mid_registrar: Improve the advertised socket logic

Instead of blindly advertising the first UDP interface in the
self-generated, outgoing Contact URIs, the mid_registrar is now
aware of the next SIP hop and properly advertises the actual
sending interface which will be used. This includes any forced
send socket logic at script level.

modules/mid_registrar/save.c

@@ -146,8 +146,15 @@ static int trim_to_single_contact(struct sip_msg *msg, str *aor)
 	char *buf;
 	int e, is_dereg = 1, len, len1;
 	struct hdr_field *ct;
+	union sockaddr_union _;
 
-	adv_sock = *get_sock_info_list(PROTO_UDP);
+	/* get the source socket on the way to the next hop */
+	adv_sock = uri2sock(msg, GET_NEXT_HOP(msg), &_, PROTO_NONE);
+	if (!adv_sock) {
+		LM_ERR("failed to obtain next hop socket, ci=%.*s\n",
+		       msg->callid->body.len, msg->callid->body.s);
+		return -1;
+	}
 
 	/* completely remove all Contact hfs, except the last one */
 	for (ct = msg->contact; ct && ct->sibling; ct = ct->sibling) {
@@ -249,6 +256,7 @@ static int overwrite_req_contacts(struct sip_msg *req,
 	uint64_t ctid;
 	struct ct_mapping *ctmap;
 	struct list_head *_;
+	union sockaddr_union __;
 
 	ul_api.lock_udomain(mri->dom, &mri->aor);
 	ul_api.get_urecord(mri->dom, &mri->aor, &r);
@@ -269,7 +277,13 @@ static int overwrite_req_contacts(struct sip_msg *req,
 		return -1;
 	}
 
-	adv_sock = *get_sock_info_list(PROTO_UDP);
+	/* get the source socket on the way to the next hop */
+	adv_sock = uri2sock(req, GET_NEXT_HOP(req), &__, PROTO_NONE);
+	if (!adv_sock) {
+		LM_ERR("failed to obtain next hop socket, ci=%.*s\n",
+		       req->callid->body.len, req->callid->body.s);
+		return -1;
+	}
 
 	c = get_first_contact(req);
 	list_for_each(_, &mri->ct_mappings) {