3rdparty/libjpeg/jdatasrc.c

/*
 * jdatasrc.c
 *
 * Copyright (C) 1994-1996, Thomas G. Lane.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file contains decompression data source routines for the case of
 * reading JPEG data from a file (or any stdio stream).  While these routines
 * are sufficient for most applications, some will want to use a different
 * source manager.
 * IMPORTANT: we assume that fread() will correctly transcribe an array of
 * JOCTETs from 8-bit-wide elements on external storage.  If char is wider
 * than 8 bits on your machine, you may need to do some tweaking.
 */

/* this is not a core library module, so it doesn't define JPEG_INTERNALS */
#include "jinclude.h"
#include "jpeglib.h"
#include "jerror.h"


/* Expanded data source object for stdio input */

typedef struct {
  struct jpeg_source_mgr pub;   /* public fields */

  FILE * infile;                /* source stream */
  JOCTET * buffer;              /* start of buffer */
  boolean start_of_file;        /* have we gotten any data yet? */
} my_source_mgr;

typedef my_source_mgr * my_src_ptr;

#define INPUT_BUF_SIZE  4096    /* choose an efficiently fread'able size */


/*
 * Initialize source --- called by jpeg_read_header
 * before any data is actually read.
 */

METHODDEF(void)
init_source (j_decompress_ptr cinfo)
{
  my_src_ptr src = (my_src_ptr) cinfo->src;

  /* We reset the empty-input-file flag for each image,
   * but we don't clear the input buffer.
   * This is correct behavior for reading a series of images from one source.
   */
  src->start_of_file = TRUE;
}


/*
 * Fill the input buffer --- called whenever buffer is emptied.
 *
 * In typical applications, this should read fresh data into the buffer
 * (ignoring the current state of next_input_byte & bytes_in_buffer),
 * reset the pointer & count to the start of the buffer, and return TRUE
 * indicating that the buffer has been reloaded.  It is not necessary to
 * fill the buffer entirely, only to obtain at least one more byte.
 *
 * There is no such thing as an EOF return.  If the end of the file has been
 * reached, the routine has a choice of ERREXIT() or inserting fake data into
 * the buffer.  In most cases, generating a warning message and inserting a
 * fake EOI marker is the best course of action --- this will allow the
 * decompressor to output however much of the image is there.  However,
 * the resulting error message is misleading if the real problem is an empty
 * input file, so we handle that case specially.
 *
 * In applications that need to be able to suspend compression due to input
 * not being available yet, a FALSE return indicates that no more data can be
 * obtained right now, but more may be forthcoming later.  In this situation,
 * the decompressor will return to its caller (with an indication of the
 * number of scanlines it has read, if any).  The application should resume
 * decompression after it has loaded more data into the input buffer.  Note
 * that there are substantial restrictions on the use of suspension --- see
 * the documentation.
 *
 * When suspending, the decompressor will back up to a convenient restart point
 * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
 * indicate where the restart point will be if the current call returns FALSE.
 * Data beyond this point must be rescanned after resumption, so move it to
 * the front of the buffer rather than discarding it.
 */

METHODDEF(boolean)
fill_input_buffer (j_decompress_ptr cinfo)
{
  my_src_ptr src = (my_src_ptr) cinfo->src;
  size_t nbytes;

  nbytes = JFREAD(src->infile, src->buffer, INPUT_BUF_SIZE);

  if (nbytes <= 0) {
    if (src->start_of_file)     /* Treat empty input file as fatal error */
      ERREXIT(cinfo, JERR_INPUT_EMPTY);
    WARNMS(cinfo, JWRN_JPEG_EOF);
    /* Insert a fake EOI marker */
    src->buffer[0] = (JOCTET) 0xFF;
    src->buffer[1] = (JOCTET) JPEG_EOI;
    nbytes = 2;
  }

  src->pub.next_input_byte = src->buffer;
  src->pub.bytes_in_buffer = nbytes;
  src->start_of_file = FALSE;

  return TRUE;
}


/*
 * Skip data --- used to skip over a potentially large amount of
 * uninteresting data (such as an APPn marker).
 *
 * Writers of suspendable-input applications must note that skip_input_data
 * is not granted the right to give a suspension return.  If the skip extends
 * beyond the data currently in the buffer, the buffer can be marked empty so
 * that the next read will cause a fill_input_buffer call that can suspend.
 * Arranging for additional bytes to be discarded before reloading the input
 * buffer is the application writer's problem.
 */

METHODDEF(void)
skip_input_data (j_decompress_ptr cinfo, long num_bytes)
{
  my_src_ptr src = (my_src_ptr) cinfo->src;

  /* Just a dumb implementation for now.  Could use fseek() except
   * it doesn't work on pipes.  Not clear that being smart is worth
   * any trouble anyway --- large skips are infrequent.
   */
  if (num_bytes > 0) {
    while (num_bytes > (long) src->pub.bytes_in_buffer) {
      num_bytes -= (long) src->pub.bytes_in_buffer;
      (void) fill_input_buffer(cinfo);
      /* note we assume that fill_input_buffer will never return FALSE,
       * so suspension need not be handled.
       */
    }
    src->pub.next_input_byte += (size_t) num_bytes;
    src->pub.bytes_in_buffer -= (size_t) num_bytes;
  }
}


