res_pjsip_sdp_rtp: include ice in ANSWER only if offered

Keep track if ICE candidates were in the SDP offer & only put them
in the corresponding SDP answer if the offer condaind ICE candidates

ASTERISK-27957 #close

Change-Id: Idf2597ee48e9a287e07aa4030bfa705430a13a92

include/asterisk/res_pjsip_session.h

@@ -85,6 +85,8 @@ struct ast_sip_session_media {
 	unsigned int held:1;
 	/*! \brief Does remote support rtcp_mux */
 	unsigned int remote_rtcp_mux:1;
+	/*! \brief Does remote support ice */
+	unsigned int remote_ice:1;
 	/*! \brief Stream type this session media handles */
 	char stream_type[1];
 };

res/res_pjsip_sdp_rtp.c

@@ -531,6 +531,10 @@ static void add_ice_to_stream(struct ast_sip_session *session, struct ast_sip_se
 		return;
 	}
 
+	if (!session_media->remote_ice) {
+		return;
+	}
+
 	if ((username = ice->get_ufrag(session_media->rtp))) {
 		attr = pjmedia_sdp_attr_create(pool, "ice-ufrag", pj_cstr(&stmp, username));
 		media->attr[media->attr_count++] = attr;
@@ -576,6 +580,33 @@ static void add_ice_to_stream(struct ast_sip_session *session, struct ast_sip_se
 	ao2_ref(candidates, -1);
 }
 
+/*! \brief Function which checks for ice attributes in an audio stream */
+static void check_ice_support(struct ast_sip_session *session, struct ast_sip_session_media *session_media,
+				   const struct pjmedia_sdp_media *remote_stream)
+{
+	struct ast_rtp_engine_ice *ice;
+	const pjmedia_sdp_attr *attr;
+	unsigned int attr_i;
+
+	if (!session->endpoint->media.rtp.ice_support || !(ice = ast_rtp_instance_get_ice(session_media->rtp))) {
+		session_media->remote_ice = 0;
+		return;
+	}
+
+	/* Find all of the candidates */
+	for (attr_i = 0; attr_i < remote_stream->attr_count; ++attr_i) {
+		attr = remote_stream->attr[attr_i];
+		if (!pj_strcmp2(&attr->name, "candidate")) {
+			session_media->remote_ice = 1;
+			break;
+		}
+	}
+
+	if (attr_i == remote_stream->attr_count) {
+		session_media->remote_ice = 0;
+	}
+}
+
 /*! \brief Function which processes ICE attributes in an audio stream */
 static void process_ice_attributes(struct ast_sip_session *session, struct ast_sip_session_media *session_media,
 				   const struct pjmedia_sdp_session *remote, const struct pjmedia_sdp_media *remote_stream)
@@ -1033,6 +1064,9 @@ static int negotiate_incoming_sdp_stream(struct ast_sip_session *session, struct
 		pj_strdup(session->inv_session->pool, &session_media->transport, &stream->desc.transport);
  	}
 
+	/* If ICE support is enabled find all the needed attributes */
+	check_ice_support(session, session_media, stream);
+
 	if (set_caps(session, session_media, stream)) {
 		return 0;
 	}

res/res_pjsip_session.c

@@ -1341,6 +1341,7 @@ static int add_session_media(void *obj, void *arg, int flags)
 		return CMP_STOP;
 	}
 	session_media->encryption = session->endpoint->media.rtp.encryption;
+	session_media->remote_ice = session->endpoint->media.rtp.ice_support;
 	session_media->keepalive_sched_id = -1;
 	session_media->timeout_sched_id = -1;
 	/* Safe use of strcpy */