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