diff --git a/examples/zran.c b/examples/zran.c index 879c47cc..1ffba7fe 100644 --- a/examples/zran.c +++ b/examples/zran.c @@ -1,114 +1,101 @@ -/* zran.c -- example of zlib/gzip stream indexing and random access - * Copyright (C) 2005, 2012, 2018 Mark Adler +/* zran.c -- example of deflate stream indexing and random access + * Copyright (C) 2005, 2012, 2018, 2023 Mark Adler * For conditions of distribution and use, see copyright notice in zlib.h - * Version 1.2 14 Oct 2018 Mark Adler */ + * Version 1.3 18 Feb 2023 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 + 1.3 18 Feb 2023 Permit raw deflate streams as well as zlib and gzip + Permit crossing gzip member boundaries when extracting + Support a size_t size when extracting (was an int) + Do a binary search over the index for an access point + Expose the access point type to enable save and load */ -/* 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 reference 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. - */ +// Illustrate the use of Z_BLOCK, inflatePrime(), and inflateSetDictionary() +// for random access of a compressed file. A file containing a raw deflate +// 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 reference for locating a desired starting +// point in the uncompressed stream. deflate_index_build() decompresses the +// input raw deflate stream a block at a time, and at the end of each block +// decides 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 +// decompression then proceeds until the desired offset in the file is reached. +// Then decompression continues to read the requested uncompressed data from +// the file. +// +// There is some fair bit of overhead to starting inflation for the random +// access, mainly copying the 32K byte dictionary. If small pieces of the file +// are being accessed, it would make sense to implement a cache to hold some +// lookahead to 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 would require +// more memory per access point, and could not be saved to a file due to the +// use of pointers in the state. The approach here allows for storage of the +// index in a file. #include #include #include +#include #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 */ -}; +#define WINSIZE 32768U // sliding window size +#define CHUNK 16384 // file input buffer size -/* See comments in zran.h. */ -void deflate_index_free(struct deflate_index *index) -{ +// 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) */ +// Add an access point to the list. If out of memory, deallocate the existing +// list and return NULL. index->mode is temporarily the allocated number of +// access points, until it is time for deflate_index_build() to return. Then +// index->mode is set to the mode of inflation. +static struct deflate_index *add_point(struct deflate_index *index, int bits, + off_t in, off_t out, unsigned left, + unsigned char *window) { if (index == NULL) { + // The list is empty. Create it, starting with eight access points. index = malloc(sizeof(struct deflate_index)); - if (index == NULL) return NULL; - index->list = malloc(sizeof(struct point) << 3); + if (index == NULL) + return NULL; + index->have = 0; + index->mode = 8; + index->list = malloc(sizeof(point_t) * index->mode); 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); + else if (index->have == index->mode) { + // The list is full. Make it bigger. + index->mode <<= 1; + point_t *next = realloc(index->list, sizeof(point_t) * index->mode); if (next == NULL) { deflate_index_free(index); return NULL; @@ -116,318 +103,291 @@ static struct deflate_index *addpoint(struct deflate_index *index, int bits, 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; + // Fill in the access point and increment how many we have. + point_t *next = (point_t *)(index->list) + index->have++; + if (index->have < 0) { + // Overflowed the int! + deflate_index_free(index); + return NULL; + } next->out = out; + next->in = in; + next->bits = bits; 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 the index, which may have been newly allocated or destroyed. 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; +// Decompression modes. These are the inflateInit2() windowBits parameter. +#define RAW -15 +#define ZLIB 15 +#define GZIP 31 + +// See comments in zran.h. +int deflate_index_build(FILE *in, off_t span, struct deflate_index **built) { + // Set up inflation state. + z_stream strm = {0}; // inflate engine (gets fired up later) + unsigned char buf[CHUNK]; // input buffer + unsigned char win[WINSIZE] = {0}; // output sliding window + off_t totin = 0; // total bytes read from input + off_t totout = 0; // total bytes uncompressed + int mode = 0; // mode: RAW, ZLIB, or GZIP (0 => not set yet) + + // Decompress from in, generating access points along the way. + int ret; // the return value from zlib, or Z_ERRNO + off_t last; // last access point uncompressed offset + struct deflate_index *index = NULL; // list of access points 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; - } + // Assure available input, at least until reaching EOF. 