Golang Msg.RecursionDesired方法代码示例

// Performs the actual query by service name (browse) or service instance name (lookup),
// start response listeners goroutines and loops over the entries channel.
func (c *client) query(params *LookupParams) error {
	var serviceName, serviceInstanceName string
	serviceName = fmt.Sprintf("%s.%s.", trimDot(params.Service), trimDot(params.Domain))
	if params.Instance != "" {
		serviceInstanceName = fmt.Sprintf("%s.%s", params.Instance, serviceName)
	}

	// send the query
	m := new(dns.Msg)
	if serviceInstanceName != "" {
		m.Question = []dns.Question{
			dns.Question{serviceInstanceName, dns.TypeSRV, dns.ClassINET},
			dns.Question{serviceInstanceName, dns.TypeTXT, dns.ClassINET},
		}
		m.RecursionDesired = false
	} else {
		m.SetQuestion(serviceName, dns.TypePTR)
		m.RecursionDesired = false
	}
	if err := c.sendQuery(m); err != nil {
		return err
	}

	return nil
}

func main() {
	if len(os.Args) <= 1 {
		log.Printf("Usage: %s domain", os.Args[0])
		os.Exit(1)
	}

	config, _ := dns.ClientConfigFromFile("/etc/resolv.conf")
	c := new(dns.Client)

	m := new(dns.Msg)
	m.SetQuestion(dns.Fqdn(os.Args[1]), dns.TypeMX)
	m.RecursionDesired = true

	r, _, err := c.Exchange(m, net.JoinHostPort(config.Servers[0], config.Port))
	if r == nil {
		log.Fatalf("*** error: %s\n", err.Error())
	}

	if r.Rcode != dns.RcodeSuccess {
		log.Fatalf(" *** invalid answer name %s after MX query for %s\n", os.Args[1], os.Args[1])
	}
	// Stuff must be in the answer section
	for _, a := range r.Answer {
		fmt.Printf("%v\n", a)
	}
}

// perform a DNS query and assert the reply code, number or answers, etc
func assertExchange(t *testing.T, z string, ty uint16, minAnswers int, maxAnswers int, expErr int) *dns.Msg {
	c := new(dns.Client)
	c.UDPSize = testUDPBufSize
	m := new(dns.Msg)
	m.RecursionDesired = true
	m.SetQuestion(z, ty)
	m.SetEdns0(testUDPBufSize, false) // we don't want to play with truncation here...

	r, _, err := c.Exchange(m, fmt.Sprintf("127.0.0.1:%d", testPort))
	t.Logf("Response:\n%+v\n", r)
	wt.AssertNoErr(t, err)
	if minAnswers == 0 && maxAnswers == 0 {
		wt.AssertStatus(t, r.Rcode, expErr, "DNS response code")
	} else {
		wt.AssertStatus(t, r.Rcode, dns.RcodeSuccess, "DNS response code")
	}
	answers := len(r.Answer)
	if minAnswers >= 0 && answers < minAnswers {
		wt.Fatalf(t, "Number of answers >= %d", minAnswers)
	}
	if maxAnswers >= 0 && answers > maxAnswers {
		wt.Fatalf(t, "Number of answers <= %d", maxAnswers)
	}
	return r
}

func (self *DnsResolver) lookupHost(host string, triesLeft int) ([]net.IP, error) {
	m1 := new(dns.Msg)
	m1.Id = dns.Id()
	m1.RecursionDesired = true
	m1.Question = make([]dns.Question, 1)
	m1.Question[0] = dns.Question{dns.Fqdn(host), dns.TypeA, dns.ClassINET}
	in, err := dns.Exchange(m1, self.Servers[self.r.Intn(len(self.Servers))])

	result := []net.IP{}

	if err != nil {
		if strings.HasSuffix(err.Error(), "i/o timeout") && triesLeft > 0 {
			triesLeft -= 1
			return self.lookupHost(host, triesLeft)
		} else {
			return result, err
		}
	}

	if in != nil && in.Rcode != dns.RcodeSuccess {
		return result, errors.New(dns.RcodeToString[in.Rcode])
	}

