code:
/* example.c -- usage example of the zlib compression library
 * Copyright (C) 1995-2004 Jean-loup Gailly.
 * For conditions of distribution and use, see copyright notice in zlib.h
 */

/* @(#) $Id$ */

#include <stdio.h>
#include "zlib.h"

#ifdef STDC
#  include <string.h>
#  include <stdlib.h>
#endif

#if defined(VMS) || defined(RISCOS)
#  define TESTFILE "foo-gz"
#else
#  define TESTFILE "foo.gz"
#endif

#define CHECK_ERR(err, msg) { \
    if (err != Z_OK) { \
        fprintf(stderr, "%s error: %d\n", msg, err); \
        exit(1); \
    } \
}

const char hello[] = "hello, hello!";
/* "hello world" would be more standard, but the repeated "hello"
 * stresses the compression code better, sorry...
 */

const char dictionary[] = "hello";
uLong dictId; /* Adler32 value of the dictionary */

void test_compress      OF((Byte *compr, uLong comprLen,
                            Byte *uncompr, uLong uncomprLen));
void test_gzio          OF((const char *fname,
                            Byte *uncompr, uLong uncomprLen));
void test_deflate       OF((Byte *compr, uLong comprLen));
void test_inflate       OF((Byte *compr, uLong comprLen,
                            Byte *uncompr, uLong uncomprLen));
void test_large_deflate OF((Byte *compr, uLong comprLen,
                            Byte *uncompr, uLong uncomprLen));
void test_large_inflate OF((Byte *compr, uLong comprLen,
                            Byte *uncompr, uLong uncomprLen));
void test_flush         OF((Byte *compr, uLong *comprLen));
void test_sync          OF((Byte *compr, uLong comprLen,
                            Byte *uncompr, uLong uncomprLen));
void test_dict_deflate  OF((Byte *compr, uLong comprLen));
void test_dict_inflate  OF((Byte *compr, uLong comprLen,
                            Byte *uncompr, uLong uncomprLen));
int  main               OF((int argc, char *argv[]));

/* ===========================================================================
 * Test compress() and uncompress()
 */
void test_compress(compr, comprLen, uncompr, uncomprLen)
    Byte *compr, *uncompr;
    uLong comprLen, uncomprLen;
{
    int err;
    uLong len = (uLong)strlen(hello)+1;

    err = compress(compr, &comprLen, (const Bytef*)hello, len);
    CHECK_ERR(err, "compress");

    strcpy((char*)uncompr, "garbage");

    err = uncompress(uncompr, &uncomprLen, compr, comprLen);
    CHECK_ERR(err, "uncompress");

    if (strcmp((char*)uncompr, hello)) {
        fprintf(stderr, "bad uncompress\n");
        exit(1);
    } else {
        printf("uncompress(): %s\n", (char *)uncompr);
    }
}

/* ===========================================================================
 * Test read/write of .gz files
 */
void test_gzio(fname, uncompr, uncomprLen)
    const char *fname; /* compressed file name */
    Byte *uncompr;
    uLong uncomprLen;
{
#ifdef NO_GZCOMPRESS
    fprintf(stderr, "NO_GZCOMPRESS -- gz* functions cannot compress\n");
#else
    int err;
    int len = (int)strlen(hello)+1;
    gzFile file;
    z_off_t pos;

    file = gzopen(fname, "wb");
    if (file == NULL) {
        fprintf(stderr, "gzopen error\n");
        exit(1);
    }
    gzputc(file, 'h');
    if (gzputs(file, "ello") != 4) {
        fprintf(stderr, "gzputs err: %s\n", gzerror(file, &err));
        exit(1);
    }
    if (gzprintf(file, ", %s!", "hello") != 8) {
        fprintf(stderr, "gzprintf err: %s\n", gzerror(file, &err));
        exit(1);
    }
    gzseek(file, 1L, SEEK_CUR); /* add one zero byte */
    gzclose(file);

    file = gzopen(fname, "rb");
    if (file == NULL) {
        fprintf(stderr, "gzopen error\n");
        exit(1);
    }
    strcpy((char*)uncompr, "garbage");

    if (gzread(file, uncompr, (unsigned)uncomprLen) != len) {
        fprintf(stderr, "gzread err: %s\n", gzerror(file, &err));
        exit(1);
    }
    if (strcmp((char*)uncompr, hello)) {
        fprintf(stderr, "bad gzread: %s\n", (char*)uncompr);
        exit(1);
    } else {
        printf("gzread(): %s\n", (char*)uncompr);
    }

    pos = gzseek(file, -8L, SEEK_CUR);
    if (pos != 6 || gztell(file) != pos) {
        fprintf(stderr, "gzseek error, pos=%ld, gztell=%ld\n",
                (long)pos, (long)gztell(file));
        exit(1);
    }

    if (gzgetc(file) != ' ') {
        fprintf(stderr, "gzgetc error\n");
        exit(1);
    }

    if (gzungetc(' ', file) != ' ') {
        fprintf(stderr, "gzungetc error\n");
        exit(1);
    }

    gzgets(file, (char*)uncompr, (int)uncomprLen);
    if (strlen((char*)uncompr) != 7) { /* " hello!" */
        fprintf(stderr, "gzgets err after gzseek: %s\n", gzerror(file, &err));
        exit(1);
    }
    if (strcmp((char*)uncompr, hello + 6)) {
        fprintf(stderr, "bad gzgets after gzseek\n");
        exit(1);
    } else {
        printf("gzgets() after gzseek: %s\n", (char*)uncompr);
    }

    gzclose(file);
#endif
}

/* ===========================================================================
 * Test deflate() with small buffers
 */
void test_deflate(compr, comprLen)
    Byte *compr;
    uLong comprLen;
{
    z_stream c_stream; /* compression stream */
    int err;
    uLong len = (uLong)strlen(hello)+1;

    c_stream.zalloc = (alloc_func)0;
    c_stream.zfree = (free_func)0;
    c_stream.opaque = (voidpf)0;

    err = deflateInit(&c_stream, Z_DEFAULT_COMPRESSION);
    CHECK_ERR(err, "deflateInit");

    c_stream.next_in  = (Bytef*)hello;
    c_stream.next_out = compr;

    while (c_stream.total_in != len && c_stream.total_out < comprLen) {
        c_stream.avail_in = c_stream.avail_out = 1; /* force small buffers */
        err = deflate(&c_stream, Z_NO_FLUSH);
        CHECK_ERR(err, "deflate");
    }
    /* Finish the stream, still forcing small buffers: */
    for (;;) {
        c_stream.avail_out = 1;
        err = deflate(&c_stream, Z_FINISH);
        if (err == Z_STREAM_END) break;
        CHECK_ERR(err, "deflate");
    }

    err = deflateEnd(&c_stream);
    CHECK_ERR(err, "deflateEnd");
}

/* ===========================================================================
 * Test inflate() with small buffers
 */
void test_inflate(compr, comprLen, uncompr, uncomprLen)
    Byte *compr, *uncompr;
    uLong comprLen, uncomprLen;
{
    int err;
    z_stream d_stream; /* decompression stream */

    strcpy((char*)uncompr, "garbage");

    d_stream.zalloc = (alloc_func)0;
    d_stream.zfree = (free_func)0;
    d_stream.opaque = (voidpf)0;

    d_stream.next_in  = compr;
    d_stream.avail_in = 0;
    d_stream.next_out = uncompr;

    err = inflateInit(&d_stream);
    CHECK_ERR(err, "inflateInit");

    while (d_stream.total_out < uncomprLen && d_stream.total_in < comprLen) {
        d_stream.avail_in = d_stream.avail_out = 1; /* force small buffers */
        err = inflate(&d_stream, Z_NO_FLUSH);
        if (err == Z_STREAM_END) break;
        CHECK_ERR(err, "inflate");
    }

    err = inflateEnd(&d_stream);
    CHECK_ERR(err, "inflateEnd");

    if (strcmp((char*)uncompr, hello)) {
        fprintf(stderr, "bad inflate\n");
        exit(1);
    } else {
        printf("inflate(): %s\n", (char *)uncompr);
    }
}

/* ===========================================================================
 * Test deflate() with large buffers and dynamic change of compression level
 */
void test_large_deflate(compr, comprLen, uncompr, uncomprLen)
    Byte *compr, *uncompr;
    uLong comprLen, uncomprLen;
{
    z_stream c_stream; /* compression stream */
    int err;

    c_stream.zalloc = (alloc_func)0;
    c_stream.zfree = (free_func)0;
    c_stream.opaque = (voidpf)0;

    err = deflateInit(&c_stream, Z_BEST_SPEED);
    CHECK_ERR(err, "deflateInit");

    c_stream.next_out = compr;
    c_stream.avail_out = (uInt)comprLen;

    /* At this point, uncompr is still mostly zeroes, so it should compress
     * very well:
     */
    c_stream.next_in = uncompr;
    c_stream.avail_in = (uInt)uncomprLen;
    err = deflate(&c_stream, Z_NO_FLUSH);
    CHECK_ERR(err, "deflate");
    if (c_stream.avail_in != 0) {
        fprintf(stderr, "deflate not greedy\n");
        exit(1);
    }

    /* Feed in already compressed data and switch to no compression: */
    deflateParams(&c_stream, Z_NO_COMPRESSION, Z_DEFAULT_STRATEGY);
    c_stream.next_in = compr;
    c_stream.avail_in = (uInt)comprLen/2;
    err = deflate(&c_stream, Z_NO_FLUSH);
    CHECK_ERR(err, "deflate");

    /* Switch back to compressing mode: */
    deflateParams(&c_stream, Z_BEST_COMPRESSION, Z_FILTERED);
    c_stream.next_in = uncompr;
    c_stream.avail_in = (uInt)uncomprLen;
    err = deflate(&c_stream, Z_NO_FLUSH);
    CHECK_ERR(err, "deflate");

    err = deflate(&c_stream, Z_FINISH);
    if (err != Z_STREAM_END) {
        fprintf(stderr, "deflate should report Z_STREAM_END\n");
        exit(1);
    }
    err = deflateEnd(&c_stream);
    CHECK_ERR(err, "deflateEnd");
}

/* ===========================================================================
 * Test inflate() with large buffers
 */
void test_large_inflate(compr, comprLen, uncompr, uncomprLen)
    Byte *compr, *uncompr;
    uLong comprLen, uncomprLen;
{
    int err;
    z_stream d_stream; /* decompression stream */

    strcpy((char*)uncompr, "garbage");

    d_stream.zalloc = (alloc_func)0;
    d_stream.zfree = (free_func)0;
    d_stream.opaque = (voidpf)0;

    d_stream.next_in  = compr;
    d_stream.avail_in = (uInt)comprLen;

    err = inflateInit(&d_stream);
    CHECK_ERR(err, "inflateInit");

    for (;;) {
        d_stream.next_out = uncompr;            /* discard the output */
        d_stream.avail_out = (uInt)uncomprLen;
        err = inflate(&d_stream, Z_NO_FLUSH);
        if (err == Z_STREAM_END) break;
        CHECK_ERR(err, "large inflate");
    }

    err = inflateEnd(&d_stream);
    CHECK_ERR(err, "inflateEnd");

    if (d_stream.total_out != 2*uncomprLen + comprLen/2) {
        fprintf(stderr, "bad large inflate: %ld\n", d_stream.total_out);
        exit(1);
    } else {
        printf("large_inflate(): OK\n");
    }
}

