Rewrite of zran in examples. See version history in zran.c.
diff --git a/examples/zran.c b/examples/zran.c
index 879c47c..1ffba7f 100644
--- a/examples/zran.c
+++ b/examples/zran.c
@@ -1,114 +1,101 @@
-/* zran.c -- example of zlib/gzip stream indexing and random access
- * Copyright (C) 2005, 2012, 2018 Mark Adler
+/* zran.c -- example of deflate stream indexing and random access
+ * Copyright (C) 2005, 2012, 2018, 2023 Mark Adler
* For conditions of distribution and use, see copyright notice in zlib.h
- * Version 1.2 14 Oct 2018 Mark Adler */
+ * Version 1.3 18 Feb 2023 Mark Adler */
/* Version History:
1.0 29 May 2005 First version
1.1 29 Sep 2012 Fix memory reallocation error
1.2 14 Oct 2018 Handle gzip streams with multiple members
Add a header file to facilitate usage in applications
+ 1.3 18 Feb 2023 Permit raw deflate streams as well as zlib and gzip
+ Permit crossing gzip member boundaries when extracting
+ Support a size_t size when extracting (was an int)
+ Do a binary search over the index for an access point
+ Expose the access point type to enable save and load
*/
-/* Illustrate the use of Z_BLOCK, inflatePrime(), and inflateSetDictionary()
- for random access of a compressed file. A file containing a 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 reference for locating a desired starting
- point in the uncompressed stream. deflate_index_build() 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 access point at or preceding that offset is located in the index.
- The input file is positioned to the specified location in the index, and if
- necessary the first few bits of the compressed data is read from the file.
- inflate is initialized with those bits and the 32K of uncompressed data, and
- 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 deflate_index_extract() for small
- lengths.
-
- Another way to build an index would be to use inflateCopy(). That would
- not be constrained to have access points at block boundaries, but 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.
- */
+// Illustrate the use of Z_BLOCK, inflatePrime(), and inflateSetDictionary()
+// for random access of a compressed file. A file containing a raw deflate
+// stream is provided on the command line. The compressed stream is decoded in
+// its entirety, and an index built with access points about every SPAN bytes
+// in the uncompressed output. The compressed file is left open, and can then
+// be read randomly, having to decompress on the average SPAN/2 uncompressed
+// bytes before getting to the desired block of data.
+//
+// An access point can be created at the start of any deflate block, by saving
+// the starting file offset and bit of that block, and the 32K bytes of
+// uncompressed data that precede that block. Also the uncompressed offset of
+// that block is saved to provide a reference for locating a desired starting
+// point in the uncompressed stream. deflate_index_build() decompresses the
+// input raw deflate stream a block at a time, and at the end of each block
+// decides if enough uncompressed data has gone by to justify the creation of a
+// new access point. If so, that point is saved in a data structure that grows
+// as needed to accommodate the points.
+//
+// To use the index, an offset in the uncompressed data is provided, for which
+// the latest access point at or preceding that offset is located in the index.
+// The input file is positioned to the specified location in the index, and if
+// necessary the first few bits of the compressed data is read from the file.
+// inflate is initialized with those bits and the 32K of uncompressed data, and
+// decompression then proceeds until the desired offset in the file is reached.
+// Then decompression continues to read the requested uncompressed data from
+// the file.
+//
+// There is some fair bit of overhead to starting inflation for the random
+// access, mainly copying the 32K byte dictionary. If small pieces of the file
+// are being accessed, it would make sense to implement a cache to hold some
+// lookahead to avoid many calls to deflate_index_extract() for small lengths.
+//
+// Another way to build an index would be to use inflateCopy(). That would not
+// be constrained to have access points at block boundaries, but would require
+// more memory per access point, and could not be saved to a file due to the
+// use of pointers in the state. The approach here allows for storage of the
+// index in a file.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
+#include <limits.h>
#include "zlib.h"
#include "zran.h"
-#define WINSIZE 32768U /* sliding window size */
-#define CHUNK 16384 /* file input buffer size */
+#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 */
-};
-
-/* See comments in zran.h. */
-void deflate_index_free(struct deflate_index *index)
-{
+// See comments in zran.h.
