// search searches the tree for qname and type. If glue is true the search *does* not
// spot when hitting NS records, but descends in search of glue. The qtype for this
// kind of search can only be AAAA or A.
func (n *Node) search(qname string, qtype uint16, glue bool) (*Node, Result) {
old := n
for n != nil {
switch c := Less(n.Elem, qname); {
case c == 0:
return n, Found
case c < 0:
old = n
n = n.Left
default:
if !glue && n.Elem.Types(dns.TypeNS) != nil {
return n, Delegation
}
old = n
n = n.Right
}
}
if dns.CountLabel(qname) < dns.CountLabel(old.Elem.Name()) {
return n, EmptyNonTerminal
}
return n, NameError
}
// lookupNameservers returns the authoritative nameservers for the given fqdn.
func lookupNameservers(fqdn string) ([]string, error) {
var authoritativeNss []string
r, err := dnsQuery(fqdn, dns.TypeNS, recursiveNameserver, true)
if err != nil {
return nil, err
}
for _, rr := range r.Answer {
if ns, ok := rr.(*dns.NS); ok {
authoritativeNss = append(authoritativeNss, strings.ToLower(ns.Ns))
}
}
if len(authoritativeNss) > 0 {
return authoritativeNss, nil
}
// Strip of the left most label to get the parent domain.
offset, _ := dns.NextLabel(fqdn, 0)
next := fqdn[offset:]
if dns.CountLabel(next) < 2 {
return nil, fmt.Errorf("Could not determine authoritative nameservers")
}
return lookupNameservers(next)
}
// 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
}
tcp := isTCP(w)
var (
r *dns.Msg
err error
try int
)
nsid := 0
if s.config.NSRotate {
// Use request Id for "random" nameserver selection.
nsid = int(req.Id) % len(s.config.Nameservers)
}
Redo:
switch tcp {
case false:
r, _, err = s.dnsUDPclient.Exchange(req, s.config.Nameservers[nsid])
case true:
r, _, err = s.dnsTCPclient.Exchange(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
}
// 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, net.IP{})
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
}
// saveDNSRR saves 1 or more DNS records to the resolver cache.
func (r *Resolver) saveDNSRR(host string, qname string, drrs []dns.RR) RRs {
var rrs RRs
cl := dns.CountLabel(qname)
for _, drr := range drrs {
rr, ok := convertRR(drr)
if !ok {
continue
}
if dns.CountLabel(rr.Name) < cl && dns.CompareDomainName(qname, rr.Name) < 2 {
// fmt.Fprintf(os.Stderr, "Warning: potential poisoning from %s: %s -> %s\n", host, qname, drr.String())
continue
}
r.cache.add(rr.Name, rr)
rrs = append(rrs, rr)
}
return rrs
}
func setDefaults(config *Config) error {
if config.ReadTimeout == 0 {
config.ReadTimeout = 2 * time.Second
}
if config.DnsAddr == "" {
config.DnsAddr = "127.0.0.1:53"
}
if config.Domain == "" {
config.Domain = "skydns.local."
}
if config.Hostmaster == "" {
config.Hostmaster = "hostmaster." + config.Domain
}
// People probably don't know that SOA's email addresses cannot
// contain @-signs, replace them with dots
config.Hostmaster = dns.Fqdn(strings.Replace(config.Hostmaster, "@", ".", -1))
if config.MinTtl == 0 {
config.MinTtl = 60
}
if config.Ttl == 0 {
config.Ttl = 3600
}
if config.Priority == 0 {
config.Priority = 10
}
if len(config.Nameservers) == 0 {
c, err := dns.ClientConfigFromFile("/etc/resolv.conf")
if err != nil {
return err
}
for _, s := range c.Servers {
config.Nameservers = append(config.Nameservers, net.JoinHostPort(s, c.Port))
}
}
config.Domain = dns.Fqdn(strings.ToLower(config.Domain))
config.DomainLabels = dns.CountLabel(config.Domain)
if config.DNSSEC != "" {
// For some reason the + are replaces by spaces in etcd. Re-replace them
keyfile := strings.Replace(config.DNSSEC, " ", "+", -1)
k, p, err := ParseKeyFile(keyfile)
if err != nil {
return err
}
if k.Header().Name != dns.Fqdn(config.Domain) {
return fmt.Errorf("ownername of DNSKEY must match SkyDNS domain")
}
k.Header().Ttl = config.Ttl
config.PubKey = k
config.KeyTag = k.KeyTag()
config.PrivKey = p
config.ClosestEncloser, config.DenyWildcard = newNSEC3CEandWildcard(config.Domain, config.Domain, config.MinTtl)
}
return nil
}
// 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
}
// Newserver returns a new Server.
