/// <summary>Compresses the encapsulation payload using GZip compression. Compressed encapsulation payload is
/// only supported with the 2.0 encoding.</summary>
/// <returns>A <see cref="CompressionResult"/> value indicating the result of the compression operation.
/// </returns>
public CompressionResult CompressPayload()
{
if (IsSealed)
{
throw new InvalidOperationException("cannot modify a sealed frame");
}
if (Encoding != Encoding.V20)
{
throw new NotSupportedException("payload compression is only supported with 2.0 encoding");
}
else
{
IList <ArraySegment <byte> > payload = Payload;
int encapsulationOffset = this is OutgoingResponseFrame ? 1 : 0;
// The encapsulation always starts in the first segment of the payload (at position 0 or 1).
Debug.Assert(encapsulationOffset < payload[0].Count);
int sizeLength = Protocol == Protocol.Ice2 ? payload[0][encapsulationOffset].ReadSizeLength20() : 4;
byte compressionStatus = payload.GetByte(encapsulationOffset + sizeLength + 2);
if (compressionStatus != 0)
{
throw new InvalidOperationException("payload is already compressed");
}
int encapsulationSize = payload.GetByteCount() - encapsulationOffset; // this includes the size length
if (encapsulationSize < _compressionMinSize)
{
return(CompressionResult.PayloadTooSmall);
}
// Reserve memory for the compressed data, this should never be greater than the uncompressed data
// otherwise we will just send the uncompressed data.
byte[] compressedData = new byte[encapsulationOffset + encapsulationSize];
// Copy the byte before the encapsulation, if any
if (encapsulationOffset == 1)
{
compressedData[0] = payload[0][0];
}
// Write the encapsulation header
int offset = encapsulationOffset + sizeLength;
compressedData[offset++] = Encoding.Major;
compressedData[offset++] = Encoding.Minor;
// Set the compression status to '1' GZip compressed
compressedData[offset++] = 1;
// Write the size of the uncompressed data
OutputStream.WriteFixedLengthSize20(encapsulationSize - sizeLength,
compressedData.AsSpan(offset, sizeLength));
offset += sizeLength;
using var memoryStream = new MemoryStream(compressedData, offset, compressedData.Length - offset);
using var gzipStream = new GZipStream(
memoryStream,
_compressionLevel == CompressionLevel.Fastest ? System.IO.Compression.CompressionLevel.Fastest :
System.IO.Compression.CompressionLevel.Optimal);
try
{
// The data to compress starts after the compression status byte, + 3 corresponds to (Encoding 2
// bytes, Compression status 1 byte)
foreach (ArraySegment <byte> segment in payload.Slice(encapsulationOffset + sizeLength + 3))
{
gzipStream.Write(segment);
}
gzipStream.Flush();
}
catch (NotSupportedException)
{
// If the data doesn't fit in the memory stream NotSupportedException is thrown when GZipStream
// try to expand the fixed size MemoryStream.
return(CompressionResult.PayloadNotCompressible);
}
int binaryContextLastSegmentOffset = -1;
if (_binaryContextOstr is OutputStream ostr)
{
// If there is a binary context, we make sure it uses its own segment(s).
OutputStream.Position binaryContextEnd = ostr.Tail;
binaryContextLastSegmentOffset = binaryContextEnd.Offset;
// When we have a _binaryContextOstr, we wrote at least the size placeholder for the binary context
// dictionary.
Debug.Assert(binaryContextEnd.Segment > PayloadEnd.Segment ||
binaryContextEnd.Offset > PayloadEnd.Offset);
// The first segment of the binary context is immediately after the payload
ArraySegment <byte> segment = Data[PayloadEnd.Segment].Slice(PayloadEnd.Offset);
if (segment.Count > 0)
{
Data.Insert(PayloadEnd.Segment + 1, segment);
if (binaryContextEnd.Segment == PayloadEnd.Segment)
{
binaryContextLastSegmentOffset -= PayloadEnd.Offset;
}
}
// else the binary context already starts with its own segment
}
int start = PayloadStart.Segment;
if (PayloadStart.Offset > 0)
{
// There is non payload bytes in the first payload segment: we move them to their own segment.
ArraySegment <byte> segment = Data[PayloadStart.Segment];
Data[PayloadStart.Segment] = segment.Slice(0, PayloadStart.Offset);
start += 1;
}
Data.RemoveRange(start, PayloadEnd.Segment - start + 1);
offset += (int)memoryStream.Position;
Data.Insert(start, new ArraySegment <byte>(compressedData, 0, offset));
PayloadStart = new OutputStream.Position(start, 0);
PayloadEnd = new OutputStream.Position(start, offset);
Size = Data.GetByteCount();
if (_binaryContextOstr != null)
{
// Recreate binary context OutputStream
_binaryContextOstr =
new OutputStream(_binaryContextOstr.Encoding,
Data,
new OutputStream.Position(Data.Count - 1, binaryContextLastSegmentOffset));
}
// Rewrite the encapsulation size
OutputStream.WriteEncapsulationSize(offset - sizeLength - encapsulationOffset,
compressedData.AsSpan(encapsulationOffset, sizeLength),
Protocol.GetEncoding());
_payload = null; // reset cache
return(CompressionResult.Success);
}
}