/*
 * An additional method that can be provided by data source modules is the
 * resync_to_restart method for error recovery in the presence of RST markers.
 * For the moment, this source module just uses the default resync method
 * provided by the JPEG library.  That method assumes that no backtracking
 * is possible.
 */


/*
 * Terminate source --- called by jpeg_finish_decompress
 * after all data has been read.  Often a no-op.
 *
 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
 * application must deal with any cleanup that should happen even
 * for error exit.
 */

METHODDEF(void)
term_source (j_decompress_ptr cinfo)
{
  /* no work necessary here */
}


/*
 * Prepare for input from a stdio stream.
 * The caller must have already opened the stream, and is responsible
 * for closing it after finishing decompression.
 */

GLOBAL(void)
jpeg_stdio_src (j_decompress_ptr cinfo, FILE * infile)
{
  my_src_ptr src;

  /* The source object and input buffer are made permanent so that a series
   * of JPEG images can be read from the same file by calling jpeg_stdio_src
   * only before the first one.  (If we discarded the buffer at the end of
   * one image, we'd likely lose the start of the next one.)
   * This makes it unsafe to use this manager and a different source
   * manager serially with the same JPEG object.  Caveat programmer.
   */
  if (cinfo->src == NULL) {     /* first time for this JPEG object? */
    cinfo->src = (struct jpeg_source_mgr *)
      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
                                  SIZEOF(my_source_mgr));
    src = (my_src_ptr) cinfo->src;
    src->buffer = (JOCTET *)
      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
                                  INPUT_BUF_SIZE * SIZEOF(JOCTET));
  }