func NewServer(members []string, domain string, dnsAddr string, httpAddr string, dataDir string, rt, wt time.Duration, secret string, nameservers []string, roundrobin bool, tlskey string, tlspem string) (s *Server) {
s = &Server{
members: members,
domain: strings.ToLower(domain),
domainLabels: dns.CountLabel(dns.Fqdn(domain)),
dnsAddr: dnsAddr,
httpAddr: httpAddr,
readTimeout: rt,
writeTimeout: wt,
router: mux.NewRouter(),
registry: registry.New(),
dataDir: dataDir,
dnsHandler: dns.NewServeMux(),
waiter: new(sync.WaitGroup),
secret: secret,
nameservers: nameservers,
roundrobin: roundrobin,
tlskey: tlskey,
tlspem: tlspem,
}
if _, err := os.Stat(s.dataDir); os.IsNotExist(err) {
log.Fatal("Data directory does not exist: ", dataDir)
return
}
// DNS
s.dnsHandler.Handle(".", s)
authWrapper := s.authHTTPWrapper
// API Routes
s.router.HandleFunc("/skydns/services/{uuid}", authWrapper(s.addServiceHTTPHandler)).Methods("PUT")
s.router.HandleFunc("/skydns/services/{uuid}", authWrapper(s.getServiceHTTPHandler)).Methods("GET")
s.router.HandleFunc("/skydns/services/{uuid}", authWrapper(s.removeServiceHTTPHandler)).Methods("DELETE")
s.router.HandleFunc("/skydns/services/{uuid}", authWrapper(s.updateServiceHTTPHandler)).Methods("PATCH")
s.router.HandleFunc("/skydns/callbacks/{uuid}", authWrapper(s.addCallbackHTTPHandler)).Methods("PUT")
// External API Routes
// /skydns/services #list all services
s.router.HandleFunc("/skydns/services/", authWrapper(s.getServicesHTTPHandler)).Methods("GET")
// /skydns/regions #list all regions
s.router.HandleFunc("/skydns/regions/", authWrapper(s.getRegionsHTTPHandler)).Methods("GET")
// /skydns/environnments #list all environments
s.router.HandleFunc("/skydns/environments/", authWrapper(s.getEnvironmentsHTTPHandler)).Methods("GET")
// Raft Routes
s.router.HandleFunc("/raft/join", s.joinHandler).Methods("POST")
return
}
func NewZone(name string) *Zone {
zone := new(Zone)
zone.Labels = make(labels)
zone.Origin = name
zone.LabelCount = dns.CountLabel(zone.Origin)
// defaults
zone.Options.Ttl = 120
zone.Options.MaxHosts = 2
zone.Options.Contact = "hostmaster." + name
zone.Options.Targeting = TargetGlobal + TargetCountry + TargetContinent
return zone
}
// ServeDNSForward forwards a request to a nameservers and returns the response.
func (s *server) ServeDNSForward(w dns.ResponseWriter, req *dns.Msg) {
StatsForwardCount.Inc(1)
if len(s.config.Nameservers) == 0 || dns.CountLabel(req.Question[0].Name) < s.config.Ndots {
s.config.log.Infof("no nameservers defined or name too short, can not forward")
m := new(dns.Msg)
m.SetReply(req)
m.SetRcode(req, dns.RcodeServerFailure)
m.Authoritative = false // no matter what set to false
m.RecursionAvailable = true // and this is still true
w.WriteMsg(m)
return
}
tcp := false
if _, ok := w.RemoteAddr().(*net.TCPAddr); ok {
tcp = true
}
var (
r *dns.Msg
err error
try int
)
// Use request Id for "random" nameserver selection.
