534 lines
21 KiB
C
534 lines
21 KiB
C
/* zran.c -- example of deflate stream indexing and random access
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* Copyright (C) 2005, 2012, 2018, 2023 Mark Adler
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* For conditions of distribution and use, see copyright notice in zlib.h
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* Version 1.4 13 Apr 2023 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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1.3 18 Feb 2023 Permit raw deflate streams as well as zlib and gzip
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Permit crossing gzip member boundaries when extracting
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Support a size_t size when extracting (was an int)
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Do a binary search over the index for an access point
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Expose the access point type to enable save and load
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1.4 13 Apr 2023 Add a NOPRIME define to not use inflatePrime()
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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 raw deflate
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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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//
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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() decompresses the
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// input raw deflate stream a block at a time, and at the end of each block
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// decides if enough uncompressed data has gone by to justify the creation of a
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// new access point. If so, that point is saved in a data structure that grows
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// as needed to accommodate the points.
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//
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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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// decompression then proceeds until the desired offset in the file is reached.
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// Then decompression continues to read the requested uncompressed data from
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// the file.
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//
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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. If small pieces of the file
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// are being accessed, it would make sense to implement a cache to hold some
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// lookahead to avoid many calls to deflate_index_extract() for small lengths.
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//
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// Another way to build an index would be to use inflateCopy(). That would not
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// be constrained to have access points at block boundaries, but would require
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// more memory per access point, and could not be saved to a 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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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <limits.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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// See comments in zran.h.
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void deflate_index_free(struct deflate_index *index) {
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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 access point to the list. If out of memory, deallocate the existing
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// list and return NULL. index->mode is temporarily the allocated number of
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// access points, until it is time for deflate_index_build() to return. Then
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// index->mode is set to the mode of inflation.
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static struct deflate_index *add_point(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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if (index == NULL) {
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// The list is empty. Create it, starting with eight access points.
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index = malloc(sizeof(struct deflate_index));
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if (index == NULL)
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return NULL;
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index->have = 0;
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index->mode = 8;
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index->list = malloc(sizeof(point_t) * index->mode);
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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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}
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else if (index->have == index->mode) {
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// The list is full. Make it bigger.
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index->mode <<= 1;
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point_t *next = realloc(index->list, sizeof(point_t) * index->mode);
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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 the access point and increment how many we have.
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point_t *next = (point_t *)(index->list) + index->have++;
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if (index->have < 0) {
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// Overflowed the int!
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deflate_index_free(index);
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return NULL;
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}
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next->out = out;
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next->in = in;
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next->bits = bits;
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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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// Return the index, which may have been newly allocated or destroyed.
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return index;
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}
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// Decompression modes. These are the inflateInit2() windowBits parameter.
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#define RAW -15
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#define ZLIB 15
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#define GZIP 31
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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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// Set up inflation state.
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z_stream strm = {0}; // inflate engine (gets fired up later)
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unsigned char buf[CHUNK]; // input buffer
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unsigned char win[WINSIZE] = {0}; // output sliding window
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off_t totin = 0; // total bytes read from input
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off_t totout = 0; // total bytes uncompressed
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int mode = 0; // mode: RAW, ZLIB, or GZIP (0 => not set yet)
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// Decompress from in, generating access points along the way.
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int ret; // the return value from zlib, or Z_ERRNO
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off_t last; // last access point uncompressed offset
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struct deflate_index *index = NULL; // list of access points
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do {
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// Assure available input, at least until reaching EOF.
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if (strm.avail_in == 0) {
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strm.avail_in = fread(buf, 1, sizeof(buf), in);
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totin += strm.avail_in;
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strm.next_in = buf;
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if (strm.avail_in < sizeof(buf) && ferror(in)) {
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ret = Z_ERRNO;
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break;
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}
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if (mode == 0) {
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// At the start of the input -- determine the type. Assume raw
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// if it is neither zlib nor gzip. This could in theory result
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// in a false positive for zlib, but in practice the fill bits
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// after a stored block are always zeros, so a raw stream won't
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// start with an 8 in the low nybble.
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mode = strm.avail_in == 0 ? RAW : // empty -- will fail
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(strm.next_in[0] & 0xf) == 8 ? ZLIB :
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strm.next_in[0] == 0x1f ? GZIP :
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/* else */ RAW;
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ret = inflateInit2(&strm, mode);
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if (ret != Z_OK)
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break;
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}
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}
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// Assure available output. This rotates the output through, for use as
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// a sliding window on the uncompressed data.
