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package acme
import (
"crypto/sha256"
"encoding/base64"
"errors"
"fmt"
"log"
"net"
"strings"
"time"
"github.com/miekg/dns"
"golang.org/x/net/publicsuffix"
)
type preCheckDNSFunc func(fqdn, value string) (bool, error)
var (
// PreCheckDNS checks DNS propagation before notifying ACME that
// the DNS challenge is ready.
PreCheckDNS preCheckDNSFunc = checkDNSPropagation
fqdnToZone = map[string]string{}
)
const defaultResolvConf = "/etc/resolv.conf"
var defaultNameservers = []string{
"google-public-dns-a.google.com:53",
"google-public-dns-b.google.com:53",
}
var RecursiveNameservers = getNameservers(defaultResolvConf, defaultNameservers)
// DNSTimeout is used to override the default DNS timeout of 10 seconds.
var DNSTimeout = 10 * time.Second
// getNameservers attempts to get systems nameservers before falling back to the defaults
func getNameservers(path string, defaults []string) []string {
config, err := dns.ClientConfigFromFile(path)
if err != nil || len(config.Servers) == 0 {
return defaults
}
systemNameservers := []string{}
for _, server := range config.Servers {
// ensure all servers have a port number
if _, _, err := net.SplitHostPort(server); err != nil {
systemNameservers = append(systemNameservers, net.JoinHostPort(server, "53"))
} else {
systemNameservers = append(systemNameservers, server)
}
}
return systemNameservers
}
// DNS01Record returns a DNS record which will fulfill the `dns-01` challenge
func DNS01Record(domain, keyAuth string) (fqdn string, value string, ttl int) {
keyAuthShaBytes := sha256.Sum256([]byte(keyAuth))
// base64URL encoding without padding
keyAuthSha := base64.URLEncoding.EncodeToString(keyAuthShaBytes[:sha256.Size])
value = strings.TrimRight(keyAuthSha, "=")
ttl = 120
fqdn = fmt.Sprintf("_acme-challenge.%s.", domain)
return
}
// dnsChallenge implements the dns-01 challenge according to ACME 7.5
type dnsChallenge struct {
jws *jws
validate validateFunc
provider ChallengeProvider
}
func (s *dnsChallenge) Solve(chlng challenge, domain string) error {
logf("[INFO][%s] acme: Trying to solve DNS-01", domain)
if s.provider == nil {
return errors.New("No DNS Provider configured")
}
// Generate the Key Authorization for the challenge
keyAuth, err := getKeyAuthorization(chlng.Token, s.jws.privKey)
if err != nil {
return err
}
err = s.provider.Present(domain, chlng.Token, keyAuth)
if err != nil {
return fmt.Errorf("Error presenting token: %s", err)
}
defer func() {
err := s.provider.CleanUp(domain, chlng.Token, keyAuth)
if err != nil {
log.Printf("Error cleaning up %s: %v ", domain, err)
}
}()
fqdn, value, _ := DNS01Record(domain, keyAuth)
logf("[INFO][%s] Checking DNS record propagation using %+v", domain, RecursiveNameservers)
var timeout, interval time.Duration
switch provider := s.provider.(type) {
case ChallengeProviderTimeout:
timeout, interval = provider.Timeout()
default:
timeout, interval = 60*time.Second, 2*time.Second
}
err = WaitFor(timeout, interval, func() (bool, error) {
return PreCheckDNS(fqdn, value)
})
if err != nil {
return err
}
return s.validate(s.jws, domain, chlng.URI, challenge{Resource: "challenge", Type: chlng.Type, Token: chlng.Token, KeyAuthorization: keyAuth})
}
// checkDNSPropagation checks if the expected TXT record has been propagated to all authoritative nameservers.
func checkDNSPropagation(fqdn, value string) (bool, error) {
// Initial attempt to resolve at the recursive NS
r, err := dnsQuery(fqdn, dns.TypeTXT, RecursiveNameservers, true)
if err != nil {
return false, err
}
if r.Rcode == dns.RcodeSuccess {
// If we see a CNAME here then use the alias
for _, rr := range r.Answer {
if cn, ok := rr.(*dns.CNAME); ok {
if cn.Hdr.Name == fqdn {
fqdn = cn.Target
break
}
}
}
}
authoritativeNss, err := lookupNameservers(fqdn)
if err != nil {
return false, err
}
return checkAuthoritativeNss(fqdn, value, authoritativeNss)
}
// checkAuthoritativeNss queries each of the given nameservers for the expected TXT record.
