Question NotServerException: Only server can spawn NetworkObjects

I get this exception from the client. On the host everything is working well. So I have two scenes, in the first I'm trying to start host/client from RoomConnection script and if everything is ok I just load game scene. When second scene is loaded in Room script I spawn player through ServerRpc function. And then I get exceptions in the console.
RoomConnection script:

Code (CSharp):

1. public void OnHostButtonClick()
2.         {
3.             RoomStats.Instance.ConnectedUserType = "Host";
4.  
5.             try
6.             {
7.                 NetworkManager.Singleton.StartHost();
8.              
9.                 SceneManager.LoadScene("Room");
10.             }
11.             catch (Exception e)
12.             {
13.                 print("Unable to host game!");
14.              
15.                 Console.WriteLine(e);
16.                 throw;
17.             }
18.         }
19.  
20.         public async void OnJoinButtonClick()
21.         {
22.             RoomStats.Instance.ConnectedUserType = "Client";
23.          
24.             bool isClientConnectedSuccessfully = false;
25.             NetworkManager.Singleton.OnClientConnectedCallback += obj => isClientConnectedSuccessfully = true;
26.          
27.             NetworkManager.Singleton.GetComponent<UNetTransport>().ConnectAddress = ipInputField.text;
28.  
29.             try
30.             {
31.                 NetworkManager.Singleton.StartClient();
32.  
33.                 await Task.Delay(5000);
34.  
35.                 if (isClientConnectedSuccessfully)
36.                 {
37.                     SceneManager.LoadScene("Room");
38.                 }
39.                 else
40.                 {
41.                     NetworkManager.Singleton.Shutdown();
42.                     print("Client can not connect to the host!");
43.                 }
44.             }
45.             catch (Exception e)
46.             {
47.                 Console.WriteLine(e);
48.                 throw;
49.             }
50.         }

Room script:

Code (CSharp):

1.         private void OnEnable()
2.         {
3.             _uNetTransport = NetworkManager.Singleton.gameObject.GetComponent<UNetTransport>();
4.  
5.             SceneManager.sceneLoaded += DisplayRoomIP;
6.             SceneManager.sceneLoaded += (scene, mode) => SpawnPlayerServerRpc();
7.         }
8.  
9.         private void DisplayRoomIP(Scene scene, LoadSceneMode mode)
10.         {
11.             string userType = RoomStats.Instance.ConnectedUserType;
12.  
13.             if (userType != "Host" && userType != "Client")
14.             {
15.                 throw new Exception("Who are you?!");
16.             }
17.  
18.             roomIP.text = userType == "Host" ? GetLocalIPAddress() : _uNetTransport.ConnectAddress;
19.         }
20.  
21.         [ServerRpc(RequireOwnership = false)]
22.         private void SpawnPlayerServerRpc()
23.         {
24.             NetworkObject player = Instantiate(playerPrefab).GetComponent<NetworkObject>();
25.             player.SpawnAsPlayerObject(NetworkManager.Singleton.LocalClientId);
26.         }

 

It looks like the RPC is being run on the client rather than the server, you won't get an indication of that until you hit something server specific. You could add a debug line at the start to be sure.

Is Room derived from NetworkBehaviour?

 

Think you can help me with my code?

 

Hard to say, create a new thread stating the problem you're having.

 

No, but I tried to add and it doesn't make difference.

 

Does Room's NetworkObject component have a NetworkObjectId, you can check it in Unity editor at runtime.

You could try updating Netcode to 1.0.0-pre.7 but it looks like you're using UNet transport and that's been removed in favour of the Unity transport so it will likely break your code.

 

So I installed new Unity Transport and updated netcode package. And now I can't connect to the host for some reasons.I just I swapped UNetTransport to UnityTransport in the RoomConnection script. Client starts and IP address get right value, but can't connect to the host as I said.

 

You don't need to install the Unity transport, it's now incorporated in the Netcode package.

I would create a new test project to sort out the connection and also to do some simple RPC testing then work out what's going on differently in your main project.

 

Could it have something to do with loading a scene in a non-networked way? I.e. if you call

NetworkManager.Singleton.SceneManager.LoadScene

instead of

SceneManager.LoadScene

, does that solve it?

 

I think it's not a problem for now. I start client and only after that I check for client has connected and then load scene. So it starts a client (I can track it in the inspector), but OnClientConnectedCallback doesn't awake for some reasons.

 

You're calling LoadScene when you start the host when really as CosmoM says you should be using Netcode's SceneManager.LoadScene call.

