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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, 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 
27 /*
28  * Initialize source --- called by jpeg_read_header
29  * before any data is actually read.
30  */
31 
32 METHODDEF(void)
init_mem_source(j_decompress_ptr cinfo)33 init_mem_source(j_decompress_ptr cinfo)
34 {
35   /* no work necessary here */
36 }
37 
38 
39 /*
40  * Fill the input buffer --- called whenever buffer is emptied.
41  *
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.
47  *
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.
55  *
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
63  * the documentation.
64  *
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.
70  */
71 
72 METHODDEF(boolean)
fill_mem_input_buffer(j_decompress_ptr cinfo)73 fill_mem_input_buffer(j_decompress_ptr cinfo)
74 {
75   static const JOCTET mybuffer[4] = {
76     (JOCTET)0xFF, (JOCTET)JPEG_EOI, 0, 0
77   };
78 
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.
82    */
83   WARNMS(cinfo, JWRN_JPEG_EOF);
84 
85   /* Insert a fake EOI marker */
86 
87   cinfo->src->next_input_byte = mybuffer;
88   cinfo->src->bytes_in_buffer = 2;
89 
90   return TRUE;
91 }
92 
93 
94 /*
95  * Skip data --- used to skip over a potentially large amount of
96  * uninteresting data (such as an APPn marker).
97  *
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.
104  */
105 
106 METHODDEF(void)
skip_input_data(j_decompress_ptr cinfo,long num_bytes)107 skip_input_data(j_decompress_ptr cinfo, long num_bytes)
108 {
109   struct jpeg_source_mgr *src = cinfo->src;
110 
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.
114    */
115   if (num_bytes > 0) {
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.
121        */
122     }
123     src->next_input_byte += (size_t)num_bytes;
124     src->bytes_in_buffer -= (size_t)num_bytes;
125   }
126 }
127 
128 
129 /*
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
134  * is possible.
135  */
136 
137 
138 /*
139  * Terminate source --- called by jpeg_finish_decompress
140  * after all data has been read.  Often a no-op.
141  *
142  * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
143  * application must deal with any cleanup that should happen even
144  * for error exit.
145  */
146 
147 METHODDEF(void)
term_source(j_decompress_ptr cinfo)148 term_source(j_decompress_ptr cinfo)
149 {
150   /* no work necessary here */
151 }
152 
153 
154 /*
155  * Prepare for input from a supplied memory buffer.
156  * The buffer must contain the whole JPEG data.
157  */
158 
159 GLOBAL(void)
jpeg_mem_src_tj(j_decompress_ptr cinfo,const unsigned char * inbuffer,unsigned long insize)160 jpeg_mem_src_tj(j_decompress_ptr cinfo, const unsigned char *inbuffer,
161                 unsigned long insize)
162 {
163   struct jpeg_source_mgr *src;
164 
165   if (inbuffer == NULL || insize == 0)  /* Treat empty input as fatal error */
166     ERREXIT(cinfo, JERR_INPUT_EMPTY);
167 
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
170    * the first one.
171    */
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
178      * by this function.
179      */
180     ERREXIT(cinfo, JERR_BUFFER_SIZE);
181   }
182 
183   src = cinfo->src;
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;
191 }
192