From b3bf36f8671ae0dc32f9fac717b567cebecb32c3 Mon Sep 17 00:00:00 2001
From: Logan oos Even <46396513+Logan007@users.noreply.github.com>
Date: Mon, 13 Sep 2021 11:33:27 +0545
Subject: [PATCH] separated 'detect_local_ip_address()' function (#781)

---
 include/n2n.h    |  2 ++
 src/edge_utils.c | 32 +++++++++++---------------------
 src/n2n.c        | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 61 insertions(+), 21 deletions(-)

diff --git a/include/n2n.h b/include/n2n.h
index 22bf343..90751c2 100644
--- a/include/n2n.h
+++ b/include/n2n.h
@@ -223,6 +223,8 @@ char * ip_subnet_to_str (dec_ip_bit_str_t buf, const n2n_ip_subnet_t *ipaddr);
 SOCKET open_socket (int local_port, in_addr_t address, int type);
 int sock_equal (const n2n_sock_t * a,
                 const n2n_sock_t * b);
+int detect_local_ip_address (n2n_sock_t* out_sock,
+                             const n2n_edge_t* eee);
 
 /* Header encryption */
 uint64_t time_stamp (void);
diff --git a/src/edge_utils.c b/src/edge_utils.c
index e790912..99776d2 100644
--- a/src/edge_utils.c
+++ b/src/edge_utils.c
@@ -204,9 +204,8 @@ int supernode_connect(n2n_edge_t *eee) {
 
     int sockopt;
     struct sockaddr_in sn_sock;
-    struct sockaddr_in local_sock;
-    int sock_len = sizeof(local_sock);
-    SOCKET probe_sock;
+    n2n_sock_t local_sock;
+    n2n_sock_str_t sockbuf;
 
     if((eee->conf.connect_tcp) && (eee->sock >= 0)) {
         closesocket(eee->sock);
@@ -266,25 +265,16 @@ int supernode_connect(n2n_edge_t *eee) {
             traceEvent(TRACE_INFO, "PMTU discovery %s", (eee->conf.disable_pmtu_discovery) ? "disabled" : "enabled");
 #endif
 
-        // detetct local port even/especially if chosen by OS...
-        if((getsockname(eee->sock, (struct sockaddr *)&local_sock, &sock_len) == 0)
-        && (local_sock.sin_family == AF_INET)
-        && (sock_len == sizeof(local_sock))) {
-            // ... and write to local preferred socket -- no matter if used or not
-            eee->conf.preferred_sock.port = ntohs(local_sock.sin_port);
-            // probe for & overwrite local address only if auto-detection mode
+        memset(&local_sock, 0, sizeof(n2n_sock_t));
+        if(detect_local_ip_address(&local_sock, eee) == 0) {
+            // always overwrite local port even/especially if chosen by OS...
+            eee->conf.preferred_sock.port = local_sock.port;
+            // only if auto-detection mode, ...
             if(eee->conf.preferred_sock_auto) {
-                probe_sock = socket(PF_INET, SOCK_DGRAM, 0);
-                // connecting the UDP socket makes getsockname read the local address it uses to connect (to the sn in this case)
-                // we cannot do it with the real (eee->sock) socket because socket does not accept any conenction from elsewhere then,
-                // e.g. from another edge instead of the supernode; hence, we use a temporary socket
-                connect(probe_sock, (struct sockaddr *)&sn_sock, sizeof(sn_sock));
-                if((getsockname(probe_sock, (struct sockaddr *)&local_sock, &sock_len) == 0)
-                && (local_sock.sin_family == AF_INET)
-                && (sock_len == sizeof(local_sock))) {
-                    memcpy(&(eee->conf.preferred_sock.addr.v4), &(local_sock.sin_addr.s_addr), IPV4_SIZE);
-                }
-                close(probe_sock);
+                // ... overwrite IP address, too (whole socket struct here)
+                memcpy(&eee->conf.preferred_sock, &local_sock, sizeof(n2n_sock_t));
+                traceEvent(TRACE_INFO, "determined local socket [%s]",
+                                       sock_to_cstr(sockbuf, &local_sock));
             }
         }
 
diff --git a/src/n2n.c b/src/n2n.c
index ad444ea..3fc78d2 100644
--- a/src/n2n.c
+++ b/src/n2n.c
@@ -61,6 +61,54 @@ SOCKET open_socket (int local_port, in_addr_t address, int type /* 0 = UDP, TCP
 }
 
 
+int detect_local_ip_address (n2n_sock_t* out_sock, const n2n_edge_t* eee) {
+
+    struct sockaddr_in local_sock;
+    struct sockaddr_in sn_sock;
+    int sock_len = sizeof(local_sock);
+    int port = 0;
+    SOCKET probe_sock;
+
+    out_sock->family = AF_INVALID;
+
+
+    // always detetct local port even/especially if chosen by OS...
+    if((getsockname(eee->sock, (struct sockaddr *)&local_sock, &sock_len) == 0)
+    && (local_sock.sin_family == AF_INET)
+    && (sock_len == sizeof(local_sock)))
+        // remember the port number
+        out_sock->port = ntohs(local_sock.sin_port);
+    else
+        return -1;
+
+    // probe for local IP address
+    probe_sock = socket(PF_INET, SOCK_DGRAM, 0);
+    // connecting the UDP socket makes getsockname read the local address it uses to connect (to the sn in this case);
+    // we cannot do it with the real (eee->sock) socket because socket does not accept any conenction from elsewhere then,
+    // e.g. from another edge instead of the supernode; as re-connecting to AF_UNSPEC might not work to release the socket
+    // on non-UNIXoids, we use a temporary socket
+    if(probe_sock >= 0) {
+        fill_sockaddr((struct sockaddr*)&sn_sock, sizeof(sn_sock), &eee->curr_sn->sock);
+        if(connect(probe_sock, (struct sockaddr *)&sn_sock, sizeof(sn_sock)) == 0) {
+            if((getsockname(probe_sock, (struct sockaddr *)&local_sock, &sock_len) == 0)
+            && (local_sock.sin_family == AF_INET)
+            && (sock_len == sizeof(local_sock))) {
+                memcpy(&(out_sock->addr.v4), &(local_sock.sin_addr.s_addr), IPV4_SIZE);
+            } else
+                return -4;
+        } else
+            return -3;
+        close(probe_sock);
+    } else
+        return -2;
+
+    out_sock->family = AF_INET;
+
+    return 0;
+}
+
+
+
 static int traceLevel = 2 /* NORMAL */;
 static int useSyslog = 0, syslog_opened = 0;
 static FILE *traceFile = NULL;