mirror of https://github.com/gorilla/websocket.git
Add file watcher example.
This commit is contained in:
Gary Burd
parent
4ec58d24a4
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# File Watch example.
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This example displays the contents of a file in the browser. If the file
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changes, the server sends the update file to the browser.
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$ go get github.com/gorilla/websocket
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$ cd `go list -f '{{.Dir}}' github.com/gorilla/websocket/examples/tail`
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$ go run tail.go <name of file>
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# open http://localhost:8080/
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# modify the file to see it update in the browser.
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@ -0,0 +1,198 @@
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// Copyright 2014 Gary Burd. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package main
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import (
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"flag"
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"io/ioutil"
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"log"
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"net/http"
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"os"
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"strconv"
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"text/template"
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"time"
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"github.com/gorilla/websocket"
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)
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const (
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// Time allowed to write the file to the client.
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writeWait = 10 * time.Second
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// Time allowed to read the next pong message from the client.
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pongWait = 60 * time.Second
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// Send pings to client with this period. Must be less than pongWait.
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pingPeriod = (pongWait * 9) / 10
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// Poll file for changes with this period.
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filePeriod = 10 * time.Second
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)
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var (
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addr = flag.String("addr", ":8080", "http service address")
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homeTempl = template.Must(template.New("").Parse(homeHTML))
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filename string
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)
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func readFileIfModified(lastMod time.Time) ([]byte, time.Time, error) {
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fi, err := os.Stat(filename)
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if err != nil {
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return nil, lastMod, err
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}
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if !fi.ModTime().After(lastMod) {
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return nil, lastMod, nil
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}
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p, err := ioutil.ReadFile(filename)
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if err != nil {
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return nil, fi.ModTime(), err
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}
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return p, fi.ModTime(), nil
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}
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func reader(ws *websocket.Conn) {
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defer ws.Close()
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ws.SetReadLimit(512)
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ws.SetReadDeadline(time.Now().Add(pongWait))
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ws.SetPongHandler(func(string) error { ws.SetReadDeadline(time.Now().Add(pongWait)); return nil })
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for {
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_, _, err := ws.ReadMessage()
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if err != nil {
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break
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}
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}
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}
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func writer(ws *websocket.Conn, lastMod time.Time) {
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lastError := ""
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pingTicker := time.NewTicker(pingPeriod)
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fileTicker := time.NewTicker(filePeriod)
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defer func() {
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pingTicker.Stop()
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fileTicker.Stop()
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ws.Close()
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}()
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for {
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select {
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case <-fileTicker.C:
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var p []byte
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var err error
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p, lastMod, err = readFileIfModified(lastMod)
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if err != nil {
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if s := err.Error(); s != lastError {
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lastError = s
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p = []byte(lastError)
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}
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} else {
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lastError = ""
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}
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if p != nil {
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ws.SetWriteDeadline(time.Now().Add(writeWait))
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if err := ws.WriteMessage(websocket.TextMessage, p); err != nil {
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return
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}
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}
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case <-pingTicker.C:
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ws.SetWriteDeadline(time.Now().Add(writeWait))
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if err := ws.WriteMessage(websocket.PingMessage, []byte{}); err != nil {
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return
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}
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}
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}
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}
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func serveWs(w http.ResponseWriter, r *http.Request) {
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if r.Method != "GET" {
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http.Error(w, "Method not allowed", 405)
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return
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}
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if r.Header.Get("Origin") != "http://"+r.Host {
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http.Error(w, "Origin not allowed", 403)
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return
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}
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ws, err := websocket.Upgrade(w, r, nil, 1024, 1024)
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if _, ok := err.(websocket.HandshakeError); ok {
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http.Error(w, "Not a websocket handshake", 400)
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return
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} else if err != nil {
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log.Println(err)
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return
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}
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var lastMod time.Time
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if n, err := strconv.ParseInt(r.FormValue("lastMod"), 16, 64); err != nil {
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lastMod = time.Unix(0, n)
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}
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go writer(ws, lastMod)
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reader(ws)
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}
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func serveHome(w http.ResponseWriter, r *http.Request) {
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if r.URL.Path != "/" {
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http.Error(w, "Not found", 404)
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return
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}
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if r.Method != "GET" {
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http.Error(w, "Method nod allowed", 405)
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return
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}
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w.Header().Set("Content-Type", "text/html; charset=utf-8")
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p, lastMod, err := readFileIfModified(time.Time{})
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if err != nil {
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p = []byte(err.Error())
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lastMod = time.Unix(0, 0)
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}
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var v = struct {
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Host string
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Data string
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LastMod string
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}{
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r.Host,
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string(p),
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strconv.FormatInt(lastMod.UnixNano(), 16),
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}
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homeTempl.Execute(w, &v)
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}
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func main() {
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flag.Parse()
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if flag.NArg() != 1 {
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log.Fatal("filename not specified")
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}
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filename = flag.Args()[0]
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http.HandleFunc("/", serveHome)
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http.HandleFunc("/ws", serveWs)
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if err := http.ListenAndServe(*addr, nil); err != nil {
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log.Fatal(err)
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}
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}
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const homeHTML = `<!DOCTYPE html>
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<html lang="en">
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<head>
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<title>WebSocket Example</title>
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</head>
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<body>
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<pre id="fileData">{{.Data}}</pre>
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<script type="text/javascript">
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(function() {
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var data = document.getElementById("fileData");
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var conn = new WebSocket("ws://{{.Host}}/ws?lastMod={{.LastMod}}");
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conn.onclose = function(evt) {
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data.textContent = 'Connection closed';
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}
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conn.onmessage = function(evt) {
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console.log('file updated');
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data.textContent = evt.data;
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}
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})();
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</script>
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</body>
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</html>
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`
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