280 lines
7.6 KiB
Go
280 lines
7.6 KiB
Go
package acme
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import (
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"crypto/sha256"
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"encoding/base64"
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"errors"
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"fmt"
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"log"
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"net"
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"strings"
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"time"
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"github.com/miekg/dns"
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"golang.org/x/net/publicsuffix"
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)
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type preCheckDNSFunc func(fqdn, value string) (bool, error)
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var (
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preCheckDNS preCheckDNSFunc = checkDNSPropagation
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fqdnToZone = map[string]string{}
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)
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var RecursiveNameservers = []string{
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"google-public-dns-a.google.com:53",
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"google-public-dns-b.google.com:53",
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}
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// DNSTimeout is used to override the default DNS timeout of 10 seconds.
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var DNSTimeout = 10 * time.Second
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// DNS01Record returns a DNS record which will fulfill the `dns-01` challenge
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func DNS01Record(domain, keyAuth string) (fqdn string, value string, ttl int) {
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keyAuthShaBytes := sha256.Sum256([]byte(keyAuth))
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// base64URL encoding without padding
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keyAuthSha := base64.URLEncoding.EncodeToString(keyAuthShaBytes[:sha256.Size])
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value = strings.TrimRight(keyAuthSha, "=")
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ttl = 120
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fqdn = fmt.Sprintf("_acme-challenge.%s.", domain)
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return
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}
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// dnsChallenge implements the dns-01 challenge according to ACME 7.5
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type dnsChallenge struct {
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jws *jws
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validate validateFunc
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provider ChallengeProvider
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}
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func (s *dnsChallenge) Solve(chlng challenge, domain string) error {
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logf("[INFO][%s] acme: Trying to solve DNS-01", domain)
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if s.provider == nil {
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return errors.New("No DNS Provider configured")
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}
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// Generate the Key Authorization for the challenge
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keyAuth, err := getKeyAuthorization(chlng.Token, s.jws.privKey)
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if err != nil {
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return err
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}
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err = s.provider.Present(domain, chlng.Token, keyAuth)
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if err != nil {
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return fmt.Errorf("Error presenting token: %s", err)
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}
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defer func() {
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err := s.provider.CleanUp(domain, chlng.Token, keyAuth)
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if err != nil {
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log.Printf("Error cleaning up %s: %v ", domain, err)
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}
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}()
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fqdn, value, _ := DNS01Record(domain, keyAuth)
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logf("[INFO][%s] Checking DNS record propagation...", domain)
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var timeout, interval time.Duration
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switch provider := s.provider.(type) {
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case ChallengeProviderTimeout:
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timeout, interval = provider.Timeout()
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default:
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timeout, interval = 60*time.Second, 2*time.Second
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}
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err = WaitFor(timeout, interval, func() (bool, error) {
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return preCheckDNS(fqdn, value)
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})
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if err != nil {
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return err
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}
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return s.validate(s.jws, domain, chlng.URI, challenge{Resource: "challenge", Type: chlng.Type, Token: chlng.Token, KeyAuthorization: keyAuth})
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}
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// checkDNSPropagation checks if the expected TXT record has been propagated to all authoritative nameservers.
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func checkDNSPropagation(fqdn, value string) (bool, error) {
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// Initial attempt to resolve at the recursive NS
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r, err := dnsQuery(fqdn, dns.TypeTXT, RecursiveNameservers, true)
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if err != nil {
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return false, err
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}
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if r.Rcode == dns.RcodeSuccess {
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// If we see a CNAME here then use the alias
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for _, rr := range r.Answer {
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if cn, ok := rr.(*dns.CNAME); ok {
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if cn.Hdr.Name == fqdn {
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fqdn = cn.Target
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break
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}
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}
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}
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}
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authoritativeNss, err := lookupNameservers(fqdn)
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if err != nil {
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return false, err
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}
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return checkAuthoritativeNss(fqdn, value, authoritativeNss)
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}
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// checkAuthoritativeNss queries each of the given nameservers for the expected TXT record.
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func checkAuthoritativeNss(fqdn, value string, nameservers []string) (bool, error) {
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for _, ns := range nameservers {
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r, err := dnsQuery(fqdn, dns.TypeTXT, []string{net.JoinHostPort(ns, "53")}, false)
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if err != nil {
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return false, err
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}
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if r.Rcode != dns.RcodeSuccess {
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return false, fmt.Errorf("NS %s returned %s for %s", ns, dns.RcodeToString[r.Rcode], fqdn)
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}
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var found bool
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for _, rr := range r.Answer {
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if txt, ok := rr.(*dns.TXT); ok {
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if strings.Join(txt.Txt, "") == value {
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found = true
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break
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}
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}
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}
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if !found {
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return false, fmt.Errorf("NS %s did not return the expected TXT record", ns)
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}
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}
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return true, nil
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}
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// dnsQuery will query a nameserver, iterating through the supplied servers as it retries
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// The nameserver should include a port, to facilitate testing where we talk to a mock dns server.
