Simon Karman

Software Engineer and Game Developer

Karman Multiplayer Library

A C# library that provides networking logic for multiplayer games

Published on 2020-10-24

Created by Simon Karman

Karman Multiplayer Library

A C# library that provides networking logic for multiplayer games.


The goal of this project is to make it easy to create multiplayer games in C#. It can be used in any frameworks or game engines you like, however it was written and tested in the Unity3D game engine.

The project provides a small layer on top of the TCP networking protocol that makes it easy to synchronise game state across multiple game instances by sending data in pre-defined packets from and to servers and clients.

Current limitations and/or drawbacks:

  • Currently under heavy development so the api might receive significant changes up until version 1.0.0 is released.
  • Additional work is required to get physics simulations up and running since the library doesn't handle latency for this.
  • UDP protocol is not (yet) supported. Once added it will provide a protocol with lower latency but without guarenteed package deliveree.
  • The 'oracle and replicator' pattern has not yet been implemented. It will provide an easy way to setup different entity types to be synched across the server and clients
  • ... and more

A roadmap for the library can be found on this trello board.

Getting Started

To get started, either directly copy the source code of this library into your project or add the compiled dll(s) as a dependency to your project. The easiest setup to get started looks like this:

// Define your game id
static readonly Guid GAME_ID = Guid.Parse("<insert your uuid here>");

// Starting a server on port 14641
KarmanServer server = new KarmanServer(GAME_ID);

// Connect to the server on the localmachine
Guid clientId = Guid.NewGuid();
Guid clientSecret = Guid.NewGuid();
KarmanClient client = new KarmanClient(clientId, GAME_ID, clientSecret);
client.Start("localhost", 14641);

// Receiving packets on the server and client with a callback
server.OnClientPacketReceived(Guid clientId, Packet packet);
client.OnPacketReceived(Packet packet);

// Send a packet from the server to a client or broadcast a packet to all connected clients

// Send a packet from the client to the server

Note: The library is currently under heavy development so the api might receive significant changes up until version 1.0.0 is released. Backwards compatibility is not guarenteed up until that point.

Development Guide

The development guide explains how the karman multiplayer library can be used. First the tcp protocol and bytes arrays are explained. Then the packets that the library uses are explained. Then the KarmanServer is discussed in depth. After that the KarmanClient is discussed. And lastly the Oracle and Replicator pattern is explained.

Byte arrays

TODO: More information about byte arrays and TCP protocol coming soon.

Reference Article:


TODO: More information about packets and packet builder coming soon.

Reference Articles:


Setting up a server is as easy as creating an instance of the KarmanServer class and then calling the Start method on it. To create the instance you have to provide a GAME_ID for you server. This game id is unique for you project, and identifies the game that this server is running. After creating the KarmanServer instance you can start the server at any time using the Start(port) method by providing the port on which the server should listen for incoming connections.

static readonly Guid GAME_ID = Guid.Parse("<insert uuid here>");
KarmanServer server = new KarmanServer(GAME_ID);

int serverPort = 14641;

Ensure that you setup your port forwarding and dns configuration appropiatly to ensure that your clients can reach your server.

Everytime something of interests happens in the server a event callback is invoked. The event callbacks can be used to execute logic when the server starts or shutsdown, clients join or leave the game, or packets from clients are received. All callbacks are executed on the same thread as was used to run the server start command. The following events exists and can be subscribed to.

server.OnRunningCallback += () => {}; // Invoked when the server has start up successfully and is now running
server.OnShutdownCallback += () => {}; // Invoked when the server has shutdown
server.OnClientJoinedCallback += (Guid clientId) => {}; // Invoked when a client joins the server
server.OnClientConnectedCallback += (Guid clientId) => {}; // Invoked when a client connects to the server
server.OnClientDisconnectedCallback += (Guid clientId) => {}; // Invoked when a client disconnects from the server
server.OnClientLeftCallback += (Guid clientId) => {}; // Invoked when a client leaves the server
server.OnClientPackedReceivedCallback += (Guid clientId, Packet packet) => {}; // Invoked for each packet received from a client

A client can joined and leave the server. A client uses a connection to connect to the server. During the period that a client is known at the server (from join to leave) it could potentially disconnect and connect multiple times. For example due to a bad networking connection. A leave will only trigger if a client explicitly expresses to leave the server by sending a LeavePacket, all details about the client be removed from the server. As a user of the karman multiplayer library you don't have to worry about connections, you're dealing with clients. However it can be interesting to know when a client has dropped its connection and when it reconnects. For example to show a message to the other players that a client is currently not connected. For this reason the OnClientConnected and OnClientDisconnected callbacks are exposed.

After your server is up and running you can send packets to connected clients. You can send a packet to an individual client or broadcast a packet to all clients that are connected.

MyCoolPacket packet = new MyCoolPacket("awesome data!");
server.Send(clientId, packet); // Send a packet to an individual client
server.Broadcast(packet); // Send a packet to all connected clients
server.Broadcast(packet, skipClientId); // Send a packet to all connected clients except one


TODO: More information about clients (incl. secrets, reconnection attempts, callbacks) coming soon.

If a client drops its connection it will attempt to reconnect using a new connection. As long as the client uses the same clientId and clientSecret it will be able to connect as a client already known on the server.

Oracle and replicator pattern

TODO: More information about oracle and replicator pattern coming soon.


A few different example implementations using the karman multiplayer library already exist.

  • Flow - You can find one example implementation in this repository. It is called 'Flow'. It is a simple Unity demo showing of the capabilities of the library and it is also used during development of the library to test new functionality.

  • B11 Party Game - A game that uses the karman multiplayer library. B11 Party Game is a multiplayer game based on Mario Party with minigames themed around the 11th board of study association Sticky. It uses version 0.1.0 of this libary and was used to prove the usefullness, stability, and speed of development of this library.

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