func ExamplePrivateHandle() {
	dns.PrivateHandle("APAIR", TypeAPAIR, NewAPAIR)
	defer dns.PrivateHandleRemove(TypeAPAIR)

	rr, err := dns.NewRR("miek.nl. APAIR (1.2.3.4    1.2.3.5)")
	if err != nil {
		log.Fatal("could not parse APAIR record: ", err)
	}
	fmt.Println(rr)
	// Output: miek.nl.	3600	IN	APAIR	1.2.3.4 1.2.3.5

	m := new(dns.Msg)
	m.Id = 12345
	m.SetQuestion("miek.nl.", TypeAPAIR)
	m.Answer = append(m.Answer, rr)

	fmt.Println(m)
	// ;; opcode: QUERY, status: NOERROR, id: 12345
	// ;; flags: rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
	//
	// ;; QUESTION SECTION:
	// ;miek.nl.	IN	 APAIR
	//
	// ;; ANSWER SECTION:
	// miek.nl.	3600	IN	APAIR	1.2.3.4 1.2.3.5
}

// parsePacket is used to parse an incoming packet
func (s *Server) parsePacket(packet []byte, from net.Addr) error {
	var msg dns.Msg
	if err := msg.Unpack(packet); err != nil {
		log.Printf("[ERR] mdns: Failed to unpack packet: %v", err)
		return err
	}
	return s.handleQuery(&msg, from)
}

// sendQuery is used to multicast a query out
func (c *client) sendQuery(q *dns.Msg) error {
	buf, err := q.Pack()
	if err != nil {
		return err
	}
	if c.ipv4UnicastConn != nil {
		c.ipv4UnicastConn.WriteToUDP(buf, ipv4Addr)
	}
	if c.ipv6UnicastConn != nil {
		c.ipv6UnicastConn.WriteToUDP(buf, ipv6Addr)
	}
	return nil
}

// sendResponse is used to send a response packet
func (s *Server) sendResponse(resp *dns.Msg, from net.Addr, unicast bool) error {
	// TODO(reddaly): Respect the unicast argument, and allow sending responses
	// over multicast.
	buf, err := resp.Pack()
	if err != nil {
		return err
	}

	// Determine the socket to send from
	addr := from.(*net.UDPAddr)
	if addr.IP.To4() != nil {
		_, err = s.ipv4List.WriteToUDP(buf, addr)
		return err
	} else {
		_, err = s.ipv6List.WriteToUDP(buf, addr)
		return err
	}
}

// Retrieve the MX records for miek.nl.
func ExampleMX() {
	config, _ := dns.ClientConfigFromFile("/etc/resolv.conf")
	c := new(dns.Client)
	m := new(dns.Msg)
	m.SetQuestion("miek.nl.", dns.TypeMX)
	m.RecursionDesired = true
	r, _, err := c.Exchange(m, config.Servers[0]+":"+config.Port)
	if err != nil {
		return
	}
	if r.Rcode != dns.RcodeSuccess {
		return
	}
	for _, a := range r.Answer {
		if mx, ok := a.(*dns.MX); ok {
			fmt.Printf("%s\n", mx.String())
		}
	}
}

// recv is used to receive until we get a shutdown
func (c *client) recv(l *net.UDPConn, msgCh chan *dns.Msg) {
	if l == nil {
		return
	}
	buf := make([]byte, 65536)
	for !c.closed {
		n, err := l.Read(buf)
		if err != nil {
			log.Printf("[ERR] mdns: Failed to read packet: %v", err)
			continue
		}
		msg := new(dns.Msg)
		if err := msg.Unpack(buf[:n]); err != nil {
			log.Printf("[ERR] mdns: Failed to unpack packet: %v", err)
			continue
		}
		select {
		case msgCh <- msg:
		case <-c.closedCh:
			return
		}
	}
}

