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, 2019, 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 void jpeg_mem_src_tj(j_decompress_ptr cinfo, const unsigned char *inbuffer,
27 unsigned long insize);
28
29
30 /*
31 * Initialize source --- called by jpeg_read_header
32 * before any data is actually read.
33 */
34
35 METHODDEF(void)
init_mem_source(j_decompress_ptr cinfo)36 init_mem_source(j_decompress_ptr cinfo)
37 {
38 /* no work necessary here */
39 }
40
41
42 /*
43 * Fill the input buffer --- called whenever buffer is emptied.
44 *
45 * In typical applications, this should read fresh data into the buffer
46 * (ignoring the current state of next_input_byte & bytes_in_buffer),
47 * reset the pointer & count to the start of the buffer, and return TRUE
48 * indicating that the buffer has been reloaded. It is not necessary to
49 * fill the buffer entirely, only to obtain at least one more byte.
50 *
51 * There is no such thing as an EOF return. If the end of the file has been
52 * reached, the routine has a choice of ERREXIT() or inserting fake data into
53 * the buffer. In most cases, generating a warning message and inserting a
54 * fake EOI marker is the best course of action --- this will allow the
55 * decompressor to output however much of the image is there. However,
56 * the resulting error message is misleading if the real problem is an empty
57 * input file, so we handle that case specially.
58 *
59 * In applications that need to be able to suspend compression due to input
60 * not being available yet, a FALSE return indicates that no more data can be
61 * obtained right now, but more may be forthcoming later. In this situation,
62 * the decompressor will return to its caller (with an indication of the
63 * number of scanlines it has read, if any). The application should resume
64 * decompression after it has loaded more data into the input buffer. Note
65 * that there are substantial restrictions on the use of suspension --- see
66 * the documentation.
67 *
68 * When suspending, the decompressor will back up to a convenient restart point
69 * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
70 * indicate where the restart point will be if the current call returns FALSE.
71 * Data beyond this point must be rescanned after resumption, so move it to
72 * the front of the buffer rather than discarding it.
73 */
74
75 METHODDEF(boolean)
fill_mem_input_buffer(j_decompress_ptr cinfo)76 fill_mem_input_buffer(j_decompress_ptr cinfo)
77 {
78 static const JOCTET mybuffer[4] = {
79 (JOCTET)0xFF, (JOCTET)JPEG_EOI, 0, 0
80 };
81
82 /* The whole JPEG data is expected to reside in the supplied memory
83 * buffer, so any request for more data beyond the given buffer size
84 * is treated as an error.
85 */
86 WARNMS(cinfo, JWRN_JPEG_EOF);
87
88 /* Insert a fake EOI marker */
89
90 cinfo->src->next_input_byte = mybuffer;
91 cinfo->src->bytes_in_buffer = 2;
92
93 return TRUE;
94 }
95
96
97 /*
98 * Skip data --- used to skip over a potentially large amount of
99 * uninteresting data (such as an APPn marker).
100 *
101 * Writers of suspendable-input applications must note that skip_input_data
102 * is not granted the right to give a suspension return. If the skip extends
103 * beyond the data currently in the buffer, the buffer can be marked empty so
104 * that the next read will cause a fill_input_buffer call that can suspend.
105 * Arranging for additional bytes to be discarded before reloading the input
106 * buffer is the application writer's problem.
107 */
108
109 METHODDEF(void)
skip_input_data(j_decompress_ptr cinfo,long num_bytes)110 skip_input_data(j_decompress_ptr cinfo, long num_bytes)
111 {
112 struct jpeg_source_mgr *src = cinfo->src;
113
114 /* Just a dumb implementation for now. Could use fseek() except
115 * it doesn't work on pipes. Not clear that being smart is worth
116 * any trouble anyway --- large skips are infrequent.
117 */
118 if (num_bytes > 0) {
119 while (num_bytes > (long)src->bytes_in_buffer) {
120 num_bytes -= (long)src->bytes_in_buffer;
121 (void)(*src->fill_input_buffer) (cinfo);
122 /* note we assume that fill_input_buffer will never return FALSE,
123 * so suspension need not be handled.
124 */
125 }
126 src->next_input_byte += (size_t)num_bytes;
127 src->bytes_in_buffer -= (size_t)num_bytes;
128 }
129 }
130
131
132 /*
133 * An additional method that can be provided by data source modules is the
134 * resync_to_restart method for error recovery in the presence of RST markers.
135 * For the moment, this source module just uses the default resync method
136 * provided by the JPEG library. That method assumes that no backtracking
137 * is possible.
138 */
139
140
141 /*
142 * Terminate source --- called by jpeg_finish_decompress
143 * after all data has been read. Often a no-op.
144 *
145 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
146 * application must deal with any cleanup that should happen even
147 * for error exit.
148 */
149
150 METHODDEF(void)
term_source(j_decompress_ptr cinfo)151 term_source(j_decompress_ptr cinfo)
152 {
153 /* no work necessary here */
154 }
155
156
157 /*
158 * Prepare for input from a supplied memory buffer.
159 * The buffer must contain the whole JPEG data.
160 */
161
162 GLOBAL(void)
jpeg_mem_src_tj(j_decompress_ptr cinfo,const unsigned char * inbuffer,unsigned long insize)163 jpeg_mem_src_tj(j_decompress_ptr cinfo, const unsigned char *inbuffer,
164 unsigned long insize)
165 {
166 struct jpeg_source_mgr *src;
167
168 if (inbuffer == NULL || insize == 0) /* Treat empty input as fatal error */
169 ERREXIT(cinfo, JERR_INPUT_EMPTY);
170
171 /* The source object is made permanent so that a series of JPEG images
172 * can be read from the same buffer by calling jpeg_mem_src only before
173 * the first one.
174 */
175 if (cinfo->src == NULL) { /* first time for this JPEG object? */
176 cinfo->src = (struct jpeg_source_mgr *)
177 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_PERMANENT,
178 sizeof(struct jpeg_source_mgr));
179 } else if (cinfo->src->init_source != init_mem_source) {
180 /* It is unsafe to reuse the existing source manager unless it was created
181 * by this function.
182 */
183 ERREXIT(cinfo, JERR_BUFFER_SIZE);
184 }
185
186 src = cinfo->src;
187 src->init_source = init_mem_source;
188 src->fill_input_buffer = fill_mem_input_buffer;
189 src->skip_input_data = skip_input_data;
190 src->resync_to_restart = jpeg_resync_to_restart; /* use default method */
191 src->term_source = term_source;
192 src->bytes_in_buffer = (size_t)insize;
193 src->next_input_byte = (const JOCTET *)inbuffer;
194 }
195