nsid := int(req.Id) % len(s.config.Nameservers)
Redo:
switch tcp {
case false:
r, _, err = s.dnsUDPclient.Exchange(req, s.config.Nameservers[nsid])
case true:
r, _, err = s.dnsTCPclient.Exchange(req, s.config.Nameservers[nsid])
}
if err == nil {
r.Compress = true
w.WriteMsg(r)
return
}
// 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
}
s.config.log.Errorf("failure to forward request %q", err)
m := new(dns.Msg)
m.SetReply(req)
m.SetRcode(req, dns.RcodeServerFailure)
w.WriteMsg(m)
}
// Newserver returns a new server.
// TODO(miek): multiple ectdAddrs
func NewServer(domain, dnsAddr string, nameservers []string, etcdAddr string) *server {
s := &server{
domain: dns.Fqdn(strings.ToLower(domain)),
domainLabels: dns.CountLabel(dns.Fqdn(domain)),
DnsAddr: dnsAddr,
client: etcd.NewClient([]string{etcdAddr}),
dnsHandler: dns.NewServeMux(),
waiter: new(sync.WaitGroup),
nameservers: nameservers,
}
// DNS
s.dnsHandler.Handle(".", s)
return s
}
func setDefaults(config *Config) error {
if config.ReadTimeout == 0 {
config.ReadTimeout = 2 * time.Second
}
if config.DnsAddr == "" {
config.DnsAddr = "127.0.0.1:53"
}
if config.Domain == "" {
config.Domain = "skydns.local"
}
if config.MinTtl == 0 {
config.MinTtl = 60
}
if config.Ttl == 0 {
config.Ttl = 3600
}
if config.Priority == 0 {
config.Priority = 10
}
if len(config.Nameservers) == 0 {
c, err := dns.ClientConfigFromFile("/etc/resolv.conf")
if err != nil {
return err
}
for _, s := range c.Servers {
config.Nameservers = append(config.Nameservers, net.JoinHostPort(s, c.Port))
}
}
config.Domain = dns.Fqdn(strings.ToLower(config.Domain))
config.DomainLabels = dns.CountLabel(config.Domain)
if config.DNSSEC != "" {
// For some reason the + are replaces by spaces in etcd. Re-replace them
keyfile := strings.Replace(config.DNSSEC, " ", "+", -1)
k, p, err := ParseKeyFile(keyfile)
if err != nil {
return err
}
if k.Header().Name != dns.Fqdn(config.Domain) {
return fmt.Errorf("ownername of DNSKEY must match SkyDNS domain")
}
k.Header().Ttl = config.Ttl
config.PubKey = k
config.KeyTag = k.KeyTag()
config.PrivKey = p
}
return nil
}
// getZoneForName returns the zone string that matches the name and a
// list of the DNS labels from name that are within the zone.
// For example, if "coredns.local" is a zone configured for the
// Kubernetes middleware, then getZoneForName("a.b.coredns.local")
// will return ("coredns.local", ["a", "b"]).
func (g Kubernetes) getZoneForName(name string) (string, []string) {
var zone string
var serviceSegments []string
for _, z := range g.Zones {
if dns.IsSubDomain(z, name) {
zone = z
serviceSegments = dns.SplitDomainName(name)
serviceSegments = serviceSegments[:len(serviceSegments)-dns.CountLabel(zone)]
break
}
}
return zone, serviceSegments
}
// Look in .../dns/stub/<zone>/xx for msg.Services. Loop through them
// extract <zone> and add them as forwarders (ip:port-combos) for
// the stub zones. Only numeric (i.e. IP address) hosts are used.