+void deflate_index_free(struct deflate_index *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. index->gzip is the allocated size of the
- index in point entries, until it is time for deflate_index_build() to
- return, at which point gzip is set to indicate a gzip file or not.
- */
-static struct deflate_index *addpoint(struct deflate_index *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) */
+// Add an access point to the list. If out of memory, deallocate the existing
+// list and return NULL. index->mode is temporarily the allocated number of
+// access points, until it is time for deflate_index_build() to return. Then
+// index->mode is set to the mode of inflation.
+static struct deflate_index *add_point(struct deflate_index *index, int bits,
+ off_t in, off_t out, unsigned left,
+ unsigned char *window) {
if (index == NULL) {
+ // The list is empty. Create it, starting with eight access points.
index = malloc(sizeof(struct deflate_index));
- if (index == NULL) return NULL;
- index->list = malloc(sizeof(struct point) << 3);
+ if (index == NULL)
+ return NULL;
+ index->have = 0;
+ index->mode = 8;
+ index->list = malloc(sizeof(point_t) * index->mode);
if (index->list == NULL) {
free(index);
return NULL;
}
- index->gzip = 8;
- index->have = 0;
}
- /* if list is full, make it bigger */
- else if (index->have == index->gzip) {
- index->gzip <<= 1;
- next = realloc(index->list, sizeof(struct point) * index->gzip);
+ else if (index->have == index->mode) {
+ // The list is full. Make it bigger.
+ index->mode <<= 1;
+ point_t *next = realloc(index->list, sizeof(point_t) * index->mode);
if (next == NULL) {
deflate_index_free(index);
return NULL;
@@ -116,318 +103,291 @@
index->list = next;
}
- /* fill in entry and increment how many we have */
- next = (struct point *)(index->list) + index->have;
- next->bits = bits;
- next->in = in;
+ // Fill in the access point and increment how many we have.
+ point_t *next = (point_t *)(index->list) + index->have++;
+ if (index->have < 0) {
+ // Overflowed the int!
+ deflate_index_free(index);
+ return NULL;
+ }
next->out = out;
+ next->in = in;
+ next->bits = bits;
if (left)
memcpy(next->window, window + WINSIZE - left, left);
if (left < WINSIZE)
memcpy(next->window + left, window, WINSIZE - left);
- index->have++;
- /* return list, possibly reallocated */
+ // Return the index, which may have been newly allocated or destroyed.
return index;
}
-/* See comments in zran.h. */
-int deflate_index_build(FILE *in, off_t span, struct deflate_index **built)
-{
- int ret;
- int gzip = 0; /* true if reading a gzip file */
- off_t totin, totout; /* our own total counters to avoid 4GB limit */
- off_t last; /* totout value of last access point */
- struct deflate_index *index; /* access points being generated */
- z_stream strm;
- unsigned char input[CHUNK];
- unsigned char window[WINSIZE];
+// Decompression modes. These are the inflateInit2() windowBits parameter.
+#define RAW -15
+#define ZLIB 15
+#define GZIP 31
- /* 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;
+// See comments in zran.h.
+int deflate_index_build(FILE *in, off_t span, struct deflate_index **built) {
+ // Set up inflation state.
+ z_stream strm = {0}; // inflate engine (gets fired up later)
+ unsigned char buf[CHUNK]; // input buffer
+ unsigned char win[WINSIZE] = {0}; // output sliding window
+ off_t totin = 0; // total bytes read from input
+ off_t totout = 0; // total bytes uncompressed
+ int mode = 0; // mode: RAW, ZLIB, or GZIP (0 => not set yet)
- /* inflate the input, maintain a sliding window, and build an index -- this
- also validates the integrity of the compressed data using the check
- information in the gzip or zlib stream */
- totin = totout = last = 0;
- index = NULL; /* will be allocated by first addpoint() */
- strm.avail_out = 0;
+ // Decompress from in, generating access points along the way.
