#include <stdlib.h>
#include <string.h>
/*
 * lowres.c
 *
 * Yannis Smaragdakis
 * 
 * This file defines a routine that reads JPEG data from a socket and
 * creates a memory buffer with this data at much lower quality (to
 * reduce storage requirements).
 * 
 * I have put a limit of two hours on the time I will work on this,
 * so this is not a mature piece of code. It should do the work,
 * though.
 *
 * Look at example.c and libjpeg.doc for more info on using the IJG code.
 */

#define LOW_QUALITY 10

#include <stdio.h>

/*
 * Include file for users of JPEG library.
 * You will need to have included system headers that define at least
 * the typedefs FILE and size_t before you can include jpeglib.h.
 * (stdio.h is sufficient on ANSI-conforming systems.)
 * You may also wish to include "jerror.h".
 */

#ifdef __cplusplus
extern "C" {
#endif

#include "jpeglib.h"

/*
 * <setjmp.h> is used for the optional error recovery mechanism shown in
 * the second part of the example.
 */

#include <setjmp.h>

extern int write_JPEG_file(JSAMPARRAY, int,int, int, int, J_COLOR_SPACE,JOCTET **, int *);

/*
 * ERROR HANDLING:
 *
 * The JPEG library's standard error handler (jerror.c) is divided into
 * several "methods" which you can override individually.  This lets you
 * adjust the behavior without duplicating a lot of code, which you might
 * have to update with each future release.
 *
 * Our example here shows how to override the "error_exit" method so that
 * control is returned to the library's caller when a fatal error occurs,
 * rather than calling exit() as the standard error_exit method does.
 *
 * We use C's setjmp/longjmp facility to return control.  This means that the
 * routine which calls the JPEG library must first execute a setjmp() call to
 * establish the return point.  We want the replacement error_exit to do a
 * longjmp().  But we need to make the setjmp buffer accessible to the
 * error_exit routine.  To do this, we make a private extension of the
 * standard JPEG error handler object.  (If we were using C++, we'd say we
 * were making a subclass of the regular error handler.)
 *
 * Here's the extended error handler struct:
 */

struct my_error_mgr {
  struct jpeg_error_mgr pub;	/* "public" fields */

  jmp_buf setjmp_buffer;	/* for return to caller */
};

typedef struct my_error_mgr * my_error_ptr;

/*
 * Here's the routine that will replace the standard error_exit method:
 */

METHODDEF(void)
my_error_exit (j_common_ptr cinfo)
{
  /* cinfo->err really points to a my_error_mgr struct, so coerce pointer */
  my_error_ptr myerr = (my_error_ptr) cinfo->err;

  /* Always display the message. */
  /* We could postpone this until after returning, if we chose. */
  (*cinfo->err->output_message) (cinfo);

  /* Return control to the setjmp point */
  longjmp(myerr->setjmp_buffer, 1);
}

#define MAX_LINESZ 200

/*
 * Sample routine for JPEG decompression.  We assume that a socket
 * from which the source is read is passed in.  
 * We want to return 1 on success, 0 on error.
 */



int
change_res_JPEG (int insocket, char ** output, int *output_size)
{
  /* This struct contains the JPEG decompression parameters and pointers to
   * working space (which is allocated as needed by the JPEG library).
   */
  struct jpeg_decompress_struct cinfo;
  /* We use our private extension JPEG error handler.
   * Note that this struct must live as long as the main JPEG parameter
   * struct, to avoid dangling-pointer problems.
   */
  struct my_error_mgr jerr;
  /* More stuff */
  JSAMPARRAY buffer;		/* Output row buffer */
  int row_stride;		/* physical row width in output buffer */
  FILE *infile = fdopen(insocket, "r");

  /* Step 1: allocate and initialize JPEG decompression object */

  /* We set up the normal JPEG error routines, then override error_exit. */
  cinfo.err = jpeg_std_error(&jerr.pub);
  jerr.pub.error_exit = my_error_exit;
  /* Establish the setjmp return context for my_error_exit to use. */
  if (setjmp(jerr.setjmp_buffer)) {
    /* If we get here, the JPEG code has signaled an error.
     * We need to clean up the JPEG object, close the input file, and return.
     */
    jpeg_destroy_decompress(&cinfo);
    fclose(infile);
    return 0;
  }
  /* Now we can initialize the JPEG decompression object. */
  jpeg_create_decompress(&cinfo);

  /* Step 2: specify data source (eg, a file) */

  jpeg_stdio_src(&cinfo, infile);

  /* Step 3: read file parameters with jpeg_read_header() */

  (void) jpeg_read_header(&cinfo, TRUE);
  /* We can ignore the return value from jpeg_read_header since
   *   (a) suspension is not possible with the stdio data source, and
   *   (b) we passed TRUE to reject a tables-only JPEG file as an error.
   * See libjpeg.doc for more info.
   */

  /* Step 4: set parameters for decompression */

  /* In this example, we don't need to change any of the defaults set by
   * jpeg_read_header(), so we do nothing here.
   */

  /* Step 5: Start decompressor */

  (void) jpeg_start_decompress(&cinfo);
  /* We can ignore the return value since suspension is not possible
   * with the stdio data source.
   */

  /* We may need to do some setup of our own at this point before reading
   * the data.  After jpeg_start_decompress() we have the correct scaled
   * output image dimensions available, as well as the output colormap
   * if we asked for color quantization.
   * In this example, we need to make an output work buffer of the right size.
   */ 
  /* JSAMPLEs per row in output buffer */
  row_stride = cinfo.output_width * cinfo.output_components;

  buffer = (*cinfo.mem->alloc_sarray)
    ((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, cinfo.output_height);

  /* Step 6: while (scan lines remain to be read) */
  /*           jpeg_read_scanlines(...); */

  while (cinfo.output_scanline < cinfo.output_height) {
    /* jpeg_read_scanlines expects an array of pointers to scanlines.*/
    (void) jpeg_read_scanlines(&cinfo, &buffer[cinfo.output_scanline], 
			       cinfo.output_height);
  }

  /* Perform the size reduction */
  write_JPEG_file(buffer, cinfo.output_width, cinfo.output_height,
		  cinfo.output_components, cinfo.out_color_space,
		  LOW_QUALITY, (JOCTET **)output, output_size);

  /* Step 7: Finish decompression */

  (void) jpeg_finish_decompress(&cinfo);
  /* YANNIS: What a deranged idea! Buffers allocated using the JPEG
     allocator are freed when the "jpeg_finish_decompress" routine is
     called, not when "jpeg_destroy_decompress" is called! 
  */

  /* Step 8: Release JPEG decompression object */
  /* This is an important step since it will release a good deal of memory. */
  jpeg_destroy_decompress(&cinfo);

  /* After finish_decompress, we can close the input file.
   * Here we postpone it until after no more JPEG errors are possible,
   * so as to simplify the setjmp error logic above.  (Actually, I don't
   * think that jpeg_destroy can do an error exit, but why assume anything...)
   */
  fclose(infile);

  /* At this point you may want to check to see whether any corrupt-data
   * warnings occurred (test whether jerr.pub.num_warnings is nonzero).
   */

  /* And we're done! */
  return 1;
}

#ifdef __cplusplus
}
#endif