Golang Client.Net方法代碼示例

func forwardQuestion(q *dns.Question, forwarders []string) []dns.RR {
	//qType := dns.Type(q.Qtype).String() // query type
	//log.Printf("[Forwarder Lookup [%s] [%s]]\n", q.Name, qType)

	myReq := new(dns.Msg)
	myReq.SetQuestion(q.Name, q.Qtype)

	if len(forwarders) == 0 {
		// we have no upstreams, so we'll just not use any
	} else if strings.TrimSpace(forwarders[0]) == "!" {
		// we've been told explicitly to not pass anything along to any upsteams
	} else {
		c := new(dns.Client)
		for _, server := range forwarders {
			c.Net = "udp"
			m, _, err := c.Exchange(myReq, strings.TrimSpace(server))

			if m != nil && m.MsgHdr.Truncated {
				c.Net = "tcp"
				m, _, err = c.Exchange(myReq, strings.TrimSpace(server))
			}

			// FIXME: Cache misses.  And cache hits, too.

			if err != nil {
				//log.Printf("[Forwarder Lookup [%s] [%s] failed: [%s]]\n", q.Name, qType, err)
				log.Println(err)
			} else {
				//log.Printf("[Forwarder Lookup [%s] [%s] success]\n", q.Name, qType)
				return m.Answer
			}
		}
	}
	return nil
}

// Returns an anonymous function configured to resolve DNS
// queries with a specific set of remote servers.
func ServerHandler(addresses []string) handler {
	randGen := rand.New(rand.NewSource(time.Now().UnixNano()))

	// This is the actual handler
	return func(w dns.ResponseWriter, req *dns.Msg) {
		nameserver := addresses[randGen.Intn(len(addresses))]
		var protocol string

		switch t := w.RemoteAddr().(type) {
		default:
			log.Printf("ERROR: Unsupported protocol %T\n", t)
			return
		case *net.UDPAddr:
			protocol = "udp"
		case *net.TCPAddr:
			protocol = "tcp"
		}

		for _, q := range req.Question {
			log.Printf("Incoming request #%v: %s %s %v - using %s\n",
				req.Id,
				dns.ClassToString[q.Qclass],
				dns.TypeToString[q.Qtype],
				q.Name, nameserver)
		}

		c := new(dns.Client)
		c.Net = protocol
		resp, rtt, err := c.Exchange(req, nameserver)

	Redo:
		switch {
		case err != nil:
			log.Printf("ERROR: %s\n", err.Error())
			sendFailure(w, req)
			return
		case req.Id != resp.Id:
			log.Printf("ERROR: Id mismatch: %v != %v\n", req.Id, resp.Id)
			sendFailure(w, req)
			return
		case resp.MsgHdr.Truncated && protocol != "tcp":
			log.Printf("WARNING: Truncated answer for request %v, retrying TCP\n", req.Id)
			c.Net = "tcp"
			resp, rtt, err = c.Exchange(req, nameserver)
			goto Redo
		}

		log.Printf("Request #%v: %.3d µs, server: %s(%s), size: %d bytes\n", resp.Id, rtt/1e3, nameserver, c.Net, resp.Len())
		w.WriteMsg(resp)
	} // end of handler
}

// shouldTransfer checks the primaries of zone, retrieves the SOA record, checks the current serial
// and the remote serial and will return true if the remote one is higher than the locally configured one.
func (z *Zone) shouldTransfer() (bool, error) {
	c := new(dns.Client)
	c.Net = "tcp" // do this query over TCP to minimize spoofing
	m := new(dns.Msg)
	m.SetQuestion(z.origin, dns.TypeSOA)

	var Err error
	serial := -1

Transfer:
	for _, tr := range z.TransferFrom {
		Err = nil
		ret, err := middleware.Exchange(c, m, tr)
		if err != nil || ret.Rcode != dns.RcodeSuccess {
			Err = err
			continue
		}
		for _, a := range ret.Answer {
			if a.Header().Rrtype == dns.TypeSOA {
				serial = int(a.(*dns.SOA).Serial)
				break Transfer
			}
		}
	}
	if serial == -1 {
		return false, Err
	}
	return less(z.Apex.SOA.Serial, uint32(serial)), Err
}

func (this Server) DoDNSquery(m dns.Msg, TransProString string, server []string, timeout time.Duration) (*dns.Msg, error) {
	dnsClient := new(dns.Client)
	if dnsClient == nil {
		return nil, errors.New("Cannot create DNS client")
	}

	dnsClient.ReadTimeout = timeout
	dnsClient.WriteTimeout = timeout
	if TransProString != "TCP" && TransProString != "UDP" {
		return nil, errors.New("TransProString run")
	}
	dnsClient.Net = strings.ToLower(TransProString)
	ServerStr := server[rand.Intn(len(server))]
	ServerAddr := net.ParseIP(ServerStr)
	if ServerAddr.To16() != nil {
		ServerStr = "[" + ServerStr + "]:" + this.Port
	} else if ServerAddr.To4() != nil {
		ServerStr = ServerStr + this.Port
	} else {
		return nil, errors.New("invalid Server Address")
	}
	dnsResponse, _, err := dnsClient.Exchange(&m, ServerStr)
	if err != nil {
		return nil, err
	}
	return dnsResponse, nil
}

