mapio.c

/******************************************************************************
 * $Id$
 *
 * Project:  MapServer
 * Purpose:  Implementations for MapServer IO redirection capability.
 * Author:   Frank Warmerdam, warmerdam@pobox.com
 *
 ******************************************************************************
 * Copyright (c) 2004, Frank Warmerdam <warmerdam@pobox.com>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies of this Software or works derived from this Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 ****************************************************************************/

#include <stdarg.h>

#include "mapserver.h"
#include "mapthread.h"

#ifdef _WIN32
#include <fcntl.h>
#include <io.h>
#endif

#ifdef MOD_WMS_ENABLED
#  include "httpd.h"
#  include "apr_strings.h"
#endif




static int is_msIO_initialized = MS_FALSE;

typedef struct msIOContextGroup_t {
  msIOContext stdin_context;
  msIOContext stdout_context;
  msIOContext stderr_context;

  int    thread_id;
  struct msIOContextGroup_t *next;
} msIOContextGroup;

static msIOContextGroup default_contexts;
static msIOContextGroup *io_context_list = NULL;
static void msIO_Initialize( void );

#ifdef msIO_printf
#  undef msIO_printf
#  undef msIO_fprintf
#  undef msIO_fwrite
#  undef msIO_fread
#  undef msIO_vfprintf
#endif

/************************************************************************/
/*                            msIO_Cleanup()                            */
/************************************************************************/

void msIO_Cleanup()

{
  if( is_msIO_initialized )

  {
    is_msIO_initialized = MS_FALSE;
    while( io_context_list != NULL ) {
      msIOContextGroup *last = io_context_list;
      io_context_list = io_context_list->next;
      free( last );
    }
  }
}

/************************************************************************/
/*                        msIO_GetContextGroup()                        */
/************************************************************************/

static msIOContextGroup *msIO_GetContextGroup()

{
  int nThreadId = msGetThreadId();
  msIOContextGroup *prev = NULL, *group = io_context_list;

  if( group != NULL && group->thread_id == nThreadId )
    return group;

  /* -------------------------------------------------------------------- */
  /*      Search for group for this thread                                */
  /* -------------------------------------------------------------------- */
  msAcquireLock( TLOCK_IOCONTEXT );
  msIO_Initialize();

  group = io_context_list;
  while( group != NULL && group->thread_id != nThreadId ) {
    prev = group;
    group = group->next;
  }

  /* -------------------------------------------------------------------- */
  /*      If we found it, make sure it is pushed to the front of the      */
  /*      link for faster finding next time, and return it.               */
  /* -------------------------------------------------------------------- */
  if( group != NULL ) {
    if( prev != NULL ) {
      prev->next = group->next;
      group->next = io_context_list;
      io_context_list = group;
    }

    msReleaseLock( TLOCK_IOCONTEXT );
    return group;
  }

  /* -------------------------------------------------------------------- */
  /*      Create a new context group for this thread.                     */
  /* -------------------------------------------------------------------- */
  group = (msIOContextGroup *) calloc(sizeof(msIOContextGroup),1);

  group->stdin_context = default_contexts.stdin_context;
  group->stdout_context = default_contexts.stdout_context;
  group->stderr_context = default_contexts.stderr_context;
  group->thread_id = nThreadId;

  group->next = io_context_list;
  io_context_list = group;

  msReleaseLock( TLOCK_IOCONTEXT );

  return group;
}

/************************************************************************/
/*                          msIO_getHandler()                           */
/************************************************************************/

msIOContext *msIO_getHandler( FILE * fp )

{
  int nThreadId = msGetThreadId();
  msIOContextGroup *group = io_context_list;

  msIO_Initialize();

  if( group == NULL || group->thread_id != nThreadId ) {
    group = msIO_GetContextGroup();
    if( group == NULL )
      return NULL;
  }

  if( fp == stdin || fp == NULL || strcmp((const char *)fp,"stdin") == 0 )
    return &(group->stdin_context);
  else if( fp == stdout || strcmp((const char *)fp,"stdout") == 0 )
    return &(group->stdout_context);
  else if( fp == stderr || strcmp((const char *)fp,"stderr") == 0 )
    return &(group->stderr_context);
  else
    return NULL;
}

