single file broadcast webserver in golang

hub.go

package hub

import (
	"bytes"
	"log"
	"net/http"
	"sync"
	"time"

	"github.com/gorilla/websocket"
)

const (
	// Time allowed to write a message to the peer.
	writeWait = 10 * time.Second

	// Time allowed to read the next pong message from the peer.
	pongWait = 60 * time.Second

	// Send pings to peer with this period. Must be less than pongWait.
	pingPeriod = (pongWait * 9) / 10

	// Maximum message size allowed from peer.
	maxMessageSize = 512
)

var (
	newline = []byte{'\n'}
	space   = []byte{' '}
)

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

// Client is a middleman between the websocket connection and the hub.
type Client struct {
	hub *Hub

	// The websocket connection.
	conn *websocket.Conn

	// Buffered channel of outbound messages.
	send chan []byte
}

// readPump pumps messages from the websocket connection to the hub.
//
// The application runs readPump in a per-connection goroutine. The application
// ensures that there is at most one reader on a connection by executing all
// reads from this goroutine.
func (c *Client) readPump() {
	defer func() {
		c.hub.unregister <- c
		c.conn.Close()
	}()
	c.conn.SetReadLimit(maxMessageSize)
	c.conn.SetReadDeadline(time.Now().Add(pongWait))
	c.conn.SetPongHandler(func(string) error { c.conn.SetReadDeadline(time.Now().Add(pongWait)); return nil })
	for {
		_, message, err := c.conn.ReadMessage()
		if err != nil {
			if websocket.IsUnexpectedCloseError(err, websocket.CloseGoingAway, websocket.CloseAbnormalClosure) {
				log.Printf("error: %v", err)
			}
			break
		}
		message = bytes.TrimSpace(bytes.Replace(message, newline, space, -1))
		c.hub.broadcastChan <- message
	}
}

// writePump pumps messages from the hub to the websocket connection.
//
// A goroutine running writePump is started for each connection. The
// application ensures that there is at most one writer to a connection by
// executing all writes from this goroutine.
func (c *Client) writePump() {
	ticker := time.NewTicker(pingPeriod)
	defer func() {
		ticker.Stop()
		c.conn.Close()
	}()
	for {
		select {
		case message, ok := <-c.send:
			c.conn.SetWriteDeadline(time.Now().Add(writeWait))
			if !ok {
				// The hub closed the channel.
				c.conn.WriteMessage(websocket.CloseMessage, []byte{})
				return
			}

			w, err := c.conn.NextWriter(websocket.TextMessage)
			if err != nil {
				return
			}
			w.Write(message)

			// Add queued chat messages to the current websocket message.
			n := len(c.send)
			for i := 0; i < n; i++ {
				w.Write(newline)
				w.Write(<-c.send)
			}

			if err := w.Close(); err != nil {
				return
			}
		case <-ticker.C:
			c.conn.SetWriteDeadline(time.Now().Add(writeWait))
			if err := c.conn.WriteMessage(websocket.PingMessage, nil); err != nil {
				return
			}
		}
	}
}

// serveWs handles websocket requests from the peer.
func serveWs(hub *Hub, w http.ResponseWriter, r *http.Request) {
	conn, err := upgrader.Upgrade(w, r, nil)
	if err != nil {
		log.Println(err)
		return
	}
	client := &Client{hub: hub, conn: conn, send: make(chan []byte, 256)}
	client.hub.register <- client

	// Allow collection of memory referenced by the caller by doing all work in
	// new goroutines.
	go client.writePump()
	go client.readPump()
}

// Hub maintains the set of active clients and broadcastChans messages to the
// clients.
type Hub struct {
	// Registered clients.
	clients map[*Client]bool

	// Inbound messages from the clients.
	broadcastChan chan []byte

	// Register requests from the clients.
	register chan *Client

	// Unregister requests from clients.
	unregister chan *Client
	// Broadcast sends message to all clients
	Broadcast func(message []byte)
}

// NewHub returns a new hub
func NewHub() *Hub {
	broadcastChan := make(chan []byte)

	return &Hub{
		broadcastChan: broadcastChan,
		register:      make(chan *Client),
		unregister:    make(chan *Client),
		clients:       make(map[*Client]bool),
		Broadcast: func(message []byte) {
			broadcastChan <- message
		},
	}
}

func (h *Hub) Run() {
	for {
		select {
		case client := <-h.register:
			h.clients[client] = true
		case client := <-h.unregister:
			if _, ok := h.clients[client]; ok {
				delete(h.clients, client)
				close(client.send)
			}
		case message := <-h.broadcastChan:
			for client := range h.clients {
				select {
				case client.send <- message:
				default:
					close(client.send)
					delete(h.clients, client)
				}
			}
		}
	}
}

func (h *Hub) RunWebserver(wg *sync.WaitGroup) {
	defer wg.Done()
	go h.Run()
	http.HandleFunc("/ws", func(w http.ResponseWriter, r *http.Request) {
		serveWs(h, w, r)
	})
	err := http.ListenAndServe(":8080", nil)
	if err != nil {
		log.Fatal("ListenAndServe: ", err)
	}
}

main.go

package main

import (
	"sync"
	"time"

	hub "github.com/DanaDynamics/broadcast/pkg/hub"
)

func broadcast(broadcastHub *hub.Hub) {
	m := []byte("hello")
	for range time.NewTicker(time.Second).C {
		broadcastHub.Broadcast(m)
	}
}

func main() {
	broadcastHub := hub.NewHub()
	wg := new(sync.WaitGroup)
	wg.Add(2)
	go broadcastHub.RunWebserver(wg)
	go broadcast(broadcastHub)
	wg.Wait()
}