add check for isdir in readdir

libs/filer/dbfs_client.go

@@ -222,6 +222,10 @@ func (w *DbfsClient) ReadDir(ctx context.Context, name string) ([]fs.DirEntry, e
 		return nil, err
 	}
 
+	if len(res.Files) == 1 && !res.Files[0].IsDir && res.Files[0].Path == absPath {
+		return nil, NotADirectory{absPath}
+	}
+
 	info := make([]fs.DirEntry, len(res.Files))
 	for i, v := range res.Files {
 		info[i] = dbfsDirEntry{dbfsFileInfo: dbfsFileInfo{fi: v}}

libs/filer/filer.go

@@ -2,6 +2,7 @@ package filer
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"io"
 	"io/fs"
@@ -50,6 +51,20 @@ func (err NoSuchDirectoryError) Is(other error) bool {
 	return other == fs.ErrNotExist
 }
 
+var ErrNotADirectory = errors.New("not a directory")
+
+type NotADirectory struct {
+	path string
+}
+
+func (err NotADirectory) Error() string {
+	return fmt.Sprintf("%s is not a directory", err.path)
+}
+
+func (err NotADirectory) Is(other error) bool {
+	return other == ErrNotADirectory
+}
+
 // Filer is used to access files in a workspace.
 // It has implementations for accessing files in WSFS and in DBFS.
 type Filer interface {

libs/filer/workspace_files_client.go

@@ -222,6 +222,12 @@ func (w *WorkspaceFilesClient) ReadDir(ctx context.Context, name string) ([]fs.D
 	objects, err := w.workspaceClient.Workspace.ListAll(ctx, workspace.ListWorkspaceRequest{
 		Path: absPath,
 	})
+
+	// TODO: add integration test for this
+	if len(objects) == 1 && objects[0].Path == absPath {
+		return nil, NotADirectory{absPath}
+	}
+
 	if err != nil {
 		// If we got an API error we deal with it below.
 		var aerr *apierr.APIError