void msIO_setHeader (const char *header, const char* value, ...)
{
  va_list args;
  va_start( args, value );
#ifdef MOD_WMS_ENABLED
  msIOContext *ioctx = msIO_getHandler (stdout);
  if(ioctx && !strcmp(ioctx->label,"apache")) {

    request_rec *r = (request_rec*) (ioctx->cbData);
    char *fullvalue = apr_pvsprintf(r->pool, value,args);
    if (strcasecmp (header, "Content-Type") == 0) {
      r->content_type = fullvalue;
    } else if (strcasecmp (header, "Status") == 0) {
      r->status = atoi (fullvalue);
    } else {
      apr_table_setn (r->headers_out,
                      apr_pstrdup (r->pool, header),
                      fullvalue
                     );
    }
  } else {
#endif // MOD_WMS_ENABLED
    msIO_fprintf(stdout,"%s: ",header);
    msIO_vfprintf(stdout,value,args);
    msIO_fprintf(stdout,"\r\n");
#ifdef MOD_WMS_ENABLED
  }
#endif
}

void msIO_sendHeaders ()
{
#ifdef MOD_WMS_ENABLED
  msIOContext *ioctx = msIO_getHandler (stdout);
  if(ioctx && !strcmp(ioctx->label,"apache")) return;
#endif // !MOD_WMS_ENABLED
  msIO_printf ("\r\n");
  fflush (stdout);
}


/************************************************************************/
/*                        msIO_installHandlers()                        */
/************************************************************************/

int msIO_installHandlers( msIOContext *stdin_context,
                          msIOContext *stdout_context,
                          msIOContext *stderr_context )

{
  msIOContextGroup *group;

  msIO_Initialize();

  group = msIO_GetContextGroup();

  if( stdin_context == NULL )
    group->stdin_context = default_contexts.stdin_context;
  else if( stdin_context != &group->stdin_context )
    group->stdin_context = *stdin_context;

  if( stdout_context == NULL )
    group->stdout_context = default_contexts.stdout_context;
  else if( stdout_context != &group->stdout_context )
    group->stdout_context = *stdout_context;

  if( stderr_context == NULL )
    group->stderr_context = default_contexts.stderr_context;
  else if( stderr_context != &group->stderr_context )
    group->stderr_context = *stderr_context;

  return MS_TRUE;
}

/************************************************************************/
/*                          msIO_contextRead()                          */
/************************************************************************/

int msIO_contextRead( msIOContext *context, void *data, int byteCount )

{
  if( context->write_channel == MS_TRUE )
    return 0;
  else
    return context->readWriteFunc( context->cbData, data, byteCount );
}

/************************************************************************/
/*                         msIO_contextWrite()                          */
/************************************************************************/

int msIO_contextWrite( msIOContext *context, const void *data, int byteCount )

{
  if( context->write_channel == MS_FALSE )
    return 0;
  else
    return context->readWriteFunc( context->cbData, (void *) data,
                                   byteCount );
}

/* ==================================================================== */
/* ==================================================================== */
/*      Stdio-like cover functions.                                     */
/* ==================================================================== */
/* ==================================================================== */

/************************************************************************/
/*                            _ms_vsprintf()                            */
/************************************************************************/

static int _ms_vsprintf(char **workBufPtr, const char *format, va_list ap )

{
  int     ret_val;
  int   workBufSize = 16000;

  *workBufPtr = (char*)malloc(workBufSize * sizeof(char));
  if (*workBufPtr == NULL) {
    msSetError( MS_MEMERR, NULL, "_ms_vsprintf()");
    return -1;
  }

#if defined(HAVE_VSNPRINTF)
  /* This should grow a big enough buffer to hold any formatted result. */
  {
    va_list wrk_args;

#ifdef va_copy
    va_copy( wrk_args, ap );
#else
    wrk_args = ap;
#endif

    while( (ret_val = vsnprintf( *workBufPtr, workBufSize,
                                 format, wrk_args)) >= workBufSize-1
           || ret_val == -1 ) {
      workBufSize *= 4;
      *workBufPtr = (char *) realloc(*workBufPtr, workBufSize );
      if (*workBufPtr == NULL) {
        msSetError( MS_MEMERR, NULL, "_ms_vsprintf()");
        va_end( wrk_args );
        return -1;
      }
#ifdef va_copy
      va_end( wrk_args );
      va_copy( wrk_args, ap );
#else
      wrk_args = ap;
#endif
    }
    va_end( wrk_args );
  }
#else
  /* We do not have vsnprintf()... there is a risk of buffer overrun */
  ret_val = vsprintf( *workBufPtr, format, ap );

  if( ret_val < 0 || ret_val >= workBufSize ) {
    msSetError(MS_MISCERR, "Possible buffer overrun.", "_ms_vsprintf()");
    msFree(*workBufPtr);
    *workBufPtr = NULL;
    return -1;
  }
#endif

  return ret_val;
}


/************************************************************************/
/*                            msIO_printf()                             */
/************************************************************************/

int msIO_printf( const char *format, ... )