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 */ + strm.avail_in = fread(buf, 1, sizeof(buf), in); 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; - } + strm.next_in = buf; + if (strm.avail_in < sizeof(buf) && ferror(in)) { + ret = Z_ERRNO; 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; + if (mode == 0) { + // At the start of the input -- determine the type. Assume raw + // if it is neither zlib nor gzip. This could in theory result + // in a false positive for zlib, but in practice the fill bits + // after a stored block are always zeros, so a raw stream won't + // start with an 8 in the low nybble. + mode = strm.avail_in == 0 ? RAW : // empty -- will fail + (strm.next_in[0] & 0xf) == 8 ? ZLIB : + strm.next_in[0] == 0x1f ? GZIP : + /* else */ RAW; + ret = inflateInit2(&strm, mode); + if (ret != Z_OK) + break; + } + } + + // Assure available output. This rotates the output through, for use as + // a sliding window on the uncompressed data. + if (strm.avail_out == 0) { + strm.avail_out = sizeof(win); + strm.next_out = win; + } + + if (mode == RAW && index == NULL) + // We skip the inflate() call at the start of raw deflate data in + // order generate an access point there. Set data_type to imitate + // the end of a header. + strm.data_type = 0x80; + else { + // Inflate and update the number of uncompressed bytes. + unsigned before = strm.avail_out; + ret = inflate(&strm, Z_BLOCK); + totout += before - strm.avail_out; + } + + if ((strm.data_type & 0xc0) == 0x80 && + (index == NULL || totout - last >= span)) { + // We are at the end of a header or a non-last deflate block, so we + // can add an access point here. Furthermore, we are either at the + // very start for the first access point, or there has been span or + // more uncompressed bytes since the last access point, so we want + // to add an access point here. + index = add_point(index, strm.data_type & 7, totin - strm.avail_in, + totout, strm.avail_out, win); + if (index == NULL) { + ret = Z_MEM_ERROR; + break; } - } while (strm.avail_in != 0); - } while (ret != Z_STREAM_END); + last = totout; + } - /* 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; + if (ret == Z_STREAM_END && mode == GZIP && + (strm.avail_in || ungetc(getc(in), in) != EOF)) + // There is more input after the end of a gzip member. Reset the + // inflate state to read another gzip member. On success, this will + // set ret to Z_OK to continue decompressing. + ret = inflateReset2(&strm, GZIP); + + // Keep going until Z_STREAM_END or error. If the compressed data ends + // prematurely without a file read error, Z_BUF_ERROR is returned. + } while (ret == Z_OK); + inflateEnd(&strm); + + if (ret != Z_STREAM_END) { + // An error was encountered. Discard the index and return a negative + // error code. + deflate_index_free(index); + return ret == Z_NEED_DICT ? Z_DATA_ERROR : ret; + } + + // Shrink the index to only the occupied access points and return it. + index->mode = mode; index->length = totout; + point_t *list = realloc(index->list, sizeof(point_t) * index->have); + if (list == NULL) { + // Seems like a realloc() to make something smaller should always work, + // but just in case. + deflate_index_free(index); + return Z_MEM_ERROR; + } + index->list = list; *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]; +// See comments in zran.h. +ptrdiff_t deflate_index_extract(FILE *in, struct deflate_index *index, + off_t offset, unsigned char *buf, size_t len) { + // Do a quick sanity check on the index. + if (index == NULL || index->have < 1 || index->list[0].out != 0) + return Z_STREAM_ERROR; - /* proceed only if something reasonable to do */ - if (len < 0) + // If nothing to extract, return zero bytes extracted. + if (len == 0 || offset < 0 || offset >= index->length) 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 */ + // Find the access point closest to but not after offset. + int lo = -1, hi = index->have; + point_t *point = index->list; + while (hi - lo > 1) { + int mid = (lo + hi) >> 1; + if (offset < point[mid].out) + hi = mid; + else + lo = mid; + } + point += lo; + + // Initialize the input file and prime the inflate engine to start there. + int ret = fseeko(in, point->in - (point->bits ? 