Add package to discover API resources. (#5213)

* Add package to discover API resources.

* Change package name discover -> discovery

pkg/discovery/discovery.go

@@ -0,0 +1,45 @@
+package discovery
+
+import (
+	"context"
+
+	"github.com/pkg/errors"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/runtime/schema"
+	"k8s.io/client-go/discovery"
+)
+
+func AllGVRs(ctx context.Context, cli discovery.DiscoveryInterface) ([]schema.GroupVersionResource, error) {
+	arls, err := cli.ServerPreferredResources()
+	if err != nil {
+		return nil, errors.Wrap(err, "Failed to list APIResources")
+	}
+	return apiToGroupVersion(arls)
+}
+
+func NamespacedGVRs(ctx context.Context, cli discovery.DiscoveryInterface) ([]schema.GroupVersionResource, error) {
+	arls, err := cli.ServerPreferredNamespacedResources()
+	if err != nil {
+		return nil, errors.Wrap(err, "Failed to list APIResources")
+	}
+	return apiToGroupVersion(arls)
+}
+
+func apiToGroupVersion(arls []*metav1.APIResourceList) ([]schema.GroupVersionResource, error) {
+	gvrs := make([]schema.GroupVersionResource, 0, len(arls))
+	for _, arl := range arls {
+		gv, err := schema.ParseGroupVersion(arl.GroupVersion)
+		if err != nil {
+			return nil, errors.Wrapf(err, "Failed to Parse GroupVersion %s", arl.GroupVersion)
+		}
+		for _, ar := range arl.APIResources {
+			// Although APIResources have Group and Version fields they're empty as of client-go v1.13.1
+			gvrs = append(gvrs, schema.GroupVersionResource{
+				Group:    gv.Group,
+				Version:  gv.Version,
+				Resource: ar.Name,
+			})
+		}
+	}
+	return gvrs, nil
+}

pkg/discovery/discovery_test.go

@@ -0,0 +1,40 @@
+package discovery
+
+import (
+	"context"
+	"testing"
+
+	. "gopkg.in/check.v1"
+
+	"github.com/kanisterio/kanister/pkg/kube"
+)
+
+// Hook up gocheck into the "go test" runner.
+func Test(t *testing.T) { TestingT(t) }
+
+type DiscoverSuite struct{}
+
+var _ = Suite(&DiscoverSuite{})
+
+func (s *DiscoverSuite) TestDiscover(c *C) {
+	ctx := context.Background()
+	cli, err := kube.NewClient()
+	c.Assert(err, IsNil)
+	gvrs, err := AllGVRs(ctx, cli.Discovery())
+	c.Assert(err, IsNil)
+	c.Assert(gvrs, Not(HasLen), 0)
+	for _, gvr := range gvrs {
+		c.Assert(gvr.Empty(), Equals, false)
+		c.Assert(gvr.Version, Not(Equals), "")
+		c.Assert(gvr.Resource, Not(Equals), "")
+	}
+
+	gvrs, err = NamespacedGVRs(ctx, cli.Discovery())
+	c.Assert(err, IsNil)
+	c.Assert(gvrs, Not(HasLen), 0)
+	for _, gvr := range gvrs {
+		c.Assert(gvr.Empty(), Equals, false)
+		c.Assert(gvr.Version, Not(Equals), "")
+		c.Assert(gvr.Resource, Not(Equals), "")
+	}
+}