func checkAuthoritativeNss(fqdn, value string, nameservers []string) (bool, error) {
for _, ns := range nameservers {
r, err := dnsQuery(fqdn, dns.TypeTXT, []string{net.JoinHostPort(ns, "53")}, false)
if err != nil {
return false, err
}
if r.Rcode != dns.RcodeSuccess {
return false, fmt.Errorf("NS %s returned %s for %s", ns, dns.RcodeToString[r.Rcode], fqdn)
}
var found bool
for _, rr := range r.Answer {
if txt, ok := rr.(*dns.TXT); ok {
if strings.Join(txt.Txt, "") == value {
found = true
break
}
}
}
if !found {
return false, fmt.Errorf("NS %s did not return the expected TXT record", ns)
}
}
return true, nil
}
// dnsQuery will query a nameserver, iterating through the supplied servers as it retries
// The nameserver should include a port, to facilitate testing where we talk to a mock dns server.
func dnsQuery(fqdn string, rtype uint16, nameservers []string, recursive bool) (in *dns.Msg, err error) {
m := new(dns.Msg)
m.SetQuestion(fqdn, rtype)
m.SetEdns0(4096, false)
if !recursive {
m.RecursionDesired = false
}
// Will retry the request based on the number of servers (n+1)
for i := 1; i <= len(nameservers)+1; i++ {
ns := nameservers[i%len(nameservers)]
udp := &dns.Client{Net: "udp", Timeout: DNSTimeout}
in, _, err = udp.Exchange(m, ns)
if err == dns.ErrTruncated {
tcp := &dns.Client{Net: "tcp", Timeout: DNSTimeout}
// If the TCP request suceeds, the err will reset to nil
in, _, err = tcp.Exchange(m, ns)
}
if err == nil {
break
}
}
return
}
// lookupNameservers returns the authoritative nameservers for the given fqdn.
func lookupNameservers(fqdn string) ([]string, error) {
var authoritativeNss []string
zone, err := FindZoneByFqdn(fqdn, RecursiveNameservers)
if err != nil {
return nil, fmt.Errorf("Could not determine the zone: %v", err)
}
r, err := dnsQuery(zone, dns.TypeNS, RecursiveNameservers, 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
}
return nil, fmt.Errorf("Could not determine authoritative nameservers")
}
// FindZoneByFqdn determines the zone apex for the given fqdn by recursing up the
// domain labels until the nameserver returns a SOA record in the answer section.
func FindZoneByFqdn(fqdn string, nameservers []string) (string, error) {
// Do we have it cached?
if zone, ok := fqdnToZone[fqdn]; ok {
return zone, nil
}
labelIndexes := dns.Split(fqdn)
for _, index := range labelIndexes {
domain := fqdn[index:]
// Give up if we have reached the TLD
if isTLD(domain) {
break
}
in, err := dnsQuery(domain, dns.TypeSOA, nameservers, true)
if err != nil {
return "", err
}
// Any response code other than NOERROR and NXDOMAIN is treated as error
if in.Rcode != dns.RcodeNameError && in.Rcode != dns.RcodeSuccess {
return "", fmt.Errorf("Unexpected response code '%s' for %s",
dns.RcodeToString[in.Rcode], domain)
}
// Check if we got a SOA RR in the answer section
if in.Rcode == dns.RcodeSuccess {
for _, ans := range in.Answer {
if soa, ok := ans.(*dns.SOA); ok {
zone := soa.Hdr.Name
fqdnToZone[fqdn] = zone
return zone, nil
}
}
}
}
return "", fmt.Errorf("Could not find the start of authority")
}
func isTLD(domain string) bool {
publicsuffix, _ := publicsuffix.PublicSuffix(UnFqdn(domain))
if publicsuffix == UnFqdn(domain) {
return true
}
return false
}
// ClearFqdnCache clears the cache of fqdn to zone mappings. Primarily used in testing.
func ClearFqdnCache() {
fqdnToZone = map[string]string{}
}
// ToFqdn converts the name into a fqdn appending a trailing dot.
func ToFqdn(name string) string {
n := len(name)
if n == 0 || name[n-1] == '.' {
return name
}
return name + "."
}
// UnFqdn converts the fqdn into a name removing the trailing dot.
func UnFqdn(name string) string {
n := len(name)
if n != 0 && name[n-1] == '.' {
return name[:n-1]
}
return name
}
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