compiler/libjpeg/jdatasrc.c

   1 /*
   2  * jdatasrc.c
   3  *
   4  * Copyright (C) 1994-1996, Thomas G. Lane.
   5  * Modified 2009-2010 by Guido Vollbeding.
   6  * This file is part of the Independent JPEG Group's software.
   7  * For conditions of distribution and use, see the accompanying README file.
   8  *
   9  * This file contains decompression data source routines for the case of
  10  * reading JPEG data from memory or from a file (or any stdio stream).
  11  * While these routines are sufficient for most applications,
  12  * some will want to use a different source manager.
  13  * IMPORTANT: we assume that fread() will correctly transcribe an array of
  14  * JOCTETs from 8-bit-wide elements on external storage.  If char is wider
  15  * than 8 bits on your machine, you may need to do some tweaking.
  16  */
  17
  18 /* this is not a core library module, so it doesn't define JPEG_INTERNALS */
  19 #include "jinclude.h"
  20 #include "jpeglib.h"
  21 #include "jerror.h"
  22
  23
  24 /* Expanded data source object for stdio input */
  25
  26 typedef struct {
  27   struct jpeg_source_mgr pub;   /* public fields */
  28
  29   FILE * infile;                /* source stream */
  30   JOCTET * buffer;              /* start of buffer */
  31   boolean start_of_file;        /* have we gotten any data yet? */
  32 } my_source_mgr;
  33
  34 typedef my_source_mgr * my_src_ptr;
  35
  36 #define INPUT_BUF_SIZE  4096    /* choose an efficiently fread'able size */
  37
  38
  39 /*
  40  * Initialize source --- called by jpeg_read_header
  41  * before any data is actually read.
  42  */
  43
  44 METHODDEF(void)
  45 init_source (j_decompress_ptr cinfo)
  46 {
  47   my_src_ptr src = (my_src_ptr) cinfo->src;
  48
  49   /* We reset the empty-input-file flag for each image,
  50    * but we don't clear the input buffer.
  51    * This is correct behavior for reading a series of images from one source.
  52    */
  53   src->start_of_file = TRUE;
  54 }
  55
  56 METHODDEF(void)
  57 init_mem_source (j_decompress_ptr cinfo)
  58 {
  59   /* no work necessary here */
  60 }
  61
  62
  63 /*
  64  * Fill the input buffer --- called whenever buffer is emptied.
  65  *
  66  * In typical applications, this should read fresh data into the buffer
  67  * (ignoring the current state of next_input_byte & bytes_in_buffer),
  68  * reset the pointer & count to the start of the buffer, and return TRUE
  69  * indicating that the buffer has been reloaded.  It is not necessary to
  70  * fill the buffer entirely, only to obtain at least one more byte.
  71  *
  72  * There is no such thing as an EOF return.  If the end of the file has been
  73  * reached, the routine has a choice of ERREXIT() or inserting fake data into
  74  * the buffer.  In most cases, generating a warning message and inserting a
  75  * fake EOI marker is the best course of action --- this will allow the
  76  * decompressor to output however much of the image is there.  However,
  77  * the resulting error message is misleading if the real problem is an empty
  78  * input file, so we handle that case specially.
  79  *
  80  * In applications that need to be able to suspend compression due to input
  81  * not being available yet, a FALSE return indicates that no more data can be
  82  * obtained right now, but more may be forthcoming later.  In this situation,
  83  * the decompressor will return to its caller (with an indication of the
  84  * number of scanlines it has read, if any).  The application should resume
  85  * decompression after it has loaded more data into the input buffer.  Note
  86  * that there are substantial restrictions on the use of suspension --- see
  87  * the documentation.
  88  *
  89  * When suspending, the decompressor will back up to a convenient restart point
  90  * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
  91  * indicate where the restart point will be if the current call returns FALSE.
  92  * Data beyond this point must be rescanned after resumption, so move it to
  93  * the front of the buffer rather than discarding it.
  94  */
  95
  96 METHODDEF(boolean)
  97 fill_input_buffer (j_decompress_ptr cinfo)
  98 {
  99   my_src_ptr src = (my_src_ptr) cinfo->src;
 100   size_t nbytes;
 101
 102   nbytes = JFREAD(src->infile, src->buffer, INPUT_BUF_SIZE);
 103
 104   if (nbytes <= 0) {
 105     if (src->start_of_file)     /* Treat empty input file as fatal error */
 106       ERREXIT(cinfo, JERR_INPUT_EMPTY);
 107     WARNMS(cinfo, JWRN_JPEG_EOF);
 108     /* Insert a fake EOI marker */
 109     src->buffer[0] = (JOCTET) 0xFF;
 110     src->buffer[1] = (JOCTET) JPEG_EOI;
 111     nbytes = 2;
 112   }
 113
 114   src->pub.next_input_byte = src->buffer;
 115   src->pub.bytes_in_buffer = nbytes;
 116   src->start_of_file = FALSE;
 117
 118   return TRUE;
 119 }
 120
 121 METHODDEF(boolean)
 122 fill_mem_input_buffer (j_decompress_ptr cinfo)
 123 {
 124   static JOCTET mybuffer[4];
 125
 126   /* The whole JPEG data is expected to reside in the supplied memory
 127    * buffer, so any request for more data beyond the given buffer size
 128    * is treated as an error.
