Tcl Source Code: Attachment Details

Overview
Artifact ID:	024b237eafe037d4ad1c12f52baa1fad67bc676b
Ticket:	1163274fffffffffffffffffffffffffffffffff
Date:	2007-11-15 05:51:25
User:	andreas_kupries
Artifact Attached:	edcaab189bf3e9d28f5fb4b90acc3727e8df259c
Filename:	tclIORTrans.c
Description:	Transform implementation.
Content:
/*
 * tclIORTrans.c --
 *
 *	This file contains the implementation of Tcl's generic transformation
 *	reflection code, which allows the implementation of Tcl channel
 *	transformations in Tcl code.
 *
 *	Parts of this file are based on code contributed by Jean-Claude
 *	Wippler.
 *
 *	See TIP #230 for the specification of this functionality.
 *
 * Copyright (c) 2007 ActiveState.
 *
 * See the file "license.terms" for information on usage and redistribution of
 * this file, and for a DISCLAIMER OF ALL WARRANTIES.
 *
 * RCS: @(#) $Id: tclIORChan.c,v 1.24 2007/04/24 02:42:18 kennykb Exp $
 */

#include <tclInt.h>
#include <tclIO.h>
#include <assert.h>

#ifndef EINVAL
#define EINVAL	9
#endif
#ifndef EOK
#define EOK	0
#endif

/* DUPLICATE of HaveVersion() in tclIO.c // TODO - MODULE_SCOPE */
static int		HaveVersion(const Tcl_ChannelType *typePtr,
			    Tcl_ChannelTypeVersion minimumVersion);

/*
 * Signatures of all functions used in the C layer of the reflection.
 */

static int		ReflectClose(ClientData clientData,
			    Tcl_Interp *interp);
static int		ReflectInput(ClientData clientData, char *buf,
			    int toRead, int *errorCodePtr);
static int		ReflectOutput(ClientData clientData, const char *buf,
			    int toWrite, int *errorCodePtr);
static void		ReflectWatch(ClientData clientData, int mask);
static int		ReflectBlock(ClientData clientData, int mode);
static Tcl_WideInt	ReflectSeekWide(ClientData clientData,
			    Tcl_WideInt offset, int mode, int *errorCodePtr);
static int		ReflectSeek(ClientData clientData, long offset,
			    int mode, int *errorCodePtr);
static int		ReflectGetOption(ClientData clientData,
			    Tcl_Interp *interp, const char *optionName,
			    Tcl_DString *dsPtr);
static int		ReflectSetOption(ClientData clientData,
			    Tcl_Interp *interp, const char *optionName,
			    const char *newValue);
static int		ReflectHandle(ClientData clientData, int direction,
				      ClientData* handle);
static int		ReflectNotify(ClientData clientData, int mask);

/*
 * The C layer channel type/driver definition used by the reflection. This is
 * a version 3 structure.
 */

static Tcl_ChannelType tclRTransformType = {
    "tclrtransform",       /* Type name.                                  */
    TCL_CHANNEL_VERSION_5, /* v5 channel */
    ReflectClose,          /* Close channel, clean instance data          */
    ReflectInput,          /* Handle read request                         */
    ReflectOutput,         /* Handle write request                        */
    ReflectSeek,           /* Move location of access point.              */
    ReflectSetOption,      /* Set options.                                */
    ReflectGetOption,      /* Get options.                                */
    ReflectWatch,          /* Initialize notifier                         */
    ReflectHandle,         /* Get OS handle from the channel.             */
    NULL,                  /* No close2 support.               NULL'able  */
    ReflectBlock,          /* Set blocking/nonblocking.                   */
    NULL,                  /* Flush channel. Not used by core. NULL'able  */
    ReflectNotify,         /* Handle events.                              */
    ReflectSeekWide,       /* Move access point (64 bit).                 */
    NULL,                  /* thread action */
    NULL,                  /* truncate */
};

/*
 * Structure of the buffer to hold transform results to be consumed by higher
 * layers upon reading from the channel, plus the functions to manage such.
 */

typedef struct _ResultBuffer_ {
  unsigned char* buf;       /* Reference to the buffer area */
  int            allocated; /* Allocated size of the buffer area */
  int            used;      /* Number of bytes in the buffer, <= allocated */
} ResultBuffer;

#define ResultLength(r) ((r)->used)
/* static int ResultLength        (ResultBuffer* r); */

static void  ResultClear          (ResultBuffer* r);
static void  ResultInit           (ResultBuffer* r);
static void  ResultAdd            (ResultBuffer* r, unsigned char* buf, int toWrite);
static int   ResultCopy           (ResultBuffer* r, unsigned char* buf, int toRead);

#define RB_INCREMENT (512)

/*
 * Instance data for a reflected transformation. ===========================
 */

typedef struct {
    Tcl_Channel chan;		/* Back reference to the channel of the
				 * transformation itself. */
    Tcl_Channel parent;         /* Reference to the channel the transformation
				 * was pushed on. */
    Tcl_Interp *interp;		/* Reference to the interpreter containing the
				 * Tcl level part of the channel. */
#ifdef TCL_THREADS
    Tcl_ThreadId thread;	/* Thread the 'interp' belongs to. */
#endif

    Tcl_TimerToken timer;

    /* See [==] as well.
     * Storage for the command prefix and the additional words required for
     * the invocation of methods in the command handler.
     *
     * argv [0] ... [.] | [argc-2] [argc-1] | [argc]  [argc+2]
     *      cmd ... pfx | method   chan     | detail1 detail2
     *      ~~~~ CT ~~~            ~~ CT ~~
     *
     * CT = Belongs to the 'Command handler Thread'.
     */

    int argc;			/* Number of preallocated words - 2 */
    Tcl_Obj **argv;		/* Preallocated array for calling the handler.
				 * args[0] is placeholder for cmd word.
				 * Followed by the arguments in the prefix,
				 * plus 4 placeholders for method, channel,
				 * and at most two varying (method specific)
				 * words. */
    int methods;		/* Bitmask of supported methods */

    /*
     * NOTE (9): Should we have predefined shared literals for the method
     * names?
     */

    int mode;			/* Mask of R/W mode */
    int interest;		/* Mask of events the channel is interested
				 * in. */
    int blocking;               /* Flag: Channel is blocking or not */
    int readIsDrained;          /* Flag: Read buffers are flushed*/

    ResultBuffer result;

} ReflectedTransform;

/*
 * Event literals. ==================================================
 */

static const char *eventOptions[] = {
    "read", "write", NULL
};
typedef enum {
    EVENT_READ, EVENT_WRITE
} EventOption;

/*
 * Method literals. ==================================================
 */

static const char *methodNames[] = {
    "clear",		/* OPT */
    "drain",		/* OPT, drain => read */
    "event",		/* OPT, event <=> watch */
    "finalize",		/*     */
    "flush",		/* OPT, flush => write */
    "initialize",	/*     */
    "limit?",		/* OPT */
    "read",		/* OPT */
    "watch",		/* OPT, watch <=> event */
    "write",		/* OPT */
    NULL
};
typedef enum {
    METH_CLEAR,
    METH_DRAIN,
    METH_EVENT,
    METH_FINAL,
    METH_FLUSH,
    METH_INIT,
    METH_LIMIT,
    METH_READ,
    METH_WATCH,
    METH_WRITE
} MethodName;

#define FLAG(m) (1 << (m))
#define REQUIRED_METHODS \
	(FLAG(METH_INIT) | FLAG(METH_FINAL))
#define RANDW \
	(TCL_READABLE | TCL_WRITABLE)

#define IMPLIES(a,b)	((!(a)) || (b))
#define NEGIMPL(a,b)
#define HAS(x,f)	(x & FLAG(f))

#ifdef TCL_THREADS
/*
 * Thread specific types and structures.
 *
 * We are here essentially creating a very specific implementation of 'thread
 * send'.
 */

/*
 * Enumeration of all operations which can be forwarded.
 */

typedef enum {
    ForwardedClear,
    ForwardedClose,
    ForwardedDrain,
    ForwardedEvent,
    ForwardedFlush,
    ForwardedInput,
    ForwardedLimit,
    ForwardedOutput,
    ForwardedWatch
} ForwardedOperation;

/*
 * Event used to forward driver invocations to the thread actually managing
 * the channel. We cannot construct the command to execute and forward
 * that. Because then it will contain a mixture of Tcl_Obj's belonging to both
 * the command handler thread (CT), and the thread managing the channel (MT),
 * executed in CT. Tcl_Obj's are not allowed to cross thread boundaries. So we
 * forward an operation code, the argument details, and reference to results.
 * The command is assembled in the CT and belongs fully to that thread. No
 * sharing problems.
 */

typedef struct ForwardParamBase {
    int code;			/* O: Ok/Fail of the cmd handler */
    char *msgStr;		/* O: Error message for handler failure */
    int mustFree;		/* O: True if msgStr is allocated, false if
				 * otherwise (static). */
} ForwardParamBase;

/*
 * Operation specific parameter/result structures. (These are "subtypes" of
 * ForwardParamBase. Where an operation does not need any special types, it
 * has no "subtype" and just uses ForwardParamBase, as listed above.)
 */

struct ForwardParamTransform {
    ForwardParamBase base;	/* "Supertype". MUST COME FIRST. */
    char *buf;			/* I: Bytes to transform,
				 * O: Bytes in transform result */
    int size;			/* I: #bytes to transform,
				 * O: #bytes in the transform result */
};
struct ForwardParamMask {
    ForwardParamBase base;	/* "Supertype". MUST COME FIRST. */
    int mask;			/* I: Mask of the signaled events,
				*  O: Mask of events which are of interest */
};
struct ForwardParamLimit {
    ForwardParamBase base;	/* "Supertype". MUST COME FIRST. */
    int max;			/* O: Character read limit */
};

/*
 * Now join all these together in a single union for convenience.
 */

typedef union ForwardParam {
    ForwardParamBase base;
    struct ForwardParamTransform transform;
    struct ForwardParamMask      mask;
    struct ForwardParamLimit     limit;
} ForwardParam;

/*
 * Forward declaration.
 */

typedef struct ForwardingResult ForwardingResult;

/*
 * General event structure, with reference to operation specific data.
 */

typedef struct ForwardingEvent {
    Tcl_Event event;		/* Basic event data, has to be first item */
    ForwardingResult *resultPtr;
    ForwardedOperation op;	/* Forwarded driver operation */
    ReflectedTransform *rtPtr;	/* Channel instance */
    ForwardParam *param;	/* Packaged arguments and return values, a
				 * ForwardParam pointer. */
} ForwardingEvent;

/*
 * Structure to manage the result of the forwarding. This is not the result of
 * the operation itself, but about the success of the forward event itself.
 * The event can be successful, even if the operation which was forwarded
 * failed. It is also there to manage the synchronization between the involved
 * threads.
 */

struct ForwardingResult {
    Tcl_ThreadId src;		/* Originating thread. */
    Tcl_ThreadId dst;		/* Thread the op was forwarded to. */
    Tcl_Condition done;		/* Condition variable the forwarder blocks
				 * on. */
    int result;			/* TCL_OK or TCL_ERROR */
    ForwardingEvent *evPtr;	/* Event the result belongs to. */
    ForwardingResult *prevPtr, *nextPtr;
				/* Links into the list of pending forwarded
				 * results. */
};

/*
 * List of forwarded operations which have not completed yet, plus the mutex
 * to protect the access to this process global list.
 */

static ForwardingResult *forwardList = NULL;
TCL_DECLARE_MUTEX(rcForwardMutex)

