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

* 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>

1 files changed, 3 insertions, 6 deletions

diff --git a/plugin/rewrite/class.go b/plugin/rewrite/class.go
index 178cf8181..243a86449 100644
--- a/plugin/rewrite/class.go
+++ b/plugin/rewrite/class.go
@@ -30,18 +30,15 @@ func newClassRule(nextAction string, args ...string) (Rule, error) {
 }
 
 // Rewrite rewrites the current request.
-func (rule *classRule) Rewrite(ctx context.Context, state request.Request) Result {
+func (rule *classRule) Rewrite(ctx context.Context, state request.Request) (ResponseRules, Result) {
 	if rule.fromClass > 0 && rule.toClass > 0 {
 		if state.Req.Question[0].Qclass == rule.fromClass {
 			state.Req.Question[0].Qclass = rule.toClass
-			return RewriteDone
+			return nil, RewriteDone
 		}
 	}
-	return RewriteIgnored
+	return nil, RewriteIgnored
 }
 
 // Mode returns the processing mode.
 func (rule *classRule) Mode() string { return rule.NextAction }
-
-// GetResponseRules return rules to rewrite the response with. Currently not implemented.
-func (rule *classRule) GetResponseRules() []ResponseRule { return []ResponseRule{} }