vendor-ed skydns

vendor/github.com/skynetservices/skydns/server/forwarding.go

@@ -0,0 +1,125 @@
+// Copyright (c) 2014 The SkyDNS Authors. All rights reserved.
+// Use of this source code is governed by The MIT License (MIT) that can be
+// found in the LICENSE file.
+
+package server
+
+import (
+	"fmt"
+
+	"github.com/miekg/dns"
+)
+
+// ServeDNSForward forwards a request to a nameservers and returns the response.
+func (s *server) ServeDNSForward(w dns.ResponseWriter, req *dns.Msg) *dns.Msg {
+	if s.config.NoRec {
+		m := s.ServerFailure(req)
+		w.WriteMsg(m)
+		return m
+	}
+
+	if len(s.config.Nameservers) == 0 || dns.CountLabel(req.Question[0].Name) < s.config.Ndots {
+		if s.config.Verbose {
+			if len(s.config.Nameservers) == 0 {
+				logf("can not forward, no nameservers defined")
+			} else {
+				logf("can not forward, name too short (less than %d labels): `%s'", s.config.Ndots, req.Question[0].Name)
+			}
+		}
+		m := s.ServerFailure(req)
+		m.RecursionAvailable = true // this is still true
+		w.WriteMsg(m)
+		return m
+	}
+
+	var (
+		r   *dns.Msg
+		err error
+	)
+
+	nsid := s.randomNameserverID(req.Id)
+	try := 0
+Redo:
+	if isTCP(w) {
+		r, err = exchangeWithRetry(s.dnsTCPclient, req, s.config.Nameservers[nsid])
+	} else {
+		r, err = exchangeWithRetry(s.dnsUDPclient, req, s.config.Nameservers[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(s.config.Nameservers) {
+		try++
+		nsid = (nsid + 1) % len(s.config.Nameservers)
+		goto Redo
+	}
+
+	logf("failure to forward request %q", err)
+	m := s.ServerFailure(req)
+	return m
+}
+
+// ServeDNSReverse is the handler for DNS requests for the reverse zone. If nothing is found
+// locally the request is forwarded to the forwarder for resolution.
+func (s *server) ServeDNSReverse(w dns.ResponseWriter, req *dns.Msg) *dns.Msg {
+	m := new(dns.Msg)
+	m.SetReply(req)
+	m.Compress = true
+	m.Authoritative = false // Set to false, because I don't know what to do wrt DNSSEC.
+	m.RecursionAvailable = true
+	var err error
+	if m.Answer, err = s.PTRRecords(req.Question[0]); err == nil {
+		// TODO(miek): Reverse DNSSEC. We should sign this, but requires a key....and more
+		// Probably not worth the hassle?
+		if err := w.WriteMsg(m); err != nil {
+			logf("failure to return reply %q", err)
+		}
+		return m
+	}
+	// Always forward if not found locally.
+	return s.ServeDNSForward(w, req)
+}
+
+// Lookup looks up name,type using the recursive nameserver defines
+// in the server's config. If none defined it returns an error.
+func (s *server) Lookup(n string, t, bufsize uint16, dnssec bool) (*dns.Msg, error) {
+	if len(s.config.Nameservers) == 0 {
+		return nil, fmt.Errorf("no nameservers configured can not lookup name")
+	}
+	if dns.CountLabel(n) < s.config.Ndots {
+		return nil, fmt.Errorf("name has fewer than %d labels", s.config.Ndots)
+	}
+	m := newExchangeMsg(n, t, bufsize, dnssec)
+
+	nsid := s.randomNameserverID(m.Id)
+	try := 0
+Redo:
+	r, err := exchangeWithRetry(s.dnsUDPclient, m, s.config.Nameservers[nsid])
+	if err == nil {
+		if r.Rcode != dns.RcodeSuccess {
+			return nil, fmt.Errorf("rcode is not equal to success")
+		}
+		// Reset TTLs to rcache TTL to make some of the other code
+		// and the tests not care about TTLs
+		for _, rr := range r.Answer {
+			rr.Header().Ttl = uint32(s.config.RCacheTtl)
+		}
+		for _, rr := range r.Extra {
+			rr.Header().Ttl = uint32(s.config.RCacheTtl)
+		}
+		return r, nil
+	}
+	// Seen an error, this can only mean, "server not reached", try again
+	// but only if we have not exausted our nameservers.
+	if try < len(s.config.Nameservers) {
+		try++
+		nsid = (nsid + 1) % len(s.config.Nameservers)
+		goto Redo
+	}
+	return nil, fmt.Errorf("failure to lookup name")
+}