From d2cd84de2ba905ee5d7f95f671c7476d21b8ef4e Mon Sep 17 00:00:00 2001
From: Lukas Martinelli <me@lukasmartinelli.ch>
Date: Sun, 1 Jan 2017 15:50:58 +0100
Subject: [PATCH] Switch filewatch implementation to fsnotify

---
 .travis.yml            |   1 +
 README.md              |   1 +
 appveyor.yml           |   1 +
 filewatch/filewatch.go | 123 ++++++++++++-----------------------------
 4 files changed, 38 insertions(+), 88 deletions(-)

diff --git a/.travis.yml b/.travis.yml
index f1f1c974..17bf4aec 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,6 +3,7 @@ os:
 - osx
 language: go
 install:
+- go get github.com/fsnotify/fsnotify
 - go get github.com/gorilla/handlers
 - go get github.com/gorilla/mux
 - go get github.com/gorilla/websocket
diff --git a/README.md b/README.md
index 10481eb9..3b0e2b28 100644
--- a/README.md
+++ b/README.md
@@ -57,6 +57,7 @@ Install the 3rd party dependencies.
 go get github.com/gorilla/handlers
 go get github.com/gorilla/mux
 go get github.com/gorilla/websocket
+go get github.com/fsnotify/fsnotify
 go get github.com/urfave/cli
 go get github.com/elazarl/go-bindata-assetfs/...
 go get github.com/jteeuwen/go-bindata/...
diff --git a/appveyor.yml b/appveyor.yml
index 4d07c960..6fbda7ca 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -16,6 +16,7 @@ install:
 - set PATH=%GOPATH%\bin;c:\go\bin;%PATH%
 - go version
 - go env
+- go get github.com/fsnotify/fsnotify
 - go get github.com/gorilla/handlers
 - go get github.com/gorilla/mux
 - go get github.com/gorilla/websocket
diff --git a/filewatch/filewatch.go b/filewatch/filewatch.go
index d00c0f78..4248212e 100644
--- a/filewatch/filewatch.go
+++ b/filewatch/filewatch.go
@@ -4,103 +4,55 @@ import (
 	"io/ioutil"
 	"log"
 	"net/http"
-	"os"
-	"strconv"
-	"time"
 
+	"github.com/fsnotify/fsnotify"
 	"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,
+	CheckOrigin:     func(r *http.Request) bool { return true },
 }
 
-func readFileIfModified(filename string, lastMod time.Time) ([]byte, time.Time, error) {
-	fi, err := os.Stat(filename)
+func writer(ws *websocket.Conn, filename string) {
+	watcher, err := fsnotify.NewWatcher()
 	if err != nil {
-		return nil, lastMod, err
+		log.Fatal(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
-}
+	defer watcher.Close()
 
-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
+	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)
+			}
 		}
-	}
-}
-
-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
-			}
-		}
+	if err = watcher.Add(filename); err != nil {
+		log.Fatal(err)
 	}
+	<-done
 }
 
 func ServeWebsocketFileWatcher(filename string, w http.ResponseWriter, r *http.Request) {
@@ -112,11 +64,6 @@ func ServeWebsocketFileWatcher(filename string, w http.ResponseWriter, r *http.R
 		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)
+	writer(ws, filename)
+	defer ws.Close()
 }