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if (strm.avail_out == 0) {
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strm.avail_out = sizeof(win);
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strm.next_out = win;
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}
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if (mode == RAW && index == NULL)
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// We skip the inflate() call at the start of raw deflate data in
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// order generate an access point there. Set data_type to imitate
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// the end of a header.
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strm.data_type = 0x80;
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else {
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// Inflate and update the number of uncompressed bytes.
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unsigned before = strm.avail_out;
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ret = inflate(&strm, Z_BLOCK);
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totout += before - strm.avail_out;
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}
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if ((strm.data_type & 0xc0) == 0x80 &&
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(index == NULL || totout - last >= span)) {
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// We are at the end of a header or a non-last deflate block, so we
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// can add an access point here. Furthermore, we are either at the
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// very start for the first access point, or there has been span or
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// more uncompressed bytes since the last access point, so we want
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// to add an access point here.
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index = add_point(index, strm.data_type & 7, totin - strm.avail_in,
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totout, strm.avail_out, win);
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if (index == NULL) {
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ret = Z_MEM_ERROR;
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break;
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}
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last = totout;
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}
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if (ret == Z_STREAM_END && mode == GZIP &&
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(strm.avail_in || ungetc(getc(in), in) != EOF))
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// There is more input after the end of a gzip member. Reset the
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// inflate state to read another gzip member. On success, this will
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// set ret to Z_OK to continue decompressing.
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ret = inflateReset2(&strm, GZIP);
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// Keep going until Z_STREAM_END or error. If the compressed data ends
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// prematurely without a file read error, Z_BUF_ERROR is returned.
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} while (ret == Z_OK);
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inflateEnd(&strm);
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if (ret != Z_STREAM_END) {
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// An error was encountered. Discard the index and return a negative
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// error code.
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deflate_index_free(index);
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return ret == Z_NEED_DICT ? Z_DATA_ERROR : ret;
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}
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// Shrink the index to only the occupied access points and return it.
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index->mode = mode;
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index->length = totout;
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point_t *list = realloc(index->list, sizeof(point_t) * index->have);
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if (list == NULL) {
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// Seems like a realloc() to make something smaller should always work,
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// but just in case.
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deflate_index_free(index);
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return Z_MEM_ERROR;
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}
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index->list = list;
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*built = index;
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return index->have;
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}
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#ifdef NOPRIME
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// Support zlib versions before 1.2.3 (July 2005), or incomplete zlib clones
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// that do not have inflatePrime().
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# define INFLATEPRIME inflatePreface
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// Append the low bits bits of value to in[] at bit position *have, updating
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// *have. value must be zero above its low bits bits. bits must be positive.
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// This assumes that any bits above the *have bits in the last byte are zeros.
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// That assumption is preserved on return, as any bits above *have + bits in
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// the last byte written will be set to zeros.
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static inline void append_bits(unsigned value, int bits,
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unsigned char *in, int *have) {
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in += *have >> 3; // where the first bits from value will go
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int k = *have & 7; // the number of bits already there
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*have += bits;
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if (k)
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*in |= value << k; // write value above the low k bits
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else
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*in = value;
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k = 8 - k; // the number of bits just appended
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while (bits > k) {
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value >>= k; // drop the bits appended
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bits -= k;
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k = 8; // now at a byte boundary
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*++in = value;
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}
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}
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// Insert enough bits in the form of empty deflate blocks in front of the the
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// low bits bits of value, in order to bring the sequence to a byte boundary.
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// Then feed that to inflate(). This does what inflatePrime() does, except that
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// a negative value of bits is not supported. bits must be in 0..16. If the
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// arguments are invalid, Z_STREAM_ERROR is returned. Otherwise the return
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// value from inflate() is returned.
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static int inflatePreface(z_stream *strm, int bits, int value) {
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// Check input.
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if (strm == Z_NULL || bits < 0 || bits > 16)
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return Z_STREAM_ERROR;
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if (bits == 0)
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return Z_OK;
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value &= (2 << (bits - 1)) - 1;
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// An empty dynamic block with an odd number of bits (95). The high bit of
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// the last byte is unused.
