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package acmeserver
import (
"context"
"errors"
"fmt"
"log"
"strings"
"time"
"github.com/miekg/dns"
"golang.org/x/crypto/acme"
)
const (
rfc2136Timeout = 600
tsigFudgeSeconds = 300
)
type dnsValidator struct {
nameservers []string
enableTSIG bool
keyName string
keyAlgo string
keySecret string
}
func newDNSValidator(config *Config) (*dnsValidator, error) {
if len(config.DNS.Nameservers) == 0 {
return nil, errors.New("no nameservers configured")
}
// Check that the TSIG parameters are consistent, if provided at all.
n := 0
if config.DNS.TSIGKeyName != "" {
n++
}
if config.DNS.TSIGKeyAlgo != "" {
n++
}
if config.DNS.TSIGKeySecret != "" {
n++
}
if n != 0 && n != 3 {
return nil, errors.New("either none or all of 'tsig_key_name', 'tsig_key_algo' and 'tsig_key_secret' must be set")
}
return &dnsValidator{
nameservers: config.DNS.Nameservers,
enableTSIG: n > 0,
keyName: dns.Fqdn(config.DNS.TSIGKeyName),
keyAlgo: config.DNS.TSIGKeyAlgo,
keySecret: config.DNS.TSIGKeySecret,
}, nil
}
func (d *dnsValidator) makeRR(fqdn, value string, ttl int) []dns.RR {
rr := new(dns.TXT)
rr.Hdr = dns.RR_Header{Name: fqdn, Rrtype: dns.TypeTXT, Class: dns.ClassINET, Ttl: uint32(ttl)}
rr.Txt = []string{value}
return []dns.RR{rr}
}
func (d *dnsValidator) makeMsg(zone string, rrs []dns.RR, remove bool) *dns.Msg {
m := new(dns.Msg)
m.SetUpdate(zone)
if remove {
m.Remove(rrs)
} else {
m.RemoveRRset(rrs)
m.Insert(rrs)
}
if d.enableTSIG {
m.SetTsig(d.keyName, d.keyAlgo, tsigFudgeSeconds, time.Now().Unix())
}
return m
}
func (d *dnsValidator) client() *dns.Client {
c := new(dns.Client)
c.SingleInflight = true
if d.enableTSIG {
// TSIG authentication / msg signing.
c.TsigSecret = map[string]string{d.keyName: d.keySecret}
}
return c
}
func (d *dnsValidator) Fulfill(ctx context.Context, client *acme.Client, domain string, chal *acme.Challenge) (func(), error) {
zone := domain[strings.Index(domain, ".")+1:]
fqdn := dns.Fqdn(domain)
value, err := client.DNS01ChallengeRecord(chal.Token)
if err != nil {
return nil, err
}
if err := d.onAllNS(ctx, func(ns string) error {
return d.updateNS(ctx, ns, zone, fqdn, value, false)
}); err != nil {
return nil, err
}
return func() {
// nolint
d.onAllNS(ctx, func(ns string) error {
return d.updateNS(ctx, ns, zone, fqdn, value, true)
})
}, nil
}
func (d *dnsValidator) updateNS(ctx context.Context, ns, zone, fqdn, value string, remove bool) error {
rrs := d.makeRR(fqdn, value, rfc2136Timeout)
m := d.makeMsg(zone, rrs, remove)
c := d.client()
// Send the query
reply, _, err := c.Exchange(m, ns)
if err != nil {
return err
}
if reply != nil && reply.Rcode != dns.RcodeSuccess {
return fmt.Errorf("DNS server replied: %s", dns.RcodeToString[reply.Rcode])
}
return nil
}
// Run a function for each configured nameserver.
func (d *dnsValidator) onAllNS(ctx context.Context, f func(string) error) error {
ch := make(chan error, len(d.nameservers))
defer close(ch)
for _, ns := range d.nameservers {
if !strings.Contains(ns, ":") {
ns += ":53"
}
go func(ns string) {
err := f(ns)
if err != nil {
log.Printf("error updating DNS server %s: %v", ns, err)
}
ch <- err
}(ns)
}
var ok bool
for i := 0; i < len(d.nameservers); i++ {
if err := <-ch; err == nil {
ok = true
}
}
if !ok {
return errors.New("all nameservers failed")
}
return nil
}