;
+    } else {
+	dataPtr->flags &= ~CHANNEL_ASYNC;
+    }
+    return 0;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TransformCloseProc --
+ *
+ *	Trap handler. Called by the generic IO system during destruction of
+ *	the transformation channel.
+ *
+ * Side effects:
+ *	Releases the memory allocated in 'Tcl_TransformObjCmd'.
+ *
+ * Result:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+TransformCloseProc(
+    ClientData instanceData,
+    Tcl_Interp *interp)
+{
+    TransformChannelData *dataPtr = instanceData;
+
+    /*
+     * Important: In this procedure 'dataPtr->self' already points to the
+     * underlying channel.
+     *
+     * There is no need to cancel an existing channel handler, this is already
+     * done. Either by 'Tcl_UnstackChannel' or by the general cleanup in
+     * 'Tcl_Close'.
+     *
+     * But we have to cancel an active timer to prevent it from firing on the
+     * removed channel.
+     */
+
+    if (dataPtr->timer != NULL) {
+	Tcl_DeleteTimerHandler(dataPtr->timer);
+	dataPtr->timer = NULL;
+    }
+
+    /*
+     * Now flush data waiting in internal buffers to output and input. The
+     * input must be done despite the fact that there is no real receiver for
+     * it anymore. But the scripts might have sideeffects other parts of the
+     * system rely on (f.e. signaling the close to interested parties).
+     */
+
+    PreserveData(dataPtr);
+    if (dataPtr->mode & TCL_WRITABLE) {
+	ExecuteCallback(dataPtr, interp, A_FLUSH_WRITE, NULL, 0,
+		TRANSMIT_DOWN, P_PRESERVE);
+    }
+
+    if ((dataPtr->mode & TCL_READABLE) && !dataPtr->readIsFlushed) {
+	dataPtr->readIsFlushed = 1;
+	ExecuteCallback(dataPtr, interp, A_FLUSH_READ, NULL, 0, TRANSMIT_IBUF,
+		P_PRESERVE);
+    }
+
+    if (dataPtr->mode & TCL_WRITABLE) {
+	ExecuteCallback(dataPtr, interp, A_DELETE_WRITE, NULL, 0,
+		TRANSMIT_DONT, P_PRESERVE);
+    }
+    if (dataPtr->mode & TCL_READABLE) {
+	ExecuteCallback(dataPtr, interp, A_DELETE_READ, NULL, 0,
+		TRANSMIT_DONT, P_PRESERVE);
+    }
+    ReleaseData(dataPtr);
+
+    /*
+     * General cleanup.
+     */
+
+    Tcl_Release(dataPtr->self);
+    dataPtr->self = NULL;
+    ReleaseData(dataPtr);
+    return TCL_OK;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TransformInputProc --
+ *
+ *	Called by the generic IO system to convert read data.
+ *
+ * Side effects:
+ *	As defined by the conversion.
+ *
+ * Result:
+ *	A transformed buffer.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+TransformInputProc(
+    ClientData instanceData,
+    char *buf,
+    int toRead,
+    int *errorCodePtr)
+{
+    TransformChannelData *dataPtr = instanceData;
+    int gotBytes, read, copied;
+    Tcl_Channel downChan;
+
+    /*
+     * Should assert(dataPtr->mode & TCL_READABLE);
+     */
+
+    if (toRead == 0 || dataPtr->self == NULL) {
+	/*
+	 * Catch a no-op. TODO: Is this a panic()?
+	 */
+	return 0;
+    }
+
+    gotBytes = 0;
+    downChan = Tcl_GetStackedChannel(dataPtr->self);
+
+    PreserveData(dataPtr);
+    while (toRead > 0) {
+	/*
+	 * Loop until the request is satisfied (or no data is available from
+	 * below, possibly EOF).
+	 */
+
+	copied = ResultCopy(&dataPtr->result, UCHARP(buf), toRead);
+	toRead -= copied;
+	buf += copied;
+	gotBytes += copied;
+
+	if (toRead == 0) {
+	    /*
+	     * The request was completely satisfied from our buffers. We can
+	     * break out of the loop and return to the caller.
+	     */
+
+	    break;
+	}
+
+	/*
+	 * Length (dataPtr->result) == 0, toRead > 0 here. Use the incoming
+	 * 'buf'! as target to store the intermediary information read from
+	 * the underlying channel.
