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 0 : init_source (j_decompress_ptr cinfo)
46 : {
47 0 : 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 0 : src->start_of_file = TRUE;
54 0 : }
55 :
56 : #if JPEG_LIB_VERSION >= 80
57 : METHODDEF(void)
58 : init_mem_source (j_decompress_ptr cinfo)
59 : {
60 : /* no work necessary here */
61 : }
62 : #endif
63 :
64 :
65 : /*
66 : * Fill the input buffer --- called whenever buffer is emptied.
67 : *
68 : * In typical applications, this should read fresh data into the buffer
69 : * (ignoring the current state of next_input_byte & bytes_in_buffer),
70 : * reset the pointer & count to the start of the buffer, and return TRUE
71 : * indicating that the buffer has been reloaded. It is not necessary to
72 : * fill the buffer entirely, only to obtain at least one more byte.
73 : *
74 : * There is no such thing as an EOF return. If the end of the file has been
75 : * reached, the routine has a choice of ERREXIT() or inserting fake data into
76 : * the buffer. In most cases, generating a warning message and inserting a
77 : * fake EOI marker is the best course of action --- this will allow the
78 : * decompressor to output however much of the image is there. However,
79 : * the resulting error message is misleading if the real problem is an empty
80 : * input file, so we handle that case specially.
81 : *
82 : * In applications that need to be able to suspend compression due to input
83 : * not being available yet, a FALSE return indicates that no more data can be
84 : * obtained right now, but more may be forthcoming later. In this situation,
85 : * the decompressor will return to its caller (with an indication of the
86 : * number of scanlines it has read, if any). The application should resume
87 : * decompression after it has loaded more data into the input buffer. Note
88 : * that there are substantial restrictions on the use of suspension --- see
89 : * the documentation.
90 : *
91 : * When suspending, the decompressor will back up to a convenient restart point
92 : * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
93 : * indicate where the restart point will be if the current call returns FALSE.
94 : * Data beyond this point must be rescanned after resumption, so move it to
95 : * the front of the buffer rather than discarding it.
96 : */
97 :
98 : METHODDEF(boolean)
99 0 : fill_input_buffer (j_decompress_ptr cinfo)
100 : {
101 0 : my_src_ptr src = (my_src_ptr) cinfo->src;
102 : size_t nbytes;
103 :
104 0 : nbytes = JFREAD(src->infile, src->buffer, INPUT_BUF_SIZE);
105 :
106 0 : if (nbytes <= 0) {
107 0 : if (src->start_of_file) /* Treat empty input file as fatal error */
108 0 : ERREXIT(cinfo, JERR_INPUT_EMPTY);
109 0 : WARNMS(cinfo, JWRN_JPEG_EOF);
110 : /* Insert a fake EOI marker */
111 0 : src->buffer[0] = (JOCTET) 0xFF;
112 0 : src->buffer[1] = (JOCTET) JPEG_EOI;
113 0 : nbytes = 2;
114 : }
115 :
116 0 : src->pub.next_input_byte = src->buffer;
117 0 : src->pub.bytes_in_buffer = nbytes;
118 0 : src->start_of_file = FALSE;
119 :
120 0 : return TRUE;
121 : }
122 :
123 : #if JPEG_LIB_VERSION >= 80
124 : METHODDEF(boolean)
125 : fill_mem_input_buffer (j_decompress_ptr cinfo)
126 : {
127 : static JOCTET mybuffer[4];
128 :
129 : /* The whole JPEG data is expected to reside in the supplied memory
130 : * buffer, so any request for more data beyond the given buffer size
131 : * is treated as an error.
132 : */
133 : WARNMS(cinfo, JWRN_JPEG_EOF);
134 : /* Insert a fake EOI marker */
135 : mybuffer[0] = (JOCTET) 0xFF;
136 : mybuffer[1] = (JOCTET) JPEG_EOI;
137 :
138 : cinfo->src->next_input_byte = mybuffer;
139 : cinfo->src->bytes_in_buffer = 2;
140 :
141 : return TRUE;
142 : }
143 : #endif
144 :
145 :
146 : /*
147 : * Skip data --- used to skip over a potentially large amount of
148 : * uninteresting data (such as an APPn marker).
149 : *
150 : * Writers of suspendable-input applications must note that skip_input_data
151 : * is not granted the right to give a suspension return. If the skip extends
152 : * beyond the data currently in the buffer, the buffer can be marked empty so
153 : * that the next read will cause a fill_input_buffer call that can suspend.
154 : * Arranging for additional bytes to be discarded before reloading the input
155 : * buffer is the application writer's problem.
