| 1 | /* zran.c -- example of zlib/gzip stream indexing and random access |
| 2 | * Copyright (C) 2005, 2012, 2018 Mark Adler |
| 3 | * For conditions of distribution and use, see copyright notice in zlib.h |
| 4 | * Version 1.2 14 Oct 2018 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 | 1.2 14 Oct 2018 Handle gzip streams with multiple members |
| 10 | Add a header file to facilitate usage in applications |
| 11 | */ |
| 12 | |
| 13 | /* Illustrate the use of Z_BLOCK, inflatePrime(), and inflateSetDictionary() |
| 14 | for random access of a compressed file. A file containing a zlib or gzip |
| 15 | stream is provided on the command line. The compressed stream is decoded in |
| 16 | its entirety, and an index built with access points about every SPAN bytes |
| 17 | in the uncompressed output. The compressed file is left open, and can then |
| 18 | be read randomly, having to decompress on the average SPAN/2 uncompressed |
| 19 | bytes before getting to the desired block of data. |
| 20 | |
| 21 | An access point can be created at the start of any deflate block, by saving |
| 22 | the starting file offset and bit of that block, and the 32K bytes of |
| 23 | uncompressed data that precede that block. Also the uncompressed offset of |
| 24 | that block is saved to provide a reference for locating a desired starting |
| 25 | point in the uncompressed stream. deflate_index_build() works by |
| 26 | decompressing the input zlib or gzip stream a block at a time, and at the |
| 27 | end of each block deciding if enough uncompressed data has gone by to |
| 28 | justify the creation of a new access point. If so, that point is saved in a |
| 29 | data structure that grows as needed to accommodate the points. |
| 30 | |
| 31 | To use the index, an offset in the uncompressed data is provided, for which |
| 32 | the latest access point at or preceding that offset is located in the index. |
| 33 | The input file is positioned to the specified location in the index, and if |
| 34 | necessary the first few bits of the compressed data is read from the file. |
| 35 | inflate is initialized with those bits and the 32K of uncompressed data, and |
| 36 | the decompression then proceeds until the desired offset in the file is |
| 37 | reached. Then the decompression continues to read the desired uncompressed |
| 38 | data from the file. |
| 39 | |
| 40 | Another approach would be to generate the index on demand. In that case, |
| 41 | requests for random access reads from the compressed data would try to use |
| 42 | the index, but if a read far enough past the end of the index is required, |
| 43 | then further index entries would be generated and added. |
| 44 | |
| 45 | There is some fair bit of overhead to starting inflation for the random |
| 46 | access, mainly copying the 32K byte dictionary. So if small pieces of the |
| 47 | file are being accessed, it would make sense to implement a cache to hold |
| 48 | some lookahead and avoid many calls to deflate_index_extract() for small |
| 49 | lengths. |
| 50 | |
| 51 | Another way to build an index would be to use inflateCopy(). That would |
| 52 | not be constrained to have access points at block boundaries, but requires |
| 53 | more memory per access point, and also cannot be saved to file due to the |
| 54 | use of pointers in the state. The approach here allows for storage of the |
| 55 | index in a file. |
| 56 | */ |
| 57 | |
| 58 | #include <stdio.h> |
| 59 | #include <stdlib.h> |
| 60 | #include <string.h> |
| 61 | #include "zlib.h" |
| 62 | #include "zran.h" |
| 63 | |
| 64 | #define WINSIZE 32768U /* sliding window size */ |
| 65 | #define CHUNK 16384 /* file input buffer size */ |
| 66 | |
| 67 | /* Access point entry. */ |
| 68 | struct point { |