+	 *
+	 * Ask the tcl level how much data it allows us to read from the
+	 * underlying channel. This feature allows the transform to signal EOF
+	 * upstream although there is none downstream. Useful to control an
+	 * unbounded 'fcopy', either through counting bytes, or by pattern
+	 * matching.
+	 */
+
+	ExecuteCallback(dataPtr, NULL, A_QUERY_MAXREAD, NULL, 0,
+		TRANSMIT_NUM /* -> maxRead */, P_PRESERVE);
+
+	if (dataPtr->maxRead >= 0) {
+	    if (dataPtr->maxRead < toRead) {
+		toRead = dataPtr->maxRead;
+	    }
+	} /* else: 'maxRead < 0' == Accept the current value of toRead. */
+	if (toRead <= 0) {
+	    break;
+	}
+	if (dataPtr->eofPending) {
+	    /*
+	     * Already saw EOF from downChan; don't ask again.
+	     * NOTE: Could move this up to avoid the last maxRead
+	     * execution.  Believe this would still be correct behavior,
+	     * but the test suite tests the whole command callback
+	     * sequence, so leave it unchanged for now.
+	     */
+
+	    break;
+	}
+
+	/*
+	 * Get bytes from the underlying channel.
+	 */
+
+	read = Tcl_ReadRaw(downChan, buf, toRead);
+	if (read < 0) {
+	    if (Tcl_InputBlocked(downChan) && (gotBytes > 0)) {
+		/*
+		 * Zero bytes available from downChan because blocked.
+		 * But nonzero bytes already copied, so total is a
+		 * valid blocked short read. Return to caller.
+		 */
+
+		break;
+	    }
+
+	    /*
+	     * Either downChan is not blocked (there's a real error).
+	     * or it is and there are no bytes copied yet.  In either
+	     * case we want to pass the "error" along to the caller,
+	     * either to report an error, or to signal to the caller
+	     * that zero bytes are available because blocked.
+	     */
+
+	    *errorCodePtr = Tcl_GetErrno();
+	    gotBytes = -1;
+	    break;
+	} else if (read == 0) {
+
+	    /*
+	     * Zero returned from Tcl_ReadRaw() always indicates EOF
+	     * on the down channel.
+	     */
+
+	    dataPtr->eofPending = 1;
+	    dataPtr->readIsFlushed = 1;
+	    ExecuteCallback(dataPtr, NULL, A_FLUSH_READ, NULL, 0,
+		    TRANSMIT_IBUF, P_PRESERVE);
+
+	    if (ResultEmpty(&dataPtr->result)) {
+		/*
+		 * We had nothing to flush.
+		 */
+
+		break;
+	    }
+
+	    continue;		/* at: while (toRead > 0) */
+	} /* read == 0 */
+
+	/*
+	 * Transform the read chunk and add the result to our read buffer
+	 * (dataPtr->result).
+	 */
+
+	if (ExecuteCallback(dataPtr, NULL, A_READ, UCHARP(buf), read,
+		TRANSMIT_IBUF, P_PRESERVE) != TCL_OK) {
+	    *errorCodePtr = EINVAL;
+	    gotBytes = -1;
+	    break;
+	}
+    } /* while toRead > 0 */
+
+    if (gotBytes == 0) {
+	dataPtr->eofPending = 0;
+    }
+    ReleaseData(dataPtr);
+    return gotBytes;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TransformOutputProc --
+ *
+ *	Called by the generic IO system to convert data waiting to be written.
+ *
+ * Side effects:
+ *	As defined by the transformation.
+ *
+ * Result:
+ *	A transformed buffer.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+TransformOutputProc(
+    ClientData instanceData,
+    const char *buf,
+    int toWrite,
+    int *errorCodePtr)
+{
+    TransformChannelData *dataPtr = instanceData;
+
+    /*
+     * Should assert(dataPtr->mode & TCL_WRITABLE);
+     */
+
+    if (toWrite == 0) {
+	/*
+	 * Catch a no-op.
+	 */
+
+	return 0;
+    }
+
+    PreserveData(dataPtr);
+    if (ExecuteCallback(dataPtr, NULL, A_WRITE, UCHARP(buf), toWrite,
+	    TRANSMIT_DOWN, P_NO_PRESERVE) != TCL_OK) {
+	*errorCodePtr = EINVAL;
+	toWrite = -1;
+    }
+    ReleaseData(dataPtr);
+
+    return toWrite;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TransformSeekProc --
+ *
+ *	This procedure is called by the generic IO level to move the access
+ *	point in a channel.
