forked from janeczku/go-dnsmasq
/
forwarding.go
300 lines (262 loc) · 8.52 KB
/
forwarding.go
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// Copyright (c) 2015 Jan Broer. 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 (
"strings"
"github.com/miekg/dns"
"github.com/tomoyamachi/go-dnsmasq/pkg/log"
)
// ServeDNSForward resolves a query by forwarding to a recursive nameserver
func (s *Server) ServeDNSForward(w dns.ResponseWriter, req *dns.Msg) *dns.Msg {
name := req.Question[0].Name
nameDots := dns.CountLabel(name) - 1
refuse := false
switch {
case s.config.NoRec:
log.Debugf("[%d] Refusing query, recursion disabled", req.Id)
refuse = true
case len(s.config.Nameservers) == 0:
log.Debugf("[%d] Refusing query, no nameservers configured", req.Id)
refuse = true
case nameDots < s.config.FwdNdots && !s.config.EnableSearch:
log.Debugf("[%d] Refusing query, qname '%s' too short to forward", req.Id, name)
refuse = true
}
if refuse {
m := new(dns.Msg)
m.SetRcode(req, dns.RcodeRefused)
return m
}
StatsForwardCount.Inc(1)
var searchEnabled, didAbsolute, didSearch bool
var absoluteRes, searchRes *dns.Msg // responses from absolute/search lookups
var absoluteErr, searchErr error // errors from absolute/search lookups
tcp := isTCP(w)
if s.config.EnableSearch && len(s.config.SearchDomains) > 0 {
searchEnabled = true
}
// If there are enough dots in the name, start with trying to
// resolve the literal name
if nameDots >= s.config.Ndots {
if nameDots >= s.config.FwdNdots {
log.Debugf("[%d] Doing initial absolute lookup", req.Id)
absoluteRes, absoluteErr = s.forwardQuery(req, tcp)
if absoluteErr != nil {
log.Errorf("[%d] Error looking up literal qname '%s' with upstreams: %v", req.Id, name, absoluteErr)
}
if absoluteErr == nil && absoluteRes.Rcode == dns.RcodeSuccess {
log.Debugf("[%d] Initial lookup yielded result. Response to client: %s",
req.Id, dns.RcodeToString[absoluteRes.Rcode])
absoluteRes.Compress = true
absoluteRes.Id = req.Id
return absoluteRes
}
didAbsolute = true
} else {
log.Debugf("[%d] Not doing absolute lookup, name too short: '%s'", req.Id, name)
}
}
// We do at least one level of search if search is enabled
// and we didn't previously fail to query the upstreams
if absoluteErr == nil && searchEnabled {
log.Debugf("[%d] Doing search lookup", req.Id)
searchRes, searchErr = s.forwardSearch(req, tcp)
if searchErr != nil {
log.Errorf("[%d] Error looking up qname '%s' with search: %v", req.Id, name, searchErr)
}
if searchErr == nil && searchRes.Rcode == dns.RcodeSuccess {
log.Debugf("[%d] Search lookup yielded result. Response to client: %s",
req.Id, dns.RcodeToString[searchRes.Rcode])
searchRes.Compress = true
searchRes.Id = req.Id
return searchRes
}
didSearch = true
}
// If we didn't yet do an absolute lookup then do that now
// if there are enough dots in the name and searching did
// not previously fail
if searchErr == nil && !didAbsolute {
if nameDots >= s.config.FwdNdots {
log.Debugf("[%d] Doing absolute lookup", req.Id)
absoluteRes, absoluteErr = s.forwardQuery(req, tcp)
if absoluteErr != nil {
log.Errorf("[%d] Error resolving literal qname '%s': %v", req.Id, name, absoluteErr)
}
if absoluteErr == nil && absoluteRes.Rcode == dns.RcodeSuccess {
log.Debugf("[%d] Absolute lookup yielded result. Response to client: %s",
req.Id, dns.RcodeToString[absoluteRes.Rcode])
absoluteRes.Compress = true
absoluteRes.Id = req.Id
return absoluteRes
}
didAbsolute = true
} else {
log.Debugf("[%d] Not doing absolute lookup, name too short: '%s'", req.Id, name)
}
}
// If we got here, we failed to get a positive result for the query.
