Websocket echo server

ws.go

package main

import (
	"flag"
	"log"
	"net/http"
	"time"

	"github.com/gorilla/websocket"
)

var addr = flag.String("addr", "localhost:4321", "http service address")

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

// connection is an middleman between the websocket connection and the hub.
type connection struct {
	// The websocket connection.
	ws *websocket.Conn

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

// readPump pumps messages from the websocket connection to the hub.
func (c *connection) readPump() {
	defer func() {
		c.ws.Close()
	}()
	c.ws.SetReadLimit(maxMessageSize)
	c.ws.SetReadDeadline(time.Now().Add(pongWait))
	c.ws.SetPongHandler(func(string) error { c.ws.SetReadDeadline(time.Now().Add(pongWait)); return nil })
	for {
		mt, message, err := c.ws.ReadMessage()
		if err != nil {
			break
		}
		log.Println("recv: ", string(message))
		err = c.ws.WriteMessage(mt, message)
		if err != nil {
			break
		}
	}
}

// write writes a message with the given message type and payload.
func (c *connection) write(mt int, payload []byte) error {
	c.ws.SetWriteDeadline(time.Now().Add(writeWait))
	return c.ws.WriteMessage(mt, payload)
}

// writePump pumps messages from the hub to the websocket connection.
func (c *connection) writePump() {
	ticker := time.NewTicker(pingPeriod)
	defer func() {
		ticker.Stop()
		c.ws.Close()
	}()
	for {
		select {
		case message, ok := <-c.send:
			if !ok {
				c.write(websocket.CloseMessage, []byte{})
				return
			}
			if err := c.write(websocket.TextMessage, message); err != nil {
				return
			}
		case <-ticker.C:
			if err := c.write(websocket.PingMessage, []byte{}); err != nil {
				return
			}
		}
	}
}

// serverWs handles websocket requests from the peer.
func serveWs(w http.ResponseWriter, r *http.Request) {
	if r.Method != "GET" {
		http.Error(w, "Method not allowed", 405)
		return
	}
	ws, err := upgrader.Upgrade(w, r, nil)
	if err != nil {
		log.Println(err)
		return
	}
	c := &connection{send: make(chan []byte, 256), ws: ws}
	go c.writePump()
	c.readPump()
}

func main() {
	flag.Parse()
	log.SetFlags(0)
	http.HandleFunc("/ws", serveWs)
	http.Handle("/", http.FileServer(http.Dir("wsstatic/")))
	err := http.ListenAndServe(*addr, nil)
	if err != nil {
		log.Fatal("ListenAndServe: ", err)
	}
}