+ *
+ * Side effects:
+ *	Moves the location at which the channel will be accessed in future
+ *	operations. Flushes all transformation buffers, then forwards it to
+ *	the underlying channel.
+ *
+ * Result:
+ *	-1 if failed, the new position if successful. An output argument
+ *	contains the POSIX error code if an error occurred, or zero.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+TransformSeekProc(
+    ClientData instanceData,	/* The channel to manipulate. */
+    long offset,		/* Size of movement. */
+    int mode,			/* How to move. */
+    int *errorCodePtr)		/* Location of error flag. */
+{
+    TransformChannelData *dataPtr = instanceData;
+    Tcl_Channel parent = Tcl_GetStackedChannel(dataPtr->self);
+    const Tcl_ChannelType *parentType = Tcl_GetChannelType(parent);
+    Tcl_DriverSeekProc *parentSeekProc = Tcl_ChannelSeekProc(parentType);
+
+    if ((offset == 0) && (mode == SEEK_CUR)) {
+	/*
+	 * This is no seek but a request to tell the caller the current
+	 * location. Simply pass the request down.
+	 */
+
+	return parentSeekProc(Tcl_GetChannelInstanceData(parent), offset,
+		mode, errorCodePtr);
+    }
+
+    /*
+     * It is a real request to change the position. Flush all data waiting for
+     * output and discard everything in the input buffers. Then pass the
+     * request down, unchanged.
+     */
+
+    PreserveData(dataPtr);
+    if (dataPtr->mode & TCL_WRITABLE) {
+	ExecuteCallback(dataPtr, NULL, A_FLUSH_WRITE, NULL, 0, TRANSMIT_DOWN,
+		P_NO_PRESERVE);
+    }
+
+    if (dataPtr->mode & TCL_READABLE) {
+	ExecuteCallback(dataPtr, NULL, A_CLEAR_READ, NULL, 0, TRANSMIT_DONT,
+		P_NO_PRESERVE);
+	ResultClear(&dataPtr->result);
+	dataPtr->readIsFlushed = 0;
+	dataPtr->eofPending = 0;
+    }
+    ReleaseData(dataPtr);
+
+    return parentSeekProc(Tcl_GetChannelInstanceData(parent), offset, mode,
+	    errorCodePtr);
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TransformWideSeekProc --
+ *
+ *	This procedure is called by the generic IO level to move the access
+ *	point in a channel, with a (potentially) 64-bit offset.
+ *
+ * Side effects:
+ *	Moves the location at which the channel will be accessed in future
+ *	operations. Flushes all transformation buffers, then forwards it to
+ *	the underlying channel.
+ *
+ * Result:
+ *	-1 if failed, the new position if successful. An output argument
+ *	contains the POSIX error code if an error occurred, or zero.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static Tcl_WideInt
+TransformWideSeekProc(
+    ClientData instanceData,	/* The channel to manipulate. */
+    Tcl_WideInt offset,		/* Size of movement. */
+    int mode,			/* How to move. */
+    int *errorCodePtr)		/* Location of error flag. */
+{
+    TransformChannelData *dataPtr = instanceData;
+    Tcl_Channel parent = Tcl_GetStackedChannel(dataPtr->self);
+    const Tcl_ChannelType *parentType	= Tcl_GetChannelType(parent);
+    Tcl_DriverSeekProc *parentSeekProc = Tcl_ChannelSeekProc(parentType);
+    Tcl_DriverWideSeekProc *parentWideSeekProc =
+	    Tcl_ChannelWideSeekProc(parentType);
+    ClientData parentData = Tcl_GetChannelInstanceData(parent);
+
+    if ((offset == Tcl_LongAsWide(0)) && (mode == SEEK_CUR)) {
+	/*
+	 * This is no seek but a request to tell the caller the current
+	 * location. Simply pass the request down.
+	 */
+
+	if (parentWideSeekProc != NULL) {
+	    return parentWideSeekProc(parentData, offset, mode, errorCodePtr);
+	}
+
+	return Tcl_LongAsWide(parentSeekProc(parentData, 0, mode,
+		errorCodePtr));
+    }
+
+    /*
+     * It is a real request to change the position. Flush all data waiting for
+     * output and discard everything in the input buffers. Then pass the
+     * request down, unchanged.