// Retrieve the DNSKEY records of a zone and convert them
// to DS records for SHA1, SHA256 and SHA384.
func ExampleDS(zone string) {
	config, _ := dns.ClientConfigFromFile("/etc/resolv.conf")
	c := new(dns.Client)
	m := new(dns.Msg)
	if zone == "" {
		zone = "miek.nl"
	}
	m.SetQuestion(dns.Fqdn(zone), dns.TypeDNSKEY)
	m.SetEdns0(4096, true)
	r, _, err := c.Exchange(m, config.Servers[0]+":"+config.Port)
	if err != nil {
		return
	}
	if r.Rcode != dns.RcodeSuccess {
		return
	}
	for _, k := range r.Answer {
		if key, ok := k.(*dns.DNSKEY); ok {
			for _, alg := range []uint8{dns.SHA1, dns.SHA256, dns.SHA384} {
				fmt.Printf("%s; %d\n", key.ToDS(alg).String(), key.Flags)
			}
		}
	}
}

// query is used to perform a lookup and stream results
func (c *client) query(params *QueryParam) error {
	// Create the service name
	serviceAddr := fmt.Sprintf("%s.%s.", trimDot(params.Service), trimDot(params.Domain))

	// Start listening for response packets
	msgCh := make(chan *dns.Msg, 32)
	go c.recv(c.ipv4UnicastConn, msgCh)
	go c.recv(c.ipv6UnicastConn, msgCh)
	go c.recv(c.ipv4MulticastConn, msgCh)
	go c.recv(c.ipv6MulticastConn, msgCh)

	// Send the query
	m := new(dns.Msg)
	m.SetQuestion(serviceAddr, dns.TypePTR)
	// RFC 6762, section 18.12.  Repurposing of Top Bit of qclass in Question
	// Section
	//
	// In the Question Section of a Multicast DNS query, the top bit of the qclass
	// field is used to indicate that unicast responses are preferred for this
	// particular question.  (See Section 5.4.)
	if params.WantUnicastResponse {
		m.Question[0].Qclass |= 1 << 15
	}
	m.RecursionDesired = false
	if err := c.sendQuery(m); err != nil {
		return err
	}

	// Map the in-progress responses
	inprogress := make(map[string]*ServiceEntry)

	// Listen until we reach the timeout
	finish := time.After(params.Timeout)
	for {
		select {
		case resp := <-msgCh:
			var inp *ServiceEntry
			for _, answer := range append(resp.Answer, resp.Extra...) {
				// TODO(reddaly): Check that response corresponds to serviceAddr?
				switch rr := answer.(type) {
				case *dns.PTR:
					// Create new entry for this
					inp = ensureName(inprogress, rr.Ptr)

				case *dns.SRV:
					// Check for a target mismatch
					if rr.Target != rr.Hdr.Name {
						alias(inprogress, rr.Hdr.Name, rr.Target)
					}

					// Get the port
					inp = ensureName(inprogress, rr.Hdr.Name)
					inp.Host = rr.Target
					inp.Port = int(rr.Port)

				case *dns.TXT:
					// Pull out the txt
					inp = ensureName(inprogress, rr.Hdr.Name)
					inp.Info = strings.Join(rr.Txt, "|")
					inp.hasTXT = true

				case *dns.A:
					// Pull out the IP
					inp = ensureName(inprogress, rr.Hdr.Name)
					inp.Addr = rr.A // @Deprecated
					inp.AddrV4 = rr.A

				case *dns.AAAA:
					// Pull out the IP
					inp = ensureName(inprogress, rr.Hdr.Name)
					inp.Addr = rr.AAAA // @Deprecated
					inp.AddrV6 = rr.AAAA
				}
			}

			if inp == nil {
				continue
			}

			// Check if this entry is complete
			if inp.complete() {
				if inp.sent {
					continue
				}
				inp.sent = true
				select {
				case params.Entries <- inp:
				default:
				}
			} else {
				// Fire off a node specific query
				m := new(dns.Msg)
				m.SetQuestion(inp.Name, dns.TypePTR)
				m.RecursionDesired = false
				if err := c.sendQuery(m); err != nil {
					log.Printf("[ERR] mdns: Failed to query instance %s: %v", inp.Name, err)
				}
			}
		case <-finish:
//.........这里部分代码省略.........