{
  va_list args;
  int ret;
  va_start( args, format );
  ret = msIO_vfprintf(stdout,format,args);
  va_end(args);
  return ret;
}

/************************************************************************/
/*                            msIO_fprintf()                            */
/************************************************************************/

int msIO_fprintf( FILE *fp, const char *format, ... )

{
  va_list args;
  int ret;
  va_start( args, format );
  ret = msIO_vfprintf(fp,format,args);
  va_end(args);
  return ret;
}

/************************************************************************/
/*                            msIO_vfprintf()                           */
/************************************************************************/

int msIO_vfprintf( FILE *fp, const char *format, va_list ap )

{
  va_list args_copy;
  int     return_val;
  msIOContext *context;
  char workBuf[8000], *largerBuf = NULL;

#if !defined(HAVE_VSNPRINTF)
  return_val = vsprintf( workBuf, format, ap);

  if( return_val < 0 || return_val >= sizeof(workBuf) ) {
    msSetError(MS_MISCERR, "Possible buffer overrun.", "msIO_vfprintf()");
    return -1;
  }

#else

#ifdef va_copy
  va_copy( args_copy, ap );
#else
  args_copy = ap;
#endif /* va_copy */

  return_val = vsnprintf( workBuf, sizeof(workBuf), format, ap );
  if (return_val == -1 || return_val >= sizeof(workBuf)-1) {
    return_val = _ms_vsprintf(&largerBuf, format, args_copy );
  }
  va_end(args_copy);

#endif /* HAVE_VSNPRINTF */

  if (return_val < 0)
    return -1;

  context = msIO_getHandler( fp );
  if( context == NULL )
    return_val = fwrite( largerBuf?largerBuf:workBuf, 1, return_val, fp );
  else
    return_val =  msIO_contextWrite( context,
                                     largerBuf?largerBuf:workBuf,
                                     return_val );

  msFree(largerBuf);

  return return_val;
}

/************************************************************************/
/*                            msIO_fwrite()                             */
/************************************************************************/

int msIO_fwrite( const void *data, size_t size, size_t nmemb, FILE *fp )

{
  msIOContext *context;

  if( size == 0 || nmemb == 0 )
    return 0;

  context = msIO_getHandler( fp );
  if( context == NULL )
    return fwrite( data, size, nmemb, fp );
  else
    return msIO_contextWrite( context, data, size * nmemb ) / size;
}

/************************************************************************/
/*                            msIO_fread()                              */
/************************************************************************/

int msIO_fread( void *data, size_t size, size_t nmemb, FILE *fp )

{
  msIOContext *context;

  if( size == 0 || nmemb == 0 )
    return 0;

  context = msIO_getHandler( fp );
  if( context == NULL )
    return fread( data, size, nmemb, fp );
  else
    return msIO_contextRead( context, data, size * nmemb ) / size;
}

/* ==================================================================== */
/* ==================================================================== */
/*      Internal default callbacks implementing stdio reading and       */
/*      writing.                                                        */
/* ==================================================================== */
/* ==================================================================== */

/************************************************************************/
/*                           msIO_stdioRead()                           */
/*                                                                      */
/*      This is the default implementation via stdio.                   */
/************************************************************************/

static int msIO_stdioRead( void *cbData, void *data, int byteCount )

{
  return fread( data, 1, byteCount, (FILE *) cbData );
}

/************************************************************************/
/*                          msIO_stdioWrite()                           */
/*                                                                      */
/*      This is the default implementation via stdio.                   */
/************************************************************************/

static int msIO_stdioWrite( void *cbData, void *data, int byteCount )

{
  return fwrite( data, 1, byteCount, (FILE *) cbData );
}

/************************************************************************/
/*                          msIO_Initialize()                           */
/************************************************************************/

static void msIO_Initialize( void )

