/*

 * jdatasrc-tj.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) 2011, 2016, 2019, 2023, 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"

void jpeg_mem_src_tj(j_decompress_ptr cinfo, const unsigned char *inbuffer,

                     size_t insize);

/*

 * Initialize source --- called by jpeg_read_header

 * before any data is actually read.

 */

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_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 supplied memory buffer.

 * The buffer must contain the whole JPEG data.

 */

GLOBAL(void)

jpeg_mem_src_tj(j_decompress_ptr cinfo, const unsigned char *inbuffer,

                size_t 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 = insize;

  src->next_input_byte = (const JOCTET *)inbuffer;

}