protected void GotInit(SctpPacket initPacket, IPEndPoint remoteEndPoint)
{
// INIT packets have specific processing rules in order to prevent resource exhaustion.
// See Section 5 of RFC 4960 https://tools.ietf.org/html/rfc4960#section-5 "Association Initialization".
SctpInitChunk initChunk = initPacket.Chunks.Single(x => x.KnownType == SctpChunkType.INIT) as SctpInitChunk;
if (initChunk.InitiateTag == 0 ||
initChunk.NumberInboundStreams == 0 ||
initChunk.NumberOutboundStreams == 0)
{
// If the value of the Initiate Tag in a received INIT chunk is found
// to be 0, the receiver MUST treat it as an error and close the
// association by transmitting an ABORT. (RFC4960 pg. 25)
// Note: A receiver of an INIT with the OS value set to 0 SHOULD
// abort the association. (RFC4960 pg. 25)
// Note: A receiver of an INIT with the MIS value of 0 SHOULD abort
// the association. (RFC4960 pg. 26)
SendError(
true,
initPacket.Header.DestinationPort,
initPacket.Header.SourcePort,
initChunk.InitiateTag,
new SctpCauseOnlyError(SctpErrorCauseCode.InvalidMandatoryParameter));
}
else
{
var initAckPacket = GetInitAck(initPacket, remoteEndPoint);
var buffer = initAckPacket.GetBytes();
Send(null, buffer, 0, buffer.Length);
}
}
/// <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>
/// Sends an SCTP packet to the remote peer.
/// </summary>
/// <param name="pkt">The packet to send.</param>
private void SendPacket(SctpPacket pkt)
{
if (!_wasAborted)
{
byte[] buffer = pkt.GetBytes();
_sctpTransport.Send(ID, buffer, 0, buffer.Length);
}
}
/// <summary>
/// Parses an SCTP packet from a serialised buffer.
/// </summary>
/// <param name="buffer">The buffer holding the serialised packet.</param>
/// <param name="offset">The position in the buffer of the packet.</param>
/// <param name="length">The length of the serialised packet in the buffer.</param>
public static SctpPacket Parse(byte[] buffer, int offset, int length)
{
var pkt = new SctpPacket();
pkt.Header = SctpHeader.Parse(buffer, offset);
(pkt.Chunks, pkt.UnrecognisedChunks) = ParseChunks(buffer, offset, length);
return(pkt);
}
/// <summary>
/// Gets an SCTP packet for a control (non-data) chunk.
/// </summary>
/// <param name="chunk">The control chunk to get a packet for.</param>
/// <returns>A single control chunk SCTP packet.</returns>
public SctpPacket GetControlPacket(SctpChunk chunk)
{
SctpPacket pkt = new SctpPacket(
_sctpSourcePort,
_sctpDestinationPort,
_remoteVerificationTag);
pkt.AddChunk(chunk);
return(pkt);
}
/// <summary>
/// Sends a SCTP chunk to the remote party.
/// </summary>
/// <param name="chunk">The chunk to send.</param>
internal void SendChunk(SctpChunk chunk)
{
if (!_wasAborted)
{
SctpPacket pkt = new SctpPacket(
_sctpSourcePort,
_sctpDestinationPort,
_remoteVerificationTag);
pkt.AddChunk(chunk);
byte[] buffer = pkt.GetBytes();
_sctpTransport.Send(ID, buffer, 0, buffer.Length);
}
}
/// <summary>
/// Creates the INIT ACK chunk and packet to send as a response to an SCTP
/// packet containing an INIT chunk.