/* ===========================================================================
 * Test deflate() with full flush
 */
void test_flush(compr, comprLen)
    Byte *compr;
    uLong *comprLen;
{
    z_stream c_stream; /* compression stream */
    int err;
    uInt len = (uInt)strlen(hello)+1;

    c_stream.zalloc = (alloc_func)0;
    c_stream.zfree = (free_func)0;
    c_stream.opaque = (voidpf)0;

    err = deflateInit(&c_stream, Z_DEFAULT_COMPRESSION);
    CHECK_ERR(err, "deflateInit");

    c_stream.next_in  = (Bytef*)hello;
    c_stream.next_out = compr;
    c_stream.avail_in = 3;
    c_stream.avail_out = (uInt)*comprLen;
    err = deflate(&c_stream, Z_FULL_FLUSH);
    CHECK_ERR(err, "deflate");

    compr[3]++; /* force an error in first compressed block */
    c_stream.avail_in = len - 3;

    err = deflate(&c_stream, Z_FINISH);
    if (err != Z_STREAM_END) {
        CHECK_ERR(err, "deflate");
    }
    err = deflateEnd(&c_stream);
    CHECK_ERR(err, "deflateEnd");

    *comprLen = c_stream.total_out;
}

/* ===========================================================================
 * Test inflateSync()
 */
void test_sync(compr, comprLen, uncompr, uncomprLen)
    Byte *compr, *uncompr;
    uLong comprLen, uncomprLen;
{
    int err;
    z_stream d_stream; /* decompression stream */

    strcpy((char*)uncompr, "garbage");

    d_stream.zalloc = (alloc_func)0;
    d_stream.zfree = (free_func)0;
    d_stream.opaque = (voidpf)0;

    d_stream.next_in  = compr;
    d_stream.avail_in = 2; /* just read the zlib header */

    err = inflateInit(&d_stream);
    CHECK_ERR(err, "inflateInit");

    d_stream.next_out = uncompr;
    d_stream.avail_out = (uInt)uncomprLen;

    inflate(&d_stream, Z_NO_FLUSH);
    CHECK_ERR(err, "inflate");

    d_stream.avail_in = (uInt)comprLen-2;   /* read all compressed data */
    err = inflateSync(&d_stream);           /* but skip the damaged part */
    CHECK_ERR(err, "inflateSync");

    err = inflate(&d_stream, Z_FINISH);
    if (err != Z_DATA_ERROR) {
        fprintf(stderr, "inflate should report DATA_ERROR\n");
        /* Because of incorrect adler32 */
        exit(1);
    }
    err = inflateEnd(&d_stream);
    CHECK_ERR(err, "inflateEnd");

    printf("after inflateSync(): hel%s\n", (char *)uncompr);
}

/* ===========================================================================
 * Test deflate() with preset dictionary
 */
void test_dict_deflate(compr, comprLen)
    Byte *compr;
    uLong comprLen;
{
    z_stream c_stream; /* compression stream */
    int err;

    c_stream.zalloc = (alloc_func)0;
    c_stream.zfree = (free_func)0;
    c_stream.opaque = (voidpf)0;

    err = deflateInit(&c_stream, Z_BEST_COMPRESSION);
    CHECK_ERR(err, "deflateInit");

    err = deflateSetDictionary(&c_stream,
                               (const Bytef*)dictionary, sizeof(dictionary));
    CHECK_ERR(err, "deflateSetDictionary");

    dictId = c_stream.adler;
    c_stream.next_out = compr;
    c_stream.avail_out = (uInt)comprLen;

    c_stream.next_in = (Bytef*)hello;
    c_stream.avail_in = (uInt)strlen(hello)+1;

    err = deflate(&c_stream, Z_FINISH);
    if (err != Z_STREAM_END) {
        fprintf(stderr, "deflate should report Z_STREAM_END\n");
        exit(1);
    }
    err = deflateEnd(&c_stream);
    CHECK_ERR(err, "deflateEnd");
}

/* ===========================================================================
 * Test inflate() with a preset dictionary
 */
void test_dict_inflate(compr, comprLen, uncompr, uncomprLen)
    Byte *compr, *uncompr;
    uLong comprLen, uncomprLen;
{
    int err;
    z_stream d_stream; /* decompression stream */

    strcpy((char*)uncompr, "garbage");

    d_stream.zalloc = (alloc_func)0;
    d_stream.zfree = (free_func)0;
    d_stream.opaque = (voidpf)0;

    d_stream.next_in  = compr;
    d_stream.avail_in = (uInt)comprLen;

    err = inflateInit(&d_stream);
    CHECK_ERR(err, "inflateInit");

    d_stream.next_out = uncompr;
    d_stream.avail_out = (uInt)uncomprLen;

    for (;;) {
        err = inflate(&d_stream, Z_NO_FLUSH);
        if (err == Z_STREAM_END) break;
        if (err == Z_NEED_DICT) {
            if (d_stream.adler != dictId) {
                fprintf(stderr, "unexpected dictionary");
                exit(1);
            }
            err = inflateSetDictionary(&d_stream, (const Bytef*)dictionary,
                                       sizeof(dictionary));
        }
        CHECK_ERR(err, "inflate with dict");
    }

    err = inflateEnd(&d_stream);
    CHECK_ERR(err, "inflateEnd");

    if (strcmp((char*)uncompr, hello)) {
        fprintf(stderr, "bad inflate with dict\n");
        exit(1);
    } else {
        printf("inflate with dictionary: %s\n", (char *)uncompr);
    }
}

/* ===========================================================================
 * Usage:  example [output.gz  [input.gz]]
 */

int main(argc, argv)
    int argc;
    char *argv[];
{
    Byte *compr, *uncompr;
    uLong comprLen = 10000*sizeof(int); /* don't overflow on MSDOS */
    uLong uncomprLen = comprLen;
    static const char* myVersion = ZLIB_VERSION;

    if (zlibVersion()[0] != myVersion[0]) {
        fprintf(stderr, "incompatible zlib version\n");
        exit(1);

    } else if (strcmp(zlibVersion(), ZLIB_VERSION) != 0) {
        fprintf(stderr, "warning: different zlib version\n");
    }

    printf("zlib version %s = 0x%04x, compile flags = 0x%lx\n",
            ZLIB_VERSION, ZLIB_VERNUM, zlibCompileFlags());

    compr    = (Byte*)calloc((uInt)comprLen, 1);
    uncompr  = (Byte*)calloc((uInt)uncomprLen, 1);
    /* compr and uncompr are cleared to avoid reading uninitialized
     * data and to ensure that uncompr compresses well.
     */
    if (compr == Z_NULL || uncompr == Z_NULL) {
        printf("out of memory\n");
        exit(1);
    }
    test_compress(compr, comprLen, uncompr, uncomprLen);

    test_gzio((argc > 1 ? argv[1] : TESTFILE),
              uncompr, uncomprLen);

    test_deflate(compr, comprLen);
    test_inflate(compr, comprLen, uncompr, uncomprLen);

    test_large_deflate(compr, comprLen, uncompr, uncomprLen);
    test_large_inflate(compr, comprLen, uncompr, uncomprLen);

    test_flush(compr, &comprLen);
    test_sync(compr, comprLen, uncompr, uncomprLen);
    comprLen = uncomprLen;

    test_dict_deflate(compr, comprLen);
    test_dict_inflate(compr, comprLen, uncompr, uncomprLen);

    free(compr);
    free(uncompr);

    return 0;
}


code:
This directory contains examples of the use of zlib.

fitblk.c
    compress just enough input to nearly fill a requested output size
    - zlib isn't designed to do this, but fitblk does it anyway

gun.c
    uncompress a gzip file
    - illustrates the use of inflateBack() for high speed file-to-file
      decompression using call-back functions
    - is approximately twice as fast as gzip -d
    - also provides Unix uncompress functionality, again twice as fast

gzappend.c
    append to a gzip file
    - illustrates the use of the Z_BLOCK flush parameter for inflate()
    - illustrates the use of deflatePrime() to start at any bit

gzjoin.c
    join gzip files without recalculating the crc or recompressing
    - illustrates the use of the Z_BLOCK flush parameter for inflate()
    - illustrates the use of crc32_combine()

gzlog.c
gzlog.h
    efficiently maintain a message log file in gzip format
    - illustrates use of raw deflate and Z_SYNC_FLUSH
    - illustrates use of gzip header extra field

zlib_how.html
    painfully comprehensive description of zpipe.c (see below)
    - describes in excruciating detail the use of deflate() and inflate()

zpipe.c
    reads and writes zlib streams from stdin to stdout
    - illustrates the proper use of deflate() and inflate()
    - deeply commented in zlib_how.html (see above)

zran.c
    index a zlib or gzip stream and randomly access it
    - illustrates the use of Z_BLOCK, inflatePrime(), and
      inflateSetDictionary() to provide random access

license: mit


code:
/* fitblk.c: example of fitting compressed output to a specified size
   Not copyrighted -- provided to the public domain
   Version 1.1  25 November 2004  Mark Adler */

/* Version history:
   1.0  24 Nov 2004  First version
   1.1  25 Nov 2004  Change deflateInit2() to deflateInit()
                     Use fixed-size, stack-allocated raw buffers
                     Simplify code moving compression to subroutines
                     Use assert() for internal errors
                     Add detailed description of approach
 */

/* Approach to just fitting a requested compressed size:

   fitblk performs three compression passes on a portion of the input
   data in order to determine how much of that input will compress to
   nearly the requested output block size.  The first pass generates
   enough deflate blocks to produce output to fill the requested
   output size plus a specfied excess amount (see the EXCESS define
   below).  The last deflate block may go quite a bit past that, but
   is discarded.  The second pass decompresses and recompresses just
   the compressed data that fit in the requested plus excess sized
   buffer.  The deflate process is terminated after that amount of
   input, which is less than the amount consumed on the first pass.
   The last deflate block of the result will be of a comparable size
   to the final product, so that the header for that deflate block and
   the compression ratio for that block will be about the same as in
   the final product.  The third compression pass decompresses the
   result of the second step, but only the compressed data up to the
   requested size minus an amount to allow the compressed stream to
   complete (see the MARGIN define below).  That will result in a
   final compressed stream whose length is less than or equal to the
   requested size.  Assuming sufficient input and a requested size
   greater than a few hundred bytes, the shortfall will typically be
   less than ten bytes.

   If the input is short enough that the first compression completes
   before filling the requested output size, then that compressed
   stream is return with no recompression.

