() recv_internal(int my_balance, int msg_value, cell in_msg_full, slice in_msg_body) impure {
  if (in_msg_body.slice_empty?()) { ;; ignore empty messages
    return ();
  }

  slice cs = in_msg_full.begin_parse();
  int flags = cs~load_uint(4);
  if (flags & 1) {
    on_bounce(in_msg_body);
    return ();
  }
  slice sender_address = cs~load_msg_addr();
  cs~load_msg_addr(); ;; skip dst
  cs~load_coins(); ;; skip value
  cs~skip_bits(1); ;; skip extracurrency collection
  cs~load_coins(); ;; skip ihr_fee
  int fwd_fee = muldiv(cs~load_coins(), 3, 2); ;; we use message fwd_fee for estimation of forward_payload costs

  int op = in_msg_body~load_uint(32);

  if (op == op::transfer()) { ;; outgoing transfer
    send_tokens(in_msg_body, sender_address, msg_value, fwd_fee);
    return ();
  }

  if (op == op::internal_transfer()) { ;; incoming transfer
    receive_tokens(in_msg_body, sender_address, my_balance, fwd_fee, msg_value);
    return ();
  }

  if (op == op::burn()) { ;; burn
    burn_tokens(in_msg_body, sender_address, msg_value, fwd_fee);
    return ();
  }

  throw(0xffff);
}