func (d dnsAPI) Recurse(w dns.ResponseWriter, req *dns.Msg) {
var client dns.Client
if isTCP(w.RemoteAddr()) {
client.Net = "tcp"
}
for _, recursor := range d.Recursors {
res, _, err := client.Exchange(req, recursor)
if err != nil {
continue
}
w.WriteMsg(res)
return
}
// Return SERVFAIL
res := &dns.Msg{}
res.RecursionAvailable = true
res.SetRcode(req, dns.RcodeServerFailure)
w.WriteMsg(res)
}
func (d dnsAPI) ServiceLookup(w dns.ResponseWriter, req *dns.Msg) {
qName := req.Question[0].Name
qType := req.Question[0].Qtype
name := strings.TrimSuffix(strings.ToLower(dns.Fqdn(qName)), d.Domain)
labels := dns.SplitDomainName(name)
tcp := isTCP(w.RemoteAddr())
res := &dns.Msg{}
res.Authoritative = true
res.RecursionAvailable = len(d.Recursors) > 0
res.SetReply(req)
defer func() {
if res.Rcode == dns.RcodeSuccess && qType == dns.TypeSOA {
// SOA answer if requested. at the end of the request to ensure we didn't hit NXDOMAIN
res.Answer = []dns.RR{d.soaRecord()}
}
if len(res.Answer) == 0 {
// Add authority section with SOA if the answer has no items
res.Ns = []dns.RR{d.soaRecord()}
}
w.WriteMsg(res)
}()
nxdomain := func() { res.SetRcode(req, dns.RcodeNameError) }
var service string
var proto string
var instanceID string
var leader bool
switch {
case len(labels) == 1:
// normal lookup
service = labels[0]
case len(labels) == 2 && strings.HasPrefix(labels[0], "_") && strings.HasPrefix(labels[1], "_"):
// RFC 2782 request looks like _postgres._tcp
service = labels[0][1:]
proto = labels[1][1:]
case len(labels) == 3 && labels[2] == "_i":
// address lookup for instance in RFC 2782 SRV record
service = labels[1]
instanceID = labels[0]
case len(labels) == 2 && labels[0] == "leader":
// leader lookup
leader = true
service = labels[1]
default:
nxdomain()
return
}
var instances []*discoverd.Instance
if !leader {
instances = d.Store.Get(service)
if instances == nil {
nxdomain()
return
}
}
if leader || instanceID != "" {
// we're doing a lookup for a single instance
var resInst *discoverd.Instance
if leader {
resInst = d.Store.GetLeader(service)
} else {
for _, inst := range instances {
if inst.ID == instanceID {
resInst = inst
break
}
}
}
if resInst == nil {
nxdomain()
return
}
addr := parseAddr(resInst)
if qType != dns.TypeA && qType != dns.TypeAAAA && qType != dns.TypeANY && qType != dns.TypeSRV ||
addr.IPv4 == nil && qType == dns.TypeA ||
addr.IPv6 == nil && qType == dns.TypeAAAA {
// no results if we're looking up an record that doesn't match the
// request type or the type is incorrect
return
}
res.Answer = make([]dns.RR, 0, 2)
if qType != dns.TypeSRV {
res.Answer = append(res.Answer, addrRecord(qName, addr))
}
if qType == dns.TypeSRV || qType == dns.TypeANY {
res.Answer = append(res.Answer, d.srvRecord(qName, service, addr, false))
}
if tcp && qType == dns.TypeSRV {
res.Extra = []dns.RR{addrRecord(qName, addr)}
}
return
}
if qType == dns.TypeSOA {
// We don't need to do any more processing, as NXDOMAIN can't be reached
// beyond this point, the SOA answer is added in the deferred function
// above
return
}
addrs := make([]*addrData, 0, len(instances))
added := make(map[string]struct{}, len(instances))
for _, inst := range instances {
if proto != "" && inst.Proto != proto {
continue
}
addr := parseAddr(inst)
if _, ok := added[addr.String]; ok {
continue
}
if addr.IPv4 == nil && qType == dns.TypeA || addr.IPv6 == nil && qType == dns.TypeAAAA {
// Skip instance if we have an IPv6 address but want IPv4 or vice versa
continue
}
if qType != dns.TypeSRV {
// skip duplicate IPs if we're not doing an SRV lookup
added[addr.String] = struct{}{}
}
addrs = append(addrs, addr)
}
if len(addrs) == 0 {
// return empty response
return
}
shuffle(addrs)
// Truncate the response if we're using UDP
if !tcp && len(addrs) > maxUDPRecords {
addrs = addrs[:maxUDPRecords]
}
res.Answer = make([]dns.RR, 0, len(addrs)*2)
for _, addr := range addrs {
if qType == dns.TypeANY || qType == dns.TypeA || qType == dns.TypeAAAA {
res.Answer = append(res.Answer, addrRecord(qName, addr))
}
}
for _, addr := range addrs {
if qType == dns.TypeANY || qType == dns.TypeSRV {
res.Answer = append(res.Answer, d.srvRecord(qName, service, addr, true))
}
}
if qType == dns.TypeSRV && tcp {
// Add extra records mapping instance IDs to addresses
res.Extra = make([]dns.RR, len(addrs))
for i, addr := range addrs {
res.Extra[i] = addrRecord(d.instanceDomain(service, addr.ID), addr)
}
}
}