/* 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;
}