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forwarding.go
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forwarding.go
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// Copyright (c) 2014 The SkyDNS Authors. All rights reserved.
// Use of this source code is governed by The MIT License (MIT) that can be
// found in the LICENSE file.
package server
import (
"fmt"
"github.com/miekg/dns"
)
// ServeDNSForward forwards a request to a nameservers and returns the response.
func (s *server) ServeDNSForward(w dns.ResponseWriter, req *dns.Msg) *dns.Msg {
if s.config.NoRec {
m := s.ServerFailure(req)
w.WriteMsg(m)
return m
}
if len(s.config.Nameservers) == 0 || dns.CountLabel(req.Question[0].Name) < s.config.Ndots {
if s.config.Verbose {
if len(s.config.Nameservers) == 0 {
logf("can not forward, no nameservers defined")
} else {
logf("can not forward, name too short (less than %d labels): `%s'", s.config.Ndots, req.Question[0].Name)
}
}
m := s.ServerFailure(req)
m.RecursionAvailable = true // this is still true
w.WriteMsg(m)
return m
}
var (
r *dns.Msg
err error
)
nsid := s.randomNameserverID(req.Id)
try := 0
Redo:
if isTCP(w) {
r, err = exchangeWithRetry(s.dnsTCPclient, req, s.config.Nameservers[nsid])
} else {
r, err = exchangeWithRetry(s.dnsUDPclient, req, s.config.Nameservers[nsid])
}
if err == nil {
r.Compress = true
r.Id = req.Id
w.WriteMsg(r)
return r
}
// Seen an error, this can only mean, "server not reached", try again
// but only if we have not exausted our nameservers.
if try < len(s.config.Nameservers) {
try++
nsid = (nsid + 1) % len(s.config.Nameservers)
goto Redo
}
logf("failure to forward request %q", err)
m := s.ServerFailure(req)
return m
}
// ServeDNSReverse is the handler for DNS requests for the reverse zone. If nothing is found
// locally the request is forwarded to the forwarder for resolution.
func (s *server) ServeDNSReverse(w dns.ResponseWriter, req *dns.Msg) *dns.Msg {
m := new(dns.Msg)
m.SetReply(req)
m.Compress = true
m.Authoritative = false // Set to false, because I don't know what to do wrt DNSSEC.
m.RecursionAvailable = true
var err error
if m.Answer, err = s.PTRRecords(req.Question[0]); err == nil {
// TODO(miek): Reverse DNSSEC. We should sign this, but requires a key....and more
// Probably not worth the hassle?
if err := w.WriteMsg(m); err != nil {
logf("failure to return reply %q", err)
}
return m
}
// Always forward if not found locally.
return s.ServeDNSForward(w, req)
}
// Lookup looks up name,type using the recursive nameserver defines
// in the server's config. If none defined it returns an error.
func (s *server) Lookup(n string, t, bufsize uint16, dnssec bool) (*dns.Msg, error) {
if len(s.config.Nameservers) == 0 {
return nil, fmt.Errorf("no nameservers configured can not lookup name")
}
if dns.CountLabel(n) < s.config.Ndots {
return nil, fmt.Errorf("name has fewer than %d labels", s.config.Ndots)
}
m := newExchangeMsg(n, t, bufsize, dnssec)
nsid := s.randomNameserverID(m.Id)
try := 0
Redo:
r, err := exchangeWithRetry(s.dnsUDPclient, m, s.config.Nameservers[nsid])
if err == nil {
if r.Rcode != dns.RcodeSuccess {
return nil, fmt.Errorf("rcode %d is not equal to success", r.Rcode)
}
// Reset TTLs to rcache TTL to make some of the other code
// and the tests not care about TTLs
for _, rr := range r.Answer {
rr.Header().Ttl = uint32(s.config.RCacheTtl)
}
for _, rr := range r.Extra {
rr.Header().Ttl = uint32(s.config.RCacheTtl)
}
return r, nil
}
// Seen an error, this can only mean, "server not reached", try again
// but only if we have not exausted our nameservers.
if try < len(s.config.Nameservers) {
try++
nsid = (nsid + 1) % len(s.config.Nameservers)
goto Redo
}
return nil, fmt.Errorf("failure to lookup name")
}