/// <summary>
/// Event handler for a packet receive on the UDP encapsulation socket.
/// </summary>
/// <param name="receiver">The UDP receiver that received the packet.</param>
/// <param name="localPort">The local port the packet was received on.</param>
/// <param name="remoteEndPoint">The remote end point the packet was received from.</param>
/// <param name="packet">A buffer containing the packet.</param>
private void OnEncapsulationSocketPacketReceived(UdpReceiver receiver, int localPort, IPEndPoint remoteEndPoint, byte[] packet)
{
try
{
if (!SctpPacket.VerifyChecksum(packet, 0, packet.Length))
{
logger.LogWarning($"SCTP packet from UDP {remoteEndPoint} dropped due to invalid checksum.");
}
else
{
var sctpPacket = SctpPacket.Parse(packet, 0, packet.Length);
// Process packet.
if (sctpPacket.Header.VerificationTag == 0)
{
GotInit(sctpPacket, remoteEndPoint);
}
else if (sctpPacket.Chunks.Any(x => x.KnownType == SctpChunkType.COOKIE_ECHO))
{
// The COOKIE ECHO chunk is the 3rd step in the SCTP handshake when the remote party has
// requested a new association be created.
var cookie = base.GetCookie(sctpPacket);
if (cookie.IsEmpty())
{
logger.LogWarning($"SCTP error acquiring handshake cookie from COOKIE ECHO chunk.");
}
else
{
logger.LogDebug($"SCTP creating new association for {remoteEndPoint}.");
var association = new SctpAssociation(this, cookie, localPort);
if (_associations.TryAdd(association.ID, association))
{
if (sctpPacket.Chunks.Count > 1)
{
// There could be DATA chunks after the COOKIE ECHO chunk.
association.OnPacketReceived(sctpPacket);
}
}
else
{
logger.LogError($"SCTP failed to add new association to dictionary.");
}
}
}
else
{
// TODO: Lookup the existing association for the packet.
_associations.Values.First().OnPacketReceived(sctpPacket);
}
}
}
catch (Exception excp)
{
logger.LogError($"Exception SctpTransport.OnEncapsulationSocketPacketReceived. {excp}");
}
}
/// <summary>
/// This method runs on a dedicated thread to listen for incoming SCTP
/// packets on the DTLS transport.
/// </summary>
private void DoReceive(object state)
{
byte[] recvBuffer = new byte[SctpAssociation.DEFAULT_ADVERTISED_RECEIVE_WINDOW];
while (!_isClosed)
{
try
{
int bytesRead = transport.Receive(recvBuffer, 0, recvBuffer.Length, RECEIVE_TIMEOUT_MILLISECONDS);
if (bytesRead == DtlsSrtpTransport.DTLS_RETRANSMISSION_CODE)
{
// Timed out waiting for a packet, this is by design and the receive attempt should
// be retired.
continue;
}
else if (bytesRead > 0)
{
if (!SctpPacket.VerifyChecksum(recvBuffer, 0, bytesRead))
{
logger.LogWarning($"SCTP packet received on DTLS transport dropped due to invalid checksum.");
}
else
{
var pkt = SctpPacket.Parse(recvBuffer, 0, bytesRead);
if (pkt.Chunks.Any(x => x.KnownType == SctpChunkType.INIT))
{
var initChunk = pkt.Chunks.First(x => x.KnownType == SctpChunkType.INIT) as SctpInitChunk;
logger.LogDebug($"SCTP INIT packet received, initial tag {initChunk.InitiateTag}, initial TSN {initChunk.InitialTSN}.");
GotInit(pkt, null);
}
else if (pkt.Chunks.Any(x => x.KnownType == SctpChunkType.COOKIE_ECHO))
{
// The COOKIE ECHO chunk is the 3rd step in the SCTP handshake when the remote party has
// requested a new association be created.
var cookie = base.GetCookie(pkt);
if (cookie.IsEmpty())
{
logger.LogWarning($"SCTP error acquiring handshake cookie from COOKIE ECHO chunk.");
}
else
{
RTCSctpAssociation.GotCookie(cookie);
if (pkt.Chunks.Count() > 1)
{
// There could be DATA chunks after the COOKIE ECHO chunk.
RTCSctpAssociation.OnPacketReceived(pkt);
}
}
}
else
{
RTCSctpAssociation.OnPacketReceived(pkt);
}
}
}
else if (_isClosed)
{
// The DTLS transport has been closed or is no longer available.
logger.LogWarning($"SCTP the RTCSctpTransport DTLS transport returned an error.");
break;
}
}
catch (ApplicationException appExcp)
{
// Treat application exceptions as recoverable, things like SCTP packet parse failures.
logger.LogWarning($"SCTP error processing RTCSctpTransport receive. {appExcp.Message}");
}
catch (TlsFatalAlert alert) when(alert.InnerException is SocketException)
{
var sockExcp = alert.InnerException as SocketException;
logger.LogWarning($"SCTP RTCSctpTransport receive socket failure {sockExcp.SocketErrorCode}.");
break;
}
catch (Exception excp)
{
logger.LogError($"SCTP fatal error processing RTCSctpTransport receive. {excp}");
break;
}
}
if (!_isClosed)
{
logger.LogWarning($"SCTP association {RTCSctpAssociation.ID} receive thread stopped.");
}
SetState(RTCSctpTransportState.Closed);
}