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      1 /*
      2  * jdatasrc-tj.c
      3  *
      4  * This file was part of the Independent JPEG Group's software:
      5  * Copyright (C) 1994-1996, Thomas G. Lane.
      6  * Modified 2009-2011 by Guido Vollbeding.
      7  * libjpeg-turbo Modifications:
      8  * Copyright (C) 2011, D. R. Commander.
      9  * For conditions of distribution and use, see the accompanying README file.
     10  *
     11  * This file contains decompression data source routines for the case of
     12  * reading JPEG data from memory or from a file (or any stdio stream).
     13  * While these routines are sufficient for most applications,
     14  * some will want to use a different source manager.
     15  * IMPORTANT: we assume that fread() will correctly transcribe an array of
     16  * JOCTETs from 8-bit-wide elements on external storage.  If char is wider
     17  * than 8 bits on your machine, you may need to do some tweaking.
     18  */
     19 
     20 /* this is not a core library module, so it doesn't define JPEG_INTERNALS */
     21 #include "jinclude.h"
     22 #include "jpeglib.h"
     23 #include "jerror.h"
     24 
     25 
     26 /*
     27  * Initialize source --- called by jpeg_read_header
     28  * before any data is actually read.
     29  */
     30 
     31 METHODDEF(void)
     32 init_mem_source (j_decompress_ptr cinfo)
     33 {
     34   /* no work necessary here */
     35 }
     36 
     37 
     38 /*
     39  * Fill the input buffer --- called whenever buffer is emptied.
     40  *
     41  * In typical applications, this should read fresh data into the buffer
     42  * (ignoring the current state of next_input_byte & bytes_in_buffer),
     43  * reset the pointer & count to the start of the buffer, and return TRUE
     44  * indicating that the buffer has been reloaded.  It is not necessary to
     45  * fill the buffer entirely, only to obtain at least one more byte.
     46  *
     47  * There is no such thing as an EOF return.  If the end of the file has been
     48  * reached, the routine has a choice of ERREXIT() or inserting fake data into
     49  * the buffer.  In most cases, generating a warning message and inserting a
     50  * fake EOI marker is the best course of action --- this will allow the
     51  * decompressor to output however much of the image is there.  However,
     52  * the resulting error message is misleading if the real problem is an empty
     53  * input file, so we handle that case specially.
     54  *
     55  * In applications that need to be able to suspend compression due to input
     56  * not being available yet, a FALSE return indicates that no more data can be
     57  * obtained right now, but more may be forthcoming later.  In this situation,
     58  * the decompressor will return to its caller (with an indication of the
     59  * number of scanlines it has read, if any).  The application should resume
     60  * decompression after it has loaded more data into the input buffer.  Note
     61  * that there are substantial restrictions on the use of suspension --- see
     62  * the documentation.
     63  *
     64  * When suspending, the decompressor will back up to a convenient restart point
     65  * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
     66  * indicate where the restart point will be if the current call returns FALSE.
     67  * Data beyond this point must be rescanned after resumption, so move it to
     68  * the front of the buffer rather than discarding it.
     69  */
     70 
     71 METHODDEF(boolean)
     72 fill_mem_input_buffer (j_decompress_ptr cinfo)
     73 {
     74   static const JOCTET mybuffer[4] = {
     75     (JOCTET) 0xFF, (JOCTET) JPEG_EOI, 0, 0
     76   };
     77 
     78   /* The whole JPEG data is expected to reside in the supplied memory
     79    * buffer, so any request for more data beyond the given buffer size
     80    * is treated as an error.
     81    */
     82   WARNMS(cinfo, JWRN_JPEG_EOF);
     83 
     84   /* Insert a fake EOI marker */
     85 
     86   cinfo->src->next_input_byte = mybuffer;
     87   cinfo->src->bytes_in_buffer = 2;
     88 
     89   return TRUE;
     90 }
     91 
     92 
     93 /*
     94  * Skip data --- used to skip over a potentially large amount of
     95  * uninteresting data (such as an APPn marker).
     96  *
     97  * Writers of suspendable-input applications must note that skip_input_data
     98  * is not granted the right to give a suspension return.  If the skip extends
     99  * beyond the data currently in the buffer, the buffer can be marked empty so
    100  * that the next read will cause a fill_input_buffer call that can suspend.
    101  * Arranging for additional bytes to be discarded before reloading the input
    102  * buffer is the application writer's problem.
    103  */
    104 
    105 METHODDEF(void)
    106 skip_input_data (j_decompress_ptr cinfo, long num_bytes)
    107 {
    108   struct jpeg_source_mgr * src = cinfo->src;
    109 
    110   /* Just a dumb implementation for now.  Could use fseek() except
    111    * it doesn't work on pipes.  Not clear that being smart is worth
    112    * any trouble anyway --- large skips are infrequent.
    113    */
    114   if (num_bytes > 0) {
    115     while (num_bytes > (long) src->bytes_in_buffer) {
    116       num_bytes -= (long) src->bytes_in_buffer;
    117       (void) (*src->fill_input_buffer) (cinfo);
    118       /* note we assume that fill_input_buffer will never return FALSE,
    119        * so suspension need not be handled.
    120        */
    121     }
    122     src->next_input_byte += (size_t) num_bytes;
    123     src->bytes_in_buffer -= (size_t) num_bytes;
    124   }
    125 }
    126 
    127 
    128 /*
    129  * An additional method that can be provided by data source modules is the
    130  * resync_to_restart method for error recovery in the presence of RST markers.
    131  * For the moment, this source module just uses the default resync method
    132  * provided by the JPEG library.  That method assumes that no backtracking
    133  * is possible.
    134  */
    135 
    136 
    137 /*
    138  * Terminate source --- called by jpeg_finish_decompress
    139  * after all data has been read.  Often a no-op.
    140  *
    141  * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
    142  * application must deal with any cleanup that should happen even
    143  * for error exit.
    144  */
    145 
    146 METHODDEF(void)
    147 term_source (j_decompress_ptr cinfo)
    148 {
    149   /* no work necessary here */
    150 }
    151 
    152 
    153 /*
    154  * Prepare for input from a supplied memory buffer.
    155  * The buffer must contain the whole JPEG data.
    156  */
    157 
    158 GLOBAL(void)
    159 jpeg_mem_src_tj (j_decompress_ptr cinfo,
    160 	      unsigned char * inbuffer, unsigned long insize)
    161 {
    162   struct jpeg_source_mgr * src;
    163 
    164   if (inbuffer == NULL || insize == 0)	/* Treat empty input as fatal error */
    165     ERREXIT(cinfo, JERR_INPUT_EMPTY);
    166 
    167   /* The source object is made permanent so that a series of JPEG images
    168    * can be read from the same buffer by calling jpeg_mem_src only before
    169    * the first one.
    170    */
    171   if (cinfo->src == NULL) {	/* first time for this JPEG object? */
    172     cinfo->src = (struct jpeg_source_mgr *)
    173       (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
    174 				  SIZEOF(struct jpeg_source_mgr));
    175   }
    176 
    177   src = cinfo->src;
    178   src->init_source = init_mem_source;
    179   src->fill_input_buffer = fill_mem_input_buffer;
    180   src->skip_input_data = skip_input_data;
    181   src->resync_to_restart = jpeg_resync_to_restart; /* use default method */
    182   src->term_source = term_source;
    183   src->bytes_in_buffer = (size_t) insize;
    184   src->next_input_byte = (JOCTET *) inbuffer;
    185 }
    186