Remote Functions and Events

Oct 07 2019, 1:22 PM PST 15 min

Remote Events and Functions are used to let Script|Scripts (on the server) and LocalScript|LocalScripts (on clients) to communicate with each other. There are some actions that only the server can perform, and others that only the client can. In some cases, the server or client will want the other to perform one of these actions. For example, data stores are only accessible on the server, but clients may want to access the information they store. In this case, a RemoteEvent or RemoteFunction can be used to both send a request from the client to the server to get information from a Articles/Data store, and to send a response from the server back to the client.

Difference between Remote Events and Functions

While RemoteEvents and RemoteFunctions are similar in that they allow communication between servers and clients, there are a few differences between them that should be known before deciding which to use.

The first difference is that RemoteFunctions are designed for two way communication, while RemoteEvents are designed for one way. A RemoteFunction sends a request and then waits for a response, while RemoteEvents just send a request.

Another major difference between the two is how they are handled. RemoteEvents use the Roblox event system. This means that any number of scripts can listen for the event to fire, and they can each handle that firing in different ways. RemoteFunctions on the other hand use a callback. For every RemoteFunction, only one callback can be defined on the server and only one for each client.

The last difference is how many different targets remote events and functions can have. For both Remote Events and Functions, a client can contact the server and the server can contact the client. In the case of RemoteEvents, the server can also contact every client at the same time.

While all of the above outlines should be considered when deciding which object to use for a specific communication task, the most important factor usually is whether the communication needs to be one or two way. As outlined above, it is recommended to use RemoteFunctions if the code needs a response, otherwise RemoteEvents should be used.

Using RemoteEvents

Remote Events are designed to provide a one way message between the server and clients. This message can be directed from one client to the server, from the server to a particular client, or from the server to all clients.

In order for both the server and clients to utilize RemoteEvents, the RemoteEvent object itself must be in a place where both can see it. It is recommended to store RemoteEvents in a folder inside of ReplicatedStorage, although in some cases it is appropriate to store events in the Workspace or in Tool|Tools.

Client to Server

In order for a client to send a message to the server, it needs to fire the RemoteEvent with the function RemoteEvent/FireServer.

-- LocalScript

local ReplicatedStorage = game:GetService("ReplicatedStorage")
local createPartEvent = ReplicatedStorage:WaitForChild("CreatePartEvent")

createPartEvent:FireServer()

The server meanwhile needs to connect a function to the RemoteEvent/OnServerEvent of the RemoteEvent.

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-- Script

local ReplicatedStorage = game:GetService("ReplicatedStorage")
local createPartEvent = Instance.new("RemoteEvent", ReplicatedStorage)
createPartEvent.Name = "CreatePartEvent"

local function onCreatePartFired(player)
	print(player.Name, "wants to create a part")
	local newPart = Instance.new("Part")
	newPart.Position = Vector3.new(0, 20, 0)
	newPart.Parent = game.Workspace
end

createPartEvent.OnServerEvent:Connect(onCreatePartFired)

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When a client calls the FireServer function, any functions on the server that are connected to OnServerEvent will fire. Note that this is not immediate - the network connection between the client and server will determine how quickly this happens.

When firing a RemoteEvent from a client to the server, data can be included in the firing. By default, the functions connected to OnServerEvent will be passed the player who fired the event as the first parameter. If any other arguments are provided in the FireServer function, they will also be included in OnServerEvent after the player argument.

-- LocalScript

local ReplicatedStorage = game:GetService("ReplicatedStorage")
local createPartEvent = ReplicatedStorage:WaitForChild("CreatePartEvent")

createPartEvent:FireServer(BrickColor.Green(), Vector3.new(10, 20, 0))

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-- Script

local ReplicatedStorage = game:GetService("ReplicatedStorage")
local createPartEvent = Instance.new("RemoteEvent", ReplicatedStorage)
createPartEvent.Name = "CreatePartEvent"

local function onCreatePartFired(player, color, position)
	print(player.Name, "wants to create a part")
	local newPart = Instance.new("Part")
	newPart.BrickColor = color
	newPart.Position = position
	newPart.Parent = game.Workspace
end

createPartEvent.OnServerEvent:Connect(onCreatePartFired)

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Server to Client

The server can send messages to the client through remote events in two ways: it can send a message to an individual client or it can send a message to every client at the same time.

In order to send a message to a single client, the RemoteEvent/FireClient function should be called from the server.