   EXCESS is chosen to be just greater than the shortfall seen in a
   two pass approach similar to the above.  That shortfall is due to
   the last deflate block compressing more efficiently with a smaller
   header on the second pass.  EXCESS is set to be large enough so
   that there is enough uncompressed data for the second pass to fill
   out the requested size, and small enough so that the final deflate
   block of the second pass will be close in size to the final deflate
   block of the third and final pass.  MARGIN is chosen to be just
   large enough to assure that the final compression has enough room
   to complete in all cases.
 */

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include "zlib.h"

#define local static

/* print nastygram and leave */
local void quit(char *why)
{
    fprintf(stderr, "fitblk abort: %s\n", why);
    exit(1);
}

#define RAWLEN 4096    /* intermediate uncompressed buffer size */

/* compress from file to def until provided buffer is full or end of
   input reached; return last deflate() return value, or Z_ERRNO if
   there was read error on the file */
local int partcompress(FILE *in, z_streamp def)
{
    int ret, flush;
    unsigned char raw[RAWLEN];

    flush = Z_NO_FLUSH;
    do {
        def->avail_in = fread(raw, 1, RAWLEN, in);
        if (ferror(in))
            return Z_ERRNO;
        def->next_in = raw;
        if (feof(in))
            flush = Z_FINISH;
        ret = deflate(def, flush);
        assert(ret != Z_STREAM_ERROR);
    } while (def->avail_out != 0 && flush == Z_NO_FLUSH);
    return ret;
}

/* recompress from inf's input to def's output; the input for inf and
   the output for def are set in those structures before calling;
   return last deflate() return value, or Z_MEM_ERROR if inflate()
   was not able to allocate enough memory when it needed to */
local int recompress(z_streamp inf, z_streamp def)
{
    int ret, flush;
    unsigned char raw[RAWLEN];

    flush = Z_NO_FLUSH;
    do {
        /* decompress */
        inf->avail_out = RAWLEN;
        inf->next_out = raw;
        ret = inflate(inf, Z_NO_FLUSH);
        assert(ret != Z_STREAM_ERROR && ret != Z_DATA_ERROR &&
               ret != Z_NEED_DICT);
        if (ret == Z_MEM_ERROR)
            return ret;

        /* compress what was decompresed until done or no room */
        def->avail_in = RAWLEN - inf->avail_out;
        def->next_in = raw;
        if (inf->avail_out != 0)
            flush = Z_FINISH;
        ret = deflate(def, flush);
        assert(ret != Z_STREAM_ERROR);
    } while (ret != Z_STREAM_END && def->avail_out != 0);
    return ret;
}

#define EXCESS 256      /* empirically determined stream overage */
#define MARGIN 8        /* amount to back off for completion */

/* compress from stdin to fixed-size block on stdout */
int main(int argc, char **argv)
{
    int ret;                /* return code */
    unsigned size;          /* requested fixed output block size */
    unsigned have;          /* bytes written by deflate() call */
    unsigned char *blk;     /* intermediate and final stream */
    unsigned char *tmp;     /* close to desired size stream */
    z_stream def, inf;      /* zlib deflate and inflate states */

    /* get requested output size */
    if (argc != 2)
        quit("need one argument: size of output block");
    ret = strtol(argv[1], argv + 1, 10);
    if (argv[1][0] != 0)
        quit("argument must be a number");
    if (ret < 8)            /* 8 is minimum zlib stream size */
        quit("need positive size of 8 or greater");
    size = (unsigned)ret;

    /* allocate memory for buffers and compression engine */
    blk = malloc(size + EXCESS);
    def.zalloc = Z_NULL;
    def.zfree = Z_NULL;
    def.opaque = Z_NULL;
    ret = deflateInit(&def, Z_DEFAULT_COMPRESSION);
    if (ret != Z_OK || blk == NULL)
        quit("out of memory");

    /* compress from stdin until output full, or no more input */
    def.avail_out = size + EXCESS;
    def.next_out = blk;
    ret = partcompress(stdin, &def);
    if (ret == Z_ERRNO)
        quit("error reading input");

    /* if it all fit, then size was undersubscribed -- done! */
    if (ret == Z_STREAM_END && def.avail_out >= EXCESS) {
        /* write block to stdout */
        have = size + EXCESS - def.avail_out;
        if (fwrite(blk, 1, have, stdout) != have || ferror(stdout))
            quit("error writing output");

        /* clean up and print results to stderr */
        ret = deflateEnd(&def);
        assert(ret != Z_STREAM_ERROR);
        free(blk);
        fprintf(stderr,
                "%u bytes unused out of %u requested (all input)\n",
                size - have, size);
        return 0;
    }

    /* it didn't all fit -- set up for recompression */
    inf.zalloc = Z_NULL;
    inf.zfree = Z_NULL;
    inf.opaque = Z_NULL;
    inf.avail_in = 0;
    inf.next_in = Z_NULL;
    ret = inflateInit(&inf);
    tmp = malloc(size + EXCESS);
    if (ret != Z_OK || tmp == NULL)
        quit("out of memory");
    ret = deflateReset(&def);
    assert(ret != Z_STREAM_ERROR);

    /* do first recompression close to the right amount */
    inf.avail_in = size + EXCESS;
    inf.next_in = blk;
    def.avail_out = size + EXCESS;
    def.next_out = tmp;
    ret = recompress(&inf, &def);
    if (ret == Z_MEM_ERROR)
        quit("out of memory");

    /* set up for next reocmpression */
    ret = inflateReset(&inf);
    assert(ret != Z_STREAM_ERROR);
    ret = deflateReset(&def);
    assert(ret != Z_STREAM_ERROR);

    /* do second and final recompression (third compression) */
    inf.avail_in = size - MARGIN;   /* assure stream will complete */
    inf.next_in = tmp;
    def.avail_out = size;
    def.next_out = blk;
    ret = recompress(&inf, &def);
    if (ret == Z_MEM_ERROR)
        quit("out of memory");
    assert(ret == Z_STREAM_END);    /* otherwise MARGIN too small */

    /* done -- write block to stdout */
    have = size - def.avail_out;
    if (fwrite(blk, 1, have, stdout) != have || ferror(stdout))
        quit("error writing output");

    /* clean up and print results to stderr */
    free(tmp);
    ret = inflateEnd(&inf);
    assert(ret != Z_STREAM_ERROR);
    ret = deflateEnd(&def);
    assert(ret != Z_STREAM_ERROR);
    free(blk);
    fprintf(stderr,
            "%u bytes unused out of %u requested (%lu input)\n",
            size - have, size, def.total_in);
    return 0;
}


code:
/* gun.c -- simple gunzip to give an example of the use of inflateBack()
 * Copyright (C) 2003, 2005 Mark Adler
 * For conditions of distribution and use, see copyright notice in zlib.h
   Version 1.3  12 June 2005  Mark Adler */

/* Version history:
   1.0  16 Feb 2003  First version for testing of inflateBack()
   1.1  21 Feb 2005  Decompress concatenated gzip streams
                     Remove use of "this" variable (C++ keyword)
                     Fix return value for in()
                     Improve allocation failure checking
                     Add typecasting for void * structures
                     Add -h option for command version and usage
                     Add a bunch of comments
   1.2  20 Mar 2005  Add Unix compress (LZW) decompression
                     Copy file attributes from input file to output file
   1.3  12 Jun 2005  Add casts for error messages [Oberhumer]
 */

/*
   gun [ -t ] [ name ... ]

   decompresses the data in the named gzip files.  If no arguments are given,
   gun will decompress from stdin to stdout.  The names must end in .gz, -gz,
   .z, -z, _z, or .Z.  The uncompressed data will be written to a file name
   with the suffix stripped.  On success, the original file is deleted.  On
   failure, the output file is deleted.  For most failures, the command will
   continue to process the remaining names on the command line.  A memory
   allocation failure will abort the command.  If -t is specified, then the
   listed files or stdin will be tested as gzip files for integrity (without
   checking for a proper suffix), no output will be written, and no files
   will be deleted.

   Like gzip, gun allows concatenated gzip streams and will decompress them,
   writing all of the uncompressed data to the output.  Unlike gzip, gun allows
   an empty file on input, and will produce no error writing an empty output
   file.

   gun will also decompress files made by Unix compress, which uses LZW
   compression.  These files are automatically detected by virtue of their
   magic header bytes.  Since the end of Unix compress stream is marked by the
   end-of-file, they cannot be concantenated.  If a Unix compress stream is
   encountered in an input file, it is the last stream in that file.

   Like gunzip and uncompress, the file attributes of the orignal compressed
   file are maintained in the final uncompressed file, to the extent that the
   user permissions allow it.

   On my Mac OS X PowerPC G4, gun is almost twice as fast as gunzip (version
   1.2.4) is on the same file, when gun is linked with zlib 1.2.2.  Also the
   LZW decompression provided by gun is about twice as fast as the standard
   Unix uncompress command.
 */

/* external functions and related types and constants */
#include <stdio.h>          /* fprintf() */
#include <stdlib.h>         /* malloc(), free() */
#include <string.h>         /* strerror(), strcmp(), strlen(), memcpy() */
#include <errno.h>          /* errno */
#include <fcntl.h>          /* open() */
#include <unistd.h>         /* read(), write(), close(), chown(), unlink() */
#include <sys/types.h>
#include <sys/stat.h>       /* stat(), chmod() */
#include <utime.h>          /* utime() */
#include "zlib.h"           /* inflateBackInit(), inflateBack(), */
                            /* inflateBackEnd(), crc32() */

/* function declaration */
#define local static

/* buffer constants */
#define SIZE 32768U         /* input and output buffer sizes */
#define PIECE 16384         /* limits i/o chunks for 16-bit int case */

/* structure for infback() to pass to input function in() -- it maintains the
   input file and a buffer of size SIZE */
struct ind {
    int infile;
    unsigned char *inbuf;
};

/* Load input buffer, assumed to be empty, and return bytes loaded and a
   pointer to them.  read() is called until the buffer is full, or until it
   returns end-of-file or error.  Return 0 on error. */
local unsigned in(void *in_desc, unsigned char **buf)
{
    int ret;
    unsigned len;
    unsigned char *next;
    struct ind *me = (struct ind *)in_desc;

    next = me->inbuf;
    *buf = next;
    len = 0;
    do {
        ret = PIECE;
        if ((unsigned)ret > SIZE - len)
            ret = (int)(SIZE - len);
        ret = (int)read(me->infile, next, ret);
        if (ret == -1) {
            len = 0;
            break;
        }
        next += ret;
        len += ret;
    } while (ret != 0 && len < SIZE);
    return len;
}

/* structure for infback() to pass to output function out() -- it maintains the
   output file, a running CRC-32 check on the output and the total number of
   bytes output, both for checking against the gzip trailer.  (The length in
   the gzip trailer is stored modulo 2^32, so it's ok if a long is 32 bits and
   the output is greater than 4 GB.) */
struct outd {
    int outfile;
    int check;                  /* true if checking crc and total */
    unsigned long crc;
    unsigned long total;
};

/* Write output buffer and update the CRC-32 and total bytes written.  write()
   is called until all of the output is written or an error is encountered.
   On success out() returns 0.  For a write failure, out() returns 1.  If the
   output file descriptor is -1, then nothing is written.
 */
local int out(void *out_desc, unsigned char *buf, unsigned len)
{
    int ret;
    struct outd *me = (struct outd *)out_desc;

    if (me->check) {
        me->crc = crc32(me->crc, buf, len);
        me->total += len;
    }
    if (me->outfile != -1)
        do {
            ret = PIECE;
            if ((unsigned)ret > len)
                ret = (int)len;
            ret = (int)write(me->outfile, buf, ret);
            if (ret == -1)
                return 1;
            buf += ret;
            len -= ret;
        } while (len != 0);
    return 0;
}

/* next input byte macro for use inside lunpipe() and gunpipe() */
#define NEXT() (have ? 0 : (have = in(indp, &next)), \
                last = have ? (have--, (int)(*next++)) : -1)

/* memory for gunpipe() and lunpipe() --
   the first 256 entries of prefix[] and suffix[] are never used, could
   have offset the index, but it's faster to waste the memory */
unsigned char inbuf[SIZE];              /* input buffer */
unsigned char outbuf[SIZE];             /* output buffer */
unsigned short prefix[65536];           /* index to LZW prefix string */
unsigned char suffix[65536];            /* one-character LZW suffix */
unsigned char match[65280 + 2];         /* buffer for reversed match or gzip
                                           32K sliding window */

/* throw out what's left in the current bits byte buffer (this is a vestigial
   aspect of the compressed data format derived from an implementation that
   made use of a special VAX machine instruction!) */
#define FLUSHCODE() \
    do { \
        left = 0; \
        rem = 0; \
        if (chunk > have) { \
            chunk -= have; \
            have = 0; \
            if (NEXT() == -1) \
                break; \
            chunk--; \
            if (chunk > have) { \
                chunk = have = 0; \
                break; \
            } \
        } \
        have -= chunk; \
        next += chunk; \
        chunk = 0; \
    } while (0)

/* Decompress a compress (LZW) file from indp to outfile.  The compress magic
   header (two bytes) has already been read and verified.  There are have bytes
   of buffered input at next.  strm is used for passing error information back
   to gunpipe().