/// </summary>
/// <param name="initPacket">The received packet containing the INIT chunk.</param>
/// <param name="remoteEP">Optional. The remote IP end point the INIT packet was
/// received on. For transports that don't use an IP transport directly this parameter
/// can be set to null and it will not form part of the COOKIE ECHO checks.</param>
/// <returns>An SCTP packet with a single INIT ACK chunk.</returns>
protected SctpPacket GetInitAck(SctpPacket initPacket, IPEndPoint remoteEP)
{
SctpInitChunk initChunk = initPacket.Chunks.Single(x => x.KnownType == SctpChunkType.INIT) as SctpInitChunk;
SctpPacket initAckPacket = new SctpPacket(
initPacket.Header.DestinationPort,
initPacket.Header.SourcePort,
initChunk.InitiateTag);
var cookie = GetInitAckCookie(
initPacket.Header.DestinationPort,
initPacket.Header.SourcePort,
initChunk.InitiateTag,
initChunk.InitialTSN,
initChunk.ARwnd,
remoteEP != null ? remoteEP.ToString() : string.Empty,
(int)(initChunk.CookiePreservative / 1000));
var json = cookie.ToJson();
var jsonBuffer = Encoding.UTF8.GetBytes(json);
using (HMACSHA256 hmac = new HMACSHA256(_hmacKey))
{
var result = hmac.ComputeHash(jsonBuffer);
cookie.HMAC = result.HexStr();
}
var jsonWithHMAC = cookie.ToJson();
var jsonBufferWithHMAC = Encoding.UTF8.GetBytes(jsonWithHMAC);
SctpInitChunk initAckChunk = new SctpInitChunk(
SctpChunkType.INIT_ACK,
cookie.Tag,
cookie.TSN,
cookie.ARwnd,
SctpAssociation.DEFAULT_NUMBER_OUTBOUND_STREAMS,
SctpAssociation.DEFAULT_NUMBER_INBOUND_STREAMS);
initAckChunk.StateCookie = jsonBufferWithHMAC;
initAckChunk.UnrecognizedPeerParameters = initChunk.UnrecognizedPeerParameters;
initAckPacket.AddChunk(initAckChunk);
return(initAckPacket);
}
/// <summary>
/// Send an SCTP packet with one of the error type chunks (ABORT or ERROR) to the remote peer.
/// </summary>
/// <param name=isAbort">Set to true to use an ABORT chunk otherwise an ERROR chunk will be used.</param>
/// <param name="desintationPort">The SCTP destination port.</param>
/// <param name="sourcePort">The SCTP source port.</param>
/// <param name="initiateTag">If available the initial tag for the remote peer.</param>
/// <param name="error">The error to send.</param>
private void SendError(
bool isAbort,
ushort destinationPort,
ushort sourcePort,
uint initiateTag,
ISctpErrorCause error)
{
SctpPacket errorPacket = new SctpPacket(
destinationPort,
sourcePort,
initiateTag);
SctpErrorChunk errorChunk = isAbort ? new SctpAbortChunk(true) : new SctpErrorChunk();
errorChunk.AddErrorCause(error);
errorPacket.AddChunk(errorChunk);
var buffer = errorPacket.GetBytes();
Send(null, buffer, 0, buffer.Length);
}
/// <summary>
/// Attempts to retrieve the cookie that should have been set by this peer from a COOKIE ECHO
/// chunk. This is the step in the handshake that a new SCTP association will be created
/// for a remote party. Providing the state cookie is valid create a new association.
/// </summary>
/// <param name="sctpPacket">The packet containing the COOKIE ECHO chunk received from the remote party.</param>
/// <returns>If the state cookie in the chunk is valid a new SCTP association will be returned. IF
/// it's not valid an empty cookie will be returned and an error response gets sent to the peer.</returns>
protected SctpTransportCookie GetCookie(SctpPacket sctpPacket)
{
var cookieEcho = sctpPacket.Chunks.Single(x => x.KnownType == SctpChunkType.COOKIE_ECHO);
var cookieBuffer = cookieEcho.ChunkValue;
var cookie = JSONParser.FromJson <SctpTransportCookie>(Encoding.UTF8.GetString(cookieBuffer));
logger.LogDebug($"Cookie: {cookie.ToJson()}");
string calculatedHMAC = GetCookieHMAC(cookieBuffer);
if (calculatedHMAC != cookie.HMAC)
{
logger.LogWarning($"SCTP COOKIE ECHO chunk had an invalid HMAC, calculated {calculatedHMAC}, cookie {cookie.HMAC}.");
SendError(
true,
sctpPacket.Header.DestinationPort,
sctpPacket.Header.SourcePort,
0,
new SctpCauseOnlyError(SctpErrorCauseCode.InvalidMandatoryParameter));
return(SctpTransportCookie.Empty);
}
else if (DateTime.Now.Subtract(DateTime.Parse(cookie.CreatedAt)).TotalSeconds > cookie.Lifetime)
{
logger.LogWarning($"SCTP COOKIE ECHO chunk was stale, created at {cookie.CreatedAt}, now {DateTime.Now.ToString("o")}, lifetime {cookie.Lifetime}s.");
var diff = DateTime.Now.Subtract(DateTime.Parse(cookie.CreatedAt).AddSeconds(cookie.Lifetime));
SendError(
true,
sctpPacket.Header.DestinationPort,
sctpPacket.Header.SourcePort,
0,
new SctpErrorStaleCookieError {
MeasureOfStaleness = (uint)(diff.TotalMilliseconds * 1000)
});
return(SctpTransportCookie.Empty);
}
else
{
return(cookie);
}
}
/// <summary>
/// Attempts to create an association with a remote party by sending an initialisation
/// control chunk.
