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tclIOUtil.c

/* 
 * tclIOUtil.c --
 *
 *    This file contains a collection of utility procedures that
 *    are shared by the platform specific IO drivers.
 *
 *    Parts of this file are based on code contributed by Karl
 *    Lehenbauer, Mark Diekhans and Peter da Silva.
 *
 * Copyright (c) 1991-1994 The Regents of the University of California.
 * Copyright (c) 1994-1997 Sun Microsystems, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution
 * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 *
 * RCS: @(#) $Id: tclIOUtil.c,v 1.9 1999/11/10 02:51:56 hobbs Exp $
 */

#include "tclInt.h"
#include "tclPort.h"

/*
 * The following typedef declarations allow for hooking into the chain
 * of functions maintained for 'Tcl_Stat(...)', 'Tcl_Access(...)' &
 * 'Tcl_OpenFileChannel(...)'.  Basically for each hookable function
 * a linked list is defined.
 */

typedef struct StatProc {
    TclStatProc_ *proc;        /* Function to process a 'stat()' call */
    struct StatProc *nextPtr;    /* The next 'stat()' function to call */
} StatProc;

typedef struct AccessProc {
    TclAccessProc_ *proc;      /* Function to process a 'access()' call */
    struct AccessProc *nextPtr;  /* The next 'access()' function to call */
} AccessProc;

typedef struct OpenFileChannelProc {
    TclOpenFileChannelProc_ *proc;  /* Function to process a
                             * 'Tcl_OpenFileChannel()' call */
    struct OpenFileChannelProc *nextPtr;
                            /* The next 'Tcl_OpenFileChannel()'
                             * function to call */
} OpenFileChannelProc;

/*
 * For each type of hookable function, a static node is declared to
 * hold the function pointer for the "built-in" routine (e.g.
 * 'TclpStat(...)') and the respective list is initialized as a pointer
 * to that node.
 * 
 * The "delete" functions (e.g. 'TclStatDeleteProc(...)') ensure that
 * these statically declared list entry cannot be inadvertently removed.
 *
 * This method avoids the need to call any sort of "initialization"
 * function.
 *
 * All three lists are protected by a global hookMutex.
 */

static StatProc defaultStatProc = {
    &TclpStat, NULL
};
static StatProc *statProcList = &defaultStatProc;

static AccessProc defaultAccessProc = {
    &TclpAccess, NULL
};
static AccessProc *accessProcList = &defaultAccessProc;

static OpenFileChannelProc defaultOpenFileChannelProc = {
    &TclpOpenFileChannel, NULL
};
static OpenFileChannelProc *openFileChannelProcList =
      &defaultOpenFileChannelProc;

TCL_DECLARE_MUTEX(hookMutex)

/*
 *---------------------------------------------------------------------------
 *
 * TclGetOpenMode --
 *
 * Description:
 *    Computes a POSIX mode mask for opening a file, from a given string,
 *    and also sets a flag to indicate whether the caller should seek to
 *    EOF after opening the file.
 *
 * Results:
 *    On success, returns mode to pass to "open". If an error occurs, the
 *    return value is -1 and if interp is not NULL, sets interp's result
 *    object to an error message.
 *
 * Side effects:
 *    Sets the integer referenced by seekFlagPtr to 1 to tell the caller
 *    to seek to EOF after opening the file.
 *
 * Special note:
 *    This code is based on a prototype implementation contributed
 *    by Mark Diekhans.
 *
 *---------------------------------------------------------------------------
 */

int
TclGetOpenMode(interp, string, seekFlagPtr)
    Tcl_Interp *interp;             /* Interpreter to use for error
                               * reporting - may be NULL. */
    char *string;             /* Mode string, e.g. "r+" or
                               * "RDONLY CREAT". */
    int *seekFlagPtr;               /* Set this to 1 if the caller
                                         * should seek to EOF during the
                                         * opening of the file. */
{
    int mode, modeArgc, c, i, gotRW;
    char **modeArgv, *flag;
#define RW_MODES (O_RDONLY|O_WRONLY|O_RDWR)

    /*
     * Check for the simpler fopen-like access modes (e.g. "r").  They
     * are distinguished from the POSIX access modes by the presence
     * of a lower-case first letter.
     */

    *seekFlagPtr = 0;
    mode = 0;