   lunpipe() will return Z_OK on success, Z_BUF_ERROR for an unexpected end of
   file, read error, or write error (a write error indicated by strm->next_in
   not equal to Z_NULL), or Z_DATA_ERROR for invalid input.
 */
local int lunpipe(unsigned have, unsigned char *next, struct ind *indp,
                  int outfile, z_stream *strm)
{
    int last;                   /* last byte read by NEXT(), or -1 if EOF */
    int chunk;                  /* bytes left in current chunk */
    int left;                   /* bits left in rem */
    unsigned rem;               /* unused bits from input */
    int bits;                   /* current bits per code */
    unsigned code;              /* code, table traversal index */
    unsigned mask;              /* mask for current bits codes */
    int max;                    /* maximum bits per code for this stream */
    int flags;                  /* compress flags, then block compress flag */
    unsigned end;               /* last valid entry in prefix/suffix tables */
    unsigned temp;              /* current code */
    unsigned prev;              /* previous code */
    unsigned final;             /* last character written for previous code */
    unsigned stack;             /* next position for reversed string */
    unsigned outcnt;            /* bytes in output buffer */
    struct outd outd;           /* output structure */

    /* set up output */
    outd.outfile = outfile;
    outd.check = 0;

    /* process remainder of compress header -- a flags byte */
    flags = NEXT();
    if (last == -1)
        return Z_BUF_ERROR;
    if (flags & 0x60) {
        strm->msg = (char *)"unknown lzw flags set";
        return Z_DATA_ERROR;
    }
    max = flags & 0x1f;
    if (max < 9 || max > 16) {
        strm->msg = (char *)"lzw bits out of range";
        return Z_DATA_ERROR;
    }
    if (max == 9)                           /* 9 doesn't really mean 9 */
        max = 10;
    flags &= 0x80;                          /* true if block compress */

    /* clear table */
    bits = 9;
    mask = 0x1ff;
    end = flags ? 256 : 255;

    /* set up: get first 9-bit code, which is the first decompressed byte, but
       don't create a table entry until the next code */
    if (NEXT() == -1)                       /* no compressed data is ok */
        return Z_OK;
    final = prev = (unsigned)last;          /* low 8 bits of code */
    if (NEXT() == -1)                       /* missing a bit */
        return Z_BUF_ERROR;
    if (last & 1) {                         /* code must be < 256 */
        strm->msg = (char *)"invalid lzw code";
        return Z_DATA_ERROR;
    }
    rem = (unsigned)last >> 1;              /* remaining 7 bits */
    left = 7;
    chunk = bits - 2;                       /* 7 bytes left in this chunk */
    outbuf[0] = (unsigned char)final;       /* write first decompressed byte */
    outcnt = 1;

    /* decode codes */
    stack = 0;
    for (;;) {
        /* if the table will be full after this, increment the code size */
        if (end >= mask && bits < max) {
            FLUSHCODE();
            bits++;
            mask <<= 1;
            mask++;
        }

        /* get a code of length bits */
        if (chunk == 0)                     /* decrement chunk modulo bits */
            chunk = bits;
        code = rem;                         /* low bits of code */
        if (NEXT() == -1) {                 /* EOF is end of compressed data */
            /* write remaining buffered output */
            if (outcnt && out(&outd, outbuf, outcnt)) {
                strm->next_in = outbuf;     /* signal write error */
                return Z_BUF_ERROR;
            }
            return Z_OK;
        }
        code += (unsigned)last << left;     /* middle (or high) bits of code */
        left += 8;
        chunk--;
        if (bits > left) {                  /* need more bits */
            if (NEXT() == -1)               /* can't end in middle of code */
                return Z_BUF_ERROR;
            code += (unsigned)last << left; /* high bits of code */
            left += 8;
            chunk--;
        }
        code &= mask;                       /* mask to current code length */
        left -= bits;                       /* number of unused bits */
        rem = (unsigned)last >> (8 - left); /* unused bits from last byte */

        /* process clear code (256) */
        if (code == 256 && flags) {
            FLUSHCODE();
            bits = 9;                       /* initialize bits and mask */
            mask = 0x1ff;
            end = 255;                      /* empty table */
            continue;                       /* get next code */
        }

        /* special code to reuse last match */
        temp = code;                        /* save the current code */
        if (code > end) {
            /* Be picky on the allowed code here, and make sure that the code
               we drop through (prev) will be a valid index so that random
               input does not cause an exception.  The code != end + 1 check is
               empirically derived, and not checked in the original uncompress
               code.  If this ever causes a problem, that check could be safely
               removed.  Leaving this check in greatly improves gun's ability
               to detect random or corrupted input after a compress header.
               In any case, the prev > end check must be retained. */
            if (code != end + 1 || prev > end) {
                strm->msg = (char *)"invalid lzw code";
                return Z_DATA_ERROR;
            }
            match[stack++] = (unsigned char)final;
            code = prev;
        }

        /* walk through linked list to generate output in reverse order */
        while (code >= 256) {
            match[stack++] = suffix[code];
            code = prefix[code];
        }
        match[stack++] = (unsigned char)code;
        final = code;

        /* link new table entry */
        if (end < mask) {
            end++;
            prefix[end] = (unsigned short)prev;
            suffix[end] = (unsigned char)final;
        }

        /* set previous code for next iteration */
        prev = temp;

        /* write output in forward order */
        while (stack > SIZE - outcnt) {
            while (outcnt < SIZE)
                outbuf[outcnt++] = match[--stack];
            if (out(&outd, outbuf, outcnt)) {
                strm->next_in = outbuf; /* signal write error */
                return Z_BUF_ERROR;
            }
            outcnt = 0;
        }
        do {
            outbuf[outcnt++] = match[--stack];
        } while (stack);

        /* loop for next code with final and prev as the last match, rem and
           left provide the first 0..7 bits of the next code, end is the last
           valid table entry */
    }
}

/* Decompress a gzip file from infile to outfile.  strm is assumed to have been
   successfully initialized with inflateBackInit().  The input file may consist
   of a series of gzip streams, in which case all of them will be decompressed
   to the output file.  If outfile is -1, then the gzip stream(s) integrity is
   checked and nothing is written.

   The return value is a zlib error code: Z_MEM_ERROR if out of memory,
   Z_DATA_ERROR if the header or the compressed data is invalid, or if the
   trailer CRC-32 check or length doesn't match, Z_BUF_ERROR if the input ends
   prematurely or a write error occurs, or Z_ERRNO if junk (not a another gzip
   stream) follows a valid gzip stream.
 */
local int gunpipe(z_stream *strm, int infile, int outfile)
{
    int ret, first, last;
    unsigned have, flags, len;
    unsigned char *next;
    struct ind ind, *indp;
    struct outd outd;

    /* setup input buffer */
    ind.infile = infile;
    ind.inbuf = inbuf;
    indp = &ind;

    /* decompress concatenated gzip streams */
    have = 0;                               /* no input data read in yet */
    first = 1;                              /* looking for first gzip header */
    strm->next_in = Z_NULL;                 /* so Z_BUF_ERROR means EOF */
    for (;;) {
        /* look for the two magic header bytes for a gzip stream */
        if (NEXT() == -1) {
            ret = Z_OK;
            break;                          /* empty gzip stream is ok */
        }
        if (last != 31 || (NEXT() != 139 && last != 157)) {
            strm->msg = (char *)"incorrect header check";
            ret = first ? Z_DATA_ERROR : Z_ERRNO;
            break;                          /* not a gzip or compress header */
        }
        first = 0;                          /* next non-header is junk */

        /* process a compress (LZW) file -- can't be concatenated after this */
        if (last == 157) {
            ret = lunpipe(have, next, indp, outfile, strm);
            break;
        }

        /* process remainder of gzip header */
        ret = Z_BUF_ERROR;
        if (NEXT() != 8) {                  /* only deflate method allowed */
            if (last == -1) break;
            strm->msg = (char *)"unknown compression method";
            ret = Z_DATA_ERROR;
            break;
        }
        flags = NEXT();                     /* header flags */
        NEXT();                             /* discard mod time, xflgs, os */
        NEXT();
        NEXT();
        NEXT();
        NEXT();
        NEXT();
        if (last == -1) break;
        if (flags & 0xe0) {
            strm->msg = (char *)"unknown header flags set";
            ret = Z_DATA_ERROR;
            break;
        }
        if (flags & 4) {                    /* extra field */
            len = NEXT();
            len += (unsigned)(NEXT()) << 8;
            if (last == -1) break;
            while (len > have) {
                len -= have;
                have = 0;
                if (NEXT() == -1) break;
                len--;
            }
            if (last == -1) break;
            have -= len;
            next += len;
        }
        if (flags & 8)                      /* file name */
            while (NEXT() != 0 && last != -1)
                ;
        if (flags & 16)                     /* comment */
            while (NEXT() != 0 && last != -1)
                ;
        if (flags & 2) {                    /* header crc */
            NEXT();
            NEXT();
        }
        if (last == -1) break;

        /* set up output */
        outd.outfile = outfile;
        outd.check = 1;
        outd.crc = crc32(0L, Z_NULL, 0);
        outd.total = 0;

        /* decompress data to output */
        strm->next_in = next;
        strm->avail_in = have;
        ret = inflateBack(strm, in, indp, out, &outd);
        if (ret != Z_STREAM_END) break;
        next = strm->next_in;
        have = strm->avail_in;
        strm->next_in = Z_NULL;             /* so Z_BUF_ERROR means EOF */

        /* check trailer */
        ret = Z_BUF_ERROR;
        if (NEXT() != (outd.crc & 0xff) ||
            NEXT() != ((outd.crc >> 8) & 0xff) ||
            NEXT() != ((outd.crc >> 16) & 0xff) ||
            NEXT() != ((outd.crc >> 24) & 0xff)) {
            /* crc error */
            if (last != -1) {
                strm->msg = (char *)"incorrect data check";
                ret = Z_DATA_ERROR;
            }
            break;
        }
        if (NEXT() != (outd.total & 0xff) ||
            NEXT() != ((outd.total >> 8) & 0xff) ||
            NEXT() != ((outd.total >> 16) & 0xff) ||
            NEXT() != ((outd.total >> 24) & 0xff)) {
            /* length error */
            if (last != -1) {
                strm->msg = (char *)"incorrect length check";
                ret = Z_DATA_ERROR;
            }
            break;
        }

        /* go back and look for another gzip stream */
    }

    /* clean up and return */
    return ret;
}

/* Copy file attributes, from -> to, as best we can.  This is best effort, so
   no errors are reported.  The mode bits, including suid, sgid, and the sticky
   bit are copied (if allowed), the owner's user id and group id are copied
   (again if allowed), and the access and modify times are copied. */
local void copymeta(char *from, char *to)
{
    struct stat was;
    struct utimbuf when;

    /* get all of from's Unix meta data, return if not a regular file */
    if (stat(from, &was) != 0 || (was.st_mode & S_IFMT) != S_IFREG)
        return;

    /* set to's mode bits, ignore errors */
    (void)chmod(to, was.st_mode & 07777);

    /* copy owner's user and group, ignore errors */
    (void)chown(to, was.st_uid, was.st_gid);

    /* copy access and modify times, ignore errors */
    when.actime = was.st_atime;
    when.modtime = was.st_mtime;
    (void)utime(to, &when);
}

/* Decompress the file inname to the file outnname, of if test is true, just
   decompress without writing and check the gzip trailer for integrity.  If
   inname is NULL or an empty string, read from stdin.  If outname is NULL or
   an empty string, write to stdout.  strm is a pre-initialized inflateBack
   structure.  When appropriate, copy the file attributes from inname to
   outname.

   gunzip() returns 1 if there is an out-of-memory error or an unexpected
   return code from gunpipe().  Otherwise it returns 0.
 */
local int gunzip(z_stream *strm, char *inname, char *outname, int test)
{
    int ret;
    int infile, outfile;

