| 1 | /* zran.c -- example of zlib/gzip stream indexing and random access |
| 2 | * Copyright (C) 2005, 2012 Mark Adler |
| 3 | * For conditions of distribution and use, see copyright notice in zlib.h |
| 4 | Version 1.1 29 Sep 2012 Mark Adler */ |
| 5 | |
| 6 | /* Version History: |
| 7 | 1.0 29 May 2005 First version |
| 8 | 1.1 29 Sep 2012 Fix memory reallocation error |
| 9 | */ |
| 10 | |
| 11 | /* Illustrate the use of Z_BLOCK, inflatePrime(), and inflateSetDictionary() |
| 12 | for random access of a compressed file. A file containing a zlib or gzip |
| 13 | stream is provided on the command line. The compressed stream is decoded in |
| 14 | its entirety, and an index built with access points about every SPAN bytes |
| 15 | in the uncompressed output. The compressed file is left open, and can then |
| 16 | be read randomly, having to decompress on the average SPAN/2 uncompressed |
| 17 | bytes before getting to the desired block of data. |
| 18 | |
| 19 | An access point can be created at the start of any deflate block, by saving |
| 20 | the starting file offset and bit of that block, and the 32K bytes of |
| 21 | uncompressed data that precede that block. Also the uncompressed offset of |
| 22 | that block is saved to provide a referece for locating a desired starting |
| 23 | point in the uncompressed stream. build_index() works by decompressing the |
| 24 | input zlib or gzip stream a block at a time, and at the end of each block |
| 25 | deciding if enough uncompressed data has gone by to justify the creation of |
| 26 | a new access point. If so, that point is saved in a data structure that |
| 27 | grows as needed to accommodate the points. |
| 28 | |
| 29 | To use the index, an offset in the uncompressed data is provided, for which |
| 30 | the latest accees point at or preceding that offset is located in the index. |
| 31 | The input file is positioned to the specified location in the index, and if |
| 32 | necessary the first few bits of the compressed data is read from the file. |
| 33 | inflate is initialized with those bits and the 32K of uncompressed data, and |
| 34 | the decompression then proceeds until the desired offset in the file is |
| 35 | reached. Then the decompression continues to read the desired uncompressed |
| 36 | data from the file. |
| 37 | |
| 38 | Another approach would be to generate the index on demand. In that case, |
| 39 | requests for random access reads from the compressed data would try to use |
| 40 | the index, but if a read far enough past the end of the index is required, |
| 41 | then further index entries would be generated and added. |
| 42 | |
| 43 | There is some fair bit of overhead to starting inflation for the random |
| 44 | access, mainly copying the 32K byte dictionary. So if small pieces of the |
| 45 | file are being accessed, it would make sense to implement a cache to hold |
| 46 | some lookahead and avoid many calls to extract() for small lengths. |
| 47 | |
| 48 | Another way to build an index would be to use inflateCopy(). That would |
| 49 | not be constrained to have access points at block boundaries, but requires |
| 50 | more memory per access point, and also cannot be saved to file due to the |
| 51 | use of pointers in the state. The approach here allows for storage of the |
| 52 | index in a file. |
| 53 | */ |
