/// <summary>
/// Parses the DATA chunk fields
/// </summary>
/// <param name="buffer">The buffer holding the serialised chunk.</param>
/// <param name="posn">The position to start parsing at.</param>
public static SctpDataChunk ParseChunk(byte[] buffer, int posn)
{
var dataChunk = new SctpDataChunk();
ushort chunkLen = dataChunk.ParseFirstWord(buffer, posn);
if (chunkLen < FIXED_PARAMETERS_LENGTH)
{
throw new ApplicationException($"SCTP data chunk cannot be parsed as buffer too short for fixed parameter fields.");
}
dataChunk.Unordered = (dataChunk.ChunkFlags & 0x04) > 0;
dataChunk.Begining = (dataChunk.ChunkFlags & 0x02) > 0;
dataChunk.Ending = (dataChunk.ChunkFlags & 0x01) > 0;
int startPosn = posn + SCTP_CHUNK_HEADER_LENGTH;
dataChunk.TSN = NetConvert.ParseUInt32(buffer, startPosn);
dataChunk.StreamID = NetConvert.ParseUInt16(buffer, startPosn + 4);
dataChunk.StreamSeqNum = NetConvert.ParseUInt16(buffer, startPosn + 6);
dataChunk.PPID = NetConvert.ParseUInt32(buffer, startPosn + 8);
int userDataPosn = startPosn + FIXED_PARAMETERS_LENGTH;
int userDataLen = chunkLen - SCTP_CHUNK_HEADER_LENGTH - FIXED_PARAMETERS_LENGTH;
if (userDataLen > 0)
{
dataChunk.UserData = new byte[userDataLen];
Buffer.BlockCopy(buffer, userDataPosn, dataChunk.UserData, 0, dataChunk.UserData.Length);
}
return(dataChunk);
}
/// <summary>
/// Parses an SCTP chunk from a buffer.
/// </summary>
/// <param name="buffer">The buffer holding the serialised chunk.</param>
/// <param name="posn">The position to start parsing at.</param>
/// <returns>An SCTP chunk instance.</returns>
public static SctpChunk Parse(byte[] buffer, int posn)
{
if (buffer.Length < posn + SCTP_CHUNK_HEADER_LENGTH)
{
throw new ApplicationException("Buffer did not contain the minimum of bytes for an SCTP chunk.");
}
byte chunkType = buffer[posn];
if (Enum.IsDefined(typeof(SctpChunkType), chunkType))
{
switch ((SctpChunkType)chunkType)
{
case SctpChunkType.ABORT:
return(SctpAbortChunk.ParseChunk(buffer, posn, true));
case SctpChunkType.DATA:
return(SctpDataChunk.ParseChunk(buffer, posn));
case SctpChunkType.ERROR:
return(SctpErrorChunk.ParseChunk(buffer, posn, false));
case SctpChunkType.SACK:
return(SctpSackChunk.ParseChunk(buffer, posn));
case SctpChunkType.COOKIE_ACK:
case SctpChunkType.COOKIE_ECHO:
case SctpChunkType.HEARTBEAT:
case SctpChunkType.HEARTBEAT_ACK:
case SctpChunkType.SHUTDOWN_ACK:
case SctpChunkType.SHUTDOWN_COMPLETE:
return(ParseBaseChunk(buffer, posn));
case SctpChunkType.INIT:
case SctpChunkType.INIT_ACK:
return(SctpInitChunk.ParseChunk(buffer, posn));
case SctpChunkType.SHUTDOWN:
return(SctpShutdownChunk.ParseChunk(buffer, posn));
default:
logger.LogDebug($"TODO: Implement parsing logic for well known chunk type {(SctpChunkType)chunkType}.");
return(ParseBaseChunk(buffer, posn));
}
}
// Shouldn't reach this point. The SCTP packet parsing logic checks if the chunk is
// recognised before attempting to parse it.
throw new ApplicationException($"SCTP chunk type of {chunkType} was not recognised.");
}
/// <summary>
/// Sends a DATA chunk to the remote peer.
/// </summary>
/// <param name="streamID">The stream ID to sent the data on.</param>
/// <param name="ppid">The payload protocol ID for the data.</param>
/// <param name="message">The byte data to send.</param>
public void SendData(ushort streamID, uint ppid, byte[] data)
{
lock (_sendQueue)
{
ushort seqnum = 0;
if (_streamSeqnums.ContainsKey(streamID))
{
unchecked
{
_streamSeqnums[streamID] = (ushort)(_streamSeqnums[streamID] + 1);
seqnum = _streamSeqnums[streamID];
}
}
else
{
_streamSeqnums.Add(streamID, 0);
}
for (int index = 0; index *_defaultMTU < data.Length; index++)
{
int offset = (index == 0) ? 0 : (index * _defaultMTU);
int payloadLength = (offset + _defaultMTU < data.Length) ? _defaultMTU : data.Length - offset;
// Future TODO: Replace with slice when System.Memory is introduced as a dependency.
