Network Signals

Network Signals are used to communicate between the client and server. They are a critical piece of building a multiplayer game.

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Overview

Imagine a scenario where a player would like to use a health potion. We first need to tell the server that a player would like to use a potion and have it apply the potion's effects.

PotionManager.ts

export default class PotionManager extends AirshipSingleton {
    // Creating a NetworkSignal
    private usePotion = new NetworkSignal<{ potion: string }>("UsePotion");

    public override Start(): void {
        if (Game.IsClient()) {
            // Tell the server that the local player is trying to use a potion
            this.usePotion.client.FireServer({ potion: "health" });
        }

        if (Game.IsServer()) {
            // Listen for a player use potion request
            this.usePotion.server.OnClientEvent((player, event) => {
                const hasPotion = DoesPlayerHavePotion(player, event.potion);
                if (!hasPotion) return;
                // Apply the potion's effect
                player.character?.SetHealth(100);
            });
        }
    }
}

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Network Signals

Example Use Cases

Client -> Server

Example	Explanation
Ability Use	Notifying the server when a player uses a special ability
Trade Request	Letting the server know two players would like to trade
Item Drop	Telling the server a player has dropped an item

Server -> Client

Example	Explanation
Weather Change	Informing clients of a weather change to keep them visually synchronized
Leaderboard Updates	Letting clients know the latest leaderboard standings
Status Effects	Communicating that a client has had a status effect applied to their character

Creating a Network Signal

Network Signals can be created inside of any script. NetworkSignal takes a single generic parameter that is the type of data passed through the signal.

Shared

const usePotion = new NetworkSignal<{ potion: string }>("UsePotion");

The NetworkSignal constructor accepts a single string parameter that uniquely identifies the signal. Providing a string that is already in use will raise an error when entering play mode.

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Client -> Server

Network Signal: Client -> Server

Firing the usePotion Network Signal on the client

Client

usePotion.client.FireServer({ potion: "health" });

Listening for usePotion Network Signals on the server

Server

usePotion.server.OnClientEvent((player, event) => {
    print(`${player.username} is using potion: ${event.potion}`);
});

The first argument passed to OnClientEvent is always the Player who fired the Network Signal.

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Server -> Client

Network Signal: Server -> Client(s)

Once the server has applied the potion, we want to tell every player about it so they can play particle effects, sounds, update UI, etc.

Server to client Network Signals can be sent to any number of players

Shared

const potionUsed 
    = new NetworkSignal<{ userId: string; potion: string }>("PotionUsed");

Telling all players a potion has been consumed

Server

potionUsed.server.FireAllClients({ userId: "1", potion: "health" });

Listening for potionUsed Network Signals on the client

Client

potionUsed.client.OnServerEvent((event) => {
    print(`User ${event.userId} has used potion: ${event.potion}`);
});

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Data Limitations

Primitive data types and their composite forms (arrays, objects) can be sent over the network when using NetworkSignals and NetworkFunctions. The following Unity types are also supported

• Vector3

• Vector2

• Quaternion

• Color

A common requirement is sending Characters and Players over the network. Send Player and Character ids and utilize the Player and Character APIs to fetch their respective objects. This ensures that only permitted data types are sent over the network, while the actual player and character objects are retrieved locally.

Caching

If a network signal receives an event, but does not have any existing connection handlers, the event will be cached until the first connection is created. At this point, all events will be passed along to the connection handler.

This is typically useful when the server sends a client a network signal event right after the client has joined, but before the client has connected to the signal. Thus, the event is not missed by the client, as it is successfully handed to the first connection to the signal on the client.

The cache is limited in size (currently hard-coded to 10,000), and will throw errors if exceeded.