code: public void close() {
          lock.lock();
          try {
              if (connectionOpen && !channelSettling) {
                  final Protos.TwoWayChannelMessage.Builder msg = Protos.TwoWayChannelMessage.newBuilder();
                  msg.setType(Protos.TwoWayChannelMessage.MessageType.CLOSE);
                  conn.sendToClient(msg.build());
                  conn.destroyConnection(CloseReason.SERVER_REQUESTED_CLOSE);
              }
          } finally {
              lock.unlock();
          }
      }
docs: <p>Closes the connection by generating a settle message for the client and calls
  {@link PaymentChannelServer.ServerConnection#destroyConnection(PaymentChannelCloseException.CloseReason)}. Note that this does not broadcast
  the payment transaction and the client may still resume the same channel if they reconnect</p>
  <p>
  <p>Note that {@link PaymentChannelServer#connectionClosed()} must still be called after the connection fully
  closes.</p>