UDPServer in Godot – Complete Guide

Welcome to our in-depth look at the UDPServer class in Godot 4, a powerful yet overlooked aspect of networking in game development. This server-side communication tool can help you create responsive and dynamic online interactions, from basic multiplayer setups to complex networked systems. Through this tutorial, you’ll discover what UDPServer is, its vital role in game networking, and why it’s an essential skill for all aspiring Godot developers. By the end, you’ll not only understand the mechanics behind a UDP server but also how to implement one in your gaming projects.

Let’s dive into the realm of network programming and learn how to keep your multiplayer games in sync with the help of UDPServer!

What is UDPServer?

UDP stands for User Datagram Protocol, a communication protocol used across the internet for time-sensitive transmissions such as video playback or game data. Unlike TCP, it doesn’t guarantee the delivery of packets, making it faster under certain conditions. Godot 4’s UDPServer is a helper class designed to simplify the creation of a server capable of handling UDP traffic.

What is it for?

This server acts as a central hub, receiving messages from clients (players) and deciding whether to establish ongoing communication with them. It’s particularly useful when you want to create lightweight and flexible interactions between different instances in a multiplayer game, all while keeping the networking code clean and maintainable.

Why should I learn it?

Understanding UDPServer can be a game-changer (pun intended) for your developmental toolkit, particularly if you’re aimed at creating network-based games. Knowing how to handle UDP traffic allows you to:

– Manage high-performance, low-latency multiplayer games
– Create a more direct communication line between clients and servers
– Give you the foundation for more advanced networking concepts

Learning this skill can significantly broaden your capabilities as a Godot developer, allowing you to create more interactive and engaging gaming experiences. Let’s get ready to put this knowledge into action!

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Setting Up the UDPServer

To get started with the UDPServer class in Godot 4, you need to initialize and start the server. This is done by creating a new instance of the UDPServer class, and then calling its `listen` method to have the server start listening for incoming packets.

var udp_server = UDPServer.new()

func _ready():
    var port = 4242
    var result = udp_server.listen(port)

    if result == OK:
        print("Server is listening on port: " + str(port))
        print("Failed to start server on port: " + str(port))

Ensure to check for errors when starting the server, as attempting to listen on a port that is already in use or otherwise unavailable will fail.

Processing Incoming Packets

Once your server is up and running, you’ll need to constantly poll it to check for new packets from clients. This is done in the `_process` function by using the `poll` method. When new data arrives, you’ll use `take_packet` to read it:

func _process(delta):
    udp_server.poll()  # Necessary to process new packets
    while udp_server.is_connection_available():
        var packet_peer = udp_server.take_packet()
        var packet = packet_peer.get_packet()

        # Assuming the packet is a string for this example
        var message = parse_utf8(packet)
        print("Received message: {0}".format(message))
        # Send a response back to the client
        var response = "Message received!"

The code above reads packets from every available connection and prints the message. It then sends a basic response back to the client.

Sending Data to Clients

Communication is a two-way street. Here’s how you can send data from the server to a client using the `put_packet` method:

var client_address = "" # Localhost
var client_port = 1234

func send_message_to_client(message):
    var packet_peer = PacketPeerUDP.new()
    if packet_peer.connect_to_host(client_address, client_port) == OK:
        print("Failed to send the message to the client.")

This function can be called with the message as a parameter whenever you need to send data to the client.

Creating a Basic Client to Communicate with the Server

You’ve set up the server, but for a complete illustration, let’s code a simple client using Godot’s UDPServer class. The client will send a message and then wait for and print the server’s response.

var udp_peer = PacketPeerUDP.new()

func _ready():
    # Connect to the server
    udp_peer.connect_to_host("", 4242)

    # Send a message to the server
    var message = "Hello from the client!"

func _process(delta):
    if udp_peer.get_available_packet_count() > 0:
        var packet = udp_peer.get_packet().get_string_from_utf8()
        print("Response from server: {0}".format(packet))

Your client should repeatedly poll (in the `_process` function) for any responses from the server and handle them accordingly, similar to how the server handles incoming messages.

