Golang Msg.IsEdns0方法代碼示例

func TestInFlightEDns0(t *T) {
	m1 := new(dns.Msg)
	m1.SetQuestion(testAnyDomain, dns.TypeA)
	m1.SetEdns0(4096, false)
	w1 := getWriter()

	m2 := new(dns.Msg)
	m2.SetQuestion(testAnyDomain, dns.TypeA)
	w2 := getWriter()

	go func() {
		handleRequest(w1, m1)
	}()
	go func() {
		handleRequest(w2, m2)
	}()
	var r1 *dns.Msg
	var r2 *dns.Msg
	for r1 == nil || r2 == nil {
		select {
		case r1 = <-w1.ReplyCh:
		case r2 = <-w2.ReplyCh:
		}
	}
	//note: this test could be flaky since we're relying on google to return
	//edns0 response when we send one vs when we don't send one
	assert.NotNil(t, r1.IsEdns0())
	assert.Nil(t, r2.IsEdns0())
}

// truncate removes answers until the given dns.Msg fits the permitted
// length of the given transmission channel and sets the TC bit.
// See https://tools.ietf.org/html/rfc1035#section-4.2.1
func truncate(m *dns.Msg, udp bool) *dns.Msg {
	max := dns.MinMsgSize
	if !udp {
		max = dns.MaxMsgSize
	} else if opt := m.IsEdns0(); opt != nil {
		max = int(opt.UDPSize())
	}

	m.Truncated = m.Len() > max
	if !m.Truncated {
		return m
	}

	m.Extra = nil // Drop all extra records first
	if m.Len() < max {
		return m
	}
	answers := m.Answer[:]
	left, right := 0, len(m.Answer)
	for {
		if left == right {
			break
		}
		mid := (left + right) / 2
		m.Answer = answers[:mid]
		if m.Len() < max {
			left = mid + 1
			continue
		}
		right = mid
	}
	return m
}

// Adds the DNS message data to the supplied MapStr.
func addDnsToMapStr(m common.MapStr, dns *mkdns.Msg, authority bool, additional bool) {
	m["id"] = dns.Id
	m["op_code"] = dnsOpCodeToString(dns.Opcode)

	m["flags"] = common.MapStr{
		"authoritative":       dns.Authoritative,
		"truncated_response":  dns.Truncated,
		"recursion_desired":   dns.RecursionDesired,
		"recursion_available": dns.RecursionAvailable,
		"authentic_data":      dns.AuthenticatedData, // [RFC4035]
		"checking_disabled":   dns.CheckingDisabled,  // [RFC4035]
	}
	m["response_code"] = dnsResponseCodeToString(dns.Rcode)

	if len(dns.Question) > 0 {
		q := dns.Question[0]
		qMapStr := common.MapStr{
			"name":  q.Name,
			"type":  dnsTypeToString(q.Qtype),
			"class": dnsClassToString(q.Qclass),
		}
		m["question"] = qMapStr

		eTLDPlusOne, err := publicsuffix.EffectiveTLDPlusOne(strings.TrimRight(q.Name, "."))
		if err == nil {
			qMapStr["etld_plus_one"] = eTLDPlusOne + "."
		}
	}

	rrOPT := dns.IsEdns0()
	if rrOPT != nil {
		m["opt"] = optToMapStr(rrOPT)
	}

	m["answers_count"] = len(dns.Answer)
	if len(dns.Answer) > 0 {
		m["answers"] = rrsToMapStrs(dns.Answer)
	}

	m["authorities_count"] = len(dns.Ns)
	if authority && len(dns.Ns) > 0 {
		m["authorities"] = rrsToMapStrs(dns.Ns)
	}

	if rrOPT != nil {
		m["additionals_count"] = len(dns.Extra) - 1
	} else {
		m["additionals_count"] = len(dns.Extra)
	}
	if additional && len(dns.Extra) > 0 {
		rrsMapStrs := rrsToMapStrs(dns.Extra)
		// We do not want OPT RR to appear in the 'additional' section,
		// that's why rrsMapStrs could be empty even though len(dns.Extra) > 0
		if len(rrsMapStrs) > 0 {
			m["additionals"] = rrsMapStrs
		}
	}

