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jpeg_memsrcdest.c

/*
* memsrc.c
*
* Copyright (C) 1994-1996, Thomas G. Lane.
* This file is part of the Independent JPEG Group's software.
* For conditions of distribution and use, see the accompanying README file.
*
* This file contains decompression data source routines for the case of
* reading JPEG data from a memory buffer that is preloaded with the entire
* JPEG file. This would not seem especially useful at first sight, but
* a number of people have asked for it.
* This is really just a stripped-down version of jdatasrc.c. Comparison
* of this code with jdatasrc.c may be helpful in seeing how to make
* custom source managers for other purposes.
*/

/* this is not a core library module, so it doesn't define JPEG_INTERNALS */
#include "config.h"

#include <stdlib.h>
#include <stdio.h>
#ifdef HAVE_LIBJPEG
#include <jpeglib.h>
#include <jerror.h>
#include "jpeg_memsrcdest.h"

/* libjpeg8 and later come with their own (API compatible) memory source
   and dest */
#if JPEG_LIB_VERSION < 80

/* Expanded data source object for memory input */

typedef struct {
      struct jpeg_source_mgr pub; /* public fields */

      JOCTET eoi_buffer[2]; /* a place to put a dummy EOI */
} my_source_mgr;

typedef my_source_mgr * my_src_ptr;


/*
* Initialize source --- called by jpeg_read_header
* before any data is actually read.
*/

METHODDEF(void)
init_source (j_decompress_ptr cinfo)
{
      /* No work, since jpeg_mem_src set up the buffer pointer and count.
      * Indeed, if we want to read multiple JPEG images from one buffer,
      * this *must* not do anything to the pointer.
      */
}


/*
* Fill the input buffer --- called whenever buffer is emptied.
*
* In this application, this routine should never be called; if it is called,
* the decompressor has overrun the end of the input buffer, implying we
* supplied an incomplete or corrupt JPEG datastream. A simple error exit
* might be the most appropriate response.
*
* But what we choose to do in this code is to supply dummy EOI markers
* in order to force the decompressor to finish processing and supply
* some sort of output image, no matter how corrupted.
*/

METHODDEF(boolean)
fill_input_buffer (j_decompress_ptr cinfo)
{
      my_src_ptr src = (my_src_ptr) cinfo->src;

      WARNMS(cinfo, JWRN_JPEG_EOF);

      /* Create a fake EOI marker */
      src->eoi_buffer[0] = (JOCTET) 0xFF;
      src->eoi_buffer[1] = (JOCTET) JPEG_EOI;
      src->pub.next_input_byte = src->eoi_buffer;
      src->pub.bytes_in_buffer = 2;

      return TRUE;
}


/*
* Skip data --- used to skip over a potentially large amount of
* uninteresting data (such as an APPn marker).
*
* If we overrun the end of the buffer, we let fill_input_buffer deal with
* it. An extremely large skip could cause some time-wasting here, but
* it really isn't supposed to happen ... and the decompressor will never
* skip more than 64K anyway.
*/

METHODDEF(void)
skip_input_data (j_decompress_ptr cinfo, long num_bytes)
{
      my_src_ptr src = (my_src_ptr) cinfo->src;

      if (num_bytes > 0) {
            while (num_bytes > (long) src->pub.bytes_in_buffer) {
                  num_bytes -= (long) src->pub.bytes_in_buffer;
                  (void) fill_input_buffer(cinfo);
                  /* note we assume that fill_input_buffer will never
                  * return FALSE, so suspension need not be handled.
                  */
            }
            src->pub.next_input_byte += (size_t) num_bytes;
            src->pub.bytes_in_buffer -= (size_t) num_bytes;
      }
}


/*
* An additional method that can be provided by data source modules is the
* resync_to_restart method for error recovery in the presence of RST markers.
* For the moment, this source module just uses the default resync method
* provided by the JPEG library. That method assumes that no backtracking
* is possible.
*/


/*
* Terminate source --- called by jpeg_finish_decompress
* after all data has been read. Often a no-op.
*
* NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
* application must deal with any cleanup that should happen even
* for error exit.
*/

METHODDEF(void)
term_source (j_decompress_ptr cinfo)
{
      /* no work necessary here */
}


/*
* Prepare for input from a memory buffer.
*/

GLOBAL(void)
jpeg_mem_src (j_decompress_ptr cinfo, unsigned char * buffer,
      unsigned long bufsize)
{
      my_src_ptr src;

      /* The source object is made permanent so that a series of JPEG images
      * can be read from a single buffer by calling jpeg_mem_src
      * only before the first one.
      * This makes it unsafe to use this manager and a different source
      * manager serially with the same JPEG object. Caveat programmer.
      */
      if (cinfo->src == NULL) { /* first time for this JPEG object? */
            cinfo->src = (struct jpeg_source_mgr *)
                  (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo,
                                        JPOOL_PERMANENT,
                                        sizeof(my_source_mgr));
      }

      src = (my_src_ptr) cinfo->src;
      src->pub.init_source = init_source;
      src->pub.fill_input_buffer = fill_input_buffer;
      src->pub.skip_input_data = skip_input_data;
      src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
      src->pub.term_source = term_source;

      src->pub.next_input_byte = buffer;
      src->pub.bytes_in_buffer = bufsize;
}



/* Memory destination source modelled after Thomas G. Lane's memory source
   support and jdatadst.c