// Perform DNS resolution
func resolve(w http.ResponseWriter, r *http.Request, server string, domain string, querytype uint16) {
	m := new(dns.Msg)
	m.SetQuestion(domain, querytype)
	m.MsgHdr.RecursionDesired = true

	w.Header().Set("Content-Type", "application/json")
	w.Header().Set("Access-Control-Allow-Origin", "*")

	c := new(dns.Client)

Redo:
	if in, _, err := c.Exchange(m, server); err == nil { // Second return value is RTT, not used for now
		if in.MsgHdr.Truncated {
			c.Net = "tcp"
			goto Redo
		}

		switch in.MsgHdr.Rcode {
		case dns.RcodeServerFailure:
			error(w, 500, 502, "The name server encountered an internal failure while processing this request (SERVFAIL)")
		case dns.RcodeNameError:
			error(w, 500, 503, "Some name that ought to exist, does not exist (NXDOMAIN)")
		case dns.RcodeRefused:
			error(w, 500, 505, "The name server refuses to perform the specified operation for policy or security reasons (REFUSED)")
		default:
			jsonify(w, r, in.Question, in.Answer, in.Ns, in.Extra)
		}
	} else {
		error(w, 500, 501, "DNS server could not be reached")
	}
}

func lookup(msg *dns.Msg, client *dns.Client, server string, edns bool) (*dns.Msg, error) {
	if edns {
		opt := &dns.OPT{
			Hdr: dns.RR_Header{
				Name:   ".",
				Rrtype: dns.TypeOPT,
			},
		}
		opt.SetUDPSize(dns.DefaultMsgSize)
		msg.Extra = append(msg.Extra, opt)
	}

	response, _, err := client.Exchange(msg, server)
	if err != nil {
		return nil, err
	}

	if msg.Id != response.Id {
		return nil, fmt.Errorf("DNS ID mismatch, request: %d, response: %d", msg.Id, response.Id)
	}

	if response.MsgHdr.Truncated {
		if client.Net == "tcp" {
			return nil, fmt.Errorf("Got truncated message on tcp")
		}

		if edns { // Truncated even though EDNS is used
			client.Net = "tcp"
		}

		return lookup(msg, client, server, !edns)
	}

	return response, nil
}

// NewDNSResolverImpl constructs a new DNS resolver object that utilizes the
// provided list of DNS servers for resolution.
func NewDNSResolverImpl(
	readTimeout time.Duration,
	servers []string,
	caaSERVFAILExceptions map[string]bool,
	stats metrics.Scope,
	clk clock.Clock,
	maxTries int,
) *DNSResolverImpl {
	// TODO(jmhodges): make constructor use an Option func pattern
	dnsClient := new(dns.Client)

	// Set timeout for underlying net.Conn
	dnsClient.ReadTimeout = readTimeout
	dnsClient.Net = "tcp"

	return &DNSResolverImpl{
		dnsClient:                dnsClient,
		servers:                  servers,
		allowRestrictedAddresses: false,
		caaSERVFAILExceptions:    caaSERVFAILExceptions,
		maxTries:                 maxTries,
		clk:                      clk,
		stats:                    stats,
		txtStats:                 stats.NewScope("TXT"),
		aStats:                   stats.NewScope("A"),
		aaaaStats:                stats.NewScope("AAAA"),
		caaStats:                 stats.NewScope("CAA"),
		mxStats:                  stats.NewScope("MX"),
	}
}

func lookup(name string, queryType uint16, client *dns.Client, servAddr string, suffix string, edns bool) (*dns.Msg, error) {
	msg := &dns.Msg{}
	lname := strings.Join([]string{name, suffix}, ".")
	msg.SetQuestion(dns.Fqdn(lname), queryType)

	if edns {
		msg.SetEdns0(dns.DefaultMsgSize, false)
	}

	response, _, err := client.Exchange(msg, servAddr)
	if err == dns.ErrTruncated {
		if client.Net == "tcp" {
			return nil, fmt.Errorf("got truncated message on TCP (64kiB limit exceeded?)")
		}
		if edns { // Truncated even though EDNS is used
			client.Net = "tcp"
		}
		return lookup(name, queryType, client, servAddr, suffix, !edns)
	}
	if err != nil {
		return nil, err
	}
	if msg.Id != response.Id {
		return nil, fmt.Errorf("DNS ID mismatch, request: %d, response: %d", msg.Id, response.Id)
	}
	return response, nil
}

