i learned

src/engine.rs

@@ -134,8 +134,10 @@ impl InputEngine for InputEngineUDP {
 impl InputEngineUDP {
    fn _get(&mut self) -> Result<Vec<char>, std::io::Error> {
       let mut buf = [0; 128];
-      let socket = self.last_socket.ok_or(std::io::Error::new(std::io::ErrorKind::Other, "no socket"))?;
-      let (amt, _) = socket.recv_from(&mut buf)?;
+      if !self.last_socket.is_some() {
+         return Ok(Vec::<char>::new());
+      }
+      let (amt, _) = self.last_socket.as_ref().unwrap().recv_from(&mut buf)?;
       let buf = &mut buf[..amt];
       return Ok(std::str::from_utf8(buf).unwrap().chars().collect());
    }