Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 1 | /* |
| 2 | * jdatasrc.c |
| 3 | * |
Thomas G. Lane | 489583f | 1996-02-07 00:00:00 +0000 | [diff] [blame^] | 4 | * Copyright (C) 1994-1996, Thomas G. Lane. |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 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 | |
Thomas G. Lane | 489583f | 1996-02-07 00:00:00 +0000 | [diff] [blame^] | 43 | METHODDEF(void) |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 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 | |
Thomas G. Lane | 489583f | 1996-02-07 00:00:00 +0000 | [diff] [blame^] | 89 | METHODDEF(boolean) |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 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 | |
Thomas G. Lane | 489583f | 1996-02-07 00:00:00 +0000 | [diff] [blame^] | 127 | METHODDEF(void) |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 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); |
Thomas G. Lane | 9ba2f5e | 1994-12-07 00:00:00 +0000 | [diff] [blame] | 140 | /* note we assume that fill_input_buffer will never return FALSE, |
| 141 | * so suspension need not be handled. |
| 142 | */ |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 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 | |
Thomas G. Lane | 489583f | 1996-02-07 00:00:00 +0000 | [diff] [blame^] | 168 | METHODDEF(void) |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 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 | |
Thomas G. Lane | 489583f | 1996-02-07 00:00:00 +0000 | [diff] [blame^] | 181 | GLOBAL(void) |
Thomas G. Lane | 36a4ccc | 1994-09-24 00:00:00 +0000 | [diff] [blame] | 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 | } |