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resolver.go
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resolver.go
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package dnsrecon
import (
"fmt"
"github.com/miekg/dns"
"net"
)
func (client *DnsClient) DnsResolver(m *dns.Msg) (*dns.Msg, error) {
r := new(dns.Msg)
var err error
key := fmt.Sprintf("%s:%d", m.Question[0].Name, m.Question[0].Qtype)
client.Cache.Mu.Lock()
rFromCache, ok := client.Cache.Lru.Get(key)
client.Cache.Mu.Unlock()
if ok && rFromCache != nil {
return rFromCache.(*dns.Msg), nil
}
var dnsserver string
for i := 0; i != 3; i++ {
err = nil
client.RatelimitRequests()
// get a new dns server if the first retry failed
if i == 2 {
dnsserver = client.GetRetryDnsServer()
} else {
dnsserver = client.GetNameserver()
}
// Check whether the error is retryable
r, _, err = client.dns.Exchange(m, dnsserver)
if err != nil {
if te, ok := err.(interface{ Temporary() bool }); ok {
if neterr, ok := err.(net.Error); ok && neterr.Timeout() {
err = fmt.Errorf("TIMEOUT")
// Retryable
continue
} else if te.Temporary() {
// Retryable
continue
} else {
// Non-retryable
return nil, fmt.Errorf("ERROR")
}
}
}
switch r.Rcode {
case dns.RcodeSuccess:
err = nil
case dns.RcodeNameError:
return nil, fmt.Errorf("NXDOMAIN")
case dns.RcodeNotImplemented:
return nil, fmt.Errorf("NOTIMP")
case dns.RcodeYXDomain:
return nil, fmt.Errorf("YXDOMAIN")
case dns.RcodeNXRrset:
return nil, fmt.Errorf("NXRRSET")
case dns.RcodeYXRrset:
return nil, fmt.Errorf("YXRRSET")
case dns.RcodeNotZone:
return nil, fmt.Errorf("NOTZONE")
case dns.RcodeNotAuth:
return nil, fmt.Errorf("NOTAUTH")
case dns.RcodeBadName:
return nil, fmt.Errorf("BADNAME")
case dns.RcodeBadTrunc:
return nil, fmt.Errorf("BADTRUNC")
case dns.RcodeServerFailure:
return nil, fmt.Errorf("SERVFAIL")
case dns.RcodeRefused:
return nil, fmt.Errorf("REFUSED")
default:
err = fmt.Errorf("ERROR")
}
if err != nil {
continue
}
break
}
if r != nil && r.Rcode == dns.RcodeSuccess {
client.Cache.Mu.Lock()
client.Cache.Lru.Add(key, r)
client.Cache.Mu.Unlock()
}
if err != nil {
client.Log.Printf("dns resolver error: %v", err)
}
return r, err
}