How to decompress gzipstream with zlib

Question

Can someone tell me which function I need to use in order to decompress a byte array that has been compressed with vb.net\'s gzipstream. I would like to use zlib.

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Answer 1

Here is a C function that does the job with zlib:

int gzip_inflate(char *compr, int comprLen, char *uncompr, int uncomprLen)
{
    int err;
    z_stream d_stream; /* decompression stream */

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

    d_stream.next_in  = (unsigned char *)compr;
    d_stream.avail_in = comprLen;

    d_stream.next_out = (unsigned char *)uncompr;
    d_stream.avail_out = uncomprLen;

    err = inflateInit2(&d_stream, 16+MAX_WBITS);
    if (err != Z_OK) return err;

    while (err != Z_STREAM_END) err = inflate(&d_stream, Z_NO_FLUSH);

    err = inflateEnd(&d_stream);
    return err;
}

The uncompressed string is returned in uncompr. It's a null-terminated C string so you can do puts(uncompr). The function above only works if the output is text. I have tested it and it works.