Fix the zran.c example to work on a multiple-member gzip file.
This commit is contained in:
parent
354fa43d12
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921d81b2a8
@ -48,6 +48,7 @@ zpipe.c
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- deeply commented in zlib_how.html (see above)
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- deeply commented in zlib_how.html (see above)
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zran.c
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zran.c
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zran.h
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index a zlib or gzip stream and randomly access it
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index a zlib or gzip stream and randomly access it
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- illustrates the use of Z_BLOCK, inflatePrime(), and
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- illustrates the use of Z_BLOCK, inflatePrime(), and
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inflateSetDictionary() to provide random access
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inflateSetDictionary() to provide random access
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256
examples/zran.c
256
examples/zran.c
@ -1,11 +1,13 @@
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/* zran.c -- example of zlib/gzip stream indexing and random access
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/* zran.c -- example of zlib/gzip stream indexing and random access
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* Copyright (C) 2005, 2012 Mark Adler
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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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* For conditions of distribution and use, see copyright notice in zlib.h
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Version 1.1 29 Sep 2012 Mark Adler */
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* Version 1.2 14 Oct 2018 Mark Adler */
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/* Version History:
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/* Version History:
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1.0 29 May 2005 First version
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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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1.1 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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*/
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/* Illustrate the use of Z_BLOCK, inflatePrime(), and inflateSetDictionary()
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/* Illustrate the use of Z_BLOCK, inflatePrime(), and inflateSetDictionary()
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@ -20,11 +22,11 @@
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the starting file offset and bit of that block, and the 32K bytes of
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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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uncompressed data that precede that block. Also the uncompressed offset of
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that block is saved to provide a referece for locating a desired starting
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that block is saved to provide a referece for locating a desired starting
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point in the uncompressed stream. build_index() works by decompressing the
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point in the uncompressed stream. deflate_index_build() works by
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input zlib or gzip stream a block at a time, and at the end of each block
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decompressing the input zlib or gzip stream a block at a time, and at the
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deciding if enough uncompressed data has gone by to justify the creation of
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end of each block deciding if enough uncompressed data has gone by to
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a new access point. If so, that point is saved in a data structure that
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justify the creation of a new access point. If so, that point is saved in a
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grows as needed to accommodate the points.
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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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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 latest access point at or preceding that offset is located in the index.
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@ -43,7 +45,8 @@
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There is some fair bit of overhead to starting inflation for the random
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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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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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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 extract() for small lengths.
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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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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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not be constrained to have access points at block boundaries, but requires
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@ -56,30 +59,21 @@
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#include <stdlib.h>
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#include <stdlib.h>
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#include <string.h>
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#include <string.h>
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#include "zlib.h"
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#include "zlib.h"
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#include "zran.h"
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#define local static
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#define SPAN 1048576L /* desired distance between access points */
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#define WINSIZE 32768U /* sliding window size */
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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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#define CHUNK 16384 /* file input buffer size */
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/* access point entry */
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/* Access point entry. */
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struct point {
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struct point {
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off_t out; /* corresponding offset in uncompressed data */
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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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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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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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unsigned char window[WINSIZE]; /* preceding 32K of uncompressed data */
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};
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};
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/* access point list */
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/* See comments in zran.h. */
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struct access {
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void deflate_index_free(struct deflate_index *index)
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int have; /* number of list entries filled in */
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int size; /* number of list entries allocated */
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struct point *list; /* allocated list */
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};
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/* Deallocate an index built by build_index() */
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local void free_index(struct access *index)
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{
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{
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if (index != NULL) {
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if (index != NULL) {
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free(index->list);
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free(index->list);
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@ -87,39 +81,43 @@ local void free_index(struct access *index)