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-- Script

local Players = game:GetService("Players")

local welcomePlayerEvent = Instance.new("RemoteEvent")
welcomePlayerEvent.Parent = game.ReplicatedStorage
welcomePlayerEvent.Name = "WelcomePlayerEvent"

local function onPlayerAdded(player)
	welcomePlayerEvent:FireClient(player)
end

Players.PlayerAdded:Connect(onPlayerAdded)

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To listen for the message on the client, a LocalScript needs to connect a function to the RemoteEvent/OnClientEvent event of the RemoteEvent.

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--LocalScript

local Players = game:GetService("Players")
local ReplicatedStorage = game:GetService("ReplicatedStorage")

local player = Players.LocalPlayer
local welcomePlayerEvent = ReplicatedStorage:WaitForChild("WelcomePlayerEvent")
local playerGui = player:WaitForChild("PlayerGui")

local welcomeScreen = Instance.new("ScreenGui")
welcomeScreen.Parent = playerGui
local welcomeMessage = Instance.new("TextLabel")
welcomeMessage.Size = UDim2.new(0, 200, 0, 50)
welcomeMessage.Parent = welcomeScreen
welcomeMessage.Visible = false
welcomeMessage.Text = "Welcome to the game!"

local function onWelcomePlayerFired()
	welcomeMessage.Visible = true
	wait(3)
	welcomeMessage.Visible = false
end

welcomePlayerEvent.OnClientEvent:Connect(onWelcomePlayerFired)

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To fire a message to all clients, the server needs to call RemoteEvent/FireAllClients. Note that in this case, a player does not have to be passed into the arguments (as the function fires the remote event on all of the connected clients).

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local Players = game:GetService("Players")

local newPlayerEvent = Instance.new("RemoteEvent")
newPlayerEvent.Parent = game.ReplicatedStorage
newPlayerEvent.Name = "NewPlayer"

local function onPlayerAdded(player)
	newPlayerEvent:FireAllClients()
end

Players.PlayerAdded:Connect(onPlayerAdded)

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To listen for this event, each client needs to connect a function to OnClientEvent.

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local Players = game:GetService("Players")
local ReplicatedStorage = game:GetService("ReplicatedStorage")

local player = Players.LocalPlayer
local newPlayerEvent = ReplicatedStorage:WaitForChild("NewPlayerEvent")
local playerGui = player:WaitForChild("PlayerGui")

local welcomeScreen = Instance.new("ScreenGui")
welcomeScreen.Parent = playerGui
local newPlayerMessage = Instance.new("TextLabel")
newPlayerMessage.Size = UDim2.new(0, 200, 0, 50)
newPlayerMessage.Parent = welcomeScreen
newPlayerMessage.Visible = false
newPlayerMessage.Text = "A new player has joined the game!"

local function onNewPlayerFired()
	newPlayerMessage.Visible = true
	wait(3)
	newPlayerMessage.Visible = false
end

newPlayerEvent.OnClientEvent:Connect(onNewPlayerFired)

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Data can be passed from server to client through remote events in the same way data is passed from client to server. Any extra information can be passed in as arguments to the FireClient and FireAllClients functions. Note that the FireClient function still needs to pass the player to send the message to as the first argument.

Using RemoteFunctions

Remote Functions are designed to provide a two way message between the server and clients. The message can originate on either the server or a client. Note that unlike a Remote Event, Remote Functions can only facilitate communication with one client at a time (there is no InvokeAll method).

In order for both the server and clients to utilize RemoteFunctions, the RemoteFunction object itself must be in a place where both can see it. It is recommended to store RemoteFunction in a folder inside of ReplicatedStorage, although in some cases it is appropriate to store events in the Workspace or in Tools.

Sending a message with a Remote Function is called “invoking”, and either the server or client can invoke the other. The other machine will need to have a function set for the onInvoke callback of the remote function. Note that the environment that defines the callback is the one that is invoked. For example, if a callback is defined on the server (with RemoteFunction/OnServerInvoke), the client will need to invoke the server to make that callback execute (with RemoteFunction/InvokeServer).

It is important to note that invoking remote functions, either on the server or client, will yield until the remote function’s callback finishes executing or returns. This means that while code in other threads on the machine that invoked the function can run, code in the same thread as the invoke will not execute until the invocation is done.

Warning: Invocations (both InvokeServer and InvokeClient will yield until to corresponding callback has been defined. If the callback is never set, then the Script or LocalScript that invoked will not resume execution.

