Proposal for Built-in Networking Module

[mopioid]

The SDK for Willow games ships with a built-in module, networking, that provides a high-level interface for messaging between copies of mods in an online game session: https://github.com/bl-sdk/willow2-mod-manager/tree/master/src/networking

This module could be adapted for Oak games by replacing each instance of its Willow-specific code with Oak-specific code, as proposed here.

Players

The Oak equivalent of Willow's PlayerReplicationInfo is PlayerState; a PlayerState instance exists for each player, and provides their PlayerID, as well as an Owner property referring to their player controller (host only).

The array of PlayerState instances (and therefore list of players) is referenced at ENGINE.GameViewport.World.GameState.PlayerArray.

The local player's PlayerState is referenced at get_pc().PlayerState

The host's PlayerState is referenced at ENGINE.GameViewport.World.GameState.HostPlayerState.

Whether the local player is currently serving as a client or not can be determined by comparing their PlayerState to that of the host's.

Transmission

Client and server transmission, respectively, can be performed with the following functions:

# /Script/Engine.PlayerController:ClientMessage

remote_pc.ClientMessage(msg, message_type, float(player_id)) # Loss of precision if player_id somehow exceeds platform float mantissa

# /Script/Engine.PlayerController:ServerChangeName

local_pc.ServerChangeName(param_encoded_message) # message type and player_id must be serialized into the payload

An additional message type for transmitting references to replicated Actors, actor_message, could be made possible with another pair of functions:

# /Script/OakGame.OakPlayerController:ClientCreatePlayerAlert

remote_pc.ClientCreatePlayerAlert(
    make_struct("UniqueNetIdRepl"), # Must be empty, or else causes disconnect.
    some_actor,
    make_struct("Vector", X=MAGIC_IDENTIFIER) # A hard-coded value used to distinguish messages belonging to the networking module
)

# /Script/OakGame.OakPlayerController:ServerCreatePlayerAlert

local_pc.ServerCreatePlayerAlert(
    make_struct("UniqueNetIdRepl"), # Must be empty, or else causes disconnect.
    some_actor,
    make_struct("Vector", X=MAGIC_IDENTIFIER, Y=float(player_id)), # Loss of precision if player_id somehow exceeds platform float mantissa
)