fix: listobjects internal server error for prefix not directory

We need to treat a prefix that has a parent component as a file
instead of a directory in the filesystem as a non existing prefix
instead of an internal server error. This error was caused
because we were not handling ENOTDIR within the fs walk.

Fixes #949

backend/walk.go

@@ -21,6 +21,7 @@ import (
 	"io/fs"
 	"sort"
 	"strings"
+	"syscall"
 
 	"github.com/aws/aws-sdk-go-v2/service/s3/types"
 	"github.com/versity/versitygw/s3response"
@@ -231,7 +232,7 @@ func Walk(ctx context.Context, fileSystem fs.FS, prefix, delimiter, marker strin
 	})
 	if err != nil {
 		// suppress file not found caused by user's prefix
-		if errors.Is(err, fs.ErrNotExist) {
+		if errors.Is(err, fs.ErrNotExist) || errors.Is(err, syscall.ENOTDIR) {
 			return WalkResults{}, nil
 		}
 		return WalkResults{}, err

tests/integration/group-tests.go

@@ -201,6 +201,7 @@ func TestListObjectsV2(s *S3Conf) {
 	ListObjectsV2_truncated_common_prefixes(s)
 	ListObjectsV2_all_objs_max_keys(s)
 	ListObjectsV2_list_all_objs(s)
+	ListObjectsV2_invalid_parent_prefix(s)
 }
 
 // VD stands for Versioning Disabled
@@ -768,6 +769,7 @@ func GetIntTests() IntTests {
 		"ListObjectsV2_truncated_common_prefixes":                             ListObjectsV2_truncated_common_prefixes,
 		"ListObjectsV2_all_objs_max_keys":                                     ListObjectsV2_all_objs_max_keys,
 		"ListObjectsV2_list_all_objs":                                         ListObjectsV2_list_all_objs,
+		"ListObjectsV2_invalid_parent_prefix":                                 ListObjectsV2_invalid_parent_prefix,
 		"ListObjectVersions_VD_success":                                       ListObjectVersions_VD_success,
 		"DeleteObject_non_existing_object":                                    DeleteObject_non_existing_object,
 		"DeleteObject_directory_object_noslash":                               DeleteObject_directory_object_noslash,

tests/integration/tests.go

@@ -4656,6 +4656,45 @@ func ListObjectsV2_list_all_objs(s *S3Conf) error {
 	})
 }
 
+func ListObjectsV2_invalid_parent_prefix(s *S3Conf) error {
+	testName := "ListObjectsV2_invalid_parent_prefix"
+	return actionHandler(s, testName, func(s3client *s3.Client, bucket string) error {
+		_, err := putObjects(s3client, []string{"file"}, bucket)
+		if err != nil {
+			return err
+		}
+
+		delim, maxKeys := "/", int32(100)
+		prefix := "file/file/file"
+
+		ctx, cancel := context.WithTimeout(context.Background(), shortTimeout)
+		out, err := s3client.ListObjectsV2(ctx, &s3.ListObjectsV2Input{
+			Bucket:    &bucket,
+			Delimiter: &delim,
+			MaxKeys:   &maxKeys,
+			Prefix:    &prefix,
+		})
+		cancel()
+		if err != nil {
+			return err
+		}
+
+		if len(out.CommonPrefixes) > 0 {
+			return fmt.Errorf("expected the common prefixes to be %v, instead got %v", []string{""}, out.CommonPrefixes)
+		}
+		if *out.MaxKeys != maxKeys {
+			return fmt.Errorf("expected the max-keys to be %v, instead got %v", maxKeys, *out.MaxKeys)
+		}
+		if *out.Delimiter != delim {
+			return fmt.Errorf("expected the delimiter to be %v, instead got %v", delim, *out.Delimiter)
+		}
+		if len(out.Contents) > 0 {
+			return fmt.Errorf("expected the objects to be %v, instead got %v", []types.Object{}, out.Contents)
+		}
+		return nil
+	})
+}
+
 func ListObjectVersions_VD_success(s *S3Conf) error {
 	testName := "ListObjectVersions_VD_success"
 	return actionHandler(s, testName, func(s3client *s3.Client, bucket string) error {