}

// ServeDNSStubForward forwards a request to a nameservers and returns the response.
func (s *server) ServeDNSStubForward(w dns.ResponseWriter, req *dns.Msg, ns []string) *dns.Msg {
	// Check EDNS0 Stub option, if set drop the packet.
	option := req.IsEdns0()
	if option != nil {
		for _, o := range option.Option {
			if o.Option() == ednsStubCode && len(o.(*dns.EDNS0_LOCAL).Data) == 1 &&
				o.(*dns.EDNS0_LOCAL).Data[0] == 1 {
				// Maybe log source IP here?
				logf("not fowarding stub request to another stub")
				return nil
			}
		}
	}

	tcp := isTCP(w)

	// Add a custom EDNS0 option to the packet, so we can detect loops
	// when 2 stubs are forwarding to each other.
	if option != nil {
		option.Option = append(option.Option, &dns.EDNS0_LOCAL{ednsStubCode, []byte{1}})
	} else {
		req.Extra = append(req.Extra, ednsStub)
	}

	var (
		r   *dns.Msg
		err error
		try int
	)

	// Use request Id for "random" nameserver selection.
	nsid := int(req.Id) % len(ns)
Redo:
	switch tcp {
	case false:
		r, _, err = s.dnsUDPclient.Exchange(req, ns[nsid])
	case true:
		r, _, err = s.dnsTCPclient.Exchange(req, ns[nsid])
	}
	if err == nil {
		r.Compress = true
		r.Id = req.Id
		w.WriteMsg(r)
		return r
	}
	// Seen an error, this can only mean, "server not reached", try again
	// but only if we have not exausted our nameservers.
	if try < len(ns) {
		try++
		nsid = (nsid + 1) % len(ns)
		goto Redo
	}

	logf("failure to forward stub request %q", err)
	m := s.ServerFailure(req)
	w.WriteMsg(m)
	return m
}

// get the maximum UDP-reply length
func getMaxReplyLen(r *dns.Msg, proto dnsProtocol) int {
	maxLen := minUDPSize
	if proto == protTCP {
		maxLen = maxUDPSize
	} else if opt := r.IsEdns0(); opt != nil {
		maxLen = int(opt.UDPSize())
	}
	return maxLen
}

func getMaxPayloadSize(req *dns.Msg) uint16 {
	opt := req.IsEdns0()
	if opt == nil {
		return dns.MinMsgSize
	}
	maxPayloadSize := opt.UDPSize()
	if maxPayloadSize < dns.MinMsgSize {
		maxPayloadSize = dns.MinMsgSize
	}
	return maxPayloadSize
}

// addStubEdns0 adds our special option to the message's OPT record.
func addStubEdns0(m *dns.Msg) *dns.Msg {
	option := m.IsEdns0()
	// Add a custom EDNS0 option to the packet, so we can detect loops when 2 stubs are forwarding to each other.
	if option != nil {
		option.Option = append(option.Option, &dns.EDNS0_LOCAL{Code: ednsStubCode, Data: []byte{1}})
		return m
	}

	m.Extra = append(m.Extra, ednsStub)
	return m
}

// hasStubEdns0 checks if the message is carrying our special edns0 zero option.
func hasStubEdns0(m *dns.Msg) bool {
	option := m.IsEdns0()
	if option == nil {
		return false
	}
	for _, o := range option.Option {
		if o.Option() == ednsStubCode && len(o.(*dns.EDNS0_LOCAL).Data) == 1 &&
			o.(*dns.EDNS0_LOCAL).Data[0] == 1 {
			return true
		}
	}
	return false
}

func Respond(w dns.ResponseWriter, req *dns.Msg, records []dns.RR) {
	m := new(dns.Msg)
	m.SetReply(req)
	m.Authoritative = true
	m.RecursionAvailable = true
	m.Compress = true
	m.Answer = records

