res_pjsip/chan_sip: Advertise 'ws' in the SIP URI transport parameter

Per RFC 7118 5.2, the SIP URI 'transport' parameter should advertise
'ws' when WebSockets are to be used as the transport. This applies to
both secure and insecure WebSockets.

There were two bugs in Asterisk with respect to this:

(1) The most egregious occurs in res_pjsip. There, we advertise 'ws' for
    insecure websockets and 'wss' for secure websockets. While this
    would seem to make sense - since 'WS' and 'WSS' are used for the Via
    Transport parameter - this is not the case for the SIP URI. This
    patch corrects that by registering the secure websockets with
    pjproject using the shorthand 'WS', and by returning 'ws' when asked
    for the transport parameter. Note that in pjproject, it is perfectly
    valid to have multiple transports use the same shorthand.

(2) In chan_sip, we return an upper-case version of the transport 'WS'
    instead of 'ws'. Since we should be strict in what we send and
    liberal in what we accept (within reason), this patch lower-cases
    the transport before appending it to the parameter.

ASTERISK-24330 #close
Reported by: cervajs, Inaki Baz Castillo

Change-Id: Iff77b645f8cc3b7cd35168a6676c26b147f22f42

channels/chan_sip.c

@@ -14153,6 +14153,7 @@ static void build_contact(struct sip_pvt *p, struct sip_request *req, int incomi
 	char tmp[SIPBUFSIZE];
 	char *user = ast_uri_encode(p->exten, tmp, sizeof(tmp), ast_uri_sip_user);
 	int use_sips;
+	char *transport = ast_strdupa(sip_get_transport(p->socket.type));
 	if (incoming) {
 		use_sips = uas_sips_contact(req);
@@ -14167,7 +14168,7 @@ static void build_contact(struct sip_pvt *p, struct sip_request *req, int incomi
 	} else {
 		ast_string_field_build(p, our_contact, "<%s:%s%s%s;transport=%s>",
 			use_sips ? "sips" : "sip", user, ast_strlen_zero(user) ? "" : "@",
-			ast_sockaddr_stringify_remote(&p->ourip), sip_get_transport(p->socket.type));
+			ast_sockaddr_stringify_remote(&p->ourip), ast_str_to_lower(transport));
 	}
 }

res/res_pjsip_transport_websocket.c

@@ -378,7 +378,6 @@ static void websocket_cb(struct ast_websocket *session, struct ast_variable *par
 static pj_bool_t websocket_on_rx_msg(pjsip_rx_data *rdata)
 {
 	static const pj_str_t STR_WS = { "ws", 2 };
-	static const pj_str_t STR_WSS = { "wss", 3 };
 	pjsip_contact_hdr *contact;
 
 	long type = rdata->tp_info.transport->key.type;
@@ -395,7 +394,7 @@ static pj_bool_t websocket_on_rx_msg(pjsip_rx_data *rdata)
 		uri->port = rdata->pkt_info.src_port;
 		ast_debug(4, "Re-wrote Contact URI host/port to %.*s:%d\n",
 			(int)pj_strlen(&uri->host), pj_strbuf(&uri->host), uri->port);
-		pj_strdup(rdata->tp_info.pool, &uri->transport_param, (type == (long)transport_type_ws) ? &STR_WS : &STR_WSS);
+		pj_strdup(rdata->tp_info.pool, &uri->transport_param, &STR_WS);
 	}
 
 	rdata->msg_info.via->rport_param = 0;
@@ -431,7 +430,7 @@ static int load_module(void)
 	CHECK_PJSIP_MODULE_LOADED();
 
 	pjsip_transport_register_type(PJSIP_TRANSPORT_RELIABLE, "WS", 5060, &transport_type_ws);
-	pjsip_transport_register_type(PJSIP_TRANSPORT_RELIABLE | PJSIP_TRANSPORT_SECURE, "WSS", 5060, &transport_type_wss);
+	pjsip_transport_register_type(PJSIP_TRANSPORT_RELIABLE | PJSIP_TRANSPORT_SECURE, "WS", 5060, &transport_type_wss);
 
 	if (ast_sip_register_service(&websocket_module) != PJ_SUCCESS) {
 		return AST_MODULE_LOAD_DECLINE;