	for _, record := range in.Answer {
		if t, ok := record.(*dns.A); ok {
			result = append(result, t.A)
		}
	}
	return result, err
}

func (c *Client) Discover(domain string, cb func(*dns.Msg)) {
	m := new(dns.Msg)
	m.SetQuestion(dns.Fqdn(domain), dns.TypePTR)
	m.RecursionDesired = true

	addr := &net.UDPAddr{
		IP:   net.ParseIP("224.0.0.251"),
		Port: 5353,
	}

	conn, err := net.ListenMulticastUDP("udp4", nil, addr)

	if err != nil {
		panic(err)
	}

	defer conn.Close()
	c.conn = conn

	out, err := m.Pack()

	if err != nil {
		panic(err)
	}

	_, err = conn.WriteToUDP(out, addr)
	if err != nil {
		panic(err)
	}

	c.handleReceiveMsg(domain, cb)
}

// Perform a DNS query and assert the reply code, number or answers, etc
func assertExchange(t *testing.T, z string, ty uint16, port int, minAnswers int, maxAnswers int, expErr int) (*dns.Msg, *dns.Msg) {
	require.NotEqual(t, 0, port, "invalid DNS server port")

	c := &dns.Client{
		UDPSize: testUDPBufSize,
	}

	m := new(dns.Msg)
	m.RecursionDesired = true
	m.SetQuestion(z, ty)
	m.SetEdns0(testUDPBufSize, false) // we don't want to play with truncation here...

	lstAddr := fmt.Sprintf("127.0.0.1:%d", port)
	r, _, err := c.Exchange(m, lstAddr)
	t.Logf("Response from '%s':\n%+v\n", lstAddr, r)
	if err != nil {
		t.Errorf("Error when querying DNS server at %s: %s", lstAddr, err)
	}
	require.NoError(t, err)
	if minAnswers == 0 && maxAnswers == 0 {
		require.Equal(t, expErr, r.Rcode, "DNS response code")
	} else {
		require.Equal(t, dns.RcodeSuccess, r.Rcode, "DNS response code")
	}
	answers := len(r.Answer)
	if minAnswers >= 0 && answers < minAnswers {
		require.FailNow(t, fmt.Sprintf("Number of answers >= %d", minAnswers))
	}
	if maxAnswers >= 0 && answers > maxAnswers {
		require.FailNow(t, fmt.Sprintf("Number of answers <= %d", maxAnswers))
	}
	return m, r
}

// dnsQuery will query a nameserver, iterating through the supplied servers as it retries
// The nameserver should include a port, to facilitate testing where we talk to a mock dns server.
func dnsQuery(fqdn string, rtype uint16, nameservers []string, recursive bool) (in *dns.Msg, err error) {
	m := new(dns.Msg)
	m.SetQuestion(fqdn, rtype)
	m.SetEdns0(4096, false)

	if !recursive {
		m.RecursionDesired = false
	}

	// Will retry the request based on the number of servers (n+1)
	for i := 1; i <= len(nameservers)+1; i++ {
		ns := nameservers[i%len(nameservers)]
		udp := &dns.Client{Net: "udp", Timeout: DNSTimeout}
		in, _, err = udp.Exchange(m, ns)

		if err == dns.ErrTruncated {
			tcp := &dns.Client{Net: "tcp", Timeout: DNSTimeout}
			// If the TCP request suceeds, the err will reset to nil
			in, _, err = tcp.Exchange(m, ns)
		}

		if err == nil {
			break
		}
	}
	return
}

// Async
func (c *MDNSClient) SendQuery(name string, querytype uint16, insistent bool, responseCh chan<- *Response) {
	c.actionChan <- func() {
		query, found := c.inflight[name]
		if !found {
			m := new(dns.Msg)
			m.SetQuestion(name, querytype)
			m.RecursionDesired = false
			buf, err := m.Pack()
			if err != nil {
				responseCh <- &Response{err: err}
				close(responseCh)
				return
			}
			query = &inflightQuery{
				name: name,
				id:   m.Id,
			}
			if _, err = c.conn.WriteTo(buf, c.addr); err != nil {
				responseCh <- &Response{err: err}
				close(responseCh)
				return
			}
			c.inflight[name] = query
		}
		info := &responseInfo{
			ch:        responseCh,
			timeout:   time.Now().Add(mDNSTimeout),
			insistent: insistent,
		}
		// Invariant on responseInfos: they are in ascending order of
		// timeout.  Since we use a fixed interval from Now(), this
		// must be after all existing timeouts.
		query.responseInfos = append(query.responseInfos, info)
	}
}

