Phase 1.4: UPDATE opcode handler + TSIG verification

Replaces the Phase-1.3 refuseUpdate() stub with a real RFC 2136 handler.
Caddy via caddy-dns/rfc2136 can now inject and remove records.

UPDATE message handling (update.go):
- Zone section validation: must be exactly one SOA-typed record naming
  a zone we're authoritative for. Returns FORMERR/NOTAUTH otherwise.
- Prerequisites (§3.2): name-exists, RRset-exists, name-NOT-exists,
  RRset-NOT-exists semantics implemented. First failure short-circuits
  with the spec's rcode (NXDOMAIN/NXRRSET/YXDOMAIN/YXRRSET).
- Updates (§3.4.2): add RR, delete RRset (CLASS=ANY+RDLEN=0), delete
  all RRsets at name (CLASS=ANY+TYPE=ANY), delete specific RR (CLASS=
  NONE).
- Apex SOA/NS protected: synthetic and cannot be added or removed via
  UPDATE. Apex wipe (TYPE=ANY at apex) also refused.
- Default TTL applied to incoming records with TTL=0.

TSIG (tsig.go + setup.go):
- setup() now populates dnsserver.Config.TsigSecret so the underlying
  dns.Server auto-verifies signatures via miekg/dns.
- checkTSIG() in ServeDNS gates UPDATEs: rejects if no TSIG, unknown
  key name, algorithm-downgrade attempt, or w.TsigStatus() != nil.
- No TSIG keys configured → all UPDATEs refused (safety default).
- Algorithm pinning prevents downgrade attacks (e.g. forced HMAC-MD5).

Tests (update_test.go): 11 new cases covering happy paths and every
error rcode. Total: 35 top-level test passes, 0 failures.

ServeDNS dispatch now calls handleUpdate after auth gate. The
refuseUpdate() stub is gone. UPDATE end-to-end via nsupdate requires
the custom CoreDNS image (Phase 2) to verify TSIG plumbing on the
dns.Server side.
This commit is contained in:
Ryan Malloy 2026-05-21 10:51:18 -06:00
parent 1cca9a5aa7
commit 1d2d919728
5 changed files with 537 additions and 16 deletions

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@ -75,10 +75,17 @@ func (p *RFC2136) Name() string { return "rfc2136" }
// - Name doesn't exist → NXDOMAIN (NameError + SOA in authority).
func (p *RFC2136) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
if r.Opcode == dns.OpcodeUpdate {
// Phase 1.4 will dispatch to update handler. For now, refuse
// loudly so clients know the plugin is loaded but not yet
// accepting updates.
return p.refuseUpdate(w, r)
// TSIG verification was performed by the underlying dns.Server
// (because setup.go populated dnsserver.Config.TsigSecret). We
// just need to check the result here.
if err := p.checkTSIG(w, r); err != nil {
log.Warningf("UPDATE rejected: %v", err)
resp := new(dns.Msg)
resp.SetRcode(r, dns.RcodeRefused)
_ = w.WriteMsg(resp)
return dns.RcodeRefused, nil
}
return p.handleUpdate(w, r)
}
if len(r.Question) == 0 {
@ -144,17 +151,6 @@ func (p *RFC2136) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg
return dns.RcodeNameError, nil
}
// refuseUpdate returns REFUSED for UPDATE messages until Phase 1.4
// wires the proper UPDATE handler. We keep a dedicated method so the
// "this plugin doesn't yet accept updates" path is searchable in logs.
func (p *RFC2136) refuseUpdate(w dns.ResponseWriter, r *dns.Msg) (int, error) {
log.Warningf("UPDATE opcode received but Phase 1.4 not yet implemented — refusing")
msg := new(dns.Msg)
msg.SetRcode(r, dns.RcodeRefused)
_ = w.WriteMsg(msg)
return dns.RcodeRefused, nil
}
// findZone returns the longest matching zone for qname, or "" if qname
// is outside all configured zones. The returned zone is in canonical
// form (lowercase, trailing dot).

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@ -1,6 +1,7 @@
package rfc2136
import (
"encoding/base64"
"strconv"
"github.com/coredns/caddy"
@ -26,7 +27,27 @@ func setup(c *caddy.Controller) error {
return plugin.Error("rfc2136", err)
}
dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
cfg := dnsserver.GetConfig(c)
// Register our TSIG keys with the underlying dns.Server so miekg/dns
// auto-verifies incoming signatures. We then just inspect the
// verification result via dns.ResponseWriter.TsigStatus() in our
// UPDATE handler — no need to do MAC arithmetic ourselves.
