Question

The deflate function of zlib accepts a Z_FULL_FLUSH option as its argument, as far as I know, when full flush is performed, a full flush point (0,0,0xFF,0xFF) will be set, subsequent data will be independent from the bytes precedes that point, hence makes the compressed data quasi random accessible. I’ve read a little bit source of dictzip, it took advantage of this feature to implement its chunk-wise random-accessibility, yet kept the compatibility with gzip. I want to reimplement dictzip compressor/decompressor using CLR provided functionality. The decompressor (random parts reader) is easy, I can just use the DeflateStream to decompress the data chunk by chunk, with no problem, but as for the creation, there is a huge obstacle, the API of DeflateStream is too high-level, it seems all deflate details are hidden, hence unexploitable. I really don’t like to include a C shared library in my C# project, it makes the cross-platform deployment very painful, and cancels the benefits of choosing coding in C# in the first place. So, what should I do? Is there any way I can circumvent this obstacle merely using managed code? Does Mono provide a lower-level wrapper for zlib so that I can call deflate with full flush option? Any advice will be appreciated!

— >8 —

Thanks to Mark Adler who provided the answer. DotNetZip (specifically Ionic.Zlib.DeflateStream) supports exactly the feature I was asking for. The following example shows how it works:

        Encoding u8 = Encoding.UTF8;
        byte[]  s1 = u8.GetBytes("the quick brown fox "),
                s2 = u8.GetBytes("jumps over the lazy dog!");
        var ms = new MemoryStream(100);
        var deflator = new DeflateStream(ms, CompressionMode.Compress, true);
        deflator.FlushMode = FlushType.Full;
        deflator.Write(s1, 0, s1.Length);
        deflator.Flush();
        var pos = ms.Position;//remember the full flush point
        deflator.Write(s2, 0, s2.Length);
        deflator.Dispose();

        var inflator = new DeflateStream(ms, CompressionMode.Decompress);
        ms.Position = pos;
        byte[] buf = new byte[100];
        inflator.Read(buf, 0, s2.Length);
        Console.WriteLine(u8.GetString(buf));//output: jumps over the lazy dog!

Answer 1

Try DotNetZip. SO won’t let me post less than 30 characters, even though that is a complete and correct answer, so I added this extraneous sentence.