fix: return better error when trying to delete non empty directory object

The posix backend will return ENOTEMPTY when trying to delete a
directory that is not empty. This normally would run successfully
on object systems. So we need to create another non-standard error
for this case. We mainly just don't want to return InternalError
for this case.

Fixes #946

tests/integration/group-tests.go

@@ -519,6 +519,7 @@ func TestPosix(s *S3Conf) {
 	PutObject_name_too_long(s)
 	HeadObject_name_too_long(s)
 	DeleteObject_name_too_long(s)
+	DeleteObject_directory_not_empty(s)
 	// posix specific versioning tests
 	if !s.versioningEnabled {
 		TestVersioningDisabled(s)
@@ -770,6 +771,7 @@ func GetIntTests() IntTests {
 		"ListObjectVersions_VD_success":                                       ListObjectVersions_VD_success,
 		"DeleteObject_non_existing_object":                                    DeleteObject_non_existing_object,
 		"DeleteObject_directory_object_noslash":                               DeleteObject_directory_object_noslash,
+		"DeleteObject_directory_not_empty":                                    DeleteObject_directory_not_empty,
 		"DeleteObject_name_too_long":                                          DeleteObject_name_too_long,
 		"DeleteObject_non_existing_dir_object":                                DeleteObject_non_existing_dir_object,
 		"DeleteObject_success":                                                DeleteObject_success,

tests/integration/tests.go

@@ -4749,6 +4749,37 @@ func DeleteObject_directory_object_noslash(s *S3Conf) error {
 	})
 }
 
+func DeleteObject_directory_not_empty(s *S3Conf) error {
+	testName := "DeleteObject_directory_not_empty"
+	return actionHandler(s, testName, func(s3client *s3.Client, bucket string) error {
+		obj := "dir/my-obj"
+		ctx, cancel := context.WithTimeout(context.Background(), shortTimeout)
+		_, err := s3client.PutObject(ctx, &s3.PutObjectInput{
+			Bucket: &bucket,
+			Key:    &obj,
+		})
+		cancel()
+		if err != nil {
+			return err
+		}
+
+		obj = "dir/"
+		ctx, cancel = context.WithTimeout(context.Background(), shortTimeout)
+		_, err = s3client.DeleteObject(ctx, &s3.DeleteObjectInput{
+			Bucket: &bucket,
+			Key:    &obj,
+		})
+		cancel()
+		// object servers will return no error, but the posix backend returns
+		// a non-standard directory not empty. This test is a posix only test
+		// to validate the specific error response.
+		if err := checkApiErr(err, s3err.GetAPIError(s3err.ErrDirectoryNotEmpty)); err != nil {
+			return err
+		}
+		return nil
+	})
+}
+
 func DeleteObject_non_existing_dir_object(s *S3Conf) error {
 	testName := "DeleteObject_non_existing_dir_object"
 	return actionHandler(s, testName, func(s3client *s3.Client, bucket string) error {