fix(fs): Cache data in stdinfs (#2288)

Signed-off-by: Dave Henderson <[email protected]>

internal/datafs/stdinfs.go

@@ -18,7 +18,8 @@ func NewStdinFS(_ *url.URL) (fs.FS, error) {
 }
 
 type stdinFS struct {
-	ctx context.Context
+	ctx  context.Context
+	data []byte
 }
 
 //nolint:gochecknoglobals
@@ -46,9 +47,15 @@ func (f *stdinFS) Open(name string) (fs.File, error) {
 		}
 	}
 
-	stdin := StdinFromContext(f.ctx)
+	if err := f.readData(); err != nil {
+		return nil, &fs.PathError{
+			Op:   "open",
+			Path: name,
+			Err:  err,
+		}
+	}
 
-	return &stdinFile{name: name, body: stdin}, nil
+	return &stdinFile{name: name, body: bytes.NewReader(f.data)}, nil
 }
 
 func (f *stdinFS) ReadFile(name string) ([]byte, error) {
@@ -60,9 +67,32 @@ func (f *stdinFS) ReadFile(name string) ([]byte, error) {
 		}
 	}
 
+	if err := f.readData(); err != nil {
+		return nil, &fs.PathError{
+			Op:   "readFile",
+			Path: name,
+			Err:  err,
+		}
+	}
+
+	return f.data, nil
+}
+
+func (f *stdinFS) readData() error {
+	if f.data != nil {
+		return nil
+	}
+
 	stdin := StdinFromContext(f.ctx)
 
-	return io.ReadAll(stdin)
+	b, err := io.ReadAll(stdin)
+	if err != nil {
+		return err
+	}
+
+	f.data = b
+
+	return nil
 }
 
 type stdinFile struct {

internal/datafs/stdinfs_test.go

@@ -99,6 +99,57 @@ func TestStdinFS(t *testing.T) {
 	_, err = f.Read(p)
 	require.Error(t, err)
 	require.ErrorIs(t, err, io.EOF)
+
+	t.Run("open/read multiple times", func(t *testing.T) {
+		ctx := ContextWithStdin(context.Background(), bytes.NewReader(content))
+		fsys = fsimpl.WithContextFS(ctx, fsys)
+
+		for i := 0; i < 3; i++ {
+			f, err := fsys.Open("foo")
+			require.NoError(t, err)
+
+			b, err := io.ReadAll(f)
+			require.NoError(t, err)
+			require.Equal(t, content, b, "read %d failed", i)
+		}
+	})
+
+	t.Run("readFile multiple times", func(t *testing.T) {
+		ctx := ContextWithStdin(context.Background(), bytes.NewReader(content))
+		fsys = fsimpl.WithContextFS(ctx, fsys)
+
+		for i := 0; i < 3; i++ {
+			b, err := fs.ReadFile(fsys, "foo")
+			require.NoError(t, err)
+			require.Equal(t, content, b, "read %d failed", i)
+		}
+	})
+
+	t.Run("open errors", func(t *testing.T) {
+		ctx := ContextWithStdin(context.Background(), &errorReader{err: fs.ErrPermission})
+
+		fsys, err := NewStdinFS(u)
+		require.NoError(t, err)
+		assert.IsType(t, &stdinFS{}, fsys)
+
+		fsys = fsimpl.WithContextFS(ctx, fsys)
+
+		_, err = fsys.Open("foo")
+		require.ErrorIs(t, err, fs.ErrPermission)
+	})
+
+	t.Run("readFile errors", func(t *testing.T) {
+		ctx := ContextWithStdin(context.Background(), &errorReader{err: fs.ErrPermission})
+
+		fsys, err := NewStdinFS(u)
+		require.NoError(t, err)
+		assert.IsType(t, &stdinFS{}, fsys)
+
+		fsys = fsimpl.WithContextFS(ctx, fsys)
+
+		_, err = fs.ReadFile(fsys, "foo")
+		require.ErrorIs(t, err, fs.ErrPermission)
+	})
 }
 
 type errorReader struct {