StopClient on server with host client kills the server

[MrGadget1024]

Describe the bug
Starting a server with Host client, then calling StopClient (with or without remote clients connected) should leave the server running normally. Connected clients should be able to continue playing, new clients should be able to join, even host client should be able to join back in with StartClient.

[IMPORTANT] How can we reproduce the issue, step by step:

1. Modify NetworkManagerHUD as follows:

void StopButtons()
{
    // stop host if host mode
    if (NetworkServer.active && NetworkClient.isConnected)
    {
        GUILayout.BeginHorizontal();
        if (GUILayout.Button("Stop Host"))
        {
            manager.StopHost();
        }
        if (GUILayout.Button("Stop Client"))
        {
            manager.StopClient();
        }
        GUILayout.EndHorizontal();
    }

2. Build Basic example and run as remote client
3. Play in editor as host
4. Click Stop Client button added in the change above
5. Observe the remote client is disconnected

Expected behavior
Remote client should still be connected and functioning normally

[miwarnec]

networkmanager has different ways to

• start server
• start host server

stopping has to be done the same way. if it was started as host, it needs to stopped as host - not only as client.

that's the way host mode always works, and the reason why Stop Client button is hidden in Network Manager HUD when in host mode - to make sure people use StopHost().

that being said, that's just UNET's overly complicated host mode.
redoing host mode in a more clean way with less 'special code' would solve this.

[miwarnec]

actually, we should probably add a check to StopClient to warn the user if called in host mode.

[miwarnec]

playing around with StopClient button.
starthost -> stopclient -> connecting external client still works fine:
https://gyazo.com/384b0ad16c47c756aadcb23e52543405

[miwarnec]

seems to be NetworkClient.Shutdown in NetMan.StopClient()

[miwarnec]

two issues in NetClient.Shutdown:

• calls NetworkIdentity.ResetStaticis which resets nextNetId to 1. that would cause duplicate netIds on server when next client connects
• DestroyAllClientObjects is what kicks the external client

[miwarnec]

NC.DestroyAllClientObjects destroys all NC.spawned.
for some reason, the other client's object is in there too:

so there's a deeper bug here..

[miwarnec]

actually, theo ther client's object is in NC.spawned because it's around the client object.

solution will be for DestroyAllClientObjects to only destroy the client-only ones.