    /*
     * Guard against international characters before using byte oriented
     * routines.
     */

    if (!(string[0] & 0x80)
          && islower(UCHAR(string[0]))) { /* INTL: ISO only. */
      switch (string[0]) {
          case 'r':
            mode = O_RDONLY;
            break;
          case 'w':
            mode = O_WRONLY|O_CREAT|O_TRUNC;
            break;
          case 'a':
            mode = O_WRONLY|O_CREAT;
                *seekFlagPtr = 1;
            break;
          default:
            error:
                if (interp != (Tcl_Interp *) NULL) {
                    Tcl_AppendResult(interp,
                            "illegal access mode \"", string, "\"",
                            (char *) NULL);
                }
            return -1;
      }
      if (string[1] == '+') {
          mode &= ~(O_RDONLY|O_WRONLY);
          mode |= O_RDWR;
          if (string[2] != 0) {
            goto error;
          }
      } else if (string[1] != 0) {
          goto error;
      }
        return mode;
    }

    /*
     * The access modes are specified using a list of POSIX modes
     * such as O_CREAT.
     *
     * IMPORTANT NOTE: We rely on Tcl_SplitList working correctly when
     * a NULL interpreter is passed in.
     */

    if (Tcl_SplitList(interp, string, &modeArgc, &modeArgv) != TCL_OK) {
        if (interp != (Tcl_Interp *) NULL) {
            Tcl_AddErrorInfo(interp,
                    "\n    while processing open access modes \"");
            Tcl_AddErrorInfo(interp, string);
            Tcl_AddErrorInfo(interp, "\"");
        }
        return -1;
    }
    
    gotRW = 0;
    for (i = 0; i < modeArgc; i++) {
      flag = modeArgv[i];
      c = flag[0];
      if ((c == 'R') && (strcmp(flag, "RDONLY") == 0)) {
          mode = (mode & ~RW_MODES) | O_RDONLY;
          gotRW = 1;
      } else if ((c == 'W') && (strcmp(flag, "WRONLY") == 0)) {
          mode = (mode & ~RW_MODES) | O_WRONLY;
          gotRW = 1;
      } else if ((c == 'R') && (strcmp(flag, "RDWR") == 0)) {
          mode = (mode & ~RW_MODES) | O_RDWR;
          gotRW = 1;
      } else if ((c == 'A') && (strcmp(flag, "APPEND") == 0)) {
          mode |= O_APPEND;
            *seekFlagPtr = 1;
      } else if ((c == 'C') && (strcmp(flag, "CREAT") == 0)) {
          mode |= O_CREAT;
      } else if ((c == 'E') && (strcmp(flag, "EXCL") == 0)) {
          mode |= O_EXCL;
      } else if ((c == 'N') && (strcmp(flag, "NOCTTY") == 0)) {
#ifdef O_NOCTTY
          mode |= O_NOCTTY;
#else
          if (interp != (Tcl_Interp *) NULL) {
                Tcl_AppendResult(interp, "access mode \"", flag,
                        "\" not supported by this system", (char *) NULL);
            }
            ckfree((char *) modeArgv);
          return -1;
#endif
      } else if ((c == 'N') && (strcmp(flag, "NONBLOCK") == 0)) {
#if defined(O_NDELAY) || defined(O_NONBLOCK)
#   ifdef O_NONBLOCK
          mode |= O_NONBLOCK;
#   else
          mode |= O_NDELAY;
#   endif
#else
            if (interp != (Tcl_Interp *) NULL) {
                Tcl_AppendResult(interp, "access mode \"", flag,
                        "\" not supported by this system", (char *) NULL);
            }
            ckfree((char *) modeArgv);
          return -1;
#endif
      } else if ((c == 'T') && (strcmp(flag, "TRUNC") == 0)) {
          mode |= O_TRUNC;
      } else {
            if (interp != (Tcl_Interp *) NULL) {
                Tcl_AppendResult(interp, "invalid access mode \"", flag,
                        "\": must be RDONLY, WRONLY, RDWR, APPEND, CREAT",
                        " EXCL, NOCTTY, NONBLOCK, or TRUNC", (char *) NULL);
            }
          ckfree((char *) modeArgv);
          return -1;
      }
    }
    ckfree((char *) modeArgv);
    if (!gotRW) {
        if (interp != (Tcl_Interp *) NULL) {
            Tcl_AppendResult(interp, "access mode must include either",
                    " RDONLY, WRONLY, or RDWR", (char *) NULL);
        }
      return -1;
    }
    return mode;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_EvalFile --
 *
 *    Read in a file and process the entire file as one gigantic
 *    Tcl command.
 *
 * Results:
 *    A standard Tcl result, which is either the result of executing
 *    the file or an error indicating why the file couldn't be read.
 *
 * Side effects:
 *    Depends on the commands in the file.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_EvalFile(interp, fileName)
    Tcl_Interp *interp;       /* Interpreter in which to process file. */
    char *fileName;           /* Name of file to process.  Tilde-substitution
                         * will be performed on this name. */
{
    int result, length;
    struct stat statBuf;
    char *oldScriptFile;
    Interp *iPtr;
    Tcl_DString nameString;
    char *name, *string;
    Tcl_Channel chan;
    Tcl_Obj *objPtr;

