gpgnet.md

GPGnet Protocol

Overview

The GPGnet protocol is used to instruct the Forged Alliance.exe binary with information about what lobby to open, which players to connect, game options, game results and potentially much more.

GPGnet is used across the apps from game to lobby server:

[FA.exe] <--> [faf-pioneer] <--> [faf-client] <--> [faf-lobby-server]

The correct order of sending is crucial in order to get players into a lobby and connected to each other.

But the GPGnet protocol can also be extended by SIM mods in the game since the message are sent in Lua code. However: A running game can never receive or process GPGnet messages, once start, it is sending only.

Binary representation

The game sends and receives GPGnet messages in a custom representation. The encoding is always Little Endian (but affects only uint32 fragments).

Here is the specification in Backus-Naur-Form:

<message>              ::= <command> <size> <chunks>
<command>              ::= <string>
<size>                 ::= uint32
<string>               ::= <size> []byte
<chunks>               ::= <chunk> | <chunk> <chunks>
<chunk>                ::= <type_int> uint32 | <type_string> <string> | <type_followup_string> <string>
<type_int>             ::= byte = 0x00
<type_string>          ::= byte = 0x01
<type_followup_string> ::= byte = 0x02

Known messages types

command	sent by	args	index	type	content
GameState	game	1	0	str	state: [Idle,Lobby, ???]
CreateLobby	client	5	0	int	lobby init mode 0 = Normal / Custom 1 = Auto
			1	int	lobby port
			2	str	local player name
			3	int	local player id
			4	int	unknown
HostGame	client	1	0	str	map name
JoinGame	client	3	0	str	net address
			1	str	remote player name
			2	int	remote player id
ConnectToPeer	client	3	0	str	net address
			1	str	remote player name
			2	int	remote player id
DisconnectFromPeer	client	1	0	int	remote player id
GameOptions	both?	?	?	?	?
GameEndedMessage	game	0

Message flow for opening a lobby

t.b.d.