 * When serialized, this header is written out as a protocol buffer, preceded
 * by a 4-byte integer representing the full packet length, and a 2-byte short
 * representing the header length.
 * When serialized, this header is written out as a protocol buffer, preceded
 * by a 4-byte integer representing the full packet length, and a 2-byte short
 * representing the header length. | PacketHeader.java