add helper for determining app protocol (#904)

* add helper for determining app protocol

* use string pointer to match with ServicePort

* the ServicePort field for AppProtocol is a string pointer

* add test

* omit type declaration

* link to kep in variable comment

* refactor: change comparison style

pkg/apis/networking/ports.go

@@ -40,6 +40,11 @@ const (
 	ServicePortNameHTTPS = "https"
 )
 
+var (
+	// AppProtocolH2C is the name of the external port of the service for HTTP/2, from https://github.com/kubernetes/enhancements/tree/master/keps/sig-network/3726-standard-application-protocols#new-standard-protocols
+	AppProtocolH2C = "kubernetes.io/h2c"
+)
+
 // ServicePortName returns the port for the app level protocol.
 func ServicePortName(proto ProtocolType) string {
 	if proto == ProtocolH2C {
@@ -55,3 +60,11 @@ func ServicePort(proto ProtocolType) int {
 	}
 	return ServiceHTTPPort
 }
+
+// AppProtocol returns the value for app level protocol based on the ProtocolType
+func AppProtocol(proto ProtocolType) *string {
+	if proto == ProtocolH2C {
+		return &AppProtocolH2C
+	}
+	return nil
+}

pkg/apis/networking/ports_test.go

@@ -36,7 +36,7 @@ func TestServicePortName(t *testing.T) {
 	}}
 	for _, c := range cases {
 		t.Run(c.name, func(t *testing.T) {
-			if got, want := ServicePortName(c.proto), c.expect; !(got == want) {
+			if got, want := ServicePortName(c.proto), c.expect; got != want {
 				t.Errorf("got = %s, want: %s", got, want)
 			}
 		})
@@ -59,7 +59,30 @@ func TestServicePort(t *testing.T) {
 	}}
 	for _, c := range cases {
 		t.Run(c.name, func(t *testing.T) {
-			if got, want := ServicePort(c.proto), c.expect; !(got == want) {
+			if got, want := ServicePort(c.proto), c.expect; got != want {
+				t.Errorf("got = %d, want: %d", got, want)
+			}
+		})
+	}
+}
+
+func TestAppProtocol(t *testing.T) {
+	cases := []struct {
+		name   string
+		proto  ProtocolType
+		expect *string
+	}{{
+		name:   "pass h2c protocol to get Serving and Activator K8s services for HTTP/2 endpoints",
+		proto:  ProtocolH2C,
+		expect: &AppProtocolH2C,
+	}, {
+		name:   "other protocols result in nil",
+		proto:  ProtocolHTTP1,
+		expect: nil,
+	}}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			if got, want := AppProtocol(c.proto), c.expect; got != want {
 				t.Errorf("got = %d, want: %d", got, want)
 			}
 		})