    name = Tcl_TranslateFileName(interp, fileName, &nameString);
    if (name == NULL) {
      return TCL_ERROR;
    }

    result = TCL_ERROR;
    objPtr = Tcl_NewObj();

    if (TclStat(name, &statBuf) == -1) {
        Tcl_SetErrno(errno);
      Tcl_AppendResult(interp, "couldn't read file \"", fileName,
            "\": ", Tcl_PosixError(interp), (char *) NULL);
      goto end;
    }
    chan = Tcl_OpenFileChannel(interp, name, "r", 0644);
    if (chan == (Tcl_Channel) NULL) {
        Tcl_ResetResult(interp);
      Tcl_AppendResult(interp, "couldn't read file \"", fileName,
            "\": ", Tcl_PosixError(interp), (char *) NULL);
      goto end;
    }
    if (Tcl_ReadChars(chan, objPtr, -1, 0) < 0) {
        Tcl_Close(interp, chan);
      Tcl_AppendResult(interp, "couldn't read file \"", fileName,
            "\": ", Tcl_PosixError(interp), (char *) NULL);
      goto end;
    }
    if (Tcl_Close(interp, chan) != TCL_OK) {
        goto end;
    }

    iPtr = (Interp *) interp;
    oldScriptFile = iPtr->scriptFile;
    iPtr->scriptFile = fileName;
    string = Tcl_GetStringFromObj(objPtr, &length);
    result = Tcl_EvalEx(interp, string, length, 0);
    iPtr->scriptFile = oldScriptFile;

    if (result == TCL_RETURN) {
      result = TclUpdateReturnInfo(iPtr);
    } else if (result == TCL_ERROR) {
      char msg[200 + TCL_INTEGER_SPACE];

      /*
       * Record information telling where the error occurred.
       */

      sprintf(msg, "\n    (file \"%.150s\" line %d)", fileName,
            interp->errorLine);
      Tcl_AddErrorInfo(interp, msg);
    }

    end:
    Tcl_DecrRefCount(objPtr);
    Tcl_DStringFree(&nameString);
    return result;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetErrno --
 *
 *    Gets the current value of the Tcl error code variable. This is
 *    currently the global variable "errno" but could in the future
 *    change to something else.
 *
 * Results:
 *    The value of the Tcl error code variable.
 *
 * Side effects:
 *    None. Note that the value of the Tcl error code variable is
 *    UNDEFINED if a call to Tcl_SetErrno did not precede this call.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_GetErrno()
{
    return errno;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_SetErrno --
 *
 *    Sets the Tcl error code variable to the supplied value.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Modifies the value of the Tcl error code variable.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_SetErrno(err)
    int err;                  /* The new value. */
{
    errno = err;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_PosixError --
 *
 *    This procedure is typically called after UNIX kernel calls
 *    return errors.  It stores machine-readable information about
 *    the error in $errorCode returns an information string for
 *    the caller's use.
 *
 * Results:
 *    The return value is a human-readable string describing the
 *    error.
 *
 * Side effects:
 *    The global variable $errorCode is reset.
 *
 *----------------------------------------------------------------------
 */

char *
Tcl_PosixError(interp)
    Tcl_Interp *interp;       /* Interpreter whose $errorCode variable
                         * is to be changed. */
{
    char *id, *msg;

    msg = Tcl_ErrnoMsg(errno);
    id = Tcl_ErrnoId();
    Tcl_SetErrorCode(interp, "POSIX", id, msg, (char *) NULL);
    return msg;
}

/*
 *----------------------------------------------------------------------
 *
 * TclStat --
 *
 *    This procedure replaces the library version of stat and lsat.
 *    The chain of functions that have been "inserted" into the
 *    'statProcList' will be called in succession until either
 *    a value of zero is returned, or the entire list is visited.
 *
 * Results:
 *      See stat documentation.
 *
 * Side effects:
 *      See stat documentation.
 *
 *----------------------------------------------------------------------
 */

int
TclStat(path, buf)
    CONST char *path;         /* Path of file to stat (in current CP). */
    struct stat *buf;         /* Filled with results of stat call. */
{
    StatProc *statProcPtr;
    int retVal = -1;