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}
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}
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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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/* Add an entry to the access point list. If out of memory, deallocate the
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existing list and return NULL. */
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existing list and return NULL. index->gzip is the allocated size of the
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local struct access *addpoint(struct access *index, int bits,
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index in point entries, until it is time for deflate_index_build() to
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off_t in, off_t out, unsigned left, unsigned char *window)
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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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{
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struct point *next;
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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 list is empty, create it (start with eight points) */
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if (index == NULL) {
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if (index == NULL) {
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index = malloc(sizeof(struct access));
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index = malloc(sizeof(struct deflate_index));
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if (index == NULL) return NULL;
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if (index == NULL) return NULL;
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index->list = malloc(sizeof(struct point) << 3);
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index->list = malloc(sizeof(struct point) << 3);
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if (index->list == NULL) {
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if (index->list == NULL) {
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free(index);
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free(index);
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return NULL;
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return NULL;
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}
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}
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index->size = 8;
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index->gzip = 8;
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index->have = 0;
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index->have = 0;
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}
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}
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/* if list is full, make it bigger */
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/* if list is full, make it bigger */
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else if (index->have == index->size) {
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else if (index->have == index->gzip) {
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index->size <<= 1;
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index->gzip <<= 1;
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next = realloc(index->list, sizeof(struct point) * index->size);
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next = realloc(index->list, sizeof(struct point) * index->gzip);
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if (next == NULL) {
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if (next == NULL) {
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free_index(index);
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deflate_index_free(index);
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return NULL;
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return NULL;
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}
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}
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index->list = next;
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index->list = next;
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}
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}
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/* fill in entry and increment how many we have */
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/* fill in entry and increment how many we have */
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next = index->list + index->have;
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next = (struct point *)(index->list) + index->have;
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next->bits = bits;
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next->bits = bits;
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next->in = in;
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next->in = in;
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next->out = out;
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next->out = out;
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@ -133,20 +131,14 @@ local struct access *addpoint(struct access *index, int bits,
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return index;
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return index;
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}
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}
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/* Make one entire pass through the compressed stream and build an index, with
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/* See comments in zran.h. */
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access points about every span bytes of uncompressed output -- span is
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int deflate_index_build(FILE *in, off_t span, struct deflate_index **built)
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chosen to balance the speed of random access against the memory requirements
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of the list, about 32K bytes per access point. Note that data after the end
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of the first zlib or gzip stream in the file is ignored. build_index()
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returns the number of access points on success (>= 1), Z_MEM_ERROR for out
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of memory, Z_DATA_ERROR for an error in the input file, or Z_ERRNO for a
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file read error. On success, *built points to the resulting index. */
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local int build_index(FILE *in, off_t span, struct access **built)
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{
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{
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int ret;
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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 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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off_t last; /* totout value of last access point */
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struct access *index; /* access points being generated */
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struct deflate_index *index; /* access points being generated */
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z_stream strm;
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z_stream strm;
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unsigned char input[CHUNK];
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unsigned char input[CHUNK];
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unsigned char window[WINSIZE];
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unsigned char window[WINSIZE];
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@ -163,7 +155,7 @@ local int build_index(FILE *in, off_t span, struct access **built)
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/* inflate the input, maintain a sliding window, and build an index -- this
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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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also validates the integrity of the compressed data using the check
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information at the end of the gzip or zlib stream */
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information in the gzip or zlib stream */
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totin = totout = last = 0;
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totin = totout = last = 0;
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index = NULL; /* will be allocated by first addpoint() */
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index = NULL; /* will be allocated by first addpoint() */