| 54 | |
| 55 | #include <stdio.h> |
| 56 | #include <stdlib.h> |
| 57 | #include <string.h> |
| 58 | #include "zlib.h" |
| 59 | |
| 60 | #define local static |
| 61 | |
| 62 | #define SPAN 1048576L /* desired distance between access points */ |
| 63 | #define WINSIZE 32768U /* sliding window size */ |
| 64 | #define CHUNK 16384 /* file input buffer size */ |
| 65 | |
| 66 | /* access point entry */ |
| 67 | struct point { |
| 68 | off_t out; /* corresponding offset in uncompressed data */ |
| 69 | off_t in; /* offset in input file of first full byte */ |
| 70 | int bits; /* number of bits (1-7) from byte at in - 1, or 0 */ |
| 71 | unsigned char window[WINSIZE]; /* preceding 32K of uncompressed data */ |
| 72 | }; |
| 73 | |
| 74 | /* access point list */ |
| 75 | struct access { |
| 76 | int have; /* number of list entries filled in */ |
| 77 | int size; /* number of list entries allocated */ |
| 78 | struct point *list; /* allocated list */ |
| 79 | }; |
| 80 | |
| 81 | /* Deallocate an index built by build_index() */ |
| 82 | local void free_index(struct access *index) |
| 83 | { |
| 84 | if (index != NULL) { |
| 85 | free(index->list); |
| 86 | free(index); |
| 87 | } |
| 88 | } |
| 89 | |
| 90 | /* Add an entry to the access point list. If out of memory, deallocate the |
| 91 | existing list and return NULL. */ |
| 92 | local struct access *addpoint(struct access *index, int bits, |
| 93 | off_t in, off_t out, unsigned left, unsigned char *window) |
| 94 | { |
| 95 | struct point *next; |
| 96 | |
| 97 | /* if list is empty, create it (start with eight points) */ |
| 98 | if (index == NULL) { |
| 99 | index = malloc(sizeof(struct access)); |
| 100 | if (index == NULL) return NULL; |
| 101 | index->list = malloc(sizeof(struct point) << 3); |
| 102 | if (index->list == NULL) { |
| 103 | free(index); |
| 104 | return NULL; |
| 105 | } |
| 106 | index->size = 8; |
| 107 | index->have = 0; |
| 108 | } |
| 109 | |
| 110 | /* if list is full, make it bigger */ |
| 111 | else if (index->have == index->size) { |
| 112 | index->size <<= 1; |
| 113 | next = realloc(index->list, sizeof(struct point) * index->size); |
| 114 | if (next == NULL) { |
| 115 | free_index(index); |
| 116 | return NULL; |
| 117 | } |
| 118 | index->list = next; |
| 119 | } |
| 120 | |
| 121 | /* fill in entry and increment how many we have */ |
| 122 | next = index->list + index->have; |
| 123 | next->bits = bits; |
| 124 | next->in = in; |
| 125 | next->out = out; |
| 126 | if (left) |
| 127 | memcpy(next->window, window + WINSIZE - left, left); |
| 128 | if (left < WINSIZE) |
| 129 | memcpy(next->window + left, window, WINSIZE - left); |
| 130 | index->have++; |
| 131 | |
| 132 | /* return list, possibly reallocated */ |
| 133 | return index; |
| 134 | } |
| 135 | |
| 136 | /* Make one entire pass through the compressed stream and build an index, with |
| 137 | access points about every span bytes of uncompressed output -- span is |
| 138 | chosen to balance the speed of random access against the memory requirements |
| 139 | of the list, about 32K bytes per access point. Note that data after the end |
| 140 | of the first zlib or gzip stream in the file is ignored. build_index() |
| 141 | returns the number of access points on success (>= 1), Z_MEM_ERROR for out |
| 142 | of memory, Z_DATA_ERROR for an error in the input file, or Z_ERRNO for a |