{
  if( is_msIO_initialized == MS_TRUE )
    return;

  default_contexts.stdin_context.label = "stdio";
  default_contexts.stdin_context.write_channel = MS_FALSE;
  default_contexts.stdin_context.readWriteFunc = msIO_stdioRead;
  default_contexts.stdin_context.cbData = (void *) stdin;

  default_contexts.stdout_context.label = "stdio";
  default_contexts.stdout_context.write_channel = MS_TRUE;
  default_contexts.stdout_context.readWriteFunc = msIO_stdioWrite;
  default_contexts.stdout_context.cbData = (void *) stdout;

  default_contexts.stderr_context.label = "stdio";
  default_contexts.stderr_context.write_channel = MS_TRUE;
  default_contexts.stderr_context.readWriteFunc = msIO_stdioWrite;
  default_contexts.stderr_context.cbData = (void *) stderr;

  default_contexts.next = NULL;
  default_contexts.thread_id = 0;

  is_msIO_initialized = MS_TRUE;
}


/* ==================================================================== */
/* ==================================================================== */
/*      FastCGI output redirection functions.                           */
/* ==================================================================== */
/* ==================================================================== */



/************************************************************************/
/*                       msIO_needBinaryStdout()                        */
/*                                                                      */
/*      This function is intended to ensure that stdout is in binary    */
/*      mode.                                                           */
/*                                                                      */
/*      But don't do it we are using FastCGI.  We will take care of     */
/*      doing it in the libfcgi library in that case for the normal     */
/*      cgi case, and for the fastcgi case the _setmode() call          */
/*      causes a crash.                                                 */
/************************************************************************/

int msIO_needBinaryStdout()

{
#if defined(_WIN32) && !defined(USE_FASTCGI)
  if(_setmode( _fileno(stdout), _O_BINARY) == -1) {
    msSetError(MS_IOERR,
               "Unable to change stdout to binary mode.",
               "msIO_needBinaryStdout()" );
    return(MS_FAILURE);
  }
#endif

  return MS_SUCCESS;
}

/************************************************************************/
/*                        msIO_needBinaryStdin()                        */
/*                                                                      */
/*      This function is intended to ensure that stdin is in binary     */
/*      mode.                                                           */
/*                                                                      */
/*      But don't do it we are using FastCGI.  We will take care of     */
/*      doing it in the libfcgi library in that case for the normal     */
/*      cgi case, and for the fastcgi case the _setmode() call          */
/*      causes a crash.                                                 */
/************************************************************************/

int msIO_needBinaryStdin()

{
#if defined(_WIN32) && !defined(USE_FASTCGI)
  if(_setmode( _fileno(stdin), _O_BINARY) == -1) {
    msSetError(MS_IOERR,
               "Unable to change stdin to binary mode.",
               "msIO_needBinaryStdin()" );
    return(MS_FAILURE);
  }
#endif

  return MS_SUCCESS;
}

/* ==================================================================== */
/*      memory buffer io handling functions.                            */
/* ==================================================================== */

/************************************************************************/
/*                         msIO_resetHandlers()                         */
/************************************************************************/

void msIO_resetHandlers()

{
  msIOContextGroup *group = msIO_GetContextGroup();

  if( group == NULL )
    return;

  if( strcmp(group->stdin_context.label,"buffer") == 0 ) {
    msIOBuffer *buf = (msIOBuffer *) group->stdin_context.cbData;

    if( buf->data != NULL )
      free( buf->data );
    free( buf );
  }

  if( strcmp(group->stdout_context.label,"buffer") == 0 ) {
    msIOBuffer *buf = (msIOBuffer *) group->stdout_context.cbData;

    if( buf->data != NULL )
      free( buf->data );
    free( buf );
  }

  if( strcmp(group->stderr_context.label,"buffer") == 0 ) {
    msIOBuffer *buf = (msIOBuffer *) group->stderr_context.cbData;

    if( buf->data != NULL )
      free( buf->data );
    free( buf );
  }

  msIO_installHandlers( NULL, NULL, NULL );
}

/************************************************************************/
/*                     msIO_installStdoutToBuffer()                     */
/************************************************************************/

void msIO_installStdoutToBuffer()