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static const unsigned char dyn[] = {
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4, 0xe0, 0x81, 8, 0, 0, 0, 0, 0x20, 0xa8, 0xab, 0x1f
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};
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const int dynlen = 95; // number of bits in the block
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// Build an input buffer for inflate that is a multiple of eight bits in
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// length, and that ends with the low bits bits of value.
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unsigned char in[(dynlen + 3 * 10 + 16 + 7) / 8];
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int have = 0;
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if (bits & 1) {
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// Insert an empty dynamic block to get to an odd number of bits, so
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// when bits bits from value are appended, we are at an even number of
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// bits.
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memcpy(in, dyn, sizeof(dyn));
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have = dynlen;
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}
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while ((have + bits) & 7)
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// Insert empty fixed blocks until appending bits bits would put us on
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// a byte boundary. This will insert at most three fixed blocks.
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append_bits(2, 10, in, &have);
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// Append the bits bits from value, which takes us to a byte boundary.
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append_bits(value, bits, in, &have);
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// Deliver the input to inflate(). There is no output space provided, but
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// inflate() can't get stuck waiting on output not ingesting all of the
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// provided input. The reason is that there will be at most 16 bits of
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// input from value after the empty deflate blocks (which themselves
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// generate no output). At least ten bits are needed to generate the first
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// output byte from a fixed block. The last two bytes of the buffer have to
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// be ingested in order to get ten bits, which is the most that value can
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// occupy.
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strm->avail_in = have >> 3;
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strm->next_in = in;
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strm->avail_out = 0;
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strm->next_out = in; // not used, but can't be NULL
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return inflate(strm, Z_NO_FLUSH);
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}
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#else
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# define INFLATEPRIME inflatePrime
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#endif
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// See comments in zran.h.
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ptrdiff_t deflate_index_extract(FILE *in, struct deflate_index *index,
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off_t offset, unsigned char *buf, size_t len) {
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// Do a quick sanity check on the index.
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if (index == NULL || index->have < 1 || index->list[0].out != 0)
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return Z_STREAM_ERROR;
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// If nothing to extract, return zero bytes extracted.
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if (len == 0 || offset < 0 || offset >= index->length)
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return 0;
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// Find the access point closest to but not after offset.
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int lo = -1, hi = index->have;
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point_t *point = index->list;
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while (hi - lo > 1) {
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int mid = (lo + hi) >> 1;
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if (offset < point[mid].out)
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hi = mid;
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else
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lo = mid;
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}
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point += lo;
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// Initialize the input file and prime the inflate engine to start there.
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int ret = fseeko(in, point->in - (point->bits ? 1 : 0), SEEK_SET);
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if (ret == -1)
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return Z_ERRNO;
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int ch = 0;
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if (point->bits && (ch = getc(in)) == EOF)
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return ferror(in) ? Z_ERRNO : Z_BUF_ERROR;
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z_stream strm = {0};
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ret = inflateInit2(&strm, RAW);
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if (ret != Z_OK)
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return ret;
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if (point->bits)
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INFLATEPRIME(&strm, point->bits, ch >> (8 - point->bits));
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inflateSetDictionary(&strm, point->window, WINSIZE);
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// Skip uncompressed bytes until offset reached, then satisfy request.
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unsigned char input[CHUNK];
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unsigned char discard[WINSIZE];
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offset -= point->out; // number of bytes to skip to get to offset
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size_t left = len; // number of bytes left to read after offset
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do {
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if (offset) {
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// Discard up to offset uncompressed bytes.
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strm.avail_out = offset < WINSIZE ? (unsigned)offset : WINSIZE;
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strm.next_out = discard;
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}
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else {
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// Uncompress up to left bytes into buf.
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strm.avail_out = left < UINT_MAX ? (unsigned)left : UINT_MAX;
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strm.next_out = buf + len - left;
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}
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// Uncompress, setting got to the number of bytes uncompressed.
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if (strm.avail_in == 0) {
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// Assure available input.
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strm.avail_in = fread(input, 1, CHUNK, in);
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if (strm.avail_in < CHUNK && ferror(in)) {
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ret = Z_ERRNO;
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break;
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}
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strm.next_in = input;
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}
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unsigned got = strm.avail_out;
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ret = inflate(&strm, Z_NO_FLUSH);
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got -= strm.avail_out;
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// Update the appropriate count.
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if (offset)
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offset -= got;
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else
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left -= got;
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// If we're at the end of a gzip member and there's more to read,
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// continue to the next gzip member.
