sampy/notes/packet_writeup.md

General packet

Client to server spesific

• Encode (encrypt) data
  • use first byte as checksum
    • every byte ^ 0xAA added together
  • xor
    • Server port ^ 0xCCCC
    • Every other byte
  • Lookup table (use byte as indexing value)

Shared

• Can be internal packet
• If packet is smaller then 3 bytes; forward to plugin handlers (*)before handling them (len(data) <= 2)

Order of operations

1. Check if banned (if true, cancel rest and handle) ¹
2. If first byte in data is (0x19, 0x1d, 0x1f, 0x24 or 0x18) custom code flow required ²
3. HandleSocketReceiveFromConnectedPlayer (cancel rest if handled)
4. Check if cheat (modified) packet (unexpected at this time, there are some packets we can expect) ³

Internal packet

condition	name	bit length	type	notes
	messageNumber	0x10	ushort
	reliability	0x04	uchar	Has to be over 5 (value > 5)
reliability in (7, 10, 9)	orderingChannel	0x05
reliability in (7, 10, 9)	orderingIndex	0x10	ushort
	isSplitPacket	0x01	bool	Drop packet as we no longer support split packet?
isSplitPacket == 0	dataBitLength	0x10	ushort
isSplitPacket == 0	data	dataBitLength	uchar*

---

1. this could be changed in custom implementation (dont allow inital connection instead) ↩︎

2. if (0x18 and length == 2) or (0x19 and length <= 2):
   handle packet and return
   elif (0x1d or 0x1f or 0x24) and length <= 2:
   handle packet, but continue ↩︎

3. if ((0x18 or 0x1a) and length <= 3) or ((0x19 or 0x1d) and length <= 2) or ((0x08 or 0x07 or 0x27) and length >= 5) or (0x37 and length < 400):
   We expect this packet, everything is ok?
   else:
   This is a cheat (modified / injected) packet that should not arrive at this time Send a packet to client that you received a modified packet (0x26) ↩︎