func tcpProbe()

in client.go [574:623]
50 lines of code
8 McCabe index (conditional complexity)

func tcpProbe(test *ethrTest, hop int, hopIP string, hopData *ethrHopData) (error, bool) {
	isLast := false
	c, err := IcmpNewConn(test.remoteIP)
	if err != nil {
		ui.printErr("Failed to create ICMP connection. Error: %v", err)
		return err, isLast
	}
	defer c.Close()
	localPortNum := uint16(8888)
	if gClientPort != 0 {
		localPortNum = gClientPort
	}
	localPortNum += uint16(hop)
	b := make([]byte, 4)
	binary.BigEndian.PutUint16(b[0:], localPortNum)
	remotePortNum, err := strconv.ParseUint(test.remotePort, 10, 16)
	binary.BigEndian.PutUint16(b[2:], uint16(remotePortNum))
	peerAddrChan := make(chan string)
	endTimeChan := make(chan time.Time)
	go func() {
		peerAddr, _, _ := icmpRecvMsg(c, TCP, time.Second*2, hopIP, b, nil, 0)
		endTimeChan <- time.Now()
		peerAddrChan <- peerAddr
	}()
	startTime := time.Now()
	conn, err := ethrDialEx(TCP, test.dialAddr, gLocalIP, localPortNum, hop, int(gTOS))
	if err != nil {
		ui.printDbg("Failed to Dial the connection. Error: %v", err)
	} else {
		conn.Close()
	}
	hopData.sent++
	peerAddr := ""
	endTime := time.Now()
	if err == nil {
		isLast = true
		peerAddr = test.remoteIP
	} else {
		endTime = <-endTimeChan
		peerAddr = <-peerAddrChan
	}
	elapsed := endTime.Sub(startTime)
	if peerAddr == "" || (hopIP != "" && peerAddr != hopIP) {
		hopData.lost++
		ui.printDbg("Neither connection completed, nor ICMP TTL exceeded received.")
		return os.ErrNotExist, isLast
	}
	genHopData(hopData, peerAddr, elapsed)
	return nil, isLast
}