+ int ret; // the return value from zlib, or Z_ERRNO
+ off_t last; // last access point uncompressed offset
+ struct deflate_index *index = NULL; // list of access points
do {
- /* get some compressed data from input file */
- strm.avail_in = fread(input, 1, CHUNK, in);
- if (ferror(in)) {
- ret = Z_ERRNO;
- goto deflate_index_build_error;
- }
+ // Assure available input, at least until reaching EOF.
if (strm.avail_in == 0) {
- ret = Z_DATA_ERROR;
- goto deflate_index_build_error;
- }
- strm.next_in = input;
-
- /* check for a gzip stream */
- if (totin == 0 && strm.avail_in >= 3 &&
- input[0] == 31 && input[1] == 139 && input[2] == 8)
- gzip = 1;
-
- /* 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 */
+ strm.avail_in = fread(buf, 1, sizeof(buf), in);
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 deflate_index_build_error;
- if (ret == Z_STREAM_END) {
- if (gzip &&
- (strm.avail_in || ungetc(getc(in), in) != EOF)) {
- ret = inflateReset(&strm);
- if (ret != Z_OK)
- goto deflate_index_build_error;
- continue;
- }
+ strm.next_in = buf;
+ if (strm.avail_in < sizeof(buf) && ferror(in)) {
+ ret = Z_ERRNO;
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 deflate_index_build_error;
- }
- last = totout;
+ if (mode == 0) {
+ // At the start of the input -- determine the type. Assume raw
+ // if it is neither zlib nor gzip. This could in theory result
+ // in a false positive for zlib, but in practice the fill bits
+ // after a stored block are always zeros, so a raw stream won't
+ // start with an 8 in the low nybble.
+ mode = strm.avail_in == 0 ? RAW : // empty -- will fail
+ (strm.next_in[0] & 0xf) == 8 ? ZLIB :
+ strm.next_in[0] == 0x1f ? GZIP :
+ /* else */ RAW;
+ ret = inflateInit2(&strm, mode);
+ if (ret != Z_OK)
+ break;
}
- } 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->gzip = gzip;
+ // Assure available output. This rotates the output through, for use as
+ // a sliding window on the uncompressed data.
+ if (strm.avail_out == 0) {
+ strm.avail_out = sizeof(win);
+ strm.next_out = win;
+ }
+
+ if (mode == RAW && index == NULL)
+ // We skip the inflate() call at the start of raw deflate data in
+ // order generate an access point there. Set data_type to imitate
+ // the end of a header.
+ strm.data_type = 0x80;
+ else {
+ // Inflate and update the number of uncompressed bytes.
+ unsigned before = strm.avail_out;
+ ret = inflate(&strm, Z_BLOCK);
+ totout += before - strm.avail_out;
+ }
+
+ if ((strm.data_type & 0xc0) == 0x80 &&
+ (index == NULL || totout - last >= span)) {
+ // We are at the end of a header or a non-last deflate block, so we
+ // can add an access point here. Furthermore, we are either at the
+ // very start for the first access point, or there has been span or
+ // more uncompressed bytes since the last access point, so we want
+ // to add an access point here.
+ index = add_point(index, strm.data_type & 7, totin - strm.avail_in,
+ totout, strm.avail_out, win);
+ if (index == NULL) {
+ ret = Z_MEM_ERROR;
+ break;
+ }
+ last = totout;
+ }
+
+ if (ret == Z_STREAM_END && mode == GZIP &&
+ (strm.avail_in || ungetc(getc(in), in) != EOF))
+ // There is more input after the end of a gzip member. Reset the
+ // inflate state to read another gzip member. On success, this will
+ // set ret to Z_OK to continue decompressing.
+ ret = inflateReset2(&strm, GZIP);
+
+ // Keep going until Z_STREAM_END or error. If the compressed data ends
+ // prematurely without a file read error, Z_BUF_ERROR is returned.
+ } while (ret == Z_OK);
+ inflateEnd(&strm);
+
+ if (ret != Z_STREAM_END) {
+ // An error was encountered. Discard the index and return a negative
+ // error code.
+ deflate_index_free(index);
+ return ret == Z_NEED_DICT ? Z_DATA_ERROR : ret;
+ }
+
+ // Shrink the index to only the occupied access points and return it.
