memfs: Reject ReadDir calls on regular files

memfs/memory.go

@@ -171,6 +171,9 @@ func (fs *Memory) ReadDir(path string) ([]gofs.DirEntry, error) {
 				return fs.ReadDir(target)
 			}
 		}
+		if !f.mode.IsDir() {
+			return nil, &os.PathError{Op: "readdir", Path: path, Err: syscall.ENOTDIR}
+		}
 	} else {
 		return nil, &os.PathError{Op: "open", Path: path, Err: syscall.ENOENT}
 	}

memfs/memory_test.go

@@ -137,6 +137,22 @@ func TestNotFound(t *testing.T) {
 	assert.ErrorIs(t, err, os.ErrNotExist)
 }
 
+func TestReadDirSymlink(t *testing.T) {
+	fs := New()
+	require.NoError(t, util.WriteFile(fs, "file", nil, 0o644))
+	require.NoError(t, fs.MkdirAll("dir", 0o755))
+	require.NoError(t, fs.Symlink("file", "file-link"))
+	require.NoError(t, fs.Symlink("dir", "dir-link"))
+
+	entries, err := fs.ReadDir("file-link")
+	require.ErrorIs(t, err, syscall.ENOTDIR)
+	assert.Nil(t, entries)
+
+	entries, err = fs.ReadDir("dir-link")
+	require.NoError(t, err)
+	assert.Empty(t, entries)
+}
+
 func TestTruncateAppend(t *testing.T) {
 	fs := New()
 	err := util.WriteFile(fs, "truncate_append", []byte("file-content"), 0o666)

test/dir_test.go

@@ -169,6 +169,21 @@ func TestDir_ReadDir(t *testing.T) {
 	})
 }
 
+func TestDir_ReadDirFile(t *testing.T) {
+	eachDirFS(t, func(t *testing.T, fs dirFS) {
+		t.Helper()
+		err := util.WriteFile(fs, "dir/file", []byte("content"), 0o644)
+		require.NoError(t, err)
+
+		entries, err := fs.ReadDir("dir/file")
+		require.Error(t, err)
+		assert.Nil(t, entries)
+
+		var pathErr *os.PathError
+		require.ErrorAs(t, err, &pathErr)
+	})
+}
+
 func TestDir_ReadDirNested(t *testing.T) {
 	eachDirFS(t, func(t *testing.T, fs dirFS) {
 		t.Helper()