    /*
     * Call each of the "stat" function in succession.  A non-return
     * value of -1 indicates the particular function has succeeded.
     */

    Tcl_MutexLock(&hookMutex);
    statProcPtr = statProcList;
    while ((retVal == -1) && (statProcPtr != NULL)) {
      retVal = (*statProcPtr->proc)(path, buf);
      statProcPtr = statProcPtr->nextPtr;
    }
    Tcl_MutexUnlock(&hookMutex);

    return (retVal);
}

/*
 *----------------------------------------------------------------------
 *
 * TclAccess --
 *
 *    This procedure replaces the library version of access.
 *    The chain of functions that have been "inserted" into the
 *    'accessProcList' will be called in succession until either
 *    a value of zero is returned, or the entire list is visited.
 *
 * Results:
 *      See access documentation.
 *
 * Side effects:
 *      See access documentation.
 *
 *----------------------------------------------------------------------
 */

int
TclAccess(path, mode)
    CONST char *path;         /* Path of file to access (in current CP). */
    int mode;                   /* Permission setting. */
{
    AccessProc *accessProcPtr;
    int retVal = -1;

    /*
     * Call each of the "access" function in succession.  A non-return
     * value of -1 indicates the particular function has succeeded.
     */

    Tcl_MutexLock(&hookMutex);
    accessProcPtr = accessProcList;
    while ((retVal == -1) && (accessProcPtr != NULL)) {
      retVal = (*accessProcPtr->proc)(path, mode);
      accessProcPtr = accessProcPtr->nextPtr;
    }
    Tcl_MutexUnlock(&hookMutex);

    return (retVal);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_OpenFileChannel --
 *
 *    The chain of functions that have been "inserted" into the
 *    'openFileChannelProcList' will be called in succession until
 *    either a valid file channel is returned, or the entire list is
 *    visited.
 *
 * Results:
 *    The new channel or NULL, if the named file could not be opened.
 *
 * Side effects:
 *    May open the channel and may cause creation of a file on the
 *    file system.
 *
 *----------------------------------------------------------------------
 */
 
Tcl_Channel
Tcl_OpenFileChannel(interp, fileName, modeString, permissions)
    Tcl_Interp *interp;                 /* Interpreter for error reporting;
                                         * can be NULL. */
    char *fileName;                     /* Name of file to open. */
    char *modeString;                   /* A list of POSIX open modes or
                                         * a string such as "rw". */
    int permissions;                    /* If the open involves creating a
                                         * file, with what modes to create
                                         * it? */
{
    OpenFileChannelProc *openFileChannelProcPtr;
    Tcl_Channel retVal = NULL;

    /*
     * Call each of the "Tcl_OpenFileChannel" function in succession.
     * A non-NULL return value indicates the particular function has
     * succeeded.
     */

    Tcl_MutexLock(&hookMutex);
    openFileChannelProcPtr = openFileChannelProcList;
    while ((retVal == NULL) && (openFileChannelProcPtr != NULL)) {
      retVal = (*openFileChannelProcPtr->proc)(interp, fileName,
            modeString, permissions);
      openFileChannelProcPtr = openFileChannelProcPtr->nextPtr;
    }
    Tcl_MutexUnlock(&hookMutex);

    return (retVal);
}

/*
 *----------------------------------------------------------------------
 *
 * TclStatInsertProc --
 *
 *    Insert the passed procedure pointer at the head of the list of
 *    functions which are used during a call to 'TclStat(...)'. The
 *    passed function should be have exactly like 'TclStat' when called
 *    during that time (see 'TclStat(...)' for more informatin).
 *    The function will be added even if it already in the list.
 *
 * Results:
 *      Normally TCL_OK; TCL_ERROR if memory for a new node in the list
 *    could not be allocated.
 *
 * Side effects:
 *      Memory allocataed and modifies the link list for 'TclStat'
 *    functions.
 *
 *----------------------------------------------------------------------
 */

int
TclStatInsertProc (proc)
    TclStatProc_ *proc;
{
    int retVal = TCL_ERROR;

    if (proc != NULL) {
      StatProc *newStatProcPtr;

      newStatProcPtr = (StatProc *)ckalloc(sizeof(StatProc));

