code: func (t *Tx) CompletedPacket() (id uint64, ok bool) {
  	for {
  		b := t.rx.Pull()
  		if b == nil {
  			return 0, false
  		}
  
  		if len(b) != 8 {
  			t.rx.Flush()
  			log.Printf("Ignoring completed packet: size (%v) is less than expected (%v)", len(b), 8)
  			continue
  		}
  
  		v := binary.LittleEndian.Uint64(b)
  
  		t.rx.Flush()
  
  		return v, true
  	}
  }
docs: // CompletedPacket returns the id of the last completed transmission. The
  // returned id, if any, refers to a value passed on a previous call to
  // Enqueue().