/// </summary>
private void SendInit()
{
if (!_wasAborted)
{
// A packet containing an INIT chunk MUST have a zero Verification Tag (RFC4960 Pg 15).
SctpPacket init = new SctpPacket(_sctpSourcePort, _sctpDestinationPort, 0);
SctpInitChunk initChunk = new SctpInitChunk(
SctpChunkType.INIT,
VerificationTag,
TSN,
ARwnd,
_numberOutboundStreams,
_numberInboundStreams);
init.AddChunk(initChunk);
SetState(SctpAssociationState.CookieWait);
byte[] buffer = init.GetBytes();
_sctpTransport.Send(ID, buffer, 0, buffer.Length);
_t1Init = new Timer(T1InitTimerExpired, init, T1_INIT_TIMER_MILLISECONDS, T1_INIT_TIMER_MILLISECONDS);
}
}
/// <summary>
/// Implements the SCTP association state machine.
/// </summary>
/// <param name="packet">An SCTP packet received from the remote party.</param>
/// <remarks>
/// SCTP Association State Diagram:
/// https://tools.ietf.org/html/rfc4960#section-4
/// </remarks>
internal void OnPacketReceived(SctpPacket packet)
{
if (_wasAborted)
{
logger.LogWarning($"SCTP packet received but association has been aborted, ignoring.");
}
else if (packet.Header.VerificationTag != VerificationTag)
{
logger.LogWarning($"SCTP packet dropped due to wrong verification tag, expected " +
$"{VerificationTag} got {packet.Header.VerificationTag}.");
}
else if (!_sctpTransport.IsPortAgnostic && packet.Header.DestinationPort != _sctpSourcePort)
{
logger.LogWarning($"SCTP packet dropped due to wrong SCTP destination port, expected " +
$"{_sctpSourcePort} got {packet.Header.DestinationPort}.");
}
else if (!_sctpTransport.IsPortAgnostic && packet.Header.SourcePort != _sctpDestinationPort)
{
logger.LogWarning($"SCTP packet dropped due to wrong SCTP source port, expected " +
$"{_sctpDestinationPort} got {packet.Header.SourcePort}.");
}
else
{
foreach (var chunk in packet.Chunks)
{
var chunkType = (SctpChunkType)chunk.ChunkType;
switch (chunkType)
{
case SctpChunkType.ABORT:
string abortReason = (chunk as SctpAbortChunk).GetAbortReason();
logger.LogWarning($"SCTP packet ABORT chunk received from remote party, reason {abortReason}.");
_wasAborted = true;
OnAbortReceived?.Invoke(abortReason);
break;
case var ct when ct == SctpChunkType.COOKIE_ACK && State != SctpAssociationState.CookieEchoed:
// https://tools.ietf.org/html/rfc4960#section-5.2.5
// At any state other than COOKIE-ECHOED, an endpoint should silently
// discard a received COOKIE ACK chunk.
break;
case var ct when ct == SctpChunkType.COOKIE_ACK && State == SctpAssociationState.CookieEchoed:
SetState(SctpAssociationState.Established);
CancelTimers();
_dataSender.StartSending();
break;
case SctpChunkType.COOKIE_ECHO:
// In standard operation an SCTP association gets created when the parent transport
// receives a COOKIE ECHO chunk. The association gets initialised from the chunk and
// does not need to process it.
// The scenarios in https://tools.ietf.org/html/rfc4960#section-5.2 describe where
// an association could receive a COOKIE ECHO.
break;
case SctpChunkType.DATA:
var dataChunk = chunk as SctpDataChunk;
if (dataChunk.UserData == null || dataChunk.UserData.Length == 0)
{
// Fatal condition:
// - If an endpoint receives a DATA chunk with no user data (i.e., the
// Length field is set to 16), it MUST send an ABORT with error cause
// set to "No User Data". (RFC4960 pg. 80)
Abort(new SctpErrorNoUserData {
TSN = (chunk as SctpDataChunk).TSN
});
}
else
{
logger.LogTrace($"SCTP data chunk received on ID {ID} with TSN {dataChunk.TSN}, payload length {dataChunk.UserData.Length}, flags {dataChunk.ChunkFlags:X2}.");
// A received data chunk can result in multiple data frames becoming available.
