Move into /desktop dir

For eventual merge into maplibre/maputnik repo

desktop/filewatch/filewatch.go

@@ -0,0 +1,69 @@
+package filewatch
+
+import (
+	"io/ioutil"
+	"log"
+	"net/http"
+
+	"github.com/fsnotify/fsnotify"
+	"github.com/gorilla/websocket"
+)
+
+var upgrader = websocket.Upgrader{
+	ReadBufferSize:  1024,
+	WriteBufferSize: 1024,
+	CheckOrigin:     func(r *http.Request) bool { return true },
+}
+
+func writer(ws *websocket.Conn, filename string) {
+	watcher, err := fsnotify.NewWatcher()
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer watcher.Close()
+
+	done := make(chan bool)
+	go func() {
+		for {
+			select {
+			case event := <-watcher.Events:
+				if event.Op&fsnotify.Write == fsnotify.Write {
+					log.Println("Modified file:", event.Name)
+					var p []byte
+					var err error
+
+					p, err = ioutil.ReadFile(filename)
+					if err != nil {
+						log.Fatal(err)
+					}
+
+					if p != nil {
+						if err := ws.WriteMessage(websocket.TextMessage, p); err != nil {
+							return
+						}
+					}
+				}
+			case err := <-watcher.Errors:
+				log.Println("Watch error:", err)
+			}
+		}
+	}()
+
+	if err = watcher.Add(filename); err != nil {
+		log.Fatal(err)
+	}
+	<-done
+}
+
+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
+	}
+
+	writer(ws, filename)
+	defer ws.Close()
+}