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.NET wrapper for libbz2

, 14 Jul 2003
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.NET wrapper for libbz2, written in MC++

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. Smile | :)

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

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About the Author

leppie
Software Developer
South Africa South Africa
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Comments and Discussions

 
GeneralStream Compress and buffer compress Pinmemberstaceyw14-Oct-04 11:53 
GeneralWhy system can't find the file Pinmemberwilliamlwl29-Mar-04 2:47 
QuestionCAB format compression? Pinmemberdragomir17-Feb-04 23:18 
AnswerRe: CAB format compression? PinmemberKalpana Volety2-Mar-14 8:43 
QuestionSo... what do I do with it? Pinmemberfadden22-Oct-03 15:37 
AnswerRe: So... what do I do with it? Pinmemberfadden23-Oct-03 14:33 
GeneralRe: So... what do I do with it? PinmemberMember 779040727-Mar-11 21:04 
GeneralAnother inspiring article by leppie PinmemberStephane Rodriguez.16-Jul-03 11:00 
GeneralRe: Another inspiring article by leppie Pinmemberleppie16-Jul-03 14:12 
Generalagain PinmemberROK_RShadow15-Jul-03 14:51 
GeneralRe: again PinmemberJan van den Baard16-Jul-03 7:31 
GeneralRe: again Pinmemberleppie16-Jul-03 8:09 
GeneralRe: again PinmemberROK_RShadow16-Jul-03 19:11 
GeneralRe: again Pinmemberleppie17-Jul-03 8:01 
GeneralRe: again PinsitebuilderPaul Watson16-Jul-03 8:19 
GeneralBTW PinmemberJörgen Sigvardsson15-Jul-03 10:35 
GeneralRe: BTW Pinmemberleppie15-Jul-03 10:45 
GeneralRe: BTW PinmemberJörgen Sigvardsson15-Jul-03 11:18 
GeneralVery off topic PinmemberJörgen Sigvardsson15-Jul-03 10:35 
GeneralRe: Very off topic Pinmemberleppie15-Jul-03 10:43 

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