| /* 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 1.3 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 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 <stdio.h> |
| #include <stdlib.h> |
| #include <string.h> |
| #include <limits.h> |
| #include "zlib.h" |
| #include "zran.h" |
| |
| #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) { |
| if (index != NULL) { |
| free(index->list); |
| free(index); |
| } |
| } |
| |
| // 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->have = 0; |
| index->mode = 8; |
| index->list = malloc(sizeof(point_t) * index->mode); |
| if (index->list == NULL) { |
| free(index); |
| return NULL; |
| } |
| } |
| |
| 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; |
| } |
| index->list = next; |
| } |
| |
| // 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); |
| |
| // Return the index, which may have been newly allocated or destroyed. |
| return index; |
| } |
| |
| // 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 { |
| // Assure available input, at least until reaching EOF. |
| if (strm.avail_in == 0) { |
| strm.avail_in = fread(buf, 1, sizeof(buf), in); |
| totin += strm.avail_in; |
| strm.next_in = buf; |
| if (strm.avail_in < sizeof(buf) && ferror(in)) { |
| ret = Z_ERRNO; |
| break; |
| } |
| |
| 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; |
| } |
| last = totout; |
| } |
| |
| 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; |
| } |
| |
| // 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; |
| |
| // If nothing to extract, return zero bytes extracted. |
| if (len == 0 || offset < 0 || offset >= index->length) |
| return 0; |
| |
| // 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; |
| 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. |
| 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 { |
| if (offset) { |
| // Discard up to offset uncompressed bytes. |
| strm.avail_out = offset < WINSIZE ? (unsigned)offset : WINSIZE; |
| strm.next_out = discard; |
| } |
| 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, 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); |
| } |
| |
| 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 (strm.avail_in < CHUNK && ferror(in)) { |
| ret = Z_ERRNO; |
| break; |
| } |
| strm.next_in = input; |
| } |
| 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) |
| break; |
| inflateReset2(&strm, RAW); |
| } |
| } |
| |
| // Continue until we have the requested data, the deflate data has |
| // ended, or an error is encountered. |
| } while (ret == Z_OK && left); |
| inflateEnd(&strm); |
| |
| // 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) { |
| // Open the input file. |
| if (argc < 2 || argc > 3) { |
| fprintf(stderr, "usage: zran file.raw [offset]\n"); |
| return 1; |
| } |
| 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. |
| off_t offset = -1; |
| 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. |
| 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; |
| 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. |
| unsigned char buf[LEN]; |
| if (offset == -1) |
| 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", |
| got == Z_MEM_ERROR ? "out of memory" : "input corrupted"); |
| else { |
| fwrite(buf, 1, got, stdout); |
| fprintf(stderr, "zran: extracted %ld bytes at %lld\n", got, offset); |
| } |
| |
| // Clean up and exit. |
| deflate_index_free(index); |
| fclose(in); |
| return 0; |
| } |
| |
| #endif |
