Building a Simple Chat Server (WebSockets + Rooms)

Chat Server Overview

This lesson explains the main concept clearly with beginner-friendly examples and background so you can learn why the code works.

We'll combine what we learned: WebSockets, goroutine pools, sync.Mutex, and JSON.

type client struct { conn *websocket.Conn; send chan []byte }

type hub struct {
    rooms map[string]map[*client]bool
    register   chan subscription
    unregister chan subscription
    broadcast  chan message
}

type subscription struct { room string; c *client }

type message struct { room string; data []byte }

Hub run loop

func (h *hub) run() {
    for {
        select {
        case sub := <-h.register:
            if h.rooms[sub.room] == nil { h.rooms[sub.room] = make(map[*client]bool) }
            h.rooms[sub.room][sub.c] = true
        case sub := <-h.unregister:
            if clients, ok := h.rooms[sub.room]; ok { delete(clients, sub.c) }
        case msg := <-h.broadcast:
            for c := range h.rooms[msg.room] { c.send <- msg.data }
        }
    }
}

Client read/write loops

func (c *client) readPump(h *hub, room string) {
    defer func() { h.unregister <- subscription{room, c}; c.conn.Close() }()
    for {
        _, data, err := c.conn.ReadMessage()
        if err != nil { break }
        h.broadcast <- message{room, data}
    }
}

func (c *client) writePump() {
    defer c.conn.Close()
    for msg := range c.send { c.conn.WriteMessage(websocket.TextMessage, msg) }
}

HTTP handler to upgrade

func serveWs(h *hub, w http.ResponseWriter, r *http.Request) {
    room := r.URL.Query().Get("room")
    conn, err := upgrader.Upgrade(w, r, nil)
    if err != nil { return }
    client := &client{conn: conn, send: make(chan []byte, 256)}
    h.register <- subscription{room, client}
    go client.writePump()
    client.readPump(h, room)
}

Deploy with Docker (see lesson‑47) and test with a simple HTML page.