/// Will very likely call send_data on the descriptor passed in (or a descriptor handed into
/// new_*_connection) before returning. Thus, be very careful with reentrancy issues! The
/// invariants around calling write_event in case a write did not fully complete must still
/// hold. Note that this function will often call send_data on many peers before returning, not
/// just this peer!
/// Will very likely call send_data on the descriptor passed in (or a descriptor handed into
/// new_*_connection) before returning. Thus, be very careful with reentrancy issues! The
/// invariants around calling write_event in case a write did not fully complete must still
/// hold. Note that this function will often call send_data on many peers before returning, not
/// just this peer!