/// <summary>
/// Answers the call request contained in the user agent server parameter. Note the
/// <see cref="AcceptCall(SIPRequest)"/> method should be used to create the user agent server.
/// Any existing call will be hungup.
/// </summary>
/// <param name="uas">The user agent server holding the pending call to answer.</param>
/// <param name="mediaSession">The media session used for this call</param>
/// <param name="customHeaders">Custom SIP-Headers to use in Answer.</param>
/// <returns>True if the call was successfully answered or false if there was a problem
/// such as incompatible codecs.</returns>
public async Task <bool> Answer(SIPServerUserAgent uas, IMediaSession mediaSession, string[] customHeaders)
{
// This call is now taking over any existing call.
if (IsCallActive)
{
Hangup();
}
if (uas.IsCancelled)
{
logger.LogDebug("The incoming call has been cancelled.");
mediaSession?.Close("call cancelled");
return(false);
}
else
{
m_cts = new CancellationTokenSource();
var sipRequest = uas.ClientTransaction.TransactionRequest;
MediaSession = mediaSession;
MediaSession.OnRtpEvent += OnRemoteRtpEvent;
MediaSession.OnRtpClosed += (reason) =>
{
if (!MediaSession.IsClosed)
{
logger.LogWarning($"RTP channel was closed with reason {reason}.");
}
};
string sdp = null;
if (!String.IsNullOrEmpty(sipRequest.Body))
{
// The SDP offer was included in the INVITE request.
SDP remoteSdp = SDP.ParseSDPDescription(sipRequest.Body);
var setRemoteResult = MediaSession.SetRemoteDescription(remoteSdp);
if (setRemoteResult != SetDescriptionResultEnum.OK)
{
logger.LogWarning($"Error setting remote description from INVITE {setRemoteResult}.");
uas.Reject(SIPResponseStatusCodesEnum.NotAcceptable, setRemoteResult.ToString());
MediaSession.Close("sdp offer not acceptable");
Hangup();
return(false);
}
else
{
var sdpAnswer = MediaSession.CreateAnswer(null);
sdp = sdpAnswer.ToString();
}
}
else
{
// No SDP offer was included in the INVITE request need to wait for the ACK.
var sdpAnnounceAddress = NetServices.GetLocalAddressForRemote(sipRequest.RemoteSIPEndPoint.GetIPEndPoint().Address);
var sdpOffer = MediaSession.CreateOffer(sdpAnnounceAddress);
sdp = sdpOffer.ToString();
}
m_uas = uas;
// In cases where the initial INVITE did not contain an SDP offer the action sequence is:
// - INVITE with no SDP offer received,
// - Reply with OK and an SDP offer,
// - Wait for ACK with SDP answer.
TaskCompletionSource <SIPDialogue> dialogueCreatedTcs = new TaskCompletionSource <SIPDialogue>(TaskCreationOptions.RunContinuationsAsynchronously);
m_uas.OnDialogueCreated += (dialogue) => dialogueCreatedTcs.TrySetResult(dialogue);
m_uas.Answer(m_sdpContentType, sdp, null, SIPDialogueTransferModesEnum.Default, customHeaders);
await Task.WhenAny(dialogueCreatedTcs.Task, Task.Delay(WAIT_DIALOG_TIMEOUT)).ConfigureAwait(false);
if (Dialogue != null)
{
if (MediaSession.RemoteDescription == null)
{
// If the initial INVITE did not contain an offer then the remote description will not yet be set.
var remoteSDP = SDP.ParseSDPDescription(Dialogue.RemoteSDP);
var setRemoteResult = MediaSession.SetRemoteDescription(remoteSDP);
if (setRemoteResult != SetDescriptionResultEnum.OK)
{
// Failed to set the remote SDP from the ACK request. Only option is to hangup.
logger.LogWarning($"Error setting remote description from ACK {setRemoteResult}.");
MediaSession.Close(setRemoteResult.ToString());
Hangup();
return(false);
}
else
{
// SDP from the ACK request was accepted. Start the RTP session.
Dialogue.DialogueState = SIPDialogueStateEnum.Confirmed;
await MediaSession.Start().ConfigureAwait(false);
return(true);
}
}
else
{
Dialogue.DialogueState = SIPDialogueStateEnum.Confirmed;
await MediaSession.Start().ConfigureAwait(false);
return(true);
}
}
else
{
logger.LogWarning("The attempt to answer a call failed as the dialog was not created. The likely cause is the ACK not being received in time.");
MediaSession.Close("dialog creation failed");
Hangup();
return(false);
}
}
}