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|
package rewrite
import (
"github.com/miekg/dns"
)
// RevertPolicy controls the overall reverting process
type RevertPolicy interface {
DoRevert() bool
DoQuestionRestore() bool
}
type revertPolicy struct {
noRevert bool
noRestore bool
}
func (p revertPolicy) DoRevert() bool {
return !p.noRevert
}
func (p revertPolicy) DoQuestionRestore() bool {
return !p.noRestore
}
// NoRevertPolicy disables all response rewrite rules
func NoRevertPolicy() RevertPolicy {
return revertPolicy{true, false}
}
// NoRestorePolicy disables the question restoration during the response rewrite
func NoRestorePolicy() RevertPolicy {
return revertPolicy{false, true}
}
// NewRevertPolicy creates a new reverter policy by dynamically specifying all
// options.
func NewRevertPolicy(noRevert, noRestore bool) RevertPolicy {
return revertPolicy{noRestore: noRestore, noRevert: noRevert}
}
// ResponseRule contains a rule to rewrite a response with.
type ResponseRule interface {
RewriteResponse(res *dns.Msg, rr dns.RR)
}
// ResponseRules describes an ordered list of response rules to apply
// after a name rewrite
type ResponseRules = []ResponseRule
// ResponseReverter reverses the operations done on the question section of a packet.
// This is need because the client will otherwise disregards the response, i.e.
// dig will complain with ';; Question section mismatch: got example.org/HINFO/IN'
type ResponseReverter struct {
dns.ResponseWriter
originalQuestion dns.Question
ResponseRules ResponseRules
revertPolicy RevertPolicy
}
// NewResponseReverter returns a pointer to a new ResponseReverter.
func NewResponseReverter(w dns.ResponseWriter, r *dns.Msg, policy RevertPolicy) *ResponseReverter {
return &ResponseReverter{
ResponseWriter: w,
originalQuestion: r.Question[0],
revertPolicy: policy,
}
}
// WriteMsg records the status code and calls the underlying ResponseWriter's WriteMsg method.
func (r *ResponseReverter) WriteMsg(res1 *dns.Msg) error {
// Deep copy 'res' as to not (e.g). rewrite a message that's also stored in the cache.
res := res1.Copy()
if r.revertPolicy.DoQuestionRestore() {
res.Question[0] = r.originalQuestion
}
if len(r.ResponseRules) > 0 {
for _, rr := range res.Ns {
r.rewriteResourceRecord(res, rr)
}
for _, rr := range res.Answer {
r.rewriteResourceRecord(res, rr)
}
for _, rr := range res.Extra {
r.rewriteResourceRecord(res, rr)
}
}
return r.ResponseWriter.WriteMsg(res)
}
func (r *ResponseReverter) rewriteResourceRecord(res *dns.Msg, rr dns.RR) {
for _, rule := range r.ResponseRules {
rule.RewriteResponse(res, rr)
}
}
// Write is a wrapper that records the size of the message that gets written.
func (r *ResponseReverter) Write(buf []byte) (int, error) {
n, err := r.ResponseWriter.Write(buf)
return n, err
}
func getRecordValueForRewrite(rr dns.RR) (name string) {
switch rr.Header().Rrtype {
case dns.TypeSRV:
return rr.(*dns.SRV).Target
case dns.TypeMX:
return rr.(*dns.MX).Mx
case dns.TypeCNAME:
return rr.(*dns.CNAME).Target
case dns.TypeNS:
return rr.(*dns.NS).Ns
case dns.TypeDNAME:
return rr.(*dns.DNAME).Target
case dns.TypeNAPTR:
return rr.(*dns.NAPTR).Replacement
case dns.TypeSOA:
return rr.(*dns.SOA).Ns
case dns.TypePTR:
return rr.(*dns.PTR).Ptr
default:
return ""
}
}
func setRewrittenRecordValue(rr dns.RR, value string) {
switch rr.Header().Rrtype {
case dns.TypeSRV:
rr.(*dns.SRV).Target = value
case dns.TypeMX:
rr.(*dns.MX).Mx = value
case dns.TypeCNAME:
rr.(*dns.CNAME).Target = value
case dns.TypeNS:
rr.(*dns.NS).Ns = value
case dns.TypeDNAME:
rr.(*dns.DNAME).Target = value
case dns.TypeNAPTR:
rr.(*dns.NAPTR).Replacement = value
case dns.TypeSOA:
rr.(*dns.SOA).Ns = value
case dns.TypePTR:
rr.(*dns.PTR).Ptr = value
}
}
|
