| /* zran.c -- example of zlib/gzip stream indexing and random access |
| * Copyright (C) 2005, 2012, 2018 Mark Adler |
| * For conditions of distribution and use, see copyright notice in zlib.h |
| * Version 1.2 14 Oct 2018 Mark Adler */ |
| |
| /* Version History: |
| 1.0 29 May 2005 First version |
| 1.1 29 Sep 2012 Fix memory reallocation error |
| 1.2 14 Oct 2018 Handle gzip streams with multiple members |
| Add a header file to facilitate usage in applications |
| */ |
| |
| /* Illustrate the use of Z_BLOCK, inflatePrime(), and inflateSetDictionary() |
| for random access of a compressed file. A file containing a zlib or gzip |
| stream is provided on the command line. The compressed stream is decoded in |
| its entirety, and an index built with access points about every SPAN bytes |
| in the uncompressed output. The compressed file is left open, and can then |
| be read randomly, having to decompress on the average SPAN/2 uncompressed |
| bytes before getting to the desired block of data. |
| |
| An access point can be created at the start of any deflate block, by saving |
| the starting file offset and bit of that block, and the 32K bytes of |
| uncompressed data that precede that block. Also the uncompressed offset of |
| that block is saved to provide a referece for locating a desired starting |
| point in the uncompressed stream. deflate_index_build() works by |
| decompressing the input zlib or gzip stream a block at a time, and at the |
| end of each block deciding if enough uncompressed data has gone by to |
| justify the creation of a new access point. If so, that point is saved in a |
| data structure that grows as needed to accommodate the points. |
| |
| To use the index, an offset in the uncompressed data is provided, for which |
| the latest access point at or preceding that offset is located in the index. |
| The input file is positioned to the specified location in the index, and if |
| necessary the first few bits of the compressed data is read from the file. |
| inflate is initialized with those bits and the 32K of uncompressed data, and |
| the decompression then proceeds until the desired offset in the file is |
| reached. Then the decompression continues to read the desired uncompressed |
| data from the file. |
| |
| Another approach would be to generate the index on demand. In that case, |
| requests for random access reads from the compressed data would try to use |
| the index, but if a read far enough past the end of the index is required, |
| then further index entries would be generated and added. |
| |
| There is some fair bit of overhead to starting inflation for the random |
| access, mainly copying the 32K byte dictionary. So if small pieces of the |
| file are being accessed, it would make sense to implement a cache to hold |
| some lookahead and avoid many calls to deflate_index_extract() for small |
| lengths. |
| |
| Another way to build an index would be to use inflateCopy(). That would |
| not be constrained to have access points at block boundaries, but requires |
| more memory per access point, and also cannot be saved to file due to the |
| use of pointers in the state. The approach here allows for storage of the |
| index in a file. |
| */ |
| |
| #include <stdio.h> |
| #include <stdlib.h> |
| #include <string.h> |
| #include "zlib.h" |
| #include "zran.h" |
| |
| #define WINSIZE 32768U /* sliding window size */ |
| #define CHUNK 16384 /* file input buffer size */ |
| |
| /* Access point entry. */ |
| struct point { |
| off_t out; /* corresponding offset in uncompressed data */ |
| off_t in; /* offset in input file of first full byte */ |
| int bits; /* number of bits (1-7) from byte at in-1, or 0 */ |
| unsigned char window[WINSIZE]; /* preceding 32K of uncompressed data */ |
| }; |
| |
| /* See comments in zran.h. */ |
| void deflate_index_free(struct deflate_index *index) |
| { |
| if (index != NULL) { |
| free(index->list); |
| free(index); |
| } |
| } |
| |
| /* Add an entry to the access point list. If out of memory, deallocate the |
