Golang Msg.Len方法代码示例

func (l Logger) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
	state := middleware.State{W: w, Req: r}
	for _, rule := range l.Rules {
		if middleware.Name(rule.NameScope).Matches(state.Name()) {
			responseRecorder := middleware.NewResponseRecorder(w)
			rcode, err := l.Next.ServeDNS(ctx, responseRecorder, r)

			if rcode > 0 {
				// There was an error up the chain, but no response has been written yet.
				// The error must be handled here so the log entry will record the response size.
				if l.ErrorFunc != nil {
					l.ErrorFunc(responseRecorder, r, rcode)
				} else {
					rc := middleware.RcodeToString(rcode)

					answer := new(dns.Msg)
					answer.SetRcode(r, rcode)
					state.SizeAndDo(answer)

					metrics.Report(state, metrics.Dropped, rc, answer.Len(), time.Now())
					w.WriteMsg(answer)
				}
				rcode = 0
			}
			rep := middleware.NewReplacer(r, responseRecorder, CommonLogEmptyValue)
			rule.Log.Println(rep.Replace(rule.Format))
			return rcode, err

		}
	}
	return l.Next.ServeDNS(ctx, w, r)
}

// set the reply for the entry
// returns True if the entry has changed the validUntil time
func (e *cacheEntry) setReply(reply *dns.Msg, ttl int, flags uint8, now time.Time) bool {
	var prevValidUntil time.Time
	if e.Status == stResolved {
		if reply != nil {
			Debug.Printf("[cache msgid %d] replacing response in cache", reply.MsgHdr.Id)
		}
		prevValidUntil = e.validUntil
	}

	e.Status = stResolved
	e.Flags = flags
	e.putTime = now

	if ttl != nullTTL {
		e.validUntil = now.Add(time.Second * time.Duration(ttl))
	} else if reply != nil {
		// calculate the validUntil from the reply TTL
		var minTTL uint32 = math.MaxUint32
		for _, rr := range reply.Answer {
			ttl := rr.Header().Ttl
			if ttl < minTTL {
				minTTL = ttl // TODO: improve the minTTL calculation (maybe we should skip some RRs)
			}
		}
		e.validUntil = now.Add(time.Second * time.Duration(minTTL))
	}

	if reply != nil {
		e.reply = *reply
		e.ReplyLen = reply.Len()
	}

	return (prevValidUntil != e.validUntil)
}

func ReportErrorCount(resp *dns.Msg, sys System) {
	if resp == nil || errorCount == nil {
		return
	}

	if resp.Truncated {
		errorCount.WithLabelValues(string(sys), string(Truncated)).Inc()
		return
	}
	if resp.Len() > dns.MaxMsgSize {
		errorCount.WithLabelValues(string(sys), string(Overflow)).Inc()
		return
	}

	switch resp.Rcode {
	case dns.RcodeServerFailure:
		errorCount.WithLabelValues(string(sys), string(Fail)).Inc()
	case dns.RcodeRefused:
		errorCount.WithLabelValues(string(sys), string(Refused)).Inc()
	case dns.RcodeNameError:
		errorCount.WithLabelValues(string(sys), string(Nxdomain)).Inc()
		// nodata ??
	}

}

// WriteMsg records the status code and calls the
// underlying ResponseWriter's WriteMsg method.
func (r *ResponseRecorder) WriteMsg(res *dns.Msg) error {
	r.rcode = res.Rcode
	// We may get called multiple times (axfr for instance).
	// Save the last message, but add the sizes.
	r.size += res.Len()
	r.msg = res
	return r.ResponseWriter.WriteMsg(res)
}

