Add websocket filewatcher

filewatch/filewatch.go

@@ -0,0 +1,122 @@
+package filewatch
+
+import (
+	"io/ioutil"
+	"log"
+	"net/http"
+	"os"
+	"strconv"
+	"time"
+
+	"github.com/gorilla/websocket"
+)
+
+// Adapted from https://github.com/gorilla/websocket
+// Copyright (c) 2013 The Gorilla WebSocket Authors
+// https://github.com/gorilla/websocket/blob/master/examples/filewatch/main.go
+
+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 upgrader = websocket.Upgrader{
+	ReadBufferSize:  1024,
+	WriteBufferSize: 1024,
+}
+
+func readFileIfModified(filename string, 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, filename string, 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(filename, 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 ServeWebsocketFileWatcher(filename string, 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, filename, lastMod)
+	reader(ws)
+}

maputnik.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/gorilla/handlers"
 	"github.com/gorilla/mux"
+	"github.com/maputnik/desktop/filewatch"
 	"github.com/urfave/cli"
 )
 
@@ -14,11 +15,39 @@ func main() {
 	app.Name = "maputnik"
 	app.Usage = "Server for integrating Maputnik locally"
 
+	app.Flags = []cli.Flag{
+		cli.StringFlag{
+			Name:  "file, f",
+			Usage: "Allow access to JSON style from web client",
+		},
+		cli.BoolFlag{
+			Name:  "watch",
+			Usage: "Notify web client about JSON style file changes",
+		},
+	}
+
 	app.Action = func(c *cli.Context) error {
 		gui := http.FileServer(assetFS())
 
 		router := mux.NewRouter().StrictSlash(true)
-		//router.Path("/api/v1/apps").Methods("GET").HandlerFunc(foo)
+
+		// Register websocket to notify we clients about file changes
+		filename := c.String("file")
+
+		if filename != "" {
+			/*
+				router.Path("/files").Methods("GET").HandlerFunc(listFiles)
+				router.Path("/files/{filename}").Methods("PUT").HandlerFunc(saveFile)
+			*/
+
+			if c.Bool("watch") {
+				router.Path("/ws").HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+					filewatch.ServeWebsocketFileWatcher(filename, w, r)
+				})
+			}
+
+		}
+
 		router.PathPrefix("/").Handler(http.StripPrefix("/", gui))
 
 		loggedRouter := handlers.LoggingHandler(os.Stdout, router)