	// Figure out the max response size
	bufsize := uint16(512)
	tcp := isTcp(w)

	if o := req.IsEdns0(); o != nil {
		bufsize = o.UDPSize()
	}

	if tcp {
		bufsize = dns.MaxMsgSize - 1
	} else if bufsize < 512 {
		bufsize = 512
	}

	if m.Len() > dns.MaxMsgSize {
		fqdn := dns.Fqdn(req.Question[0].Name)
		log.WithFields(log.Fields{"fqdn": fqdn}).Debug("Response too big, dropping Extra")
		m.Extra = nil
		if m.Len() > dns.MaxMsgSize {
			log.WithFields(log.Fields{"fqdn": fqdn}).Debug("Response still too big")
			m := new(dns.Msg)
			m.SetRcode(m, dns.RcodeServerFailure)
		}
	}

	if m.Len() > int(bufsize) && !tcp {
		log.Debug("Too big 1")
		m.Extra = nil
		if m.Len() > int(bufsize) {
			log.Debug("Too big 2")
			m.Answer = nil
			m.Truncated = true
		}
	}

	err := w.WriteMsg(m)
	if err != nil {
		log.Warn("Failed to return reply: ", err, m.Len())
	}

}

// our ServeDNS interface, which gets invoked on every DNS message
func (this ServerProxy) ServeDNS(w dns.ResponseWriter, request *dns.Msg) {
	// see if we have our groovy custom EDNS0 option
	client_supports_appfrag := false
	opt := request.IsEdns0()
	if opt != nil {
		for ofs, e := range opt.Option {
			if e.Option() == dns.EDNS0LOCALSTART {
				_D("%s QID:%d found EDNS0LOCALSTART", w.RemoteAddr(), request.Id)
				client_supports_appfrag = true
				// go ahead and use the maximum UDP size for the local communication
				// with our server
				opt.SetUDPSize(65535)
				// remove the fragmentation option
				opt.Option = append(opt.Option[0:ofs], opt.Option[ofs+1:]...)
				// in principle we should only have one of these options
				break
			}
		}
	}

	// proxy the query
	c := new(dns.Client)
	c.ReadTimeout = this.timeout
	c.WriteTimeout = this.timeout
	response, rtt, err := c.Exchange(request, this.SERVERS[rand.Intn(this.s_len)])
	if err != nil {
		_D("%s QID:%d error proxying query: %s", w.RemoteAddr(), request.Id, err)
		this.SRVFAIL(w, request)
		return
	}
	_D("%s QID:%d request took %s", w.RemoteAddr(), request.Id, rtt)

	// if the client does not support fragmentation, we just send the response back and finish
	if !client_supports_appfrag {
		_D("%s QID:%d sending raw response to client", w.RemoteAddr(), request.Id)
		w.WriteMsg(response)
		return
	}

	// otherwise lets get our fragments
	all_frags := frag(response)

	// send our fragments
	for n, frag := range all_frags {
		_D("%s QID:%d sending fragment %d", w.RemoteAddr(), request.Id, n)
		w.WriteMsg(&frag)
	}
}

// extract out the total fragments and sequence number from the EDNS0 informaton in a packet
func get_fragment_info(msg *dns.Msg) (num_frags int, sequence_num int) {
	num_frags = -1
	sequence_num = -1
	resp_edns0 := msg.IsEdns0()
	if resp_edns0 != nil {
		for _, opt := range resp_edns0.Option {
			if opt.Option() == dns.EDNS0LOCALSTART+1 {
				num_frags = int(opt.(*dns.EDNS0_LOCAL).Data[0])
				sequence_num = int(opt.(*dns.EDNS0_LOCAL).Data[1])
				// we only expect this option to be here once
				break
			}
		}
	}
	return num_frags, sequence_num
}

func getMsgKey(r *dns.Msg) string {
	k := ""
	for _, q := range r.Question {
		k += getQuestionKey(q)
	}