/*
 * Function containing the generic code executing a forward, and wrapper
 * macros for the actual operations we wish to forward. Uses ForwardProc as
 * the event function executed by the thread receiving a forwarding event
 * (which executes the appropriate function and collects the result, if any).
 *
 * The two ExitProcs are handlers so that things do not deadlock when either
 * thread involved in the forwarding exits. They also clean things up so that
 * we don't leak resources when threads go away.
 */

static void		ForwardOpToOwnerThread(ReflectedTransform *rtPtr,
			    ForwardedOperation op, const VOID *param);
static int		ForwardProc(Tcl_Event *evPtr, int mask);
static void		SrcExitProc(ClientData clientData);
static void		DstExitProc(ClientData clientData);

#define FreeReceivedError(p) \
	if ((p)->base.mustFree) { \
	    ckfree((p)->base.msgStr); \
	}
#define PassReceivedErrorInterp(i,p) \
	if ((i) != NULL) { \
	    Tcl_SetChannelErrorInterp((i), \
		    Tcl_NewStringObj((p)->base.msgStr, -1)); \
	} \
	FreeReceivedError(p)
#define PassReceivedError(c,p) \
	Tcl_SetChannelError((c), Tcl_NewStringObj((p)->base.msgStr, -1)); \
	FreeReceivedError(p)
#define ForwardSetStaticError(p,emsg) \
	(p)->base.code = TCL_ERROR; \
	(p)->base.mustFree = 0; \
	(p)->base.msgStr = (char *) (emsg)
#define ForwardSetDynamicError(p,emsg) \
	(p)->base.code = TCL_ERROR; \
	(p)->base.mustFree = 1; \
	(p)->base.msgStr = (char *) (emsg)

static void		ForwardSetObjError(ForwardParam *p,
			    Tcl_Obj *objPtr);
#endif /* TCL_THREADS */

#define SetChannelErrorStr(c,msgStr) \
	Tcl_SetChannelError((c), Tcl_NewStringObj((msgStr), -1))

static Tcl_Obj *	MarshallError(Tcl_Interp *interp);
static void		UnmarshallErrorResult(Tcl_Interp *interp,
			    Tcl_Obj *msgObj);

/*
 * Static functions for this file:
 */

static int		EncodeEventMask(Tcl_Interp *interp,
			    const char *objName, Tcl_Obj *obj, int *mask);
static Tcl_Obj *	DecodeEventMask(int mask);
static ReflectedTransform * NewReflectedTransform(Tcl_Interp *interp,
			    Tcl_Obj *cmdpfxObj, int mode, Tcl_Obj *handleObj,
			    Tcl_Channel parentChan);
static Tcl_Obj *	NextHandle(void);
static void		FreeReflectedTransform(ReflectedTransform *rtPtr);
static int		InvokeTclMethod(ReflectedTransform *rtPtr,
			    const char *method, Tcl_Obj *argOneObj,
			    Tcl_Obj *argTwoObj, Tcl_Obj **resultObjPtr);

/*
 * Global constant strings (messages). ==================
 * These string are used directly as bypass errors, thus they have to be valid
 * Tcl lists where the last element is the message itself. Hence the
 * list-quoting to keep the words of the message together. See also [x].
 */

static const char *msg_read_badlimit = "{Tcl driver returned bad read limit '0'}";
static const char *msg_read_unsup = "{read not supported by Tcl driver}";
static const char *msg_write_unsup = "{write not supported by Tcl driver}";
#ifdef TCL_THREADS
static const char *msg_send_originlost = "{Origin thread lost}";
static const char *msg_send_dstlost = "{Destination thread lost}";
#endif /* TCL_THREADS */

/*
 * Timer management (flushing out buffered data via artificial events).
 */

/*
 * Number of milliseconds to wait before firing an event to try to
 * flush out information waiting in buffers (fileevent support).
 */

#define FLUSH_DELAY (5)

static void TimerKill  (ReflectedTransform* rtPtr);
static void TimerSetup (ReflectedTransform* rtPtr);
static void TimerRun   (ClientData clientData);

/*
 * Helper functions encapsulating some of the thread forwarding to make the
 * control flow in callers easier.
 */

static int  TransformRead  (ReflectedTransform* rtPtr, int* errorCodePtr, unsigned char* buf, int toRead);
static int  TransformWrite (ReflectedTransform* rtPtr, int* errorCodePtr, unsigned char* buf, int toWrite);
static int  TransformDrain (ReflectedTransform* rtPtr, int* errorCodePtr);
static int  TransformFlush (ReflectedTransform* rtPtr, int* errorCodePtr);
static void TransformClear (ReflectedTransform* rtPtr);
static int  TransformLimit (ReflectedTransform* rtPtr, int* errorCodePtr, int* maxPtr);
static int  TransformMask  (ReflectedTransform* rtPtr);

/*
 * Main methods to plug into the 'chan' ensemble'. ==================
 */

/*
 *----------------------------------------------------------------------
 *
 * TclChanPushObjCmd --
 *
 *	This function is invoked to process the "chan push" Tcl command.
 *	See the user documentation for details on what it does.
 *
 * Results:
 *	A standard Tcl result. The handle of the new channel is placed in the
 *	interp result.
 *
 * Side effects:
 *	Creates a new channel.
 *
 *----------------------------------------------------------------------
 */

int
TclChanPushObjCmd(
    ClientData clientData,
    Tcl_Interp *interp,
    int objc,
    Tcl_Obj *const *objv)
{
    ReflectedTransform *rtPtr;	/* Instance data of the new channel */
    Tcl_Obj*    chanObj;        /* Handle of parent channel */
    Tcl_Channel parentChan;     /* Token of parent channel */
    int mode;			/* R/W mode of parent, later the new
				 * channel. Has to match the abilities of the
				 * handler commands */
    Tcl_Obj *cmdObj;		/* Command prefix, list of words */
    Tcl_Obj *cmdNameObj;	/* Command name */
    Tcl_Obj *rcId;		/* Handle of the new channel */
    Tcl_Obj *modeObj;		/* mode in obj form for method call */

    int listc;			/* Result of 'initialize', and of */
    Tcl_Obj **listv;		/* its sublist in the 2nd element */
    int methIndex;		/* Encoded method name */
    int result;			/* Result code for 'initialize' */
    Tcl_Obj *resObj;		/* Result data for 'initialize' */
    int methods;		/* Bitmask for supported methods. */
    Tcl_Obj *err;		/* Error message */

    /*
     * Syntax:   chan push CHANNEL CMDPREFIX
     *           [0]  [1]  [2]     [3]
     *
     * Actually: rPush CHANNEL CMDPREFIX
     *           [0]   [1]     [2]
     */

#define CHAN	(1)
#define CMD	(2)

    /*
     * Number of arguments...
     */

    if (objc != 3) {
	Tcl_WrongNumArgs(interp, 1, objv, "channel cmdprefix");
	return TCL_ERROR;
    }

    /*
     * First argument is a channel handle.
     */

    chanObj    = objv[CHAN];
    parentChan = Tcl_GetChannel (interp, Tcl_GetString (chanObj), &mode);
    if (parentChan == NULL) {
	return TCL_ERROR;
    }
    parentChan = Tcl_GetTopChannel (parentChan);

    /*
     * Second argument is command prefix, i.e. list of words, first word is
     * name of handler command, other words are fixed arguments. Run
     * 'initialize' method to get the list of supported methods. Validate
     * this.
     */

    cmdObj = objv[CMD];

    /*
     * Basic check that the command prefix truly is a list.
     */

    if (Tcl_ListObjIndex(interp, cmdObj, 0, &cmdNameObj) != TCL_OK) {
	return TCL_ERROR;
    }

    /*
     * Now create the transformation (channel).
     */

    rcId  = NextHandle();
    rtPtr = NewReflectedTransform(interp, cmdObj, mode, rcId, parentChan);

    /*
     * Invoke 'initialize' and validate that the handler is present and ok.
     * Squash the transformation if not.
     *
     * Note: The conversion of 'mode' back into a Tcl_Obj ensures that
     * 'initialize' is invoked with canonical mode names, and no
     * abbreviations. Using modeObj directly could feed abbreviations into the
     * handler, and the handler is not specified to handle such.
     */

    modeObj = DecodeEventMask(mode);
    result  = InvokeTclMethod(rtPtr, "initialize", modeObj, NULL, &resObj);
    Tcl_DecrRefCount(modeObj);
    if (result != TCL_OK) {
	UnmarshallErrorResult(interp, resObj);
	Tcl_DecrRefCount(resObj);	/* Remove reference held from invoke */
	goto error;
    }

    /*
     * Verify the result.
     * - List, of method names. Convert to mask.
     *   Check for non-optionals through the mask.
     *   Compare open mode against optional r/w.
     */

    if (Tcl_ListObjGetElements(NULL, resObj, &listc, &listv) != TCL_OK) {
	TclNewLiteralStringObj(err, "chan handler \"");
	Tcl_AppendObjToObj(err, cmdObj);
	Tcl_AppendToObj(err, " initialize\" returned non-list: ", -1);
	Tcl_AppendObjToObj(err, resObj);
	Tcl_SetObjResult(interp, err);
	Tcl_DecrRefCount(resObj);
	goto error;
    }

    methods = 0;
    while (listc > 0) {
	if (Tcl_GetIndexFromObj(interp, listv[listc-1], methodNames,
		"method", TCL_EXACT, &methIndex) != TCL_OK) {
	    TclNewLiteralStringObj(err, "chan handler \"");
	    Tcl_AppendObjToObj(err, cmdObj);
	    Tcl_AppendToObj(err, " initialize\" returned ", -1);
	    Tcl_AppendObjToObj(err, Tcl_GetObjResult(interp));
	    Tcl_SetObjResult(interp, err);
	    Tcl_DecrRefCount(resObj);
	    goto error;
	}

	methods |= FLAG(methIndex);
	listc--;
    }
    Tcl_DecrRefCount(resObj);

    if ((REQUIRED_METHODS & methods) != REQUIRED_METHODS) {
	TclNewLiteralStringObj(err, "chan handler \"");
	Tcl_AppendObjToObj(err, cmdObj);
	Tcl_AppendToObj(err, "\" does not support all required methods", -1);
	Tcl_SetObjResult(interp, err);
	goto error;
    }

    /*
     * Mode tell us what the parent channel supports. The methods tell us what
     * the handler supports. We remove the non-supported bits from the mode
     * and check that the channel is not completely inacessible. Afterward the
     * mode tells us which methods are still required, and these methods will
     * also be supported by the handler, by design of the check.
     */

    if (!HAS(methods, METH_READ))  { mode &= ~TCL_READABLE; }
    if (!HAS(methods, METH_WRITE)) { mode &= ~TCL_WRITABLE; }

    if (!mode) {
	TclNewLiteralStringObj(err, "chan handler \"");
	Tcl_AppendObjToObj(err, cmdObj);
	Tcl_AppendToObj(err, "\" makes the channel inacessible", -1);
	Tcl_SetObjResult(interp, err);
	goto error;
    }

