message: fix data decryption in UDP ServerClient
diff: @@ -99,6 +99,9 @@ impl ServerClient {
  let recv_n = try_timeout(self.socket.recv(&mut recv_buf), Some(timeout)).await?;
  let mut cur = if let CipherCategory::None = self.method.category() {
  + recv_buf.truncate(recv_n);
  + Cursor::new(recv_buf)
  + } else {
  let decrypt_buf = match decrypt_payload(context, self.method, &self.key, &recv_buf[..recv_n])? {
  None => {
  error!("UDP packet too short, received length {}", recv_n);
  @@ -108,9 +111,6 @@ impl ServerClient {
  Some(b) => b,
  };
  Cursor::new(decrypt_buf)
  - } else {
  - recv_buf.truncate(recv_n);
  - Cursor::new(recv_buf)
  };
  // SERVER -> CLIENT protocol: ADDRESS + PAYLOAD
  