/*

* 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 <stdio.h>

#include <jpeglib.h>

#include <jerror.h>

/* 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, const JOCTET * buffer, size_t 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;

}