    /*
     * The mode and support for it is ok, now check the internal constraints.
     */

    if (!IMPLIES(HAS(methods, METH_WATCH), HAS(methods, METH_EVENT))) {
	TclNewLiteralStringObj(err, "chan handler \"");
	Tcl_AppendObjToObj(err, cmdObj);
	Tcl_AppendToObj(err, "\" supports \"watch\" but not \"event\"", -1);
	Tcl_SetObjResult(interp, err);
	goto error;
    }

    if (!IMPLIES(HAS(methods, METH_EVENT), HAS(methods, METH_WATCH))) {
	TclNewLiteralStringObj(err, "chan handler \"");
	Tcl_AppendObjToObj(err, cmdObj);
	Tcl_AppendToObj(err, "\" supports \"event\" but not \"watch\"", -1);
	Tcl_SetObjResult(interp, err);
	goto error;
    }

    if (!IMPLIES(HAS(methods, METH_DRAIN), HAS(methods, METH_READ))) {
	TclNewLiteralStringObj(err, "chan handler \"");
	Tcl_AppendObjToObj(err, cmdObj);
	Tcl_AppendToObj(err, "\" supports \"drain\" but not \"read\"", -1);
	Tcl_SetObjResult(interp, err);
	goto error;
    }

    if (!IMPLIES(HAS(methods, METH_FLUSH), HAS(methods, METH_WRITE))) {
	TclNewLiteralStringObj(err, "chan handler \"");
	Tcl_AppendObjToObj(err, cmdObj);
	Tcl_AppendToObj(err, "\" supports \"flush\" but not \"write\"", -1);
	Tcl_SetObjResult(interp, err);
	goto error;
    }

    Tcl_ResetResult(interp);

    /*
     * Everything is fine now.
     */

    rtPtr->methods = methods;
    rtPtr->mode    = mode;
    rtPtr->chan    = Tcl_StackChannel (interp, &tclRTransformType,
				       (ClientData) rtPtr, mode,
				       rtPtr->parent);
    /*
     * Return handle as result of command.
     */

    Tcl_AppendResult (interp, Tcl_GetChannelName (rtPtr->chan),
		    (char*) NULL);
    return TCL_OK;

 error:
    /*
     * We are not going through ReflectClose as we never had a channel
     * structure.
     */

    FreeReflectedTransform(rtPtr);
    return TCL_ERROR;

#undef CHAN
#undef CMD
}

/*
 *----------------------------------------------------------------------
 *
 * TclChanPopObjCmd --
 *
 *	This function is invoked to process the "chan pop" Tcl command.
 *	See the user documentation for details on what it does.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	Posts events to a reflected channel, invokes event handlers. The
 *	latter implies that arbitrary side effects are possible.
 *
 *----------------------------------------------------------------------
 */

int
TclChanPopObjCmd(
    ClientData clientData,
    Tcl_Interp *interp,
    int objc,
    Tcl_Obj *const *objv)
{
    /*
     * Syntax:   chan pop CHANNEL
     *           [0]  [1] [2]
     *
     * Actually: rPop CHANNEL
     *           [0]  [1]
     */

#define CHAN	(1)

    const char *chanId;		/* Tcl level channel handle */
    Tcl_Channel chan;		/* Channel associated to the handle */
    int         mode;           /* Channel r/w mode */

    /*
     * Number of arguments...
     */

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

    /*
     * First argument is a channel, which may have a (reflected)
     * transformation.
     */

    chanId = TclGetString(objv[CHAN]);
    chan   = Tcl_GetChannel(interp, chanId, &mode);

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

    /* Removing transformations is generic, and not restricted to reflected
     * transformations.
     */

    Tcl_UnstackChannel(interp, chan);

    /* TODO: Check for inactive reflected transformations at the top and */
    /* TODO: remove them as well. */

    return TCL_OK;

#undef CHAN
}

/*
 * Channel error message marshalling utilities.
 */

static Tcl_Obj*
MarshallError(
    Tcl_Interp *interp)
{
    /*
     * Capture the result status of the interpreter into a string. => List of
     * options and values, followed by the error message. The result has
     * refCount 0.
     */

    Tcl_Obj *returnOpt = Tcl_GetReturnOptions(interp, TCL_ERROR);

    /*
     * => returnOpt.refCount == 0. We can append directly.
     */

    Tcl_ListObjAppendElement(NULL, returnOpt, Tcl_GetObjResult(interp));
    return returnOpt;
}

static void
UnmarshallErrorResult(
    Tcl_Interp *interp,
    Tcl_Obj *msgObj)
{
    int lc;
    Tcl_Obj **lv;
    int explicitResult;
    int numOptions;

    /*
     * Process the caught message.
     *
     * Syntax = (option value)... ?message?
     *
     * Bad syntax causes a panic. This is OK because the other side uses
     * Tcl_GetReturnOptions and list construction functions to marshall the
     * information; if we panic here, something has gone badly wrong already.
     */

    if (Tcl_ListObjGetElements(interp, msgObj, &lc, &lv) != TCL_OK) {
	Tcl_Panic("TclChanCaughtErrorBypass: Bad syntax of caught result");
    }
    if (interp == NULL) {
	return;
    }

    explicitResult = lc & 1;		/* Odd number of values? */
    numOptions = lc - explicitResult;

    if (explicitResult) {
	Tcl_SetObjResult(interp, lv[lc-1]);
    }

    (void) Tcl_SetReturnOptions(interp, Tcl_NewListObj(numOptions, lv));
    ((Interp *)interp)->flags &= ~ERR_ALREADY_LOGGED;
}

/*
 * Driver functions. ================================================
 */

/*
 *----------------------------------------------------------------------
 *
 * ReflectClose --
 *
 *	This function is invoked when the channel is closed, to delete the
 *	driver specific instance data.
 *
 * Results:
 *	A posix error.
 *
 * Side effects:
 *	Releases memory. Arbitrary, as it calls upon a script.
 *
 *----------------------------------------------------------------------
 */

static int
ReflectClose(
    ClientData clientData,
    Tcl_Interp *interp)
{
    ReflectedTransform *rtPtr = (ReflectedTransform *) clientData;
    int result;			/* Result code for 'close' */
    Tcl_Obj *resObj;		/* Result data for 'close' */

    if (interp == NULL) {
	/*
	 * This call comes from TclFinalizeIOSystem. There are no
	 * interpreters, and therefore we cannot call upon the handler command
	 * anymore. Threading is irrelevant as well. We simply clean up all
	 * our C level data structures and leave the Tcl level to the other
	 * finalization functions.
	 */

	/*
	 * THREADED => Forward this to the origin thread
	 *
	 * Note: Have a thread delete handler for the origin thread. Use this
	 * to clean up the structure!
	 */

#ifdef TCL_THREADS
	if (rtPtr->thread != Tcl_GetCurrentThread()) {
	    ForwardParam p;

	    ForwardOpToOwnerThread(rtPtr, ForwardedClose, &p);
	    result = p.base.code;

	    /*
	     * FreeReflectedTransform is done in the forwarded operation!, in
	     * the other thread. rtPtr here is gone!
	     */

	    if (result != TCL_OK) {
		FreeReceivedError(&p);
	    }
	    return EOK;
	}
#endif

	FreeReflectedTransform(rtPtr);
	return EOK;
    }

    /*
     * In the reflected channel implementation a cleaned method mask here
     * implies that the channel creation was aborted, and "finalize" must not
     * be called. for transformations however we are not going through here on
     * such an abort, but directly through FreeReflectedTransform. So for us
     * that check is not necessary. We always go through 'finalize'.
     */

    if (HAS(rtPtr->methods, METH_DRAIN) && (!rtPtr->readIsDrained)) {
	int errorCode;
	if (!TransformDrain (rtPtr, &errorCode)) {
	    return errorCode;
	}
    }

    if (HAS(rtPtr->methods, METH_FLUSH)) {
	int errorCode;
	if (!TransformFlush (rtPtr, &errorCode)) {
	    return errorCode;
	}
    }

    /*
     * Are we in the correct thread?
     */

#ifdef TCL_THREADS
    if (rtPtr->thread != Tcl_GetCurrentThread()) {
	ForwardParam p;

	ForwardOpToOwnerThread(rtPtr, ForwardedClose, &p);
	result = p.base.code;

	/*
	 * FreeReflectedTransform is done in the forwarded operation!, in the
	 * other thread. rtPtr here is gone!
	 */

	if (result != TCL_OK) {
	    PassReceivedErrorInterp(interp, &p);
	}
    } else {
#endif
	result = InvokeTclMethod(rtPtr, "finalize", NULL, NULL, &resObj);
	if ((result != TCL_OK) && (interp != NULL)) {
	    Tcl_SetChannelErrorInterp(interp, resObj);
	}

	Tcl_DecrRefCount(resObj);	/* Remove reference we held from the
					 * invoke */
	FreeReflectedTransform(rtPtr);
#ifdef TCL_THREADS
    }
#endif
    return (result == TCL_OK) ? EOK : EINVAL;
}

/*
 *----------------------------------------------------------------------
 *
 * ReflectInput --
 *
 *	This function is invoked when more data is requested from the channel.
 *
 * Results:
 *	The number of bytes read.
 *
 * Side effects:
 *	Allocates memory. Arbitrary, as it calls upon a script.
 *
 *----------------------------------------------------------------------
 */

static int
ReflectInput(
	     ClientData clientData,
	     char *buf,
	     int toRead,
	     int *errorCodePtr)
{
    ReflectedTransform *rtPtr = (ReflectedTransform *) clientData;
    int gotBytes, copied, read;

    /*
     * The following check can be done before thread redirection, because we
     * are reading from an item which is readonly, i.e. will never change
     * during the lifetime of the channel.
     */

    if (!(rtPtr->methods & FLAG(METH_READ))) {
	SetChannelErrorStr(rtPtr->chan, msg_read_unsup);
	*errorCodePtr = EINVAL;
	return -1;
    }

    gotBytes = 0;

    while (toRead > 0) {
	/* Loop until the request is satisfied (or no data available from
	 * below, possibly EOF).
	 */

	copied    = ResultCopy (&rtPtr->result, (unsigned char*) buf, toRead);
	toRead   -= copied;
	buf      += copied;
	gotBytes += copied;

	if (toRead == 0) {
	    return gotBytes;
	}

	/*
	 * The buffer is exhausted, but the caller wants even more. We now
	 * have to go to the underlying channel, get more bytes and then
	 * transform them for delivery. We may not get that we want (full EOF
	 * or temporary out of data).
	 */

	/*
	 * Length (rtPtr->result) == 0, toRead > 0 here. Use 'buf'! as target
	 * to store the intermediary information read from the parent channel.
	 *
	 * Ask the transform 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' for example, either through counting bytes, or by
	 * pattern matching.
	 */

	if ((rtPtr->methods & FLAG(METH_LIMIT))) {
	    int maxRead = -1;
	    if (!TransformLimit (rtPtr, errorCodePtr, &maxRead)) {
		return -1;
	    }
	    if (maxRead == 0) {
		SetChannelErrorStr(rtPtr->chan, msg_read_badlimit);
		return -1;
	    } else if (maxRead > 0) {
		if (maxRead < toRead) {
		    toRead = maxRead;
		}
	    } /* else: 'maxRead < 0' == Accept the current value of toRead */
	}

	if (toRead <= 0) {
	    return gotBytes;
	}

	read = Tcl_ReadRaw (rtPtr->parent, buf, toRead);
	if (read < 0) {
	    /* Report errors to caller.
	     * The state of the seek system is unchanged!
	     */

	    if ((Tcl_GetErrno () == EAGAIN) && (gotBytes > 0)) {
		/* EAGAIN is a special situation.  If we had some data
		 * before we report that instead of the request to re-try.
		 */

		return gotBytes;
	    }

	    *errorCodePtr = Tcl_GetErrno ();
	    return -1;      
	}

	if (read == 0) {
	    /*
	     * Check wether we hit on EOF in 'parent' or not. If not
	     * differentiate between blocking and non-blocking modes. In
	     * non-blocking mode we ran temporarily out of data. Signal this
	     * to the caller via EWOULDBLOCK and error return (-1). In the
	     * other cases we simply return what we got and let the caller
	     * wait for more. On the other hand, if we got an EOF we have to
	     * convert and flush all waiting partial data.
	     */

	    if (!Tcl_Eof (rtPtr->parent)) {
		/* The state of the seek system is unchanged! */

		if (gotBytes == 0 && !rtPtr->blocking) {
		    *errorCodePtr = EWOULDBLOCK;
		    return -1;
		} else {
		    return gotBytes;
		}
	    } else {
		/* Eof in parent */
		if (rtPtr->readIsDrained) {
		    return gotBytes;
		}