 129    */
 130   WARNMS(cinfo, JWRN_JPEG_EOF);
 131   /* Insert a fake EOI marker */
 132   mybuffer[0] = (JOCTET) 0xFF;
 133   mybuffer[1] = (JOCTET) JPEG_EOI;
 134
 135   cinfo->src->next_input_byte = mybuffer;
 136   cinfo->src->bytes_in_buffer = 2;
 137
 138   return TRUE;
 139 }
 140
 141
 142 /*
 143  * Skip data --- used to skip over a potentially large amount of
 144  * uninteresting data (such as an APPn marker).
 145  *
 146  * Writers of suspendable-input applications must note that skip_input_data
 147  * is not granted the right to give a suspension return.  If the skip extends
 148  * beyond the data currently in the buffer, the buffer can be marked empty so
 149  * that the next read will cause a fill_input_buffer call that can suspend.
 150  * Arranging for additional bytes to be discarded before reloading the input
 151  * buffer is the application writer's problem.
 152  */
 153
 154 METHODDEF(void)
 155 skip_input_data (j_decompress_ptr cinfo, long num_bytes)
 156 {
 157   struct jpeg_source_mgr * src = cinfo->src;
 158
 159   /* Just a dumb implementation for now.  Could use fseek() except
 160    * it doesn't work on pipes.  Not clear that being smart is worth
 161    * any trouble anyway --- large skips are infrequent.
 162    */
 163   if (num_bytes > 0) {
 164     while (num_bytes > (long) src->bytes_in_buffer) {
 165       num_bytes -= (long) src->bytes_in_buffer;
 166       (void) (*src->fill_input_buffer) (cinfo);
 167       /* note we assume that fill_input_buffer will never return FALSE,
 168        * so suspension need not be handled.
 169        */
 170     }
 171     src->next_input_byte += (size_t) num_bytes;
 172     src->bytes_in_buffer -= (size_t) num_bytes;
 173   }
 174 }
 175
 176
 177 /*
 178  * An additional method that can be provided by data source modules is the
 179  * resync_to_restart method for error recovery in the presence of RST markers.
 180  * For the moment, this source module just uses the default resync method
 181  * provided by the JPEG library.  That method assumes that no backtracking
 182  * is possible.
 183  */
 184
 185
 186 /*
 187  * Terminate source --- called by jpeg_finish_decompress
 188  * after all data has been read.  Often a no-op.
 189  *
 190  * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
 191  * application must deal with any cleanup that should happen even
 192  * for error exit.
 193  */
 194
 195 METHODDEF(void)
 196 term_source (j_decompress_ptr cinfo)
 197 {
 198   /* no work necessary here */
 199 }
 200
 201
 202 /*
 203  * Prepare for input from a stdio stream.
 204  * The caller must have already opened the stream, and is responsible
 205  * for closing it after finishing decompression.
 206  */
 207
 208 GLOBAL(void)
 209 jpeg_stdio_src (j_decompress_ptr cinfo, FILE * infile)
 210 {
 211   my_src_ptr src;
 212
 213   /* The source object and input buffer are made permanent so that a series
 214    * of JPEG images can be read from the same file by calling jpeg_stdio_src
 215    * only before the first one.  (If we discarded the buffer at the end of
 216    * one image, we'd likely lose the start of the next one.)
 217    * This makes it unsafe to use this manager and a different source
 218    * manager serially with the same JPEG object.  Caveat programmer.
 219    */
 220   if (cinfo->src == NULL) {     /* first time for this JPEG object? */
 221     cinfo->src = (struct jpeg_source_mgr *)
 222       (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
 223                                   SIZEOF(my_source_mgr));
 224     src = (my_src_ptr) cinfo->src;
 225     src->buffer = (JOCTET *)
 226       (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
 227                                   INPUT_BUF_SIZE * SIZEOF(JOCTET));
 228   }
 229
 230   src = (my_src_ptr) cinfo->src;
 231   src->pub.init_source = init_source;
 232   src->pub.fill_input_buffer = fill_input_buffer;
 233   src->pub.skip_input_data = skip_input_data;
 234   src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
 235   src->pub.term_source = term_source;
 236   src->infile = infile;
 237   src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
 238   src->pub.next_input_byte = NULL; /* until buffer loaded */
 239 }
 240
 241
 242 /*
 243  * Prepare for input from a supplied memory buffer.
 244  * The buffer must contain the whole JPEG data.
 245  */
 246
 247 GLOBAL(void)
 248 jpeg_mem_src (j_decompress_ptr cinfo,
 249               unsigned char * inbuffer, unsigned long insize)
 250 {
 251   struct jpeg_source_mgr * src;
 252
 253   if (inbuffer == NULL || insize == 0)  /* Treat empty input as fatal error */
 254     ERREXIT(cinfo, JERR_INPUT_EMPTY);
 255
 256   /* The source object is made permanent so that a series of JPEG images
 257    * can be read from the same buffer by calling jpeg_mem_src only before
 258    * the first one.
 259    */
 260   if (cinfo->src == NULL) {     /* first time for this JPEG object? */
 261     cinfo->src = (struct jpeg_source_mgr *)
 262       (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
 263                                   SIZEOF(struct jpeg_source_mgr));
 264   }
 265
 266   src = cinfo->src;
 267   src->init_source = init_mem_source;
 268   src->fill_input_buffer = fill_mem_input_buffer;
 269   src->skip_input_data = skip_input_data;
 270   src->resync_to_restart = jpeg_resync_to_restart; /* use default method */
 271   src->term_source = term_source;
 272   src->bytes_in_buffer = (size_t) insize;
 273   src->next_input_byte = (JOCTET *) inbuffer;
 274 }