| 143 | file read error. On success, *built points to the resulting index. */ |
| 144 | local int build_index(FILE *in, off_t span, struct access **built) |
| 145 | { |
| 146 | int ret; |
| 147 | off_t totin, totout; /* our own total counters to avoid 4GB limit */ |
| 148 | off_t last; /* totout value of last access point */ |
| 149 | struct access *index; /* access points being generated */ |
| 150 | z_stream strm; |
| 151 | unsigned char input[CHUNK]; |
| 152 | unsigned char window[WINSIZE]; |
| 153 | |
| 154 | /* initialize inflate */ |
| 155 | strm.zalloc = Z_NULL; |
| 156 | strm.zfree = Z_NULL; |
| 157 | strm.opaque = Z_NULL; |
| 158 | strm.avail_in = 0; |
| 159 | strm.next_in = Z_NULL; |
| 160 | ret = inflateInit2(&strm, 47); /* automatic zlib or gzip decoding */ |
| 161 | if (ret != Z_OK) |
| 162 | return ret; |
| 163 | |
| 164 | /* inflate the input, maintain a sliding window, and build an index -- this |
| 165 | also validates the integrity of the compressed data using the check |
| 166 | information at the end of the gzip or zlib stream */ |
| 167 | totin = totout = last = 0; |
| 168 | index = NULL; /* will be allocated by first addpoint() */ |
| 169 | strm.avail_out = 0; |
| 170 | do { |
| 171 | /* get some compressed data from input file */ |
| 172 | strm.avail_in = fread(input, 1, CHUNK, in); |
| 173 | if (ferror(in)) { |
| 174 | ret = Z_ERRNO; |
| 175 | goto build_index_error; |
| 176 | } |
| 177 | if (strm.avail_in == 0) { |
| 178 | ret = Z_DATA_ERROR; |
| 179 | goto build_index_error; |
| 180 | } |
| 181 | strm.next_in = input; |
| 182 | |
| 183 | /* process all of that, or until end of stream */ |
| 184 | do { |
| 185 | /* reset sliding window if necessary */ |
| 186 | if (strm.avail_out == 0) { |
| 187 | strm.avail_out = WINSIZE; |
| 188 | strm.next_out = window; |
| 189 | } |
| 190 | |
| 191 | /* inflate until out of input, output, or at end of block -- |
| 192 | update the total input and output counters */ |
| 193 | totin += strm.avail_in; |
| 194 | totout += strm.avail_out; |
| 195 | ret = inflate(&strm, Z_BLOCK); /* return at end of block */ |
| 196 | totin -= strm.avail_in; |
| 197 | totout -= strm.avail_out; |
| 198 | if (ret == Z_NEED_DICT) |
| 199 | ret = Z_DATA_ERROR; |
| 200 | if (ret == Z_MEM_ERROR || ret == Z_DATA_ERROR) |
| 201 | goto build_index_error; |
| 202 | if (ret == Z_STREAM_END) |
| 203 | break; |
| 204 | |
| 205 | /* if at end of block, consider adding an index entry (note that if |
| 206 | data_type indicates an end-of-block, then all of the |
| 207 | uncompressed data from that block has been delivered, and none |
| 208 | of the compressed data after that block has been consumed, |
| 209 | except for up to seven bits) -- the totout == 0 provides an |
| 210 | entry point after the zlib or gzip header, and assures that the |
| 211 | index always has at least one access point; we avoid creating an |
| 212 | access point after the last block by checking bit 6 of data_type |
| 213 | */ |
| 214 | if ((strm.data_type & 128) && !(strm.data_type & 64) && |
| 215 | (totout == 0 || totout - last > span)) { |
| 216 | index = addpoint(index, strm.data_type & 7, totin, |
| 217 | totout, strm.avail_out, window); |
| 218 | if (index == NULL) { |
| 219 | ret = Z_MEM_ERROR; |
| 220 | goto build_index_error; |
| 221 | } |
| 222 | last = totout; |