		/*
		 * Now this is a bit different. The partial data waiting is
		 * converted and returned.
		 */

		if (HAS(rtPtr->methods, METH_DRAIN)) {
		    if(!TransformDrain (rtPtr, errorCodePtr)) {
			return -1;
		    }
		}

		if (ResultLength (&rtPtr->result) == 0) {
		    /* The drain delivered nothing */
		    return gotBytes;
		}
		continue; /* at: while (toRead > 0) */
	    }
	} /* read == 0 */

	/*
	 * Transform the read chunk, which was not empty. Anything we got back
	 * is a transformation result is put into our buffers, and the next
	 * iteration will put it into the result.
	 */

	if (!TransformRead (rtPtr, errorCodePtr, buf, read)) {
	    return -1;
	}
    } /* while toRead > 0 */

    return gotBytes;

}

/*
 *----------------------------------------------------------------------
 *
 * ReflectOutput --
 *
 *	This function is invoked when data is writen to the channel.
 *
 * Results:
 *	The number of bytes actually written.
 *
 * Side effects:
 *	Allocates memory. Arbitrary, as it calls upon a script.
 *
 *----------------------------------------------------------------------
 */

static int
ReflectOutput(
    ClientData clientData,
    const char *buf,
    int toWrite,
    int *errorCodePtr)
{
    ReflectedTransform *rtPtr = (ReflectedTransform *) clientData;

    /*
     * The following check can be done before thread redirection, because we
     * are reading from an item which is readonly, i.e. will never change
     * during the lifetime of the channel.
     */

    if (!(rtPtr->methods & FLAG(METH_WRITE))) {
	SetChannelErrorStr(rtPtr->chan, msg_write_unsup);
	*errorCodePtr = EINVAL;
	return -1;
    }

    if (toWrite == 0) {
	/* Nothing came in to write, ignore the call
	 */
	return 0;
    }

    /*
     * Discard partial data in the input buffers, i.e. on the read side. Like
     * we do when explicitly seeking as well.
     */

    if ((rtPtr->methods & FLAG(METH_CLEAR))) {
	TransformClear (rtPtr);
    }

    /*
     * Hand the data to the transformation itself. Anything it deigned to
     * return to us is a (partial) transformation result and written to the
     * parent channel for further processing.
     */

    if (!TransformWrite (rtPtr, errorCodePtr, (unsigned char*) buf, toWrite)) {
	return -1;
    }

    *errorCodePtr = EOK;
    return toWrite;
}

/*
 *----------------------------------------------------------------------
 *
 * ReflectSeekWide / ReflectSeek --
 *
 *	This function is invoked when the user wishes to seek on the channel.
 *
 * Results:
 *	The new location of the access point.
 *
 * Side effects:
 *	Allocates memory. Arbitrary, per the parent channel, and the called scripts.
 *
 *----------------------------------------------------------------------
 */

static Tcl_WideInt
ReflectSeekWide(
    ClientData clientData,
    Tcl_WideInt offset,
    int seekMode,
    int *errorCodePtr)
{
    ReflectedTransform *rtPtr = (ReflectedTransform *) clientData;
    Channel* parent = (Channel*) rtPtr->parent;
    Tcl_WideInt curPos;		/* Position on the device. */

    Tcl_DriverSeekProc *seekProc      =
	Tcl_ChannelSeekProc(Tcl_GetChannelType (rtPtr->parent));

    /*
     * Fail if the parent channel is not seekable.
     */

    if (seekProc == NULL) {
	Tcl_SetErrno(EINVAL);
	return Tcl_LongAsWide(-1);
    }

    /*
     * Check if we can leave out involving the Tcl level, i.e. transformation
     * handler. This is true for tell requests, and transformations which
     * support neither flush, nor drain. For these cases we can pass the
     * request down and the result back up unchanged.
     */

    if (
	((seekMode != SEEK_CUR) || (offset != 0)) &&
	(HAS(rtPtr->methods, METH_CLEAR) ||
	 HAS(rtPtr->methods, METH_FLUSH))
	) {
	/*
	 * Neither a tell request, nor clear/flush both not supported.  We
	 * have to go through the Tcl level to clear and/or flush the
	 * transformation.
	 */

	if ((rtPtr->methods & FLAG(METH_CLEAR))) {
	    TransformClear (rtPtr);
	}

	if (HAS(rtPtr->methods, METH_FLUSH)) {
	    if (!TransformFlush (rtPtr, errorCodePtr)) {
		return -1;
	    }
	}
    }

    /*
     * Now seek to the new position in the channel as requested by the
     * caller. Note that we prefer the wideSeekProc if that is available and
     * non-NULL...
     */

    if (HaveVersion(parent->typePtr, TCL_CHANNEL_VERSION_3) &&
	parent->typePtr->wideSeekProc != NULL) {
	curPos = (parent->typePtr->wideSeekProc) (parent->instanceData,
						  offset, seekMode, errorCodePtr);
    } else if (offset < Tcl_LongAsWide(LONG_MIN) ||
	       offset > Tcl_LongAsWide(LONG_MAX)) {
	*errorCodePtr = EOVERFLOW;
	curPos = Tcl_LongAsWide(-1);
    } else {
	curPos = Tcl_LongAsWide((parent->typePtr->seekProc) (
							     parent->instanceData, Tcl_WideAsLong(offset), seekMode,
							     errorCodePtr));
    }
    if (curPos == Tcl_LongAsWide(-1)) {
	Tcl_SetErrno(*errorCodePtr);
    }

    *errorCodePtr = EOK;
    return curPos;
}

static int
ReflectSeek(
    ClientData clientData,
    long offset,
    int seekMode,
    int *errorCodePtr)
{
    /*
     * This function can be invoked from a transformation which is based on
     * standard seeking, i.e. non-wide. Because of this we have to implement
     * it, a dummy is not enough. We simply delegate the call to the wide
     * routine.
     */

    return (int) ReflectSeekWide(clientData, Tcl_LongAsWide(offset), seekMode,
	    errorCodePtr);
}

/*
 *----------------------------------------------------------------------
 *
 * ReflectWatch --
 *
 *	This function is invoked to tell the channel what events the I/O
 *	system is interested in.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Allocates memory. Arbitrary, as it calls upon a script.
 *
 *----------------------------------------------------------------------
 */

static void
ReflectWatch(
    ClientData clientData,
    int mask)
{
    ReflectedTransform *rtPtr = (ReflectedTransform *) clientData;
    Tcl_DriverWatchProc* watchProc;

    /* ASSERT rtPtr->methods & FLAG(METH_WATCH) */

    /*
     * We restrict the interest to what the transformation can support. IOW
     * there will never be write events for a channel which is not writable.
     * Analoguously for read events and non-readable channels.
     */

    mask &= rtPtr->mode;

    if (mask == rtPtr->interest) {
	/*
	 * Same old, same old, why should we do something?
	 */

	return;
    }

    rtPtr->interest = mask;

    /* We will be notified automatically about events on the channel below via
     * a call to 'ReflectNotify'. For this to work we have to pass the
     * interest to the parent, possibly with more events added in by the
     * transformation (--> TransformMask).
     */

    watchProc = Tcl_ChannelWatchProc (Tcl_GetChannelType (rtPtr->parent));
    (*watchProc) (Tcl_GetChannelInstanceData(rtPtr->parent),
		  mask | TransformMask (rtPtr));

    /*
     * Management of the internal timer.
     */

    if (!(mask & TCL_READABLE) || (ResultLength(&rtPtr->result) == 0)) {
	/*
	 * A pending timer may exist, but either is there no (more) interest
	 * in the events it generates or nothing is available for
	 * reading. Remove it, if existing.
	 */

	TimerKill (rtPtr);
    } else {
	/*
	 * There might be no pending timer, but there is interest in readable
	 * events and we actually have data waiting, so generate a timer to
	 * flush that if it does not exist.
	 */

	TimerSetup (rtPtr);
    }
}

static int
TransformMask (ReflectedTransform* rtPtr)
{
    Tcl_Obj *resObj;
    int mask;

    /* We are allowed to add additional events of interest to a watch mask if
     * we want to, if the transformation needs them. For this we have to ask
     * it, with all that entails (thread forwarding).
     */

    /*
     * Are we in the correct thread?
     */

#ifdef TCL_THREADS
    if (rtPtr->thread != Tcl_GetCurrentThread()) {
	ForwardParam p;

	ForwardOpToOwnerThread(rtPtr, ForwardedWatch, &p);

	return p.mask.mask;
    }
#endif

    if (InvokeTclMethod(rtPtr, "watch", NULL, NULL, &resObj) != TCL_OK) {
	Tcl_SetChannelError(rtPtr->chan, resObj);
	Tcl_DecrRefCount(resObj);	/* Remove reference held from invoke */
	return 0;
    }

    if (EncodeEventMask(rtPtr->interp, "mask", resObj, &mask) != TCL_OK) {
	Tcl_SetChannelError (rtPtr->chan, Tcl_GetObjResult(rtPtr->interp));
	Tcl_DecrRefCount(resObj);
	return 0;
    }

    Tcl_DecrRefCount(resObj);
    return mask;
}

/*
 *----------------------------------------------------------------------
 *
 * ReflectBlock --
 *
 *	This function is invoked to tell the channel which blocking behaviour
 *	is required of it.
 *
 * Results:
 *	A posix error number.
 *
 * Side effects:
 *	Allocates memory. Arbitrary, as it calls upon a script.
 *
 *----------------------------------------------------------------------
 */

static int
ReflectBlock(
    ClientData clientData,
    int nonblocking)
{
    ReflectedTransform *rtPtr = (ReflectedTransform *) clientData;

    /*
     * Transformations simply record the blocking mode in their C level
     * structure for use by --> ReflectInput. The Tcl level doesn't see this
     * information or change. As such thread forwarding is not required.
     */

    rtPtr->blocking = !nonblocking;
    return EOK;
}

/*
 *----------------------------------------------------------------------
 *
 * ReflectSetOption --
 *
 *	This function is invoked to configure a channel option.
 *
 * Results:
 *	A standard Tcl result code.
 *
 * Side effects:
 *	Arbitrary, per the parent channel.
 *
 *----------------------------------------------------------------------
 */

static int
ReflectSetOption(
    ClientData clientData,	/* Channel to query */
    Tcl_Interp *interp,		/* Interpreter to leave error messages in */
    const char *optionName,	/* Name of requested option */
    const char *newValue)	/* The new value */
{
    ReflectedTransform *rtPtr = (ReflectedTransform *) clientData;

    /*
     * Transformations have no options. Thus the call is passed down unchanged
     * to the parent channel for processing. Its results are passed back
     * unchanged as well. This all happens in the thread we are in. As the Tcl
     * level is not involved there is no need for thread forwarding.
     */

