// Copyright 2013 The Gorilla WebSocket Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import (
"flag"
"html/template"
"io/ioutil"
"log"
"net/http"
"os"
"strconv"
"time"
"github.com/gorilla/websocket"
)
const (
// Time allowed to write the file to the client.
writeWait = 10 * time.Second
// Time allowed to read the next pong message from the client.
pongWait = 60 * time.Second
// Send pings to client with this period. Must be less than pongWait.
pingPeriod = (pongWait * 9) / 10
// Poll file for changes with this period.
filePeriod = 10 * time.Second
)
var (
addr = flag.String("addr", ":8080", "http service address")
homeTempl = template.Must(template.New("").Parse(homeHTML))
filename string
upgrader = websocket.Upgrader{
ReadBufferSize: 1024,
WriteBufferSize: 1024,
}
)
func readFileIfModified(lastMod time.Time) ([]byte, time.Time, error) {
fi, err := os.Stat(filename)
if err != nil {
return nil, lastMod, err
}
if !fi.ModTime().After(lastMod) {
return nil, lastMod, nil
}
p, err := ioutil.ReadFile(filename)
if err != nil {
return nil, fi.ModTime(), err
}
return p, fi.ModTime(), nil
}
func reader(ws *websocket.Conn) {
defer ws.Close()
ws.SetReadLimit(512)
ws.SetReadDeadline(time.Now().Add(pongWait))
ws.SetPongHandler(func(string) error { ws.SetReadDeadline(time.Now().Add(pongWait)); return nil })
for {
_, _, err := ws.ReadMessage()
if err != nil {
break
}
}
}
func writer(ws *websocket.Conn, lastMod time.Time) {
lastError := ""
pingTicker := time.NewTicker(pingPeriod)
fileTicker := time.NewTicker(filePeriod)
defer func() {
pingTicker.Stop()
fileTicker.Stop()
ws.Close()
}()
for {
select {
case <-fileTicker.C:
var p []byte
var err error
p, lastMod, err = readFileIfModified(lastMod)
if err != nil {
if s := err.Error(); s != lastError {
lastError = s
p = []byte(lastError)
}
} else {
lastError = ""
}
if p != nil {
ws.SetWriteDeadline(time.Now().Add(writeWait))
if err := ws.WriteMessage(websocket.TextMessage, p); err != nil {
return
}
}
case <-pingTicker.C:
ws.SetWriteDeadline(time.Now().Add(writeWait))
if err := ws.WriteMessage(websocket.PingMessage, []byte{}); err != nil {
return
}
}
}
}
func serveWs(w http.ResponseWriter, r *http.Request) {
ws, err := upgrader.Upgrade(w, r, nil)
if err != nil {
if _, ok := err.(websocket.HandshakeError); !ok {
log.Println(err)
}
return
}
var lastMod time.Time
if n, err := strconv.ParseInt(r.FormValue("lastMod"), 16, 64); err == nil {
lastMod = time.Unix(0, n)
}
go writer(ws, lastMod)
reader(ws)
}
func serveHome(w http.ResponseWriter, r *http.Request) {
if r.URL.Path != "/" {
http.Error(w, "Not found", http.StatusNotFound)
return
}
if r.Method != "GET" {
http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
return
}
w.Header().Set("Content-Type", "text/html; charset=utf-8")
p, lastMod, err := readFileIfModified(time.Time{})
if err != nil {
p = []byte(err.Error())
lastMod = time.Unix(0, 0)
}
var v = struct {
Host string
Data string
LastMod string
}{
r.Host,
string(p),
strconv.FormatInt(lastMod.UnixNano(), 16),
}
homeTempl.Execute(w, &v)
}
func main() {
flag.Parse()
if flag.NArg() != 1 {
log.Fatal("filename not specified")
}
filename = flag.Args()[0]
http.HandleFunc("/", serveHome)
http.HandleFunc("/ws", serveWs)
if err := http.ListenAndServe(*addr, nil); err != nil {
log.Fatal(err)
}
}
const homeHTML = `
WebSocket Example
{{.Data}}
`