That’s all for setting up and basic communication between a UDPServer and clients. In the next part, we’ll expand on managing multiple clients and handling more complex data structures. Stay tuned to take your server skills to the next level!Managing multiple clients in a UDPServer is a common requirement for multiplayer games. Here’s how you can maintain a list of connected clients and send messages to each one:

Tracking Connected Clients

A common strategy is to associate each client with a unique identifier, such as their IP address and port. To manage these connections, you might use a dictionary:

var clients = {}  # Dictionary to hold client info

func _process(delta):
    udp_server.poll()  # Process new packets

    while udp_server.is_connection_available():
        var packet_peer = udp_server.take_packet()
        var client_info = packet_peer.get_packet_ip() + ":" + str(packet_peer.get_packet_port())

        # Add client if they're not already in the dictionary
        if not clients.has(client_info):
            clients[client_info] = packet_peer
            print("New client connected: {0}".format(client_info))

In the above code, when a new packet arrives, we check to see if the client has already been added to our list. If not, we add them.

Processing and Responding to Messages from Clients

When we have multiple clients, we’ll want to process each message accordingly and potentially send a response:

func process_packet(packet_peer):
    var data = packet_peer.get_packet()
    # Assuming the data is a string for this example
    var message = parse_utf8(data)

    print("Received message from client: {0}".format(message))

    # Send a response to the client
    var response = "Your message: \"{0}\" has been received".format(message)

The function `process_packet` receives a `PacketPeerUDP` instance, retrieves the message, logs it, and sends a response back.

Handling Disconnects and Timeouts

In real-world scenarios, you also need to handle client disconnects, which could be due to network timeouts or the client closing the connection:

func disconnect_client(client_info):
    print("Client disconnected: {0}".format(client_info))

You would typically call this `disconnect_client` method with the appropriate client info when a timeout or disconnection is detected.

Setting a Heartbeat

To manage timeouts proactively, you might implement a ‘heartbeat’ system where the client sends a message at regular intervals to let the server know it’s still connected:

func _process(delta):
    # ... existing code ...

    for client_info in clients.keys():
        # Check for heartbeat and disconnect if necessary
        if is_client_timeout(client_info):

This for-loop would run in your server’s `_process` method, checking if any clients have timed out and should be disconnected.

Broader Broadcasts

Sometimes, you want to send a message to all connected clients—a ‘broadcast’. Here’s how you might implement that:

func broadcast_message(message):
    var data = message.to_utf8()
    for client_info in clients:
        var packet_peer = clients[client_info]

broadcast_message("Server broadcast: new player has joined!")

The `broadcast_message` function sends a given message to all connected clients.

These code examples and strategies enhance your understanding of managing client connections with UDPServer in Godot 4. With this knowledge, you’re well on your way to building robust, multiplayer networked games. As always, experiment with the code, test different scenarios, and you’ll gain confidence in your network programming skills!We’ve covered the basics of managing connections and communication with the UDPServer class in Godot 4. As you advance in creating more complex multiplayer systems, it becomes essential to perform operations like broadcasting messages to specific groups of clients, efficiently handling large numbers of connections, and gracefully handling packet loss and ordering. Let’s develop our server capabilities with further code examples.

Dividing Clients into Groups

In some games, you might want to send messages only to specific groups of clients, such as teams or players in certain areas. Here’s how you can organize clients into groups and send group-specific messages:

var groups = {"red_team": [], "blue_team": []}

func add_client_to_group(client_info, group_name):
    if groups.has(group_name):
        print("Client added to group: %s" % group_name)
        print("Group does not exist: %s" % group_name)

func send_message_to_group(message, group_name):
    if groups.has(group_name):
        for client_info in groups[group_name]:
            var packet_peer = clients[client_info]

Clients can be added to the desired groups and messages will only be sent to the clients within those groups. This approach helps to control the flow of information in a room or team-based multiplayer game.