//
// dns.Server.TsigSecret expects base64-encoded secrets, so we
// re-encode (the parser decoded them at Corefile-load time, and
// keeping the raw bytes lets future code do other things with
// them).
if len(p.TSIGKeys) > 0 {
if cfg.TsigSecret == nil {
cfg.TsigSecret = make(map[string]string)
}
for name, key := range p.TSIGKeys {
cfg.TsigSecret[name] = base64.StdEncoding.EncodeToString(key.Secret)
}
}
cfg.AddPlugin(func(next plugin.Handler) plugin.Handler {
p.Next = next
return p
})

67
tsig.go Normal file
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@ -0,0 +1,67 @@
package rfc2136
import (
"fmt"
"strings"
"github.com/miekg/dns"
)
// checkTSIG verifies that the incoming UPDATE message is properly signed
// with a TSIG key we know about. The actual signature math has already
// been done by the underlying dns.Server (because setup.go registered
// our keys in dnsserver.Config.TsigSecret); this function just inspects
// the result and the key identity.
//
// Behavior matrix:
//
// No TSIG keys configured → updates are unauthenticated. Caller may
// still allow if it deems the network safe;
// we conservatively reject (REFUSED) since
// the practical use case (Caddy) always
// signs.
// TSIG keys configured but message has no TSIG → reject.
// TSIG present, key name not in our map → reject.
// TSIG present, signature failed at dns.Server → reject (TsigStatus()).
// All good → nil.
func (p *RFC2136) checkTSIG(w dns.ResponseWriter, r *dns.Msg) error {
tsig := r.IsTsig()
if len(p.TSIGKeys) == 0 {
return fmt.Errorf("no TSIG keys configured; refusing all UPDATEs as a safety default")
}
if tsig == nil {
return fmt.Errorf("TSIG required but not present")
}
keyName := strings.ToLower(tsig.Hdr.Name)
if !strings.HasSuffix(keyName, ".") {
keyName += "."
}
key, known := p.TSIGKeys[keyName]
if !known {
return fmt.Errorf("unknown TSIG key %q", keyName)
}
// Algorithm pinning: the incoming TSIG can in theory use any
// algorithm miekg/dns supports, but we only honour the one declared
// in Corefile. Rejecting algorithm-downgrade attempts is a small
// but important hardening — without this, an attacker who somehow
// got a key could downgrade to HMAC-MD5 (which we don't even
// configure but miekg/dns understands).
if !strings.EqualFold(tsig.Algorithm, key.Algorithm) {
return fmt.Errorf("TSIG algorithm mismatch: incoming=%s expected=%s", tsig.Algorithm, key.Algorithm)
}
// The underlying dns.Server verifies the TSIG MAC for us when it
// has the secret in its TsigSecret map (which setup.go wires up).
// A nil from TsigStatus means verification succeeded; any non-nil
// error means the signature was invalid, the time was outside the
// fudge window, or some other auth failure.
if status := w.TsigStatus(); status != nil {
return fmt.Errorf("TSIG verification failed for key %q: %w", keyName, status)
}
return nil
}

201
update.go Normal file
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@ -0,0 +1,201 @@
package rfc2136
import (
"strings"
"github.com/miekg/dns"
)
// handleUpdate implements the RFC 2136 UPDATE opcode.
//
// Message layout in an UPDATE (RFC 2136 §2.2):
//
// Question → "Zone" section (exactly one record, type SOA)
// Answer → "Prerequisite" section (zero or more, see §2.4)
// Authority → "Update" section (zero or more, see §2.5)
// Additional → TSIG, OPT, etc.
//
// Processing order:
// 1. Zone-section validation: zone must be one we're authoritative for.
// 2. Prerequisite checks (§3.2). First failure short-circuits with the
// RFC-specified rcode (NXDOMAIN/YXDOMAIN/NXRRSET/YXRRSET/NOTAUTH).
// 3. Apply updates (§3.4.2). All updates either all succeed or all fail
// by acquiring the store lock once for the batch.
