sync: support reloading sync config when the config file changes

Signed-off-by: Petu Eusebiu <peusebiu@cisco.com>

pkg/cli/config_reloader.go

@@ -0,0 +1,72 @@
+package cli
+
+import (
+	"github.com/fsnotify/fsnotify"
+	"github.com/rs/zerolog/log"
+	"zotregistry.io/zot/pkg/api"
+	"zotregistry.io/zot/pkg/api/config"
+)
+
+type HotReloader struct {
+	watcher  *fsnotify.Watcher
+	filePath string
+	ctlr     *api.Controller
+}
+
+func NewHotReloader(ctlr *api.Controller, filePath string) (*HotReloader, error) {
+	// creates a new file watcher
+	watcher, err := fsnotify.NewWatcher()
+	if err != nil {
+		return nil, err
+	}
+
+	hotReloader := &HotReloader{
+		watcher:  watcher,
+		filePath: filePath,
+		ctlr:     ctlr,
+	}
+
+	return hotReloader, nil
+}
+
+func (hr *HotReloader) Start() {
+	done := make(chan bool)
+	// run watcher
+	go func() {
+		defer hr.watcher.Close()
+
+		go func() {
+			for {
+				select {
+				// watch for events
+				case event := <-hr.watcher.Events:
+					if event.Op == fsnotify.Write {
+						log.Info().Msg("config file changed, trying to reload config")
+
+						newConfig := config.New()
+
+						err := LoadConfiguration(newConfig, hr.filePath)
+						if err != nil {
+							log.Error().Err(err).Msg("couldn't reload config, retry writing it.")
+
+							continue
+						}
+
+						hr.ctlr.LoadNewConfig(newConfig)
+					}
+				// watch for errors
+				case err := <-hr.watcher.Errors:
+					log.Error().Err(err).Msgf("fsnotfy error while watching config %s", hr.filePath)
+					panic(err)
+				}
+			}
+		}()
+
+		if err := hr.watcher.Add(hr.filePath); err != nil {
+			log.Error().Err(err).Msgf("error adding config file %s to FsNotify watcher", hr.filePath)
+			panic(err)
+		}
+
+		<-done
+	}()
+}