+ index->mode = mode;
index->length = totout;
+ point_t *list = realloc(index->list, sizeof(point_t) * index->have);
+ if (list == NULL) {
+ // Seems like a realloc() to make something smaller should always work,
+ // but just in case.
+ deflate_index_free(index);
+ return Z_MEM_ERROR;
+ }
+ index->list = list;
*built = index;
return index->have;
-
- /* return error */
- deflate_index_build_error:
- (void)inflateEnd(&strm);
- deflate_index_free(index);
- return ret;
}
-/* See comments in zran.h. */
-int deflate_index_extract(FILE *in, struct deflate_index *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];
+// See comments in zran.h.
+ptrdiff_t deflate_index_extract(FILE *in, struct deflate_index *index,
+ off_t offset, unsigned char *buf, size_t len) {
+ // Do a quick sanity check on the index.
+ if (index == NULL || index->have < 1 || index->list[0].out != 0)
+ return Z_STREAM_ERROR;
- /* proceed only if something reasonable to do */
- if (len < 0)
+ // If nothing to extract, return zero bytes extracted.
+ if (len == 0 || offset < 0 || offset >= index->length)
return 0;
- /* find where in stream to start */
- here = index->list;
- ret = index->have;
- while (--ret && here[1].out <= offset)
- here++;
+ // Find the access point closest to but not after offset.
+ int lo = -1, hi = index->have;
+ point_t *point = index->list;
+ while (hi - lo > 1) {
+ int mid = (lo + hi) >> 1;
+ if (offset < point[mid].out)
+ hi = mid;
+ else
+ lo = mid;
+ }
+ point += lo;
- /* initialize 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 */
+ // Initialize the input file and prime the inflate engine to start there.
+ int ret = fseeko(in, point->in - (point->bits ? 1 : 0), SEEK_SET);
+ if (ret == -1)
+ return Z_ERRNO;
+ int ch = 0;
+ if (point->bits && (ch = getc(in)) == EOF)
+ return ferror(in) ? Z_ERRNO : Z_BUF_ERROR;
+ z_stream strm = {0};
+ ret = inflateInit2(&strm, RAW);
if (ret != Z_OK)
return ret;
- ret = fseeko(in, here->in - (here->bits ? 1 : 0), SEEK_SET);
- if (ret == -1)
- goto deflate_index_extract_ret;
- if (here->bits) {
- ret = getc(in);
- if (ret == -1) {
- ret = ferror(in) ? Z_ERRNO : Z_DATA_ERROR;
- goto deflate_index_extract_ret;
- }
- (void)inflatePrime(&strm, here->bits, ret >> (8 - here->bits));
- }
- (void)inflateSetDictionary(&strm, here->window, WINSIZE);
+ if (point->bits)
+ inflatePrime(&strm, point->bits, ch >> (8 - point->bits));
+ inflateSetDictionary(&strm, point->window, WINSIZE);
- /* skip uncompressed bytes until offset reached, then satisfy request */
- offset -= here->out;
- strm.avail_in = 0;
- skip = 1; /* while skipping to offset */
+ // Skip uncompressed bytes until offset reached, then satisfy request.
+ unsigned char input[CHUNK];
+ unsigned char discard[WINSIZE];
+ offset -= point->out; // number of bytes to skip to get to offset
+ size_t left = len; // number of bytes left to read after offset
do {
- /* define where to put uncompressed data, and how much */
- if (offset > WINSIZE) { /* skip WINSIZE bytes */
- strm.avail_out = WINSIZE;
+ if (offset) {
+ // Discard up to offset uncompressed bytes.
+ strm.avail_out = offset < WINSIZE ? (unsigned)offset : WINSIZE;
strm.next_out = discard;
- offset -= WINSIZE;
}
- else if (offset > 0) { /* last skip */
- strm.avail_out = (unsigned)offset;
- strm.next_out = discard;
- offset = 0;
- }
- else if (skip) { /* at offset now */
- strm.avail_out = len;
- strm.next_out = buf;
- skip = 0; /* only do this once */
+ else {
+ // Uncompress up to left bytes into buf.