156 : */
157 :
158 : METHODDEF(void)
159 0 : skip_input_data (j_decompress_ptr cinfo, long num_bytes)
160 : {
161 0 : struct jpeg_source_mgr * src = cinfo->src;
162 :
163 : /* Just a dumb implementation for now. Could use fseek() except
164 : * it doesn't work on pipes. Not clear that being smart is worth
165 : * any trouble anyway --- large skips are infrequent.
166 : */
167 0 : if (num_bytes > 0) {
168 0 : while (num_bytes > (long) src->bytes_in_buffer) {
169 0 : num_bytes -= (long) src->bytes_in_buffer;
170 0 : (void) (*src->fill_input_buffer) (cinfo);
171 : /* note we assume that fill_input_buffer will never return FALSE,
172 : * so suspension need not be handled.
173 : */
174 : }
175 0 : src->next_input_byte += (size_t) num_bytes;
176 0 : src->bytes_in_buffer -= (size_t) num_bytes;
177 : }
178 0 : }
179 :
180 :
181 : /*
182 : * An additional method that can be provided by data source modules is the
183 : * resync_to_restart method for error recovery in the presence of RST markers.
184 : * For the moment, this source module just uses the default resync method
185 : * provided by the JPEG library. That method assumes that no backtracking
186 : * is possible.
187 : */
188 :
189 :
190 : /*
191 : * Terminate source --- called by jpeg_finish_decompress
192 : * after all data has been read. Often a no-op.
193 : *
194 : * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
195 : * application must deal with any cleanup that should happen even
196 : * for error exit.
197 : */
198 :
199 : METHODDEF(void)
200 0 : term_source (j_decompress_ptr cinfo)
201 : {
202 : /* no work necessary here */
203 0 : }
204 :
205 :
206 : /*
207 : * Prepare for input from a stdio stream.
208 : * The caller must have already opened the stream, and is responsible
209 : * for closing it after finishing decompression.
210 : */
211 :
212 : GLOBAL(void)
213 0 : jpeg_stdio_src (j_decompress_ptr cinfo, FILE * infile)
214 : {
215 : my_src_ptr src;
216 :
217 : /* The source object and input buffer are made permanent so that a series
218 : * of JPEG images can be read from the same file by calling jpeg_stdio_src
219 : * only before the first one. (If we discarded the buffer at the end of
220 : * one image, we'd likely lose the start of the next one.)
221 : * This makes it unsafe to use this manager and a different source
222 : * manager serially with the same JPEG object. Caveat programmer.
223 : */
224 0 : if (cinfo->src == NULL) { /* first time for this JPEG object? */
225 0 : cinfo->src = (struct jpeg_source_mgr *)
226 0 : (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
227 : SIZEOF(my_source_mgr));
228 0 : src = (my_src_ptr) cinfo->src;
229 0 : src->buffer = (JOCTET *)
230 0 : (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
231 : INPUT_BUF_SIZE * SIZEOF(JOCTET));
232 : }
233 :
234 0 : src = (my_src_ptr) cinfo->src;
235 0 : src->pub.init_source = init_source;
236 0 : src->pub.fill_input_buffer = fill_input_buffer;
237 0 : src->pub.skip_input_data = skip_input_data;
238 0 : src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
239 0 : src->pub.term_source = term_source;
240 0 : src->infile = infile;
241 0 : src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
242 0 : src->pub.next_input_byte = NULL; /* until buffer loaded */
243 0 : }
244 :
245 :
246 : #if JPEG_LIB_VERSION >= 80
247 : /*
248 : * Prepare for input from a supplied memory buffer.
249 : * The buffer must contain the whole JPEG data.
250 : */
251 :
252 : GLOBAL(void)
253 : jpeg_mem_src (j_decompress_ptr cinfo,
254 : unsigned char * inbuffer, unsigned long insize)
255 : {
256 : struct jpeg_source_mgr * src;
257 :
258 : if (inbuffer == NULL || insize == 0) /* Treat empty input as fatal error */
259 : ERREXIT(cinfo, JERR_INPUT_EMPTY);
260 :
261 : /* The source object is made permanent so that a series of JPEG images
262 : * can be read from the same buffer by calling jpeg_mem_src only before
263 : * the first one.
264 : */
265 : if (cinfo->src == NULL) { /* first time for this JPEG object? */
266 : cinfo->src = (struct jpeg_source_mgr *)
267 : (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
268 : SIZEOF(struct jpeg_source_mgr));
269 : }
270 :
271 : src = cinfo->src;
272 : src->init_source = init_mem_source;
273 : src->fill_input_buffer = fill_mem_input_buffer;
274 : src->skip_input_data = skip_input_data;
275 : src->resync_to_restart = jpeg_resync_to_restart; /* use default method */
276 : src->term_source = term_source;
277 : src->bytes_in_buffer = (size_t) insize;
278 : src->next_input_byte = (JOCTET *) inbuffer;
279 : }
280 : #endif
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