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if (ret == Z_STREAM_END && index->mode == GZIP) {
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// Discard the gzip trailer.
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unsigned drop = 8; // length of gzip trailer
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if (strm.avail_in >= drop) {
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strm.avail_in -= drop;
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strm.next_in += drop;
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}
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else {
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// Read and discard the remainder of the gzip trailer.
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drop -= strm.avail_in;
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strm.avail_in = 0;
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do {
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if (getc(in) == EOF)
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// The input does not have a complete trailer.
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return ferror(in) ? Z_ERRNO : Z_BUF_ERROR;
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} while (--drop);
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}
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if (strm.avail_in || ungetc(getc(in), in) != EOF) {
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// There's more after the gzip trailer. Use inflate to skip the
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// gzip header and resume the raw inflate there.
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inflateReset2(&strm, GZIP);
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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 (strm.avail_in < CHUNK && ferror(in)) {
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ret = Z_ERRNO;
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break;
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}
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strm.next_in = input;
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}
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strm.avail_out = WINSIZE;
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strm.next_out = discard;
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ret = inflate(&strm, Z_BLOCK); // stop at end of header
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} while (ret == Z_OK && (strm.data_type & 0x80) == 0);
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if (ret != Z_OK)
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break;
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inflateReset2(&strm, RAW);
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}
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}
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// Continue until we have the requested data, the deflate data has
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// ended, or an error is encountered.
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} while (ret == Z_OK && left);
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inflateEnd(&strm);
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// Return the number of uncompressed bytes read into buf, or the error.
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return ret == Z_OK || ret == Z_STREAM_END ? len - left : 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
|
|
// data is extracted from there instead.
|
|
int main(int argc, char **argv) {
|
|
// Open the input file.
|
|
if (argc < 2 || argc > 3) {
|
|
fprintf(stderr, "usage: zran file.raw [offset]\n");
|
|
return 1;
|
|
}
|
|
FILE *in = fopen(argv[1], "rb");
|
|
if (in == NULL) {
|
|
fprintf(stderr, "zran: could not open %s for reading\n", argv[1]);
|
|
return 1;
|
|
}
|
|
|
|
// Get optional offset.
|
|
off_t offset = -1;
|
|
if (argc == 3) {
|
|
char *end;
|
|
offset = strtoll(argv[2], &end, 10);
|
|
if (*end || offset < 0) {
|
|
fprintf(stderr, "zran: %s is not a valid offset\n", argv[2]);
|
|
return 1;
|
|
}
|
|
}
|
|
|
|
// Build index.
|
|
struct deflate_index *index = NULL;
|
|
int len = deflate_index_build(in, SPAN, &index);
|
|
if (len < 0) {
|
|
fclose(in);
|
|
switch (len) {
|
|
case Z_MEM_ERROR:
|
|
fprintf(stderr, "zran: out of memory\n");
|
|
break;
|
|
case Z_BUF_ERROR:
|
|
fprintf(stderr, "zran: %s ended prematurely\n", argv[1]);
|
|
break;
|
|
case Z_DATA_ERROR:
|
|
fprintf(stderr, "zran: compressed data error in %s\n", argv[1]);
|
|
break;
|
|
case Z_ERRNO:
|
|
fprintf(stderr, "zran: read error on %s\n", argv[1]);
|
|
break;
|
|
default:
|
|
fprintf(stderr, "zran: error %d while building index\n", len);
|
|
}
|
|
return 1;
|
|
}
|
|
fprintf(stderr, "zran: built index with %d access points\n", len);
|
|
|
|
// Use index by reading some bytes from an arbitrary offset.
|
|
unsigned char buf[LEN];
|
|
if (offset == -1)
|
|
offset = ((index->length + 1) << 1) / 3;
|
|
ptrdiff_t got = deflate_index_extract(in, index, offset, buf, LEN);
|
|
if (got < 0)
|
|
fprintf(stderr, "zran: extraction failed: %s error\n",
|
|
got == Z_MEM_ERROR ? "out of memory" : "input corrupted");
|
|
else {
|
|
fwrite(buf, 1, got, stdout);
|
|
fprintf(stderr, "zran: extracted %ld bytes at %lld\n", got, offset);
|
|
}
|
|
|
|
// Clean up and exit.
|
|
deflate_index_free(index);
|
|
fclose(in);
|
|
return 0;
|
|
}
|
|
|
|
#endif
|