I think you're missing the benefit of the OnClientConnectedCallback by having it set a variable, if you use a function you can do away with having to wait a fixed amount of time before checking the variable is set. Also if you let the server's SceneManager handle the scene loading it will switch it to the Room scene automatically.

For the RPC Issue, are you spawning Room at runtime or does it already exist in the Room scene? Did you check that the Room's NetworkObject component had a NetworkObjectId, the client's should match the host.

If you want to make your project available I can take a look at it.

 

So I created a new empty project to make all from the start. And I made scene loading through netcode's scene management. And now from the client I can't load a room scene because of NotServerException: Only server can start a scene event, but I'm using [ServerRpc] attribute. So probably I make it in the wrong way? Should I use another attribute to make action on the server?
UPD: Yeah, Room object already exist in the scene.

 

If you have this code for the host:

Code (CSharp):

1.      try
2.             {
3.                 NetworkManager.Singleton.StartHost();
4.                
5.                 NetworkManager.Singleton.SceneManager.LoadScene("Room", LoadSceneMode.Single);
6.             }

The client will switch to the Room scene on connection, you don't need the ServerRpc call.

It's likely, if you're making scene changes yourself and not through server's SceneManager existing network objects won't be spawned, but again check the NetworkObjectId.

 

Client can't connect to the host for some reasons. Connection address gets right value

Code (CSharp):

1. public class RoomConnection : NetworkBehaviour
2. {
3.     [SerializeField] private TMP_InputField ipInputField;
4.  
5.     public void OnHostButtonClick()
6.     {
7.         RoomStats.Instance.ConnectedUserType = "Host";
8.  
9.         try
10.         {
11.             NetworkManager.Singleton.StartHost();
12.          
13.             NetworkManager.Singleton.SceneManager.LoadScene("Room", LoadSceneMode.Single);
14.         }
15.         catch (Exception e)
16.         {
17.             Console.WriteLine(e);
18.             throw;
19.         }
20.     }
21.  
22.     public void OnJoinButtonClick()
23.     {
24.         RoomStats.Instance.ConnectedUserType = "Client";
25.  
26.         NetworkManager.Singleton.gameObject.GetComponent<UnityTransport>().ConnectionData.Address = ipInputField.text;
27.  
28.         NetworkManager.Singleton.OnClientConnectedCallback += obj => print("Yep");
29.         NetworkManager.Singleton.StartClient();
30.     }
31. }

UPD: RoomConnection object id = 0
Room object id = 2
Player (host) object id = 3
Idk which object has id 1

 

For testing remove any code you don't need, and/or use plenty of Debug output to check values are correct.

For now use the default Unity transport values, in the editor it should look something like this.

 

Yeah, everything works perfectly if I use default connection ip address.

 

I don't know your development setup and why you're not using localhost but you might also need to set the Server Listen Address.

 

Server Listen Address doesn't work. Do you mean default ip under localhost?

 

I've never had to use a separate Server Listen Address but as you're having connection problems I thought it worth a try.

Yes I was wondering why you weren't using the 127.0.0.1 loopback address during development?

 

Haha, I don't even remember why I did this actually I guess it was something like password, because I tried to make connection approval by following Dapper Dino tutorial, but it didn't work. The byte array that I received on the callback was always equals to null. I tried to do this again right now, I thought maybe problem was in UNetTransport, but no. So maybe you can help me with this? Should I create a new thread? I tried to google this problem, but didn't find the answer.

 

I've not done a lot with connection approval, I just use it as a way of getting the player name to the server.

Code (CSharp):

1.             NetworkManager.Singleton.NetworkConfig.ConnectionData = Encoding.ASCII.GetBytes(PlayerPrefs.GetString("name"));

In ConnectionApprovalCallback:

Code (CSharp):

1.        public void ConnectionApprovalCallback(byte[] connectionData, ulong clientId, NetworkManager.ConnectionApprovedDelegate callback)
2.         {
3.             Debug.Log("ConnectionApprovalCallback clientId: " + clientId + " name: " + Encoding.ASCII.GetString(connectionData));
4.  
5.             ServerClientManager clientManager = ServerClientsManager.Instance().InitialiseClient(clientId, Encoding.ASCII.GetString(connectionData));
6.  
7.             clientManager.ClientState = ClientState.Authenticated;
8.  
9.             callback(false, null, true, null, null);
10.         }

 

I see. I get null connection data for some reasons...

 

I set connectionData just before StartClient() if it helps.

