/// <summary>
/// Processes a data frame that is now ready and that is part of an SCTP stream.
/// Stream frames must be delivered in order.
/// </summary>
/// <param name="frame">The data frame that became ready from the latest DATA chunk receive.</param>
/// <returns>A sorted list of frames for the matching stream ID. Will be empty
/// if the supplied frame is out of order for its stream.</returns>
private List <SctpDataFrame> ProcessStreamFrame(SctpDataFrame frame)
{
// Relying on unsigned short wrapping.
unchecked
{
// This is a stream chunk. Need to ensure in order delivery.
var sortedFrames = new List <SctpDataFrame>();
if (!_streamLatestSeqNums.ContainsKey(frame.StreamID))
{
// First frame for this stream.
_streamLatestSeqNums.Add(frame.StreamID, frame.StreamSeqNum);
sortedFrames.Add(frame);
}
else if ((ushort)(_streamLatestSeqNums[frame.StreamID] + 1) == frame.StreamSeqNum)
{
// Expected seqnum for stream.
_streamLatestSeqNums[frame.StreamID] = frame.StreamSeqNum;
sortedFrames.Add(frame);
// There could also be out of order frames that can now be delivered.
if (_streamOutOfOrderFrames.ContainsKey(frame.StreamID) &&
_streamOutOfOrderFrames[frame.StreamID].Count > 0)
{
var outOfOrder = _streamOutOfOrderFrames[frame.StreamID];
ushort nextSeqnum = (ushort)(_streamLatestSeqNums[frame.StreamID] + 1);
while (outOfOrder.ContainsKey(nextSeqnum) &&
outOfOrder.TryGetValue(nextSeqnum, out var nextFrame))
{
sortedFrames.Add(nextFrame);
_streamLatestSeqNums[frame.StreamID] = nextSeqnum;
outOfOrder.Remove(nextSeqnum);
nextSeqnum++;
}
}
}
else
{
// Stream seqnum is out of order.
if (!_streamOutOfOrderFrames.ContainsKey(frame.StreamID))
{
_streamOutOfOrderFrames[frame.StreamID] = new Dictionary <ushort, SctpDataFrame>();
}
if (_streamOutOfOrderFrames[frame.StreamID].Count > MAXIMUM_OUTOFORDER_FRAMES)
{
logger.LogWarning($"SCTP data receiver exceeded the maximum queue size for out of order frames for stream ID {frame.StreamID}.");
// TODO https://tools.ietf.org/html/rfc4960#section-6.2 says to drop the chunk with the highest TSN that's ahead of the
// ack'ed TSN.
}
else
{
_streamOutOfOrderFrames[frame.StreamID].Add(frame.StreamSeqNum, frame);
}
}
return(sortedFrames);
}
}
/// <summary>
/// Extracts a fragmented chunk from the receive dictionary and passes it to the ULP.
/// </summary>
/// <param name="fragments">The dictionary containing the chunk fragments.</param>
/// <param name="beginTSN">The beginning TSN for the fragment.</param>
/// <param name="endTSN">The end TSN for the fragment.</param>
private SctpDataFrame GetFragmentedChunk(Dictionary <uint, SctpDataChunk> fragments, uint beginTSN, uint endTSN)
{
unchecked
{
byte[] full = new byte[MAX_FRAME_SIZE];
int posn = 0;
var beginChunk = fragments[beginTSN];
var frame = new SctpDataFrame(beginChunk.Unordered, beginChunk.StreamID, beginChunk.StreamSeqNum, beginChunk.PPID, full);
uint afterEndTSN = endTSN + 1;
uint tsn = beginTSN;
while (tsn != afterEndTSN)
{
var fragment = fragments[tsn].UserData;
Buffer.BlockCopy(fragment, 0, full, posn, fragment.Length);
posn += fragment.Length;
fragments.Remove(tsn);
tsn++;
}
frame.UserData = frame.UserData.Take(posn).ToArray();
return(frame);
}
}
/// <summary>
/// Event handler for a DATA chunk being received. The chunk can be either a DCEP message or data channel data
/// payload.
/// </summary>
/// <param name="dataFrame">The received data frame which could represent one or more chunks depending
/// on fragmentation..</param>
private void OnDataFrameReceived(SctpDataFrame dataFrame)
{
switch (dataFrame)
{
case var frame when frame.PPID == (uint)DataChannelPayloadProtocols.WebRTC_DCEP:
switch (frame.UserData[0])
{
case (byte)DataChannelMessageTypes.ACK:
OnDataChannelOpened?.Invoke(frame.StreamID);
break;
case (byte)DataChannelMessageTypes.OPEN:
var dcepOpen = DataChannelOpenMessage.Parse(frame.UserData, 0);
logger.LogDebug($"DCEP OPEN channel type {dcepOpen.ChannelType}, priority {dcepOpen.Priority}, " +
$"reliability {dcepOpen.Reliability}, label {dcepOpen.Label}, protocol {dcepOpen.Protocol}.");
DataChannelTypes channelType = DataChannelTypes.DATA_CHANNEL_RELIABLE;
if (Enum.IsDefined(typeof(DataChannelTypes), dcepOpen.ChannelType))
{
channelType = (DataChannelTypes)dcepOpen.ChannelType;
}
else
{
logger.LogWarning($"DECP OPEN channel type of {dcepOpen.ChannelType} not recognised, defaulting to {channelType}.");
}
OnNewDataChannel?.Invoke(
frame.StreamID,
channelType,
dcepOpen.Priority,
dcepOpen.Reliability,
dcepOpen.Label,
dcepOpen.Protocol);
break;
default:
logger.LogWarning($"DCEP message type {frame.UserData[0]} not recognised, ignoring.");
break;
}
break;
default:
OnDataChannelData?.Invoke(dataFrame);
break;
}
}
/// <summary>
/// Handler for processing new data chunks.
/// </summary>
/// <param name="dataChunk">The newly received data chunk.</param>
/// <returns>If the received chunk resulted in a full chunk becoming available one
/// or more new frames will be returned otherwise an empty frame is returned. Multiple
/// frames may be returned if this chunk is part of a stream and was received out
/// or order. For unordered chunks the list will always have a single entry.</returns>
public List <SctpDataFrame> OnDataChunk(SctpDataChunk dataChunk)
{
var sortedFrames = new List <SctpDataFrame>();
var frame = SctpDataFrame.Empty;
if (_inOrderReceiveCount == 0 &&
GetDistance(_initialTSN, dataChunk.TSN) > _windowSize)
{
logger.LogWarning($"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);
}
}