| 69 | off_t out; /* corresponding offset in uncompressed data */ |
| 70 | off_t in; /* offset in input file of first full byte */ |
| 71 | int bits; /* number of bits (1-7) from byte at in-1, or 0 */ |
| 72 | unsigned char window[WINSIZE]; /* preceding 32K of uncompressed data */ |
| 73 | }; |
| 74 | |
| 75 | /* See comments in zran.h. */ |
| 76 | void deflate_index_free(struct deflate_index *index) |
| 77 | { |
| 78 | if (index != NULL) { |
| 79 | free(index->list); |
| 80 | free(index); |
| 81 | } |
| 82 | } |
| 83 | |
| 84 | /* Add an entry to the access point list. If out of memory, deallocate the |
| 85 | existing list and return NULL. index->gzip is the allocated size of the |
| 86 | index in point entries, until it is time for deflate_index_build() to |
| 87 | return, at which point gzip is set to indicate a gzip file or not. |
| 88 | */ |
| 89 | static struct deflate_index *addpoint(struct deflate_index *index, int bits, |
| 90 | off_t in, off_t out, unsigned left, |
| 91 | unsigned char *window) |
| 92 | { |
| 93 | struct point *next; |
| 94 | |
| 95 | /* if list is empty, create it (start with eight points) */ |
| 96 | if (index == NULL) { |
| 97 | index = malloc(sizeof(struct deflate_index)); |
| 98 | if (index == NULL) return NULL; |
| 99 | index->list = malloc(sizeof(struct point) << 3); |
| 100 | if (index->list == NULL) { |
| 101 | free(index); |
| 102 | return NULL; |
| 103 | } |
| 104 | index->gzip = 8; |
| 105 | index->have = 0; |
| 106 | } |
| 107 | |
| 108 | /* if list is full, make it bigger */ |
| 109 | else if (index->have == index->gzip) { |
| 110 | index->gzip <<= 1; |
| 111 | next = realloc(index->list, sizeof(struct point) * index->gzip); |
| 112 | if (next == NULL) { |
| 113 | deflate_index_free(index); |
| 114 | return NULL; |
| 115 | } |
| 116 | index->list = next; |
| 117 | } |
| 118 | |
| 119 | /* fill in entry and increment how many we have */ |
| 120 | next = (struct point *)(index->list) + index->have; |
| 121 | next->bits = bits; |
| 122 | next->in = in; |
| 123 | next->out = out; |
| 124 | if (left) |
| 125 | memcpy(next->window, window + WINSIZE - left, left); |
| 126 | if (left < WINSIZE) |
| 127 | memcpy(next->window + left, window, WINSIZE - left); |
| 128 | index->have++; |
| 129 | |
| 130 | /* return list, possibly reallocated */ |
| 131 | return index; |
| 132 | } |
| 133 | |
| 134 | /* See comments in zran.h. */ |
| 135 | int deflate_index_build(FILE *in, off_t span, struct deflate_index **built) |
| 136 | { |
| 137 | int ret; |
| 138 | int gzip = 0; /* true if reading a gzip file */ |
| 139 | off_t totin, totout; /* our own total counters to avoid 4GB limit */ |
| 140 | off_t last; /* totout value of last access point */ |
| 141 | struct deflate_index *index; /* access points being generated */ |
| 142 | z_stream strm; |
| 143 | unsigned char input[CHUNK]; |
| 144 | unsigned char window[WINSIZE]; |
| 145 | |
| 146 | /* initialize inflate */ |
| 147 | strm.zalloc = Z_NULL; |
| 148 | strm.zfree = Z_NULL; |
| 149 | strm.opaque = Z_NULL; |
| 150 | strm.avail_in = 0; |
| 151 | strm.next_in = Z_NULL; |
| 152 | ret = inflateInit2(&strm, 47); /* automatic zlib or gzip decoding */ |
| 153 | if (ret != Z_OK) |
| 154 | return ret; |
| 155 | |
| 156 | /* inflate the input, maintain a sliding window, and build an index -- this |
| 157 | also validates the integrity of the compressed data using the check |
| 158 | information in the gzip or zlib stream */ |
| 159 | totin = totout = last = 0; |
| 160 | index = NULL; /* will be allocated by first addpoint() */ |
| 161 | strm.avail_out = 0; |
| 162 | do { |
| 163 | /* get some compressed data from input file */ |
| 164 | strm.avail_in = fread(input, 1, CHUNK, in); |
| 165 | if (ferror(in)) { |
| 166 | ret = Z_ERRNO; |