1 : 0), SEEK_SET); + if (ret == -1) + return Z_ERRNO; + int ch = 0; + if (point->bits && (ch = getc(in)) == EOF) + return ferror(in) ? Z_ERRNO : Z_BUF_ERROR; + z_stream strm = {0}; + ret = inflateInit2(&strm, RAW); 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); + if (point->bits) + inflatePrime(&strm, point->bits, ch >> (8 - point->bits)); + inflateSetDictionary(&strm, point->window, WINSIZE); - /* skip uncompressed bytes until offset reached, then satisfy request */ - offset -= here->out; - strm.avail_in = 0; - skip = 1; /* while skipping to offset */ + // Skip uncompressed bytes until offset reached, then satisfy request. + unsigned char input[CHUNK]; + unsigned char discard[WINSIZE]; + offset -= point->out; // number of bytes to skip to get to offset + size_t left = len; // number of bytes left to read after 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; + if (offset) { + // Discard up to offset uncompressed bytes. + strm.avail_out = offset < WINSIZE ? (unsigned)offset : WINSIZE; 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 */ + else { + // Uncompress up to left bytes into buf. + strm.avail_out = left < UINT_MAX ? (unsigned)left : UINT_MAX; + strm.next_out = buf + len - left; } - /* 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; + // Uncompress, setting got to the number of bytes uncompressed. + if (strm.avail_in == 0) { + // Assure available input. + strm.avail_in = fread(input, 1, CHUNK, in); + if (strm.avail_in < CHUNK && ferror(in)) { + ret = Z_ERRNO; + break; + } + strm.next_in = input; + } + unsigned got = strm.avail_out; + ret = inflate(&strm, Z_NO_FLUSH); + got -= strm.avail_out; + + // Update the appropriate count. + if (offset) + offset -= got; + else + left -= got; + + // If we're at the end of a gzip member and there's more to read, + // continue to the next gzip member. + if (ret == Z_STREAM_END && index->mode == GZIP) { + // Discard the gzip trailer. + unsigned drop = 8; // length of gzip trailer + if (strm.avail_in >= drop) { + strm.avail_in -= drop; + strm.next_in += drop; + } + else { + // Read and discard the remainder of the gzip trailer. + drop -= strm.avail_in; + strm.avail_in = 0; + do { + if (getc(in) == EOF) + // The input does not have a complete trailer. + return ferror(in) ? Z_ERRNO : Z_BUF_ERROR; + } while (--drop); } - 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; + if (strm.avail_in || ungetc(getc(in), in) != EOF) { + // There's more after the gzip trailer. Use inflate to skip the + // gzip header and resume the raw inflate there. + inflateReset2(&strm, GZIP); do { if (strm.avail_in == 0) { strm.avail_in = fread(input, 1, CHUNK, in); - if (ferror(in)) { + if (strm.avail_in < CHUNK && ferror(in)) { ret = Z_ERRNO; - goto deflate_index_extract_ret; - } - if (strm.avail_in == 0) { - ret = Z_DATA_ERROR; - goto deflate_index_extract_ret; + break; } 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); + strm.avail_out = WINSIZE; + strm.next_out = discard; + ret = inflate(&strm, Z_BLOCK); // stop at end of header + } while (ret == Z_OK && (strm.data_type & 0x80) == 0); if (ret != Z_OK) - goto deflate_index_extract_ret; + break; + inflateReset2(&strm, RAW); } + } - /* 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; + // Continue until we have the requested data, the deflate data has + // ended, or an error is encountered. + } while (ret == Z_OK && left); + inflateEnd(&strm); - /* clean up and return the bytes read, or the negative error */ - deflate_index_extract_ret: - (void)inflateEnd(&strm); - return ret; + // Return the number of uncompressed bytes read into buf, or the error. + return ret == Z_OK || ret == Z_STREAM_END ? len - left : 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]; +#define SPAN 1048576L // desired distance between access points +#define LEN 16384 // number of bytes to extract - /* open input file */ +// 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) { + // Open the input file. if (argc < 2 || argc > 3) { - fprintf(stderr, "usage: zran file.gz [offset]\n"); + fprintf(stderr, "usage: zran file.raw [offset]\n"); return 1; } - in = fopen(argv[1], "rb"); + FILE *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 */ + // Get optional offset. + off_t offset = -1; if (argc == 3) { char *end; offset = strtoll(argv[2], &end, 10); @@ -437,14 +397,18 @@ int main(int argc, char **argv) } } - /* build index */ - len = deflate_index_build(in, SPAN, &index); + // Build index. + struct deflate_index *index = NULL; + int 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_BUF_ERROR: + fprintf(stderr, "zran: %s ended prematurely\n", argv[1]); + break; case Z_DATA_ERROR: fprintf(stderr, "zran: compressed data error in %s\n", argv[1]); break; @@ -458,19 +422,20 @@ int main(int argc, char **argv) } fprintf(stderr, "zran: built index with %d access points\n", len); - /* use index by reading some bytes from an arbitrary offset */ + // Use index by reading some bytes from an arbitrary offset. + unsigned char buf[LEN]; if (offset == -1) - offset = (index->length << 1) / 3; - len = deflate_index_extract(in, index, offset, buf, LEN); - if (len < 0) + offset = ((index->length + 1) << 1) / 3; + ptrdiff_t got = deflate_index_extract(in, index, offset, buf, LEN); + if (got < 0) fprintf(stderr, "zran: extraction failed: %s error\n", - len == Z_MEM_ERROR ? "out of memory" : "input corrupted"); + got == 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); + fwrite(buf, 1, got, stdout); + fprintf(stderr, "zran: extracted %ld bytes at %lld\n", got, offset); } - /* clean up and exit */ + // Clean up and exit. deflate_index_free(index); fclose(in); return 0; diff --git a/examples/zran.h b/examples/zran.h index 2314125d..ebf780d0 100644 --- a/examples/zran.h +++ b/examples/zran.h @@ -1,40 +1,51 @@ -/* zran.h -- example of zlib/gzip stream indexing and random access - * Copyright (C) 2005, 2012, 2018 Mark Adler +/* zran.h -- example of deflated stream indexing and random access + * Copyright (C) 2005, 2012, 2018, 2023 Mark Adler * For conditions of distribution and use, see copyright notice in zlib.h - * Version 1.2 14 Oct 2018 Mark Adler */ + * Version 1.3 18 Feb 2023 Mark Adler */ #include #include "zlib.h" -/* Access point list. */ +// Access point. +typedef struct point { + off_t out; // offset in uncompressed data + off_t in; // offset in compressed file of first full byte + int bits; // 0, or number of bits (1-7) from byte at in-1 + unsigned char window[32768]; // preceding 32K of uncompressed data +} point_t; + +// Access point list. struct deflate_index { - int have; /* number of list entries */ - int gzip; /* 1 if the index is of a gzip file, 0 if it is of a - zlib stream */ - off_t length; /* total length of uncompressed data */ - void *list; /* allocated list of entries */ + int have; // number of access points in list + int mode; // -15 for raw, 15 for zlib, or 31 for gzip + off_t length; // total length of uncompressed data + point_t *list; // allocated list of access points }; -/* Make one entire pass through a zlib or gzip compressed stream and build an - index, with access points about every span bytes of uncompressed output. - gzip files with multiple members are indexed in their entirety. span should - be chosen to balance the speed of random access against the memory - requirements of the list, about 32K bytes per access point. The return value - is the number of access points on success (>= 1), Z_MEM_ERROR for out of - memory, Z_DATA_ERROR for an error in the input file, or Z_ERRNO for a file - read error. On success, *built points to the resulting index. */ +// Make one pass through a zlib, gzip, or raw deflate compressed stream and +// build an index, with access points about every span bytes of uncompressed +// output. gzip files with multiple members are fully indexed. span should be +// chosen to balance the speed of random access against the memory requirements +// of the list, which is about 32K bytes per access point. The return value is +// the number of access points on success (>= 1), Z_MEM_ERROR for out of +// memory, Z_BUF_ERROR for a premature end of input, Z_DATA_ERROR for a format +// or verification error in the input file, or Z_ERRNO for a file read error. +// On success, *built points to the resulting index. int deflate_index_build(FILE *in, off_t span, struct deflate_index **built); -/* Deallocate an index built by deflate_index_build() */ -void deflate_index_free(struct deflate_index *index); +// Use the index to read len bytes from offset into buf. Return the number of +// bytes read or a negative error code. If data is requested past the end of +// the uncompressed data, then deflate_index_extract() will return a value less +// than len, indicating how much was actually read into buf. If given a valid +// index, this function should not return an error unless the file was modified +// somehow since the index was generated, given that deflate_index_build() had +// validated all of the input. If nevertheless there is a failure, Z_BUF_ERROR +// is returned if the compressed data ends prematurely, Z_DATA_ERROR if the +// deflate compressed data is not valid, Z_MEM_ERROR if out of memory, +// Z_STREAM_ERROR if the index is not valid, or Z_ERRNO if there is an error +// reading or seeking on the input file. +ptrdiff_t deflate_index_extract(FILE *in, struct deflate_index *index, + off_t offset, unsigned char *buf, size_t len); -/* Use the index to read len bytes from offset into buf. Return bytes read or - negative for error (Z_DATA_ERROR or Z_MEM_ERROR). If data is requested past - the end of the uncompressed data, then deflate_index_extract() will return a - value less than len, indicating how much was actually read into buf. This - function should not return a data error unless the file was modified since - the index was generated, since deflate_index_build() validated all of the - input. deflate_index_extract() will return Z_ERRNO if there is an error on - reading or seeking the input file. */ -int deflate_index_extract(FILE *in, struct deflate_index *index, off_t offset, - unsigned char *buf, int len); +// Deallocate an index built by deflate_index_build(). +void deflate_index_free(struct deflate_index *index);