Multiplayer Basics

Server (peer 1)
    ├── Owns game state by default
    ├── Spawns and validates objects
    └── Routes RPCs
Client (peer 2, 3, …)
    ├── Sends input to server via RPC
    └── Receives state updates from server

# chat.gd
extends Node

# Any peer can call; server validates then broadcasts to all peers.
@rpc("any_peer", "reliable")
func send_chat_message(text: String) -> void:
	if not multiplayer.is_server():
		return
	var sender_id := multiplayer.get_remote_sender_id()
	_broadcast_chat.rpc(sender_id, text)


# Only the authority (server) can call this; runs on every peer.
@rpc("authority", "reliable", "call_local")
func _broadcast_chat(sender_id: int, text: String) -> void:
	print("[%d]: %s" % [sender_id, text])


# Client → server: request to spawn an object.
@rpc("any_peer", "reliable")
func request_spawn(scene_path: String, spawn_position: Vector2) -> void:
	if not multiplayer.is_server():
		return
	# Server validates and performs the actual spawn.
	var scene: PackedScene = load(scene_path)
	if scene == null:
		return
	var instance := scene.instantiate()
	instance.global_position = spawn_position
	get_tree().root.add_child(instance)


# High-frequency sync; unreliable_ordered + a channel keeps this off other RPC traffic.
@rpc("authority", "unreliable_ordered", "call_local", 1)
func sync_position(pos: Vector2) -> void:
	global_position = pos

# Send to everyone (including self if call_local is set):
send_chat_message.rpc("Hello!")

# Send to one specific peer:
send_chat_message.rpc_id(target_peer_id, "Hello!")

// Chat.cs
using Godot;

public partial class Chat : Node
{
    // Any peer can call; executes on the server only.
    [Rpc(MultiplayerApi.RpcMode.AnyPeer, TransferMode = MultiplayerPeer.TransferModeEnum.Reliable)]
    public void SendChatMessage(string text)
    {
        if (!Multiplayer.IsServer()) return;
        int senderId = Multiplayer.GetRemoteSenderId();
        Rpc(MethodName.BroadcastChat, senderId, text);
    }

    // Authority only; runs on every peer including the caller.
    [Rpc(MultiplayerApi.RpcMode.Authority,
         CallLocal = true,
         TransferMode = MultiplayerPeer.TransferModeEnum.Reliable)]
    private void BroadcastChat(int senderId, string text)
        => GD.Print($"[{senderId}]: {text}");

    // Client → server: request a spawn.
    [Rpc(MultiplayerApi.RpcMode.AnyPeer, TransferMode = MultiplayerPeer.TransferModeEnum.Reliable)]
    public void RequestSpawn(string scenePath, Vector2 spawnPosition)
    {
        if (!Multiplayer.IsServer()) return;
        var scene = GD.Load<PackedScene>(scenePath);
        if (scene == null) return;
        var instance = scene.Instantiate<Node2D>();
        instance.GlobalPosition = spawnPosition;
        GetTree().Root.AddChild(instance);
    }

    // High-frequency position sync.
    [Rpc(MultiplayerApi.RpcMode.Authority,
         CallLocal = true,
         TransferMode = MultiplayerPeer.TransferModeEnum.UnreliableOrdered,
         TransferChannel = 1)]
    public void SyncPosition(Vector2 pos)
        => GlobalPosition = pos;
}

// Broadcast to all:
Rpc(MethodName.SendChatMessage, "Hello!");

// Send to one peer:
RpcId(targetPeerId, MethodName.SendChatMessage, "Hello!");

# player.gd
extends CharacterBody2D

func _ready() -> void:
	# multiplayer.get_unique_id() = this peer's ID; server assigns authority during spawn (see Section 6).
	pass


func _physics_process(delta: float) -> void:
	# Guard: authority-only input and movement.
	if not is_multiplayer_authority():
		return

	var direction := Input.get_vector("ui_left", "ui_right", "ui_up", "ui_down")
	velocity = direction * 200.0
	move_and_slide()

	sync_position.rpc(global_position)


@rpc("authority", "unreliable_ordered", "call_local", 1)
func sync_position(pos: Vector2) -> void:
	if not is_multiplayer_authority():
		global_position = pos


func print_authority_info() -> void:
	print("My peer ID : %d" % multiplayer.get_unique_id())
	print("Authority  : %d" % get_multiplayer_authority())
	print("Am I auth? : %s" % str(is_multiplayer_authority()))

// Player.cs
using Godot;

public partial class Player : CharacterBody2D
{
    public override void _PhysicsProcess(double delta)
    {
        // Guard: authority-only input.
        if (!IsMultiplayerAuthority()) return;

        var direction = Input.GetVector("ui_left", "ui_right", "ui_up", "ui_down");
        Velocity = direction * 200f;
        MoveAndSlide();

        Rpc(MethodName.SyncPosition, GlobalPosition);
    }

    [Rpc(MultiplayerApi.RpcMode.Authority,
         CallLocal = true,
         TransferMode = MultiplayerPeer.TransferModeEnum.UnreliableOrdered,
         TransferChannel = 1)]
    private void SyncPosition(Vector2 pos)
    {
        if (!IsMultiplayerAuthority())
            GlobalPosition = pos;
    }
}