+     */
+
+    PreserveData(dataPtr);
+    if (dataPtr->mode & TCL_WRITABLE) {
+	ExecuteCallback(dataPtr, NULL, A_FLUSH_WRITE, NULL, 0, TRANSMIT_DOWN,
+		P_NO_PRESERVE);
+    }
+
+    if (dataPtr->mode & TCL_READABLE) {
+	ExecuteCallback(dataPtr, NULL, A_CLEAR_READ, NULL, 0, TRANSMIT_DONT,
+		P_NO_PRESERVE);
+	ResultClear(&dataPtr->result);
+	dataPtr->readIsFlushed = 0;
+	dataPtr->eofPending = 0;
+    }
+    ReleaseData(dataPtr);
+
+    /*
+     * If we have a wide seek capability, we should stick with that.
+     */
+
+    if (parentWideSeekProc != NULL) {
+	return parentWideSeekProc(parentData, offset, mode, errorCodePtr);
+    }
+
+    /*
+     * We're transferring to narrow seeks at this point; this is a bit complex
+     * because we have to check whether the seek is possible first (i.e.
+     * whether we are losing information in truncating the bits of the
+     * offset). Luckily, there's a defined error for what happens when trying
+     * to go out of the representable range.
+     */
+
+    if (offset<Tcl_LongAsWide(LONG_MIN) || offset>Tcl_LongAsWide(LONG_MAX)) {
+	*errorCodePtr = EOVERFLOW;
+	return Tcl_LongAsWide(-1);
+    }
+
+    return Tcl_LongAsWide(parentSeekProc(parentData, Tcl_WideAsLong(offset),
+	    mode, errorCodePtr));
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TransformSetOptionProc --
+ *
+ *	Called by generic layer to handle the reconfiguration of channel
+ *	specific options. As this channel type does not have such, it simply
+ *	passes all requests downstream.
+ *
+ * Side effects:
+ *	As defined by the channel downstream.
+ *
+ * Result:
+ *	A standard TCL error code.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+TransformSetOptionProc(
+    ClientData instanceData,
+    Tcl_Interp *interp,
+    const char *optionName,
+    const char *value)
+{
+    TransformChannelData *dataPtr = instanceData;
+    Tcl_Channel downChan = Tcl_GetStackedChannel(dataPtr->self);
+    Tcl_DriverSetOptionProc *setOptionProc;
+
+    setOptionProc = Tcl_ChannelSetOptionProc(Tcl_GetChannelType(downChan));
+    if (setOptionProc == NULL) {
+	return TCL_ERROR;
+    }
+
+    return setOptionProc(Tcl_GetChannelInstanceData(downChan), interp,
+	    optionName, value);
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TransformGetOptionProc --
+ *
+ *	Called by generic layer to handle requests for the values of channel
+ *	specific options. As this channel type does not have such, it simply
+ *	passes all requests downstream.
+ *
+ * Side effects:
+ *	As defined by the channel downstream.
+ *
+ * Result:
+ *	A standard TCL error code.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+TransformGetOptionProc(
+    ClientData instanceData,
+    Tcl_Interp *interp,
+    const char *optionName,
+    Tcl_DString *dsPtr)
+{
+    TransformChannelData *dataPtr = instanceData;
+    Tcl_Channel downChan = Tcl_GetStackedChannel(dataPtr->self);
+    Tcl_DriverGetOptionProc *getOptionProc;
+
+    getOptionProc = Tcl_ChannelGetOptionProc(Tcl_GetChannelType(downChan));
+    if (getOptionProc != NULL) {
+	return getOptionProc(Tcl_GetChannelInstanceData(downChan), interp,
+		optionName, dsPtr);
+    } else if (optionName == NULL) {
+	/*
+	 * Request is query for all options, this is ok.
+	 */
+
+	return TCL_OK;
+    }
+
+    /*
+     * Request for a specific option has to fail, since we don't have any.
+     */
+
+    return TCL_ERROR;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TransformWatchProc --
+ *
+ *	Initialize the notifier to watch for events from this channel.
+ *
+ * Side effects:
+ *	Sets up the notifier so that a future event on the channel will be
+ *	seen by Tcl.
