request: stop echoing unhandled EDNS options (#8514)

Signed-off-by: houyuwushang <liuluoqianqiu@outlook.com>

plugin/pkg/edns/edns.go

@@ -15,18 +15,15 @@ type supported struct {
 	sync.RWMutex
 }
 
-// SetSupportedOption adds a new supported option the set of EDNS0 options that we support. Plugins typically call
-// this in their setup code to signal support for a new option.
-// By default we support:
-// dns.EDNS0NSID, dns.EDNS0EXPIRE, dns.EDNS0COOKIE, dns.EDNS0TCPKEEPALIVE, dns.EDNS0PADDING. These
-// values are not in this map and checked directly in the server.
+// SetSupportedOption adds an EDNS0 option to the set of options that CoreDNS may copy from a request to an
+// OPT-less response. Plugins typically call this in their setup code to signal support for a custom option.
 func SetSupportedOption(option uint16) {
 	sup.Lock()
 	sup.m[option] = struct{}{}
 	sup.Unlock()
 }
 
-// SupportedOption returns true if the option code is supported as an extra EDNS0 option.
+// SupportedOption returns true if the option code was explicitly registered.
 func SupportedOption(option uint16) bool {
 	sup.RLock()
 	_, ok := sup.m[option]

plugin/rewrite/rewrite_test.go

@@ -1193,16 +1193,12 @@ func TestRewriteEDNS0RevertDoesNotLeakThroughScrubWriter(t *testing.T) {
 	if o == nil {
 		t.Fatal("expected EDNS0 option record in response")
 	}
-	var foundCookie bool
 	for _, opt := range o.Option {
 		if opt.Option() == 0xffee {
 			t.Fatalf("expected rewritten EDNS0 option to be reverted, got %v", o.Option)
 		}
 		if opt.Option() == dns.EDNS0COOKIE {
-			foundCookie = true
+			t.Fatalf("expected request EDNS0 cookie option not to be copied to the response, got %v", o.Option)
 		}
 	}
-	if !foundCookie {
-		t.Fatalf("expected original EDNS0 cookie option to be preserved, got %v", o.Option)
-	}
 }