    Tcl_DriverSetOptionProc *setOptionProc = 
      Tcl_ChannelSetOptionProc (Tcl_GetChannelType (rtPtr->parent));

    if (setOptionProc != NULL) {
      return (*setOptionProc) (Tcl_GetChannelInstanceData (rtPtr->parent),
			       interp, optionName, newValue);
    } else {
      return TCL_ERROR;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * ReflectGetOption --
 *
 *	This function is invoked to retrieve all or a channel options.
 *
 * Results:
 *	A standard Tcl result code.
 *
 * Side effects:
 *	Arbitrary, per the parent channel.
 *
 *----------------------------------------------------------------------
 */

static int
ReflectGetOption(
    ClientData clientData,	/* Channel to query */
    Tcl_Interp *interp,		/* Interpreter to leave error messages in */
    const char *optionName,	/* Name of reuqested option */
    Tcl_DString *dsPtr)		/* String to place the result into */
{
    ReflectedTransform *rtPtr = (ReflectedTransform *) clientData;

    /*
     * Transformations have no options. Thus the call is passed down unchanged
     * to the parent channel for processing. Its results are passed back
     * unchanged as well. This all happens in the thread we are in. As the Tcl
     * level is not involved there is no need for thread forwarding.
     *
     * Note that the parent not having a driver for option retrieval is not an
     * immediate error. A query for all options is ok. Only a request for a
     * specific option has to fail.
     */

    Tcl_DriverGetOptionProc *getOptionProc = 
      Tcl_ChannelGetOptionProc (Tcl_GetChannelType (rtPtr->parent));

    if (getOptionProc != NULL) {
      return (*getOptionProc) (Tcl_GetChannelInstanceData (rtPtr->parent),
			       interp, optionName, dsPtr);
    } else if (optionName == (char*) NULL) {
      return TCL_OK;
    } else {
      return TCL_ERROR;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * ReflectHandle --
 *
 *	This function is invoked to retrieve the associated file handle.
 *
 * Results:
 *	A standard Tcl result code.
 *
 * Side effects:
 *	Arbitrary, per the parent channel.
 *
 *----------------------------------------------------------------------
 */

static int
ReflectHandle(
	      ClientData  clientData,
	      int         direction,
	      ClientData* handlePtr)
{
    ReflectedTransform *rtPtr = (ReflectedTransform *) clientData;

    /*
     * Transformations have no handle of their own. As such we simply query
     * the parent channel for it. This way the qery will ripple down through
     * all transformations until reaches the base channel. Which then returns
     * its handle, or fails. The former will then ripple up the stack.
     *
     * This all happens in the thread we are in. As the Tcl level is not
     * involved no forwarding is required.
     */

    return Tcl_GetChannelHandle (rtPtr->parent, direction, handlePtr);
}
/*
 *----------------------------------------------------------------------
 *
 * ReflectNotify --
 *
 *	This function is invoked to reported incoming events.
 *
 * Results:
 *	A standard Tcl result code.
 *
 * Side effects:
 *	Arbitrary, per the parent channel.
 *
 *----------------------------------------------------------------------
 */

static int
ReflectNotify(
	      ClientData clientData,
	      int mask)
{
    ReflectedTransform *rtPtr = (ReflectedTransform *) clientData;
    Tcl_Obj* maskObj;

    /*
     * An event occured in the underlying channel.  This transformation may or
     * many not process such events. If not we return the incoming mask
     * unchanged for further processing by the core.
     *
     * We do 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 ReflectWatch).
     */

    TimerKill (rtPtr);

    /*
     * The following check can be done before thread redirection, because we
     * are reading from an item which is readonly, i.e. will never change
     * during the lifetime of the channel.
     */

    if (!(rtPtr->methods & FLAG(METH_EVENT))) {
	/*
	 * No processing by the transformation, pass unchanged
	 */

	return mask;
    }

    /*
     * Another quick check we can do, does the mask contain events which are
     * of interest to the transformation ? For if not we can simply pass the
     * data up without incurring the expense of invoking the Tcl handler.
     *
     * NOTE that --> ReflectWatch updates the 'interest' field in the current
     * thread as well, so no mutex exclusion is required when querying the
     * field.
     */

    if ((mask & rtPtr->interest) == 0) {
	return mask;
    }

    /*
     * Are we in the correct thread?
     */

#ifdef TCL_THREADS
    if (rtPtr->thread != Tcl_GetCurrentThread()) {
	ForwardParam p;

	p.mask.mask = mask & rtPtr->interest;

	ForwardOpToOwnerThread(rtPtr, ForwardedEvent, &p);

	return mask & ~rtPtr->interest;
    }
#endif

    /*
     * We call the Tcl level only with events of interest to the
     * transformation, and pass the remainder up.
     */

    maskObj = DecodeEventMask(mask & rtPtr->interest);
    (void) InvokeTclMethod(rtPtr, "event", maskObj, NULL, NULL);
    Tcl_DecrRefCount(maskObj);

    return mask & ~rtPtr->interest;
}

/*
 * Helpers. =========================================================
 */

/*
 *----------------------------------------------------------------------
 *
 * EncodeEventMask --
 *
 *	This function takes a list of event items and constructs the
 *	equivalent internal bitmask. The list has to contain at least one
 *	element. Elements are "read", "write", or any unique abbreviation
 *	thereof. Note that the bitmask is not changed if problems are
 *	encountered.
 *
 * Results:
 *	A standard Tcl error code. A bitmask where TCL_READABLE and/or
 *	TCL_WRITABLE can be set.
 *
 * Side effects:
 *	May shimmer 'obj' to a list representation. May place an error message
 *	into the interp result.
 *
 *----------------------------------------------------------------------
 * DUPLICATE of 'EncodeEventMask' in tclIORChan.c
 */

static int
EncodeEventMask(
    Tcl_Interp *interp,
    const char *objName,
    Tcl_Obj *obj,
    int *mask)
{
    int events;			/* Mask of events to post */
    int listc;			/* #elements in eventspec list */
    Tcl_Obj **listv;		/* Elements of eventspec list */
    int evIndex;		/* Id of event for an element of the eventspec
				 * list. */

    if (Tcl_ListObjGetElements(interp, obj, &listc, &listv) != TCL_OK) {
	return TCL_ERROR;
    }

    if (listc < 1) {
	Tcl_AppendResult(interp, "bad ", objName, " list: is empty", NULL);
	return TCL_ERROR;
    }

    events = 0;
    while (listc > 0) {
	if (Tcl_GetIndexFromObj(interp, listv[listc-1], eventOptions,
		objName, 0, &evIndex) != TCL_OK) {
	    return TCL_ERROR;
	}
	switch (evIndex) {
	case EVENT_READ:
	    events |= TCL_READABLE;
	    break;
	case EVENT_WRITE:
	    events |= TCL_WRITABLE;
	    break;
	}
	listc --;
    }

    *mask = events;
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * DecodeEventMask --
 *
 *	This function takes an internal bitmask of events and constructs the
 *	equivalent list of event items.
 *
 * Results:
 *	A Tcl_Obj reference. The object will have a refCount of one. The user
 *	has to decrement it to release the object.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 * DUPLICATE of 'DecodeEventMask' in tclIORChan.c
 */

static Tcl_Obj *
DecodeEventMask(
    int mask)
{
    register const char *eventStr;
    Tcl_Obj *evObj;

    switch (mask & RANDW) {
    case RANDW:
	eventStr = "read write";
	break;
    case TCL_READABLE:
	eventStr = "read";
	break;
    case TCL_WRITABLE:
	eventStr = "write";
	break;
    default:
	eventStr = "";
	break;
    }

    evObj = Tcl_NewStringObj(eventStr, -1);
    Tcl_IncrRefCount(evObj);
    return evObj;
}

/*
 *----------------------------------------------------------------------
 *
 * NewReflectedTransform --
 *
 *	This function is invoked to allocate and initialize the instance data
 *	of a new reflected channel.
 *
 * Results:
 *	A heap-allocated channel instance.
 *
 * Side effects:
 *	Allocates memory.
 *
 *----------------------------------------------------------------------
 */

static ReflectedTransform *
NewReflectedTransform(
    Tcl_Interp *interp,
    Tcl_Obj *cmdpfxObj,
    int mode,
    Tcl_Obj *handleObj,
    Tcl_Channel parentChan)
{
    ReflectedTransform *rtPtr;
    int listc;
    Tcl_Obj **listv;
    int i;

    rtPtr = (ReflectedTransform *) ckalloc(sizeof(ReflectedTransform));

    /* rtPtr->chan: Assigned by caller. Dummy data here. */
    /* rtPtr->methods: Assigned by caller. Dummy data here. */

    rtPtr->chan = NULL;
    rtPtr->parent = parentChan;
    rtPtr->interp = interp;
#ifdef TCL_THREADS
    rtPtr->thread = Tcl_GetCurrentThread();
#endif
    rtPtr->timer  = (Tcl_TimerToken) NULL;
    rtPtr->methods = 0;
    rtPtr->mode = 0;
    rtPtr->interest = 0;		/* Initially no interest registered */
    rtPtr->readIsDrained = 0;
    rtPtr->blocking = 1; /* Initially a blocking channel ?
			  * TODO // Query parent for current mode.
			  */

    ResultInit (&rtPtr->result);

    /*
     * Method placeholder.
     */

    /* ASSERT: cmdpfxObj is a Tcl List */

    Tcl_ListObjGetElements(interp, cmdpfxObj, &listc, &listv);

    /*
     * See [==] as well.
     * Storage for the command prefix and the additional words required for
     * the invocation of methods in the command handler.
     *
     * listv [0] [listc-1] | [listc]  [listc+1] |
     * argv  [0]   ... [.] | [argc-2] [argc-1]  | [argc]  [argc+2]
     *       cmd   ... pfx | method   chan      | detail1 detail2
     */

    rtPtr->argc = listc + 2;
    rtPtr->argv = (Tcl_Obj**) ckalloc(sizeof(Tcl_Obj*) * (listc+4));

    /*
     * Duplicate object references.
     */

    for (i=0; i<listc ; i++) {
	Tcl_Obj *word = rtPtr->argv[i] = listv[i];
	Tcl_IncrRefCount(word);
    }

    i++;				/* Skip placeholder for method */

    /*
     * See [x] in FreeReflectedTransform for release
     */
    rtPtr->argv[i] = handleObj;
    Tcl_IncrRefCount(handleObj);

    /*
     * The next two objects are kept empty, varying arguments.
     */

    /*
     * Initialization complete.
     */

    return rtPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * NextHandle --
 *
 *	This function is invoked to generate a channel handle for a new
 *	reflected channel.
 *
 * Results:
 *	A Tcl_Obj containing the string of the new channel handle. The
 *	refcount of the returned object is -- zero --.
 *
 * Side effects:
 *	May allocate memory. Mutex protected critical section locks out other
 *	threads for a short time.
 *
 *----------------------------------------------------------------------
 */

static Tcl_Obj *
NextHandle(void)
{
    /*
     * Count number of generated reflected channels. Used for id generation.
     * Ids are never reclaimed and there is no dealing with wrap around. On
     * the other hand, "unsigned long" should be big enough except for
     * absolute longrunners (generate a 100 ids per second => overflow will
     * occur in 1 1/3 years).
     */

    TCL_DECLARE_MUTEX(rtCounterMutex)
    static unsigned long rtCounter = 0;
    Tcl_Obj *resObj;

    Tcl_MutexLock(&rtCounterMutex);
    resObj = Tcl_ObjPrintf("rt%lu", rtCounter);
    rtCounter++;
    Tcl_MutexUnlock(&rtCounterMutex);

    return resObj;
}

static void
FreeReflectedTransform(
    ReflectedTransform *rtPtr)
{
    int i, n;