+ *
+ * Result:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+	/* ARGSUSED */
+static void
+TransformWatchProc(
+    ClientData instanceData,	/* Channel to watch. */
+    int mask)			/* Events of interest. */
+{
+    TransformChannelData *dataPtr = instanceData;
+    Tcl_Channel downChan;
+
+    /*
+     * The caller expressed interest in events occuring for this channel. We
+     * are forwarding the call to the underlying channel now.
+     */
+
+    dataPtr->watchMask = mask;
+
+    /*
+     * No channel handlers any more. We will be notified automatically about
+     * events on the channel below via a call to our 'TransformNotifyProc'.
+     * But we have to pass the interest down now. We are allowed to add
+     * additional 'interest' to the mask if we want to. But this
+     * transformation has no such interest. It just passes the request down,
+     * unchanged.
+     */
+
+    if (dataPtr->self == NULL) {
+	return;
+    }
+    downChan = Tcl_GetStackedChannel(dataPtr->self);
+
+    Tcl_GetChannelType(downChan)->watchProc(
+	    Tcl_GetChannelInstanceData(downChan), mask);
+
+    /*
+     * Management of the internal timer.
+     */
+
+    if ((dataPtr->timer != NULL) &&
+	    (!(mask & TCL_READABLE) || ResultEmpty(&dataPtr->result))) {
+	/*
+	 * A pending timer exists, but either is there no (more) interest in
+	 * the events it generates or nothing is available for reading, so
+	 * remove it.
+	 */
+
+	Tcl_DeleteTimerHandler(dataPtr->timer);
+	dataPtr->timer = NULL;
+    }
+
+    if ((dataPtr->timer == NULL) && (mask & TCL_READABLE)
+	    && !ResultEmpty(&dataPtr->result)) {
+	/*
+	 * There is no pending timer, but there is interest in readable events
+	 * and we actually have data waiting, so generate a timer to flush
+	 * that.
+	 */
+
+	dataPtr->timer = Tcl_CreateTimerHandler(FLUSH_DELAY,
+		TransformChannelHandlerTimer, dataPtr);
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TransformGetFileHandleProc --
+ *
+ *	Called from Tcl_GetChannelHandle to retrieve OS specific file handle
+ *	from inside this channel.
+ *
+ * Side effects:
+ *	None.
+ *
+ * Result:
+ *	The appropriate Tcl_File or NULL if not present.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+TransformGetFileHandleProc(
+    ClientData instanceData,	/* Channel to query. */
+    int direction,		/* Direction of interest. */
+    ClientData *handlePtr)	/* Place to store the handle into. */
+{
+    TransformChannelData *dataPtr = instanceData;
+
+    /*
+     * Return the handle belonging to parent channel. IOW, pass the request
+     * down and the result up.
+     */
+
+    return Tcl_GetChannelHandle(Tcl_GetStackedChannel(dataPtr->self),
+	    direction, handlePtr);
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TransformNotifyProc --
+ *
+ *	Handler called by Tcl to inform us of activity on the underlying
+ *	channel.
+ *
+ * Side effects:
+ *	May process the incoming event by itself.
+ *
+ * Result:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+TransformNotifyProc(
+    ClientData clientData,	/* The state of the notified
+				 * transformation. */
+    int mask)			/* The mask of occuring events. */
+{
+    TransformChannelData *dataPtr = clientData;
+
+    /*
+     * An event occured in the underlying channel. This transformation doesn't
+     * process such events thus returns the incoming mask unchanged.
+     */
+
+    if (dataPtr->timer != NULL) {
+	/*
+	 * Delete an existing timer. It was not fired, yet we are here, so the
+	 * channel below generated such an event and we don't have to. The
+	 * renewal of the interest after the execution of channel handlers
+	 * will eventually cause us to recreate the timer (in
+	 * TransformWatchProc).
+	 */
+
+	Tcl_DeleteTimerHandler(dataPtr->timer);
+	dataPtr->timer = NULL;
+    }
+    return mask;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TransformChannelHandlerTimer --
+ *
+ *	Called by the notifier (-> timer) to flush out information waiting in
+ *	the input buffer.
+ *
+ * Side effects:
+ *	As of 'Tcl_NotifyChannel'.