    /* open files */
    if (inname == NULL || *inname == 0) {
        inname = "-";
        infile = 0;     /* stdin */
    }
    else {
        infile = open(inname, O_RDONLY, 0);
        if (infile == -1) {
            fprintf(stderr, "gun cannot open %s\n", inname);
            return 0;
        }
    }
    if (test)
        outfile = -1;
    else if (outname == NULL || *outname == 0) {
        outname = "-";
        outfile = 1;    /* stdout */
    }
    else {
        outfile = open(outname, O_CREAT | O_TRUNC | O_WRONLY, 0666);
        if (outfile == -1) {
            close(infile);
            fprintf(stderr, "gun cannot create %s\n", outname);
            return 0;
        }
    }
    errno = 0;

    /* decompress */
    ret = gunpipe(strm, infile, outfile);
    if (outfile > 2) close(outfile);
    if (infile > 2) close(infile);

    /* interpret result */
    switch (ret) {
    case Z_OK:
    case Z_ERRNO:
        if (infile > 2 && outfile > 2) {
            copymeta(inname, outname);          /* copy attributes */
            unlink(inname);
        }
        if (ret == Z_ERRNO)
            fprintf(stderr, "gun warning: trailing garbage ignored in %s\n",
                    inname);
        break;
    case Z_DATA_ERROR:
        if (outfile > 2) unlink(outname);
        fprintf(stderr, "gun data error on %s: %s\n", inname, strm->msg);
        break;
    case Z_MEM_ERROR:
        if (outfile > 2) unlink(outname);
        fprintf(stderr, "gun out of memory error--aborting\n");
        return 1;
    case Z_BUF_ERROR:
        if (outfile > 2) unlink(outname);
        if (strm->next_in != Z_NULL) {
            fprintf(stderr, "gun write error on %s: %s\n",
                    outname, strerror(errno));
        }
        else if (errno) {
            fprintf(stderr, "gun read error on %s: %s\n",
                    inname, strerror(errno));
        }
        else {
            fprintf(stderr, "gun unexpected end of file on %s\n",
                    inname);
        }
        break;
    default:
        if (outfile > 2) unlink(outname);
        fprintf(stderr, "gun internal error--aborting\n");
        return 1;
    }
    return 0;
}

/* Process the gun command line arguments.  See the command syntax near the
   beginning of this source file. */
int main(int argc, char **argv)
{
    int ret, len, test;
    char *outname;
    unsigned char *window;
    z_stream strm;

    /* initialize inflateBack state for repeated use */
    window = match;                         /* reuse LZW match buffer */
    strm.zalloc = Z_NULL;
    strm.zfree = Z_NULL;
    strm.opaque = Z_NULL;
    ret = inflateBackInit(&strm, 15, window);
    if (ret != Z_OK) {
        fprintf(stderr, "gun out of memory error--aborting\n");
        return 1;
    }

    /* decompress each file to the same name with the suffix removed */
    argc--;
    argv++;
    test = 0;
    if (argc && strcmp(*argv, "-h") == 0) {
        fprintf(stderr, "gun 1.3 (12 Jun 2005)\n");
        fprintf(stderr, "Copyright (c) 2005 Mark Adler\n");
        fprintf(stderr, "usage: gun [-t] [file1.gz [file2.Z ...]]\n");
        return 0;
    }
    if (argc && strcmp(*argv, "-t") == 0) {
        test = 1;
        argc--;
        argv++;
    }
    if (argc)
        do {
            if (test)
                outname = NULL;
            else {
                len = (int)strlen(*argv);
                if (strcmp(*argv + len - 3, ".gz") == 0 ||
                    strcmp(*argv + len - 3, "-gz") == 0)
                    len -= 3;
                else if (strcmp(*argv + len - 2, ".z") == 0 ||
                    strcmp(*argv + len - 2, "-z") == 0 ||
                    strcmp(*argv + len - 2, "_z") == 0 ||
                    strcmp(*argv + len - 2, ".Z") == 0)
                    len -= 2;
                else {
                    fprintf(stderr, "gun error: no gz type on %s--skipping\n",
                            *argv);
                    continue;
                }
                outname = malloc(len + 1);
                if (outname == NULL) {
                    fprintf(stderr, "gun out of memory error--aborting\n");
                    ret = 1;
                    break;
                }
                memcpy(outname, *argv, len);
                outname[len] = 0;
            }
            ret = gunzip(&strm, *argv, outname, test);
            if (outname != NULL) free(outname);
            if (ret) break;
        } while (argv++, --argc);
    else
        ret = gunzip(&strm, NULL, NULL, test);

    /* clean up */
    inflateBackEnd(&strm);
    return ret;
}


code:
/* gzappend -- command to append to a gzip file

  Copyright (C) 2003 Mark Adler, all rights reserved
  version 1.1, 4 Nov 2003

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the author be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.

  Mark Adler    madler@alumni.caltech.edu
 */

/*
 * Change history:
 *
 * 1.0  19 Oct 2003     - First version
 * 1.1   4 Nov 2003     - Expand and clarify some comments and notes
 *                      - Add version and copyright to help
 *                      - Send help to stdout instead of stderr
 *                      - Add some preemptive typecasts
 *                      - Add L to constants in lseek() calls
 *                      - Remove some debugging information in error messages
 *                      - Use new data_type definition for zlib 1.2.1
 *                      - Simplfy and unify file operations
 *                      - Finish off gzip file in gztack()
 *                      - Use deflatePrime() instead of adding empty blocks
 *                      - Keep gzip file clean on appended file read errors
 *                      - Use in-place rotate instead of auxiliary buffer
 *                        (Why you ask?  Because it was fun to write!)
 */

/*
   gzappend takes a gzip file and appends to it, compressing files from the
   command line or data from stdin.  The gzip file is written to directly, to
   avoid copying that file, in case it's large.  Note that this results in the
   unfriendly behavior that if gzappend fails, the gzip file is corrupted.

   This program was written to illustrate the use of the new Z_BLOCK option of
   zlib 1.2.x's inflate() function.  This option returns from inflate() at each
   block boundary to facilitate locating and modifying the last block bit at
   the start of the final deflate block.  Also whether using Z_BLOCK or not,
   another required feature of zlib 1.2.x is that inflate() now provides the
   number of unusued bits in the last input byte used.  gzappend will not work
   with versions of zlib earlier than 1.2.1.

   gzappend first decompresses the gzip file internally, discarding all but
   the last 32K of uncompressed data, and noting the location of the last block
   bit and the number of unused bits in the last byte of the compressed data.
   The gzip trailer containing the CRC-32 and length of the uncompressed data
   is verified.  This trailer will be later overwritten.

   Then the last block bit is cleared by seeking back in the file and rewriting
   the byte that contains it.  Seeking forward, the last byte of the compressed
   data is saved along with the number of unused bits to initialize deflate.

   A deflate process is initialized, using the last 32K of the uncompressed
   data from the gzip file to initialize the dictionary.  If the total
   uncompressed data was less than 32K, then all of it is used to initialize
   the dictionary.  The deflate output bit buffer is also initialized with the
   last bits from the original deflate stream.  From here on, the data to
   append is simply compressed using deflate, and written to the gzip file.
   When that is complete, the new CRC-32 and uncompressed length are written
   as the trailer of the gzip file.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include "zlib.h"

#define local static
#define LGCHUNK 14
#define CHUNK (1U << LGCHUNK)
#define DSIZE 32768U

/* print an error message and terminate with extreme prejudice */
local void bye(char *msg1, char *msg2)
{
    fprintf(stderr, "gzappend error: %s%s\n", msg1, msg2);
    exit(1);
}

/* return the greatest common divisor of a and b using Euclid's algorithm,
   modified to be fast when one argument much greater than the other, and
   coded to avoid unnecessary swapping */
local unsigned gcd(unsigned a, unsigned b)
{
    unsigned c;

    while (a && b)
        if (a > b) {
            c = b;
            while (a - c >= c)
                c <<= 1;
            a -= c;
        }
        else {
            c = a;
            while (b - c >= c)
                c <<= 1;
            b -= c;
        }
    return a + b;
}

/* rotate list[0..len-1] left by rot positions, in place */
local void rotate(unsigned char *list, unsigned len, unsigned rot)
{
    unsigned char tmp;
    unsigned cycles;
    unsigned char *start, *last, *to, *from;

    /* normalize rot and handle degenerate cases */
    if (len < 2) return;
    if (rot >= len) rot %= len;
    if (rot == 0) return;

    /* pointer to last entry in list */
    last = list + (len - 1);

    /* do simple left shift by one */
    if (rot == 1) {
        tmp = *list;
        memcpy(list, list + 1, len - 1);
        *last = tmp;
        return;
    }

    /* do simple right shift by one */
    if (rot == len - 1) {
        tmp = *last;
        memmove(list + 1, list, len - 1);
        *list = tmp;
        return;
    }

    /* otherwise do rotate as a set of cycles in place */
    cycles = gcd(len, rot);             /* number of cycles */
    do {
        start = from = list + cycles;   /* start index is arbitrary */
        tmp = *from;                    /* save entry to be overwritten */
        for (;;) {
            to = from;                  /* next step in cycle */
            from += rot;                /* go right rot positions */
            if (from > last) from -= len;   /* (pointer better not wrap) */
            if (from == start) break;   /* all but one shifted */
            *to = *from;                /* shift left */
        }
        *to = tmp;                      /* complete the circle */
    } while (--cycles);
}

/* structure for gzip file read operations */
typedef struct {
    int fd;                     /* file descriptor */
    int size;                   /* 1 << size is bytes in buf */
    unsigned left;              /* bytes available at next */
    unsigned char *buf;         /* buffer */
    unsigned char *next;        /* next byte in buffer */
    char *name;                 /* file name for error messages */
} file;

/* reload buffer */
local int readin(file *in)
{
    int len;

    len = read(in->fd, in->buf, 1 << in->size);
    if (len == -1) bye("error reading ", in->name);
    in->left = (unsigned)len;
    in->next = in->buf;
    return len;
}

/* read from file in, exit if end-of-file */
local int readmore(file *in)
{
    if (readin(in) == 0) bye("unexpected end of ", in->name);
    return 0;
}

#define read1(in) (in->left == 0 ? readmore(in) : 0, \
                   in->left--, *(in->next)++)

/* skip over n bytes of in */
local void skip(file *in, unsigned n)
{
    unsigned bypass;

    if (n > in->left) {
        n -= in->left;
        bypass = n & ~((1U << in->size) - 1);
        if (bypass) {
            if (lseek(in->fd, (off_t)bypass, SEEK_CUR) == -1)
                bye("seeking ", in->name);
            n -= bypass;
        }
        readmore(in);
        if (n > in->left)
            bye("unexpected end of ", in->name);
    }
    in->left -= n;
    in->next += n;
}

/* read a four-byte unsigned integer, little-endian, from in */
unsigned long read4(file *in)
{
    unsigned long val;

    val = read1(in);
    val += (unsigned)read1(in) << 8;
    val += (unsigned long)read1(in) << 16;
    val += (unsigned long)read1(in) << 24;
    return val;
}

/* skip over gzip header */
local void gzheader(file *in)
{
    int flags;
    unsigned n;

    if (read1(in) != 31 || read1(in) != 139) bye(in->name, " not a gzip file");
    if (read1(in) != 8) bye("unknown compression method in", in->name);
    flags = read1(in);
    if (flags & 0xe0) bye("unknown header flags set in", in->name);
    skip(in, 6);
    if (flags & 4) {
        n = read1(in);
        n += (unsigned)(read1(in)) << 8;
        skip(in, n);
    }
    if (flags & 8) while (read1(in) != 0) ;
    if (flags & 16) while (read1(in) != 0) ;
    if (flags & 2) skip(in, 2);
}