 

Yeah, that's the point, I do it too.

 

Is connectionData null or an empty array? When not set it's an empty array. It might be worth reading back connectionData to check what you're assigning is what's expected.

 

It returns an empty byte array.

Code (CSharp):

1.     public class RoomConnection : NetworkBehaviour
2.     {
3.         [SerializeField] private TMP_InputField passwordInputField;
4.  
5.         public void OnHostButtonClick()
6.         {
7.             RoomStats.Instance.ConnectedUserType = "Host";
8.  
9.             try
10.             {
11.                 NetworkManager.Singleton.ConnectionApprovalCallback += ApprovalCheck;
12.                 NetworkManager.Singleton.StartHost();
13.             }
14.             catch (Exception e)
15.             {
16.                 print("Unable to host game!");
17.                
18.                 Console.WriteLine(e);
19.                 throw;
20.             }
21.         }
22.        
23.         public void OnJoinButtonClick()
24.         {
25.             RoomStats.Instance.ConnectedUserType = "Client";
26.  
27.             try
28.             {
29.                 NetworkManager.Singleton.NetworkConfig.ConnectionData = Encoding.ASCII.GetBytes(passwordInputField.text);
30.                 print("first " + NetworkManager.Singleton.NetworkConfig.ConnectionData.Length);
31.                 NetworkManager.Singleton.StartClient();
32.             }
33.             catch (Exception e)
34.             {
35.                 Console.WriteLine(e);
36.                 throw;
37.             }
38.         }
39.        
40.         private void ApprovalCheck(byte[] connectionData, ulong userID, NetworkManager.ConnectionApprovedDelegate callback)
41.         {
42.             print("second " + connectionData.Length);
43.             string password = Encoding.ASCII.GetString(connectionData);
44.  
45.             if (password == passwordInputField.text)
46.             {
47.                 NetworkManager.Singleton.SceneManager.LoadScene("Room", LoadSceneMode.Single);
48.             }
49.             else
50.             {
51.                 print("Bruh");
52.             }
53.         }
54.     }

 

I have something similar in test working fine, I'm out of ideas unfortunately.

 

It's ok, anyway huge thank you!

 

It looks to me like the client is not subscribed to the approval callback, shouldn't it be? This works for me:

Code (CSharp):

1. [System.Serializable]
2. public class ConnectionPayload {
3.     public int playerTeam;
4.     public string playerName;
5.  
6.     public ConnectionPayload(int team,string name) {
7.         playerTeam=team;
8.         playerName=name;
9.     }
10. }
11.  
12. public class Login : NetworkBehaviour {
13.     private void OnEnable() {
14.         NetworkManager.Singleton.ConnectionApprovalCallback+=ApprovalCheck;
15.     }
16.  
17.     public void Join(int playerTeam,string playerName) {
18.         string payload=JsonUtility.ToJson(new ConnectionPayload(playerteam,playerName));
19.         byte[] payloadBytes=System.Text.Encoding.UTF8.GetBytes(payload);
20.         NetworkManager.Singleton.NetworkConfig.ConnectionData=payloadBytes;
21.         NetworkManager.Singleton.StartClient();
22.     }
23.  
24.     private void ApprovalCheck(byte[] connectionData,ulong clientId,NetworkManager.ConnectionApprovedDelegate Callback) {
25.         if (clientId!=0) { //Approval check is not called reliably for the host, but we have the host's data anyway, so skip it
26.             ConnectionPayload payload=JsonUtility.FromJson<ConnectionPayload>(System.Text.Encoding.ASCII.GetString(connectionData));
27.             //Store data somewhere
28.         }
29.         //Call Callback
30.     }
31. }

 

I'd say that is the problem. In pre7 I'm getting a warning if the client isn't subscribed.

 

I tried to put subscription into the OnEnable method, but now it looks like approval callback never called.
Also if put subscription before the start host I get this console warning.