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func dnsQuery(fqdn string, rtype uint16, nameservers []string, recursive bool) (in *dns.Msg, err error) {
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m := new(dns.Msg)
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m.SetQuestion(fqdn, rtype)
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m.SetEdns0(4096, false)
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if !recursive {
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m.RecursionDesired = false
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}
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// Will retry the request based on the number of servers (n+1)
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for i := 1; i <= len(nameservers)+1; i++ {
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ns := nameservers[i%len(nameservers)]
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udp := &dns.Client{Net: "udp", Timeout: DNSTimeout}
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in, _, err = udp.Exchange(m, ns)
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if err == dns.ErrTruncated {
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tcp := &dns.Client{Net: "tcp", Timeout: DNSTimeout}
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// If the TCP request suceeds, the err will reset to nil
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in, _, err = tcp.Exchange(m, ns)
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}
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if err == nil {
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break
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}
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}
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return
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}
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// lookupNameservers returns the authoritative nameservers for the given fqdn.
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func lookupNameservers(fqdn string) ([]string, error) {
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var authoritativeNss []string
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zone, err := FindZoneByFqdn(fqdn, RecursiveNameservers)
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if err != nil {
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return nil, err
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}
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r, err := dnsQuery(zone, dns.TypeNS, RecursiveNameservers, true)
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if err != nil {
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return nil, err
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}
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for _, rr := range r.Answer {
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if ns, ok := rr.(*dns.NS); ok {
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authoritativeNss = append(authoritativeNss, strings.ToLower(ns.Ns))
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}
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}
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if len(authoritativeNss) > 0 {
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return authoritativeNss, nil
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}
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return nil, fmt.Errorf("Could not determine authoritative nameservers")
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}
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// FindZoneByFqdn determines the zone of the given fqdn
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func FindZoneByFqdn(fqdn string, nameservers []string) (string, error) {
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// Do we have it cached?
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if zone, ok := fqdnToZone[fqdn]; ok {
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return zone, nil
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}
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// Query the authoritative nameserver for a hopefully non-existing SOA record,
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// in the authority section of the reply it will have the SOA of the
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// containing zone. rfc2308 has this to say on the subject:
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// Name servers authoritative for a zone MUST include the SOA record of
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// the zone in the authority section of the response when reporting an
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// NXDOMAIN or indicating that no data (NODATA) of the requested type exists
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in, err := dnsQuery(fqdn, dns.TypeSOA, nameservers, true)
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if err != nil {
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return "", err
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}
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if in.Rcode != dns.RcodeNameError {
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if in.Rcode != dns.RcodeSuccess {
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return "", fmt.Errorf("The NS returned %s for %s", dns.RcodeToString[in.Rcode], fqdn)
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}
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// We have a success, so one of the answers has to be a SOA RR
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for _, ans := range in.Answer {
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if soa, ok := ans.(*dns.SOA); ok {
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return checkIfTLD(fqdn, soa)
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}
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}
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// Or it is NODATA, fall through to NXDOMAIN
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}
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// Search the authority section for our precious SOA RR
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for _, ns := range in.Ns {
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if soa, ok := ns.(*dns.SOA); ok {
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return checkIfTLD(fqdn, soa)
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}
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}
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return "", fmt.Errorf("The NS did not return the expected SOA record in the authority section")
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}
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func checkIfTLD(fqdn string, soa *dns.SOA) (string, error) {
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zone := soa.Hdr.Name
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// If we ended up on one of the TLDs, it means the domain did not exist.
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publicsuffix, _ := publicsuffix.PublicSuffix(UnFqdn(zone))
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if publicsuffix == UnFqdn(zone) {
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return "", fmt.Errorf("Could not determine zone authoritatively")
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}
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fqdnToZone[fqdn] = zone
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return zone, nil
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}
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// ClearFqdnCache clears the cache of fqdn to zone mappings. Primarily used in testing.
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func ClearFqdnCache() {
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fqdnToZone = map[string]string{}
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}
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// ToFqdn converts the name into a fqdn appending a trailing dot.
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func ToFqdn(name string) string {
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n := len(name)
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if n == 0 || name[n-1] == '.' {
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return name
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}
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return name + "."
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}
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// UnFqdn converts the fqdn into a name removing the trailing dot.
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func UnFqdn(name string) string {
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n := len(name)
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if n != 0 && name[n-1] == '.' {
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return name[:n-1]
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}
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return name
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}
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