HKMP datagrams have the following format:

| length | ushort | | sequence | ushort | | ack | ushort | | ack_field | uint (bitfield) | | packet_type | ushort | | packet_data | bytes |

For the different packet types available, see ClientPacketType and ServerPacketType in protocol.h. To see what format they are in and/or what they do, just read the code lol (sorry).