// Only the first zone configured on e is used for the lookup.
func (e *Etcd) updateStubZones() {
zone := e.Zones[0]
services, err := e.Records(stubDomain+"."+zone, false)
if err != nil {
return
}
stubmap := make(map[string]proxy.Proxy)
// track the nameservers on a per domain basis, but allow a list on the domain.
nameservers := map[string][]string{}
for _, serv := range services {
if serv.Port == 0 {
serv.Port = 53
}
ip := net.ParseIP(serv.Host)
if ip == nil {
log.Printf("[WARNING] Non IP address stub nameserver: %s", serv.Host)
continue
}
domain := msg.Domain(serv.Key)
labels := dns.SplitDomainName(domain)
// If the remaining name equals any of the zones we have, we ignore it.
for _, z := range e.Zones {
// Chop of left most label, because that is used as the nameserver place holder
// and drop the right most labels that belong to zone.
// We must *also* chop of dns.stub. which means cutting two more labels.
domain = dns.Fqdn(strings.Join(labels[1:len(labels)-dns.CountLabel(z)-2], "."))
if domain == z {
log.Printf("[WARNING] Skipping nameserver for domain we are authoritative for: %s", domain)
continue
}
nameservers[domain] = append(nameservers[domain], net.JoinHostPort(serv.Host, strconv.Itoa(serv.Port)))
}
}
for domain, nss := range nameservers {
stubmap[domain] = proxy.New(nss)
}
// atomic swap (at least that's what we hope it is)
if len(stubmap) > 0 {
e.Stubmap = &stubmap
}
return
}
// 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) {
StatsLookupCount.Inc(1)
promExternalRequestCount.WithLabelValues("lookup").Inc()
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 := new(dns.Msg)
m.SetQuestion(n, t)
m.SetEdns0(bufsize, dnssec)
nsid := int(m.Id) % len(s.config.Nameservers)
try := 0
Redo:
r, _, err := s.dnsUDPclient.Exchange(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")
}
// 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) {
StatsLookupCount.Inc(1)
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 := new(dns.Msg)
m.SetQuestion(n, t)
m.SetEdns0(bufsize, dnssec)
c := &dns.Client{Net: "udp", ReadTimeout: 2 * s.config.ReadTimeout, WriteTimeout: 2 * s.config.ReadTimeout}
nsid := int(m.Id) % len(s.config.Nameservers)
try := 0
Redo:
// Move this to use s.udpClient/s.tcpClient code instead of allocating a new client for every query.
r, _, err := c.Exchange(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")
}
func setDefaults(config *Config) error {
if config.ReadTimeout == 0 {
config.ReadTimeout = 2 * time.Second
}
if config.WriteTimeout == 0 {
config.WriteTimeout = 2 * time.Second
}
if config.DnsAddr == "" {
config.DnsAddr = "127.0.0.1:53"
}
if config.Domain == "" {
config.Domain = "skydns.local"
}
if len(config.Nameservers) == 0 {
c, err := dns.ClientConfigFromFile("/etc/resolv.conf")
if err != nil {
return err
}
for _, s := range c.Servers {
config.Nameservers = append(config.Nameservers, net.JoinHostPort(s, c.Port))
}
}
if config.DNSSEC != "" {
k, p, err := ParseKeyFile(config.DNSSEC)
if err != nil {
return err
}
if k.Header().Name != dns.Fqdn(config.Domain) {
return fmt.Errorf("ownername of DNSKEY must match SkyDNS domain")
}
config.PubKey = k
config.KeyTag = k.KeyTag()
config.PrivKey = p
}
config.Domain = dns.Fqdn(strings.ToLower(config.Domain))
config.DomainLabels = dns.CountLabel(config.Domain)
return nil
}
func getKey(req *dns.Msg) (*CacheKey, error) {
questions := req.Question
if len(questions) != 1 {
return nil, errors.New("Invalid number of questions")
}
question := questions[0]
if question.Qclass != dns.ClassINET {
return nil, errors.New("Unsupported question class")
}
if dns.CountLabel(question.Name) < *minLabelsCount {
