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