  src = (my_src_ptr) cinfo->src;
  src->pub.init_source = init_source;
  src->pub.fill_input_buffer = fill_input_buffer;
  src->pub.skip_input_data = skip_input_data;
  src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
  src->pub.term_source = term_source;
  src->infile = infile;
  src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
  src->pub.next_input_byte = NULL; /* until buffer loaded */
}
1	/*
2	* jdatasrc.c
3	*
4	* Copyright (C) 1994-1996, Thomas G. Lane.
5	* This file is part of the Independent JPEG Group's software.
6	* For conditions of distribution and use, see the accompanying README file.
7	*
8	* This file contains decompression data source routines for the case of
9	* reading JPEG data from a file (or any stdio stream). While these routines
10	* are sufficient for most applications, some will want to use a different
11	* source manager.
12	* IMPORTANT: we assume that fread() will correctly transcribe an array of
13	* JOCTETs from 8-bit-wide elements on external storage. If char is wider
14	* than 8 bits on your machine, you may need to do some tweaking.
15	*/
16
17	/* this is not a core library module, so it doesn't define JPEG_INTERNALS */
18	#include "jinclude.h"
19	#include "jpeglib.h"
20	#include "jerror.h"
21
22
23	/* Expanded data source object for stdio input */
24
25	typedef struct {
26	struct jpeg_source_mgr pub; /* public fields */
27
28	FILE * infile; /* source stream */
29	JOCTET * buffer; /* start of buffer */
30	boolean start_of_file; /* have we gotten any data yet? */
31	} my_source_mgr;
32
33	typedef my_source_mgr * my_src_ptr;
34
35	#define INPUT_BUF_SIZE 4096 /* choose an efficiently fread'able size */
36
37
38	/*
39	* Initialize source --- called by jpeg_read_header
40	* before any data is actually read.
41	*/
42
43	METHODDEF(void)
44	init_source (j_decompress_ptr cinfo)
45	{
46	my_src_ptr src = (my_src_ptr) cinfo->src;
47
48	/* We reset the empty-input-file flag for each image,
49	* but we don't clear the input buffer.
50	* This is correct behavior for reading a series of images from one source.
51	*/
52	src->start_of_file = TRUE;
53	}
54
55
56	/*
57	* Fill the input buffer --- called whenever buffer is emptied.
58	*
59	* In typical applications, this should read fresh data into the buffer
60	* (ignoring the current state of next_input_byte & bytes_in_buffer),
61	* reset the pointer & count to the start of the buffer, and return TRUE
62	* indicating that the buffer has been reloaded. It is not necessary to
63	* fill the buffer entirely, only to obtain at least one more byte.
64	*
65	* There is no such thing as an EOF return. If the end of the file has been
66	* reached, the routine has a choice of ERREXIT() or inserting fake data into
67	* the buffer. In most cases, generating a warning message and inserting a
68	* fake EOI marker is the best course of action --- this will allow the
69	* decompressor to output however much of the image is there. However,
70	* the resulting error message is misleading if the real problem is an empty
71	* input file, so we handle that case specially.
72	*
73	* In applications that need to be able to suspend compression due to input
74	* not being available yet, a FALSE return indicates that no more data can be
75	* obtained right now, but more may be forthcoming later. In this situation,
76	* the decompressor will return to its caller (with an indication of the
77	* number of scanlines it has read, if any). The application should resume
78	* decompression after it has loaded more data into the input buffer. Note
79	* that there are substantial restrictions on the use of suspension --- see
80	* the documentation.
81	*
82	* When suspending, the decompressor will back up to a convenient restart point
83	* (typically the start of the current MCU). next_input_byte & bytes_in_buffer
84	* indicate where the restart point will be if the current call returns FALSE.
85	* Data beyond this point must be rescanned after resumption, so move it to
86	* the front of the buffer rather than discarding it.
87	*/
88
89	METHODDEF(boolean)
90	fill_input_buffer (j_decompress_ptr cinfo)
91	{
92	my_src_ptr src = (my_src_ptr) cinfo->src;
93	size_t nbytes;
94
95	nbytes = JFREAD(src->infile, src->buffer, INPUT_BUF_SIZE);
96
97	if (nbytes <= 0) {
98	if (src->start_of_file) /* Treat empty input file as fatal error */
99	ERREXIT(cinfo, JERR_INPUT_EMPTY);
100	WARNMS(cinfo, JWRN_JPEG_EOF);
101	/* Insert a fake EOI marker */
102	src->buffer[0] = (JOCTET) 0xFF;
103	src->buffer[1] = (JOCTET) JPEG_EOI;
104	nbytes = 2;
105	}
106
107	src->pub.next_input_byte = src->buffer;
108	src->pub.bytes_in_buffer = nbytes;
109	src->start_of_file = FALSE;
110
111	return TRUE;
112	}
113
114
115	/*
116	* Skip data --- used to skip over a potentially large amount of
117	* uninteresting data (such as an APPn marker).
118	*
119	* Writers of suspendable-input applications must note that skip_input_data
120	* is not granted the right to give a suspension return. If the skip extends
121	* beyond the data currently in the buffer, the buffer can be marked empty so
122	* that the next read will cause a fill_input_buffer call that can suspend.
123	* Arranging for additional bytes to be discarded before reloading the input
124	* buffer is the application writer's problem.
125	*/
126
127	METHODDEF(void)
128	skip_input_data (j_decompress_ptr cinfo, long num_bytes)
129	{
130	my_src_ptr src = (my_src_ptr) cinfo->src;
131
132	/* Just a dumb implementation for now. Could use fseek() except
133	* it doesn't work on pipes. Not clear that being smart is worth
134	* any trouble anyway --- large skips are infrequent.
135	*/
136	if (num_bytes > 0) {
137	while (num_bytes > (long) src->pub.bytes_in_buffer) {
138	num_bytes -= (long) src->pub.bytes_in_buffer;
139	(void) fill_input_buffer(cinfo);
140	/* note we assume that fill_input_buffer will never return FALSE,
141	* so suspension need not be handled.
142	*/
143	}
144	src->pub.next_input_byte += (size_t) num_bytes;
145	src->pub.bytes_in_buffer -= (size_t) num_bytes;
146	}
147	}
148
149
150	/*
151	* An additional method that can be provided by data source modules is the
152	* resync_to_restart method for error recovery in the presence of RST markers.
153	* For the moment, this source module just uses the default resync method
154	* provided by the JPEG library. That method assumes that no backtracking
155	* is possible.
156	*/
157
158
159	/*
160	* Terminate source --- called by jpeg_finish_decompress
161	* after all data has been read. Often a no-op.
162	*
163	* NB: not called by jpeg_abort or jpeg_destroy; surrounding
164	* application must deal with any cleanup that should happen even
165	* for error exit.
166	*/
167
168	METHODDEF(void)
169	term_source (j_decompress_ptr cinfo)
170	{
171	/* no work necessary here */
172	}
173
174
175	/*
176	* Prepare for input from a stdio stream.
177	* The caller must have already opened the stream, and is responsible
178	* for closing it after finishing decompression.
179	*/
180
181	GLOBAL(void)
182	jpeg_stdio_src (j_decompress_ptr cinfo, FILE * infile)
183	{
184	my_src_ptr src;
185
186	/* The source object and input buffer are made permanent so that a series
187	* of JPEG images can be read from the same file by calling jpeg_stdio_src
188	* only before the first one. (If we discarded the buffer at the end of
189	* one image, we'd likely lose the start of the next one.)
190	* This makes it unsafe to use this manager and a different source
191	* manager serially with the same JPEG object. Caveat programmer.
192	*/
193	if (cinfo->src == NULL) { /* first time for this JPEG object? */
194	cinfo->src = (struct jpeg_source_mgr *)
195	(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
196	SIZEOF(my_source_mgr));
197	src = (my_src_ptr) cinfo->src;
198	src->buffer = (JOCTET *)
199	(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
200	INPUT_BUF_SIZE * SIZEOF(JOCTET));
201	}
202
203	src = (my_src_ptr) cinfo->src;
204	src->pub.init_source = init_source;
205	src->pub.fill_input_buffer = fill_input_buffer;
206	src->pub.skip_input_data = skip_input_data;
207	src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
208	src->pub.term_source = term_source;
209	src->infile = infile;
210	src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
211	src->pub.next_input_byte = NULL; /* until buffer loaded */
212	}