Client to Server

A Remote Function is invoked on the client when that client wants the server to do something, and then wants to be notified that the server is done. This is commonly done to fetch information from the server and then do something with that information, but it can be used in a few other applications.

When a client wants to use a remote function, it will invoke the server with the RemoteFunction/InvokeServer function.

-- LocalScript

local ReplicatedStorage = game:GetService("ReplicatedStorage")

local createPartRequest = ReplicatedStorage:WaitForChild("CreatePartRequest")

local newPart = createPartRequest:InvokeServer()
print("The server created this part for me:", newPart)

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-- Server

local ReplicatedStorage = game:GetService("ReplicatedStorage")

local createPartRequest = Instance.new("RemoteFunction")
createPartRequest.Parent = ReplicatedStorage
createPartRequest.Name = "CreatePartRequest"

local function onCreatePartRequested(player)
	print(player.Name, "wants to create a new part")
	local newPart = Instance.new("Part")
	newPart.Parent = game.Workspace
	return newPart
end

createPartRequest.OnServerInvoke = onCreatePartRequested

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Note that binding a function to RemoteFunction/OnServerInvoke is done with the assignment operator =, and not with an event. That is because OnServerInvoke is a callback and expects a function to be assigned to it. When the RemoteFunction is invoked, it will execute the function that was assigned to the onInvoke function.

Only one function can be assigned to OnServerInvoke at a time. If multiple functions are assigned, only the last function to be assigned will be used.

Server to Client

Clients invoking the server is often used because the server either has access to information the client does not, or the client is requesting a game action that only the server can perform. Going the other way (the server invoking a client) is not done often in practice. Clients typically do not have information the server doesn’t have and the actions that only a client can take (displaying a GUI for instance), often do not require a callback. That said, the server invoking clients is still an action that the Roblox engine will support and may be useful in niche situations.

Invoking a client is very similar to invoking the server, except in this case the invocation has to pass the player to invoke. The function used to do this is RemoteFunction/InvokeClient.

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-- Server

local Players = game:GetService("Players")
local ReplicatedStorage = game:GetService("ReplicatedStorage")

local createPopupRequest = Instance.new("RemoteFunction")
createPopupRequest.Name = "CreatePopupRequest"
createPopupRequest.Parent = ReplicatedStorage
Players.CharacterAutoLoads = false

local function onPlayerAdded(player)
	createPopupRequest:InvokeClient(player)
	player:LoadCharacter()
end

Players.PlayerAdded:Connect(onPlayerAdded)

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Note that unlike invoking the server, invoking the client with InvokeClient requires that the client be specified by passing in the player.

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-- LocalScript

local Players = game:GetService("Players")
local ReplicatedStorage = game:GetService("ReplicatedStorage")

local player = Players.LocalPlayer
local playerGui = player:WaitForChild("PlayerGui")
local createPopupRequest = ReplicatedStorage:WaitForChild("CreatePopupRequest")

local function onCreatePopupRequested()
	local screen = Instance.new("ScreenGui")
	screen.Parent = playerGui
	local closeButton = Instance.new("TextButton")
	closeButton.Text = "Welcome to the game! Click me to play!"
	closeButton.Size = UDim2.new(0, 300, 0, 50)
	closeButton.Parent = screen
	
	closeButton.MouseButton1Click:Wait()
	closeButton.Visible = false
end

createPopupRequest.OnClientInvoke = onCreatePopupRequested

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When handling the invocation from the client note that nothing has to be passed in by default (unlike invoking the server where the player is passed in).

Warning: If a client disconnects or leaves the game while it is being invoked from the server, the InvokeClient function will error. It is therefore recommended to wrap this function in a pcall so it does stop the execution of other code.

Client to Client Communication

Sometimes a game will need to send information from one client to another. Roblox does not support direct client to client contact, so any communication must first go through the server. This is typically done using remote events (although functions could be used if desired). First, the sending client would call FireServer. On the server, the function connected to OnServerEvent would hear this firing, and itself would then call FireClient.

In this example, each player has a TextBox where they can type another player’s name and a button to click. When they click the button, it sends a message to the other player.