| 167 | goto deflate_index_build_error; |
| 168 | } |
| 169 | if (strm.avail_in == 0) { |
| 170 | ret = Z_DATA_ERROR; |
| 171 | goto deflate_index_build_error; |
| 172 | } |
| 173 | strm.next_in = input; |
| 174 | |
| 175 | /* check for a gzip stream */ |
| 176 | if (totin == 0 && strm.avail_in >= 3 && |
| 177 | input[0] == 31 && input[1] == 139 && input[2] == 8) |
| 178 | gzip = 1; |
| 179 | |
| 180 | /* process all of that, or until end of stream */ |
| 181 | do { |
| 182 | /* reset sliding window if necessary */ |
| 183 | if (strm.avail_out == 0) { |
| 184 | strm.avail_out = WINSIZE; |
| 185 | strm.next_out = window; |
| 186 | } |
| 187 | |
| 188 | /* inflate until out of input, output, or at end of block -- |
| 189 | update the total input and output counters */ |
| 190 | totin += strm.avail_in; |
| 191 | totout += strm.avail_out; |
| 192 | ret = inflate(&strm, Z_BLOCK); /* return at end of block */ |
| 193 | totin -= strm.avail_in; |
| 194 | totout -= strm.avail_out; |
| 195 | if (ret == Z_NEED_DICT) |
| 196 | ret = Z_DATA_ERROR; |
| 197 | if (ret == Z_MEM_ERROR || ret == Z_DATA_ERROR) |
| 198 | goto deflate_index_build_error; |
| 199 | if (ret == Z_STREAM_END) { |
| 200 | if (gzip && |
| 201 | (strm.avail_in || ungetc(getc(in), in) != EOF)) { |
| 202 | ret = inflateReset(&strm); |
| 203 | if (ret != Z_OK) |
| 204 | goto deflate_index_build_error; |
| 205 | continue; |
| 206 | } |
| 207 | break; |
| 208 | } |
| 209 | |
| 210 | /* if at end of block, consider adding an index entry (note that if |
| 211 | data_type indicates an end-of-block, then all of the |
| 212 | uncompressed data from that block has been delivered, and none |
| 213 | of the compressed data after that block has been consumed, |
| 214 | except for up to seven bits) -- the totout == 0 provides an |
| 215 | entry point after the zlib or gzip header, and assures that the |
| 216 | index always has at least one access point; we avoid creating an |
| 217 | access point after the last block by checking bit 6 of data_type |
| 218 | */ |
| 219 | if ((strm.data_type & 128) && !(strm.data_type & 64) && |
| 220 | (totout == 0 || totout - last > span)) { |
| 221 | index = addpoint(index, strm.data_type & 7, totin, |
| 222 | totout, strm.avail_out, window); |
| 223 | if (index == NULL) { |
| 224 | ret = Z_MEM_ERROR; |
| 225 | goto deflate_index_build_error; |
| 226 | } |
| 227 | last = totout; |
| 228 | } |
| 229 | } while (strm.avail_in != 0); |
| 230 | } while (ret != Z_STREAM_END); |
| 231 | |
| 232 | /* clean up and return index (release unused entries in list) */ |
| 233 | (void)inflateEnd(&strm); |
| 234 | index->list = realloc(index->list, sizeof(struct point) * index->have); |
| 235 | index->gzip = gzip; |
| 236 | index->length = totout; |
| 237 | *built = index; |
| 238 | return index->have; |
| 239 | |
| 240 | /* return error */ |
| 241 | deflate_index_build_error: |
| 242 | (void)inflateEnd(&strm); |
| 243 | deflate_index_free(index); |
| 244 | return ret; |
| 245 | } |
| 246 | |
| 247 | /* See comments in zran.h. */ |
| 248 | int deflate_index_extract(FILE *in, struct deflate_index *index, off_t offset, |
| 249 | unsigned char *buf, int len) |
| 250 | { |
| 251 | int ret, skip; |
| 252 | z_stream strm; |
| 253 | struct point *here; |
| 254 | unsigned char input[CHUNK]; |
| 255 | unsigned char discard[WINSIZE]; |
| 256 | |
| 257 | /* proceed only if something reasonable to do */ |
| 258 | if (len < 0) |
| 259 | return 0; |
| 260 | |
| 261 | /* find where in stream to start */ |
| 262 | here = index->list; |
| 263 | ret = index->have; |
| 264 | while (--ret && here[1].out <= offset) |
| 265 | here++; |
| 266 | |
| 267 | /* initialize file and inflate state to start there */ |
| 268 | strm.zalloc = Z_NULL; |
| 269 | strm.zfree = Z_NULL; |
