Use API discovery to determine the preferred API versions for Gateway…

… API types.

Clusters may not always have the v1 CRDs installed. This means gwctl will have
to use whatever version is available in the cluster. Hence, we will use API
Discovery to determine the "preferred" API version as per the kube-apiserver and
then use a dynamic client to fetch that specific versioned resource.

Once that specific versioned resource is fetched (e.g. v1beta1.Gateway), it will
be converted to a concrete type used within gwctl (eg. v1.Gateway), which will
usually be a more newer/stable version. For most cases, this conversion should
not result in any losses. If in the future, a need arises for such special
cases, we should be able to extend the approach by configuring some conversion
functions (eg. conversion function for v1beta1.Gateway -> v1.Gateway).

gwctl/cmd/describe.go

@@ -77,10 +77,7 @@ func runDescribe(cmd *cobra.Command, args []string, params *utils.CmdParams) {
 		ns = metav1.NamespaceAll
 	}
 
-	discoverer := resourcediscovery.Discoverer{
-		K8sClients:    params.K8sClients,
-		PolicyManager: params.PolicyManager,
-	}
+	discoverer := resourcediscovery.NewDiscoverer(params.K8sClients, params.PolicyManager)
 	policiesPrinter := &printer.PoliciesPrinter{Out: params.Out}
 	httpRoutesPrinter := &printer.HTTPRoutesPrinter{Out: params.Out}
 	gwPrinter := &printer.GatewaysPrinter{Out: params.Out}

gwctl/cmd/get.go

@@ -75,10 +75,7 @@ func runGet(cmd *cobra.Command, args []string, params *utils.CmdParams) {
 		ns = ""
 	}
 
-	discoverer := resourcediscovery.Discoverer{
-		K8sClients:    params.K8sClients,
-		PolicyManager: params.PolicyManager,
-	}
+	discoverer := resourcediscovery.NewDiscoverer(params.K8sClients, params.PolicyManager)
 	realClock := clock.RealClock{}
 	nsPrinter := &printer.NamespacesPrinter{Out: params.Out, Clock: realClock}
 	gwPrinter := &printer.GatewaysPrinter{Out: params.Out, Clock: realClock}

gwctl/pkg/common/clients.go

@@ -22,6 +22,7 @@ import (
 
 	apiextensionsv1 "k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1"
 	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/runtime/schema"
 	"k8s.io/client-go/discovery"
 	"k8s.io/client-go/dynamic"
 	fakedynamicclient "k8s.io/client-go/dynamic/fake"
@@ -94,9 +95,52 @@ func MustClientsForTest(t *testing.T, initRuntimeObjects ...runtime.Object) *K8s
 	}
 
 	fakeClient := fakeclient.NewClientBuilder().WithScheme(scheme).WithRuntimeObjects(initRuntimeObjects...).Build()
-	fakeDC := fakedynamicclient.NewSimpleDynamicClient(scheme, initRuntimeObjects...)
 	fakeDiscoveryClient := fakeclientset.NewSimpleClientset().Discovery()
 
+	// Setup a fake DynamicClient, which requires some special handling.
+	//
+	// When objects are injected using `NewSimpleDynamicClient` or
+	// `NewSimpleDynamicClientWithCustomListKinds` to the fake resource tracker,
+	// internally it will use the `meta.UnsafeGuessKindToResource()` function.
+	// This incorrectly guesses the GVR of Gateway with Resource being guessed as
+	// "gatewaies" (missing 'y'). In order to get around this, we will have to
+	// create Gateway objects separately.
+	//
+	// Also, becomes of this incorrect guessing, we need to register the
+	// GatewayList type separately as well.
+	gatewayv1GVR := schema.GroupVersionResource{
+		Group:    gatewayv1.GroupVersion.Group,
+		Version:  gatewayv1.GroupVersion.Version,
+		Resource: "gateways",
+	}
+	gvrToListKind := map[schema.GroupVersionResource]string{
+		gatewayv1GVR: "GatewayList",
+	}
+	for _, obj := range initRuntimeObjects {
+		if crd, ok := obj.(*apiextensionsv1.CustomResourceDefinition); ok {
+			gvr := schema.GroupVersionResource{
+				Group:    crd.Spec.Group,
+				Version:  crd.Spec.Versions[0].Name,
+				Resource: crd.Spec.Names.Plural, // CRD Kinds directly map to the Resource.
+			}
+			gvrToListKind[gvr] = crd.Spec.Names.Kind + "List"
+		}
+	}
+	fakeDC := fakedynamicclient.NewSimpleDynamicClientWithCustomListKinds(scheme, gvrToListKind)
+	for _, obj := range initRuntimeObjects {
+		var err error
+		if gateway, ok := obj.(*gatewayv1.Gateway); ok {
+			// Register Gateway with correct GVR (since the guessed GVR is incorrect).
+			err = fakeDC.Tracker().Create(gatewayv1GVR, gateway, gateway.Namespace)
+		} else {
+			// Register non-Gateway resources automatically without GVR.
+			err = fakeDC.Tracker().Add(obj)
+		}
+		if err != nil {
+			t.Fatalf("Failed to add object to fake DynamicClient: %v", err)
+		}
+	}
+
 	return &K8sClients{
 		Client:          fakeClient,
 		DC:              fakeDC,