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dns.go
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dns.go
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// Copyright 2019, Shulhan <ms@kilabit.info>. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package dkim
import (
"errors"
"fmt"
"github.com/shuLhan/share/lib/dns"
)
var dnsClientPool *dns.UDPClientPool
func newDNSClientPool() (err error) {
var ns []string
if len(DefaultNameServers) > 0 {
ns = DefaultNameServers
} else {
ns = dns.GetSystemNameServers("")
if len(ns) == 0 {
ns = append(ns, "1.1.1.1")
}
}
dnsClientPool, err = dns.NewUDPClientPool(ns)
if err != nil {
err = errors.New("dkim: newDNSClientPool: " + err.Error())
return err
}
return nil
}
func lookupDNS(opt QueryOption, dname string) (key *Key, err error) {
if opt == QueryOptionTXT {
key, err = lookupDNSTXT(dname)
}
return key, err
}
func lookupDNSTXT(dname string) (key *Key, err error) {
if len(dname) == 0 {
return nil, nil
}
if dnsClientPool == nil {
err = newDNSClientPool()
if err != nil {
return nil, err
}
}
dnsClient := dnsClientPool.Get()
q := dns.MessageQuestion{
Name: dname,
Type: dns.RecordTypeTXT,
}
dnsMsg, err := dnsClient.Lookup(q, true)
if err != nil {
dnsClientPool.Put(dnsClient)
return nil, fmt.Errorf("dkim: LookupKey: %w", err)
}
if dnsMsg.Header.RCode != dns.RCodeOK {
dnsClientPool.Put(dnsClient)
return nil, fmt.Errorf("dkim: LookupKey: DNS response status: %d",
dnsMsg.Header.RCode)
}
if len(dnsMsg.Answer) == 0 {
dnsClientPool.Put(dnsClient)
return nil, fmt.Errorf("dkim: LookupKey: empty answer on '%s'", dname)
}
dnsClientPool.Put(dnsClient)
answers := dnsMsg.FilterAnswers(dns.RecordTypeTXT)
if len(answers) == 0 {
return nil, fmt.Errorf("dkim: LookupKey: no TXT record on '%s'", dname)
}
if len(answers) != 1 {
return nil, fmt.Errorf("dkim: LookupKey: multiple TXT records on '%s'", dname)
}
txt := answers[0].Value.(string)
return ParseTXT([]byte(txt), answers[0].TTL)
}