s3: remove empty parent folder on delete

fix https://github.com/chrislusf/seaweedfs/issues/1637

weed/filer/filer_delete_entry.go

@@ -3,6 +3,7 @@ package filer
 import (
 	"context"
 	"fmt"
+	"strings"
 
 	"github.com/chrislusf/seaweedfs/weed/glog"
 	"github.com/chrislusf/seaweedfs/weed/pb/filer_pb"
@@ -22,7 +23,7 @@ func (f *Filer) DeleteEntryMetaAndData(ctx context.Context, p util.FullPath, isR
 		return findErr
 	}
 
-	isCollection := f.isBucket(entry)
+	isDeleteCollection := f.isBucket(entry)
 
 	var chunks []*filer_pb.FileChunk
 	var hardLinkIds []HardLinkId
@@ -31,7 +32,7 @@ func (f *Filer) DeleteEntryMetaAndData(ctx context.Context, p util.FullPath, isR
 		// delete the folder children, not including the folder itself
 		var dirChunks []*filer_pb.FileChunk
 		var dirHardLinkIds []HardLinkId
-		dirChunks, dirHardLinkIds, err = f.doBatchDeleteFolderMetaAndData(ctx, entry, isRecursive, ignoreRecursiveError, shouldDeleteChunks && !isCollection, isFromOtherCluster, signatures)
+		dirChunks, dirHardLinkIds, err = f.doBatchDeleteFolderMetaAndData(ctx, entry, isRecursive, ignoreRecursiveError, shouldDeleteChunks && !isDeleteCollection, isFromOtherCluster, signatures)
 		if err != nil {
 			glog.V(0).Infof("delete directory %s: %v", p, err)
 			return fmt.Errorf("delete directory %s: %v", p, err)
@@ -46,7 +47,7 @@ func (f *Filer) DeleteEntryMetaAndData(ctx context.Context, p util.FullPath, isR
 		return fmt.Errorf("delete file %s: %v", p, err)
 	}
 
-	if shouldDeleteChunks && !isCollection {
+	if shouldDeleteChunks && !isDeleteCollection {
 		f.DirectDeleteChunks(chunks)
 	}
 	// A case not handled:
@@ -55,10 +56,15 @@ func (f *Filer) DeleteEntryMetaAndData(ctx context.Context, p util.FullPath, isR
 		f.maybeDeleteHardLinks(hardLinkIds)
 	}
 
-	if isCollection {
+	if isDeleteCollection {
 		collectionName := entry.Name()
 		f.doDeleteCollection(collectionName)
 		f.deleteBucket(collectionName)
+	} else {
+		parent, _ := p.DirAndName()
+		if err := f.removeEmptyParentFolder(ctx, util.FullPath(parent)); err != nil {
+			glog.Errorf("clean up empty folders for %s : %v", p, err)
+		}
 	}
 
 	return nil
@@ -153,3 +159,25 @@ func (f *Filer) maybeDeleteHardLinks(hardLinkIds []HardLinkId) {
 		}
 	}
 }
+
+func (f *Filer) removeEmptyParentFolder(ctx context.Context, dir util.FullPath) error {
+	if !strings.HasPrefix(string(dir), f.DirBucketsPath) {
+		return nil
+	}
+	parent, _ := dir.DirAndName()
+	if parent == f.DirBucketsPath {
+		// should not delete bucket itself
+		return nil
+	}
+	entries, err := f.ListDirectoryEntries(ctx, dir, "", false, 1, "")
+	if err != nil {
+		return err
+	}
+	if len(entries) > 0 {
+		return nil
+	}
+	if err := f.Store.DeleteEntry(ctx, dir); err != nil {
+		return err
+	}
+	return f.removeEmptyParentFolder(ctx, util.FullPath(parent))
+}