// Sign signs a message m, it takes care of negative or nodata responses as
// well by synthesising NSEC3 records. It will also cache the signatures, using
// a hash of the signed data as a key.
// We also fake the origin TTL in the signature, because we don't want to
// throw away signatures when services decide to have longer TTL. So we just
// set the origTTL to 60.
// TODO(miek): revisit origTTL
func (s *server) Sign(m *dns.Msg, bufsize uint16) {
	now := time.Now().UTC()
	incep := uint32(now.Add(-3 * time.Hour).Unix())     // 2+1 hours, be sure to catch daylight saving time and such
	expir := uint32(now.Add(7 * 24 * time.Hour).Unix()) // sign for a week

	defer func() {
		promCacheSize.WithLabelValues("signature").Set(float64(s.scache.Size()))
	}()

	for _, r := range rrSets(m.Answer) {
		if r[0].Header().Rrtype == dns.TypeRRSIG {
			continue
		}
		if !dns.IsSubDomain(s.config.Domain, r[0].Header().Name) {
			continue
		}
		if sig, err := s.signSet(r, now, incep, expir); err == nil {
			m.Answer = append(m.Answer, sig)
		}
	}
	for _, r := range rrSets(m.Ns) {
		if r[0].Header().Rrtype == dns.TypeRRSIG {
			continue
		}
		if !dns.IsSubDomain(s.config.Domain, r[0].Header().Name) {
			continue
		}
		if sig, err := s.signSet(r, now, incep, expir); err == nil {
			m.Ns = append(m.Ns, sig)
		}
	}
	for _, r := range rrSets(m.Extra) {
		if r[0].Header().Rrtype == dns.TypeRRSIG || r[0].Header().Rrtype == dns.TypeOPT {
			continue
		}
		if !dns.IsSubDomain(s.config.Domain, r[0].Header().Name) {
			continue
		}
		if sig, err := s.signSet(r, now, incep, expir); err == nil {
			m.Extra = append(m.Extra, sig)
		}
	}
	if bufsize >= 512 || bufsize <= 4096 {
		// TCP here?
		promErrorCount.WithLabelValues("truncated").Inc()
		m.Truncated = m.Len() > int(bufsize)
	}
	o := new(dns.OPT)
	o.Hdr.Name = "."
	o.Hdr.Rrtype = dns.TypeOPT
	o.SetDo()
	o.SetUDPSize(4096) // TODO(miek): echo client
	m.Extra = append(m.Extra, o)
	return
}

// DefaultErrorFunc responds to an DNS request with an error.
func DefaultErrorFunc(w dns.ResponseWriter, r *dns.Msg, rcode int) {
	state := middleware.State{W: w, Req: r}
	rc := middleware.RcodeToString(rcode)

	answer := new(dns.Msg)
	answer.SetRcode(r, rcode)
	state.SizeAndDo(answer)

	metrics.Report(state, metrics.Dropped, rc, answer.Len(), time.Now())
	w.WriteMsg(answer)
}

func truncateResp(resp *dns.Msg, maxSize int, isTCP bool) {
	if !isTCP {
		resp.Truncated = true
	}

	// trim the Answer RRs one by one till the whole message fits
	// within the reply size
	for resp.Len() > maxSize {
		resp.Answer = resp.Answer[:len(resp.Answer)-1]
	}
}

// metricSizeAndDuration sets the size and duration metrics.
func metricSizeAndDuration(resp *dns.Msg, start time.Time, tcp bool) {
	net := "udp"
	rlen := float64(0)
	if tcp {
		net = "tcp"
	}
	if resp != nil {
		rlen = float64(resp.Len())
	}
	promRequestDuration.WithLabelValues(net).Observe(float64(time.Since(start)) / float64(time.Second))
	promResponseSize.WithLabelValues(net).Observe(rlen)
}

func ReportDuration(resp *dns.Msg, start time.Time, sys System) {
	if requestDuration == nil || responseSize == nil {
		return
	}

	rlen := float64(0)
	if resp != nil {
		rlen = float64(resp.Len())
	}
	requestDuration.WithLabelValues(string(sys)).Observe(float64(time.Since(start)) / float64(time.Second))
	responseSize.WithLabelValues(string(sys)).Observe(rlen)
}