func TestDNSForward(t *testing.T) {
	s := newTestServer("", "", "8.8.8.8:53")
	defer s.Stop()

	c := new(dns.Client)
	m := new(dns.Msg)
	m.SetQuestion("www.example.com.", dns.TypeA)
	resp, _, err := c.Exchange(m, "localhost:"+StrPort)
	if err != nil {
		t.Fatal(err)
	}
	if len(resp.Answer) == 0 || resp.Rcode != dns.RcodeSuccess {
		t.Fatal("Answer expected to have A records or rcode not equal to RcodeSuccess")
	}
	// TCP
	c.Net = "tcp"
	resp, _, err = c.Exchange(m, "localhost:"+StrPort)
	if err != nil {
		t.Fatal(err)
	}
	if len(resp.Answer) == 0 || resp.Rcode != dns.RcodeSuccess {
		t.Fatal("Answer expected to have A records or rcode not equal to RcodeSuccess")
	}
	// TODO(miek): DNSSEC DO query
}

func TestDNSForwardLocal(t *testing.T) {
	forwardServer := newTestServer(t, false)
	service := &msg.Service{
		Host: "199.43.132.53", Key: "a.skydns.test.",
	}
	addService(t, forwardServer, service.Key, 0, service)
	defer delService(t, forwardServer, service.Key)

	s := newTestServer(t, false)
	s.config.Nameservers = []string{forwardServer.config.DnsAddr}
	s.config.ForwardLocal = true
	defer s.Stop()

	c := new(dns.Client)
	m := new(dns.Msg)
	m.SetQuestion("a.skydns.test.", dns.TypeA)
	resp, _, err := c.Exchange(m, "127.0.0.1:"+StrPort)
	if err != nil {
		// try twice
		resp, _, err = c.Exchange(m, "127.0.0.1:"+StrPort)
		if err != nil {
			t.Fatal(err)
		}
	}
	if len(resp.Answer) == 0 || resp.Rcode != dns.RcodeSuccess {
		t.Fatal("answer expected to have A records or rcode not equal to RcodeSuccess")
	}
	// TCP
	c.Net = "tcp"
	resp, _, err = c.Exchange(m, "127.0.0.1:"+StrPort)
	if err != nil {
		t.Fatal(err)
	}
	if len(resp.Answer) == 0 || resp.Rcode != dns.RcodeSuccess {
		t.Fatal("answer expected to have A records or rcode not equal to RcodeSuccess")
	}

	m.SetQuestion("bbbbb.skydns.test.", dns.TypeA)
	resp, _, err = c.Exchange(m, "127.0.0.1:"+StrPort)
	if err != nil {
		t.Fatal(err)
	}
	if len(resp.Answer) != 0 {
		t.Fatal("answer expected to have zero A records")
	}

	// disable recursion and check
	s.config.NoRec = true

	m.SetQuestion("a.skydns.test.", dns.TypeA)
	resp, _, err = c.Exchange(m, "127.0.0.1:"+StrPort)
	if err != nil {
		t.Fatal(err)
	}
	if resp.Rcode != dns.RcodeServerFailure {
		t.Fatal("answer expected to have rcode equal to RcodeFailure")
	}
}

func (r *Resolver) exchange(m *dns.Msg, a string, original []string) (res *dns.Msg, err error) {
	question := m.Question[0]
	sort.Strings(original)
	key := cachekey{question, fmt.Sprintf("%v", original)}
	if r.Debug {
		log.Println("KEY: ", key)
	}
	rt, ok := r.cache.Get(key)
	if ok {
		if r.Debug {
			log.Println("Cache HIT")
		}
		r1 := rt.(*dns.Msg)
		res = r1.Copy()
		return
	}
	if r.Debug {
		log.Println("Cache MISS")
		log.Println("QUERY: ", question.Name, "via", a)
	}
	res, err = dns.Exchange(m, a)
	if err != nil {
		if r.Debug {
			log.Println(err)
		}
		return
	}
	//Retry in case it was truncated
	if res.Truncated {
		if r.Debug {
			log.Println("truncated, retrying with tcp")
		}

		cl := new(dns.Client)
		cl.Net = "tcp"
		res, _, err = cl.Exchange(m, a)
		if err != nil {
			if r.Debug {
				log.Println(err)
			}
			return
		}