	//RFC 1035 defines this as the max
	//since some clients (read: go) don't support edns0, this is the default
	//if they do send edns0 we'll raise it to what they sent
	limit := dns.MinMsgSize
	opt := r.IsEdns0()
	if opt != nil {
		limit = int(opt.UDPSize())
		llog.Debug("received edns0 limit", llog.KV{"limit": limit})
	}
	k += strconv.Itoa(limit)
	return k
}

// SizeAndDo adds an OPT record that the reflects the intent from state.
// The returned bool indicated if an record was found and normalised.
func (s *State) SizeAndDo(m *dns.Msg) bool {
	o := s.Req.IsEdns0() // TODO(miek): speed this up
	if o == nil {
		return false
	}
	o.Hdr.Name = "."
	o.Hdr.Rrtype = dns.TypeOPT
	o.SetVersion(0)
	if mo := m.IsEdns0(); mo != nil {
		mo.Hdr.Name = "."
		mo.Hdr.Rrtype = dns.TypeOPT
		mo.SetVersion(0)
		mo.SetUDPSize(o.UDPSize())
		if o.Do() {
			mo.SetDo()
		}
		return true
	}
	m.Extra = append(m.Extra, o)
	return true
}

func Respond(w dns.ResponseWriter, req *dns.Msg, m *dns.Msg) {
	// Figure out the max response size
	bufsize := uint16(512)
	tcp := isTcp(w)

	if o := req.IsEdns0(); o != nil {
		bufsize = o.UDPSize()
	}

	if tcp {
		bufsize = dns.MaxMsgSize - 1
	} else if bufsize < 512 {
		bufsize = 512
	}

	// Make sure the payload fits the buffer size. If the message is too large we strip the Extra section.
	// If it's still too large we return a truncated message for UDP queries and ServerFailure for TCP queries.
	if m.Len() > int(bufsize) {
		fqdn := dns.Fqdn(req.Question[0].Name)
		log.WithFields(log.Fields{"fqdn": fqdn}).Debug("Response too big, dropping Authority and Extra")
		m.Extra = nil
		if m.Len() > int(bufsize) {
			if tcp {
				log.WithFields(log.Fields{"fqdn": fqdn}).Debug("Response still too big, return ServerFailure")
				m = new(dns.Msg)
				m.SetRcode(req, dns.RcodeServerFailure)
			} else {
				log.WithFields(log.Fields{"fqdn": fqdn}).Debug("Response still too big, return truncated message")
				m.Answer = nil
				m.Truncated = true
			}
		}
	}

	err := w.WriteMsg(m)
	if err != nil {
		log.Warn("Failed to return reply: ", err, m.Len())
	}

}

// Edns0Version checks the EDNS version in the request. If error
// is nil everything is OK and we can invoke the middleware. If non-nil, the
// returned Msg is valid to be returned to the client (and should). For some
// reason this response should not contain a question RR in the question section.
func Edns0Version(req *dns.Msg) (*dns.Msg, error) {
	opt := req.IsEdns0()
	if opt == nil {
		return nil, nil
	}
	if opt.Version() == 0 {
		return nil, nil
	}
	m := new(dns.Msg)
	m.SetReply(req)
	// zero out question section, wtf.
	m.Question = nil

	o := new(dns.OPT)
	o.Hdr.Name = "."
	o.Hdr.Rrtype = dns.TypeOPT
	o.SetVersion(0)
	o.SetExtendedRcode(dns.RcodeBadVers)
	m.Extra = []dns.RR{o}

	return m, errors.New("EDNS0 BADVERS")
}