    TimerKill   (rtPtr);
    ResultClear (&rtPtr->result);

    n = rtPtr->argc - 2;
    for (i=0; i<n; i++) {
	Tcl_DecrRefCount(rtPtr->argv[i]);
    }

    /*
     * See [x] in NewReflectedTransform for lock
     * n+1 = argc-1.
     */
    Tcl_DecrRefCount(rtPtr->argv[n+1]);

    ckfree((char*) rtPtr->argv);
    ckfree((char*) rtPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * InvokeTclMethod --
 *
 *	This function is used to invoke the Tcl level of a reflected channel.
 *	It handles all the command assembly, invokation, and generic state and
 *	result mgmt. It does *not* handle thread redirection; that is the
 *	responsibility of clients of this function.
 *
 * Results:
 *	Result code and data as returned by the method.
 *
 * Side effects:
 *	Arbitrary, as it calls upon a Tcl script.
 *
 *----------------------------------------------------------------------
 * Semi-DUPLICATE of 'InvokeTclMethod' in tclIORChan.c
 * - Semi because different structures are used.
 * - Still possible to factor out the commonalities into a separate structure.
 */

static int
InvokeTclMethod(
    ReflectedTransform *rtPtr,
    const char *method,
    Tcl_Obj *argOneObj,		/* NULL'able */
    Tcl_Obj *argTwoObj,		/* NULL'able */
    Tcl_Obj **resultObjPtr)	/* NULL'able */
{
    int cmdc;			/* #words in constructed command */
    Tcl_Obj *methObj = NULL;	/* Method name in object form */
    Tcl_InterpState sr;		/* State of handler interp */
    int result;			/* Result code of method invokation */
    Tcl_Obj *resObj = NULL;	/* Result of method invokation. */

    /*
     * NOTE (5): Decide impl. issue: Cache objects with method names?
     * Requires TSD data as reflections can be created in many different
     * threads.
     */

    /*
     * Insert method into the pre-allocated area, after the command prefix,
     * before the channel id.
     */

    methObj = Tcl_NewStringObj(method, -1);
    Tcl_IncrRefCount(methObj);
    rtPtr->argv[rtPtr->argc - 2] = methObj;

    /*
     * Append the additional argument containing method specific details
     * behind the channel id. If specified.
     */

    cmdc = rtPtr->argc;
    if (argOneObj) {
	Tcl_IncrRefCount(argOneObj);
	rtPtr->argv[cmdc] = argOneObj;
	cmdc++;
	if (argTwoObj) {
	    Tcl_IncrRefCount(argTwoObj);
	    rtPtr->argv[cmdc] = argTwoObj;
	    cmdc++;
	}
    }

    /*
     * And run the handler... This is done in auch a manner which leaves any
     * existing state intact.
     */

    sr = Tcl_SaveInterpState(rtPtr->interp, 0 /* Dummy */);
    Tcl_Preserve(rtPtr->interp);
    result = Tcl_EvalObjv(rtPtr->interp, cmdc, rtPtr->argv, TCL_EVAL_GLOBAL);

    /*
     * We do not try to extract the result information if the caller has no
     * interest in it. I.e. there is no need to put effort into creating
     * something which is discarded immediately after.
     */

    if (resultObjPtr) {
	if (result == TCL_OK) {
	    /*
	     * Ok result taken as is, also if the caller requests that there
	     * is no capture.
	     */

	    resObj = Tcl_GetObjResult(rtPtr->interp);
	} else {
	    /*
	     * Non-ok result is always treated as an error. We have to capture
	     * the full state of the result, including additional options.
	     *
	     * This is complex and ugly, and would be completely unnecessary
	     * if we only added support for a TCL_FORBID_EXCEPTIONS flag.
	     */
	    if (result != TCL_ERROR) {
		Tcl_Obj *cmd = Tcl_NewListObj(cmdc, rtPtr->argv);
		int cmdLen;
		const char *cmdString = Tcl_GetStringFromObj(cmd, &cmdLen);

		Tcl_IncrRefCount(cmd);
		Tcl_ResetResult(rtPtr->interp);
		Tcl_SetObjResult(rtPtr->interp, Tcl_ObjPrintf(
			"chan handler returned bad code: %d", result));
		Tcl_LogCommandInfo(rtPtr->interp, cmdString, cmdString, cmdLen);
		Tcl_DecrRefCount(cmd);
		result = TCL_ERROR;
	    }
	    Tcl_AppendObjToErrorInfo(rtPtr->interp, Tcl_ObjPrintf(
		    "\n    (chan handler subcommand \"%s\")", method));
	    resObj = MarshallError(rtPtr->interp);
	}
	Tcl_IncrRefCount(resObj);
    }
    Tcl_RestoreInterpState(rtPtr->interp, sr);
    Tcl_Release(rtPtr->interp);

    /*
     * Cleanup of the dynamic parts of the command.
     */

    Tcl_DecrRefCount(methObj);
    if (argOneObj) {
	Tcl_DecrRefCount(argOneObj);
	if (argTwoObj) {
	    Tcl_DecrRefCount(argTwoObj);
	}
    }

    /*
     * The resObj has a ref count of 1 at this location. This means that the
     * caller of InvokeTclMethod has to dispose of it (but only if it was
     * returned to it).
     */

    if (resultObjPtr != NULL) {
	*resultObjPtr = resObj;
    }

    /*
     * There no need to handle the case where nothing is returned, because for
     * that case resObj was not set anyway.
     */

    return result;
}

#ifdef TCL_THREADS
static void
ForwardOpToOwnerThread(
    ReflectedTransform *rtPtr,	/* Channel instance */
    ForwardedOperation op,	/* Forwarded driver operation */
    const VOID *param)		/* Arguments */
{
    Tcl_ThreadId dst = rtPtr->thread;
    ForwardingEvent *evPtr;
    ForwardingResult *resultPtr;
    int result;

    /*
     * Create and initialize the event and data structures.
     */

    evPtr = (ForwardingEvent *) ckalloc(sizeof(ForwardingEvent));
    resultPtr = (ForwardingResult *) ckalloc(sizeof(ForwardingResult));

    evPtr->event.proc = ForwardProc;
    evPtr->resultPtr = resultPtr;
    evPtr->op = op;
    evPtr->rtPtr = rtPtr;
    evPtr->param = (ForwardParam *) param;

    resultPtr->src = Tcl_GetCurrentThread();
    resultPtr->dst = dst;
    resultPtr->done = NULL;
    resultPtr->result = -1;
    resultPtr->evPtr = evPtr;

    /*
     * Now execute the forward.
     */

    Tcl_MutexLock(&rcForwardMutex);
    TclSpliceIn(resultPtr, forwardList);

    /*
     * Ensure cleanup of the event if any of the two involved threads exits
     * while this event is pending or in progress.
     */

    Tcl_CreateThreadExitHandler(SrcExitProc, (ClientData) evPtr);
    Tcl_CreateThreadExitHandler(DstExitProc, (ClientData) evPtr);

    /*
     * Queue the event and poke the other thread's notifier.
     */

    Tcl_ThreadQueueEvent(dst, (Tcl_Event *)evPtr, TCL_QUEUE_TAIL);
    Tcl_ThreadAlert(dst);

    /*
     * (*) Block until the other thread has either processed the transfer or
     * rejected it.
     */

    while (resultPtr->result < 0) {
	/*
	 * NOTE (1): Is it possible that the current thread goes away while
	 * waiting here? IOW Is it possible that "SrcExitProc" is called
	 * while we are here? See complementary note (2) in "SrcExitProc"
	 */

	Tcl_ConditionWait(&resultPtr->done, &rcForwardMutex, NULL);
    }

    /*
     * Unlink result from the forwarder list.
     */

    TclSpliceOut(resultPtr, forwardList);

    resultPtr->nextPtr = NULL;
    resultPtr->prevPtr = NULL;

    Tcl_MutexUnlock(&rcForwardMutex);
    Tcl_ConditionFinalize(&resultPtr->done);

    /*
     * Kill the cleanup handlers now, and the result structure as well, before
     * returning the success code.
     *
     * Note: The event structure has already been deleted.
     */

    Tcl_DeleteThreadExitHandler(SrcExitProc, (ClientData) evPtr);
    Tcl_DeleteThreadExitHandler(DstExitProc, (ClientData) evPtr);

    result = resultPtr->result;
    ckfree((char*) resultPtr);
}

static int
ForwardProc(
    Tcl_Event *evGPtr,
    int mask)
{
    /*
     * Notes regarding access to the referenced data.
     *
     * In principle the data belongs to the originating thread (see
     * evPtr->src), however this thread is currently blocked at (*), i.e.
     * quiescent. Because of this we can treat the data as belonging to us,
     * without fear of race conditions. I.e. we can read and write as we like.
     *
     * The only thing we cannot be sure of is the resultPtr. This can be be
     * NULLed if the originating thread went away while the event is handled
     * here now.
     */

    ForwardingEvent *evPtr = (ForwardingEvent *) evGPtr;
    ForwardingResult *resultPtr = evPtr->resultPtr;
    ReflectedTransform *rtPtr = evPtr->rtPtr;
    Tcl_Interp *interp = rtPtr->interp;
    ForwardParam *paramPtr = evPtr->param;
    Tcl_Obj *resObj = NULL;	/* Interp result of InvokeTclMethod */

    /*
     * Ignore the event if no one is waiting for its result anymore.
     */

    if (!resultPtr) {
	return 1;
    }

    paramPtr->base.code = TCL_OK;
    paramPtr->base.msgStr = NULL;
    paramPtr->base.mustFree = 0;

    switch (evPtr->op) {
	/*
	 * The destination thread for the following operations is
	 * rtPtr->thread, which contains rtPtr->interp, the interp we have to
	 * call upon for the driver.
	 */

    case ForwardedClose:
	/*
	 * No parameters/results.
	 */

	if (InvokeTclMethod(rtPtr, "finalize", NULL, NULL, &resObj) != TCL_OK) {
	    ForwardSetObjError(paramPtr, resObj);
	}

	/*
	 * Freeing is done here, in the origin thread, because the argv[]
	 * objects belong to this thread. Deallocating them in a different
	 * thread is not allowed
	 */