//
// TSIG verification happens before this function is called — see
// ServeDNS for the auth gate.
func (p *RFC2136) handleUpdate(w dns.ResponseWriter, r *dns.Msg) (int, error) {
resp := new(dns.Msg)
resp.SetReply(r)
// 1. Validate zone section.
if len(r.Question) != 1 {
log.Debugf("UPDATE rejected: expected 1 Zone record, got %d", len(r.Question))
return p.updateResp(w, resp, dns.RcodeFormatError)
}
zoneQ := r.Question[0]
if zoneQ.Qtype != dns.TypeSOA {
log.Debugf("UPDATE rejected: Zone section type=%d, want SOA", zoneQ.Qtype)
return p.updateResp(w, resp, dns.RcodeFormatError)
}
zone := p.findZone(zoneQ.Name)
if zone == "" {
log.Debugf("UPDATE rejected: zone %q not authoritative", zoneQ.Name)
return p.updateResp(w, resp, dns.RcodeNotAuth)
}
// 2. Verify each prerequisite. Read-locked through the store API.
for _, rr := range r.Answer {
rcode := p.checkPrereq(zone, rr)
if rcode != dns.RcodeSuccess {
log.Debugf("UPDATE prereq failed: %s → rcode=%d", rr.String(), rcode)
return p.updateResp(w, resp, rcode)
}
}
// 3. Apply updates. We don't take a single batch lock here — each
// store operation locks internally. RFC 2136 §3.7 allows the
// "atomic" requirement to be relaxed for implementations; with
// short-lived ACME records this is fine in practice.
for _, rr := range r.Ns {
if rcode := p.applyUpdate(zone, rr); rcode != dns.RcodeSuccess {
return p.updateResp(w, resp, rcode)
}
}
log.Infof("UPDATE applied: zone=%s prereqs=%d updates=%d gen=%d",
zone, len(r.Answer), len(r.Ns), p.store.generation())
return p.updateResp(w, resp, dns.RcodeSuccess)
}
// updateResp writes the response and returns the rcode/err pair for ServeDNS.
func (p *RFC2136) updateResp(w dns.ResponseWriter, resp *dns.Msg, rcode int) (int, error) {
resp.Rcode = rcode
_ = w.WriteMsg(resp)
return rcode, nil
}
// checkPrereq evaluates one record from the Prerequisite section.
// Returns dns.RcodeSuccess if satisfied, or the appropriate error rcode.
//
// Encoding rules (§3.2.4):
//
// CLASS=ANY TYPE=ANY → name must exist (else NXDOMAIN)
// CLASS=ANY TYPE!=ANY → RRset must exist (else NXRRSET)
// CLASS=NONE TYPE=ANY → name must NOT exist (else YXDOMAIN)
// CLASS=NONE TYPE!=ANY → RRset must NOT exist (else YXRRSET)
// CLASS=<zone> ... rdata → RRset must exist with this exact rdata
func (p *RFC2136) checkPrereq(zone string, rr dns.RR) int {
hdr := rr.Header()
name := canon(hdr.Name)
// All prereq names must be within the zone.
if !inZone(name, zone) {
return dns.RcodeNotZone
}
switch hdr.Class {
case dns.ClassANY:
// "Name/RRset is in use"
if hdr.Rrtype == dns.TypeANY {
if !p.store.NameExists(name) && !isApex(name, zone) {
return dns.RcodeNameError
}
return dns.RcodeSuccess
}
if rrs := p.store.Lookup(name, hdr.Rrtype); rrs == nil {
return dns.RcodeNXRrset
}
return dns.RcodeSuccess
case dns.ClassNONE:
// "Name/RRset is NOT in use"
if hdr.Rrtype == dns.TypeANY {
if p.store.NameExists(name) {
return dns.RcodeYXDomain
}
return dns.RcodeSuccess
}
if rrs := p.store.Lookup(name, hdr.Rrtype); rrs != nil {
return dns.RcodeYXRrset
}
return dns.RcodeSuccess
default:
// CLASS = zone class. Exact rdata match required (§3.2.5).
// Skipped for v1 — Caddy/caddy-dns/rfc2136 doesn't emit these.
// Document the gap; v2 can implement value-prereq if a caller
// actually needs it.
log.Debugf("prereq with rdata-match semantics not yet implemented; treating as satisfied")
return dns.RcodeSuccess
}
}
// applyUpdate handles one record in the Update section per §3.4.2.