return nil, errors.New("Not enough labels")
}
dnssec := false
for _, extra := range req.Extra {
if extra.Header().Rrtype == dns.TypeOPT {
dnssec = extra.(*dns.OPT).Do()
}
}
CacheKey := CacheKey{Name: strings.ToLower(question.Name),
Qtype: question.Qtype, DNSSEC: dnssec}
return &CacheKey, nil
}
func (r *Resolver) iterateParents(qname string, qtype string, depth int) (RRs, error) {
chanRRs := make(chan RRs, MaxNameservers)
chanErrs := make(chan error, MaxNameservers)
for pname, ok := qname, true; ok; pname, ok = parent(pname) {
if pname == qname && qtype == "NS" { // If we’re looking for [foo.com,NS], then skip to [com,NS]
continue
}
// Only query TLDs against the root nameservers
if pname == "." && dns.CountLabel(qname) != 1 {
// fmt.Fprintf(os.Stderr, "Warning: non-TLD query at root: dig +norecurse %s %s\n", qname, qtype)
return nil, nil
}
// Get nameservers
nrrs, err := r.resolve(pname, "NS", depth)
if err == NXDOMAIN {
return nil, err
}
if err != nil {
continue
}
// Early out for specific queries
if len(nrrs) > 0 && qtype != "" {
rrs, err := r.cacheGet(qname, qtype)
if err != nil {
return nil, err
}
if len(rrs) > 0 {
return rrs, nil
}
}
// Query all nameservers in parallel
count := 0
for _, nrr := range nrrs {
if nrr.Type != "NS" {
continue
}
go func(host string) {
rrs, err := r.exchange(host, qname, qtype, depth)
if err != nil {
chanErrs <- err
} else {
chanRRs <- rrs
}
}(nrr.Value)
count++
if count >= MaxNameservers {
break
}
}
// Wait for first response
for ; count > 0; count-- {
select {
case rrs := <-chanRRs:
for _, nrr := range nrrs {
if nrr.Name == qname {
rrs = append(rrs, nrr)
}
}
return r.resolveCNAMEs(qname, qtype, rrs, depth)
case err = <-chanErrs:
if err == NXDOMAIN {
return nil, err
}
}
}
// NS queries naturally recurse, so stop further iteration
if qtype == "NS" {
return nil, err
}
}
return nil, ErrNoResponse
}
// ServeDNSForward forwards a request to a nameservers and returns the response.
func (s *server) ServeDNSForward(w dns.ResponseWriter, req *dns.Msg) *dns.Msg {
StatsForwardCount.Inc(1)
promExternalRequestCount.WithLabelValues("recursive").Inc()
if s.config.NoRec {
m := new(dns.Msg)
m.SetReply(req)
m.SetRcode(req, dns.RcodeServerFailure)
m.Authoritative = false
m.RecursionAvailable = false
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 := new(dns.Msg)
m.SetReply(req)
m.SetRcode(req, dns.RcodeServerFailure)
m.Authoritative = false // no matter what set to false
m.RecursionAvailable = true // and this is still true
w.WriteMsg(m)
return m
}
tcp := isTCP(w)
var (
r *dns.Msg
err error
try int
)
// Use request Id for "random" nameserver selection.
nsid := int(req.Id) % len(s.config.Nameservers)
Redo:
switch tcp {
case false:
r, _, err = s.dnsUDPclient.Exchange(req, s.config.Nameservers[nsid])
case true:
r, _, err = s.dnsTCPclient.Exchange(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 := new(dns.Msg)
m.SetReply(req)
m.SetRcode(req, dns.RcodeServerFailure)
w.WriteMsg(m)
return m
}
// ServeDNSForward resolves a query by forwarding to a recursive nameserver
func (s *server) ServeDNSForward(w dns.ResponseWriter, req *dns.Msg) *dns.Msg {
name := req.Question[0].Name
nameDots := dns.CountLabel(name) - 1
refuse := false
switch {
case s.config.NoRec:
log.Debugf("[%d] Refusing query, recursion disabled", req.Id)
refuse = true
case len(s.config.Nameservers) == 0:
log.Debugf("[%d] Refusing query, no nameservers configured", req.Id)
refuse = true
case nameDots < s.config.FwdNdots && !s.config.EnableSearch:
log.Debugf("[%d] Refusing query, qname '%s' too short to forward", req.Id, name)
refuse = true
}
if refuse {