| existing list and return NULL. index->gzip is the allocated size of the |
| index in point entries, until it is time for deflate_index_build() to |
| return, at which point gzip is set to indicate a gzip file or not. |
| */ |
| static struct deflate_index *addpoint(struct deflate_index *index, int bits, |
| off_t in, off_t out, unsigned left, |
| unsigned char *window) |
| { |
| struct point *next; |
| |
| /* if list is empty, create it (start with eight points) */ |
| if (index == NULL) { |
| index = malloc(sizeof(struct deflate_index)); |
| if (index == NULL) return NULL; |
| index->list = malloc(sizeof(struct point) << 3); |
| if (index->list == NULL) { |
| free(index); |
| return NULL; |
| } |
| index->gzip = 8; |
| index->have = 0; |
| } |
| |
| /* if list is full, make it bigger */ |
| else if (index->have == index->gzip) { |
| index->gzip <<= 1; |
| next = realloc(index->list, sizeof(struct point) * index->gzip); |
| if (next == NULL) { |
| deflate_index_free(index); |
| return NULL; |
| } |
| index->list = next; |
| } |
| |
| /* fill in entry and increment how many we have */ |
| next = (struct point *)(index->list) + index->have; |
| next->bits = bits; |
| next->in = in; |
| next->out = out; |
| if (left) |
| memcpy(next->window, window + WINSIZE - left, left); |
| if (left < WINSIZE) |
| memcpy(next->window + left, window, WINSIZE - left); |
| index->have++; |
| |
| /* return list, possibly reallocated */ |
| return index; |
| } |
| |
| /* See comments in zran.h. */ |
| int deflate_index_build(FILE *in, off_t span, struct deflate_index **built) |
| { |
| int ret; |
| int gzip = 0; /* true if reading a gzip file */ |
| off_t totin, totout; /* our own total counters to avoid 4GB limit */ |
| off_t last; /* totout value of last access point */ |
| struct deflate_index *index; /* access points being generated */ |
| z_stream strm; |
| unsigned char input[CHUNK]; |
| unsigned char window[WINSIZE]; |
| |
| /* initialize inflate */ |
| strm.zalloc = Z_NULL; |
| strm.zfree = Z_NULL; |
| strm.opaque = Z_NULL; |
| strm.avail_in = 0; |
| strm.next_in = Z_NULL; |
| ret = inflateInit2(&strm, 47); /* automatic zlib or gzip decoding */ |
| if (ret != Z_OK) |
| return ret; |
| |
| /* inflate the input, maintain a sliding window, and build an index -- this |
| also validates the integrity of the compressed data using the check |
| information in the gzip or zlib stream */ |
| totin = totout = last = 0; |
| index = NULL; /* will be allocated by first addpoint() */ |
| strm.avail_out = 0; |
| do { |
| /* get some compressed data from input file */ |
| strm.avail_in = fread(input, 1, CHUNK, in); |
| if (ferror(in)) { |
| ret = Z_ERRNO; |
| goto deflate_index_build_error; |
| } |
| if (strm.avail_in == 0) { |
| ret = Z_DATA_ERROR; |
| goto deflate_index_build_error; |
| } |
| strm.next_in = input; |
| |
| /* check for a gzip stream */ |
| if (totin == 0 && strm.avail_in >= 3 && |
| input[0] == 31 && input[1] == 139 && input[2] == 8) |
| gzip = 1; |
| |
| /* process all of that, or until end of stream */ |
| do { |
| /* reset sliding window if necessary */ |
| if (strm.avail_out == 0) { |
| strm.avail_out = WINSIZE; |
| strm.next_out = window; |
| } |
| |
| /* inflate until out of input, output, or at end of block -- |
| update the total input and output counters */ |
| totin += strm.avail_in; |
| totout += strm.avail_out; |
| ret = inflate(&strm, Z_BLOCK); /* return at end of block */ |
| totin -= strm.avail_in; |
| totout -= strm.avail_out; |
| if (ret == Z_NEED_DICT) |
| ret = Z_DATA_ERROR; |
| if (ret == Z_MEM_ERROR || ret == Z_DATA_ERROR) |
| goto deflate_index_build_error; |
| if (ret == Z_STREAM_END) { |
| if (gzip && |
| (strm.avail_in || ungetc(getc(in), in) != EOF)) { |
| ret = inflateReset(&strm); |
| if (ret != Z_OK) |
| goto deflate_index_build_error; |
| continue; |
| } |
| break; |
| } |
| |
| /* if at end of block, consider adding an index entry (note that if |
| data_type indicates an end-of-block, then all of the |
