removed '-p' cli option requirement for (#775)

src/edge.c

@@ -626,8 +626,9 @@ static int setOption (int optkey, char *optargument, n2n_tuntap_priv_config_t *e
                     break;
                 } else {
                     conf->preferred_sock.family = AF_INET;
-                    // port is set after parsing all cli parameters
+                    // port is set after parsing all cli parameters during supernode_connect()
                 }
+
             }
 
             break;
@@ -1063,18 +1064,6 @@ int main (int argc, char* argv[]) {
     if(conf.encrypt_key && !strcmp((char*)conf.community_name, conf.encrypt_key))
         traceEvent(TRACE_WARNING, "community and encryption key must differ, otherwise security will be compromised");
 
-    // so far, preferred local sock (-e) only works with a fixed port provided (-p)
-    if(conf.preferred_sock.family != AF_INVALID) {
-        conf.preferred_sock.port = conf.local_port;
-        if(conf.local_port == 0) {
-            traceEvent(TRACE_WARNING, "preferred local socket requires a port to be provided (-p), skipping");
-            conf.preferred_sock.family = AF_INVALID;
-            in_addr_t address_tmp = INADDR_NONE;
-            memcpy(&(conf.preferred_sock.addr.v4), &(address_tmp), IPV4_SIZE);
-        }
-    }
-
-
     if((eee = edge_init(&conf, &rc)) == NULL) {
         traceEvent(TRACE_ERROR, "failed in edge_init");
         exit(1);

src/edge_utils.c

@@ -203,6 +203,8 @@ void reset_sup_attempts (n2n_edge_t *eee) {
 int supernode_connect(n2n_edge_t *eee) {
 
     int sockopt;
+    struct sockaddr_in sock;
+    int sock_len = sizeof(sock);
 
     if((eee->conf.connect_tcp) && (eee->sock >= 0)) {
         closesocket(eee->sock);
@@ -225,10 +227,15 @@ int supernode_connect(n2n_edge_t *eee) {
             return -1;
         }
 
-        if(eee->cb.sock_opened)
-            eee->cb.sock_opened(eee);
+        // detetct local port, even/especially if chosen by OS...
+        if((getsockname(eee->sock, (struct sockaddr *)&sock, &sock_len) == 0)
+        && (sock.sin_family == AF_INET)
+        && (sock_len == sizeof(sock))) {
+            // ... and write to local preferred socket -- no matter if used or not
+            eee->conf.preferred_sock.port = ntohs(sock.sin_port);
+        }
 
-        struct sockaddr_in sock;
+        // variable 'sock' gets re-used from here on (for sn)
         sock.sin_family = eee->curr_sn->sock.family;
         sock.sin_port = htons(eee->curr_sn->sock.port);
         memcpy(&(sock.sin_addr.s_addr), &(eee->curr_sn->sock.addr.v4), IPV4_SIZE);
@@ -267,6 +274,9 @@ int supernode_connect(n2n_edge_t *eee) {
         else
             traceEvent(TRACE_INFO, "PMTU discovery %s", (eee->conf.disable_pmtu_discovery) ? "disabled" : "enabled");
 #endif
+
+        if(eee->cb.sock_opened)
+            eee->cb.sock_opened(eee);
     }
 
     return 0;