xl: Fix healing empty directories (#8013)

After some extensive refactors, it turned out empty directories
are not healed and heal status is also not reported correctly.

This commit fixes it and adds the appropriate unit tests

cmd/xl-v1-healing.go

@@ -501,10 +501,14 @@ func (xl xlObjects) healObjectDir(ctx context.Context, bucket, object string, dr
 			drive = storageDisks[i].String()
 		}
 		switch err {
+		case nil:
+			hr.Before.Drives[i] = madmin.HealDriveInfo{State: madmin.DriveStateOk}
+			hr.After.Drives[i] = madmin.HealDriveInfo{State: madmin.DriveStateOk}
 		case errDiskNotFound:
 			hr.Before.Drives[i] = madmin.HealDriveInfo{State: madmin.DriveStateOffline}
 			hr.After.Drives[i] = madmin.HealDriveInfo{State: madmin.DriveStateOffline}
-		case errVolumeNotFound:
+		case errVolumeNotFound, errFileNotFound:
+			// Bucket or prefix/directory not found
 			hr.Before.Drives[i] = madmin.HealDriveInfo{Endpoint: drive, State: madmin.DriveStateMissing}
 			hr.After.Drives[i] = madmin.HealDriveInfo{Endpoint: drive, State: madmin.DriveStateMissing}
 		default:
@@ -517,7 +521,8 @@ func (xl xlObjects) healObjectDir(ctx context.Context, bucket, object string, dr
 	}
 	for i, err := range errs {
 		switch err {
-		case errVolumeNotFound:
+		case errVolumeNotFound, errFileNotFound:
+			// Bucket or prefix/directory not found
 			merr := storageDisks[i].MakeVol(pathJoin(bucket, object))
 			switch merr {
 			case nil, errVolumeExists:

cmd/xl-v1-healing_test.go

@@ -250,3 +250,79 @@ func TestHealObjectXL(t *testing.T) {
 		t.Errorf("Expected %v but received %v", InsufficientReadQuorum{}, err)
 	}
 }
+
+// Tests healing of empty directories
+func TestHealEmptyDirectoryXL(t *testing.T) {
+	nDisks := 16
+	fsDirs, err := getRandomDisks(nDisks)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer removeRoots(fsDirs)
+
+	// Everything is fine, should return nil
+	obj, _, err := initObjectLayer(mustGetNewEndpointList(fsDirs...))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	bucket := "bucket"
+	object := "empty-dir/"
+	var opts ObjectOptions
+
+	err = obj.MakeBucketWithLocation(context.Background(), bucket, "")
+	if err != nil {
+		t.Fatalf("Failed to make a bucket - %v", err)
+	}
+
+	// Upload an empty directory
+	_, err = obj.PutObject(context.Background(), bucket, object, mustGetPutObjReader(t, bytes.NewReader([]byte{}), 0, "", ""), opts)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Remove the object backend files from the first disk.
+	xl := obj.(*xlObjects)
+	firstDisk := xl.storageDisks[0]
+	err = firstDisk.DeleteFile(bucket, object)
+	if err != nil {
+		t.Fatalf("Failed to delete a file - %v", err)
+	}
+
+	// Heal the object
+	hr, err := obj.HealObject(context.Background(), bucket, object, false, false, madmin.HealNormalScan)
+	if err != nil {
+		t.Fatalf("Failed to heal object - %v", err)
+	}
+
+	// Check if the empty directory is restored in the first disk
+	_, err = firstDisk.StatVol(pathJoin(bucket, object))
+	if err != nil {
+		t.Fatalf("Expected object to be present but stat failed - %v", err)
+	}
+
+	// Check the state of the object in the first disk (should be missing)
+	if hr.Before.Drives[0].State != madmin.DriveStateMissing {
+		t.Fatalf("Unexpected drive state: %v", hr.Before.Drives[0].State)
+	}
+
+	// Check the state of all other disks (should be ok)
+	for i, h := range append(hr.Before.Drives[1:], hr.After.Drives...) {
+		if h.State != madmin.DriveStateOk {
+			t.Fatalf("Unexpected drive state (%d): %v", i+1, h.State)
+		}
+	}
+
+	// Heal the same object again
+	hr, err = obj.HealObject(context.Background(), bucket, object, false, false, madmin.HealNormalScan)
+	if err != nil {
+		t.Fatalf("Failed to heal object - %v", err)
+	}
+
+	// Check that Before & After states are all okay
+	for i, h := range append(hr.Before.Drives, hr.After.Drives...) {
+		if h.State != madmin.DriveStateOk {
+			t.Fatalf("Unexpected drive state (%d): %v", i+1, h.State)
+		}
+	}
+}