tor-browser

jdatasrc.c (10087B)

---

/*
* jdatasrc.c
*
* This file was part of the Independent JPEG Group's software:
* Copyright (C) 1994-1996, Thomas G. Lane.
* Modified 2009-2011 by Guido Vollbeding.
* libjpeg-turbo Modifications:
* Copyright (C) 2013, 2016, 2022, D. R. Commander.
* For conditions of distribution and use, see the accompanying README.ijg
* file.
*
* This file contains decompression data source routines for the case of
* reading JPEG data from memory or from a file (or any stdio stream).
* While these routines are sufficient for most applications,
* some will want to use a different source manager.
* IMPORTANT: we assume that fread() will correctly transcribe an array of
* JOCTETs from 8-bit-wide elements on external storage.  If char is wider
* than 8 bits on your machine, you may need to do some tweaking.
*/

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


/* Expanded data source object for stdio input */

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

 FILE *infile;                 /* source stream */
 JOCTET *buffer;               /* start of buffer */
 boolean start_of_file;        /* have we gotten any data yet? */
} my_source_mgr;

typedef my_source_mgr *my_src_ptr;

#define INPUT_BUF_SIZE  4096    /* choose an efficiently fread'able size */


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

METHODDEF(void)
init_source(j_decompress_ptr cinfo)
{
 my_src_ptr src = (my_src_ptr)cinfo->src;

 /* We reset the empty-input-file flag for each image,
  * but we don't clear the input buffer.
  * This is correct behavior for reading a series of images from one source.
  */
 src->start_of_file = TRUE;
}

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


/*
* Fill the input buffer --- called whenever buffer is emptied.
*
* In typical applications, this should read fresh data into the buffer
* (ignoring the current state of next_input_byte & bytes_in_buffer),
* reset the pointer & count to the start of the buffer, and return TRUE
* indicating that the buffer has been reloaded.  It is not necessary to
* fill the buffer entirely, only to obtain at least one more byte.
*
* There is no such thing as an EOF return.  If the end of the file has been
* reached, the routine has a choice of ERREXIT() or inserting fake data into
* the buffer.  In most cases, generating a warning message and inserting a
* fake EOI marker is the best course of action --- this will allow the
* decompressor to output however much of the image is there.  However,
* the resulting error message is misleading if the real problem is an empty
* input file, so we handle that case specially.
*
* In applications that need to be able to suspend compression due to input
* not being available yet, a FALSE return indicates that no more data can be
* obtained right now, but more may be forthcoming later.  In this situation,
* the decompressor will return to its caller (with an indication of the
* number of scanlines it has read, if any).  The application should resume
* decompression after it has loaded more data into the input buffer.  Note
* that there are substantial restrictions on the use of suspension --- see
* the documentation.
*
* When suspending, the decompressor will back up to a convenient restart point
* (typically the start of the current MCU). next_input_byte & bytes_in_buffer
* indicate where the restart point will be if the current call returns FALSE.
* Data beyond this point must be rescanned after resumption, so move it to
* the front of the buffer rather than discarding it.
*/

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

 nbytes = fread(src->buffer, 1, INPUT_BUF_SIZE, src->infile);

 if (nbytes <= 0) {
   if (src->start_of_file)     /* Treat empty input file as fatal error */
     ERREXIT(cinfo, JERR_INPUT_EMPTY);
   WARNMS(cinfo, JWRN_JPEG_EOF);
   /* Insert a fake EOI marker */
   src->buffer[0] = (JOCTET)0xFF;
   src->buffer[1] = (JOCTET)JPEG_EOI;
   nbytes = 2;
 }

 src->pub.next_input_byte = src->buffer;
 src->pub.bytes_in_buffer = nbytes;
 src->start_of_file = FALSE;

 return TRUE;
}

METHODDEF(boolean)
fill_mem_input_buffer(j_decompress_ptr cinfo)
{
 static const JOCTET mybuffer[4] = {
   (JOCTET)0xFF, (JOCTET)JPEG_EOI, 0, 0
 };

