Client and server over WebSocket

One thing that isn’t evident in the simple client-serve example is that the NetworkDriver instantiates a NetworkInterface object internally. However, you might still need to request a particular NetworkInterface object.

The NetworkInterface defines the operations a NetworkDriver requires to establish and coordinate connections. By default, in most platforms, the NetworkInterface object is an instance of the UDPNetworkInterface, which, as implied by the name, encapsulates a UDP socket. However, you can't normally open a UDP socket in a Web browser. As a result, the default network interface in the WebGL player is the WebSocketNetworkInterface, which encapsulates a TCP socket using the WebSocket protocol.

The distinction between the UDPNetworkInterface and the WebSocketNetworkInterface is important because of the fundamental network constraint that a client can only directly connect to a server with the same underlying socket type. In other words, a TCP socket can only connect to another TCP socket, and the same applies to UDP. If you plan to create a server for WebGL players to connect to, you have to tell the network driver to use the WebSocketNetworInterface explicitly:

   m_Driver = NetworkDriver.Create(new WebSocketNetworkInterface());

If you plan to share networking code between clients for multiple platforms, including WebGL, you might opt to have a WebSocket server for all platforms. In this case, ensure you assign the WebSocketNetworkInterface to the non-WebGL clients.

Alternatively, suppose you plan to have a server dedicated to browsers and another for other platforms. In that case, you can specify a different NetworkDriver instantiation with compiler definitions that depend on the platforms your project supports.

   #if UNITY_WEBGL
    m_Driver = NetworkDriver.Create(new WebSocketNetworkInterface());
    #else
    m_Driver = NetworkDriver.Create(new UDPNetworkInterface());
    #endif

note

Because the WebGL player is constrained by browser capabilities, it’s currently impossible to start a server in a WebGL player (even with the WebSocketNetworkInterface). Web browsers (to date) don't permit applications to open sockets for incoming connections, and trying to do so results in an exception. On the other hand, creating a server while playing in the Unity Editor is still perfectly valid. In some cases, you might want to use the UNITY_EDITOR compiler definition to create a NetworkDriver with the WebSocketNetworkInterface only when using the Unity Editor.

   #if UNITY_WEBGL && !UNITY_EDITOR
    m_Driver = NetworkDriver.Create(new WebSocketNetworkInterface());
    #else
    m_Driver = NetworkDriver.Create(new UDPNetworkInterface());
    #endif