| 223 | } |
| 224 | } while (strm.avail_in != 0); |
| 225 | } while (ret != Z_STREAM_END); |
| 226 | |
| 227 | /* clean up and return index (release unused entries in list) */ |
| 228 | (void)inflateEnd(&strm); |
| 229 | index->list = realloc(index->list, sizeof(struct point) * index->have); |
| 230 | index->size = index->have; |
| 231 | *built = index; |
| 232 | return index->size; |
| 233 | |
| 234 | /* return error */ |
| 235 | build_index_error: |
| 236 | (void)inflateEnd(&strm); |
| 237 | if (index != NULL) |
| 238 | free_index(index); |
| 239 | return ret; |
| 240 | } |
| 241 | |
| 242 | /* Use the index to read len bytes from offset into buf, return bytes read or |
| 243 | negative for error (Z_DATA_ERROR or Z_MEM_ERROR). If data is requested past |
| 244 | the end of the uncompressed data, then extract() will return a value less |
| 245 | than len, indicating how much as actually read into buf. This function |
| 246 | should not return a data error unless the file was modified since the index |
| 247 | was generated. extract() may also return Z_ERRNO if there is an error on |
| 248 | reading or seeking the input file. */ |
| 249 | local int extract(FILE *in, struct access *index, off_t offset, |
| 250 | unsigned char *buf, int len) |
| 251 | { |
| 252 | int ret, skip; |
| 253 | z_stream strm; |
| 254 | struct point *here; |
| 255 | unsigned char input[CHUNK]; |
| 256 | unsigned char discard[WINSIZE]; |
| 257 | |
| 258 | /* proceed only if something reasonable to do */ |
| 259 | if (len < 0) |
| 260 | return 0; |
| 261 | |
| 262 | /* find where in stream to start */ |
| 263 | here = index->list; |
| 264 | ret = index->have; |
| 265 | while (--ret && here[1].out <= offset) |
| 266 | here++; |
| 267 | |
| 268 | /* initialize file and inflate state to start there */ |
| 269 | strm.zalloc = Z_NULL; |
| 270 | strm.zfree = Z_NULL; |
| 271 | strm.opaque = Z_NULL; |
| 272 | strm.avail_in = 0; |
| 273 | strm.next_in = Z_NULL; |
| 274 | ret = inflateInit2(&strm, -15); /* raw inflate */ |
| 275 | if (ret != Z_OK) |
| 276 | return ret; |
| 277 | ret = fseeko(in, here->in - (here->bits ? 1 : 0), SEEK_SET); |
| 278 | if (ret == -1) |
| 279 | goto extract_ret; |
| 280 | if (here->bits) { |
| 281 | ret = getc(in); |
| 282 | if (ret == -1) { |
| 283 | ret = ferror(in) ? Z_ERRNO : Z_DATA_ERROR; |
| 284 | goto extract_ret; |
| 285 | } |
| 286 | (void)inflatePrime(&strm, here->bits, ret >> (8 - here->bits)); |
| 287 | } |
| 288 | (void)inflateSetDictionary(&strm, here->window, WINSIZE); |
| 289 | |
| 290 | /* skip uncompressed bytes until offset reached, then satisfy request */ |
| 291 | offset -= here->out; |
| 292 | strm.avail_in = 0; |
| 293 | skip = 1; /* while skipping to offset */ |
| 294 | do { |
| 295 | /* define where to put uncompressed data, and how much */ |
| 296 | if (offset == 0 && skip) { /* at offset now */ |
| 297 | strm.avail_out = len; |
| 298 | strm.next_out = buf; |
| 299 | skip = 0; /* only do this once */ |
| 300 | } |
| 301 | if (offset > WINSIZE) { /* skip WINSIZE bytes */ |
| 302 | strm.avail_out = WINSIZE; |
| 303 | strm.next_out = discard; |
| 304 | offset -= WINSIZE; |
| 305 | } |
| 306 | else if (offset != 0) { /* last skip */ |
| 307 | strm.avail_out = (unsigned)offset; |
| 308 | strm.next_out = discard; |
| 309 | offset = 0; |
| 310 | } |
| 311 | |
