.NET wrapper for libbz2

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BzipStream

BzipStream is a small .NET wrapper for the Bzip2 compression utility. Bz2 compression is similar to Gzip where only one file/chunk/blob is compressed, unlike zip, rar, ace, etc. Its normally used to compress a tarball (.tar file).

Below is the implementation diagram:

public class BzipStream : Stream
{
  public BzipStream(string filename, FileAccess mode);
  public override void Close();
  public static byte[] Compress(byte[] buffer);
  public static byte[] Compress(byte[] buffer, int level);
  public static byte[] Decompress(byte[] buffer);
  public override void Flush();
  public static BzipStream OpenRead(string filename);
  public static BzipStream OpenWrite(string filename);
  public override int Read(byte[] buffer, int start, int length);
  public override long Seek(long pos, SeekOrigin origin);
  public override void SetLength(long len);
  public override void Write(byte[] buffer, int start, int length);
  public override bool CanRead { get; }
  public override bool CanSeek { get; }
  public override bool CanWrite { get; }
  public override long Length { get; }
  public override long Position { get; set; }
}

The De/Compress methods are utility methods to quickly de/compress a byte[]. The following methods are implemented but not supported:

• Length
• Position
• Seek

Also FileAccess.ReadWrite is NOT supported.

Usage (C#)

BzipStream bz = new BzipStream("file.bz2", FileAccess.Write);

Stream s = File.OpenRead("file");
int len = 8192;
byte[] buffer = new byte[len];
while ((len = s.Read(buffer, 0, len)) > 0)
{
  bz.Write(buffer, 0, len);
}
s.Close();
bz.Close();

//or using utility methods
byte[] cbuff = BzipStream.Compress(buffer);

buffer = BzipStream.Decompress(cbuff);

Implementation

libbz2 is compiled to vanilla C, and a single file (dotbz2.cpp) carries the MC++ implementation (and ONLY that file has "managed" compile flags set). Many people have been asking how to do this. Very easy. Just look.

The basic pattern is:

1. Get .NET object
2. Allocate memory on the heap
3. Copy object and get an IntPtr
4. Cast the IntPtr to void*
5. Cast to <T>*
6. Do unmanaged function
7. Cast result to void*
8. Cast to IntPtr
9. Copy from heap to object
10. Free heap memory

Steps 7 and 8 are not really necessary as we have a reference to the IntPtr already.

Conclusion

Just a small example of how to wrap a C library in MC++. Suggestions welcome. I could paste the code, its only 185 lines. Don't flame me for the length of the article. :)

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