1 files changed, 31 insertions, 0 deletions
diff --git a/request/edns0.go b/request/edns0.go
new file mode 100644
index 000000000..89eb6b468
--- /dev/null
+++ b/request/edns0.go
@@ -0,0 +1,31 @@
+package request
+
+import (
+	"github.com/coredns/coredns/plugin/pkg/edns"
+
+	"github.com/miekg/dns"
+)
+
+func supportedOptions(o []dns.EDNS0) []dns.EDNS0 {
+	var supported = make([]dns.EDNS0, 0, 3)
+	// For as long as possible try avoid looking up in the map, because that need an Rlock.
+	for _, opt := range o {
+		switch code := opt.Option(); code {
+		case dns.EDNS0NSID:
+			fallthrough
+		case dns.EDNS0EXPIRE:
+			fallthrough
+		case dns.EDNS0COOKIE:
+			fallthrough
+		case dns.EDNS0TCPKEEPALIVE:
+			fallthrough
+		case dns.EDNS0PADDING:
+			supported = append(supported, opt)
+		default:
+			if edns.SupportedOption(code) {
+				supported = append(supported, opt)
+			}
+		}
+	}
+	return supported
+}