| 312 | /* uncompress until avail_out filled, or end of stream */ |
| 313 | do { |
| 314 | if (strm.avail_in == 0) { |
| 315 | strm.avail_in = fread(input, 1, CHUNK, in); |
| 316 | if (ferror(in)) { |
| 317 | ret = Z_ERRNO; |
| 318 | goto extract_ret; |
| 319 | } |
| 320 | if (strm.avail_in == 0) { |
| 321 | ret = Z_DATA_ERROR; |
| 322 | goto extract_ret; |
| 323 | } |
| 324 | strm.next_in = input; |
| 325 | } |
| 326 | ret = inflate(&strm, Z_NO_FLUSH); /* normal inflate */ |
| 327 | if (ret == Z_NEED_DICT) |
| 328 | ret = Z_DATA_ERROR; |
| 329 | if (ret == Z_MEM_ERROR || ret == Z_DATA_ERROR) |
| 330 | goto extract_ret; |
| 331 | if (ret == Z_STREAM_END) |
| 332 | break; |
| 333 | } while (strm.avail_out != 0); |
| 334 | |
| 335 | /* if reach end of stream, then don't keep trying to get more */ |
| 336 | if (ret == Z_STREAM_END) |
| 337 | break; |
| 338 | |
| 339 | /* do until offset reached and requested data read, or stream ends */ |
| 340 | } while (skip); |
| 341 | |
| 342 | /* compute number of uncompressed bytes read after offset */ |
| 343 | ret = skip ? 0 : len - strm.avail_out; |
| 344 | |
| 345 | /* clean up and return bytes read or error */ |
| 346 | extract_ret: |
| 347 | (void)inflateEnd(&strm); |
| 348 | return ret; |
| 349 | } |
| 350 | |
| 351 | /* Demonstrate the use of build_index() and extract() by processing the file |
| 352 | provided on the command line, and the extracting 16K from about 2/3rds of |
| 353 | the way through the uncompressed output, and writing that to stdout. */ |
| 354 | int main(int argc, char **argv) |
| 355 | { |
| 356 | int len; |
| 357 | off_t offset; |
| 358 | FILE *in; |
| 359 | struct access *index = NULL; |
| 360 | unsigned char buf[CHUNK]; |
| 361 | |
| 362 | /* open input file */ |
| 363 | if (argc != 2) { |
| 364 | fprintf(stderr, "usage: zran file.gz\n"); |
| 365 | return 1; |
| 366 | } |
| 367 | in = fopen(argv[1], "rb"); |
| 368 | if (in == NULL) { |
| 369 | fprintf(stderr, "zran: could not open %s for reading\n", argv[1]); |
| 370 | return 1; |
| 371 | } |
| 372 | |
| 373 | /* build index */ |
| 374 | len = build_index(in, SPAN, &index); |
| 375 | if (len < 0) { |
| 376 | fclose(in); |
| 377 | switch (len) { |
| 378 | case Z_MEM_ERROR: |
| 379 | fprintf(stderr, "zran: out of memory\n"); |
| 380 | break; |
| 381 | case Z_DATA_ERROR: |
| 382 | fprintf(stderr, "zran: compressed data error in %s\n", argv[1]); |
| 383 | break; |
| 384 | case Z_ERRNO: |
| 385 | fprintf(stderr, "zran: read error on %s\n", argv[1]); |
| 386 | break; |
| 387 | default: |
| 388 | fprintf(stderr, "zran: error %d while building index\n", len); |
| 389 | } |
| 390 | return 1; |
| 391 | } |
| 392 | fprintf(stderr, "zran: built index with %d access points\n", len); |
| 393 | |
| 394 | /* use index by reading some bytes from an arbitrary offset */ |
| 395 | offset = (index->list[index->have - 1].out << 1) / 3; |
| 396 | len = extract(in, index, offset, buf, CHUNK); |
| 397 | if (len < 0) |
| 398 | fprintf(stderr, "zran: extraction failed: %s error\n", |
| 399 | len == Z_MEM_ERROR ? "out of memory" : "input corrupted"); |
| 400 | else { |
| 401 | fwrite(buf, 1, len, stdout); |
| 402 | fprintf(stderr, "zran: extracted %d bytes at %llu\n", len, offset); |
| 403 | } |
| 404 | |
| 405 | /* clean up and exit */ |
| 406 | free_index(index); |
| 407 | fclose(in); |
| 408 | return 0; |
| 409 | } |