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())
	}

}

func TestFit(t *testing.T) {
	m := new(dns.Msg)
	m.SetQuestion("miek.nl", dns.TypeA)

	rr, _ := dns.NewRR("www.miek.nl. IN SRV 10 10 8080 blaat.miek.nl.")
	for i := 0; i < 101; i++ {
		m.Answer = append(m.Answer, rr)
	}
	// Uncompresses length is now 4424. Try trimming this to 1927
	Fit(m, 1927, true)

	if m.Len() > 1927 {
		t.Fatalf("failed to fix message, expected < %d, got %d", 1927, m.Len())
	}
}

// trimAnswers makes sure a UDP response is not longer than allowed by RFC 1035.
// We first enforce an arbitrary limit, and then make sure the response doesn't
// exceed 512 bytes.
func trimAnswers(resp *dns.Msg) (trimmed bool) {
	numAnswers := len(resp.Answer)

	// This cuts UDP responses to a useful but limited number of responses.
	if numAnswers > maxServiceResponses {
		resp.Answer = resp.Answer[:maxServiceResponses]
	}

	// This enforces the hard limit of 512 bytes per the RFC.
	for len(resp.Answer) > 0 && resp.Len() > 512 {
		resp.Answer = resp.Answer[:len(resp.Answer)-1]
	}

	return len(resp.Answer) < numAnswers
}

// trimUDPAnswers makes sure a UDP response is not longer than allowed by RFC
// 1035.  Enforce an arbitrary limit that can be further ratcheted down by
// config, and then make sure the response doesn't exceed 512 bytes.
func trimUDPAnswers(config *DNSConfig, resp *dns.Msg) (trimmed bool) {
	numAnswers := len(resp.Answer)

	// This cuts UDP responses to a useful but limited number of responses.
	maxAnswers := lib.MinInt(maxUDPAnswerLimit, config.UDPAnswerLimit)
	if numAnswers > maxAnswers {
		resp.Answer = resp.Answer[:maxAnswers]
	}

	// This enforces the hard limit of 512 bytes per the RFC.
	for len(resp.Answer) > 0 && resp.Len() > 512 {
		resp.Answer = resp.Answer[:len(resp.Answer)-1]
	}

	return len(resp.Answer) < numAnswers
}

func truncateResp(resp *dns.Msg, maxSize int, isTCP bool) {
	if !isTCP {
		resp.Truncated = true
	}

	srv := resp.Question[0].Qtype == dns.TypeSRV
	// trim the Answer RRs one by one till the whole message fits
	// within the reply size
	for resp.Len() > maxSize {
		resp.Answer = resp.Answer[:len(resp.Answer)-1]

		if srv && len(resp.Extra) > 0 {
			resp.Extra = resp.Extra[:len(resp.Extra)-1]
		}
	}
}

// set the reply for the entry
// returns True if the entry has changed the validUntil time
func (e *cacheEntry) setReply(reply *dns.Msg, ttl int, flags uint8, now time.Time) bool {
	var prevValidUntil time.Time
	if e.Status == stResolved {
		if reply != nil {
			Log.Debugf("[cache msgid %d] replacing response in cache", reply.MsgHdr.Id)
		}
		prevValidUntil = e.validUntil
	}

	// make sure we do not overwrite noLocalReplies entries
	if flags&CacheNoLocalReplies != 0 {
		if e.Flags&CacheNoLocalReplies != 0 {
			return false
		}
	}

	if ttl != nullTTL {
		e.validUntil = now.Add(time.Second * time.Duration(ttl))
	} else if reply != nil {
		// calculate the validUntil from the reply TTL
		var minTTL uint32 = math.MaxUint32
		for _, rr := range reply.Answer {
			ttl := rr.Header().Ttl
			if ttl < minTTL {
				minTTL = ttl // TODO: improve the minTTL calculation (maybe we should skip some RRs)
			}
		}
		e.validUntil = now.Add(time.Second * time.Duration(minTTL))
	} else {
		Log.Warningf("[cache] no valid TTL could be calculated")
	}

	e.Status = stResolved
	e.Flags = flags
	e.putTime = now

	if reply != nil {
		e.reply = *reply.Copy()
		e.ReplyLen = reply.Len()
	}

	return (prevValidUntil != e.validUntil)
}