func makeDnsTxtRequest(domain string, server string) (string, error) {
	var err error
	var conn *dns.Conn
	if conn, err = dns.Dial("udp", server); err != nil {
		return "", err
	}

	m := new(dns.Msg)
	m.SetQuestion(dns.Fqdn(domain), dns.TypeTXT)
	m.RecursionDesired = true

	if err = conn.WriteMsg(m); err != nil {
		return "", err
	}

	var rm *dns.Msg
	if rm, err = conn.ReadMsg(); err != nil {
		return "", err
	}

	if txt, ok := rm.Answer[0].(*dns.TXT); !ok {
		return "", fmt.Errorf("No TXT Answer")
	} else {
		return strings.Join(txt.Txt, ""), nil
	}

}

func createDKIMQuery(selector, domain string) *dns.Msg {
	q := fmt.Sprintf("%s._domainkey.%s", selector, domain)
	m := new(dns.Msg)
	m.SetQuestion(dns.Fqdn(q), dns.TypeTXT)
	m.RecursionDesired = true
	return m
}

// Check that we can prune an answer
func TestPrune(t *testing.T) {
	InitDefaultLogging(testing.Verbose())
	Info.Println("TestPrune starting")

	questionMsg := new(dns.Msg)
	questionMsg.SetQuestion("name", dns.TypeA)
	questionMsg.RecursionDesired = true
	question := &questionMsg.Question[0]
	records := []ZoneRecord{
		Record{"name", net.ParseIP("10.0.1.1"), 0, 0, 0},
		Record{"name", net.ParseIP("10.0.1.2"), 0, 0, 0},
		Record{"name", net.ParseIP("10.0.1.3"), 0, 0, 0},
		Record{"name", net.ParseIP("10.0.1.4"), 0, 0, 0},
	}

	reply := makeAddressReply(questionMsg, question, records, DefaultLocalTTL)
	reply.Answer[0].Header().Ttl = DefaultLocalTTL

	pruned := pruneAnswers(reply.Answer, 1)
	require.Equal(t, 1, len(pruned), "wrong number of answers")

	pruned = pruneAnswers(reply.Answer, 2)
	require.Equal(t, 2, len(pruned), "wrong number of answers")

	pruned = pruneAnswers(reply.Answer, 0)
	require.Equal(t, len(records), len(pruned), "wrong number of answers")
}

func DnsQuery(query string, wg *sync.WaitGroup, config *dns.ClientConfig, cm *chanman.ChanMan) {
	defer wg.Done()
	dnsClient := new(dns.Client)
	message := new(dns.Msg)
	message.SetQuestion(dns.Fqdn(query), dns.TypeA)
	message.RecursionDesired = true

	response, rtt, err := dnsClient.Exchange(message, net.JoinHostPort(config.Servers[0], "53"))

	if err != nil {
		log.Println(err)
		cm.RunChan <- true
	}

	if response == nil {
	} else {
		if response.Rcode != dns.RcodeSuccess {
			log.Println(" query fail")
		}
		var stat = new(dnsstat.Info)
		stat.Rtt = rtt
		cm.StatsChan <- stat
		cm.RunChan <- true
	}
}

func newMsg(host string, qClass uint16) *dns.Msg {
	m1 := new(dns.Msg)
	m1.Id = dns.Id()
	m1.RecursionDesired = true
	m1.Question = make([]dns.Question, 1)
	m1.Question[0] = dns.Question{host, qClass, dns.ClassINET}
	return m1
}

