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
31METHODDEF(void)
32init_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
71METHODDEF(boolean)
72fill_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
105METHODDEF(void)
106skip_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
146METHODDEF(void)
147term_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
158GLOBAL(void)
159jpeg_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