Golang Msg.Truncated方法代碼示例

func makeTruncatedReply(r *dns.Msg) *dns.Msg {
	// for truncated response, we create a minimal reply with the Truncated bit set
	reply := new(dns.Msg)
	reply.SetReply(r)
	reply.Truncated = true
	return reply
}

// 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
}

func returnTruncated(w dns.ResponseWriter, req *dns.Msg) {
	m := new(dns.Msg)
	m.SetReply(req)
	m.Answer = make([]dns.RR, 1)
	m.Answer[0] = &dns.A{Hdr: dns.RR_Header{Name: m.Question[0].Name, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 0}, A: net.ParseIP("127.0.0.1").To4()}
	m.Truncated = true
	w.WriteMsg(m)
}

func (w *truncatingWriter) WriteMsg(m *dns.Msg) error {
	_, isUDP := w.RemoteAddr().(*net.UDPAddr)

	if isUDP && len(m.Answer) > w.maxAnswers {
		m.Answer = m.Answer[:w.maxAnswers]
		m.Truncated = true
	}

	return w.ResponseWriter.WriteMsg(m)
}

func cacheMsg(m *dns.Msg, tc cacheTestCase) *dns.Msg {
	m.RecursionAvailable = tc.RecursionAvailable
	m.AuthenticatedData = tc.AuthenticatedData
	m.Authoritative = tc.Authoritative
	m.Truncated = tc.Truncated
	m.Answer = tc.in.Answer
	m.Ns = tc.in.Ns
	//	m.Extra = tc.in.Extra , not the OPT record!
	return m
}

// 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
}

func sendTruncated(w dns.ResponseWriter, msgHdr dns.MsgHdr) {
	emptyResp := new(dns.Msg)
	emptyResp.MsgHdr = msgHdr
	emptyResp.Response = true
	if _, isTCP := w.RemoteAddr().(*net.TCPAddr); isTCP {
		dns.HandleFailed(w, emptyResp)
		return
	}
	emptyResp.Truncated = true
	w.WriteMsg(emptyResp)
}

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]
	}
}

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 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]
		}
	}
}

// Scrub scrubs the reply message so that it will fit the client's buffer. If even after dropping
// the additional section, it still does not fit the TC bit will be set on the message. Note,
// the TC bit will be set regardless of protocol, even TCP message will get the bit, the client
// should then retry with pigeons.
// TODO(referral).
func (s *State) Scrub(reply *dns.Msg) (*dns.Msg, Result) {
	size := s.Size()
	l := reply.Len()
	if size >= l {
		return reply, ScrubIgnored
	}
	// TODO(miek): check for delegation

	// If not delegation, drop additional section.
	reply.Extra = nil
	s.SizeAndDo(reply)
	l = reply.Len()
	if size >= l {
		return reply, ScrubDone
	}
	// Still?!! does not fit.
	reply.Truncated = true
	return reply, ScrubDone
}

// Fit will make m fit the size. If a message is larger than size then entire
// additional section is dropped. If it is still to large and the transport
// is udp we return a truncated message.
// If the transport is tcp we are going to drop RR from the answer section
// until it fits. When this is case the returned bool is true.
func Fit(m *dns.Msg, size int, tcp bool) (*dns.Msg, bool) {
	if m.Len() > size {
		// Check for OPT Records at the end and keep those. TODO(miek)
		m.Extra = nil
	}
	if m.Len() < size {
		return m, false
	}

	// With TCP setting TC does not mean anything.
	if !tcp {
		m.Truncated = true
		// fall through here, so we at least return a message that can
		// fit the udp buffer.
	}

	// Additional section is gone, binary search until we have length that fits.
	min, max := 0, len(m.Answer)
	original := make([]dns.RR, len(m.Answer))
	copy(original, m.Answer)
	for {
		if min == max {
			break
		}

		mid := (min + max) / 2
		m.Answer = original[:mid]

		if m.Len() < size {
			min++
			continue
		}
		max = mid

	}
	if max > 1 {
		max--
	}
	m.Answer = m.Answer[:max]
	return m, true
}

// 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

	for _, r := range rrSets(m.Answer) {
		if r[0].Header().Rrtype == dns.TypeRRSIG {
			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 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 {
			continue
		}
		if sig, err := s.signSet(r, now, incep, expir); err == nil {
			m.Extra = append(m.Extra, sig)
		}
	}
	if bufsize >= 512 || bufsize <= 4096 {
		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
}

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())
	}

}

func truncateResponse(response *dns.Msg, maxSize int) {
	if len(response.Answer) <= 1 || maxSize <= 0 {
		return
	}

	// take a copy of answers, as we're going to mutate response
	answers := response.Answer

	// search for smallest i that is too big
	i := sort.Search(len(response.Answer), func(i int) bool {
		// return true if too big
		response.Answer = answers[:i+1]
		return response.Len() > maxSize
	})
	if i == len(answers) {
		response.Answer = answers
		return
	}

	response.Answer = answers[:i]
	response.Truncated = true
}