Add file watcher example.

examples/filewatch/README.md

@@ -0,0 +1,10 @@
+# File Watch example.
+
+This example displays the contents of a file in the browser. If the file
+changes, the server sends the update file to the browser.
+
+    $ go get github.com/gorilla/websocket
+    $ cd `go list -f '{{.Dir}}' github.com/gorilla/websocket/examples/tail`
+    $ go run tail.go <name of file>
+    # open http://localhost:8080/
+    # modify the file to see it update in the browser.

examples/filewatch/main.go

@@ -0,0 +1,198 @@
+// Copyright 2014 Gary Burd. 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"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"os"
+	"strconv"
+	"text/template"
+	"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
+)
+
+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) {
+	if r.Method != "GET" {
+		http.Error(w, "Method not allowed", 405)
+		return
+	}
+	if r.Header.Get("Origin") != "http://"+r.Host {
+		http.Error(w, "Origin not allowed", 403)
+		return
+	}
+	ws, err := websocket.Upgrade(w, r, nil, 1024, 1024)
+	if _, ok := err.(websocket.HandshakeError); ok {
+		http.Error(w, "Not a websocket handshake", 400)
+		return
+	} else if err != nil {
+		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", 404)
+		return
+	}
+	if r.Method != "GET" {
+		http.Error(w, "Method nod allowed", 405)
+		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 = `<!DOCTYPE html>
+<html lang="en">
+    <head>
+        <title>WebSocket Example</title>
+    </head>
+    <body>
+        <pre id="fileData">{{.Data}}</pre>
+        <script type="text/javascript">
+            (function() {
+                var data = document.getElementById("fileData");
+                var conn = new WebSocket("ws://{{.Host}}/ws?lastMod={{.LastMod}}");
+                conn.onclose = function(evt) {
+                    data.textContent = 'Connection closed';
+                }
+                conn.onmessage = function(evt) {
+                    console.log('file updated');
+                    data.textContent = evt.data;
+                }
+            })();
+        </script>
+    </body>
+</html>
+`