Merge "res_pjsip: Handle deferred SDP hold/unhold properly."

res/res_pjsip_session.c

@@ -1125,7 +1125,54 @@ static pj_bool_t session_reinvite_on_rx_request(pjsip_rx_data *rdata)
 	}
 
 	if (!sdp_info->sdp) {
+		const pjmedia_sdp_session *local;
+		int i;
+
 		ast_queue_unhold(session->channel);
+
+		pjmedia_sdp_neg_get_active_local(session->inv_session->neg, &local);
+		if (!local) {
+			return PJ_FALSE;
+		}
+
+		/*
+		 * Some devices indicate hold with deferred SDP reinvites (i.e. no SDP in the reinvite).
+		 * When hold is initially indicated, we
+		 * - Receive an INVITE with no SDP
+		 * - Send a 200 OK with SDP, indicating sendrecv in the media streams
+		 * - Receive an ACK with SDP, indicating sendonly in the media streams
+		 *
+		 * At this point, the pjmedia negotiator saves the state of the media direction so that
+		 * if we are to send any offers, we'll offer recvonly in the media streams. This is
+		 * problematic if the device is attempting to unhold, though. If the device unholds
+		 * by sending a reinvite with no SDP, then we will respond with a 200 OK with recvonly.
+		 * According to RFC 3264, if an offerer offers recvonly, then the answerer MUST respond
+		 * with sendonly or inactive. The result of this is that the stream is not off hold.
+		 *
+		 * Therefore, in this case, when we receive a reinvite while the stream is on hold, we
+		 * need to be sure to offer sendrecv. This way, the answerer can respond with sendrecv
+		 * in order to get the stream off hold. If this is actually a different purpose reinvite
+		 * (like a session timer refresh), then the answerer can respond to our sendrecv with
+		 * sendonly, keeping the stream on hold.
+		 */
+		for (i = 0; i < local->media_count; ++i) {
+			pjmedia_sdp_media *m = local->media[i];
+			pjmedia_sdp_attr *recvonly;
+			pjmedia_sdp_attr *inactive;
+
+			recvonly = pjmedia_sdp_attr_find2(m->attr_count, m->attr, "recvonly", NULL);
+			inactive = pjmedia_sdp_attr_find2(m->attr_count, m->attr, "inactive", NULL);
+			if (recvonly || inactive) {
+				pjmedia_sdp_attr *to_remove = recvonly ?: inactive;
+				pjmedia_sdp_attr *sendrecv;
+
+				pjmedia_sdp_attr_remove(&m->attr_count, m->attr, to_remove);
+
+				sendrecv = pjmedia_sdp_attr_create(session->inv_session->pool, "sendrecv", NULL);
+				pjmedia_sdp_media_add_attr(m, sendrecv);
+			}
+		}
+
 		return PJ_FALSE;
 	}