How to implement a Go server for real-time multiplayer games?

Implementing a real-time multiplayer game server with Go requires a good grasp of Go programming, concurrency, and networking. Here is a step-by-step guide to show you how you can do it. This guide assumes you're familiar with the basics of Go.

When creating a multiplayer server, we will take advantage of Go's powerful concurrency features, particularly Goroutines and Channels. We will also use the Gorilla WebSocket package, which is a Go implementation of the WebSocket protocol.

Step 0 - Install Dependencies

First, we need to install Gorilla WebSocket. Following command installs the library.

go get github.com/gorilla/websocket



Step 1 - Set Up the Server

We start by creating a simple HTML server. It serves index.html to the client and creates a WebSocket endpoint /ws.

package main

import (
  "net/http"
  "github.com/gorilla/websocket"
)

var upgrader = websocket.Upgrader{
  ReadBufferSize: 1024,
  WriteBufferSize: 1024,
}

func main() {
  // Serve index.html
  http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
     http.ServeFile(w, r, "index.html")
  })

  // Handle WebSocket requests
  http.HandleFunc("/ws", handleWebSocket)

  // Start the server
  err := http.ListenAndServe(":8080", nil)
  if err != nil {
     panic("Error: " + err.Error())
  }
}



Step 2 - Handle WebSocket Connections

When a client connects to the /ws endpoint, we upgrade the connection to WebSocket and then spawn a new Goroutine to handle communication with the client. Messages sent from a client are received in a continuous loop and broadcasted to all other connected clients.

func handleWebSocket(w http.ResponseWriter, r *http.Request) {
  ws, err := upgrader.Upgrade(w, r, nil)
  if err != nil {
     panic("WebSocket upgrade failed: " + err.Error())
  }
 
  // Create a client object
  client := &Client{socket: ws, send: make(chan []byte, 1024)}

  // Register the new client
  register <- client

  go client.write()
  go client.read()
}

type Client struct {
  socket *websocket.Conn
  send   chan []byte
}

func (c *Client) read() {
  defer func() {
     unregister <- c
     _ = c.socket.Close()
  }()

  for {
     _, message, err := c.socket.ReadMessage()
     if err != nil {
        break
     }
     broadcast <- message
  }
}

func (c *Client) write() {
  defer func() {
     _ = c.socket.Close()
  }()

  for {
     select {
     case message, ok := <- c.send:
        if !ok {
           _ = c.socket.WriteMessage(websocket.CloseMessage, []byte{})
           return
        }

        _ = c.socket.WriteMessage(websocket.TextMessage, message)
     }
  }
}

var (
  clients    = make(map[*Client]bool)
  broadcast  = make(chan []byte)
  register   = make(chan *Client)
  unregister = make(chan *Client)
)



Step 3 - Handle Client Registration, Unregistration and Broadcasting Messages

Finally, we handle client registrations, unregistrations, and broadcasting messages. The handleMessages function runs in the main Goroutine and all the communication takes place through channels.

func main() {
  // ...

  go handleMessages()

  // Start the server
  err := http.ListenAndServe(":8080", nil)
  // ...
}

func handleMessages() {
  for {
     select {
     case client := <-register:
        clients[client] = true
     
     case client := <-unregister:
        if _, ok := clients[client]; ok {
           delete(clients, client)
           close(client.send)
        }

     case message := <-broadcast:
        for client := range clients {
           select {
           case client.send <- message:
           default:
              delete(clients, client)
              close(client.send)
           }
        }
     }
  }
}



That's it! You've developed a simple real-time multiplayer server in Go. This server accepts WebSocket connections, broadcasts incoming messages to all connected clients, and handles new client registrations as well as client unregistrations. Note that there's a lot more to implement in a real-world application, but this guide will help you get started with real-time multiplayer games in Go.