feat: integrate fsnotify to watch local file changes

implements the helm/chartmuseum#545

Signed-off-by: scnace <scbizu@gmail.com>

Author: scbizu

event.go

@@ -0,0 +1,9 @@
+package storage
+
+// EventType represents the type of event kind
+type EventType uint8
+
+const (
+	EventPutObject EventType = iota + 1
+	EventDeleteObject
+)

go.mod

@@ -9,6 +9,7 @@ require (
 	github.com/aliyun/aliyun-oss-go-sdk v2.2.0+incompatible
 	github.com/aws/aws-sdk-go v1.43.16
 	github.com/baidubce/bce-sdk-go v0.9.105
+	github.com/fsnotify/fsnotify v1.5.1
 	github.com/gophercloud/gophercloud v0.24.0
 	github.com/oracle/oci-go-sdk v24.3.0+incompatible
 	github.com/stretchr/testify v1.7.0

go.sum

@@ -137,6 +137,8 @@ github.com/envoyproxy/go-control-plane v0.9.9-0.20210217033140-668b12f5399d/go.m
 github.com/envoyproxy/go-control-plane v0.9.9-0.20210512163311-63b5d3c536b0/go.mod h1:hliV/p42l8fGbc6Y9bQ70uLwIvmJyVE5k4iMKlh8wCQ=
 github.com/envoyproxy/go-control-plane v0.9.10-0.20210907150352-cf90f659a021/go.mod h1:AFq3mo9L8Lqqiid3OhADV3RfLJnjiw63cSpi+fDTRC0=
 github.com/envoyproxy/protoc-gen-validate v0.1.0/go.mod h1:iSmxcyjqTsJpI2R4NaDN7+kN2VEUnK/pcBlmesArF7c=
+github.com/fsnotify/fsnotify v1.5.1 h1:mZcQUHVQUQWoPXXtuf9yuEXKudkV2sx1E06UadKWpgI=
+github.com/fsnotify/fsnotify v1.5.1/go.mod h1:T3375wBYaZdLLcVNkcVbzGHY7f1l/uK5T5Ai1i3InKU=
 github.com/ghodss/yaml v1.0.0/go.mod h1:4dBDuWmgqj2HViK6kFavaiC9ZROes6MMH2rRYeMEF04=
 github.com/go-gl/glfw v0.0.0-20190409004039-e6da0acd62b1/go.mod h1:vR7hzQXu2zJy9AVAgeJqvqgH9Q5CA+iKCZ2gyEVpxRU=
 github.com/go-gl/glfw/v3.3/glfw v0.0.0-20191125211704-12ad95a8df72/go.mod h1:tQ2UAYgL5IevRw8kRxooKSPJfGvJ9fJQFa0TUsXzTg8=

local.go

@@ -17,28 +17,93 @@ limitations under the License.
 package storage
 
 import (
+	"fmt"
 	"io/ioutil"
 	"os"
+	"sync"
 
 	pathutil "path"
 	"path/filepath"
+
+	"github.com/fsnotify/fsnotify"
 )
 
 // LocalFilesystemBackend is a storage backend for local filesystem storage
 type LocalFilesystemBackend struct {
 	RootDirectory string
 }
 
+type NewLocalFilesystemBackendOption struct {
+	notifier map[EventType]func()
+}
+
+var watcherOnce sync.Once
+var globalWatcher *fsnotify.Watcher
+
+func WithEventNotifier(e EventType, fn func()) func(*NewLocalFilesystemBackendOption) {
+	return func(option *NewLocalFilesystemBackendOption) {
+		if option.notifier == nil {
+			option.notifier = make(map[EventType]func())
+		}
+		option.notifier[e] = fn
+	}
+}
+
 // NewLocalFilesystemBackend creates a new instance of LocalFilesystemBackend
-func NewLocalFilesystemBackend(rootDirectory string) *LocalFilesystemBackend {
+func NewLocalFilesystemBackend(rootDirectory string, opts ...func(*NewLocalFilesystemBackendOption)) *LocalFilesystemBackend {
+	var option NewLocalFilesystemBackendOption
+	for _, opt := range opts {
+		opt(&option)
+	}
 	absPath, err := filepath.Abs(rootDirectory)
 	if err != nil {
 		panic(err)
 	}
-	b := &LocalFilesystemBackend{RootDirectory: absPath}
+	b := &LocalFilesystemBackend{
+		RootDirectory: absPath,
+	}
+
+	watcherOnce.Do(func() {
+		globalWatcher, err = fsnotify.NewWatcher()
+		if err != nil {
+			panic(err)
+		}
+		// since it is a longTerm watcher , we do not need to close it
+		go func() {
+			for {
+				select {
+				case event, ok := <-globalWatcher.Events:
+					if !ok {
+						continue
+					}
+					if event.Op&fsnotify.Write == fsnotify.Write {
+						if option.notifier != nil {
+							for _, op := range option.notifier {
+								op()
+							}
+						}
+					}
+				case _, ok := <-globalWatcher.Errors:
+					if !ok {
+						continue
+					}
+				}
+			}
+		}()
+
+		if err := globalWatcher.Add(b.RootDirectory); err != nil {
+			panic(err)
+		}
+	})
+
 	return b
 }
 
+func (b LocalFilesystemBackend) AddWatherPath(path string) error {
+	// TODO: to ensure that we should lock here ?
+	return globalWatcher.Add(path)
+}
+
 // ListObjects lists all objects in root directory (depth 1)
 func (b LocalFilesystemBackend) ListObjects(prefix string) ([]Object, error) {
 	var objects []Object
@@ -84,6 +149,7 @@ func (b LocalFilesystemBackend) PutObject(path string, content []byte) error {
 	_, err := os.Stat(folderPath)
 	if err != nil {
 		if os.IsNotExist(err) {
+			// NOTE: works for dynamic depth tenant
 			err := os.MkdirAll(folderPath, 0774)
 			if err != nil {
 				return err
@@ -95,17 +161,25 @@ func (b LocalFilesystemBackend) PutObject(path string, content []byte) error {
 			if err != nil {
 				return err
 			}
+			// also adds the fsnotify watcher path
+			if err := b.AddWatherPath(folderPath); err != nil {
+				return err
+			}
 		} else {
 			return err
 		}
 	}
-	err = ioutil.WriteFile(fullpath, content, 0644)
-	return err
+	if err = ioutil.WriteFile(fullpath, content, 0644); err != nil {
+		return err
+	}
+	return nil
 }
 
 // DeleteObject removes an object from root directory
 func (b LocalFilesystemBackend) DeleteObject(path string) error {
 	fullpath := pathutil.Join(b.RootDirectory, path)
-	err := os.Remove(fullpath)
-	return err
+	if err := os.Remove(fullpath); err != nil {
+		return fmt.Errorf("failed to delete object %s: %w", path, err)
+	}
+	return nil
 }