| uncompressed data from that block has been delivered, and none |
| of the compressed data after that block has been consumed, |
| except for up to seven bits) -- the totout == 0 provides an |
| entry point after the zlib or gzip header, and assures that the |
| index always has at least one access point; we avoid creating an |
| access point after the last block by checking bit 6 of data_type |
| */ |
| if ((strm.data_type & 128) && !(strm.data_type & 64) && |
| (totout == 0 || totout - last > span)) { |
| index = addpoint(index, strm.data_type & 7, totin, |
| totout, strm.avail_out, window); |
| if (index == NULL) { |
| ret = Z_MEM_ERROR; |
| goto deflate_index_build_error; |
| } |
| last = totout; |
| } |
| } while (strm.avail_in != 0); |
| } while (ret != Z_STREAM_END); |
| |
| /* clean up and return index (release unused entries in list) */ |
| (void)inflateEnd(&strm); |
| index->list = realloc(index->list, sizeof(struct point) * index->have); |
| index->gzip = gzip; |
| index->length = totout; |
| *built = index; |
| return index->have; |
| |
| /* return error */ |
| deflate_index_build_error: |
| (void)inflateEnd(&strm); |
| deflate_index_free(index); |
| return ret; |
| } |
| |
| /* See comments in zran.h. */ |
| int deflate_index_extract(FILE *in, struct deflate_index *index, off_t offset, |
| unsigned char *buf, int len) |
| { |
| int ret, skip; |
| z_stream strm; |
| struct point *here; |
| unsigned char input[CHUNK]; |
| unsigned char discard[WINSIZE]; |
| |
| /* proceed only if something reasonable to do */ |
| if (len < 0) |
| return 0; |
| |
| /* find where in stream to start */ |
| here = index->list; |
| ret = index->have; |
| while (--ret && here[1].out <= offset) |
| here++; |
| |
| /* initialize file and inflate state to start there */ |
| strm.zalloc = Z_NULL; |
| strm.zfree = Z_NULL; |
| strm.opaque = Z_NULL; |
| strm.avail_in = 0; |
| strm.next_in = Z_NULL; |
| ret = inflateInit2(&strm, -15); /* raw inflate */ |
| if (ret != Z_OK) |
| return ret; |
| ret = fseeko(in, here->in - (here->bits ? 1 : 0), SEEK_SET); |
| if (ret == -1) |
| goto deflate_index_extract_ret; |
| if (here->bits) { |
| ret = getc(in); |
| if (ret == -1) { |
| ret = ferror(in) ? Z_ERRNO : Z_DATA_ERROR; |
| goto deflate_index_extract_ret; |
| } |
| (void)inflatePrime(&strm, here->bits, ret >> (8 - here->bits)); |
| } |
| (void)inflateSetDictionary(&strm, here->window, WINSIZE); |
| |
| /* skip uncompressed bytes until offset reached, then satisfy request */ |
| offset -= here->out; |
| strm.avail_in = 0; |
| skip = 1; /* while skipping to offset */ |
| do { |
| /* define where to put uncompressed data, and how much */ |
| if (offset > WINSIZE) { /* skip WINSIZE bytes */ |
| strm.avail_out = WINSIZE; |
| strm.next_out = discard; |
| offset -= WINSIZE; |
| } |
| else if (offset > 0) { /* last skip */ |
| strm.avail_out = (unsigned)offset; |
| strm.next_out = discard; |
| offset = 0; |
| } |
| else if (skip) { /* at offset now */ |
| strm.avail_out = len; |
| strm.next_out = buf; |
| skip = 0; /* only do this once */ |
| } |
| |
| /* uncompress until avail_out filled, or end of stream */ |
| do { |
| if (strm.avail_in == 0) { |
| strm.avail_in = fread(input, 1, CHUNK, in); |
| if (ferror(in)) { |
| ret = Z_ERRNO; |
| goto deflate_index_extract_ret; |
| } |
| if (strm.avail_in == 0) { |
| ret = Z_DATA_ERROR; |
| goto deflate_index_extract_ret; |
| } |
| strm.next_in = input; |
| } |
| ret = inflate(&strm, Z_NO_FLUSH); /* normal inflate */ |
| if (ret == Z_NEED_DICT) |
| ret = Z_DATA_ERROR; |
| if (ret == Z_MEM_ERROR || ret == Z_DATA_ERROR) |
| goto deflate_index_extract_ret; |
| if (ret == Z_STREAM_END) { |
| /* the raw deflate stream has ended */ |
| if (index->gzip == 0) |
| /* this is a zlib stream that has ended -- done */ |
| break; |
| |
| /* near the end of a gzip member, which might be followed by |
| another gzip member -- skip the gzip trailer and see if |
| there is more input after it */ |
| if (strm.avail_in < 8) { |
| fseeko(in, 8 - strm.avail_in, SEEK_CUR); |
| strm.avail_in = 0; |
