localstack
@@ -7,12 +7,14 @@ package main
 
 import (
 	"archive/zip"
+	"context"
 	"fmt"
 	"github.com/jessevdk/go-flags"
 	log "github.com/sirupsen/logrus"
 	"go.amzn.com/lambda/interop"
 	"go.amzn.com/lambda/rapidcore"
 	"io"
+	"io/fs"
 	"math"
 	"net/http"
 	"os"
@@ -196,6 +198,69 @@ func DownloadCodeArchive(url string) {
 
 }
 
+func resetListener(changeChannel <-chan bool, server *CustomInteropServer) {
+	for {
+		_, more := <-changeChannel
+		if !more {
+			return
+		}
+		log.Println("Resetting environment...")
+		_, err := server.Reset("HotReload", 2000)
+		if err != nil {
+			log.Warnln("Error resetting server: ", err)
+		}
+	}
+
+}
+
+func RunHotReloadingListener(server *CustomInteropServer, targetPaths []string, opts *LsOpts, ctx context.Context) {
+	if !opts.HotReloading {
+		log.Debugln("Hot reloading disabled.")
+		return
+	}
+	defaultDebouncingDuration := 500 * time.Millisecond
+	log.Infoln("Hot reloading enabled, starting filewatcher.", targetPaths)
+	changeListener, err := NewChangeListener(defaultDebouncingDuration)
+	if err != nil {
+		log.Errorln("Hot reloading disabled due to change listener error.", err)
+		return
+	}
+	defer changeListener.Close()
+	go changeListener.Start()
+	changeListener.AddTargetPaths(targetPaths)
+	go resetListener(changeListener.debouncedChannel, server)
+
+	<-ctx.Done()
+	log.Infoln("Closing down filewatcher.")
+
+}
+
+func getSubFolders(dirPath string) []string {
+	var subfolders []string
+	err := filepath.WalkDir(dirPath, func(path string, d fs.DirEntry, err error) error {
+		if err == nil && d.IsDir() {
+			subfolders = append(subfolders, path)
+		}
+		return err
+	})
+	if err != nil {
+		log.Errorln("Error listing directory contents: ", err)
+		return subfolders
+	}
+	return subfolders
+}
+
+func getSubFoldersInList(prefix string, pathList []string) (oldFolders []string, newFolders []string) {
+	for _, pathItem := range pathList {
+		if strings.HasPrefix(pathItem, prefix) {
+			oldFolders = append(oldFolders, pathItem)
+		} else {
+			newFolders = append(newFolders, pathItem)
+		}
+	}
+	return
+}
+
 func InitHandler(sandbox Sandbox, functionVersion string, timeout int64) (time.Time, time.Time) {
 	additionalFunctionEnvironmentVariables := map[string]string{}
 

@@ -0,0 +1,69 @@
+// This package is adapted from https://github.com/gohugoio/hugo/tree/master/watcher/filenotify, Apache-2.0 License.
+
+// Package filenotify provides a mechanism for watching file(s) for changes.
+// Generally leans on fsnotify, but provides a poll-based notifier which fsnotify does not support.
+// These are wrapped up in a common interface so that either can be used interchangeably in your code.
+//
+// This package is adapted from https://github.com/moby/moby/tree/master/pkg/filenotify, Apache-2.0 License.
+// Hopefully this can be replaced with an external package sometime in the future, see https://github.com/fsnotify/fsnotify/issues/9
+package filenotify
+
+import (
+	log "github.com/sirupsen/logrus"
+	"golang.org/x/sys/unix"
+	"strings"
+	"time"
+
+	"github.com/fsnotify/fsnotify"
+)
+
+// FileWatcher is an interface for implementing file notification watchers
+type FileWatcher interface {
+	Events() <-chan fsnotify.Event
+	Errors() <-chan error
+	Add(name string) error
+	Remove(name string) error
+	Close() error
+}
+
+func shouldUseEventWatcher() bool {
+	// Whether to use an event watcher or polling mechanism
+	var utsname unix.Utsname
+	err := unix.Uname(&utsname)
+	release := strings.TrimRight(string(utsname.Release[:]), "\x00")
+	log.Println("Release detected: ", release)
+	// cheap check if we are in Docker desktop or not.
+	// We could also inspect the mounts, but that would be more complicated and needs more parsing
+	return err == nil && !(strings.Contains(release, "linuxkit") || strings.Contains(release, "WSL2"))
+}
+
+// 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) {
+	if shouldUseEventWatcher() {
+		if watcher, err := NewEventWatcher(); err == nil {
+			log.Debugln("Using event based filewatcher")
+			return watcher, nil
+		}
+	}
+	log.Debugln("Using polling based filewatcher")
+	return NewPollingWatcher(interval), nil
+}
+
+// NewPollingWatcher returns a poll-based file watcher
+func NewPollingWatcher(interval time.Duration) FileWatcher {
+	return &filePoller{
+		interval: interval,
+		done:     make(chan struct{}),
+		events:   make(chan fsnotify.Event),
+		errors:   make(chan error),
+	}
+}
+
+// NewEventWatcher returns a fs-event based file watcher
+func NewEventWatcher() (FileWatcher, error) {
+	watcher, err := fsnotify.NewWatcher()
+	if err != nil {
+		return nil, err
+	}
+	return &fsNotifyWatcher{watcher}, nil
+}
@@ -0,0 +1,22 @@
+// This package is adapted from https://github.com/gohugoio/hugo/tree/master/watcher/filenotify, Apache-2.0 License.
+
+// Package filenotify is adapted from https://github.com/moby/moby/tree/master/pkg/filenotify, Apache-2.0 License.
+// Hopefully this can be replaced with an external package sometime in the future, see https://github.com/fsnotify/fsnotify/issues/9
+package filenotify
+
+import "github.com/fsnotify/fsnotify"
+
+// fsNotifyWatcher wraps the fsnotify package to satisfy the FileNotifier interface
+type fsNotifyWatcher struct {
+	*fsnotify.Watcher
+}
+
+// Events returns the fsnotify event channel receiver
+func (w *fsNotifyWatcher) Events() <-chan fsnotify.Event {
+	return w.Watcher.Events
+}
+
+// Errors returns the fsnotify error channel receiver
+func (w *fsNotifyWatcher) Errors() <-chan error {
+	return w.Watcher.Errors
+}