	FreeReflectedTransform(rtPtr);
	break;

    case ForwardedInput: {
	Tcl_Obj *bufObj = Tcl_NewByteArrayObj((unsigned char *) paramPtr->transform.buf,
					      paramPtr->transform.size);

	if (InvokeTclMethod(rtPtr, "read", bufObj, NULL, &resObj) != TCL_OK) {
	    ForwardSetObjError(paramPtr, resObj);
	    paramPtr->transform.size = -1;
	} else {
	    /*
	     * Process a regular return. Contains the transformation result.
	     * Sent it back to the request originator.
	     */

	    int bytec;		/* Number of returned bytes */
	    unsigned char *bytev; /* Array of returned bytes */

	    bytev = Tcl_GetByteArrayFromObj(resObj, &bytec);

	    paramPtr->transform.size = bytec;

	    if (bytec > 0) {
		paramPtr->transform.buf = ckalloc (bytec);
		memcpy(paramPtr->transform.buf, bytev, (size_t)bytec);
	    } else {
		paramPtr->transform.buf = NULL;
	    }
	}
	break;
    }

    case ForwardedOutput: {
	Tcl_Obj *bufObj = Tcl_NewByteArrayObj((unsigned char *) paramPtr->transform.buf,
					      paramPtr->transform.size);

	if (InvokeTclMethod(rtPtr, "write", bufObj, NULL, &resObj) != TCL_OK) {
	    ForwardSetObjError(paramPtr, resObj);
	    paramPtr->transform.size = -1;
	} else {
	    /*
	     * Process a regular return. Contains the transformation result.
	     * Sent it back to the request originator.
	     */

	    int bytec;		/* Number of returned bytes */
	    unsigned char *bytev; /* Array of returned bytes */

	    bytev = Tcl_GetByteArrayFromObj(resObj, &bytec);

	    paramPtr->transform.size = bytec;

	    if (bytec > 0) {
		paramPtr->transform.buf = ckalloc (bytec);
		memcpy(paramPtr->transform.buf, bytev, (size_t)bytec);
	    } else {
		paramPtr->transform.buf = NULL;
	    }
	}
	break;
    }

    case ForwardedDrain: {
	if (InvokeTclMethod(rtPtr, "drain", NULL, NULL, &resObj) != TCL_OK) {
	    ForwardSetObjError(paramPtr, resObj);
	    paramPtr->transform.size = -1;
	} else {
	    /*
	     * Process a regular return. Contains the transformation result.
	     * Sent it back to the request originator.
	     */

	    int bytec;		/* Number of returned bytes */
	    unsigned char *bytev; /* Array of returned bytes */

	    bytev = Tcl_GetByteArrayFromObj(resObj, &bytec);

	    paramPtr->transform.size = bytec;

	    if (bytec > 0) {
		paramPtr->transform.buf = ckalloc (bytec);
		memcpy(paramPtr->transform.buf, bytev, (size_t)bytec);
	    } else {
		paramPtr->transform.buf = NULL;
	    }
	}
	break;
    }

    case ForwardedFlush: {
	if (InvokeTclMethod(rtPtr, "flush", NULL, NULL, &resObj) != TCL_OK) {
	    ForwardSetObjError(paramPtr, resObj);
	    paramPtr->transform.size = -1;
	} else {
	    /*
	     * Process a regular return. Contains the transformation result.
	     * Sent it back to the request originator.
	     */

	    int bytec;		/* Number of returned bytes */
	    unsigned char *bytev; /* Array of returned bytes */

	    bytev = Tcl_GetByteArrayFromObj(resObj, &bytec);

	    paramPtr->transform.size = bytec;

	    if (bytec > 0) {
		paramPtr->transform.buf = ckalloc (bytec);
		memcpy(paramPtr->transform.buf, bytev, (size_t)bytec);
	    } else {
		paramPtr->transform.buf = NULL;
	    }
	}
	break;
    }

    case ForwardedEvent: {
	Tcl_Obj *maskObj = DecodeEventMask(paramPtr->mask.mask);

	(void) InvokeTclMethod(rtPtr, "event", maskObj, NULL, NULL);
	Tcl_DecrRefCount(maskObj);
	break;
    }

    case ForwardedClear: {
	(void) InvokeTclMethod(rtPtr, "clear", NULL, NULL, NULL);
	break;
    }

    case ForwardedLimit: {
	Tcl_Obj* resObj;

	if (InvokeTclMethod(rtPtr, "limit", NULL, NULL, &resObj) != TCL_OK) {
	    ForwardSetObjError(paramPtr, resObj);
	    paramPtr->limit.max = -1;
	} else if (Tcl_GetIntFromObj(interp, resObj, &paramPtr->limit.max) != TCL_OK) {
	    ForwardSetObjError(paramPtr, MarshallError(interp));
	    paramPtr->limit.max = -1;
	}

	Tcl_DecrRefCount(resObj);
	break;
    }

    case ForwardedWatch: {
	Tcl_Obj* resObj;

	if (InvokeTclMethod(rtPtr, "watch", NULL, NULL, &resObj) != TCL_OK) {
	    ForwardSetObjError(paramPtr, resObj);
	    paramPtr->mask.mask = 0;
	} else if (EncodeEventMask(rtPtr->interp, "mask", resObj, &paramPtr->mask.mask) != TCL_OK) {
	    ForwardSetObjError(paramPtr, MarshallError(interp));
	    paramPtr->mask.mask = 0;
	}

	Tcl_DecrRefCount(resObj);
	break;
    }

    default:
	/*
	 * Bad operation code.
	 */
	Tcl_Panic("Bad operation code in ForwardProc");
	break;
    }

    /*
     * Remove the reference we held on the result of the invoke, if we had
     * such.
     */

    if (resObj != NULL) {
	Tcl_DecrRefCount(resObj);
    }

    if (resultPtr) {
	/*
	 * Report the forwarding result synchronously to the waiting caller.
	 * This unblocks (*) as well. This is wrapped into a conditional
	 * because the caller may have exited in the mean time.
	 */

	Tcl_MutexLock(&rcForwardMutex);
	resultPtr->result = TCL_OK;
	Tcl_ConditionNotify(&resultPtr->done);
	Tcl_MutexUnlock(&rcForwardMutex);
    }

    return 1;
}

static void
SrcExitProc(
    ClientData clientData)
{
    ForwardingEvent *evPtr = (ForwardingEvent *) clientData;
    ForwardingResult *resultPtr;
    ForwardParam *paramPtr;

    /*
     * NOTE (2): Can this handler be called with the originator blocked?
     */

    /*
     * The originator for the event exited. It is not sure if this can happen,
     * as the originator should be blocked at (*) while the event is in
     * transit/pending.
     *
     * We make sure that the event cannot refer to the result anymore, remove
     * it from the list of pending results and free the structure. Locking the
     * access ensures that we cannot get in conflict with "ForwardProc",
     * should it already execute the event.
     */

    Tcl_MutexLock(&rcForwardMutex);

    resultPtr = evPtr->resultPtr;
    paramPtr = evPtr->param;

    evPtr->resultPtr = NULL;
    resultPtr->evPtr = NULL;
    resultPtr->result = TCL_ERROR;

    ForwardSetStaticError(paramPtr, msg_send_originlost);

    /*
     * See below: TclSpliceOut(resultPtr, forwardList);
     */

    Tcl_MutexUnlock(&rcForwardMutex);

    /*
     * This unlocks (*). The structure will be spliced out and freed by
     * "ForwardProc". Maybe.
     */

    Tcl_ConditionNotify(&resultPtr->done);
}

static void
DstExitProc(
    ClientData clientData)
{
    ForwardingEvent *evPtr = (ForwardingEvent *) clientData;
    ForwardingResult *resultPtr = evPtr->resultPtr;
    ForwardParam *paramPtr = evPtr->param;

    /*
     * NOTE (3): It is not clear if the event still exists when this handler
     * is called. We might have to use 'resultPtr' as our clientData instead.
     */

    /*
     * The receiver for the event exited, before processing the event. We
     * detach the result now, wake the originator up and signal failure.
     */

    evPtr->resultPtr = NULL;
    resultPtr->evPtr = NULL;
    resultPtr->result = TCL_ERROR;

    ForwardSetStaticError(paramPtr, msg_send_dstlost);

    Tcl_ConditionNotify(&resultPtr->done);
}

static void
ForwardSetObjError(
    ForwardParam *paramPtr,
    Tcl_Obj *obj)
{
    int len;
    const char *msgStr = Tcl_GetStringFromObj(obj, &len);

    len++;
    ForwardSetDynamicError(paramPtr, ckalloc((unsigned) len));
    memcpy(paramPtr->base.msgStr, msgStr, (unsigned) len);
}
#endif

/*
 *----------------------------------------------------------------------
 *
 *	TimerKill --
 *
 *	Timer management. Removes the internal timer
 *	if it exists.
 *
 *	Sideeffects:
 *		See above.
 *
 *	Result:
 *		None.
 *
 *----------------------------------------------------------------------
 */

static void
TimerKill (ReflectedTransform* rtPtr)
{
    if (rtPtr->timer == (Tcl_TimerToken) NULL) return;

    /* Delete an existing flush-out timer, prevent it from firing on a
     * removed/dead channel.
     */

    Tcl_DeleteTimerHandler (rtPtr->timer);
    rtPtr->timer = (Tcl_TimerToken) NULL;
}

/*
 *----------------------------------------------------------------------
 *
 *	TimerSetup --
 *
 *	Timer management. Creates the internal timer
 *	if it does not exist.
 *
 *	Sideeffects:
 *		See above.
 *
 *	Result:
 *		None.
 *
 *----------------------------------------------------------------------
 */

static void
TimerSetup (ReflectedTransform* rtPtr)
{
    if (rtPtr->timer != (Tcl_TimerToken) NULL) return;

    rtPtr->timer = Tcl_CreateTimerHandler (FLUSH_DELAY, TimerRun,
					   (ClientData) rtPtr);
}

/*
 *----------------------------------------------------------------------
 *
 *	TimerRun --
 *
 *	Called by the notifier (-> timer) to flush out
 *	information waiting in channel buffers.
 *
 *	Sideeffects:
 *		As of 'Tcl_NotifyChannel'.
 *
 *	Result:
 *		None.
 *
 *----------------------------------------------------------------------
 */

static void
TimerRun (ClientData clientData)
{
    ReflectedTransform* rtPtr = (ReflectedTransform*) clientData;

    rtPtr->timer = (Tcl_TimerToken) NULL;
    Tcl_NotifyChannel (rtPtr->chan, TCL_READABLE);
}


/*
 *----------------------------------------------------------------------
 *
 *	ResultInit --
 *
 *	Initializes the specified buffer structure. The
 *	structure will contain valid information for an
 *	emtpy buffer.
 *
 *	Sideeffects:
 *		See above.
 *
 *	Result:
 *		None.
 *
 *----------------------------------------------------------------------
 */

static void
ResultInit (ResultBuffer* r) /* Reference to the structure to initialize */
{
    r->used      = 0;
    r->allocated = 0;
    r->buf       = (unsigned char*) NULL;
}
/*
 *----------------------------------------------------------------------
 *
 *	ResultClear --
 *
 *	Deallocates any memory allocated by 'ResultAdd'.
 *
 *	Sideeffects:
 *		See above.
 *
 *	Result:
 *		None.
 *
 *----------------------------------------------------------------------
 */

static void
ResultClear (ResultBuffer* r) /* Reference to the buffer to clear out */
{
    r->used = 0;

    if (!r->allocated) return;

    Tcl_Free ((char*) r->buf);
    r->buf       = (unsigned char*) NULL;
    r->allocated = 0;
}

/*
 *----------------------------------------------------------------------
 *
 *	ResultAdd --
 *
 *	Adds the bytes in the specified array to the
 *	buffer, by appending it.
 *
 *	Sideeffects:
 *		See above.
 *
 *	Result:
 *		None.
 *
 *----------------------------------------------------------------------
 */

static void
ResultAdd (r, buf, toWrite)
     ResultBuffer*  r;       /* The buffer to extend */
     unsigned char* buf;     /* The buffer to read from */
     int            toWrite; /* The number of bytes in 'buf' */
{
    if ((r->used + toWrite + 1) > r->allocated) {
	/* Extension of the internal buffer is required.
	 * NOTE: Currently linear. Should be doubling to amortize.
	 */

	if (r->allocated == 0) {
	    r->allocated = toWrite + RB_INCREMENT;
	    r->buf       = (unsigned char*) Tcl_Alloc (r->allocated);
	} else {
	    r->allocated += toWrite + RB_INCREMENT;
	    r->buf        = (unsigned char*) Tcl_Realloc((char*) r->buf,
							 r->allocated);
	}
    }

    /* now copy data */
    memcpy (r->buf + r->used, buf, toWrite);
    r->used += toWrite;
}

