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Overview

Sakuya AC uses a packet-based communication system to handle all network traffic between YSFlight clients and servers. The PacketManager class provides the core functionality for identifying and routing packets.

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PacketManager

The PacketManager class is responsible for parsing incoming network data and identifying packet types.

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Location

lib/PacketManager/PacketManager.py

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Methods

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get_packet_type
method
Returns the message type of a packet by reading its header.Parameters:
  • data (bytes): Raw packet data (minimum 4 bytes)
Returns:
  • str | None: Packet type name from MESSAGE_TYPES, or None if data is too short
Example:
from lib.PacketManager.PacketManager import PacketManager

pm = PacketManager()
packet_type = pm.get_packet_type(data)
# Returns: "FSNETCMD_AIRPLANESTATE", "FSNETCMD_LOGON", etc.

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Packet Structure

All YSFlight packets follow a common structure:
  1. Size Header (4 bytes): Packet length excluding the size header itself
  2. Packet Type (4 bytes): Integer ID identifying the packet type
  3. Payload: Packet-specific data
# Reading a packet
header = await reader.readexactly(4)  # Size header
length = unpack("I", header)[0]
packet = await reader.read(length)    # Packet type + payload
data = header + packet                 # Full packet with size

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Message Types

All packet types are defined in lib/PacketManager/packets/constants.py as the MESSAGE_TYPES list:
  • Connection Packets (0-3): NULL, LOGON, LOGOFF, ERROR
  • Flight Packets (11-13): AIRPLANESTATE, UNJOIN, REMOVEAIRPLANE
  • Join Packets (8-10): JOINREQUEST, JOINAPPROVAL, REJECTJOINREQ
  • Command Packets (30-36): AIRCMD, TEXTMESSAGE, WEAPONCONFIG
  • Combat Packets (18-22): LOCKON, MISSILELAUNCH, GETDAMAGE
  • Environment Packets (33, 48-50): ENVIRONMENT, FOGCOLOR, SKYCOLOR

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Packet Decoding Pattern

All packet classes follow a consistent pattern: 
from lib.PacketManager.packets import FSNETCMD_AIRPLANESTATE

# Decode received packet
packet = FSNETCMD_AIRPLANESTATE(data, should_decode=True)
print(packet.position)  # Access decoded fields

# Encode new packet
buffer = FSNETCMD_AIRPLANESTATE.encode(
    remote_time=0.0,
    player_id=1,
    packet_version=5,
    position=[0, 0, 0],
    # ... other fields
    with_size=True  # Include size header
)

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Usage in Proxy

In proxy.py, packets are intercepted and processed: 
# Identify packet type
packet_type = PacketManager().get_packet_type(packet)

# Decode based on type
if packet_type == "FSNETCMD_LOGON":
    decode = FSNETCMD_LOGON(packet)
    player.login(decode)
elif packet_type == "FSNETCMD_AIRPLANESTATE":
    decode = FSNETCMD_AIRPLANESTATE(packet)
    player.aircraft.add_state(decode)
elif packet_type == "FSNETCMD_TEXTMESSAGE":
    msg = FSNETCMD_TEXTMESSAGE(packet)
    # Process chat message

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Packet Modification

Packets can be modified before forwarding: 
# Stop aircraft from firing
if packet_type == "FSNETCMD_AIRPLANESTATE":
    modified_packet = FSNETCMD_AIRPLANESTATE(data).stop_firing()
    writer.write(modified_packet)

# Add smoke effect
if packet_type == "FSNETCMD_AIRPLANESTATE":
    smoke_packet = FSNETCMD_AIRPLANESTATE(data).smoke()
    writer.write(smoke_packet)

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Creating New Packets

You can create packets to send to clients or servers: 
from lib.PacketManager.packets import FSNETCMD_TEXTMESSAGE, FSNETCMD_AIRCMD

# Send chat message
message = FSNETCMD_TEXTMESSAGE.encode("Welcome to the server!", with_size=True)
message_to_client.append(message)

# Control aircraft
afterburer_on = FSNETCMD_AIRCMD.set_afterburner(aircraft_id, True, with_size=True)
message_to_client.append(afterburner_on)

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Best Practices

  1. Always use with_size=True when sending packets over the network
  2. Check packet length before decoding to avoid errors
  3. Use should_decode=False if you only need to forward the packet
  4. Handle packet versions for AIRPLANESTATE (versions 0-5 have different structures)
  5. Validate packet data before processing to prevent crashes

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