net,sip: check if destination is reachable when selecting transport

include/re_net.h

@@ -43,6 +43,7 @@ int  net_hostaddr(int af, struct sa *ip);
 int  net_dst_source_addr_get(struct sa *dst, struct sa *ip);
 int  net_default_source_addr_get(int af, struct sa *ip);
 int  net_default_gateway_get(int af, struct sa *gw);
+int  net_check_conn(const struct sa *src, const struct sa *dst);
 
 
 /* Net sockets */

src/net/net.c

@@ -95,6 +95,48 @@ int net_dst_source_addr_get(struct sa *dst, struct sa *ip)
 }
 
 
+/**
+ * Check if connection from source to destination is possible
+ *
+ * @param src Source IP address
+ * @param dst Destination IP address
+ *
+ * @return 0 if success, otherwise errorcode
+ */
+int net_check_conn(const struct sa *src, const struct sa *dst)
+{
+	struct udp_sock *us;
+	struct sa srctmp;
+	struct sa dsttmp;
+	int port;
+	int err = 0;
+
+	if (!sa_isset(src, SA_ADDR) || !sa_isset(dst, SA_ADDR))
+		return EINVAL;
+
+	srctmp = *src;
+	dsttmp = *dst;
+	sa_cpy_scopeid(&dsttmp, src);
+	for (port = sa_port(src) + 3; port < sa_port(src) + 23; port++) {
+		err = udp_listen(&us, &srctmp, NULL, NULL);
+		if (!err)
+			break;
+
+		sa_set_port(&srctmp, port);
+	}
+
+	if (err)
+		return err;
+
+	err = udp_connect(us, &dsttmp);
+	if (err)
+		goto out;
+out:
+	mem_deref(us);
+	return err;
+}
+
+
 /**
  * Get the default source IP address
  *

src/sip/transp.c

@@ -23,6 +23,7 @@
 #include <re_http.h>
 #include <re_websock.h>
 #include <re_sip.h>
+#include <re_net.h>
 #include "sip.h"
 
 
@@ -150,19 +151,25 @@ static const struct sip_transport *transp_find(struct sip *sip,
 					       int af, const struct sa *dst)
 {
 	struct le *le;
-	(void)dst;
 
 	for (le = sip->transpl.head; le; le = le->next) {
 
 		const struct sip_transport *transp = le->data;
+		const struct sa *src = &transp->laddr;
 
 		if (transp->tp != tp)
 			continue;
 
-		if (af != AF_UNSPEC && sa_af(&transp->laddr) != af)
+		if (af != AF_UNSPEC && sa_af(src) != af)
 			continue;
 
-		if (sa_is_linklocal(&transp->laddr) != sa_is_linklocal(dst))
+		if (!sa_isset(dst, SA_ADDR))
+			return transp;
+
+		if (sa_is_linklocal(src) != sa_is_linklocal(dst))
+			continue;
+
+		if (net_check_conn(src, dst))
 			continue;
 
 		return transp;