+ strm.avail_out = left < UINT_MAX ? (unsigned)left : UINT_MAX;
+ strm.next_out = buf + len - left;
}
- /* uncompress 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 deflate_index_extract_ret;
- }
- if (strm.avail_in == 0) {
- ret = Z_DATA_ERROR;
- goto deflate_index_extract_ret;
- }
- strm.next_in = input;
+ // Uncompress, setting got to the number of bytes uncompressed.
+ if (strm.avail_in == 0) {
+ // Assure available input.
+ strm.avail_in = fread(input, 1, CHUNK, in);
+ if (strm.avail_in < CHUNK && ferror(in)) {
+ ret = Z_ERRNO;
+ break;
}
- 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 deflate_index_extract_ret;
- if (ret == Z_STREAM_END) {
- /* the raw deflate stream has ended */
- if (index->gzip == 0)
- /* this is a zlib stream that has ended -- done */
- break;
+ strm.next_in = input;
+ }
+ unsigned got = strm.avail_out;
+ ret = inflate(&strm, Z_NO_FLUSH);
+ got -= strm.avail_out;
- /* 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;
+ // Update the appropriate count.
+ if (offset)
+ offset -= got;
+ else
+ left -= got;
- /* 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;
+ // If we're at the end of a gzip member and there's more to read,
+ // continue to the next gzip member.
+ if (ret == Z_STREAM_END && index->mode == GZIP) {
+ // Discard the gzip trailer.
+ unsigned drop = 8; // length of gzip trailer
+ if (strm.avail_in >= drop) {
+ strm.avail_in -= drop;
+ strm.next_in += drop;
+ }
+ else {
+ // Read and discard the remainder of the gzip trailer.
+ drop -= strm.avail_in;
+ strm.avail_in = 0;
+ do {
+ if (getc(in) == EOF)
+ // The input does not have a complete trailer.
+ return ferror(in) ? Z_ERRNO : Z_BUF_ERROR;
+ } while (--drop);
+ }
+
+ if (strm.avail_in || ungetc(getc(in), in) != EOF) {
+ // There's more after the gzip trailer. Use inflate to skip the
+ // gzip header and resume the raw inflate there.
+ inflateReset2(&strm, GZIP);
do {
if (strm.avail_in == 0) {
strm.avail_in = fread(input, 1, CHUNK, in);
- if (ferror(in)) {
+ if (strm.avail_in < CHUNK && ferror(in)) {
ret = Z_ERRNO;
- goto deflate_index_extract_ret;
- }
- if (strm.avail_in == 0) {
- ret = Z_DATA_ERROR;
- goto deflate_index_extract_ret;
+ break;
}
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);
+ strm.avail_out = WINSIZE;
+ strm.next_out = discard;
+ ret = inflate(&strm, Z_BLOCK); // stop at end of header
+ } while (ret == Z_OK && (strm.data_type & 0x80) == 0);
if (ret != Z_OK)
- goto deflate_index_extract_ret;
+ break;
+ inflateReset2(&strm, RAW);
}
+ }
- /* continue to process the available input before reading more */
- } while (strm.avail_out != 0);
+ // Continue until we have the requested data, the deflate data has
+ // ended, or an error is encountered.
+ } while (ret == Z_OK && left);
+ inflateEnd(&strm);
- if (ret == Z_STREAM_END)
- /* reached the end of the compressed data -- return the data that
- was available, possibly less than requested */
- break;
-
- /* do until offset reached and requested data read */
- } while (skip);
-
- /* compute the number of uncompressed bytes read after the offset */
- ret = skip ? 0 : len - strm.avail_out;
-
- /* clean up and return the bytes read, or the negative error */
- deflate_index_extract_ret:
- (void)inflateEnd(&strm);
- return ret;
+ // Return the number of uncompressed bytes read into buf, or the error.