{
  msIOContextGroup *group = msIO_GetContextGroup();
  msIOContext  context;

  context.label = "buffer";
  context.write_channel = MS_TRUE;
  context.readWriteFunc = msIO_bufferWrite;
  context.cbData = calloc(sizeof(msIOBuffer),1);

  msIO_installHandlers( &group->stdin_context,
                        &context,
                        &group->stderr_context );
}

/************************************************************************/
/*                    msIO_installStdinFromBuffer()                     */
/************************************************************************/

void msIO_installStdinFromBuffer()

{
  msIOContextGroup *group = msIO_GetContextGroup();
  msIOContext  context;

  context.label = "buffer";
  context.write_channel = MS_FALSE;
  context.readWriteFunc = msIO_bufferRead;
  context.cbData = calloc(sizeof(msIOBuffer),1);

  msIO_installHandlers( &context,
                        &group->stdout_context,
                        &group->stderr_context );
}

/************************************************************************/
/*                 msIO_stripStdoutBufferContentType()                  */
/*                                                                      */
/*      Strip off Content-Type header from buffer, and return to        */
/*      caller.  Returned string is the callers responsibility to       */
/*      call msFree() on to deallocate.  This function will return      */
/*      NULL if there is no Content-Type header.                        */
/************************************************************************/

char *msIO_stripStdoutBufferContentType()

{
  /* -------------------------------------------------------------------- */
  /*      Find stdout buffer.                                             */
  /* -------------------------------------------------------------------- */
  msIOContext *ctx = msIO_getHandler( (FILE *) "stdout" );
  msIOBuffer  *buf;
  char *content_type = NULL;
  int end_of_ct, start_of_data;

  if( ctx == NULL || ctx->write_channel == MS_FALSE
      || strcmp(ctx->label,"buffer") != 0 ) {
    msSetError( MS_MISCERR, "Can't identify msIO buffer.",
                "msIO_stripStdoutBufferContentType" );
    return NULL;
  }

  buf = (msIOBuffer *) ctx->cbData;

  /* -------------------------------------------------------------------- */
  /*      Return NULL if we don't have a Content-Type header.             */
  /* -------------------------------------------------------------------- */
  if( buf->data_offset < 14
      || strncasecmp((const char*) buf->data,"Content-Type: ",14) != 0 )
    return NULL;

  /* -------------------------------------------------------------------- */
  /*      Find newline marker at end of content type argument.            */
  /* -------------------------------------------------------------------- */
  end_of_ct = 13;
  while( end_of_ct+1 < buf->data_offset
         && buf->data[end_of_ct+1] != '\r' )
    end_of_ct++;

  if( end_of_ct+1 == buf->data_offset ) {
    msSetError( MS_MISCERR, "Corrupt Content-Type header.",
                "msIO_stripStdoutBufferContentType" );
    return NULL;
  }

  /* -------------------------------------------------------------------- */
  /*      Continue on to the start of data ...                            */
  /*      Go to next line and skip if empty.                              */
  /* -------------------------------------------------------------------- */
  start_of_data = end_of_ct+3;
  if( start_of_data  < buf->data_offset
      && buf->data[start_of_data] == '\r' )
    start_of_data +=2;
  
  if( start_of_data == buf->data_offset ) {
    msSetError( MS_MISCERR, "Corrupt Content-Type header.",
                "msIO_stripStdoutBufferContentType" );
    return NULL;
  }

  /* -------------------------------------------------------------------- */
  /*      Copy out content type. Note we go against the coding guidelines */
  /*      here and use strncpy() instead of strlcpy() as the source       */
  /*      buffer may not be NULL terminated - strlcpy() requires NULL     */
  /*      terminated sources (see issue #4672).                           */
  /* -------------------------------------------------------------------- */
  content_type = (char *) malloc(end_of_ct-14+2);
  strncpy( content_type, (const char *) buf->data + 14, end_of_ct - 14 + 2);
  content_type[end_of_ct-14+1] = '\0';