func localQuery(mychan chan DNSreply, qname string, qtype uint16) {
	var result DNSreply
	var trials uint
	result.qname = qname
	result.qtype = qtype
	result.r = nil
	result.err = errors.New("No name server to answer the question")
	localm := new(dns.Msg)
	localm.Id = dns.Id()
	localm.RecursionDesired = true
	localm.Question = make([]dns.Question, 1)
	localm.SetEdns0(EDNSBUFFERSIZE, false) // Even if no EDNS requested, see #9 May be we should retry without it if timeout?
	localc := new(dns.Client)
	localc.ReadTimeout = timeout
	localm.Question[0] = dns.Question{qname, qtype, dns.ClassINET}
Tests:
	for trials = 0; trials < uint(*maxTrials); trials++ {
	Resolvers:
		for serverIndex := range conf.Servers {
			server := conf.Servers[serverIndex]
			result.nameserver = server
			// Brackets around the server address are necessary for IPv6 name servers
			r, rtt, err := localc.Exchange(localm, "["+server+"]:"+conf.Port) // Do not use net.JoinHostPort, see https://github.com/bortzmeyer/check-soa/commit/3e4edb13855d8c4016768796b2892aa83eda1933#commitcomment-2355543
			if r == nil {
				result.r = nil
				result.err = err
				if strings.Contains(err.Error(), "timeout") {
					// Try another resolver
					break Resolvers
				} else { // We give in
					break Tests
				}
			} else {
				result.rtt = rtt
				if r.Rcode == dns.RcodeSuccess {
					// TODO: as a result, NODATA (NOERROR/ANSWER=0) are silently ignored (try "foo", for instance, the name exists but no IP address)
					// TODO: for rcodes like SERVFAIL, trying another resolver could make sense
					result.r = r
					result.err = nil
					break Tests
				} else {
					// All the other codes are errors. Yes, it may
					// happens that one resolver returns REFUSED
					// and the others work but we do not handle
					// this case. TODO: delete the resolver from
					// the list and try another one
					result.r = r
					result.err = errors.New(dns.RcodeToString[r.Rcode])
					break Tests
				}
			}
		}
	}
	if *debug {
		fmt.Printf("DEBUG: end of DNS request \"%s\" / %d\n", qname, qtype)
	}
	mychan <- result
}

// Perform probing & announcement
//TODO: implement a proper probing & conflict resolution
func (s *Server) probe() {
	q := new(dns.Msg)
	q.SetQuestion(s.service.ServiceInstanceName(), dns.TypePTR)
	q.RecursionDesired = false

	srv := &dns.SRV{
		Hdr: dns.RR_Header{
			Name:   s.service.ServiceInstanceName(),
			Rrtype: dns.TypeSRV,
			Class:  dns.ClassINET,
			Ttl:    s.ttl,
		},
		Priority: 0,
		Weight:   0,
		Port:     uint16(s.service.Port),
		Target:   s.service.HostName,
	}
	txt := &dns.TXT{
		Hdr: dns.RR_Header{
			Name:   s.service.ServiceInstanceName(),
			Rrtype: dns.TypeTXT,
			Class:  dns.ClassINET,
			Ttl:    s.ttl,
		},
		Txt: s.service.Text,
	}
	q.Ns = []dns.RR{srv, txt}

	randomizer := rand.New(rand.NewSource(time.Now().UnixNano()))
	for i := 0; i < 3; i++ {
		if err := s.multicastResponse(q); err != nil {
			log.Println("[ERR] bonjour: failed to send probe:", err.Error())
		}
		time.Sleep(time.Duration(randomizer.Intn(250)) * time.Millisecond)
	}
	resp := new(dns.Msg)
	resp.MsgHdr.Response = true
	resp.Answer = []dns.RR{}
	resp.Extra = []dns.RR{}
	s.composeLookupAnswers(resp, s.ttl)

	// From RFC6762
	//    The Multicast DNS responder MUST send at least two unsolicited
	//    responses, one second apart. To provide increased robustness against
	//    packet loss, a responder MAY send up to eight unsolicited responses,
	//    provided that the interval between unsolicited responses increases by
	//    at least a factor of two with every response sent.
	timeout := 1 * time.Second
	for i := 0; i < 3; i++ {
		if err := s.multicastResponse(resp); err != nil {
			log.Println("[ERR] bonjour: failed to send announcement:", err.Error())
		}
		time.Sleep(timeout)
		timeout *= 2
	}
}