/* decompress gzip file "name", return strm with a deflate stream ready to
   continue compression of the data in the gzip file, and return a file
   descriptor pointing to where to write the compressed data -- the deflate
   stream is initialized to compress using level "level" */
local int gzscan(char *name, z_stream *strm, int level)
{
    int ret, lastbit, left, full;
    unsigned have;
    unsigned long crc, tot;
    unsigned char *window;
    off_t lastoff, end;
    file gz;

    /* open gzip file */
    gz.name = name;
    gz.fd = open(name, O_RDWR, 0);
    if (gz.fd == -1) bye("cannot open ", name);
    gz.buf = malloc(CHUNK);
    if (gz.buf == NULL) bye("out of memory", "");
    gz.size = LGCHUNK;
    gz.left = 0;

    /* skip gzip header */
    gzheader(&gz);

    /* prepare to decompress */
    window = malloc(DSIZE);
    if (window == NULL) bye("out of memory", "");
    strm->zalloc = Z_NULL;
    strm->zfree = Z_NULL;
    strm->opaque = Z_NULL;
    ret = inflateInit2(strm, -15);
    if (ret != Z_OK) bye("out of memory", " or library mismatch");

    /* decompress the deflate stream, saving append information */
    lastbit = 0;
    lastoff = lseek(gz.fd, 0L, SEEK_CUR) - gz.left;
    left = 0;
    strm->avail_in = gz.left;
    strm->next_in = gz.next;
    crc = crc32(0L, Z_NULL, 0);
    have = full = 0;
    do {
        /* if needed, get more input */
        if (strm->avail_in == 0) {
            readmore(&gz);
            strm->avail_in = gz.left;
            strm->next_in = gz.next;
        }

        /* set up output to next available section of sliding window */
        strm->avail_out = DSIZE - have;
        strm->next_out = window + have;

        /* inflate and check for errors */
        ret = inflate(strm, Z_BLOCK);
        if (ret == Z_STREAM_ERROR) bye("internal stream error!", "");
        if (ret == Z_MEM_ERROR) bye("out of memory", "");
        if (ret == Z_DATA_ERROR)
            bye("invalid compressed data--format violated in", name);

        /* update crc and sliding window pointer */
        crc = crc32(crc, window + have, DSIZE - have - strm->avail_out);
        if (strm->avail_out)
            have = DSIZE - strm->avail_out;
        else {
            have = 0;
            full = 1;
        }

        /* process end of block */
        if (strm->data_type & 128) {
            if (strm->data_type & 64)
                left = strm->data_type & 0x1f;
            else {
                lastbit = strm->data_type & 0x1f;
                lastoff = lseek(gz.fd, 0L, SEEK_CUR) - strm->avail_in;
            }
        }
    } while (ret != Z_STREAM_END);
    inflateEnd(strm);
    gz.left = strm->avail_in;
    gz.next = strm->next_in;

    /* save the location of the end of the compressed data */
    end = lseek(gz.fd, 0L, SEEK_CUR) - gz.left;

    /* check gzip trailer and save total for deflate */
    if (crc != read4(&gz))
        bye("invalid compressed data--crc mismatch in ", name);
    tot = strm->total_out;
    if ((tot & 0xffffffffUL) != read4(&gz))
        bye("invalid compressed data--length mismatch in", name);

    /* if not at end of file, warn */
    if (gz.left || readin(&gz))
        fprintf(stderr,
            "gzappend warning: junk at end of gzip file overwritten\n");

    /* clear last block bit */
    lseek(gz.fd, lastoff - (lastbit != 0), SEEK_SET);
    if (read(gz.fd, gz.buf, 1) != 1) bye("reading after seek on ", name);
    *gz.buf = (unsigned char)(*gz.buf ^ (1 << ((8 - lastbit) & 7)));
    lseek(gz.fd, -1L, SEEK_CUR);
    if (write(gz.fd, gz.buf, 1) != 1) bye("writing after seek to ", name);

    /* if window wrapped, build dictionary from window by rotating */
    if (full) {
        rotate(window, DSIZE, have);
        have = DSIZE;
    }

    /* set up deflate stream with window, crc, total_in, and leftover bits */
    ret = deflateInit2(strm, level, Z_DEFLATED, -15, 8, Z_DEFAULT_STRATEGY);
    if (ret != Z_OK) bye("out of memory", "");
    deflateSetDictionary(strm, window, have);
    strm->adler = crc;
    strm->total_in = tot;
    if (left) {
        lseek(gz.fd, --end, SEEK_SET);
        if (read(gz.fd, gz.buf, 1) != 1) bye("reading after seek on ", name);
        deflatePrime(strm, 8 - left, *gz.buf);
    }
    lseek(gz.fd, end, SEEK_SET);

    /* clean up and return */
    free(window);
    free(gz.buf);
    return gz.fd;
}

/* append file "name" to gzip file gd using deflate stream strm -- if last
   is true, then finish off the deflate stream at the end */
local void gztack(char *name, int gd, z_stream *strm, int last)
{
    int fd, len, ret;
    unsigned left;
    unsigned char *in, *out;

    /* open file to compress and append */
    fd = 0;
    if (name != NULL) {
        fd = open(name, O_RDONLY, 0);
        if (fd == -1)
            fprintf(stderr, "gzappend warning: %s not found, skipping ...\n",
                    name);
    }

    /* allocate buffers */
    in = fd == -1 ? NULL : malloc(CHUNK);
    out = malloc(CHUNK);
    if (out == NULL) bye("out of memory", "");

    /* compress input file and append to gzip file */
    do {
        /* get more input */
        len = fd == -1 ? 0 : read(fd, in, CHUNK);
        if (len == -1) {
            fprintf(stderr,
                    "gzappend warning: error reading %s, skipping rest ...\n",
                    name);
            len = 0;
        }
        strm->avail_in = (unsigned)len;
        strm->next_in = in;
        if (len) strm->adler = crc32(strm->adler, in, (unsigned)len);

        /* compress and write all available output */
        do {
            strm->avail_out = CHUNK;
            strm->next_out = out;
            ret = deflate(strm, last && len == 0 ? Z_FINISH : Z_NO_FLUSH);
            left = CHUNK - strm->avail_out;
            while (left) {
                len = write(gd, out + CHUNK - strm->avail_out - left, left);
                if (len == -1) bye("writing gzip file", "");
                left -= (unsigned)len;
            }
        } while (strm->avail_out == 0 && ret != Z_STREAM_END);
    } while (len != 0);

    /* write trailer after last entry */
    if (last) {
        deflateEnd(strm);
        out[0] = (unsigned char)(strm->adler);
        out[1] = (unsigned char)(strm->adler >> 8);
        out[2] = (unsigned char)(strm->adler >> 16);
        out[3] = (unsigned char)(strm->adler >> 24);
        out[4] = (unsigned char)(strm->total_in);
        out[5] = (unsigned char)(strm->total_in >> 8);
        out[6] = (unsigned char)(strm->total_in >> 16);
        out[7] = (unsigned char)(strm->total_in >> 24);
        len = 8;
        do {
            ret = write(gd, out + 8 - len, len);
            if (ret == -1) bye("writing gzip file", "");
            len -= ret;
        } while (len);
        close(gd);
    }

    /* clean up and return */
    free(out);
    if (in != NULL) free(in);
    if (fd > 0) close(fd);
}

/* process the compression level option if present, scan the gzip file, and
   append the specified files, or append the data from stdin if no other file
   names are provided on the command line -- the gzip file must be writable
   and seekable */
int main(int argc, char **argv)
{
    int gd, level;
    z_stream strm;

    /* ignore command name */
    argv++;

    /* provide usage if no arguments */
    if (*argv == NULL) {
        printf("gzappend 1.1 (4 Nov 2003) Copyright (C) 2003 Mark Adler\n");
        printf(
            "usage: gzappend [-level] file.gz [ addthis [ andthis ... ]]\n");
        return 0;
    }

    /* set compression level */
    level = Z_DEFAULT_COMPRESSION;
    if (argv[0][0] == '-') {
        if (argv[0][1] < '0' || argv[0][1] > '9' || argv[0][2] != 0)
            bye("invalid compression level", "");
        level = argv[0][1] - '0';
        if (*++argv == NULL) bye("no gzip file name after options", "");
    }

    /* prepare to append to gzip file */
    gd = gzscan(*argv++, &strm, level);

    /* append files on command line, or from stdin if none */
    if (*argv == NULL)
        gztack(NULL, gd, &strm, 1);
    else
        do {
            gztack(*argv, gd, &strm, argv[1] == NULL);
        } while (*++argv != NULL);
    return 0;
}


code:
/* gzjoin -- command to join gzip files into one gzip file

  Copyright (C) 2004 Mark Adler, all rights reserved
  version 1.0, 11 Dec 2004

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the author be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.

  Mark Adler    madler@alumni.caltech.edu
 */

/*
 * Change history:
 *
 * 1.0  11 Dec 2004     - First version
 * 1.1  12 Jun 2005     - Changed ssize_t to long for portability
 */

/*
   gzjoin takes one or more gzip files on the command line and writes out a
   single gzip file that will uncompress to the concatenation of the
   uncompressed data from the individual gzip files.  gzjoin does this without
   having to recompress any of the data and without having to calculate a new
   crc32 for the concatenated uncompressed data.  gzjoin does however have to
   decompress all of the input data in order to find the bits in the compressed
   data that need to be modified to concatenate the streams.

   gzjoin does not do an integrity check on the input gzip files other than
   checking the gzip header and decompressing the compressed data.  They are
   otherwise assumed to be complete and correct.

   Each joint between gzip files removes at least 18 bytes of previous trailer
   and subsequent header, and inserts an average of about three bytes to the
   compressed data in order to connect the streams.  The output gzip file
   has a minimal ten-byte gzip header with no file name or modification time.

   This program was written to illustrate the use of the Z_BLOCK option of
   inflate() and the crc32_combine() function.  gzjoin will not compile with
   versions of zlib earlier than 1.2.3.
 */

#include <stdio.h>      /* fputs(), fprintf(), fwrite(), putc() */
#include <stdlib.h>     /* exit(), malloc(), free() */
#include <fcntl.h>      /* open() */
#include <unistd.h>     /* close(), read(), lseek() */
#include "zlib.h"
    /* crc32(), crc32_combine(), inflateInit2(), inflate(), inflateEnd() */

#define local static

/* exit with an error (return a value to allow use in an expression) */
local int bail(char *why1, char *why2)
{
    fprintf(stderr, "gzjoin error: %s%s, output incomplete\n", why1, why2);
    exit(1);
    return 0;
}

/* -- simple buffered file input with access to the buffer -- */

#define CHUNK 32768         /* must be a power of two and fit in unsigned */

/* bin buffered input file type */
typedef struct {
    char *name;             /* name of file for error messages */
    int fd;                 /* file descriptor */
    unsigned left;          /* bytes remaining at next */
    unsigned char *next;    /* next byte to read */
    unsigned char *buf;     /* allocated buffer of length CHUNK */
} bin;

/* close a buffered file and free allocated memory */
local void bclose(bin *in)
{
    if (in != NULL) {
        if (in->fd != -1)
            close(in->fd);
        if (in->buf != NULL)
            free(in->buf);
        free(in);
    }
}

/* open a buffered file for input, return a pointer to type bin, or NULL on
   failure */
local bin *bopen(char *name)
{
    bin *in;

    in = malloc(sizeof(bin));
    if (in == NULL)
        return NULL;
    in->buf = malloc(CHUNK);
    in->fd = open(name, O_RDONLY, 0);
    if (in->buf == NULL || in->fd == -1) {
        bclose(in);
        return NULL;
    }
    in->left = 0;
    in->next = in->buf;
    in->name = name;
    return in;
}