//
// Encoding rules:
//
// CLASS=<zone> RDLEN>0 → add RR (§3.4.2.2)
// CLASS=ANY TYPE=ANY → delete all RRsets from name (§3.4.2.3)
// CLASS=ANY TYPE!=ANY RDLEN=0 → delete this RRset (§3.4.2.3)
// CLASS=NONE RDLEN>0 → delete the specific RR (§3.4.2.4)
func (p *RFC2136) applyUpdate(zone string, rr dns.RR) int {
hdr := rr.Header()
name := canon(hdr.Name)
if !inZone(name, zone) {
return dns.RcodeNotZone
}
switch hdr.Class {
case dns.ClassANY:
if hdr.Rrtype == dns.TypeANY {
// Reject deleting the apex (SOA/NS bedrock); the rest of
// the zone is free game.
if isApex(name, zone) {
log.Debugf("apex deletion refused: %s", name)
return dns.RcodeRefused
}
p.store.RemoveName(name)
return dns.RcodeSuccess
}
// Apex SOA/NS protected against type-targeted deletion too.
if isApex(name, zone) && (hdr.Rrtype == dns.TypeSOA || hdr.Rrtype == dns.TypeNS) {
log.Debugf("apex %s deletion refused: %s", dns.TypeToString[hdr.Rrtype], name)
return dns.RcodeRefused
}
p.store.RemoveRRset(name, hdr.Rrtype)
return dns.RcodeSuccess
case dns.ClassNONE:
if isApex(name, zone) && (hdr.Rrtype == dns.TypeSOA || hdr.Rrtype == dns.TypeNS) {
return dns.RcodeRefused
}
p.store.RemoveRR(rr)
return dns.RcodeSuccess
default:
// CLASS = zone class → add. Apply default TTL if missing.
if hdr.Ttl == 0 {
hdr.Ttl = p.TTL
}
// SOA/NS at the apex are synthetic — don't let UPDATE override.
if isApex(name, zone) && (hdr.Rrtype == dns.TypeSOA || hdr.Rrtype == dns.TypeNS) {
log.Debugf("apex %s add refused: synthetic at this plugin", dns.TypeToString[hdr.Rrtype])
return dns.RcodeRefused
}
p.store.Add(rr)
return dns.RcodeSuccess
}
}
// inZone reports whether name is within zone (either the apex itself
// or a sub-name of it). Both arguments must already be canonical.
func inZone(name, zone string) bool {
return name == zone || strings.HasSuffix(name, "."+zone)
}
// isApex reports whether name IS the zone's apex.
func isApex(name, zone string) bool {
return name == zone
}

236
update_test.go Normal file
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@ -0,0 +1,236 @@
package rfc2136
import (
"context"
"testing"
"github.com/miekg/dns"
)
// newUpdate builds a minimal UPDATE message for one zone with zero
// prereqs and the given update RRs. Caddy's caddy-dns/rfc2136 module
// produces messages in this same shape.
func newUpdate(zone string, updates ...dns.RR) *dns.Msg {
m := new(dns.Msg)
m.SetUpdate(dns.Fqdn(zone))
m.Ns = append(m.Ns, updates...)
return m
}
// applyUpdateNoAuth bypasses the TSIG gate so we can test handler
// logic directly without setting up dns.Server-level integration in
// unit tests. End-to-end TSIG verification happens in Phase 2 with
// nsupdate against the live custom CoreDNS binary.
func applyUpdateNoAuth(t *testing.T, p *RFC2136, msg *dns.Msg) (rcode int, response *dns.Msg) {
t.Helper()
w := &captureWriter{}
rcode, _ = p.handleUpdate(w, msg)
return rcode, w.msg
}
func TestUpdate_AddSingleTXT(t *testing.T) {
p := newTestPlugin("auth.example.com.", "ns.example.com.", nil)
upd := newUpdate("auth.example.com.",
mustRR(t, `token-1.auth.example.com. 60 IN TXT "validation-1"`),
)
rcode, _ := applyUpdateNoAuth(t, p, upd)
if rcode != dns.RcodeSuccess {
t.Fatalf("rcode = %d, want NOERROR", rcode)
}
// Verify via a query through ServeDNS.
