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.
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.
18 /* this is not a core library module, so it doesn't define JPEG_INTERNALS */
24 /* Expanded data source object for stdio input */
27 struct jpeg_source_mgr pub; /* public fields */
29 FILE * infile; /* source stream */
30 JOCTET * buffer; /* start of buffer */
31 boolean start_of_file; /* have we gotten any data yet? */
34 typedef my_source_mgr * my_src_ptr;
36 #define INPUT_BUF_SIZE 4096 /* choose an efficiently fread'able size */
40 * Initialize source --- called by jpeg_read_header
41 * before any data is actually read.
45 init_source (j_decompress_ptr cinfo)
47 my_src_ptr src = (my_src_ptr) cinfo->src;
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.
53 src->start_of_file = TRUE;
56 #if JPEG_LIB_VERSION >= 80
58 init_mem_source (j_decompress_ptr cinfo)
60 /* no work necessary here */
66 * Fill the input buffer --- called whenever buffer is emptied.
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.
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.
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
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.
99 fill_input_buffer (j_decompress_ptr cinfo)
101 my_src_ptr src = (my_src_ptr) cinfo->src;
104 nbytes = JFREAD(src->infile, src->buffer, INPUT_BUF_SIZE);
107 if (src->start_of_file) /* Treat empty input file as fatal error */
108 ERREXIT(cinfo, JERR_INPUT_EMPTY);
109 WARNMS(cinfo, JWRN_JPEG_EOF);
110 /* Insert a fake EOI marker */
111 src->buffer[0] = (JOCTET) 0xFF;
112 src->buffer[1] = (JOCTET) JPEG_EOI;
116 src->pub.next_input_byte = src->buffer;
117 src->pub.bytes_in_buffer = nbytes;
118 src->start_of_file = FALSE;
123 #if JPEG_LIB_VERSION >= 80
125 fill_mem_input_buffer (j_decompress_ptr cinfo)
127 static JOCTET mybuffer[4];
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.
133 WARNMS(cinfo, JWRN_JPEG_EOF);
134 /* Insert a fake EOI marker */
135 mybuffer[0] = (JOCTET) 0xFF;
136 mybuffer[1] = (JOCTET) JPEG_EOI;
138 cinfo->src->next_input_byte = mybuffer;
139 cinfo->src->bytes_in_buffer = 2;
147 * Skip data --- used to skip over a potentially large amount of
148 * uninteresting data (such as an APPn marker).
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.
159 skip_input_data (j_decompress_ptr cinfo, long num_bytes)
161 struct jpeg_source_mgr * src = cinfo->src;
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.
168 while (num_bytes > (long) src->bytes_in_buffer) {
169 num_bytes -= (long) src->bytes_in_buffer;
170 (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.
175 src->next_input_byte += (size_t) num_bytes;
176 src->bytes_in_buffer -= (size_t) num_bytes;
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
191 * Terminate source --- called by jpeg_finish_decompress
192 * after all data has been read. Often a no-op.
194 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
195 * application must deal with any cleanup that should happen even
200 term_source (j_decompress_ptr cinfo)
202 /* no work necessary here */
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.
213 jpeg_stdio_src (j_decompress_ptr cinfo, FILE * infile)
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.
224 if (cinfo->src == NULL) { /* first time for this JPEG object? */
225 cinfo->src = (struct jpeg_source_mgr *)
226 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
227 SIZEOF(my_source_mgr));
228 src = (my_src_ptr) cinfo->src;
229 src->buffer = (JOCTET *)
230 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
231 INPUT_BUF_SIZE * SIZEOF(JOCTET));
234 src = (my_src_ptr) cinfo->src;
235 src->pub.init_source = init_source;
236 src->pub.fill_input_buffer = fill_input_buffer;
237 src->pub.skip_input_data = skip_input_data;
238 src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
239 src->pub.term_source = term_source;
240 src->infile = infile;
241 src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
242 src->pub.next_input_byte = NULL; /* until buffer loaded */
246 #if JPEG_LIB_VERSION >= 80
248 * Prepare for input from a supplied memory buffer.
249 * The buffer must contain the whole JPEG data.
253 jpeg_mem_src (j_decompress_ptr cinfo,
254 unsigned char * inbuffer, unsigned long insize)
256 struct jpeg_source_mgr * src;
258 if (inbuffer == NULL || insize == 0) /* Treat empty input as fatal error */
259 ERREXIT(cinfo, JERR_INPUT_EMPTY);
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
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));
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;