From ba28a02302759867e299350a91822e6eb1c4ad41 Mon Sep 17 00:00:00 2001
From: Daniel Fangl <daniel.fangl@localstack.cloud>
Date: Tue, 6 Feb 2024 10:52:18 +0100
Subject: [PATCH] Allow manual specification of filewatcher behavior (#29)

---
 cmd/localstack/awsutil.go               |  4 ++--
 cmd/localstack/filenotify/filenotify.go | 20 +++++++++++++++++---
 cmd/localstack/hotreloading.go          |  4 ++--
 cmd/localstack/main.go                  |  4 +++-
 4 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/cmd/localstack/awsutil.go b/cmd/localstack/awsutil.go
index de18378..7fa02c4 100644
--- a/cmd/localstack/awsutil.go
+++ b/cmd/localstack/awsutil.go
@@ -156,14 +156,14 @@ func RunDNSRewriter(opts *LsOpts, ctx context.Context) {
 	log.Debugln("DNS server stopped")
 }
 
-func RunHotReloadingListener(server *CustomInteropServer, targetPaths []string, ctx context.Context) {
+func RunHotReloadingListener(server *CustomInteropServer, targetPaths []string, ctx context.Context, fileWatcherStrategy string) {
 	if len(targetPaths) == 1 && targetPaths[0] == "" {
 		log.Debugln("Hot reloading disabled.")
 		return
 	}
 	defaultDebouncingDuration := 500 * time.Millisecond
 	log.Infoln("Hot reloading enabled, starting filewatcher.", targetPaths)
-	changeListener, err := NewChangeListener(defaultDebouncingDuration)
+	changeListener, err := NewChangeListener(defaultDebouncingDuration, fileWatcherStrategy)
 	if err != nil {
 		log.Errorln("Hot reloading disabled due to change listener error.", err)
 		return
diff --git a/cmd/localstack/filenotify/filenotify.go b/cmd/localstack/filenotify/filenotify.go
index 1c1d708..579a76a 100644
--- a/cmd/localstack/filenotify/filenotify.go
+++ b/cmd/localstack/filenotify/filenotify.go
@@ -38,14 +38,28 @@ func shouldUseEventWatcher() bool {
 }
 
 // New tries to use a fs-event watcher, and falls back to the poller if there is an error
-func New(interval time.Duration) (FileWatcher, error) {
+func New(interval time.Duration, fileWatcherStrategy string) (FileWatcher, error) {
+	if fileWatcherStrategy != "" {
+		log.Debugln("Forced usage of filewatcher strategy: ", fileWatcherStrategy)
+		if fileWatcherStrategy == "event" {
+			if watcher, err := NewEventWatcher(); err == nil {
+				return watcher, nil
+			} else {
+				log.Fatalln("Event based filewatcher is selected, but unable to start. Please try setting the filewatcher to polling. Error: ", err)
+			}
+		} else if fileWatcherStrategy == "polling" {
+			return NewPollingWatcher(interval), nil
+		} else {
+			log.Fatalf("Invalid filewatcher strategy %s. Only event and polling are allowed.\n", fileWatcherStrategy)
+		}
+	}
 	if shouldUseEventWatcher() {
 		if watcher, err := NewEventWatcher(); err == nil {
-			log.Debugln("Using event based filewatcher")
+			log.Debugln("Using event based filewatcher (autodetected)")
 			return watcher, nil
 		}
 	}
-	log.Debugln("Using polling based filewatcher")
+	log.Debugln("Using polling based filewatcher (autodetected)")
 	return NewPollingWatcher(interval), nil
 }
 
diff --git a/cmd/localstack/hotreloading.go b/cmd/localstack/hotreloading.go
index 9218465..a0c4467 100644
--- a/cmd/localstack/hotreloading.go
+++ b/cmd/localstack/hotreloading.go
@@ -16,8 +16,8 @@ type ChangeListener struct {
 	watchedFolders     []string
 }
 
-func NewChangeListener(debouncingInterval time.Duration) (*ChangeListener, error) {
-	watcher, err := filenotify.New(200 * time.Millisecond)
+func NewChangeListener(debouncingInterval time.Duration, fileWatcherStrategy string) (*ChangeListener, error) {
+	watcher, err := filenotify.New(200*time.Millisecond, fileWatcherStrategy)
 	if err != nil {
 		log.Errorln("Cannot create change listener due to filewatcher error.", err)
 		return nil, err
diff --git a/cmd/localstack/main.go b/cmd/localstack/main.go
index 02bf247..e6eb026 100644
--- a/cmd/localstack/main.go
+++ b/cmd/localstack/main.go
@@ -21,6 +21,7 @@ type LsOpts struct {
 	User                string
 	CodeArchives        string
 	HotReloadingPaths   []string
+	FileWatcherStrategy string
 	EnableDnsServer     string
 	LocalstackIP        string
 	InitLogLevel        string
@@ -52,6 +53,7 @@ func InitLsOpts() *LsOpts {
 		// optional or empty
 		CodeArchives:        os.Getenv("LOCALSTACK_CODE_ARCHIVES"),
 		HotReloadingPaths:   strings.Split(GetenvWithDefault("LOCALSTACK_HOT_RELOADING_PATHS", ""), ","),
+		FileWatcherStrategy: os.Getenv("LOCALSTACK_FILE_WATCHER_STRATEGY"),
 		EnableDnsServer:     os.Getenv("LOCALSTACK_ENABLE_DNS_SERVER"),
 		EnableXRayTelemetry: os.Getenv("LOCALSTACK_ENABLE_XRAY_TELEMETRY"),
 		LocalstackIP:        os.Getenv("LOCALSTACK_HOSTNAME"),
@@ -230,7 +232,7 @@ func main() {
 	if err != nil {
 		log.Fatalln(err)
 	}
-	go RunHotReloadingListener(interopServer, lsOpts.HotReloadingPaths, fileWatcherContext)
+	go RunHotReloadingListener(interopServer, lsOpts.HotReloadingPaths, fileWatcherContext, lsOpts.FileWatcherStrategy)
 
 	// start runtime init. It is important to start `InitHandler` synchronously because we need to ensure the
 	// notification channels and status fields are properly initialized before `AwaitInitialized`