Efficiently Handling Many Clients

As your server grows to support more clients, efficiency becomes crucial. The following demonstrates a method for consistently checking and updating the list of connected clients:

const MAX_CLIENTS = 100

func _process(delta):
    udp_server.poll()  # Process new packets
    var current_clients = clients.keys()

    # If we have room for more clients, check for new connections
    if current_clients.size() < MAX_CLIENTS:

    # ... existing code for handling messages...

By including a limit on the maximum number of clients, you can conserve resources and ensure the server remains responsive.

Handling Packet Loss and Ordering

UDP does not guarantee packet delivery or order, so it’s important to implement your own checks if your application needs them. Here’s a simple system for ensuring messages arrive in order:

var next_expected_packet = 0
var pending_packets = {}

func process_packet(packet_peer):
    var packet = packet_peer.get_packet()
    var packet_id = packet.get_32()  # Assuming first 32 bits are the ID
    var message = packet.get_string_from_utf8()  # Rest is the message

    if packet_id == next_expected_packet:
        print("Received expected packet: %s" % message)
        next_expected_packet += 1

        # Process any pending packets that are now in order
    elif packet_id > next_expected_packet:
        print("Packet out of order, buffering: %s" % message)
        pending_packets[packet_id] = message

func check_pending_packets():
    while pending_packets.has(next_expected_packet):
        print("Processing buffered packet: %s" % pending_packets[next_expected_packet])
        next_expected_packet += 1

This system keeps track of what the next expected packet is and stores out-of-order packets until they can be processed.

Creating More Complex Data Structures for Packets

In most cases, you’ll want to send more complex data than a simple message string. For instance, you could create a game state structure that’s serialized and sent to each client:

func serialize_game_state(game_state):
    var buffer = PoolByteArray()

    # Example of game state components
    return buffer

func deserialize_game_state(packet):
    var game_state_strings = parse_utf8(packet).split(",")

    var game_state = {
        "player_positions": game_state_strings[0],
        "enemy_positions": game_state_strings[1],
        "score": int(game_state_strings[2])
    return game_state

This code shows how you can serialize a game state into a byte array and deserialize it on the other end for consistent game world updates.

With these strategies, you’re furthering your skills for managing a high-performance UDP server in Godot 4. Remember, performance tuning and network optimization are ongoing processes—you’ll need to adjust your strategies based on the specific demands of your game and feedback from real-world testing. Keep refining, testing, and above all, keep coding!

Continuing Your Game Development Journey

Congratulations on making it this far with your integration of the UDPServer class into your Godot 4 projects! Your commitment to learning is what will propel you forward in the ever-evolving world of game development. But don’t stop here; there’s an entire universe of game-making knowledge waiting for you to conquer it. To keep expanding your Godot expertise and to delve deeper into all that this incredible engine has to offer, consider exploring our comprehensive Godot Game Development Mini-Degree. This collection of courses is meticulously crafted to guide you through the ins and outs of creating cross-platform games, providing a strong foundation that you can build upon no matter your level of expertise.

Should your thirst for knowledge go beyond the contents of the Mini-Degree, our broad catalog of Godot courses is perfect for lifelong learners like you, eager to master new concepts and techniques in 2D, 3D, and the heart of game logic. As you level up from beginner to professional, Zenva will be with you every step of the way – our learning paths are open 24/7, allowing you to learn at your own pace and on your own schedule. Embrace the journey ahead, and may your passion for game development drive you to new heights.


Stepping into the realm of networking with Godot’s UDPServer class opens up a world where your games become more than just a solitary experience—they evolve into interactive, social creations that can connect players across the globe. Each line of code you write is a thread in the tapestry of an immersive multiplayer experience. Whether you’re just starting out your journey or looking to polish your skills, always remember that every great game started with a single function, a single class, a single idea.

At Zenva, we’re here to turn those ideas into reality, step by step. Our Godot Game Development Mini-Degree is designed to be your companion on this adventure, providing the resources you need to craft the games you’ve always wanted to play. Let us be the co-op partner in your game development quest—with Zenva, the next level is always within reach.

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