actually copy data to file

server/server.go

@@ -201,6 +201,21 @@ func (session *Session) Data(r io.Reader) error {
 		}
 	}()
 
+	n, err := io.Copy(f, r)
+	if err != nil {
+		session.log.Error("failed to receive message data to temporary data file", zap.Error(err))
+
+		return ErrBadGateway
+	}
+
+	session.log.Sugar().Debugf("received message with %d bytes", n)
+
+	if _, err := f.Seek(0, 0); err != nil {
+		session.log.Error("failed to seek to beginning of temporary data file", zap.Error(err))
+
+		return ErrBadGateway
+	}
+
 	_, action, err := session.rspam.BodyReadFrom(f)
 	if err != nil {
 		session.log.Error("rspamd failed to process message body", zap.Error(err))