From 9c22d2856266c35ec5e2264c39b390082d3b53c1 Mon Sep 17 00:00:00 2001
From: Logan oos Even <46396513+Logan007@users.noreply.github.com>
Date: Thu, 16 Sep 2021 12:20:35 +0545
Subject: [PATCH] relocated 'detect_local_ip_address()' (#791)

---
 include/n2n.h    |  2 --
 src/edge_utils.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/include/n2n.h b/include/n2n.h
index 42bb342..30e1ba0 100644
--- a/include/n2n.h
+++ b/include/n2n.h
@@ -223,8 +223,6 @@ 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 85e757c..4be00bf 100644
--- a/src/edge_utils.c
+++ b/src/edge_utils.c
@@ -198,6 +198,53 @@ void reset_sup_attempts (n2n_edge_t *eee) {
 }
 
 
+// detect local IP address by probing a connection to the supernode
+static 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;
+    socklen_t sock_len = sizeof(local_sock);
+    SOCKET probe_sock;
+    int ret = 0;
+
+    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
+        ret = -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((int)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
+                ret = -4;
+        } else
+            ret = -3;
+        closesocket(probe_sock);
+    } else
+        ret = -2;
+
+    out_sock->family = AF_INET;
+
+    return ret;
+}
+
+
 // open socket, close it before if TCP
 // in case of TCP, 'connect()' is required
 int supernode_connect(n2n_edge_t *eee) {