| 270 | strm.opaque = Z_NULL; |
| 271 | strm.avail_in = 0; |
| 272 | strm.next_in = Z_NULL; |
| 273 | ret = inflateInit2(&strm, -15); /* raw inflate */ |
| 274 | if (ret != Z_OK) |
| 275 | return ret; |
| 276 | ret = fseeko(in, here->in - (here->bits ? 1 : 0), SEEK_SET); |
| 277 | if (ret == -1) |
| 278 | goto deflate_index_extract_ret; |
| 279 | if (here->bits) { |
| 280 | ret = getc(in); |
| 281 | if (ret == -1) { |
| 282 | ret = ferror(in) ? Z_ERRNO : Z_DATA_ERROR; |
| 283 | goto deflate_index_extract_ret; |
| 284 | } |
| 285 | (void)inflatePrime(&strm, here->bits, ret >> (8 - here->bits)); |
| 286 | } |
| 287 | (void)inflateSetDictionary(&strm, here->window, WINSIZE); |
| 288 | |
| 289 | /* skip uncompressed bytes until offset reached, then satisfy request */ |
| 290 | offset -= here->out; |
| 291 | strm.avail_in = 0; |
| 292 | skip = 1; /* while skipping to offset */ |
| 293 | do { |
| 294 | /* define where to put uncompressed data, and how much */ |
| 295 | if (offset > WINSIZE) { /* skip WINSIZE bytes */ |
| 296 | strm.avail_out = WINSIZE; |
| 297 | strm.next_out = discard; |
| 298 | offset -= WINSIZE; |
| 299 | } |
| 300 | else if (offset > 0) { /* last skip */ |
| 301 | strm.avail_out = (unsigned)offset; |
| 302 | strm.next_out = discard; |
| 303 | offset = 0; |
| 304 | } |
| 305 | else if (skip) { /* at offset now */ |
| 306 | strm.avail_out = len; |
| 307 | strm.next_out = buf; |
| 308 | skip = 0; /* only do this once */ |
| 309 | } |
| 310 | |
| 311 | /* uncompress until avail_out filled, or end of stream */ |
| 312 | do { |
| 313 | if (strm.avail_in == 0) { |
| 314 | strm.avail_in = fread(input, 1, CHUNK, in); |
| 315 | if (ferror(in)) { |
| 316 | ret = Z_ERRNO; |
| 317 | goto deflate_index_extract_ret; |
| 318 | } |
| 319 | if (strm.avail_in == 0) { |
| 320 | ret = Z_DATA_ERROR; |
| 321 | goto deflate_index_extract_ret; |
| 322 | } |
| 323 | strm.next_in = input; |
| 324 | } |
| 325 | ret = inflate(&strm, Z_NO_FLUSH); /* normal inflate */ |
| 326 | if (ret == Z_NEED_DICT) |
| 327 | ret = Z_DATA_ERROR; |
| 328 | if (ret == Z_MEM_ERROR || ret == Z_DATA_ERROR) |
| 329 | goto deflate_index_extract_ret; |
| 330 | if (ret == Z_STREAM_END) { |
| 331 | /* the raw deflate stream has ended */ |
| 332 | if (index->gzip == 0) |
| 333 | /* this is a zlib stream that has ended -- done */ |
| 334 | break; |
| 335 | |
| 336 | /* near the end of a gzip member, which might be followed by |
| 337 | another gzip member -- skip the gzip trailer and see if |
| 338 | there is more input after it */ |
| 339 | if (strm.avail_in < 8) { |
| 340 | fseeko(in, 8 - strm.avail_in, SEEK_CUR); |
| 341 | strm.avail_in = 0; |
| 342 | } |
| 343 | else { |
| 344 | strm.avail_in -= 8; |
| 345 | strm.next_in += 8; |
| 346 | } |
| 347 | if (strm.avail_in == 0 && ungetc(getc(in), in) == EOF) |
| 348 | /* the input ended after the gzip trailer -- done */ |
| 349 | break; |
| 350 | |
| 351 | /* there is more input, so another gzip member should follow -- |
| 352 | validate and skip the gzip header */ |
| 353 | ret = inflateReset2(&strm, 31); |
| 354 | if (ret != Z_OK) |
| 355 | goto deflate_index_extract_ret; |
| 356 | do { |
| 357 | if (strm.avail_in == 0) { |
| 358 | strm.avail_in = fread(input, 1, CHUNK, in); |
| 359 | if (ferror(in)) { |
| 360 | ret = Z_ERRNO; |
| 361 | goto deflate_index_extract_ret; |
| 362 | } |
| 363 | if (strm.avail_in == 0) { |
| 364 | ret = Z_DATA_ERROR; |
| 365 | goto deflate_index_extract_ret; |
| 366 | } |
| 367 | strm.next_in = input; |
| 368 | } |
| 369 | ret = inflate(&strm, Z_BLOCK); |
| 370 | if (ret == Z_MEM_ERROR || ret == Z_DATA_ERROR) |
| 371 | goto deflate_index_extract_ret; |
| 372 | } while ((strm.data_type & 128) == 0); |
| 373 | |
| 374 | /* set up to continue decompression of the raw deflate stream |