// If we did an absolute query, return that result, otherwise return
// a no-data response with the rcode from the last search we did.
if didAbsolute && absoluteErr == nil {
log.Debugf("[%d] Failed to resolve query. Returning response of absolute lookup: %s",
req.Id, dns.RcodeToString[absoluteRes.Rcode])
absoluteRes.Compress = true
absoluteRes.Id = req.Id
return absoluteRes
}
if didSearch && searchErr == nil {
log.Debugf("[%d] Failed to resolve query. Returning no-data response: %s",
req.Id, dns.RcodeToString[searchRes.Rcode])
m := new(dns.Msg)
m.SetRcode(req, searchRes.Rcode)
return m
}
// If we got here, we either failed to forward the query or the qname was too
// short to forward.
log.Debugf("[%d] Error forwarding query. Returning SRVFAIL.", req.Id)
m := new(dns.Msg)
m.SetRcode(req, dns.RcodeServerFailure)
return m
}
// forwardSearch resolves a query by suffixing with search paths
func (s *Server) forwardSearch(req *dns.Msg, tcp bool) (*dns.Msg, error) {
var r *dns.Msg
var nodata *dns.Msg // stores the copy of a NODATA reply
var searchName string // stores the current name suffixed with search domain
var err error
var didSearch bool
name := req.Question[0].Name // original qname
reqCopy := req.Copy()
for _, domain := range s.config.SearchDomains {
if strings.HasSuffix(name, domain) {
continue
}
searchName = strings.ToLower(appendDomain(name, domain))
reqCopy.Question[0] = dns.Question{searchName, reqCopy.Question[0].Qtype, reqCopy.Question[0].Qclass}
didSearch = true
r, err = s.forwardQuery(reqCopy, tcp)
if err != nil {
// No Server currently available, give up
break
}
switch r.Rcode {
case dns.RcodeSuccess:
// In case of NO_DATA keep searching, otherwise a wildcard entry
// could keep us from finding the answer higher in the search list
if len(r.Answer) == 0 && !r.MsgHdr.Truncated {
nodata = r.Copy()
continue
}
case dns.RcodeNameError:
fallthrough
case dns.RcodeServerFailure:
// try next search element if any
continue
}
// anything else implies that we are done searching
break
}
if !didSearch {
m := new(dns.Msg)
m.SetRcode(req, dns.RcodeNameError)
return m, nil
}
if err == nil {
if r.Rcode == dns.RcodeSuccess {
if len(r.Answer) > 0 {
cname := new(dns.CNAME)
cname.Hdr = dns.RR_Header{Name: name, Rrtype: dns.TypeCNAME, Class: dns.ClassINET, Ttl: 360}
cname.Target = searchName
answers := []dns.RR{cname}
for _, rr := range r.Answer {
answers = append(answers, rr)
}
r.Answer = answers
}
// If we ever got a NODATA, return this instead of a negative result
} else if nodata != nil {
r = nodata
}
// Restore original question
r.Question[0] = req.Question[0]
}
if err != nil && nodata != nil {
r = nodata
r.Question[0] = req.Question[0]
err = nil
}
return r, err
}
// forwardQuery sends the query to nameservers retrying once on error
func (s *Server) forwardQuery(req *dns.Msg, tcp bool) (*dns.Msg, error) {
var nservers []string // Nameservers to use for this query
var nsIdx int
var r *dns.Msg
var err error
nservers = s.config.Nameservers
// Check whether the name matches a stub zone
if s.config.Stub != nil {
for zone, srv := range s.config.Stub {
if strings.HasSuffix(req.Question[0].Name, zone) {
nservers = srv
StatsStubForwardCount.Inc(1)
break
}
}
}
for try := 1; try <= 2; try++ {
log.Debugf("[%d] Querying upstream %s for qname '%s'",
req.Id, nservers[nsIdx], req.Question[0].Name)
switch tcp {
case false:
r, _, err = s.dnsUDPclient.Exchange(req, nservers[nsIdx])
case true:
r, _, err = s.dnsTCPclient.Exchange(req, nservers[nsIdx])
}
if err == nil {
log.Debugf("[%d] Response code from upstream: %s", req.Id, dns.RcodeToString[r.Rcode])
switch r.Rcode {
// SUCCESS
case dns.RcodeSuccess:
fallthrough
case dns.RcodeNameError:
fallthrough
// NO RECOVERY
case dns.RcodeFormatError:
fallthrough
case dns.RcodeRefused:
fallthrough
case dns.RcodeNotImplemented:
return r, err
}
}
if err != nil {
log.Debugf("[%d] Failed to query upstream %s for qname '%s': %v",
req.Id, nservers[nsIdx], req.Question[0].Name, err)
}
// Continue with next available Server
if len(nservers)-1 > nsIdx {
nsIdx++
} else {
nsIdx = 0
}
}
return r, err
}
// 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
m.RecursionAvailable = true
if records, err := s.PTRRecords(req.Question[0]); err == nil && len(records) > 0 {
m.Answer = records
return m
}
// Always forward if not found locally.
return s.ServeDNSForward(w, req)
}