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-- LocalScript

local ReplicatedStorage = game:GetService("ReplicatedStorage")
local Players = game:GetService("Players")

local player = Players.LocalPlayer
local playerGui = player:WaitForChild("PlayerGui")
local messageScreen = playerGui:WaitForChild("MessageScreen")
local recipientInput = messageScreen:WaitForChild("RecipientInput")
local sendButton = messageScreen:WaitForChild("SendButton")
local messageLabel = messageScreen:WaitForChild("MessageLabel")

local sendMessageEvent = ReplicatedStorage:WaitForChild("SendMessageEvent")

local function onSendButtonClicked()
	local recipientName = recipientInput.Text
	local recipient = Players:FindFirstChild(recipientName)
	if recipient then
		sendMessageEvent:FireServer(recipient)
	end
end

local function onMessageReceived(sender)
	messageLabel.Text = sender.Name .. " says hello!"
	messageLabel.Visible = true
	wait(3)
	messageLabel.Visible = false
end

sendButton.MouseButton1Click:Connect(onSendButtonClicked)
sendMessageEvent.OnClientEvent:Connect(onMessageReceived)

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This local script handles both sending messages and receiving them from the server, although two scripts could also have been used (one for sending and one for receiving).

On the server:

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-- Script

local ReplicatedStorage = game:GetService("ReplicatedStorage")
local Players = game:GetService("Players")

local sendMessageEvent = Instance.new("RemoteEvent")
sendMessageEvent.Name = "SendMessageEvent"
sendMessageEvent.Parent = ReplicatedStorage

local function onSendMessageFired(sender, recipient)
	if recipient:IsA("Player") and recipient.Parent == Players then
		sendMessageEvent:FireClient(recipient, sender)
	end
end

sendMessageEvent.OnServerEvent:Connect(onSendMessageFired)

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The server simply receives the message, checks that the input is valid, and then fires an event at the recipient player.

Notice that in the above example the server checked if the information it got from the event was valid before continuing. This practice is recommended as it helps catch errors and overall makes code more robust.

Limitations

Bandwidth

For most devices and connections, a Roblox server can only send and receive about 50 KB/sec of data to each client, not including physics updates. That said, it is highly recommended to maintain a lower value during normal gameplay as sudden spikes in data transfer can cause lag and an overall subpar user experience.

Every time a remote event is fired or a remote function invoked, a packet of data is sent over the network between the server and client. This packet is counted towards the 50 KB/sec limit. If too many packets are sent (remote event or function used often), or too much data is sent per packet (lots of large arguments to the event or function), the latency of the connected clients can be adversely affected.

Parameters

Any type of Roblox object (Enumeration value, instance, userdata) can be passed as a parameter in a RemoteEvent firing or RemoteFunction invocation. Lua types (such as numbers, strings, boolean) can also be passed, although there there are some limitations on how data can be passed.

Mixed Tables

If a table is passed with mixed indices (some values indexed by number, others by string), then only the data indexed by number will be passed. If the table does not have mixed indices, then no data will be lost.

For example, consider the following code:

local data = {}
data["one"] = "Pear"
data["two"] = "Orange"
data[1] = "Apple"
data[2] = "Banana"

remoteEvent:FireServer(data)

The table that is being passed has mixed indices, some numbers and some strings. When the server receieves this table, it will only see the indexes 1 and 2 (containing “Apple” and “Banana”). The other data will be lost in the transfer.

Note that sub tables do not have to be indexed with the same type as their parent. For example, the following table will transfer fine:

local playerData = {}
playerData["Inventory"] = {}
playerData["Inventory"][1] = "Sword"
playerData["Inventory"][2] = "Bow"
playerData["Inventory"][3] = "Rope"
playerData["Gold"] = 20
playerData["Experience"] = 500

remoteEvent:FireServer(playerData)

As long as each individual subtable is indexed with the same type, all of the data will be preserved.

Metatables

If a table has a metatable, all of the metatable information will be lost in the transfer.

For example, consider the following code:

local Car = {}
Car.NumWheels = 4
Car.__index = Car

local truck = {}
truck.Name = "MyTruck"
setmetatable(truck, Car)

remoteEvent:FireServer(truck)

When the server gets the event, the truck table that was passed will only have the Name element, not the NumWheels as that was part of the Car metatable.

Non-replicated Instances

If the value being sent is only visible to the sender then nil will be passed instead of the value. For example, if a server tries to pass a descendant of ServerStorage, the client listening to the event will see nil passed as the value.

local part = Instance.new("Part", ServerStorage)
remoteEvent:FireClient(player, part)

In the above code, when the client receives the event it will only see nil passed in and will not have reference to the part.

Tags:

datastore
client-server