      if (newStatProcPtr != NULL) {
          newStatProcPtr->proc = proc;
          Tcl_MutexLock(&hookMutex);
          newStatProcPtr->nextPtr = statProcList;
          statProcList = newStatProcPtr;
          Tcl_MutexUnlock(&hookMutex);

          retVal = TCL_OK;
      }
    }

    return (retVal);
}

/*
 *----------------------------------------------------------------------
 *
 * TclStatDeleteProc --
 *
 *    Removed the passed function pointer from the list of 'TclStat'
 *    functions.  Ensures that the built-in stat function is not
 *    removvable.
 *
 * Results:
 *      TCL_OK if the procedure pointer was successfully removed,
 *    TCL_ERROR otherwise.
 *
 * Side effects:
 *      Memory is deallocated and the respective list updated.
 *
 *----------------------------------------------------------------------
 */

int
TclStatDeleteProc (proc)
    TclStatProc_ *proc;
{
    int retVal = TCL_ERROR;
    StatProc *tmpStatProcPtr;
    StatProc *prevStatProcPtr = NULL;

    Tcl_MutexLock(&hookMutex);
    tmpStatProcPtr = statProcList;
    /*
     * Traverse the 'statProcList' looking for the particular node
     * whose 'proc' member matches 'proc' and remove that one from
     * the list.  Ensure that the "default" node cannot be removed.
     */

    while ((retVal == TCL_ERROR) && (tmpStatProcPtr != &defaultStatProc)) {
      if (tmpStatProcPtr->proc == proc) {
          if (prevStatProcPtr == NULL) {
            statProcList = tmpStatProcPtr->nextPtr;
          } else {
            prevStatProcPtr->nextPtr = tmpStatProcPtr->nextPtr;
          }

          Tcl_Free((char *)tmpStatProcPtr);

          retVal = TCL_OK;
      } else {
          prevStatProcPtr = tmpStatProcPtr;
          tmpStatProcPtr = tmpStatProcPtr->nextPtr;
      }
    }

    Tcl_MutexUnlock(&hookMutex);
    return (retVal);
}

/*
 *----------------------------------------------------------------------
 *
 * TclAccessInsertProc --
 *
 *    Insert the passed procedure pointer at the head of the list of
 *    functions which are used during a call to 'TclAccess(...)'. The
 *    passed function should be have exactly like 'TclAccess' when
 *    called during that time (see 'TclAccess(...)' for more informatin).
 *    The function will be added even if it already in the list.
 *
 * Results:
 *      Normally TCL_OK; TCL_ERROR if memory for a new node in the list
 *    could not be allocated.
 *
 * Side effects:
 *      Memory allocataed and modifies the link list for 'TclAccess'
 *    functions.
 *
 *----------------------------------------------------------------------
 */

int
TclAccessInsertProc(proc)
    TclAccessProc_ *proc;
{
    int retVal = TCL_ERROR;

    if (proc != NULL) {
      AccessProc *newAccessProcPtr;

      newAccessProcPtr = (AccessProc *)ckalloc(sizeof(AccessProc));

      if (newAccessProcPtr != NULL) {
          newAccessProcPtr->proc = proc;
          Tcl_MutexLock(&hookMutex);
          newAccessProcPtr->nextPtr = accessProcList;
          accessProcList = newAccessProcPtr;
          Tcl_MutexUnlock(&hookMutex);

          retVal = TCL_OK;
      }
    }

    return (retVal);
}

/*
 *----------------------------------------------------------------------
 *
 * TclAccessDeleteProc --
 *
 *    Removed the passed function pointer from the list of 'TclAccess'
 *    functions.  Ensures that the built-in access function is not
 *    removvable.
 *
 * Results:
 *      TCL_OK if the procedure pointer was successfully removed,
 *    TCL_ERROR otherwise.
 *
 * Side effects:
 *      Memory is deallocated and the respective list updated.
 *
 *----------------------------------------------------------------------
 */

int
TclAccessDeleteProc(proc)
    TclAccessProc_ *proc;
{
    int retVal = TCL_ERROR;
    AccessProc *tmpAccessProcPtr;
    AccessProc *prevAccessProcPtr = NULL;

    /*
     * Traverse the 'accessProcList' looking for the particular node
     * whose 'proc' member matches 'proc' and remove that one from
     * the list.  Ensure that the "default" node cannot be removed.
     */