// For example if a stream has out of order frames already received and the next
// in order frame arrives then all the in order ones will be supplied.
var sortedFrames = _dataReceiver.OnDataChunk(dataChunk);
var sack = _dataReceiver.GetSackChunk();
if (sack != null)
{
SendChunk(sack);
}
foreach (var frame in sortedFrames)
{
OnData?.Invoke(frame);
}
}
break;
case SctpChunkType.ERROR:
var errorChunk = chunk as SctpErrorChunk;
foreach (var err in errorChunk.ErrorCauses)
{
logger.LogWarning($"SCTP error {err.CauseCode}.");
}
break;
case SctpChunkType.HEARTBEAT:
// The HEARTBEAT ACK sends back the same chunk but with the type changed.
chunk.ChunkType = (byte)SctpChunkType.HEARTBEAT_ACK;
SendChunk(chunk);
break;
case var ct when ct == SctpChunkType.INIT_ACK && State != SctpAssociationState.CookieWait:
// https://tools.ietf.org/html/rfc4960#section-5.2.3
// If an INIT ACK is received by an endpoint in any state other than the
// COOKIE - WAIT state, the endpoint should discard the INIT ACK chunk.
break;
case var ct when ct == SctpChunkType.INIT_ACK && State == SctpAssociationState.CookieWait:
if (_t1Init != null)
{
_t1Init.Dispose();
_t1Init = null;
}
var initAckChunk = chunk as SctpInitChunk;
if (initAckChunk.InitiateTag == 0 ||
initAckChunk.NumberInboundStreams == 0 ||
initAckChunk.NumberOutboundStreams == 0)
{
// Fatal conditions:
// - The Initiate Tag MUST NOT take the value 0. (RFC4960 pg 30).
// - Note: A receiver of an INIT ACK with the OS value set to 0 SHOULD
// destroy the association discarding its TCB. (RFC4960 pg 31).
// - Note: A receiver of an INIT ACK with the MIS value set to 0 SHOULD
// destroy the association discarding its TCB. (RFC4960 pg 31).
Abort(new SctpCauseOnlyError(SctpErrorCauseCode.InvalidMandatoryParameter));
}
else
{
InitRemoteProperties(initAckChunk.InitiateTag, initAckChunk.InitialTSN, initAckChunk.ARwnd);
var cookie = initAckChunk.StateCookie;
// The cookie chunk parameter can be changed to a COOKE ECHO CHUNK by changing the first two bytes.
// But it's more convenient to create a new chunk.
var cookieEchoChunk = new SctpChunk(SctpChunkType.COOKIE_ECHO)
{
ChunkValue = cookie
};
var cookieEchoPkt = GetControlPacket(cookieEchoChunk);
if (initAckChunk.UnrecognizedPeerParameters.Count > 0)
{
var errChunk = new SctpErrorChunk();
foreach (var unrecognised in initAckChunk.UnrecognizedPeerParameters)
{
var unrecognisedParams = new SctpErrorUnrecognizedParameters {
UnrecognizedParameters = unrecognised.GetBytes()
};
errChunk.AddErrorCause(unrecognisedParams);
}
cookieEchoPkt.AddChunk(errChunk);
}
SendPacket(cookieEchoPkt);
SetState(SctpAssociationState.CookieEchoed);
_t1Cookie = new Timer(T1CookieTimerExpired, cookieEchoPkt, T1_COOKIE_TIMER_MILLISECONDS, T1_COOKIE_TIMER_MILLISECONDS);
}
break;
case var ct when ct == SctpChunkType.INIT_ACK && State != SctpAssociationState.CookieWait:
logger.LogWarning($"SCTP association received INIT_ACK chunk in wrong state of {State}, ignoring.");
break;
case SctpChunkType.SACK:
_dataSender.GotSack(chunk as SctpSackChunk);
break;
case var ct when ct == SctpChunkType.SHUTDOWN && State == SctpAssociationState.Established:
// TODO: Check outstanding data chunks.
var shutdownAck = new SctpChunk(SctpChunkType.SHUTDOWN_ACK);
SendChunk(shutdownAck);
SetState(SctpAssociationState.ShutdownAckSent);
break;
case var ct when ct == SctpChunkType.SHUTDOWN_ACK && State == SctpAssociationState.ShutdownSent:
SetState(SctpAssociationState.Closed);
var shutCompleteChunk = new SctpChunk(SctpChunkType.SHUTDOWN_COMPLETE,
(byte)(_remoteVerificationTag != 0 ? SHUTDOWN_CHUNK_TBIT_FLAG : 0x00));
var shutCompletePkt = GetControlPacket(shutCompleteChunk);
shutCompletePkt.Header.VerificationTag = packet.Header.VerificationTag;
SendPacket(shutCompletePkt);
break;
case var ct when ct == SctpChunkType.SHUTDOWN_COMPLETE &&
(State == SctpAssociationState.ShutdownAckSent || State == SctpAssociationState.ShutdownSent):
_wasShutdown = true;
SetState(SctpAssociationState.Closed);
break;
default:
logger.LogWarning($"SCTP association no rule for {chunkType} in state of {State}.");
break;
}
}
}
}
/// <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);
}
