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
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.
21 /* this is not a core library module, so it doesn't define JPEG_INTERNALS */
28 * Initialize source --- called by jpeg_read_header
29 * before any data is actually read.
33 init_mem_source (j_decompress_ptr cinfo)
35 /* no work necessary here */
40 * Fill the input buffer --- called whenever buffer is emptied.
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.
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.
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
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.
73 fill_mem_input_buffer (j_decompress_ptr cinfo)
75 static const JOCTET mybuffer[4] = {
76 (JOCTET) 0xFF, (JOCTET) JPEG_EOI, 0, 0
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.
83 WARNMS(cinfo, JWRN_JPEG_EOF);
85 /* Insert a fake EOI marker */
87 cinfo->src->next_input_byte = mybuffer;
88 cinfo->src->bytes_in_buffer = 2;
95 * Skip data --- used to skip over a potentially large amount of
96 * uninteresting data (such as an APPn marker).
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.
107 skip_input_data (j_decompress_ptr cinfo, long num_bytes)
109 struct jpeg_source_mgr *src = cinfo->src;
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.
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.
123 src->next_input_byte += (size_t) num_bytes;
124 src->bytes_in_buffer -= (size_t) num_bytes;
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
139 * Terminate source --- called by jpeg_finish_decompress
140 * after all data has been read. Often a no-op.
142 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
143 * application must deal with any cleanup that should happen even
148 term_source (j_decompress_ptr cinfo)
150 /* no work necessary here */
155 * Prepare for input from a supplied memory buffer.
156 * The buffer must contain the whole JPEG data.
160 jpeg_mem_src_tj (j_decompress_ptr cinfo,
161 const unsigned char *inbuffer, unsigned long insize)
163 struct jpeg_source_mgr *src;
165 if (inbuffer == NULL || insize == 0) /* Treat empty input as fatal error */
166 ERREXIT(cinfo, JERR_INPUT_EMPTY);
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
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
180 ERREXIT(cinfo, JERR_BUFFER_SIZE);
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;