support for gateways sending TLS with SRTP but not dtls (#66)

data/srtp-transcoding.json

@@ -8,7 +8,7 @@
   },
   "teams": {
     "transport-protocol": "RTP/SAVP",
-    "ICE": "force",
+    "ICE": "default",
     "SDES": "off",
     "flags": ["generate mid", "SDES-no", "media handover", "port latching"],
     "rtcp-mux": ["accept"]

lib/call-session.js

@@ -3,6 +3,7 @@ const SrsClient = require('@jambonz/siprec-client-utils');
 const {
   makeRtpEngineOpts,
   SdpWantsSrtp,
+  SdpDoesNotWantDTLS,
   nudgeCallCounts,
   roundTripTime,
   parseConnectionIp
@@ -152,7 +153,8 @@ class CallSession extends Emitter {
     this.logger.debug(`using feature server ${featureServer}`);
 
     const wantsSrtp = this.req.locals.possibleWebRtcClient = SdpWantsSrtp(sdp);
-    this.rtpEngineOpts = makeRtpEngineOpts(this.req, wantsSrtp, false, this.isFromMSTeams);
+    const doesNotWantDTLS = wantsSrtp && SdpDoesNotWantDTLS(sdp);
+    this.rtpEngineOpts = makeRtpEngineOpts(this.req, wantsSrtp, false, this.isFromMSTeams || doesNotWantDTLS);
     this.rtpEngineResource = {destroy: this.del.bind(null, this.rtpEngineOpts.common)};
     const obj = parseUri(this.req.uri);
     let proxy, host, uri;

lib/utils.js

@@ -41,6 +41,9 @@ function makeRtpEngineOpts(req, srcIsUsingSrtp, dstIsUsingSrtp, teams = false) {
   };
 }
 
+const SdpDoesNotWantDTLS = (sdp) => {
+  return /m=audio.*\s+RTP\/SAVP/.test(sdp);
+};
 const SdpWantsSrtp = (sdp) => {
   return /m=audio.*SAVP/.test(sdp);
 };
@@ -178,6 +181,7 @@ const parseConnectionIp = (sdp) => {
 module.exports = {
   isWSS,
   SdpWantsSrtp,
+  SdpDoesNotWantDTLS,
   getAppserver,
   makeRtpEngineOpts,
   makeAccountCallCountKey,