	}

	if r.Debug {
		log.Println(res)
	}
	if res.Rcode != dns.RcodeSuccess {
		return
	}
	if r.Debug {
		log.Println("Inserting into cache")
	}
	r.cache.Add(key, res)
	return
}

/*
 * sendRequest() - send a DNS query
 */
func sendRequest(ctx *Context, m *dns.Msg, transport string, timeout time.Duration) (response *dns.Msg, rtt time.Duration, err error) {

	c := new(dns.Client)
	c.Timeout = timeout
	c.Net = transport // "udp" or "tcp"
	response, rtt, err = c.Exchange(m, addressString(ctx.server, ctx.port))
	return

}

func queryRemote(r *dns.Msg, ch chan *dns.Msg) {
	c := new(dns.Client)
	c.Net = "tcp"
	in, _, err := c.Exchange(r, *remoteDNS)
	if err == nil {
		ch <- in
	} else {
		logger.Printf("Failed to query, %q", err)
	}
}

// tcpLookupIP is a helper to initiate a TCP-based DNS lookup for the given host.
// The built-in Go resolver will do a UDP lookup first, and will only use TCP if
// the response has the truncate bit set, which isn't common on DNS servers like
// Consul's. By doing the TCP lookup directly, we get the best chance for the
// largest list of hosts to join. Since joins are relatively rare events, it's ok
// to do this rather expensive operation.
func (m *Memberlist) tcpLookupIP(host string, defaultPort uint16) ([]ipPort, error) {
	// Don't attempt any TCP lookups against non-fully qualified domain
	// names, since those will likely come from the resolv.conf file.
	if !strings.Contains(host, ".") {
		return nil, nil
	}

	// Make sure the domain name is terminated with a dot (we know there's
	// at least one character at this point).
	dn := host
	if dn[len(dn)-1] != '.' {
		dn = dn + "."
	}

	// See if we can find a server to try.
	cc, err := dns.ClientConfigFromFile(m.config.DNSConfigPath)
	if err != nil {
		return nil, err
	}
	if len(cc.Servers) > 0 {
		// We support host:port in the DNS config, but need to add the
		// default port if one is not supplied.
		server := cc.Servers[0]
		if !hasPort(server) {
			server = net.JoinHostPort(server, cc.Port)
		}

		// Do the lookup.
		c := new(dns.Client)
		c.Net = "tcp"
		msg := new(dns.Msg)
		msg.SetQuestion(dn, dns.TypeANY)
		in, _, err := c.Exchange(msg, server)
		if err != nil {
			return nil, err
		}

		// Handle any IPs we get back that we can attempt to join.
		var ips []ipPort
		for _, r := range in.Answer {
			switch rr := r.(type) {
			case (*dns.A):
				ips = append(ips, ipPort{rr.A, defaultPort})
			case (*dns.AAAA):
				ips = append(ips, ipPort{rr.AAAA, defaultPort})
			case (*dns.CNAME):
				m.logger.Printf("[DEBUG] memberlist: Ignoring CNAME RR in TCP-first answer for '%s'", host)
			}
		}
		return ips, nil
	}

	return nil, nil
}

func doQuery(c dns.Client, m dns.Msg, ds, dp string, queryType uint16, close chan struct{}) *dns.Msg {
	//	r := &dns.Msg{}
	//	var ee error
	//fmt.Println(utils.GetDebugLine(), " doQuery: ", " m.Question: ", m.Question,
	//	" ds: ", ds, " dp: ", dp, " queryType ", queryType)
	utils.ServerLogger.Debug(" doQuery: m.Question: %v ds: %s dp: %s queryType: %v", m.Question, ds, dp, queryType)
	select {
	case <-close:
		return nil
	default:
		for l := 0; l < 3; l++ {
			r, _, ee := c.Exchange(&m, ds+":"+dp)
			if (ee != nil) || (r == nil) || (r.Answer == nil) {
				utils.ServerLogger.Error(" doQuery: retry: %s times error: %s", strconv.Itoa(l), ee.Error())
				if (queryType == dns.TypeA) || (queryType == dns.TypeCNAME) {
					if strings.Contains(ee.Error(), "connection refused") {
						if c.Net == TCP {
							c.Net = UDP
						}
					} else if (ee == dns.ErrTruncated) && queryType == dns.TypeA {
						utils.ServerLogger.Error(" doQuery: response truncated: %v", r)
						//					m.SetEdns0(4096,false)
						//					m.SetQuestion(dns.Fqdn(domainName),dns.TypeCNAME)
						c.Net = TCP
					} else {
						if c.Net == TCP {
							c.Net = UDP
						} else {
							c.Net = TCP
						}
					}
				}
			} else {
				return r
			}
		}
	}

	return nil
}