feat: add adminapi endpoints helpers

internal/adminapi/endpoints.go

@@ -0,0 +1,83 @@
+package adminapi
+
+import (
+	"context"
+	"fmt"
+
+	discoveryv1 "k8s.io/api/discovery/v1"
+	"k8s.io/apimachinery/pkg/labels"
+	"k8s.io/apimachinery/pkg/selection"
+	"k8s.io/apimachinery/pkg/types"
+	"k8s.io/apimachinery/pkg/util/sets"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+)
+
+// GetURLsForService performs an endpoint lookup, using provided kubeClient
+// to list provided Admin API Service EndpointSlices.
+func GetURLsForService(ctx context.Context, kubeClient client.Client, service types.NamespacedName) (sets.Set[string], error) {
+	const (
+		defaultEndpointSliceListPagingLimit = 100
+	)
+
+	// Get all the EndpointSlices assigned to the provided service.
+	labelReq, err := labels.NewRequirement("kubernetes.io/service-name", selection.Equals, []string{service.Name})
+	if err != nil {
+		return nil, err
+	}
+
+	var (
+		addresses     = sets.New[string]()
+		continueToken string
+		labelSelector = labels.NewSelector().Add(*labelReq)
+	)
+	for {
+		var endpointsList discoveryv1.EndpointSliceList
+		if err := kubeClient.List(ctx, &endpointsList, &client.ListOptions{
+			LabelSelector: labelSelector,
+			Namespace:     service.Namespace,
+			Continue:      continueToken,
+			Limit:         defaultEndpointSliceListPagingLimit,
+		}); err != nil {
+			return nil, err
+		}
+
+		for _, es := range endpointsList.Items {
+			addresses = addresses.Union(AddressesFromEndpointSlice(es))
+		}
+
+		if endpointsList.Continue == "" {
+			break
+		}
+	}
+	return addresses, nil
+}
+
+// AddressesFromEndpointSlice returns a list of Admin API addresses when given
+// an Endpointslice.
+func AddressesFromEndpointSlice(endpoints discoveryv1.EndpointSlice) sets.Set[string] {
+	addresses := sets.New[string]()
+	for _, p := range endpoints.Ports {
+		if p.Name == nil {
+			continue
+		}
+
+		// NOTE: consider making this configurable.
+		if *p.Name != "admin" {
+			continue
+		}
+
+		for _, e := range endpoints.Endpoints {
+			if e.Conditions.Ready == nil || !*e.Conditions.Ready {
+				continue
+			}
+
+			for _, addr := range e.Addresses {
+				// NOTE: We assume https here because the referenced Admin API
+				// server will live in another Pod/elsewhere so allowing http would
+				// not be considered best practice.
+				addresses.Insert(fmt.Sprintf("https://%s:%d", addr, *p.Port))
+			}
+		}
+	}
+	return addresses
+}