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strm.avail_out = 0;
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strm.avail_out = 0;
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@ -172,14 +164,19 @@ local int build_index(FILE *in, off_t span, struct access **built)
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strm.avail_in = fread(input, 1, CHUNK, in);
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strm.avail_in = fread(input, 1, CHUNK, in);
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if (ferror(in)) {
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if (ferror(in)) {
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ret = Z_ERRNO;
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ret = Z_ERRNO;
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goto build_index_error;
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goto deflate_index_build_error;
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}
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}
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if (strm.avail_in == 0) {
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if (strm.avail_in == 0) {
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ret = Z_DATA_ERROR;
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ret = Z_DATA_ERROR;
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goto build_index_error;
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goto deflate_index_build_error;
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}
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}
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strm.next_in = input;
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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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/* process all of that, or until end of stream */
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do {
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do {
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/* reset sliding window if necessary */
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/* reset sliding window if necessary */
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@ -198,9 +195,17 @@ local int build_index(FILE *in, off_t span, struct access **built)
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if (ret == Z_NEED_DICT)
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if (ret == Z_NEED_DICT)
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ret = Z_DATA_ERROR;
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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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if (ret == Z_MEM_ERROR || ret == Z_DATA_ERROR)
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goto build_index_error;
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goto deflate_index_build_error;
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if (ret == Z_STREAM_END)
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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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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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/* 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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data_type indicates an end-of-block, then all of the
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@ -217,7 +222,7 @@ local int build_index(FILE *in, off_t span, struct access **built)
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totout, strm.avail_out, window);
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totout, strm.avail_out, window);
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if (index == NULL) {
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if (index == NULL) {
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ret = Z_MEM_ERROR;
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ret = Z_MEM_ERROR;
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goto build_index_error;
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goto deflate_index_build_error;
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}
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}
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last = totout;
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last = totout;
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}
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}
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@ -227,27 +232,21 @@ local int build_index(FILE *in, off_t span, struct access **built)
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/* clean up and return index (release unused entries in list) */
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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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(void)inflateEnd(&strm);
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index->list = realloc(index->list, sizeof(struct point) * index->have);
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index->list = realloc(index->list, sizeof(struct point) * index->have);
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index->size = 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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*built = index;
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return index->size;
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return index->have;
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/* return error */
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/* return error */
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build_index_error:
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deflate_index_build_error:
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(void)inflateEnd(&strm);
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(void)inflateEnd(&strm);
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if (index != NULL)
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deflate_index_free(index);
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free_index(index);
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return ret;
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return ret;
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}
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}
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/* Use the index to read len bytes from offset into buf, return bytes read or
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/* See comments in zran.h. */
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negative for error (Z_DATA_ERROR or Z_MEM_ERROR). If data is requested past
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int deflate_index_extract(FILE *in, struct deflate_index *index, off_t offset,
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the end of the uncompressed data, then extract() will return a value less
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unsigned char *buf, int len)
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than len, indicating how much as actually read into buf. This function
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should not return a data error unless the file was modified since the index
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was generated. extract() may also return Z_ERRNO if there is an error on
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reading or seeking the input file. */
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local int extract(FILE *in, struct access *index, off_t offset,
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unsigned char *buf, int len)
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{
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{
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int ret, skip;
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int ret, skip;
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z_stream strm;
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z_stream strm;
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@ -276,12 +275,12 @@ local int extract(FILE *in, struct access *index, off_t offset,
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return ret;
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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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ret = fseeko(in, here->in - (here->bits ? 1 : 0), SEEK_SET);
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if (ret == -1)
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if (ret == -1)
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goto extract_ret;
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goto deflate_index_extract_ret;
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if (here->bits) {
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if (here->bits) {
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ret = getc(in);
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ret = getc(in);