  /* -------------------------------------------------------------------- */
  /*      Move data to front of buffer, and reset length.                 */
  /* -------------------------------------------------------------------- */
  memmove( buf->data, buf->data+start_of_data,
           buf->data_offset - start_of_data );
  buf->data[buf->data_offset - start_of_data] = '\0';
  buf->data_offset -= start_of_data;

  return content_type;
}

/************************************************************************/
/*                 msIO_stripStdoutBufferContentHeaders()               */
/*                                                                      */
/*      Strip off Content-* headers from buffer.                        */
/************************************************************************/

void msIO_stripStdoutBufferContentHeaders()
{
  /* -------------------------------------------------------------------- */
  /*      Find stdout buffer.                                             */
  /* -------------------------------------------------------------------- */
  msIOContext *ctx = msIO_getHandler( (FILE *) "stdout" );
  msIOBuffer  *buf;
  int start_of_data;

  if( ctx == NULL || ctx->write_channel == MS_FALSE
      || strcmp(ctx->label,"buffer") != 0 ) {
    msSetError( MS_MISCERR, "Can't identify msIO buffer.",
                "msIO_stripStdoutBufferContentHeaders" );
    return;
  }

  buf = (msIOBuffer *) ctx->cbData;

  /* -------------------------------------------------------------------- */
  /*      Exit if we don't have any content-* header.                     */
  /* -------------------------------------------------------------------- */
  if( buf->data_offset < 8
      || strncasecmp((const char*) buf->data,"Content-",8) != 0 )
    return;

  /* -------------------------------------------------------------------- */
  /*      Loop over all content-* headers.                                */
  /* -------------------------------------------------------------------- */
  start_of_data = 0;
  while( buf->data_offset > start_of_data
         && strncasecmp((const char*) buf->data+start_of_data,"Content-",8) == 0 ) {
    /* -------------------------------------------------------------------- */
    /*      Find newline marker at end of content-* header argument.        */
    /* -------------------------------------------------------------------- */
    start_of_data +=7;
    while( start_of_data+1 < buf->data_offset
           && buf->data[start_of_data+1] != '\r' )
      start_of_data++;

    if( start_of_data+1 == buf->data_offset ) {
      msSetError( MS_MISCERR, "Corrupt Content-* header.",
                  "msIO_stripStdoutBufferContentHeaders" );
      return;
    }
    /* -------------------------------------------------------------------- */
    /*      Go to next line.                                                */
    /* -------------------------------------------------------------------- */
    start_of_data +=3;
  }

  /* -------------------------------------------------------------------- */
  /*      Continue on to the start of data ...                            */
  /*      Skip next line if empty.                                        */
  /* -------------------------------------------------------------------- */
  if( start_of_data  < buf->data_offset
      && buf->data[start_of_data] == '\r' )
    start_of_data +=2;

  if( start_of_data == buf->data_offset ) {
    msSetError( MS_MISCERR, "Corrupt Content-* header.",
                "msIO_stripStdoutBufferContentHeaders" );
    return;
  }

  /* -------------------------------------------------------------------- */
  /*      Move data to front of buffer, and reset length.                 */
  /* -------------------------------------------------------------------- */
  memmove( buf->data, buf->data+start_of_data,
           buf->data_offset - start_of_data );
  buf->data[buf->data_offset - start_of_data] = '\0';
  buf->data_offset -= start_of_data;

  return;
}

/************************************************************************/
/*                          msIO_bufferWrite()                          */
/************************************************************************/

int msIO_bufferWrite( void *cbData, void *data, int byteCount )

{
  msIOBuffer *buf = (msIOBuffer *) cbData;

  /*
  ** Grow buffer if needed.
  */
  if( buf->data_offset + byteCount > buf->data_len ) {
    buf->data_len = buf->data_len * 2 + byteCount + 100;
    if( buf->data == NULL )
      buf->data = (unsigned char *) malloc(buf->data_len);
    else
      buf->data = (unsigned char *) realloc(buf->data, buf->data_len);

    if( buf->data == NULL ) {
      msSetError( MS_MEMERR,
                  "Failed to allocate %d bytes for capture buffer.",
                  "msIO_bufferWrite()", buf->data_len );
      buf->data_len = 0;
      return 0;
    }
  }

  /*
  ** Copy result into buffer.
  */

  memcpy( buf->data + buf->data_offset, data, byteCount );
  buf->data_offset += byteCount;

  return byteCount;
}

/************************************************************************/
/*                          msIO_bufferRead()                           */
/************************************************************************/

int msIO_bufferRead( void *cbData, void *data, int byteCount )

{
  /*    msIOBuffer *buf = (msIOBuffer *) cbData; */

  /* not implemented yet. */

  return 0;
}