Bruce Ge

I was using Gzip Encoder to compress wcf message, it surprised me that sometimes the compression message size is even bigger than the original size, so I looked the code, I found within GZipMessageEncoderFactory.cs, the method "CompressBuffer" in the GZipMessageEncoderFactory class is not quite right. it was like this originally:

private static ArraySegment<byte> CompressBuffer(ArraySegment<byte> buffer, BufferManager bufferManager, int messageOffset)
{
   ....
  var byteArray = new ArraySegment<byte>(bufferedBytes, messageOffset,
                                                       bufferedBytes.Length - messageOffset);

  return byteArray;
}

if we use the method above, the count of the new ArraySegment<T> will be the bufferedBytes, as BufferManager using TakeBuffer method to grab a buffer which is the nearest bigger 2^N byte, e.g. if input param is 522 bytes for TakeBuffer method, it will grab a buffer which has 1024 bytes. And the constructor of ArraySegment will take the third parameter(bold above) to reflects the actual size of the ArraySegment, if size of the bufferedBytes(first params) is less than third parameter, it will fill byte0 to the rest. that is why sometimes the size is even bigger than the original size. 

it should be like this:

private static ArraySegment<byte> CompressBuffer(ArraySegment<byte> buffer, BufferManager bufferManager, int messageOffset)
{
   ....
  var byteArray = new ArraySegment<byte>(bufferedBytes, messageOffset,
                       compressedBytes.Length);

  return byteArray;
}

Also I found the Gzip compression doesn't have high compression ratio, I decided to use 7zip and gzip combination then, I found a good article about 7zip: 7Zip (LZMA) In-Memory Compression with C#, after adding it to my project, I can use it straight forward:

private static ArraySegment<byte> CompressBuffer(ArraySegment<byte> buffer, BufferManager bufferManager, int messageOffset)
{
 using (var memoryStream = new MemoryStream())
 {
  var zipperStream = new GZipStream(memoryStream, CompressionMode.Compress, true);

  using (zipperStream)
   zipperStream.Write(buffer.Array,
      buffer.Offset, buffer.Count);

  byte[] compressedBytes1 = memoryStream.ToArray();
  byte[] compressedBytes = SevenZip.Compression.LZMA.SevenZipHelper.Compress(compressedBytes1);
  byte[] bufferedBytes = bufferManager.TakeBuffer(
     compressedBytes.Length + messageOffset);

  Array.Copy(compressedBytes, 0, bufferedBytes, messageOffset,
     compressedBytes.Length);

  bufferManager.ReturnBuffer(buffer.Array);
  var byteArray = new ArraySegment<byte>(bufferedBytes, messageOffset,
     compressedBytes.Length);

  return byteArray;
 }
}

//Helper method to decompress an array of bytes
private static ArraySegment<byte> DecompressBuffer(ArraySegment<byte> buffer, BufferManager bufferManager)
{
 var memoryStream1 = new MemoryStream(buffer.Array, buffer.Offset, buffer.Count - buffer.Offset);
 var memoryStream=new MemoryStream(SevenZip.Compression.LZMA.SevenZipHelper.Decompress(memoryStream1.ToArray()));

 var decompressedStream = new MemoryStream();
 int totalRead = 0;
 int blockSize = 1024;
 byte[] tempBuffer = bufferManager.TakeBuffer(blockSize);
 using (var gzStream = new GZipStream(memoryStream, CompressionMode.Decompress))
 {
  while (true)
  {
   int bytesRead = gzStream.Read(tempBuffer, 0, blockSize);
   if (bytesRead == 0)
    break;
   decompressedStream.Write(tempBuffer, 0, bytesRead);
   totalRead += bytesRead;
  }
 }
 bufferManager.ReturnBuffer(tempBuffer);
  
 byte[] decompressedBytes = decompressedStream.ToArray();
 byte[] bufferManagerBuffer = bufferManager.TakeBuffer(decompressedBytes.Length + buffer.Offset);
 Array.Copy(buffer.Array, 0, bufferManagerBuffer, 0, buffer.Offset);
 Array.Copy(decompressedBytes, 0, bufferManagerBuffer, buffer.Offset, decompressedBytes.Length);

 var byteArray = new ArraySegment<byte>(bufferManagerBuffer, buffer.Offset, decompressedBytes.Length);
 bufferManager.ReturnBuffer(buffer.Array);

 return byteArray;
}