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if (ret == -1) {
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if (ret == -1) {
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ret = ferror(in) ? Z_ERRNO : Z_DATA_ERROR;
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ret = ferror(in) ? Z_ERRNO : Z_DATA_ERROR;
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goto extract_ret;
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goto deflate_index_extract_ret;
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}
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}
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(void)inflatePrime(&strm, here->bits, ret >> (8 - here->bits));
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(void)inflatePrime(&strm, here->bits, ret >> (8 - here->bits));
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}
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}
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@ -293,21 +292,21 @@ local int extract(FILE *in, struct access *index, off_t offset,
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skip = 1; /* while skipping to offset */
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skip = 1; /* while skipping to offset */
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do {
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do {
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/* define where to put uncompressed data, and how much */
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/* define where to put uncompressed data, and how much */
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if (offset == 0 && 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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if (offset > WINSIZE) { /* skip WINSIZE bytes */
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if (offset > WINSIZE) { /* skip WINSIZE bytes */
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strm.avail_out = WINSIZE;
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strm.avail_out = WINSIZE;
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strm.next_out = discard;
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strm.next_out = discard;
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offset -= WINSIZE;
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offset -= WINSIZE;
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}
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}
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else if (offset != 0) { /* last skip */
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else if (offset > 0) { /* last skip */
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strm.avail_out = (unsigned)offset;
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strm.avail_out = (unsigned)offset;
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strm.next_out = discard;
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strm.next_out = discard;
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offset = 0;
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offset = 0;
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}
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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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/* uncompress until avail_out filled, or end of stream */
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do {
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do {
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@ -315,11 +314,11 @@ local int extract(FILE *in, struct access *index, off_t offset,
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strm.avail_in = fread(input, 1, CHUNK, in);
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strm.avail_in = fread(input, 1, CHUNK, in);
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if (ferror(in)) {
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if (ferror(in)) {
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ret = Z_ERRNO;
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ret = Z_ERRNO;
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goto extract_ret;
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goto deflate_index_extract_ret;
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}
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}
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if (strm.avail_in == 0) {
|
if (strm.avail_in == 0) {
|
||||||
ret = Z_DATA_ERROR;
|
ret = Z_DATA_ERROR;
|
||||||
goto extract_ret;
|
goto deflate_index_extract_ret;
|
||||||
}
|
}
|
||||||
strm.next_in = input;
|
strm.next_in = input;
|
||||||
}
|
}
|
||||||
@ -327,41 +326,99 @@ local int extract(FILE *in, struct access *index, off_t offset,
|
|||||||
if (ret == Z_NEED_DICT)
|
if (ret == Z_NEED_DICT)
|
||||||
ret = Z_DATA_ERROR;
|
ret = Z_DATA_ERROR;
|
||||||
if (ret == Z_MEM_ERROR || ret == Z_DATA_ERROR)
|
if (ret == Z_MEM_ERROR || ret == Z_DATA_ERROR)
|
||||||
goto extract_ret;
|
goto deflate_index_extract_ret;
|
||||||
if (ret == Z_STREAM_END)
|
if (ret == Z_STREAM_END) {
|
||||||
break;
|
/* 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);
|
} while (strm.avail_out != 0);
|
||||||
|
|
||||||
/* if reach end of stream, then don't keep trying to get more */
|
|
||||||
if (ret == Z_STREAM_END)
|
if (ret == Z_STREAM_END)
|
||||||
|
/* reached the end of the compressed data -- return the data that
|
||||||
|
was available, possibly less than requested */
|
||||||
break;
|
break;
|
||||||
|
|
||||||
/* do until offset reached and requested data read, or stream ends */
|
/* do until offset reached and requested data read */
|
||||||
} while (skip);
|
} while (skip);
|
||||||
|
|
||||||
/* compute number of uncompressed bytes read after offset */
|
/* compute the number of uncompressed bytes read after the offset */
|
||||||
ret = skip ? 0 : len - strm.avail_out;
|
ret = skip ? 0 : len - strm.avail_out;
|
||||||
|
|
||||||
/* clean up and return bytes read or error */
|
/* clean up and return the bytes read, or the negative error */
|
||||||
extract_ret:
|
deflate_index_extract_ret:
|
||||||
(void)inflateEnd(&strm);
|
(void)inflateEnd(&strm);
|
||||||
return ret;
|
return ret;
|
||||||
}
|
}
|
||||||
|
|
||||||
/* Demonstrate the use of build_index() and extract() by processing the file
|
#ifdef TEST
|
||||||
provided on the command line, and the extracting 16K from about 2/3rds of
|
|
||||||
the way through the uncompressed output, and writing that to stdout. */
|
#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 main(int argc, char **argv)
|
||||||
{
|
{
|
||||||
int len;
|
int len;
|
||||||
off_t offset;
|
off_t offset = -1;
|
||||||
FILE *in;
|
FILE *in;
|
||||||
struct access *index = NULL;
|
struct deflate_index *index = NULL;
|
||||||
unsigned char buf[CHUNK];
|
unsigned char buf[LEN];
|
||||||
|
|
||||||
/* open input file */
|
/* open input file */
|
||||||
if (argc != 2) {
|
if (argc < 2 || argc > 3) {
|
||||||
fprintf(stderr, "usage: zran file.gz\n");
|
fprintf(stderr, "usage: zran file.gz [offset]\n");
|
||||||
return 1;
|
return 1;
|
||||||
}
|
}
|
||||||
in = fopen(argv[1], "rb");
|
in = fopen(argv[1], "rb");
|
||||||
@ -370,8 +427,18 @@ int main(int argc, char **argv)
|
|||||||
return 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 */
|
/* build index */
|
||||||
len = build_index(in, SPAN, &index);
|
len = deflate_index_build(in, SPAN, &index);
|
||||||
if (len < 0) {
|
if (len < 0) {
|
||||||
fclose(in);
|
fclose(in);
|
||||||
switch (len) {
|
switch (len) {
|
||||||
@ -392,8 +459,9 @@ int main(int argc, char **argv)
|
|||||||
fprintf(stderr, "zran: built index with %d access points\n", len);
|
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 */
|
||||||
offset = (index->list[index->have - 1].out << 1) / 3;
|
if (offset == -1)
|
||||||
len = extract(in, index, offset, buf, CHUNK);
|
offset = (index->length << 1) / 3;
|
||||||
|
len = deflate_index_extract(in, index, offset, buf, LEN);
|
||||||
if (len < 0)
|
if (len < 0)
|
||||||
fprintf(stderr, "zran: extraction failed: %s error\n",
|
fprintf(stderr, "zran: extraction failed: %s error\n",
|
||||||
len == Z_MEM_ERROR ? "out of memory" : "input corrupted");
|
len == Z_MEM_ERROR ? "out of memory" : "input corrupted");
|
||||||
@ -403,7 +471,9 @@ int main(int argc, char **argv)
|
|||||||
}
|
}
|
||||||
|
|
||||||
/* clean up and exit */
|
/* clean up and exit */
|
||||||
free_index(index);
|
deflate_index_free(index);
|
||||||
fclose(in);
|
fclose(in);
|
||||||
return 0;
|
return 0;
|
||||||
}
|
}
|
||||||
|
|
||||||
|
#endif
|
||||||
|
40
examples/zran.h
Normal file
40
examples/zran.h
Normal file
@ -0,0 +1,40 @@
|
|||||||
|
/* zran.h -- 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 */
|
||||||
|
|
||||||
|
#include <stdio.h>
|
||||||
|
#include "zlib.h"
|
||||||
|
|
||||||
|
/* 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 */
|
||||||
|
};
|
||||||
|
|
||||||
|
/* 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. */
|
||||||
|
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 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);
|
Loading…
Reference in New Issue
Block a user