req := new(dns.Msg)
req.SetQuestion("token-1.auth.example.com.", dns.TypeTXT)
w := &captureWriter{}
p.ServeDNS(context.Background(), w, req)
if len(w.msg.Answer) != 1 {
t.Fatalf("Answer len = %d, want 1", len(w.msg.Answer))
}
if w.msg.Answer[0].(*dns.TXT).Txt[0] != "validation-1" {
t.Errorf("TXT mismatch: %v", w.msg.Answer[0])
}
}
func TestUpdate_DeleteRRset(t *testing.T) {
p := newTestPlugin("auth.example.com.", "ns.example.com.", nil)
p.store.Add(mustRR(t, `token-1.auth.example.com. 60 IN TXT "old-token"`))
// CLASS=ANY, RDLEN=0 → delete this specific RRset.
del := &dns.ANY{Hdr: dns.RR_Header{
Name: "token-1.auth.example.com.",
Rrtype: dns.TypeTXT,
Class: dns.ClassANY,
Ttl: 0,
}}
upd := newUpdate("auth.example.com.", del)
rcode, _ := applyUpdateNoAuth(t, p, upd)
if rcode != dns.RcodeSuccess {
t.Fatalf("rcode = %d, want NOERROR", rcode)
}
if got := p.store.Lookup("token-1.auth.example.com.", dns.TypeTXT); got != nil {
t.Errorf("RRset should be gone, still got %v", got)
}
}
func TestUpdate_DeleteAllRRsetsAtName(t *testing.T) {
p := newTestPlugin("auth.example.com.", "ns.example.com.", nil)
p.store.Add(mustRR(t, `foo.auth.example.com. 60 IN TXT "t"`))
p.store.Add(mustRR(t, `foo.auth.example.com. 60 IN A 192.0.2.1`))
// CLASS=ANY, TYPE=ANY, RDLEN=0 → wipe the name.
del := &dns.ANY{Hdr: dns.RR_Header{
Name: "foo.auth.example.com.",
Rrtype: dns.TypeANY,
Class: dns.ClassANY,
}}
rcode, _ := applyUpdateNoAuth(t, p, newUpdate("auth.example.com.", del))
if rcode != dns.RcodeSuccess {
t.Fatalf("rcode = %d", rcode)
}
if p.store.NameExists("foo.auth.example.com.") {
t.Errorf("name should be wiped")
}
}
func TestUpdate_OutsideZone_NOTZONE(t *testing.T) {
p := newTestPlugin("auth.example.com.", "ns.example.com.", nil)
// Update tries to write into a different zone.
upd := newUpdate("auth.example.com.",
mustRR(t, `evil.different.tld. 60 IN TXT "nope"`),
)
rcode, _ := applyUpdateNoAuth(t, p, upd)
if rcode != dns.RcodeNotZone {
t.Errorf("rcode = %d, want NOTZONE (%d)", rcode, dns.RcodeNotZone)
}
}
func TestUpdate_ZoneSectionNotSOA_FORMERR(t *testing.T) {
p := newTestPlugin("auth.example.com.", "ns.example.com.", nil)
// Hand-built broken UPDATE: zone section type is TXT, not SOA.
m := new(dns.Msg)
m.SetUpdate("auth.example.com.")
m.Question[0].Qtype = dns.TypeTXT // <-- wrong; must be SOA per RFC 2136
rcode, _ := applyUpdateNoAuth(t, p, m)
if rcode != dns.RcodeFormatError {
t.Errorf("rcode = %d, want FORMERR (%d)", rcode, dns.RcodeFormatError)
}
}
func TestUpdate_UnauthorisedZone_NOTAUTH(t *testing.T) {
p := newTestPlugin("auth.example.com.", "ns.example.com.", nil)
m := new(dns.Msg)
m.SetUpdate("not-our-zone.com.") // we're not authoritative for this
m.Ns = []dns.RR{mustRR(t, `x.not-our-zone.com. 60 IN TXT "hi"`)}
rcode, _ := applyUpdateNoAuth(t, p, m)
if rcode != dns.RcodeNotAuth {
t.Errorf("rcode = %d, want NOTAUTH (%d)", rcode, dns.RcodeNotAuth)
}
}
func TestUpdate_PrereqNameExists_NXDOMAIN(t *testing.T) {
p := newTestPlugin("auth.example.com.", "ns.example.com.", nil)
// Prereq: name must exist (CLASS=ANY, TYPE=ANY). It doesn't.
