maildir: implement MoveMessages handling

Implement MoveMessages in the maildir worker. go-maildir supports Move
operations by default, and is functionally equivalent to a OS-level
rename. Creation date of the file is preserved by using Move, which is
used by at least one maildir-to-IMAP synchronizer (isync/mbsync). The
previous move method of copy-and-delete would reset the creation date of
the message, and potentially cause sorting issues in other email
clients.

Signed-off-by: Tim Culverhouse <tim@timculverhouse.com>
Acked-by: Robin Jarry <robin@jarry.cc>

worker/maildir/container.go

@@ -205,3 +205,23 @@ func (c *Container) copyMessage(
 	_, err := src.Copy(dest, key)
 	return err
 }
+
+func (c *Container) MoveAll(dest maildir.Dir, src maildir.Dir, uids []uint32) ([]uint32, error) {
+	var success []uint32
+	for _, uid := range uids {
+		if err := c.moveMessage(dest, src, uid); err != nil {
+			return success, fmt.Errorf("could not move message %d: %w", uid, err)
+		}
+		success = append(success, uid)
+	}
+	return success, nil
+}
+
+func (c *Container) moveMessage(dest maildir.Dir, src maildir.Dir, uid uint32) error {
+	key, ok := c.uids.GetKey(uid)
+	if !ok {
+		return fmt.Errorf("could not find key for message id %d", uid)
+	}
+	err := src.Move(dest, key)
+	return err
+}

worker/maildir/worker.go

@@ -294,6 +294,8 @@ func (w *Worker) handleMessage(msg types.WorkerMessage) error {
 		return w.handleAnsweredMessages(msg)
 	case *types.CopyMessages:
 		return w.handleCopyMessages(msg)
+	case *types.MoveMessages:
+		return w.handleMoveMessages(msg)
 	case *types.AppendMessage:
 		return w.handleAppendMessage(msg)
 	case *types.SearchDirectory:
@@ -655,6 +657,20 @@ func (w *Worker) handleCopyMessages(msg *types.CopyMessages) error {
 	return nil
 }
 
+func (w *Worker) handleMoveMessages(msg *types.MoveMessages) error {
+	dest := w.c.Dir(msg.Destination)
+	moved, err := w.c.MoveAll(dest, *w.selected, msg.Uids)
+	destInfo := w.getDirectoryInfo(msg.Destination)
+	w.worker.PostMessage(&types.DirectoryInfo{
+		Info: destInfo,
+	}, nil)
+	w.worker.PostMessage(&types.MessagesDeleted{
+		Message: types.RespondTo(msg),
+		Uids:    moved,
+	}, nil)
+	return err
+}
+
 func (w *Worker) handleAppendMessage(msg *types.AppendMessage) error {
 	// since we are the "master" maildir process, we can modify the maildir directly
 	dest := w.c.Dir(msg.Destination)