| 375 | that follows the gzip header */ |
| 376 | ret = inflateReset2(&strm, -15); |
| 377 | if (ret != Z_OK) |
| 378 | goto deflate_index_extract_ret; |
| 379 | } |
| 380 | |
| 381 | /* continue to process the available input before reading more */ |
| 382 | } while (strm.avail_out != 0); |
| 383 | |
| 384 | if (ret == Z_STREAM_END) |
| 385 | /* reached the end of the compressed data -- return the data that |
| 386 | was available, possibly less than requested */ |
| 387 | break; |
| 388 | |
| 389 | /* do until offset reached and requested data read */ |
| 390 | } while (skip); |
| 391 | |
| 392 | /* compute the number of uncompressed bytes read after the offset */ |
| 393 | ret = skip ? 0 : len - strm.avail_out; |
| 394 | |
| 395 | /* clean up and return the bytes read, or the negative error */ |
| 396 | deflate_index_extract_ret: |
| 397 | (void)inflateEnd(&strm); |
| 398 | return ret; |
| 399 | } |
| 400 | |
| 401 | #ifdef TEST |
| 402 | |
| 403 | #define SPAN 1048576L /* desired distance between access points */ |
| 404 | #define LEN 16384 /* number of bytes to extract */ |
| 405 | |
| 406 | /* Demonstrate the use of deflate_index_build() and deflate_index_extract() by |
| 407 | processing the file provided on the command line, and extracting LEN bytes |
| 408 | from 2/3rds of the way through the uncompressed output, writing that to |
| 409 | stdout. An offset can be provided as the second argument, in which case the |
| 410 | data is extracted from there instead. */ |
| 411 | int main(int argc, char **argv) |
| 412 | { |
| 413 | int len; |
| 414 | off_t offset = -1; |
| 415 | FILE *in; |
| 416 | struct deflate_index *index = NULL; |
| 417 | unsigned char buf[LEN]; |
| 418 | |
| 419 | /* open input file */ |
| 420 | if (argc < 2 || argc > 3) { |
| 421 | fprintf(stderr, "usage: zran file.gz [offset]\n"); |
| 422 | return 1; |
| 423 | } |
| 424 | in = fopen(argv[1], "rb"); |
| 425 | if (in == NULL) { |
| 426 | fprintf(stderr, "zran: could not open %s for reading\n", argv[1]); |
| 427 | return 1; |
| 428 | } |
| 429 | |
| 430 | /* get optional offset */ |
| 431 | if (argc == 3) { |
| 432 | char *end; |
| 433 | offset = strtoll(argv[2], &end, 10); |
| 434 | if (*end || offset < 0) { |
| 435 | fprintf(stderr, "zran: %s is not a valid offset\n", argv[2]); |
| 436 | return 1; |
| 437 | } |
| 438 | } |
| 439 | |
| 440 | /* build index */ |
| 441 | len = deflate_index_build(in, SPAN, &index); |
| 442 | if (len < 0) { |
| 443 | fclose(in); |
| 444 | switch (len) { |
| 445 | case Z_MEM_ERROR: |
| 446 | fprintf(stderr, "zran: out of memory\n"); |
| 447 | break; |
| 448 | case Z_DATA_ERROR: |
| 449 | fprintf(stderr, "zran: compressed data error in %s\n", argv[1]); |
| 450 | break; |
| 451 | case Z_ERRNO: |
| 452 | fprintf(stderr, "zran: read error on %s\n", argv[1]); |
| 453 | break; |
| 454 | default: |
| 455 | fprintf(stderr, "zran: error %d while building index\n", len); |
| 456 | } |
| 457 | return 1; |
| 458 | } |
| 459 | fprintf(stderr, "zran: built index with %d access points\n", len); |
| 460 | |
| 461 | /* use index by reading some bytes from an arbitrary offset */ |
| 462 | if (offset == -1) |
| 463 | offset = (index->length << 1) / 3; |
| 464 | len = deflate_index_extract(in, index, offset, buf, LEN); |
| 465 | if (len < 0) |
| 466 | fprintf(stderr, "zran: extraction failed: %s error\n", |
| 467 | len == Z_MEM_ERROR ? "out of memory" : "input corrupted"); |
| 468 | else { |
| 469 | fwrite(buf, 1, len, stdout); |
| 470 | fprintf(stderr, "zran: extracted %d bytes at %llu\n", len, offset); |
| 471 | } |
| 472 | |
| 473 | /* clean up and exit */ |
| 474 | deflate_index_free(index); |
| 475 | fclose(in); |
| 476 | return 0; |
| 477 | } |
| 478 | |
| 479 | #endif |