| } |
| else { |
| strm.avail_in -= 8; |
| strm.next_in += 8; |
| } |
| if (strm.avail_in == 0 && ungetc(getc(in), in) == EOF) |
| /* the input ended after the gzip trailer -- done */ |
| break; |
| |
| /* there is more input, so another gzip member should follow -- |
| validate and skip the gzip header */ |
| ret = inflateReset2(&strm, 31); |
| if (ret != Z_OK) |
| goto deflate_index_extract_ret; |
| do { |
| if (strm.avail_in == 0) { |
| strm.avail_in = fread(input, 1, CHUNK, in); |
| if (ferror(in)) { |
| ret = Z_ERRNO; |
| goto deflate_index_extract_ret; |
| } |
| if (strm.avail_in == 0) { |
| ret = Z_DATA_ERROR; |
| goto deflate_index_extract_ret; |
| } |
| strm.next_in = input; |
| } |
| ret = inflate(&strm, Z_BLOCK); |
| if (ret == Z_MEM_ERROR || ret == Z_DATA_ERROR) |
| goto deflate_index_extract_ret; |
| } while ((strm.data_type & 128) == 0); |
| |
| /* set up to continue decompression of the raw deflate stream |
| that follows the gzip header */ |
| ret = inflateReset2(&strm, -15); |
| if (ret != Z_OK) |
| goto deflate_index_extract_ret; |
| } |
| |
| /* continue to process the available input before reading more */ |
| } while (strm.avail_out != 0); |
| |
| if (ret == Z_STREAM_END) |
| /* reached the end of the compressed data -- return the data that |
| was available, possibly less than requested */ |
| break; |
| |
| /* do until offset reached and requested data read */ |
| } while (skip); |
| |
| /* compute the number of uncompressed bytes read after the offset */ |
| ret = skip ? 0 : len - strm.avail_out; |
| |
| /* clean up and return the bytes read, or the negative error */ |
| deflate_index_extract_ret: |
| (void)inflateEnd(&strm); |
| return ret; |
| } |
| |
| #ifdef TEST |
| |
| #define SPAN 1048576L /* desired distance between access points */ |
| #define LEN 16384 /* number of bytes to extract */ |
| |
| /* Demonstrate the use of deflate_index_build() and deflate_index_extract() by |
| processing the file provided on the command line, and extracting LEN bytes |
| from 2/3rds of the way through the uncompressed output, writing that to |
| stdout. An offset can be provided as the second argument, in which case the |
| data is extracted from there instead. */ |
| int main(int argc, char **argv) |
| { |
| int len; |
| off_t offset = -1; |
| FILE *in; |
| struct deflate_index *index = NULL; |
| unsigned char buf[LEN]; |
| |
| /* open input file */ |
| if (argc < 2 || argc > 3) { |
| fprintf(stderr, "usage: zran file.gz [offset]\n"); |
| return 1; |
| } |
| in = fopen(argv[1], "rb"); |
| if (in == NULL) { |
| fprintf(stderr, "zran: could not open %s for reading\n", argv[1]); |
| return 1; |
| } |
| |
| /* get optional offset */ |
| if (argc == 3) { |
| char *end; |
| offset = strtoll(argv[2], &end, 10); |
| if (*end || offset < 0) { |
| fprintf(stderr, "zran: %s is not a valid offset\n", argv[2]); |
| return 1; |
| } |
| } |
| |
| /* build index */ |
| len = deflate_index_build(in, SPAN, &index); |
| if (len < 0) { |
| fclose(in); |
| switch (len) { |
| case Z_MEM_ERROR: |
| fprintf(stderr, "zran: out of memory\n"); |
| break; |
| case Z_DATA_ERROR: |
| fprintf(stderr, "zran: compressed data error in %s\n", argv[1]); |
| break; |
| case Z_ERRNO: |
| fprintf(stderr, "zran: read error on %s\n", argv[1]); |
| break; |
| default: |
| fprintf(stderr, "zran: error %d while building index\n", len); |
| } |
| return 1; |
| } |
| fprintf(stderr, "zran: built index with %d access points\n", len); |
| |
| /* use index by reading some bytes from an arbitrary offset */ |
| if (offset == -1) |
| offset = (index->length << 1) / 3; |
| len = deflate_index_extract(in, index, offset, buf, LEN); |
| if (len < 0) |
| fprintf(stderr, "zran: extraction failed: %s error\n", |
| len == Z_MEM_ERROR ? "out of memory" : "input corrupted"); |
| else { |
| fwrite(buf, 1, len, stdout); |
| fprintf(stderr, "zran: extracted %d bytes at %llu\n", len, offset); |
| } |
| |
| /* clean up and exit */ |
| deflate_index_free(index); |
| fclose(in); |
| return 0; |
| } |
| |
| #endif |