 /* The whole JPEG data is expected to reside in the supplied memory
  * buffer, so any request for more data beyond the given buffer size
  * is treated as an error.
  */
 WARNMS(cinfo, JWRN_JPEG_EOF);

 /* Insert a fake EOI marker */

 cinfo->src->next_input_byte = mybuffer;
 cinfo->src->bytes_in_buffer = 2;

 return TRUE;
}


/*
* Skip data --- used to skip over a potentially large amount of
* uninteresting data (such as an APPn marker).
*
* Writers of suspendable-input applications must note that skip_input_data
* is not granted the right to give a suspension return.  If the skip extends
* beyond the data currently in the buffer, the buffer can be marked empty so
* that the next read will cause a fill_input_buffer call that can suspend.
* Arranging for additional bytes to be discarded before reloading the input
* buffer is the application writer's problem.
*/

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

 /* Just a dumb implementation for now.  Could use fseek() except
  * it doesn't work on pipes.  Not clear that being smart is worth
  * any trouble anyway --- large skips are infrequent.
  */
 if (num_bytes > 0) {
   while (num_bytes > (long)src->bytes_in_buffer) {
     num_bytes -= (long)src->bytes_in_buffer;
     (void)(*src->fill_input_buffer) (cinfo);
     /* note we assume that fill_input_buffer will never return FALSE,
      * so suspension need not be handled.
      */
   }
   src->next_input_byte += (size_t)num_bytes;
   src->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 stdio stream.
* The caller must have already opened the stream, and is responsible
* for closing it after finishing decompression.
*/

GLOBAL(void)
jpeg_stdio_src(j_decompress_ptr cinfo, FILE *infile)
{
 my_src_ptr src;

 /* The source object and input buffer are made permanent so that a series
  * of JPEG images can be read from the same file by calling jpeg_stdio_src
  * only before the first one.  (If we discarded the buffer at the end of
  * one image, we'd likely lose the start of the next one.)
  */
 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->buffer = (JOCTET *)
     (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_PERMANENT,
                                 INPUT_BUF_SIZE * sizeof(JOCTET));
 } else if (cinfo->src->init_source != init_source) {
   /* It is unsafe to reuse the existing source manager unless it was created
    * by this function.  Otherwise, there is no guarantee that the opaque
    * structure is the right size.  Note that we could just create a new
    * structure, but the old structure would not be freed until
    * jpeg_destroy_decompress() was called.
    */
   ERREXIT(cinfo, JERR_BUFFER_SIZE);
 }

 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->infile = infile;
 src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
 src->pub.next_input_byte = NULL; /* until buffer loaded */
}


/*
* Prepare for input from a supplied memory buffer.
* The buffer must contain the whole JPEG data.
*/

GLOBAL(void)
jpeg_mem_src(j_decompress_ptr cinfo, const unsigned char *inbuffer,
            unsigned long insize)
{
 struct jpeg_source_mgr *src;

 if (inbuffer == NULL || insize == 0)  /* Treat empty input as fatal error */
   ERREXIT(cinfo, JERR_INPUT_EMPTY);

 /* The source object is made permanent so that a series of JPEG images
  * can be read from the same buffer by calling jpeg_mem_src only before
  * the first one.
  */
 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(struct jpeg_source_mgr));
 } else if (cinfo->src->init_source != init_mem_source) {
   /* It is unsafe to reuse the existing source manager unless it was created
    * by this function.
    */
   ERREXIT(cinfo, JERR_BUFFER_SIZE);
 }

 src = cinfo->src;
 src->init_source = init_mem_source;
 src->fill_input_buffer = fill_mem_input_buffer;
 src->skip_input_data = skip_input_data;
 src->resync_to_restart = jpeg_resync_to_restart; /* use default method */
 src->term_source = term_source;
 src->bytes_in_buffer = (size_t)insize;
 src->next_input_byte = (const JOCTET *)inbuffer;
}