/// <summary>
/// Provides a filter for compressing a <see cref="Stream"/> with LZMA.
/// </summary>
/// <param name="stream">The underlying <see cref="Stream"/> to write the compressed data to.</param>
/// <param name="bufferSize">The maximum number of uncompressed bytes to buffer. 32k (the step size of <see cref="SevenZip"/>) is a sensible minimum.</param>
/// <remarks>
/// This method internally uses multi-threading and a <see cref="CircularBufferStream"/>.
/// The <paramref name="stream"/> may be closed with a delay.
/// </remarks>
private static Stream GetCompressionStream(Stream stream, int bufferSize = 128 * 1024)
{
var bufferStream = new CircularBufferStream(bufferSize);
var encoder = new Encoder();
var consumerThread = new Thread(() =>
{
try
{
// Write LZMA header
encoder.SetCoderProperties(
new[] {CoderPropId.DictionarySize, CoderPropId.PosStateBits, CoderPropId.LitContextBits, CoderPropId.LitPosBits, CoderPropId.Algorithm, CoderPropId.NumFastBytes, CoderPropId.MatchFinder, CoderPropId.EndMarker},
new object[] {1 << 23, 2, 3, 0, 2, 128, "bt4", true});
encoder.WriteCoderProperties(stream);
// Write "uncompressed length" header
var uncompressedLengthData = BitConverter.GetBytes(TarLzmaExtractor.UnknownSize);
if (!BitConverter.IsLittleEndian) Array.Reverse(uncompressedLengthData);
stream.Write(uncompressedLengthData);
encoder.Code(
inStream: bufferStream, outStream: stream,
inSize: TarLzmaExtractor.UnknownSize, outSize: TarLzmaExtractor.UnknownSize,
progress: null);
}
catch (ObjectDisposedException)
{
// If the buffer stream is closed too early the user probably just canceled the compression process
}
finally
{
stream.Dispose();
}
}) {IsBackground = true};
consumerThread.Start();
return new DisposeWarpperStream(bufferStream, disposeHandler: () =>
{
bufferStream.DoneWriting();
consumerThread.Join();
});
}
internal static void WriteLzmaProperties(Encoder encoder)
{
#region LZMA properties definition
CoderPropId[] propIDs =
{
CoderPropId.DictionarySize,
CoderPropId.PosStateBits,
CoderPropId.LitContextBits,
CoderPropId.LitPosBits,
CoderPropId.Algorithm,
CoderPropId.NumFastBytes,
CoderPropId.MatchFinder,
CoderPropId.EndMarker
};
object[] properties =
{
_lzmaDictionarySize,
2,
3,
0,
2,
256,
"bt4",
false
};
#endregion
encoder.SetCoderProperties(propIDs, properties);
}
