fix: #2536 NetworkServer won't accept connections while listen=false

Assets/Mirror/Core/NetworkServer.cs

@@ -71,12 +71,7 @@ public static partial class NetworkServer
             new Dictionary<uint, NetworkIdentity>();
 
         /// <summary>Single player mode can set listen=false to not accept incoming connections.</summary>
-        static bool _listen = true;
+        public static bool listen;
-        public static bool listen
-        {
-            get { return _listen; }
-            set { _listen = value; }
-        }
 
         // DEPRECATED 2024-10-14
         [Obsolete("NetworkServer.dontListen was replaced with NetworkServer.listen. The new value is the opposite, and avoids double negatives like 'dontListen=false'")]
@@ -685,6 +680,13 @@ static void OnTransportConnectedWithAddress(int connectionId, string clientAddre
 
         static bool IsConnectionAllowed(int connectionId, string address)
         {
+            // only accept connections while listening
+            if (!listen)
+            {
+                Debug.Log($"Server not listening, rejecting connectionId={connectionId} with address={address}");
+                return false;
+            }
+
             // connectionId needs to be != 0 because 0 is reserved for local player
             // note that some transports like kcp generate connectionId by
             // hashing which can be < 0 as well, so we need to allow < 0!

Assets/Mirror/Tests/Editor/NetworkServer/NetworkServerTest.cs

@@ -1107,6 +1107,22 @@ public void UnSpawnAndClearAuthority()
             Assert.That(comp.onStopAuthorityCalled, Is.EqualTo(1));
         }
 
+        // test to prevent https://github.com/MirrorNetworking/Mirror/issues/2536
+        [Test]
+        public void SetListenToFalse()
+        {
+            // start the server with listen=true
+            NetworkServer.Listen(1);
+
+            // set listen=false at runtime
+            NetworkServer.listen = false;
+
+            // try connecting a client. should be reject while not listening.
+            NetworkClient.Connect("127.0.0.1");
+            UpdateTransport();
+            Assert.That(NetworkServer.connections.Count, Is.EqualTo(0));
+        }
+
         // test to reproduce a bug where stopping the server would not call
         // OnStopServer on scene objects:
         // https://github.com/vis2k/Mirror/issues/2119
@@ -1152,7 +1168,7 @@ public void ShutdownCleanup()
             NetworkServer.Shutdown();
 
             // state cleared?
-            Assert.That(NetworkServer.dontListen, Is.False);
+            Assert.That(NetworkServer.listen, Is.True);
             Assert.That(NetworkServer.active, Is.False);
             Assert.That(NetworkServer.isLoadingScene, Is.False);