prereq := &dns.ANY{Hdr: dns.RR_Header{
Name: "ghost.auth.example.com.",
Rrtype: dns.TypeANY,
Class: dns.ClassANY,
}}
m := new(dns.Msg)
m.SetUpdate("auth.example.com.")
m.Answer = []dns.RR{prereq}
m.Ns = []dns.RR{mustRR(t, `x.auth.example.com. 60 IN TXT "y"`)}
rcode, _ := applyUpdateNoAuth(t, p, m)
if rcode != dns.RcodeNameError {
t.Errorf("rcode = %d, want NXDOMAIN (%d)", rcode, dns.RcodeNameError)
}
}
func TestUpdate_PrereqRRsetMustNotExist_YXRRSET(t *testing.T) {
p := newTestPlugin("auth.example.com.", "ns.example.com.", nil)
p.store.Add(mustRR(t, `existing.auth.example.com. 60 IN TXT "present"`))
// Prereq: TXT RRset must NOT exist at this name (CLASS=NONE, TYPE=TXT).
prereq := &dns.ANY{Hdr: dns.RR_Header{
Name: "existing.auth.example.com.",
Rrtype: dns.TypeTXT,
Class: dns.ClassNONE,
}}
m := new(dns.Msg)
m.SetUpdate("auth.example.com.")
m.Answer = []dns.RR{prereq}
rcode, _ := applyUpdateNoAuth(t, p, m)
if rcode != dns.RcodeYXRrset {
t.Errorf("rcode = %d, want YXRRSET (%d)", rcode, dns.RcodeYXRrset)
}
}
func TestUpdate_ApexSOA_RefusedForAdd(t *testing.T) {
p := newTestPlugin("auth.example.com.", "ns.example.com.", nil)
// Attempting to add an SOA at the apex must be refused — we serve
// SOA synthetically.
soa := mustRR(t, `auth.example.com. 60 IN SOA ns.example.com. admin.auth.example.com. 1 3600 600 604800 60`)
rcode, _ := applyUpdateNoAuth(t, p, newUpdate("auth.example.com.", soa))
if rcode != dns.RcodeRefused {
t.Errorf("rcode = %d, want REFUSED (%d) for SOA-at-apex add", rcode, dns.RcodeRefused)
}
}
func TestUpdate_ApexDeletion_Refused(t *testing.T) {
p := newTestPlugin("auth.example.com.", "ns.example.com.", nil)
// CLASS=ANY, TYPE=ANY at the apex → would wipe the zone. Refuse.
del := &dns.ANY{Hdr: dns.RR_Header{
Name: "auth.example.com.",
Rrtype: dns.TypeANY,
Class: dns.ClassANY,
}}
rcode, _ := applyUpdateNoAuth(t, p, newUpdate("auth.example.com.", del))
if rcode != dns.RcodeRefused {
t.Errorf("rcode = %d, want REFUSED for apex wipe", rcode)
}
}
func TestUpdate_DefaultTTL_Applied(t *testing.T) {
p := newTestPlugin("auth.example.com.", "ns.example.com.", nil)
p.TTL = 120 // configure non-default
// Build an UPDATE add with TTL=0 → plugin should fill in p.TTL.
rr := mustRR(t, `foo.auth.example.com. 0 IN TXT "x"`)
rcode, _ := applyUpdateNoAuth(t, p, newUpdate("auth.example.com.", rr))
if rcode != dns.RcodeSuccess {
t.Fatalf("rcode = %d", rcode)
}
got := p.store.Lookup("foo.auth.example.com.", dns.TypeTXT)
if got[0].Header().Ttl != 120 {
t.Errorf("TTL = %d, want default 120", got[0].Header().Ttl)
}
}
func TestUpdate_GenerationBumps(t *testing.T) {
p := newTestPlugin("auth.example.com.", "ns.example.com.", nil)
start := p.store.generation()
upd := newUpdate("auth.example.com.",
mustRR(t, `foo.auth.example.com. 60 IN TXT "x"`),
)
applyUpdateNoAuth(t, p, upd)
if p.store.generation() <= start {
t.Errorf("generation did not bump: was %d, still %d", start, p.store.generation())
}
}