Code (CSharp):

1. public class RoomConnection : NetworkBehaviour
2. {
3.     [SerializeField] private TMP_InputField passwordField;
4.    
5.     private void OnEnable()
6.     {
7.         NetworkManager.Singleton.ConnectionApprovalCallback += ApprovalCheck;
8.     }
9.  
10.     public void OnHostButtonClick()
11.     {
12.         NetworkManager.Singleton.StartHost();
13.     }
14.    
15.     public void OnJoinButtonClick()
16.     {
17.         NetworkManager.Singleton.NetworkConfig.ConnectionData = Encoding.ASCII.GetBytes(passwordField.text);
18.         NetworkManager.Singleton.StartClient();
19.     }
20.  
21.     private void ApprovalCheck(byte[] connectionData, ulong userID, NetworkManager.ConnectionApprovedDelegate callback)
22.     {
23.         print("here");
24.         if (NetworkManager.Singleton.IsHost)
25.         {
26.             print("Yep");
27.         }
28.         else
29.         {
30.             string password = Encoding.ASCII.GetString(connectionData);
31.  
32.             if (password == passwordField.text)
33.             {
34.                 print("Yep");
35.             }
36.             else
37.             {
38.                 print("Nope");
39.             }
40.         }
41.     }
42. }

I always get different errors even if I do it in the same way. It's a very strange thing...

 

You should be able to subscribe just before the StartHost/Client calls. Here's the test code I use, the EnableCallbacks are just doing multiple subscribes in one call.

Code (CSharp):

1. public class StartSceneController : MonoBehaviour
2. {
3.     ServerNetworkCallbackService serverNetworkCallbackService = new ServerNetworkCallbackService();
4.     ClientNetworkCallbackService clientNetworkCallbackService = new ClientNetworkCallbackService();
5.  
6.     private void Start()
7.     {
8.         Application.targetFrameRate = 15;
9.     }
10.  
11.     public void OnClickStartHost()
12.     {
13.         serverNetworkCallbackService.EnableCallbacks();
14.         NetworkManager.Singleton.StartHost();
15.         NetworkManager.Singleton.SceneManager.LoadScene("RpcScene", LoadSceneMode.Single);
16.     }
17.  
18.     public void OnClickStartClient()
19.     {
20.         clientNetworkCallbackService.EnableCallbacks();
21.         NetworkManager.Singleton.NetworkConfig.ConnectionData = Encoding.ASCII.GetBytes("TEST");
22.  
23.         Debug.Log("connectionData: " +  NetworkManager.Singleton.NetworkConfig.ConnectionData.Length);
24.         NetworkManager.Singleton.StartClient();
25.     }
26.  
27.     private void OnDestroy()
28.     {
29.     //    serverNetworkCallbackService.DisableCallbacks();
30.     }
31. }

 

Something like that?
For this variant callback still doesn't work

Code (CSharp):

1.     public void OnHostButtonClick()
2.     {
3.         NetworkManager.Singleton.ConnectionApprovalCallback += ApprovalCheck;
4.         NetworkManager.Singleton.StartHost();
5.     }
6.    
7.     public void OnJoinButtonClick()
8.     {
9.         NetworkManager.Singleton.ConnectionApprovalCallback += ApprovalCheck;
10.         NetworkManager.Singleton.NetworkConfig.ConnectionData = Encoding.ASCII.GetBytes(passwordField.text);
11.         NetworkManager.Singleton.StartClient();
12.     }

 

What errors are you seeing?

You might want to remove everything that isn't essential for the test to narrow down the problem. Just a game object and MonoBehaviour script for the button handling and callback, and the NetworkManager.

 

So I remade everything from zero. Now it works.

Code (CSharp):

1. public class RoomConnection : MonoBehaviour
2. {
3.     [SerializeField] private TMP_InputField passwordField;
4.    
5.     public void Host()
6.     {
7.         NetworkManager.Singleton.ConnectionApprovalCallback += ApprovalCheck;
8.        
9.         SavePassword(passwordField.text);
10.  
11.         NetworkManager.Singleton.StartHost();
12.     }
13.    
14.     public void Join()
15.     {
16.         NetworkManager.Singleton.NetworkConfig.ConnectionData = Encoding.ASCII.GetBytes(passwordField.text);
17.         NetworkManager.Singleton.StartClient();
18.     }
19.    
20.     private void ApprovalCheck(byte[] connectionData, ulong clientID, NetworkManager.ConnectionApprovedDelegate callback)
21.     {
22.         bool approve = Encoding.ASCII.GetString(connectionData) == GetPassword();
23.        
24.         callback(true, null, approve, Vector3.zero, Quaternion.identity);
25.     }
26.  
27.     private void SavePassword(string password)
28.     {
29.         PlayerPrefs.SetString("RoomPassword", password);
30.     }
31.  
32.     private string GetPassword()
33.     {
34.         try
35.         {
36.             return PlayerPrefs.GetString("RoomPassword");
37.         }
38.         catch (Exception e)
39.         {
40.             Debug.Log(e);
41.             return null;
42.         }
43.     }
44. }

Huge thanks to you guys!