m := new(dns.Msg)
m.SetRcode(req, dns.RcodeRefused)
writeMsg(w, m)
return m
}
StatsForwardCount.Inc(1)
var searchEnabled, didAbsolute, didSearch bool
var absoluteRes, searchRes *dns.Msg // responses from absolute/search lookups
var absoluteErr, searchErr error // errors from absolute/search lookups
tcp := isTCP(w)
if s.config.EnableSearch && len(s.config.SearchDomains) > 0 {
searchEnabled = true
}
// If there are enough dots in the name, start with trying to
// resolve the literal name
if nameDots >= s.config.Ndots {
if nameDots >= s.config.FwdNdots {
log.Debugf("[%d] Doing initial absolute lookup", req.Id)
absoluteRes, absoluteErr = s.forwardQuery(req, tcp)
if absoluteErr != nil {
log.Errorf("[%d] Error looking up literal qname '%s' with upstreams: %v", req.Id, name, absoluteErr)
}
if absoluteErr == nil && absoluteRes.Rcode == dns.RcodeSuccess {
log.Debugf("[%d] Initial lookup yielded result. Response to client: %s",
req.Id, dns.RcodeToString[absoluteRes.Rcode])
absoluteRes.Compress = true
absoluteRes.Id = req.Id
writeMsg(w, absoluteRes)
return absoluteRes
}
didAbsolute = true
} else {
log.Debugf("[%d] Not doing absolute lookup, name too short: '%s'", req.Id, name)
}
}
// We do at least one level of search if search is enabled
// and we didn't previously fail to query the upstreams
if absoluteErr == nil && searchEnabled {
log.Debugf("[%d] Doing search lookup", req.Id)
searchRes, searchErr = s.forwardSearch(req, tcp)
if searchErr != nil {
log.Errorf("[%d] Error looking up qname '%s' with search: %v", req.Id, name, searchErr)
}
if searchErr == nil && searchRes.Rcode == dns.RcodeSuccess {
log.Debugf("[%d] Search lookup yielded result. Response to client: %s",
req.Id, dns.RcodeToString[searchRes.Rcode])
searchRes.Compress = true
searchRes.Id = req.Id
writeMsg(w, searchRes)
return searchRes
}
didSearch = true
}
// If we didn't yet do an absolute lookup then do that now
// if there are enough dots in the name and searching did
// not previously fail
if searchErr == nil && !didAbsolute {
if nameDots >= s.config.FwdNdots {
log.Debugf("[%d] Doing absolute lookup", req.Id)
absoluteRes, absoluteErr = s.forwardQuery(req, tcp)
if absoluteErr != nil {
log.Errorf("[%d] Error resolving literal qname '%s': %v", req.Id, name, absoluteErr)
}
if absoluteErr == nil && absoluteRes.Rcode == dns.RcodeSuccess {
log.Debugf("[%d] Absolute lookup yielded result. Response to client: %s",
req.Id, dns.RcodeToString[absoluteRes.Rcode])
absoluteRes.Compress = true
absoluteRes.Id = req.Id
writeMsg(w, absoluteRes)
return absoluteRes
}
didAbsolute = true
} else {
log.Debugf("[%d] Not doing absolute lookup, name too short: '%s'", req.Id, name)
}
}
// If we got here, we failed to get a positive result for the query.
// If we did an absolute query, return that result, otherwise return
// a no-data response with the rcode from the last search we did.
if didAbsolute && absoluteErr == nil {
log.Debugf("[%d] Failed to resolve query. Returning response of absolute lookup: %s",
req.Id, dns.RcodeToString[absoluteRes.Rcode])
absoluteRes.Compress = true
absoluteRes.Id = req.Id
writeMsg(w, absoluteRes)
return absoluteRes
}
if didSearch && searchErr == nil {
log.Debugf("[%d] Failed to resolve query. Returning no-data response: %s",
req.Id, dns.RcodeToString[searchRes.Rcode])
m := new(dns.Msg)
m.SetRcode(req, searchRes.Rcode)
writeMsg(w, m)
return m
}
// If we got here, we either failed to forward the query or the qname was too
// short to forward.
log.Debugf("[%d] Error forwarding query. Returning SRVFAIL.", req.Id)
m := new(dns.Msg)
m.SetRcode(req, dns.RcodeServerFailure)
writeMsg(w, m)
return m
}