/* load buffer from file, return -1 on read error, 0 or 1 on success, with
   1 indicating that end-of-file was reached */
local int bload(bin *in)
{
    long len;

    if (in == NULL)
        return -1;
    if (in->left != 0)
        return 0;
    in->next = in->buf;
    do {
        len = (long)read(in->fd, in->buf + in->left, CHUNK - in->left);
        if (len < 0)
            return -1;
        in->left += (unsigned)len;
    } while (len != 0 && in->left < CHUNK);
    return len == 0 ? 1 : 0;
}

/* get a byte from the file, bail if end of file */
#define bget(in) (in->left ? 0 : bload(in), \
                  in->left ? (in->left--, *(in->next)++) : \
                    bail("unexpected end of file on ", in->name))

/* get a four-byte little-endian unsigned integer from file */
local unsigned long bget4(bin *in)
{
    unsigned long val;

    val = bget(in);
    val += (unsigned long)(bget(in)) << 8;
    val += (unsigned long)(bget(in)) << 16;
    val += (unsigned long)(bget(in)) << 24;
    return val;
}

/* skip bytes in file */
local void bskip(bin *in, unsigned skip)
{
    /* check pointer */
    if (in == NULL)
        return;

    /* easy case -- skip bytes in buffer */
    if (skip <= in->left) {
        in->left -= skip;
        in->next += skip;
        return;
    }

    /* skip what's in buffer, discard buffer contents */
    skip -= in->left;
    in->left = 0;

    /* seek past multiples of CHUNK bytes */
    if (skip > CHUNK) {
        unsigned left;

        left = skip & (CHUNK - 1);
        if (left == 0) {
            /* exact number of chunks: seek all the way minus one byte to check
               for end-of-file with a read */
            lseek(in->fd, skip - 1, SEEK_CUR);
            if (read(in->fd, in->buf, 1) != 1)
                bail("unexpected end of file on ", in->name);
            return;
        }

        /* skip the integral chunks, update skip with remainder */
        lseek(in->fd, skip - left, SEEK_CUR);
        skip = left;
    }

    /* read more input and skip remainder */
    bload(in);
    if (skip > in->left)
        bail("unexpected end of file on ", in->name);
    in->left -= skip;
    in->next += skip;
}

/* -- end of buffered input functions -- */

/* skip the gzip header from file in */
local void gzhead(bin *in)
{
    int flags;

    /* verify gzip magic header and compression method */
    if (bget(in) != 0x1f || bget(in) != 0x8b || bget(in) != 8)
        bail(in->name, " is not a valid gzip file");

    /* get and verify flags */
    flags = bget(in);
    if ((flags & 0xe0) != 0)
        bail("unknown reserved bits set in ", in->name);

    /* skip modification time, extra flags, and os */
    bskip(in, 6);

    /* skip extra field if present */
    if (flags & 4) {
        unsigned len;

        len = bget(in);
        len += (unsigned)(bget(in)) << 8;
        bskip(in, len);
    }

    /* skip file name if present */
    if (flags & 8)
        while (bget(in) != 0)
            ;

    /* skip comment if present */
    if (flags & 16)
        while (bget(in) != 0)
            ;

    /* skip header crc if present */
    if (flags & 2)
        bskip(in, 2);
}

/* write a four-byte little-endian unsigned integer to out */
local void put4(unsigned long val, FILE *out)
{
    putc(val & 0xff, out);
    putc((val >> 8) & 0xff, out);
    putc((val >> 16) & 0xff, out);
    putc((val >> 24) & 0xff, out);
}

/* Load up zlib stream from buffered input, bail if end of file */
local void zpull(z_streamp strm, bin *in)
{
    if (in->left == 0)
        bload(in);
    if (in->left == 0)
        bail("unexpected end of file on ", in->name);
    strm->avail_in = in->left;
    strm->next_in = in->next;
}

/* Write header for gzip file to out and initialize trailer. */
local void gzinit(unsigned long *crc, unsigned long *tot, FILE *out)
{
    fwrite("\x1f\x8b\x08\0\0\0\0\0\0\xff", 1, 10, out);
    *crc = crc32(0L, Z_NULL, 0);
    *tot = 0;
}

/* Copy the compressed data from name, zeroing the last block bit of the last
   block if clr is true, and adding empty blocks as needed to get to a byte
   boundary.  If clr is false, then the last block becomes the last block of
   the output, and the gzip trailer is written.  crc and tot maintains the
   crc and length (modulo 2^32) of the output for the trailer.  The resulting
   gzip file is written to out.  gzinit() must be called before the first call
   of gzcopy() to write the gzip header and to initialize crc and tot. */
local void gzcopy(char *name, int clr, unsigned long *crc, unsigned long *tot,
                  FILE *out)
{
    int ret;                /* return value from zlib functions */
    int pos;                /* where the "last block" bit is in byte */
    int last;               /* true if processing the last block */
    bin *in;                /* buffered input file */
    unsigned char *start;   /* start of compressed data in buffer */
    unsigned char *junk;    /* buffer for uncompressed data -- discarded */
    z_off_t len;            /* length of uncompressed data (support > 4 GB) */
    z_stream strm;          /* zlib inflate stream */

    /* open gzip file and skip header */
    in = bopen(name);
    if (in == NULL)
        bail("could not open ", name);
    gzhead(in);

    /* allocate buffer for uncompressed data and initialize raw inflate
       stream */
    junk = malloc(CHUNK);
    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);
    if (junk == NULL || ret != Z_OK)
        bail("out of memory", "");

    /* inflate and copy compressed data, clear last-block bit if requested */
    len = 0;
    zpull(&strm, in);
    start = strm.next_in;
    last = start[0] & 1;
    if (last && clr)
        start[0] &= ~1;
    strm.avail_out = 0;
    for (;;) {
        /* if input used and output done, write used input and get more */
        if (strm.avail_in == 0 && strm.avail_out != 0) {
            fwrite(start, 1, strm.next_in - start, out);
            start = in->buf;
            in->left = 0;
            zpull(&strm, in);
        }

        /* decompress -- return early when end-of-block reached */
        strm.avail_out = CHUNK;
        strm.next_out = junk;
        ret = inflate(&strm, Z_BLOCK);
        switch (ret) {
        case Z_MEM_ERROR:
            bail("out of memory", "");
        case Z_DATA_ERROR:
            bail("invalid compressed data in ", in->name);
        }

        /* update length of uncompressed data */
        len += CHUNK - strm.avail_out;

        /* check for block boundary (only get this when block copied out) */
        if (strm.data_type & 128) {
            /* if that was the last block, then done */
            if (last)
                break;

            /* number of unused bits in last byte */
            pos = strm.data_type & 7;

            /* find the next last-block bit */
            if (pos != 0) {
                /* next last-block bit is in last used byte */
                pos = 0x100 >> pos;
                last = strm.next_in[-1] & pos;
                if (last && clr)
                    strm.next_in[-1] &= ~pos;
            }
            else {
                /* next last-block bit is in next unused byte */
                if (strm.avail_in == 0) {
                    /* don't have that byte yet -- get it */
                    fwrite(start, 1, strm.next_in - start, out);
                    start = in->buf;
                    in->left = 0;
                    zpull(&strm, in);
                }
                last = strm.next_in[0] & 1;
                if (last && clr)
                    strm.next_in[0] &= ~1;
            }
        }
    }

    /* update buffer with unused input */
    in->left = strm.avail_in;
    in->next = strm.next_in;

    /* copy used input, write empty blocks to get to byte boundary */
    pos = strm.data_type & 7;
    fwrite(start, 1, in->next - start - 1, out);
    last = in->next[-1];
    if (pos == 0 || !clr)
        /* already at byte boundary, or last file: write last byte */
        putc(last, out);
    else {
        /* append empty blocks to last byte */
        last &= ((0x100 >> pos) - 1);       /* assure unused bits are zero */
        if (pos & 1) {
            /* odd -- append an empty stored block */
            putc(last, out);
            if (pos == 1)
                putc(0, out);               /* two more bits in block header */
            fwrite("\0\0\xff\xff", 1, 4, out);
        }
        else {
            /* even -- append 1, 2, or 3 empty fixed blocks */
            switch (pos) {
            case 6:
                putc(last | 8, out);
                last = 0;
            case 4:
                putc(last | 0x20, out);
                last = 0;
            case 2:
                putc(last | 0x80, out);
                putc(0, out);
            }
        }
    }

    /* update crc and tot */
    *crc = crc32_combine(*crc, bget4(in), len);
    *tot += (unsigned long)len;

    /* clean up */
    inflateEnd(&strm);
    free(junk);
    bclose(in);

    /* write trailer if this is the last gzip file */
    if (!clr) {
        put4(*crc, out);
        put4(*tot, out);
    }
}

/* join the gzip files on the command line, write result to stdout */
int main(int argc, char **argv)
{
    unsigned long crc, tot;     /* running crc and total uncompressed length */

    /* skip command name */
    argc--;
    argv++;

    /* show usage if no arguments */
    if (argc == 0) {
        fputs("gzjoin usage: gzjoin f1.gz [f2.gz [f3.gz ...]] > fjoin.gz\n",
              stderr);
        return 0;
    }

    /* join gzip files on command line and write to stdout */
    gzinit(&crc, &tot, stdout);
    while (argc--)
        gzcopy(*argv++, argc, &crc, &tot, stdout);

    /* done */
    return 0;
}


code:
/*
 * gzlog.c
 * Copyright (C) 2004 Mark Adler
 * For conditions of distribution and use, see copyright notice in gzlog.h
 * version 1.0, 26 Nov 2004
 *
 */

#include <string.h>             /* memcmp() */
#include <stdlib.h>             /* malloc(), free(), NULL */
#include <sys/types.h>          /* size_t, off_t */
#include <unistd.h>             /* read(), close(), sleep(), ftruncate(), */
                                /* lseek() */
#include <fcntl.h>              /* open() */
#include <sys/file.h>           /* flock() */
#include "zlib.h"               /* deflateInit2(), deflate(), deflateEnd() */

#include "gzlog.h"              /* interface */
#define local static

/* log object structure */
typedef struct {
    int id;                 /* object identifier */
    int fd;                 /* log file descriptor */
    off_t extra;            /* offset of extra "ap" subfield */
    off_t mark_off;         /* offset of marked data */
    off_t last_off;         /* offset of last block */
    unsigned long crc;      /* uncompressed crc */
    unsigned long len;      /* uncompressed length (modulo 2^32) */
    unsigned stored;        /* length of current stored block */
} gz_log;

#define GZLOGID 19334       /* gz_log object identifier */

#define LOCK_RETRY 1            /* retry lock once a second */
#define LOCK_PATIENCE 1200      /* try about twenty minutes before forcing */

/* acquire a lock on a file */
local int lock(int fd)
{
    int patience;

    /* try to lock every LOCK_RETRY seconds for LOCK_PATIENCE seconds */
    patience = LOCK_PATIENCE;
    do {
        if (flock(fd, LOCK_EX + LOCK_NB) == 0)
            return 0;
        (void)sleep(LOCK_RETRY);
        patience -= LOCK_RETRY;
    } while (patience > 0);

    /* we've run out of patience -- give up */
    return -1;
}

/* release lock */
local void unlock(int fd)
{
    (void)flock(fd, LOCK_UN);
}

/* release a log object */
local void log_clean(gz_log *log)
{
    unlock(log->fd);
    (void)close(log->fd);
    free(log);
}

/* read an unsigned long from a byte buffer little-endian */
local unsigned long make_ulg(unsigned char *buf)
{
    int n;
    unsigned long val;

    val = (unsigned long)(*buf++);
    for (n = 8; n < 32; n += 8)
        val += (unsigned long)(*buf++) << n;
    return val;
}

