Always try to resolve a hostname to IPv4 first

src/Connection.c

@@ -151,11 +151,21 @@ static void ClInternalConnectionTerminated(long errorCode)
     PltCloseThread(&terminationCallbackThread);
 }
 
-static int resolveHostName(const char*host)
+static int resolveHostName(const char* host)
 {
     struct addrinfo hints, *res;
     int err;
 
+    // We must first try IPv4-only because GFE doesn't listen on IPv6,
+    // so we'll only want to use an IPv6 address if it's the only address we have.
+    // For NAT64 networks, the IPv4 address resolution will fail but the IPv6 address
+    // will give us working connectivity to the host. All other networks will use IPv4
+    // addresses.
+    memset(&hints, 0, sizeof(hints));
+    hints.ai_family = AF_INET;
+    hints.ai_flags = AI_ADDRCONFIG;
+    err = getaddrinfo(host, NULL, &hints, &res);
+    if (err != 0 || res == NULL) {
         memset(&hints, 0, sizeof(hints));
         hints.ai_family = AF_UNSPEC;
         hints.ai_flags = AI_ADDRCONFIG;
@@ -169,6 +179,7 @@ static int resolveHostName(const char*host)
             Limelog("getaddrinfo() returned success without addresses\n");
             return -1;
         }
+    }
 
     // Use the first address in the list
     memcpy(&RemoteAddr, res->ai_addr, res->ai_addrlen);