/*
 *----------------------------------------------------------------------
 *
 *	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.
 *
 *	Sideeffects:
 *		See above.
 *
 *	Result:
 *		The number of actually copied bytes,
 *		possibly less than 'toRead'.
 *
 *----------------------------------------------------------------------
 */

static int
ResultCopy (ResultBuffer*  r,      /* The buffer to read from */
	    unsigned char* buf,    /* The buffer to copy into */
	    int            toRead) /* Number of requested bytes */
{
    int copied;

    if (r->used == 0) {
	/* Nothing to copy in the case of an empty buffer.
	 */

	copied = 0;
	goto done;
    }

    if (r->used == toRead) {
	/* We have just enough. Copy everything to the caller.
	 */

	memcpy ((VOID*) buf, (VOID*) r->buf, toRead);
	r->used = 0;
	copied  = toRead;
	goto done;
    }

    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  ((VOID*) buf,    (VOID*) r->buf,            toRead);
	memmove ((VOID*) r->buf, (VOID*) (r->buf + toRead), r->used - toRead);

	r->used -= toRead;
	copied   = toRead;
	goto done;
    }

    /* There is not enough in the buffer to satisfy the caller, so
     * take everything.
     */

    memcpy ((VOID*) buf, (VOID*) r->buf, r->used);
    toRead  = r->used;
    r->used = 0;
    copied  = toRead;

    /* -- common postwork code ------- */

 done:
    return copied;
}


static int
TransformRead (
       ReflectedTransform* rtPtr,
       int* errorCodePtr,
       unsigned char* buf,
       int toRead)
{
    Tcl_Obj* bufObj;
    Tcl_Obj* resObj;
    int bytec;			/* Number of returned bytes */
    unsigned char *bytev;	/* Array of returned bytes */

    /*
     * Are we in the correct thread?
     */

#ifdef TCL_THREADS
    if (rtPtr->thread != Tcl_GetCurrentThread()) {
	ForwardParam p;

	p.transform.buf  = buf;
	p.transform.size = toRead;

	ForwardOpToOwnerThread(rtPtr, ForwardedInput, &p);

	if (p.base.code != TCL_OK) {
	    PassReceivedError(rtPtr->chan, &p);
	    *errorCodePtr = EINVAL;
	    return 0;
	} else {
	    *errorCodePtr = EOK;
	}

	ResultAdd (&rtPtr->result, p.transform.buf, p.transform.size);
	ckfree (p.transform.buf);
    } else {
#endif
	/* ASSERT: rtPtr->method & FLAG(METH_READ) */
	/* ASSERT: rtPtr->mode & TCL_READABLE */

	bufObj = Tcl_NewByteArrayObj((unsigned char *) buf, toRead);
	if (InvokeTclMethod(rtPtr, "read", bufObj, NULL, &resObj) != TCL_OK) {
	    Tcl_SetChannelError(rtPtr->chan, resObj);
	    Tcl_DecrRefCount(resObj);	/* Remove reference held from invoke */
	    *errorCodePtr = EINVAL;
	    return 0;
	}

	bytev = Tcl_GetByteArrayFromObj(resObj, &bytec);
	ResultAdd (&rtPtr->result, bytev, bytec);
	Tcl_DecrRefCount(resObj);	/* Remove reference held from invoke */
#ifdef TCL_THREADS
    }
#endif

    return 1;
}

static int
TransformWrite (
	ReflectedTransform* rtPtr,
	int* errorCodePtr,
	unsigned char* buf,
	int toWrite)
{
    Tcl_Obj *bufObj;
    Tcl_Obj *resObj;
    int bytec;			/* Number of returned bytes */
    unsigned char *bytev;	/* Array of returned bytes */
    int res;

    /*
     * Are we in the correct thread?
     */

#ifdef TCL_THREADS
    if (rtPtr->thread != Tcl_GetCurrentThread()) {
	ForwardParam p;

	p.transform.buf  = buf;
	p.transform.size = toWrite;

	ForwardOpToOwnerThread(rtPtr, ForwardedOutput, &p);

	if (p.base.code != TCL_OK) {
	    PassReceivedError(rtPtr->chan, &p);
	    *errorCodePtr = EINVAL;
	    return 0;
	} else {
	    *errorCodePtr = EOK;
	}

	res = Tcl_WriteRaw (rtPtr->parent,
			    (char*) p.transform.buf, p.transform.size);
	ckfree (p.transform.buf);
    } else {
#endif
	/* ASSERT: rtPtr->method & FLAG(METH_WRITE) */
	/* ASSERT: rtPtr->mode & TCL_WRITABLE */

	bufObj = Tcl_NewByteArrayObj((unsigned char *) buf, toWrite);
	if (InvokeTclMethod(rtPtr, "write", bufObj, NULL, &resObj) != TCL_OK) {
	    Tcl_SetChannelError(rtPtr->chan, resObj);
	    Tcl_DecrRefCount(resObj);	/* Remove reference held from invoke */
	    return 0;
	}

	*errorCodePtr = EOK;

	bytev = Tcl_GetByteArrayFromObj(resObj, &bytec);
	res   = Tcl_WriteRaw (rtPtr->parent,  (char*) bytev, bytec);
	Tcl_DecrRefCount(resObj);		/* Remove reference held from invoke */
#ifdef TCL_THREADS
    }
#endif

    if (res < 0) {
	*errorCodePtr = EINVAL;
	return 0;
    }

    return 1;
}



static int
TransformDrain(
      ReflectedTransform* rtPtr,
      int* errorCodePtr)
{
    Tcl_Obj* resObj;
    int bytec;			/* Number of returned bytes */
    unsigned char *bytev;	/* Array of returned bytes */

    /*
     * Are we in the correct thread?
     */

#ifdef TCL_THREADS
    if (rtPtr->thread != Tcl_GetCurrentThread()) {
	ForwardParam p;

	ForwardOpToOwnerThread(rtPtr, ForwardedDrain, &p);

	if (p.base.code != TCL_OK) {
	    PassReceivedError(rtPtr->chan, &p);
	    *errorCodePtr = EINVAL;
	    return 0;
	} else {
	    *errorCodePtr = EOK;
	}

	ResultAdd (&rtPtr->result, p.transform.buf, p.transform.size);
	ckfree (p.transform.buf);
    } else {
#endif
	if (InvokeTclMethod(rtPtr, "drain", NULL, NULL, &resObj)!=TCL_OK) {
	    Tcl_SetChannelError(rtPtr->chan, resObj);
	    Tcl_DecrRefCount(resObj);	/* Remove reference held from invoke */
	    *errorCodePtr = EINVAL;
	    return 0;
	}

	bytev = Tcl_GetByteArrayFromObj(resObj, &bytec);
	ResultAdd (&rtPtr->result, bytev, bytec);

	Tcl_DecrRefCount(resObj);	/* Remove reference held from invoke */

#ifdef TCL_THREADS
    }
#endif

    rtPtr->readIsDrained = 1;
    return 1;
}


static int
TransformFlush(
      ReflectedTransform* rtPtr,
      int* errorCodePtr)
{
    Tcl_Obj* resObj;
    int bytec;			/* Number of returned bytes */
    unsigned char *bytev;	/* Array of returned bytes */
    int res;

    /*
     * Are we in the correct thread?
     */

#ifdef TCL_THREADS
    if (rtPtr->thread != Tcl_GetCurrentThread()) {
	ForwardParam p;

	ForwardOpToOwnerThread(rtPtr, ForwardedFlush, &p);

	if (p.base.code != TCL_OK) {
	    PassReceivedError(rtPtr->chan, &p);
	    *errorCodePtr = EINVAL;
	    return 0;
	} else {
	    *errorCodePtr = EOK;
	}

	res = Tcl_WriteRaw (rtPtr->parent,
			    (char*) p.transform.buf, p.transform.size);
	ckfree(p.transform.buf);
    } else {
#endif
	if (InvokeTclMethod(rtPtr, "flush", NULL, NULL, &resObj)!=TCL_OK) {
	    Tcl_SetChannelError(rtPtr->chan, resObj);
	    Tcl_DecrRefCount(resObj);	/* Remove reference held from invoke */
	    *errorCodePtr = EINVAL;
	    return 0;
	}

	bytev = Tcl_GetByteArrayFromObj(resObj, &bytec);
	res   = Tcl_WriteRaw (rtPtr->parent,  (char*) bytev, bytec);
	Tcl_DecrRefCount(resObj);	/* Remove reference held from invoke */

#ifdef TCL_THREADS
    }
#endif
    if (res < 0) {
	*errorCodePtr = EINVAL;
	return 0;
    }

    return 1;
}

static void
TransformClear (
	ReflectedTransform* rtPtr)
{
    /*
     * Are we in the correct thread?
     */

#ifdef TCL_THREADS
    if (rtPtr->thread != Tcl_GetCurrentThread()) {
	ForwardParam p;

	ForwardOpToOwnerThread(rtPtr, ForwardedClear, &p);
	return;
    } else {
#endif
	/* ASSERT: rtPtr->method & FLAG(METH_READ) */
	/* ASSERT: rtPtr->mode & TCL_READABLE */

	(void) InvokeTclMethod(rtPtr, "clear", NULL, NULL, NULL);

#ifdef TCL_THREADS
    }
#endif

    rtPtr->readIsDrained = 0;
    ResultClear (&rtPtr->result);
}

static int
TransformLimit (
	ReflectedTransform* rtPtr,
	int* errorCodePtr,
	int* maxPtr)
{
    Tcl_Obj* resObj;

    /*
     * Are we in the correct thread?
     */

#ifdef TCL_THREADS
    if (rtPtr->thread != Tcl_GetCurrentThread()) {
	ForwardParam p;

	ForwardOpToOwnerThread(rtPtr, ForwardedLimit, &p);

	if (p.base.code != TCL_OK) {
	    PassReceivedError(rtPtr->chan, &p);
	    *errorCodePtr = EINVAL;
	    return 0;
	} else {
	    *errorCodePtr = EOK;
	    *maxPtr = p.limit.max;
	    return 1;
	}
    }
#endif

    /* ASSERT: rtPtr->method & FLAG(METH_WRITE) */
    /* ASSERT: rtPtr->mode & TCL_WRITABLE */

    if (InvokeTclMethod(rtPtr, "limit?", NULL, NULL, &resObj) != TCL_OK) {
	Tcl_SetChannelError(rtPtr->chan, resObj);
	Tcl_DecrRefCount(resObj);	/* Remove reference held from invoke */
	*errorCodePtr = EINVAL;
	return 0;
    }

    if (Tcl_GetIntFromObj(rtPtr->interp, resObj, maxPtr) != TCL_OK) {
	Tcl_DecrRefCount(resObj);	/* Remove reference held from invoke */
	Tcl_SetChannelError(rtPtr->chan, MarshallError(rtPtr->interp));
	*errorCodePtr = EINVAL;
	return 0;
    }

    Tcl_DecrRefCount(resObj);		/* Remove reference held from invoke */
    return 1;
}

/* DUPLICATE of HaveVersion() in tclIO.c
 *----------------------------------------------------------------------
 *
 * HaveVersion --
 *
 *	Return whether a channel type is (at least) of a given version.
 *
 * Results:
 *	True if the minimum version is exceeded by the version actually
 *	present.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

static int
HaveVersion(
    const Tcl_ChannelType *chanTypePtr,
    Tcl_ChannelTypeVersion minimumVersion)
{
    Tcl_ChannelTypeVersion actualVersion = Tcl_ChannelVersion(chanTypePtr);

    return (PTR2INT(actualVersion)) >= (PTR2INT(minimumVersion));
}

/*
 * Local Variables:
 * mode: c
 * c-basic-offset: 4
 * fill-column: 78
 * End:
 */