+ *
+ * Result:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static void
+TransformChannelHandlerTimer(
+    ClientData clientData)	/* Transformation to query. */
+{
+    TransformChannelData *dataPtr = clientData;
+
+    dataPtr->timer = NULL;
+    if (!(dataPtr->watchMask&TCL_READABLE) || ResultEmpty(&dataPtr->result)) {
+	/*
+	 * The timer fired, but either is there no (more) interest in the
+	 * events it generates or nothing is available for reading, so ignore
+	 * it and don't recreate it.
+	 */
+
+	return;
+    }
+    Tcl_NotifyChannel(dataPtr->self, TCL_READABLE);
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * ResultClear --
+ *
+ *	Deallocates any memory allocated by 'ResultAdd'.
+ *
+ * Side effects:
+ *	See above.
+ *
+ * Result:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static inline void
+ResultClear(
+    ResultBuffer *r)		/* Reference to the buffer to clear out. */
+{
+    r->used = 0;
+
+    if (r->allocated) {
+	ckfree(r->buf);
+	r->buf = NULL;
+	r->allocated = 0;
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * ResultInit --
+ *
+ *	Initializes the specified buffer structure. The structure will contain
+ *	valid information for an emtpy buffer.
+ *
+ * Side effects:
+ *	See above.
+ *
+ * Result:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static inline void
+ResultInit(
+    ResultBuffer *r)		/* Reference to the structure to
+				 * initialize. */
+{
+    r->used = 0;
+    r->allocated = 0;
+    r->buf = NULL;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * ResultEmpty --
+ *
+ *	Returns whether the number of bytes stored in the buffer is zero.
+ *
+ * Side effects:
+ *	None.
+ *
+ * Result:
+ *	A boolean.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static inline int
+ResultEmpty(
+    ResultBuffer *r)		/* The structure to query. */
+{
+    return r->used == 0;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * ResultCopy --
+ *
+ *	Copies the requested number of bytes from the buffer into the
+ *	specified array and removes them from the buffer afterward. Copies
+ *	less if there is not enough data in the buffer.
+ *
+ * Side effects:
+ *	See above.
+ *
+ * Result:
+ *	The number of actually copied bytes, possibly less than 'toRead'.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static inline int
+ResultCopy(
+    ResultBuffer *r,		/* The buffer to read from. */
+    unsigned char *buf,		/* The buffer to copy into. */
+    size_t toRead)		/* Number of requested bytes. */
+{
+    if (r->used == 0) {
+	/*
+	 * Nothing to copy in the case of an empty buffer.
+	 */
+
+	return 0;
+    } else if (r->used == toRead) {
+	/*
+	 * We have just enough. Copy everything to the caller.
+	 */
+
+	memcpy(buf, r->buf, toRead);
+	r->used = 0;
+    } else if (r->used > toRead) {
+	/*
+	 * The internal buffer contains more than requested. Copy the
+	 * requested subset to the caller, and shift the remaining bytes down.
+	 */
+
+	memcpy(buf, r->buf, toRead);
+	memmove(r->buf, r->buf + toRead, r->used - toRead);
+	r->used -= toRead;
+    } else {
+	/*
+	 * There is not enough in the buffer to satisfy the caller, so take
+	 * everything.
+	 */
+
+	memcpy(buf, r->buf, r->used);
+	toRead = r->used;
+	r->used = 0;
+    }
+    return toRead;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * ResultAdd --
+ *
+ *	Adds the bytes in the specified array to the buffer, by appending it.
+ *
+ * Side effects:
+ *	See above.
+ *
+ * Result:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static inline void
+ResultAdd(
+    ResultBuffer *r,		/* The buffer to extend. */
+    unsigned char *buf,		/* The buffer to read from. */
+    size_t toWrite)		/* The number of bytes in 'buf'. */
+{
+    if (r->used + toWrite > r->allocated) {
+	/*
+	 * Extension of the internal buffer is required.
+	 */
+
+	if (r->allocated == 0) {
+	    r->allocated = toWrite + INCREMENT;
+	    r->buf = ckalloc(r->allocated);
+	} else {
+	    r->allocated += toWrite + INCREMENT;
+	    r->buf = ckrealloc(r->buf, r->allocated);
+	}
+    }
+
+    /*
+     * Now we may copy the data.
+     */
+
+    memcpy(r->buf + r->used, buf, toWrite);
+    r->used += toWrite;
+}
+
+/*
+ * Local Variables:
+ * mode: c
+ * c-basic-offset: 4
+ * fill-column: 78
+ * End:
+ */