+ return ret == Z_OK || ret == Z_STREAM_END ? len - left : ret;
}
#ifdef TEST
-#define SPAN 1048576L /* desired distance between access points */
-#define LEN 16384 /* number of bytes to extract */
+#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 len;
- off_t offset = -1;
- FILE *in;
- struct deflate_index *index = NULL;
- unsigned char buf[LEN];
-
- /* open input file */
+// Demonstrate the use of deflate_index_build() and deflate_index_extract() by
+// processing the file provided on the command line, and extracting LEN bytes
+// from 2/3rds of the way through the uncompressed output, writing that to
+// stdout. An offset can be provided as the second argument, in which case the
+// data is extracted from there instead.
+int main(int argc, char **argv) {
+ // Open the input file.
if (argc < 2 || argc > 3) {
- fprintf(stderr, "usage: zran file.gz [offset]\n");
+ fprintf(stderr, "usage: zran file.raw [offset]\n");
return 1;
}
- in = fopen(argv[1], "rb");
+ 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 */
+ // Get optional offset.
+ off_t offset = -1;
if (argc == 3) {
char *end;
offset = strtoll(argv[2], &end, 10);
@@ -437,14 +397,18 @@
}
}
- /* build index */
- len = deflate_index_build(in, SPAN, &index);
+ // 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;
@@ -458,19 +422,20 @@
}
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.
+ unsigned char buf[LEN];
if (offset == -1)
- offset = (index->length << 1) / 3;
- len = deflate_index_extract(in, index, offset, buf, LEN);
- if (len < 0)
+ 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",
- len == Z_MEM_ERROR ? "out of memory" : "input corrupted");
+ got == 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);
+ fwrite(buf, 1, got, stdout);
+ fprintf(stderr, "zran: extracted %ld bytes at %lld\n", got, offset);
}
- /* clean up and exit */
+ // Clean up and exit.
deflate_index_free(index);
fclose(in);
return 0;
diff --git a/examples/zran.h b/examples/zran.h
index 2314125..ebf780d 100644
--- a/examples/zran.h
+++ b/examples/zran.h
@@ -1,40 +1,51 @@
-/* zran.h -- example of zlib/gzip stream indexing and random access
- * Copyright (C) 2005, 2012, 2018 Mark Adler
+/* zran.h -- example of deflated stream indexing and random access
+ * Copyright (C) 2005, 2012, 2018, 2023 Mark Adler
* For conditions of distribution and use, see copyright notice in zlib.h
- * Version 1.2 14 Oct 2018 Mark Adler */
+ * Version 1.3 18 Feb 2023 Mark Adler */
#include <stdio.h>
#include "zlib.h"
-/* Access point list. */
+// Access point.
+typedef struct point {
+ off_t out; // offset in uncompressed data
+ off_t in; // offset in compressed file of first full byte
+ int bits; // 0, or number of bits (1-7) from byte at in-1
+ unsigned char window[32768]; // preceding 32K of uncompressed data
+} point_t;
+
+// 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 */
+ int have; // number of access points in list
+ int mode; // -15 for raw, 15 for zlib, or 31 for gzip
+ off_t length; // total length of uncompressed data
+ point_t *list; // allocated list of access points
};
-/* 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. */
+// Make one pass through a zlib, gzip, or raw deflate compressed stream and
+// build an index, with access points about every span bytes of uncompressed
+// output. gzip files with multiple members are fully indexed. span should be
+// chosen to balance the speed of random access against the memory requirements
+// of the list, which is 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_BUF_ERROR for a premature end of input, Z_DATA_ERROR for a format
+// or verification 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 the number of
+// bytes read or a negative error code. 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. If given a valid
+// index, this function should not return an error unless the file was modified
+// somehow since the index was generated, given that deflate_index_build() had
+// validated all of the input. If nevertheless there is a failure, Z_BUF_ERROR
+// is returned if the compressed data ends prematurely, Z_DATA_ERROR if the
+// deflate compressed data is not valid, Z_MEM_ERROR if out of memory,
+// Z_STREAM_ERROR if the index is not valid, or Z_ERRNO if there is an error
+// reading or seeking on the input file.
+ptrdiff_t deflate_index_extract(FILE *in, struct deflate_index *index,
+ off_t offset, unsigned char *buf, size_t len);
-/* 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);
+// Deallocate an index built by deflate_index_build().
+void deflate_index_free(struct deflate_index *index);
