Rewrite SRV targets and additional names in response (#4287)

* Rewrite plugin - rewrite SRV targets and names in response answer and additional records Signed-off-by: Nic Colledge <nic@njcolledge.net> * Added README content to describe new behaviour Signed-off-by: Nic Colledge <nic@njcolledge.net> * Added more record types to rewrite handling based on PR/Issue feedback Signed-off-by: Nic Colledge <nic@njcolledge.net> * Updated README.md for plugin Signed-off-by: Nic Colledge <nic@njcolledge.net> * Updated unit tests. Small refactor of getTarget... function. Signed-off-by: Nic Colledge <nic@njcolledge.net> * Refactor to add response value rewrite as answer value option Signed-off-by: Nic Colledge <nic@njcolledge.net> * Removed TODO comment, added test for NAPTR record. Signed-off-by: Nic Colledge <nic@njcolledge.net>
2025-12-06 10:25:10 -05:00 · 2021-02-23 09:12:40 +00:00
parent fe2b5f630d
commit 0103931263
10 changed files with 322 additions and 130 deletions
--- a/plugin/rewrite/reverter.go
+++ b/plugin/rewrite/reverter.go
@@ -42,46 +42,116 @@ func (r *ResponseReverter) WriteMsg(res1 *dns.Msg) error {

 	res.Question[0] = r.originalQuestion
 	if r.ResponseRewrite {
-		for _, rr := range res.Answer {
-			var (
-				isNameRewritten bool
-				isTTLRewritten  bool
-				name            = rr.Header().Name
-				ttl             = rr.Header().Ttl
-			)
-			for _, rule := range r.ResponseRules {
-				if rule.Type == "" {
-					rule.Type = "name"
-				}
-				switch rule.Type {
-				case "name":
-					regexGroups := rule.Pattern.FindStringSubmatch(name)
-					if len(regexGroups) == 0 {
-						continue
-					}
-					s := rule.Replacement
-					for groupIndex, groupValue := range regexGroups {
-						groupIndexStr := "{" + strconv.Itoa(groupIndex) + "}"
-						s = strings.Replace(s, groupIndexStr, groupValue, -1)
-					}
-					name = s
-					isNameRewritten = true
-				case "ttl":
-					ttl = rule.TTL
-					isTTLRewritten = true
-				}
-			}
-			if isNameRewritten {
-				rr.Header().Name = name
-			}
-			if isTTLRewritten {
-				rr.Header().Ttl = ttl
-			}
+		for _, rr := range res.Ns {
+			rewriteResourceRecord(res, rr, r)
 		}
+
+		for _, rr := range res.Answer {
+			rewriteResourceRecord(res, rr, r)
+		}
+
+		for _, rr := range res.Extra {
+			rewriteResourceRecord(res, rr, r)
+		}
+
 	}
 	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
+	)
+
+	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
+		}
+	}
+
+	if isNameRewritten {
+		rr.Header().Name = name
+	}
+	if isTTLRewritten {
+		rr.Header().Ttl = ttl
+	}
+	if isValueRewritten {
+		setRewrittenRecordValue(rr, value)
+	}
+}
+
+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
+	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
+	}
+}
+
+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)