    Tcl_MutexLock(&hookMutex);
    tmpAccessProcPtr = accessProcList;
    while ((retVal == TCL_ERROR) && (tmpAccessProcPtr != &defaultAccessProc)) {
      if (tmpAccessProcPtr->proc == proc) {
          if (prevAccessProcPtr == NULL) {
            accessProcList = tmpAccessProcPtr->nextPtr;
          } else {
            prevAccessProcPtr->nextPtr = tmpAccessProcPtr->nextPtr;
          }

          Tcl_Free((char *)tmpAccessProcPtr);

          retVal = TCL_OK;
      } else {
          prevAccessProcPtr = tmpAccessProcPtr;
          tmpAccessProcPtr = tmpAccessProcPtr->nextPtr;
      }
    }
    Tcl_MutexUnlock(&hookMutex);

    return (retVal);
}

/*
 *----------------------------------------------------------------------
 *
 * TclOpenFileChannelInsertProc --
 *
 *    Insert the passed procedure pointer at the head of the list of
 *    functions which are used during a call to
 *    'Tcl_OpenFileChannel(...)'. The passed function should be have
 *    exactly like 'Tcl_OpenFileChannel' when called during that time
 *    (see 'Tcl_OpenFileChannel(...)' for more informatin). The
 *    function will be added even if it already in the list.
 *
 * Results:
 *      Normally TCL_OK; TCL_ERROR if memory for a new node in the list
 *    could not be allocated.
 *
 * Side effects:
 *      Memory allocataed and modifies the link list for
 *    'Tcl_OpenFileChannel' functions.
 *
 *----------------------------------------------------------------------
 */

int
TclOpenFileChannelInsertProc(proc)
    TclOpenFileChannelProc_ *proc;
{
    int retVal = TCL_ERROR;

    if (proc != NULL) {
      OpenFileChannelProc *newOpenFileChannelProcPtr;

      newOpenFileChannelProcPtr =
            (OpenFileChannelProc *)ckalloc(sizeof(OpenFileChannelProc));

      if (newOpenFileChannelProcPtr != NULL) {
          newOpenFileChannelProcPtr->proc = proc;
          Tcl_MutexLock(&hookMutex);
          newOpenFileChannelProcPtr->nextPtr = openFileChannelProcList;
          openFileChannelProcList = newOpenFileChannelProcPtr;
          Tcl_MutexUnlock(&hookMutex);

          retVal = TCL_OK;
      }
    }

    return (retVal);
}

/*
 *----------------------------------------------------------------------
 *
 * TclOpenFileChannelDeleteProc --
 *
 *    Removed the passed function pointer from the list of
 *    'Tcl_OpenFileChannel' functions.  Ensures that the built-in
 *    open file channel function is not removvable.
 *
 * Results:
 *      TCL_OK if the procedure pointer was successfully removed,
 *    TCL_ERROR otherwise.
 *
 * Side effects:
 *      Memory is deallocated and the respective list updated.
 *
 *----------------------------------------------------------------------
 */

int
TclOpenFileChannelDeleteProc(proc)
    TclOpenFileChannelProc_ *proc;
{
    int retVal = TCL_ERROR;
    OpenFileChannelProc *tmpOpenFileChannelProcPtr = openFileChannelProcList;
    OpenFileChannelProc *prevOpenFileChannelProcPtr = NULL;

    /*
     * Traverse the 'openFileChannelProcList' looking for the particular
     * node whose 'proc' member matches 'proc' and remove that one from
     * the list.  Ensure that the "default" node cannot be removed.
     */

    Tcl_MutexLock(&hookMutex);
    tmpOpenFileChannelProcPtr = openFileChannelProcList;
    while ((retVal == TCL_ERROR) &&
          (tmpOpenFileChannelProcPtr != &defaultOpenFileChannelProc)) {
      if (tmpOpenFileChannelProcPtr->proc == proc) {
          if (prevOpenFileChannelProcPtr == NULL) {
            openFileChannelProcList = tmpOpenFileChannelProcPtr->nextPtr;
          } else {
            prevOpenFileChannelProcPtr->nextPtr =
                  tmpOpenFileChannelProcPtr->nextPtr;
          }

          Tcl_Free((char *)tmpOpenFileChannelProcPtr);

          retVal = TCL_OK;
      } else {
          prevOpenFileChannelProcPtr = tmpOpenFileChannelProcPtr;
          tmpOpenFileChannelProcPtr = tmpOpenFileChannelProcPtr->nextPtr;
      }
    }
    Tcl_MutexUnlock(&hookMutex);

    return (retVal);
}

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