streamdata: edit metadata

This edits metadata in a robust way.

Signed-off-by: Yonah <contrib@gensokyo.uk>

streamdata.go

@@ -224,6 +224,46 @@ func (c *Channel) Add(ident *Ident, f func(v *VOD, w io.Writer) error) error {
 	return nil
 }
 
+// Edit loads a [VOD] by its [Ident], and writes the modified [VOD] back to the
+// on-disk representation.
+func (c *Channel) Edit(ident *Ident, f func(v *VOD) error) error {
+	v, err := c.Load(ident)
+	if err != nil {
+		return err
+	}
+
+	err = f(v)
+	if err != nil {
+		return err
+	}
+
+	pathname := path.Join(
+		channelPathVOD,
+		"."+ident.String(),
+	)
+
+	var w *os.File
+	if w, err = c.root.OpenFile(
+		pathname,
+		os.O_WRONLY|os.O_CREATE|os.O_EXCL,
+		0444,
+	); err != nil {
+		return err
+	} else if err = json.NewEncoder(w).Encode(v); err != nil {
+		_ = w.Close()
+		_ = c.root.Remove(pathname)
+		return err
+	} else if err = w.Close(); err != nil {
+		_ = c.root.Remove(pathname)
+		return err
+	} else {
+		return c.root.Rename(pathname, path.Join(
+			channelPathVOD,
+			ident.String(),
+		))
+	}
+}
+
 // Path returns a pathname by [Ident].
 func (c *Channel) Path(ident *Ident) string {
 	return path.Join(

streamdata_test.go

@@ -356,6 +356,28 @@ func TestChannel(t *testing.T) {
 		t.Errorf("(rf) Add: %#v", data)
 	}
 
+	wantVODEdit := streamdata.VOD{
+		Title:    "edit\x00",
+		Date:     time.Unix(0xdeadbeef, 0).UTC(),
+		Category: "\t\x00",
+		Mirror:   "https://satori.hifuu.internal/edit.mp4\x00",
+	}
+	if err := c.Edit(&streamdata.Ident{Channel: 0xcafe}, func(v *streamdata.VOD) error {
+		if *v != (streamdata.VOD{}) {
+			t.Errorf("Edit: v = %#v", v)
+		}
+
+		*v = wantVODEdit
+		return nil
+	}); err != nil {
+		t.Fatalf("Edit: error = %v", err)
+	}
+	if gotVODEdit, err := c.Load(&streamdata.Ident{Channel: 0xcafe}); err != nil {
+		t.Fatalf("(edit) Load: error = %v", err)
+	} else if *gotVODEdit != wantVODEdit {
+		t.Errorf("Edit: %#v, want %#v", *gotVODEdit, wantVODEdit)
+	}
+
 	if err := os.Chmod(path.Join(d, "vod", wantIdent), 0); err != nil {
 		t.Fatal(err)
 	}