   Copyright (C) 2010, Hans de Goede

   This code may be used under the same conditions as Thomas G. Lane's memory
   source (see the copyright header at the top of this file).
 */

typedef struct {
      struct jpeg_destination_mgr pub; /* public fields */

      JOCTET **buffer;              /* start of buffer */
      unsigned long buf_size, *outsize;
} my_destination_mgr;

typedef my_destination_mgr * my_dest_ptr;

#define OUTPUT_BUF_SIZE 32768   /* choose an efficiently fwrite'able size */


/*
 * Initialize destination --- called by jpeg_start_compress
 * before any data is actually written.
 */

METHODDEF(void)
init_destination (j_compress_ptr cinfo)
{
      /* No work, since jpeg_mem_dest set up the buffer pointer and count.
      * Indeed, if we want to write multiple JPEG images to one buffer,
      * this *must* not do anything to the pointer.
      */
}

/*
 * Empty the output buffer --- called whenever buffer fills up.
 *
 * In typical applications, this should write the entire output buffer
 * (ignoring the current state of next_output_byte & free_in_buffer), 
 * reset the pointer & count to the start of the buffer, and return TRUE
 * indicating that the buffer has been dumped.
 *
 * In applications that need to be able to suspend compression due to output
 * overrun, a FALSE return indicates that the buffer cannot be emptied now. 
 * In this situation, the compressor will return to its caller (possibly with
 * an indication that it has not accepted all the supplied scanlines).  The  
 * application should resume compression after it has made more room in the  
 * output buffer.  Note that there are substantial restrictions on the use of
 * suspension --- see the documentation.
 *
 * When suspending, the compressor will back up to a convenient restart point
 * (typically the start of the current MCU). next_output_byte & free_in_buffer
 * indicate where the restart point will be if the current call returns FALSE.
 * Data beyond this point will be regenerated after resumption, so do not
 * write it out when emptying the buffer externally.
 */

METHODDEF(boolean)
empty_output_buffer (j_compress_ptr cinfo)
{
      my_dest_ptr dest = (my_dest_ptr) cinfo->dest;

      *dest->buffer = realloc (*dest->buffer, dest->buf_size + OUTPUT_BUF_SIZE);
      if (!*dest->buffer)
            ERREXIT1(cinfo, JERR_OUT_OF_MEMORY, 0);

      dest->pub.next_output_byte = *dest->buffer + dest->buf_size;
      dest->pub.free_in_buffer = OUTPUT_BUF_SIZE;
      dest->buf_size += OUTPUT_BUF_SIZE;

      return TRUE;
}

/*
 * Terminate destination --- called by jpeg_finish_compress   
 * after all data has been written.  Usually needs to flush buffer.
 *
 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
 * application must deal with any cleanup that should happen even
 * for error exit.
 */

METHODDEF(void)
term_destination (j_compress_ptr cinfo)
{
      my_dest_ptr dest = (my_dest_ptr) cinfo->dest;

      *dest->outsize = dest->buf_size - dest->pub.free_in_buffer;
}

GLOBAL(void)
jpeg_mem_dest (j_compress_ptr cinfo, unsigned char ** outbuffer,
      unsigned long * outsize)
{
      my_dest_ptr dest;

      /* The destination object is made permanent so that multiple JPEG images
       * can be written to the same file without re-executing jpeg_stdio_dest.
       * This makes it dangerous to use this manager and a different destination
       * manager serially with the same JPEG object, because their private object
       * sizes may be different.  Caveat programmer.
       */
      if (cinfo->dest == NULL) {  /* first time for this JPEG object? */
            cinfo->dest = (struct jpeg_destination_mgr *)
                  (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo,
                                        JPOOL_PERMANENT,
                                        sizeof(my_destination_mgr));
      }

      dest = (my_dest_ptr) cinfo->dest;
      dest->pub.init_destination = init_destination;
      dest->pub.empty_output_buffer = empty_output_buffer;
      dest->pub.term_destination = term_destination;
      dest->buffer = outbuffer;
      dest->buf_size = *outsize;
      dest->outsize = outsize;

      if (*dest->buffer == NULL || dest->buf_size == 0) {
            /* Allocate initial buffer */
            *dest->buffer = malloc(OUTPUT_BUF_SIZE);
            if (*dest->buffer == NULL)
                  ERREXIT1(cinfo, JERR_OUT_OF_MEMORY, 10);
            dest->buf_size = OUTPUT_BUF_SIZE;
      }

      dest->pub.next_output_byte = *dest->buffer;
      dest->pub.free_in_buffer = dest->buf_size;
}

#endif
#endif

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