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, 2016, D. R. Commander.
9 * For conditions of distribution and use, see the accompanying README.ijg
10 * file.
11 *
12 * This file contains decompression data source routines for the case of
13 * reading JPEG data from memory or from a file (or any stdio stream).
14 * While these routines are sufficient for most applications,
15 * some will want to use a different source manager.
16 * IMPORTANT: we assume that fread() will correctly transcribe an array of
17 * JOCTETs from 8-bit-wide elements on external storage.  If char is wider
18 * than 8 bits on your machine, you may need to do some tweaking.
19 */
20
21/* this is not a core library module, so it doesn't define JPEG_INTERNALS */
22#include "jinclude.h"
23#include "jpeglib.h"
24#include "jerror.h"
25
26
27/*
28 * Initialize source --- called by jpeg_read_header
29 * before any data is actually read.
30 */
31
32METHODDEF(void)
33init_mem_source (j_decompress_ptr cinfo)
34{
35  /* no work necessary here */
36}
37
38
39/*
40 * Fill the input buffer --- called whenever buffer is emptied.
41 *
42 * In typical applications, this should read fresh data into the buffer
43 * (ignoring the current state of next_input_byte & bytes_in_buffer),
44 * reset the pointer & count to the start of the buffer, and return TRUE
45 * indicating that the buffer has been reloaded.  It is not necessary to
46 * fill the buffer entirely, only to obtain at least one more byte.
47 *
48 * There is no such thing as an EOF return.  If the end of the file has been
49 * reached, the routine has a choice of ERREXIT() or inserting fake data into
50 * the buffer.  In most cases, generating a warning message and inserting a
51 * fake EOI marker is the best course of action --- this will allow the
52 * decompressor to output however much of the image is there.  However,
53 * the resulting error message is misleading if the real problem is an empty
54 * input file, so we handle that case specially.
55 *
56 * In applications that need to be able to suspend compression due to input
57 * not being available yet, a FALSE return indicates that no more data can be
58 * obtained right now, but more may be forthcoming later.  In this situation,
59 * the decompressor will return to its caller (with an indication of the
60 * number of scanlines it has read, if any).  The application should resume
61 * decompression after it has loaded more data into the input buffer.  Note
62 * that there are substantial restrictions on the use of suspension --- see
63 * the documentation.
64 *
65 * When suspending, the decompressor will back up to a convenient restart point
66 * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
67 * indicate where the restart point will be if the current call returns FALSE.
68 * Data beyond this point must be rescanned after resumption, so move it to
69 * the front of the buffer rather than discarding it.
70 */
71
72METHODDEF(boolean)
73fill_mem_input_buffer (j_decompress_ptr cinfo)
74{
75  static const JOCTET mybuffer[4] = {
76    (JOCTET) 0xFF, (JOCTET) JPEG_EOI, 0, 0
77  };
78
79  /* The whole JPEG data is expected to reside in the supplied memory
80   * buffer, so any request for more data beyond the given buffer size
81   * is treated as an error.
82   */
83  WARNMS(cinfo, JWRN_JPEG_EOF);
84
85  /* Insert a fake EOI marker */
86
87  cinfo->src->next_input_byte = mybuffer;
88  cinfo->src->bytes_in_buffer = 2;
89
90  return TRUE;
91}
92
93
94/*
95 * Skip data --- used to skip over a potentially large amount of
96 * uninteresting data (such as an APPn marker).
97 *
98 * Writers of suspendable-input applications must note that skip_input_data
99 * is not granted the right to give a suspension return.  If the skip extends
100 * beyond the data currently in the buffer, the buffer can be marked empty so
101 * that the next read will cause a fill_input_buffer call that can suspend.
102 * Arranging for additional bytes to be discarded before reloading the input
103 * buffer is the application writer's problem.
104 */
105
106METHODDEF(void)
107skip_input_data (j_decompress_ptr cinfo, long num_bytes)
108{
109  struct jpeg_source_mgr *src = cinfo->src;
110
111  /* Just a dumb implementation for now.  Could use fseek() except
112   * it doesn't work on pipes.  Not clear that being smart is worth
113   * any trouble anyway --- large skips are infrequent.
114   */
115  if (num_bytes > 0) {
116    while (num_bytes > (long) src->bytes_in_buffer) {
117      num_bytes -= (long) src->bytes_in_buffer;
118      (void) (*src->fill_input_buffer) (cinfo);
119      /* note we assume that fill_input_buffer will never return FALSE,
120       * so suspension need not be handled.
121       */
122    }
123    src->next_input_byte += (size_t) num_bytes;
124    src->bytes_in_buffer -= (size_t) num_bytes;
125  }
126}
127
128
129/*
130 * An additional method that can be provided by data source modules is the
131 * resync_to_restart method for error recovery in the presence of RST markers.
132 * For the moment, this source module just uses the default resync method
133 * provided by the JPEG library.  That method assumes that no backtracking
134 * is possible.
135 */
136
137
138/*
139 * Terminate source --- called by jpeg_finish_decompress
140 * after all data has been read.  Often a no-op.
141 *
142 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
143 * application must deal with any cleanup that should happen even
144 * for error exit.
145 */
146
147METHODDEF(void)
148term_source (j_decompress_ptr cinfo)
149{
150  /* no work necessary here */
151}
152
153
154/*
155 * Prepare for input from a supplied memory buffer.
156 * The buffer must contain the whole JPEG data.
157 */
158
159GLOBAL(void)
160jpeg_mem_src_tj (j_decompress_ptr cinfo,
161                 const unsigned char *inbuffer, unsigned long insize)
162{
163  struct jpeg_source_mgr *src;
164
165  if (inbuffer == NULL || insize == 0)  /* Treat empty input as fatal error */
166    ERREXIT(cinfo, JERR_INPUT_EMPTY);
167
168  /* The source object is made permanent so that a series of JPEG images
169   * can be read from the same buffer by calling jpeg_mem_src only before
170   * the first one.
171   */
172  if (cinfo->src == NULL) {     /* first time for this JPEG object? */
173    cinfo->src = (struct jpeg_source_mgr *)
174      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
175                                  sizeof(struct jpeg_source_mgr));
176  } else if (cinfo->src->init_source != init_mem_source) {
177    /* It is unsafe to reuse the existing source manager unless it was created
178     * by this function.
179     */
180    ERREXIT(cinfo, JERR_BUFFER_SIZE);
181  }
182
183  src = cinfo->src;
184  src->init_source = init_mem_source;
185  src->fill_input_buffer = fill_mem_input_buffer;
186  src->skip_input_data = skip_input_data;
187  src->resync_to_restart = jpeg_resync_to_restart; /* use default method */
188  src->term_source = term_source;
189  src->bytes_in_buffer = (size_t) insize;
190  src->next_input_byte = (const JOCTET *) inbuffer;
191}
192