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 } 213