byte[] payload = new byte[payloadLength];
Buffer.BlockCopy(data, offset, payload, 0, payloadLength);
bool isBegining = index == 0;
bool isEnd = ((offset + payloadLength) >= data.Length) ? true : false;
SctpDataChunk dataChunk = new SctpDataChunk(
false,
isBegining,
isEnd,
TSN,
streamID,
seqnum,
ppid,
payload);
_sendQueue.Enqueue(dataChunk);
TSN = (TSN == UInt32.MaxValue) ? 0 : TSN + 1;
}
_senderMre.Set();
}
}
/// <summary>
/// Handler for processing new data chunks.
/// </summary>
/// <param name="dataChunk">The newly received data chunk.</param>
/// <returns>If the received chunk resulted in a full chunk becoming available one
/// or more new frames will be returned otherwise an empty frame is returned. Multiple
/// frames may be returned if this chunk is part of a stream and was received out
/// or order. For unordered chunks the list will always have a single entry.</returns>
public List <SctpDataFrame> OnDataChunk(SctpDataChunk dataChunk)
{
var sortedFrames = new List <SctpDataFrame>();
var frame = SctpDataFrame.Empty;
if (_inOrderReceiveCount == 0 &&
GetDistance(_initialTSN, dataChunk.TSN) > _windowSize)
{
logger.LogWarning($"SCTP data receiver received a data chunk with a {dataChunk.TSN} " +
$"TSN when the initial TSN was {_initialTSN} and a " +
$"window size of {_windowSize}, ignoring.");
}
else if (_inOrderReceiveCount > 0 &&
GetDistance(_lastInOrderTSN, dataChunk.TSN) > _windowSize)
{
logger.LogWarning($"SCTP data receiver received a data chunk with a {dataChunk.TSN} " +
$"TSN when the expected TSN was {_lastInOrderTSN + 1} and a " +
$"window size of {_windowSize}, ignoring.");
}
else if (_inOrderReceiveCount > 0 &&
!IsNewer(_lastInOrderTSN, dataChunk.TSN))
{
logger.LogWarning($"SCTP data receiver received an old data chunk with {dataChunk.TSN} " +
$"TSN when the expected TSN was {_lastInOrderTSN + 1}, ignoring.");
}
else if (!_forwardTSN.ContainsKey(dataChunk.TSN))
{
logger.LogTrace($"SCTP receiver got data chunk with TSN {dataChunk.TSN}, " +
$"last in order TSN {_lastInOrderTSN}, in order receive count {_inOrderReceiveCount}.");
// Relying on unsigned integer wrapping.
unchecked
{
if ((_inOrderReceiveCount > 0 && _lastInOrderTSN + 1 == dataChunk.TSN) ||
(_inOrderReceiveCount == 0 && dataChunk.TSN == _initialTSN))
{
_inOrderReceiveCount++;
_lastInOrderTSN = dataChunk.TSN;
// See if the in order TSN can be bumped using any out of order chunks
// already received.
if (_inOrderReceiveCount > 0 && _forwardTSN.Count > 0)
{
while (_forwardTSN.ContainsKey(_lastInOrderTSN + 1))
{
_lastInOrderTSN++;
_inOrderReceiveCount++;
_forwardTSN.Remove(_lastInOrderTSN);
}
}
}
else
{
_forwardTSN.Add(dataChunk.TSN, 1);
}
}
// Now go about processing the data chunk.
if (dataChunk.Begining && dataChunk.Ending)
{
// Single packet chunk.
frame = new SctpDataFrame(
dataChunk.Unordered,
dataChunk.StreamID,
dataChunk.StreamSeqNum,
dataChunk.PPID,
dataChunk.UserData);
}
else
{
// This is a data chunk fragment.
_fragmentedChunks.Add(dataChunk.TSN, dataChunk);
(var begin, var end) = GetChunkBeginAndEnd(_fragmentedChunks, dataChunk.TSN);
if (begin != null && end != null)
{
frame = GetFragmentedChunk(_fragmentedChunks, begin.Value, end.Value);
}
}
}
else
{
logger.LogTrace($"SCTP duplicate TSN received for {dataChunk.TSN}.");
if (!_duplicateTSN.ContainsKey(dataChunk.TSN))
{
_duplicateTSN.Add(dataChunk.TSN, 1);
}
else
{
_duplicateTSN[dataChunk.TSN] = _duplicateTSN[dataChunk.TSN] + 1;
}
}
if (!frame.IsEmpty() && !dataChunk.Unordered)
{
return(ProcessStreamFrame(frame));
}
else
{
if (!frame.IsEmpty())
{
sortedFrames.Add(frame);
}
return(sortedFrames);
}
}