lib/dns: add option to set hook on server when receiving answer

The hook function, OnAnswerReceived, will be triggered when server
receive valid answer but before its put to caches.

2 files changed, 12 insertions, 0 deletions

diff --git a/lib/dns/server.go b/lib/dns/server.go
index ca2baa5b..438c36dd 100644
--- a/lib/dns/server.go
+++ b/lib/dns/server.go
@@ -690,6 +690,11 @@ func (srv *Server) processResponse(req *request, res *Message) (an *Answer, inse
 	}
 
 	an = newAnswer(res, false)
+
+	if srv.opts.OnAnswerReceived != nil {
+		srv.opts.OnAnswerReceived(an)
+	}
+
 	an, inserted = srv.Caches.upsert(an)
 
 	return an, inserted, nil
diff --git a/lib/dns/server_options.go b/lib/dns/server_options.go
index 20629c2b..9c042b5a 100644
--- a/lib/dns/server_options.go
+++ b/lib/dns/server_options.go
@@ -31,6 +31,9 @@ const (
 	DebugLevelConnPacket = 4
 )
 
+// HookFunc define type function that will be triggered on specific event.
+type HookFunc func(answer *Answer)
+
 // ServerOptions describes options for running a DNS server.
 type ServerOptions struct {
 	primaryUDP []net.Addr // List of parent name server addresses using UDP.
@@ -53,6 +56,10 @@ type ServerOptions struct {
 	// TLSPrivateKey contains path to certificate private key file.
 	TLSPrivateKey string `ini:"dns:server:tls.private_key"`
 
+	// OnAnswerReceived define the hook to be triggered when server
+	// receive valid answer, before its put to caches.
+	OnAnswerReceived HookFunc `json:"-" ini:"-"`
+
 	// NameServers contains list of parent name servers.
 	//
 	// Answer that does not exist on local will be forwarded to parent