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plugin/rewrite: streamline the ResponseRule handling. (#4473)

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* plugin/rewrite: streamline the ResponseRule handling.

The functionality of a response rule is now completely encapsulated behind
a `ResponseRule` interface. This significantly simplifies the complete
processing flow, it enables more flexible response handling and it is possible
to eliminate lots of state flags, ifs and switches.

Based on the new flexibility the pull request also enables to support a
response name rewrite for all name rewrite types.
To be compatible, an explicit `answer auto` option is added to support
a best effort response rewrite (name and value).
Additionally now all name rewrite rules support additional name and value
reponse rewrite options.

Using this feature it is also possible now to rewrite a complete sub domain
hierarchy to a single domain name combined with a correct rewrite (#2389).

Signed-off-by: Uwe Krueger <uwe.krueger@sap.com>

* revert policy

Signed-off-by: Uwe Krueger <uwe.krueger@sap.com>

Co-authored-by: Miek Gieben <miek@miek.nl>
This commit is contained in:
Uwe Krueger
2021-05-04 10:05:45 +02:00
committed by GitHub
parent 696c8731d6
commit 40edf1e566
13 changed files with 889 additions and 521 deletions
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137
plugin/rewrite/reverter.go
View File

@@ -1,37 +1,69 @@
package rewrite
import (
"regexp"
"strconv"
"strings"
"github.com/miekg/dns"
)
// ResponseRule contains a rule to rewrite a response with.
type ResponseRule struct {
Active bool
Type string
Pattern *regexp.Regexp
Replacement string
TTL uint32
// 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(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
ResponseRewrite bool
ResponseRules []ResponseRule
ResponseRules ResponseRules
revertPolicy RevertPolicy
}
// NewResponseReverter returns a pointer to a new ResponseReverter.
func NewResponseReverter(w dns.ResponseWriter, r *dns.Msg) *ResponseReverter {
func NewResponseReverter(w dns.ResponseWriter, r *dns.Msg, policy RevertPolicy) *ResponseReverter {
return &ResponseReverter{
ResponseWriter: w,
originalQuestion: r.Question[0],
revertPolicy: policy,
}
}
@@ -40,61 +72,33 @@ 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()
res.Question[0] = r.originalQuestion
if r.ResponseRewrite {
if r.revertPolicy.DoQuestionRestore() {
res.Question[0] = r.originalQuestion
}
if len(r.ResponseRules) > 0 {
for _, rr := range res.Ns {
rewriteResourceRecord(res, rr, r)
r.rewriteResourceRecord(res, rr)
}
for _, rr := range res.Answer {
rewriteResourceRecord(res, rr, r)
r.rewriteResourceRecord(res, rr)
}
for _, rr := range res.Extra {
rewriteResourceRecord(res, rr, r)
r.rewriteResourceRecord(res, rr)
}
}
return r.ResponseWriter.WriteMsg(res)
}
func rewriteResourceRecord(res *dns.Msg, rr dns.RR, r *ResponseReverter) {
var (
isNameRewritten bool
isTTLRewritten bool
isValueRewritten bool
name = rr.Header().Name
ttl = rr.Header().Ttl
value string
)
func (r *ResponseReverter) rewriteResourceRecord(res *dns.Msg, rr dns.RR) {
for _, rule := range r.ResponseRules {
if rule.Type == "" {
rule.Type = "name"
}
switch rule.Type {
case "name":
rewriteString(rule, &name, &isNameRewritten)
case "value":
value = getRecordValueForRewrite(rr)
if value != "" {
rewriteString(rule, &value, &isValueRewritten)
}
case "ttl":
ttl = rule.TTL
isTTLRewritten = true
}
rule.RewriteResponse(rr)
}
}
if isNameRewritten {
rr.Header().Name = name
}
if isTTLRewritten {
rr.Header().Ttl = ttl
}
if isValueRewritten {
setRewrittenRecordValue(rr, value)
}
// 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) {
@@ -136,24 +140,3 @@ func setRewrittenRecordValue(rr dns.RR, value string) {
rr.(*dns.SOA).Ns = value
}
}
func rewriteString(rule ResponseRule, str *string, isStringRewritten *bool) {
regexGroups := rule.Pattern.FindStringSubmatch(*str)
if len(regexGroups) == 0 {
return
}
s := rule.Replacement
for groupIndex, groupValue := range regexGroups {
groupIndexStr := "{" + strconv.Itoa(groupIndex) + "}"
s = strings.Replace(s, groupIndexStr, groupValue, -1)
}
*isStringRewritten = true
*str = s
}
// 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
}