/// <summary>
/// Gets a cookie to send in an INIT ACK chunk. This SCTP
/// transport for a WebRTC peer connection needs to use the same
/// local tag and TSN in every chunk as only a single association
/// is ever maintained.
/// </summary>
protected override SctpTransportCookie GetInitAckCookie(
ushort sourcePort,
ushort destinationPort,
uint remoteTag,
uint remoteTSN,
uint remoteARwnd,
string remoteEndPoint,
int lifeTimeExtension = 0)
{
var cookie = new SctpTransportCookie
{
SourcePort = sourcePort,
DestinationPort = destinationPort,
RemoteTag = remoteTag,
RemoteTSN = remoteTSN,
RemoteARwnd = remoteARwnd,
RemoteEndPoint = remoteEndPoint,
Tag = RTCSctpAssociation.VerificationTag,
TSN = RTCSctpAssociation.TSN,
ARwnd = SctpAssociation.DEFAULT_ADVERTISED_RECEIVE_WINDOW,
CreatedAt = DateTime.Now.ToString("o"),
Lifetime = DEFAULT_COOKIE_LIFETIME_SECONDS + lifeTimeExtension,
HMAC = string.Empty
};
return(cookie);
}
/// <summary>
/// Create a new SCTP association instance from the cookie that was previously
/// sent to the remote party in an INIT ACK chunk.
/// </summary>
public SctpAssociation(
SctpTransport sctpTransport,
SctpTransportCookie cookie,
int localTransportPort)
{
_sctpTransport = sctpTransport;
ID = $"{cookie.SourcePort}:{cookie.DestinationPort}:{localTransportPort}";
State = SctpAssociationState.Closed;
GotCookie(cookie);
}
/// <summary>
/// Initialises the association state based on the echoed cookie (the cookie that we sent
/// to the remote party and was then echoed back to us). An association can only be initialised
/// from a cookie prior to it being used and prior to it ever having entered the established state.
/// </summary>
/// <param name="cookie">The echoed cookie that was returned from the remote party.</param>
public void GotCookie(SctpTransportCookie cookie)
{
// The CookieEchoed state is allowed, even though a cookie should be creating a brand
// new association rather than one that has already sent an INIT, in order to deal with
// a race condition where both SCTP end points attempt to establish the association at
// the same time using the same ports.
if (_wasAborted || _wasShutdown)
{
logger.LogWarning($"SCTP association cannot initialise with a cookie after an abort or shutdown.");
}
else if (!(State == SctpAssociationState.Closed || State == SctpAssociationState.CookieEchoed))
{
throw new ApplicationException($"SCTP association cannot initialise with a cookie in state {State}.");
}
else
{
_sctpSourcePort = cookie.SourcePort;
_sctpDestinationPort = cookie.DestinationPort;
VerificationTag = cookie.Tag;
ARwnd = cookie.ARwnd;
Destination = !string.IsNullOrEmpty(cookie.RemoteEndPoint) ?
IPSocket.Parse(cookie.RemoteEndPoint) : null;
if (_dataReceiver == null)
{
_dataReceiver = new SctpDataReceiver(ARwnd, _defaultMTU, cookie.RemoteTSN);
}
if (_dataSender == null)
{
_dataSender = new SctpDataSender(ID, this.SendChunk, _defaultMTU, cookie.TSN, cookie.RemoteARwnd);
}
InitRemoteProperties(cookie.RemoteTag, cookie.RemoteTSN, cookie.RemoteARwnd);
var cookieAckChunk = new SctpChunk(SctpChunkType.COOKIE_ACK);
SendChunk(cookieAckChunk);
SetState(SctpAssociationState.Established);
_dataSender.StartSending();
CancelTimers();
}
}