Server web socket connection.

abstract class WebSocketConnection {
  /**
   * Sets the callback to be called when a message have been
   * received. The type on [message] is either [:String:] or
   * [:List<int>:] depending on whether it is a text or binary
   * message. If the message is empty [message] will be [:null:].
   */
  void set onMessage(void callback(message));

  /**
   * Sets the callback to be called when the web socket connection is
   * closed. [status] indicate the reason for closing. For network
   * errors the value of [status] will be
   * WebSocketStatus.ABNORMAL_CLOSURE]. In this callbach it is
   * possible to call [close] if [close] has not already been called.
   * If [close] has still not been called after the close callback
   * returns the received close status will automatically be echoed
   * back to the other end to finish the close handshake.
   */
  void set onClosed(void callback(int status, String reason));

  /**
   * Sends a message. The [message] must be a [:String:] a
   * [:List<int>:] or [:null:].
   */
  send(Object message);

  /**
   * Close the web socket connection. The default value for [status]
   * and [reason] are [:null:].
   */
  close([int status, String reason]);

  /**
   * WebSocketConnection is hashable.
   */
  int get hashCode;
}