code: public static Message buildDisconnected(String serverId) {
      Disconnected dis = Disconnected.newBuilder()
                                     .setServerId(serverId)
                                     .build();
      return Message.newBuilder().setType(MessageType.DISCONNECTED)
                                 .setDisconnected(dis)
                                 .build();
    }
docs: Creates a DISCONNECTED message.
  
  @param serverId the ID of the disconnected peer.
  @return a protobuf message.