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 /*

  * 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, D. R. Commander.

  * 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 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;

 }

 #if JPEG_LIB_VERSION >= 80 || defined(MEM_SRCDST_SUPPORTED)

 METHODDEF(void)

 init_mem_source (j_decompress_ptr cinfo)

 {

   /* no work necessary here */

 }

 #endif

 /*

  * 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 = JFREAD(src->infile, src->buffer, INPUT_BUF_SIZE);

   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;

 }

 #if JPEG_LIB_VERSION >= 80 || defined(MEM_SRCDST_SUPPORTED)

 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;

 }

 #endif

 /*

  * 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.)

    * 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->buffer = (JOCTET *)

       (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,

 				  INPUT_BUF_SIZE * SIZEOF(JOCTET));

   }

   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 */

 }

 #if JPEG_LIB_VERSION >= 80 || defined(MEM_SRCDST_SUPPORTED)

 /*

  * 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,

 	      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));

   }

   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 = (JOCTET *) inbuffer;

 }

 #endif