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