a

internal/storage/storage.go

@@ -232,6 +232,42 @@ func (s *Store) GetBodyParts(ctx context.Context, userID, messageID int64) (*Bod
 	return bp, nil
 }
 
+// GetAttachmentData decrypts and returns the bytes of the n-th attachment (0-based) for a message.
+// Also returns filename and content-type. Returns an error when the attachment does not exist.
+func (s *Store) GetAttachmentData(ctx context.Context, userID, messageID int64, n int) (data []byte, filename, contentType string, err error) {
+	att, err := s.db.GetAttachmentByIndex(ctx, messageID, n)
+	if err != nil {
+		return nil, "", "", fmt.Errorf("storage: get attachment index: %w", err)
+	}
+	if att == nil {
+		return nil, "", "", fmt.Errorf("storage: attachment %d not found for message %d", n, messageID)
+	}
+
+	key, err := s.crypt.DeriveKey("messages", userID)
+	if err != nil {
+		return nil, "", "", fmt.Errorf("storage: derive key: %w", err)
+	}
+
+	var encData []byte
+	if att.DataPath != "" {
+		encData, err = os.ReadFile(att.DataPath)
+		if err != nil {
+			return nil, "", "", fmt.Errorf("storage: read attachment file: %w", err)
+		}
+	} else {
+		encData = att.DataEnc
+	}
+	if len(encData) == 0 {
+		return nil, "", "", fmt.Errorf("storage: attachment data empty")
+	}
+
+	plain, err := crypto.Decrypt(key, encData)
+	if err != nil {
+		return nil, "", "", fmt.Errorf("storage: decrypt attachment: %w", err)
+	}
+	return plain, att.Filename, att.ContentType, nil
+}
+
 // parseMIME walks a raw RFC822 message and extracts body parts and attachments.
 func parseMIME(raw []byte) (bodyText, bodyHTML string, attachments []parsedAttachment) {
 	m, err := mail.ReadMessage(bytes.NewReader(raw))