/* read an off_t from a byte buffer little-endian */
local off_t make_off(unsigned char *buf)
{
    int n;
    off_t val;

    val = (off_t)(*buf++);
    for (n = 8; n < 64; n += 8)
        val += (off_t)(*buf++) << n;
    return val;
}

/* write an unsigned long little-endian to byte buffer */
local void dice_ulg(unsigned long val, unsigned char *buf)
{
    int n;

    for (n = 0; n < 4; n++) {
        *buf++ = val & 0xff;
        val >>= 8;
    }
}

/* write an off_t little-endian to byte buffer */
local void dice_off(off_t val, unsigned char *buf)
{
    int n;

    for (n = 0; n < 8; n++) {
        *buf++ = val & 0xff;
        val >>= 8;
    }
}

/* initial, empty gzip file for appending */
local char empty_gz[] = {
    0x1f, 0x8b,                 /* magic gzip id */
    8,                          /* compression method is deflate */
    4,                          /* there is an extra field */
    0, 0, 0, 0,                 /* no modification time provided */
    0, 0xff,                    /* no extra flags, no OS */
    20, 0, 'a', 'p', 16, 0,     /* extra field with "ap" subfield */
    32, 0, 0, 0, 0, 0, 0, 0,    /* offset of uncompressed data */
    32, 0, 0, 0, 0, 0, 0, 0,    /* offset of last block */
    1, 0, 0, 0xff, 0xff,        /* empty stored block (last) */
    0, 0, 0, 0,                 /* crc */
    0, 0, 0, 0                  /* uncompressed length */
};

/* initialize a log object with locking */
void *gzlog_open(char *path)
{
    unsigned xlen;
    unsigned char temp[20];
    unsigned sub_len;
    int good;
    gz_log *log;

    /* allocate log structure */
    log = malloc(sizeof(gz_log));
    if (log == NULL)
        return NULL;
    log->id = GZLOGID;

    /* open file, creating it if necessary, and locking it */
    log->fd = open(path, O_RDWR | O_CREAT, 0600);
    if (log->fd < 0) {
        free(log);
        return NULL;
    }
    if (lock(log->fd)) {
        close(log->fd);
        free(log);
        return NULL;
    }

    /* if file is empty, write new gzip stream */
    if (lseek(log->fd, 0, SEEK_END) == 0) {
        if (write(log->fd, empty_gz, sizeof(empty_gz)) != sizeof(empty_gz)) {
            log_clean(log);
            return NULL;
        }
    }

    /* check gzip header */
    (void)lseek(log->fd, 0, SEEK_SET);
    if (read(log->fd, temp, 12) != 12 || temp[0] != 0x1f ||
        temp[1] != 0x8b || temp[2] != 8 || (temp[3] & 4) == 0) {
        log_clean(log);
        return NULL;
    }

    /* process extra field to find "ap" sub-field */
    xlen = temp[10] + (temp[11] << 8);
    good = 0;
    while (xlen) {
        if (xlen < 4 || read(log->fd, temp, 4) != 4)
            break;
        sub_len = temp[2];
        sub_len += temp[3] << 8;
        xlen -= 4;
        if (memcmp(temp, "ap", 2) == 0 && sub_len == 16) {
            good = 1;
            break;
        }
        if (xlen < sub_len)
            break;
        (void)lseek(log->fd, sub_len, SEEK_CUR);
        xlen -= sub_len;
    }
    if (!good) {
        log_clean(log);
        return NULL;
    }

    /* read in "ap" sub-field */
    log->extra = lseek(log->fd, 0, SEEK_CUR);
    if (read(log->fd, temp, 16) != 16) {
        log_clean(log);
        return NULL;
    }
    log->mark_off = make_off(temp);
    log->last_off = make_off(temp + 8);

    /* get crc, length of gzip file */
    (void)lseek(log->fd, log->last_off, SEEK_SET);
    if (read(log->fd, temp, 13) != 13 ||
        memcmp(temp, "\001\000\000\377\377", 5) != 0) {
        log_clean(log);
        return NULL;
    }
    log->crc = make_ulg(temp + 5);
    log->len = make_ulg(temp + 9);

    /* set up to write over empty last block */
    (void)lseek(log->fd, log->last_off + 5, SEEK_SET);
    log->stored = 0;
    return (void *)log;
}

/* maximum amount to put in a stored block before starting a new one */
#define MAX_BLOCK 16384

/* write a block to a log object */
int gzlog_write(void *obj, char *data, size_t len)
{
    size_t some;
    unsigned char temp[5];
    gz_log *log;

    /* check object */
    log = (gz_log *)obj;
    if (log == NULL || log->id != GZLOGID)
        return 1;

    /* write stored blocks until all of the input is written */
    do {
        some = MAX_BLOCK - log->stored;
        if (some > len)
            some = len;
        if (write(log->fd, data, some) != some)
            return 1;
        log->crc = crc32(log->crc, data, some);
        log->len += some;
        len -= some;
        data += some;
        log->stored += some;

        /* if the stored block is full, end it and start another */
        if (log->stored == MAX_BLOCK) {
            (void)lseek(log->fd, log->last_off, SEEK_SET);
            temp[0] = 0;
            dice_ulg(log->stored + ((unsigned long)(~log->stored) << 16),
                     temp + 1);
            if (write(log->fd, temp, 5) != 5)
                return 1;
            log->last_off = lseek(log->fd, log->stored, SEEK_CUR);
            (void)lseek(log->fd, 5, SEEK_CUR);
            log->stored = 0;
        }
    } while (len);
    return 0;
}

/* recompress the remaining stored deflate data in place */
local int recomp(gz_log *log)
{
    z_stream strm;
    size_t len, max;
    unsigned char *in;
    unsigned char *out;
    unsigned char temp[16];

    /* allocate space and read it all in (it's around 1 MB) */
    len = log->last_off - log->mark_off;
    max = len + (len >> 12) + (len >> 14) + 11;
    out = malloc(max);
    if (out == NULL)
        return 1;
    in = malloc(len);
    if (in == NULL) {
        free(out);
        return 1;
    }
    (void)lseek(log->fd, log->mark_off, SEEK_SET);
    if (read(log->fd, in, len) != len) {
        free(in);
        free(out);
        return 1;
    }

    /* recompress in memory, decoding stored data as we go */
    /* note: this assumes that unsigned is four bytes or more */
    /*       consider not making that assumption */
    strm.zalloc = Z_NULL;
    strm.zfree = Z_NULL;
    strm.opaque = Z_NULL;
    if (deflateInit2(&strm, Z_BEST_COMPRESSION, Z_DEFLATED, -15, 8,
        Z_DEFAULT_STRATEGY) != Z_OK) {
        free(in);
        free(out);
        return 1;
    }
    strm.next_in = in;
    strm.avail_out = max;
    strm.next_out = out;
    while (len >= 5) {
        if (strm.next_in[0] != 0)
            break;
        strm.avail_in = strm.next_in[1] + (strm.next_in[2] << 8);
        strm.next_in += 5;
        len -= 5;
        if (strm.avail_in != 0) {
            if (len < strm.avail_in)
                break;
            len -= strm.avail_in;
            (void)deflate(&strm, Z_NO_FLUSH);
            if (strm.avail_in != 0 || strm.avail_out == 0)
                break;
        }
    }
    (void)deflate(&strm, Z_SYNC_FLUSH);
    (void)deflateEnd(&strm);
    free(in);
    if (len != 0 || strm.avail_out == 0) {
        free(out);
        return 1;
    }

    /* overwrite stored data with compressed data */
    (void)lseek(log->fd, log->mark_off, SEEK_SET);
    len = max - strm.avail_out;
    if (write(log->fd, out, len) != len) {
        free(out);
        return 1;
    }
    free(out);

    /* write last empty block, crc, and length */
    log->mark_off = log->last_off = lseek(log->fd, 0, SEEK_CUR);
    temp[0] = 1;
    dice_ulg(0xffffL << 16, temp + 1);
    dice_ulg(log->crc, temp + 5);
    dice_ulg(log->len, temp + 9);
    if (write(log->fd, temp, 13) != 13)
        return 1;

    /* truncate file to discard remaining stored data and old trailer */
    ftruncate(log->fd, lseek(log->fd, 0, SEEK_CUR));

    /* update extra field to point to new last empty block */
    (void)lseek(log->fd, log->extra, SEEK_SET);
    dice_off(log->mark_off, temp);
    dice_off(log->last_off, temp + 8);
    if (write(log->fd, temp, 16) != 16)
        return 1;
    return 0;
}

/* maximum accumulation of stored blocks before compressing */
#define MAX_STORED 1048576

/* close log object */
int gzlog_close(void *obj)
{
    unsigned char temp[8];
    gz_log *log;

    /* check object */
    log = (gz_log *)obj;
    if (log == NULL || log->id != GZLOGID)
        return 1;

    /* go to start of most recent block being written */
    (void)lseek(log->fd, log->last_off, SEEK_SET);

    /* if some stuff was put there, update block */
    if (log->stored) {
        temp[0] = 0;
        dice_ulg(log->stored + ((unsigned long)(~log->stored) << 16),
                 temp + 1);
        if (write(log->fd, temp, 5) != 5)
            return 1;
        log->last_off = lseek(log->fd, log->stored, SEEK_CUR);
    }

    /* write last block (empty) */
    if (write(log->fd, "\001\000\000\377\377", 5) != 5)
        return 1;

    /* write updated crc and uncompressed length */
    dice_ulg(log->crc, temp);
    dice_ulg(log->len, temp + 4);
    if (write(log->fd, temp, 8) != 8)
        return 1;

    /* put offset of that last block in gzip extra block */
    (void)lseek(log->fd, log->extra + 8, SEEK_SET);
    dice_off(log->last_off, temp);
    if (write(log->fd, temp, 8) != 8)
        return 1;

    /* if more than 1 MB stored, then time to compress it */
    if (log->last_off - log->mark_off > MAX_STORED) {
        if (recomp(log))
            return 1;
    }

    /* unlock and close file */
    log_clean(log);
    return 0;
}


code:
/* gzlog.h
  Copyright (C) 2004 Mark Adler, all rights reserved
  version 1.0, 26 Nov 2004

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the author be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.

  Mark Adler    madler@alumni.caltech.edu
 */

/*
   The gzlog object allows writing short messages to a gzipped log file,
   opening the log file locked for small bursts, and then closing it.  The log
   object works by appending stored data to the gzip file until 1 MB has been
   accumulated.  At that time, the stored data is compressed, and replaces the
   uncompressed data in the file.  The log file is truncated to its new size at
   that time.  After closing, the log file is always valid gzip file that can
   decompressed to recover what was written.

   A gzip header "extra" field contains two file offsets for appending.  The
   first points to just after the last compressed data.  The second points to
   the last stored block in the deflate stream, which is empty.  All of the
   data between those pointers is uncompressed.
 */

/* Open a gzlog object, creating the log file if it does not exist.  Return
   NULL on error.  Note that gzlog_open() could take a long time to return if
   there is difficulty in locking the file. */
void *gzlog_open(char *path);

/* Write to a gzlog object.  Return non-zero on error.  This function will
   simply write data to the file uncompressed.  Compression of the data
   will not occur until gzlog_close() is called.  It is expected that
   gzlog_write() is used for a short message, and then gzlog_close() is
   called.  If a large amount of data is to be written, then the application
   should write no more than 1 MB at a time with gzlog_write() before
   calling gzlog_close() and then gzlog_open() again. */
int gzlog_write(void *log, char *data, size_t len);

/* Close a gzlog object.  Return non-zero on error.  The log file is locked
   until this function is called.  This function will compress stored data
   at the end of the gzip file if at least 1 MB has been accumulated.  Note
   that the file will not be a valid gzip file until this function completes.
 */
int gzlog_close(void *log);