vendor-ed skydns

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

@@ -0,0 +1,124 @@
+// 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 (
+	"net"
+	"strconv"
+	"strings"
+
+	"github.com/miekg/dns"
+	"github.com/skynetservices/skydns/msg"
+)
+
+const ednsStubCode = dns.EDNS0LOCALSTART + 10
+
+// ednsStub is the EDNS0 record we add to stub queries. Queries which have this record are
+// not forwarded again.
+var ednsStub = func() *dns.OPT {
+	o := new(dns.OPT)
+	o.Hdr.Name = "."
+	o.Hdr.Rrtype = dns.TypeOPT
+	e := new(dns.EDNS0_LOCAL)
+	e.Code = ednsStubCode
+	e.Data = []byte{1}
+	o.Option = append(o.Option, e)
+	return o
+}()
+
+// Look in .../dns/stub/<domain>/xx for msg.Services. Loop through them
+// extract <domain> and add them as forwarders (ip:port-combos) for
+// the stub zones. Only numeric (i.e. IP address) hosts are used.
+func (s *server) UpdateStubZones() {
+	stubmap := make(map[string][]string)
+
+	services, err := s.backend.Records("stub.dns."+s.config.Domain, false)
+	if err != nil {
+		logf("stub zone update failed: %s", err)
+		return
+	}
+	for _, serv := range services {
+		if serv.Port == 0 {
+			serv.Port = 53
+		}
+		ip := net.ParseIP(serv.Host)
+		if ip == nil {
+			logf("stub zone non-address %s seen for: %s", serv.Key, serv.Host)
+			continue
+		}
+
+		domain := msg.Domain(serv.Key)
+		// Chop of left most label, because that is used as the nameserver place holder
+		// and drop the right most labels that belong to localDomain.
+		labels := dns.SplitDomainName(domain)
+		domain = dns.Fqdn(strings.Join(labels[1:len(labels)-dns.CountLabel(s.config.localDomain)], "."))
+
+		// If the remaining name equals s.config.LocalDomain we ignore it.
+		if domain == s.config.localDomain {
+			logf("not adding stub zone for my own domain")
+			continue
+		}
+		stubmap[domain] = append(stubmap[domain], net.JoinHostPort(serv.Host, strconv.Itoa(serv.Port)))
+	}
+
+	s.config.stub = &stubmap
+}
+
+// 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
+			}
+		}
+	}
+
+	// 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
+	)
+
+	// Use request Id for "random" nameserver selection.
+	nsid := int(req.Id) % len(ns)
+	try := 0
+Redo:
+	if isTCP(w) {
+		r, err = exchangeWithRetry(s.dnsTCPclient, req, ns[nsid])
+	} else {
+		r, err = exchangeWithRetry(s.dnsUDPclient, 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
+}