Server.addWebsocketHandler

Adds a WebSocket handler to server for requests prefixed by path.

If path is null or "/", then this will be the default handler for all requests that don't have a more specific handler.

When a path has a WebSocket handler registered, server will check incoming requests for WebSocket handshakes after all other handlers have run (unless some earlier handler has already set a status code on the message), and update the request's status, response headers, and response body accordingly.

If origin is non-null, then only requests containing a matching "Origin" header will be accepted. If protocols is non-null, then only requests containing a compatible "Sec-WebSocket-Protocols" header will be accepted. More complicated requirements can be handled by adding a normal handler to path, and having it perform whatever checks are needed and setting a failure status code if the handshake should be rejected.