Implement getter machinery to generically fetch all injected clients (#2054)

client/injection/apiextensions/client/client.go

@@ -29,6 +29,9 @@ import (
 
 func init() {
 	injection.Default.RegisterClient(withClient)
+	injection.Default.RegisterClientFetcher(func(ctx context.Context) interface{} {
+		return Get(ctx)
+	})
 }
 
 // Key is used as the key for associating information with a context.Context.

client/injection/apiextensions/client/fake/fake.go

@@ -31,6 +31,9 @@ import (
 
 func init() {
 	injection.Fake.RegisterClient(withClient)
+	injection.Fake.RegisterClientFetcher(func(ctx context.Context) interface{} {
+		return Get(ctx)
+	})
 }
 
 func withClient(ctx context.Context, cfg *rest.Config) context.Context {

client/injection/kube/client/client.go

@@ -29,6 +29,9 @@ import (
 
 func init() {
 	injection.Default.RegisterClient(withClient)
+	injection.Default.RegisterClientFetcher(func(ctx context.Context) interface{} {
+		return Get(ctx)
+	})
 }
 
 // Key is used as the key for associating information with a context.Context.

client/injection/kube/client/fake/fake.go

@@ -31,6 +31,9 @@ import (
 
 func init() {
 	injection.Fake.RegisterClient(withClient)
+	injection.Fake.RegisterClientFetcher(func(ctx context.Context) interface{} {
+		return Get(ctx)
+	})
 }
 
 func withClient(ctx context.Context, cfg *rest.Config) context.Context {

codegen/cmd/injection-gen/generators/client.go

@@ -66,7 +66,11 @@ func (g *clientGenerator) GenerateType(c *generator.Context, t *types.Type, w io
 		"clientSetNewForConfigOrDie": c.Universe.Function(types.Name{Package: g.clientSetPackage, Name: "NewForConfigOrDie"}),
 		"clientSetInterface":         c.Universe.Type(types.Name{Package: g.clientSetPackage, Name: "Interface"}),
 		"injectionRegisterClient":    c.Universe.Function(types.Name{Package: "knative.dev/pkg/injection", Name: "Default.RegisterClient"}),
-		"restConfig":                 c.Universe.Type(types.Name{Package: "k8s.io/client-go/rest", Name: "Config"}),
+		"injectionRegisterClientFetcher": c.Universe.Function(types.Name{
+			Package: "knative.dev/pkg/injection",
+			Name:    "Default.RegisterClientFetcher",
+		}),
+		"restConfig": c.Universe.Type(types.Name{Package: "k8s.io/client-go/rest", Name: "Config"}),
 		"loggingFromContext": c.Universe.Function(types.Name{
 			Package: "knative.dev/pkg/logging",
 			Name:    "FromContext",
@@ -85,6 +89,9 @@ func (g *clientGenerator) GenerateType(c *generator.Context, t *types.Type, w io
 var injectionClient = `
 func init() {
 	{{.injectionRegisterClient|raw}}(withClient)
+	{{.injectionRegisterClientFetcher|raw}}(func(ctx context.Context) interface{} {
+		return Get(ctx)
+	})
 }
 
 // Key is used as the key for associating information with a context.Context.

codegen/cmd/injection-gen/generators/fake_client.go

@@ -71,6 +71,10 @@ func (g *fakeClientGenerator) GenerateType(c *generator.Context, t *types.Type,
 			Package: "knative.dev/pkg/injection",
 			Name:    "Fake.RegisterClient",
 		}),
+		"injectionRegisterClientFetcher": c.Universe.Function(types.Name{
+			Package: "knative.dev/pkg/injection",
+			Name:    "Fake.RegisterClientFetcher",
+		}),
 		"loggingFromContext": c.Universe.Function(types.Name{
 			Package: "knative.dev/pkg/logging",
 			Name:    "FromContext",
@@ -91,6 +95,9 @@ func (g *fakeClientGenerator) GenerateType(c *generator.Context, t *types.Type,
 var injectionFakeClient = `
 func init() {
 	{{.injectionRegisterClient|raw}}(withClient)
+	{{.injectionRegisterClientFetcher|raw}}(func(ctx context.Context) interface{} {
+		return Get(ctx)
+	})
 }
 
 func withClient(ctx {{.contextContext|raw}}, cfg *{{.restConfig|raw}}) {{.contextContext|raw}} {

injection/clients.go

@@ -26,6 +26,10 @@ import (
 // client type to a context.
 type ClientInjector func(context.Context, *rest.Config) context.Context
 
+// ClientFetcher holds the type of a callback that returns a particular client type
+// from a context.
+type ClientFetcher func(context.Context) interface{}
+
 func (i *impl) RegisterClient(ci ClientInjector) {
 	i.m.Lock()
 	defer i.m.Unlock()
@@ -40,3 +44,21 @@ func (i *impl) GetClients() []ClientInjector {
 	// Copy the slice before returning.
 	return append(i.clients[:0:0], i.clients...)
 }
+
+func (i *impl) RegisterClientFetcher(f ClientFetcher) {
+	i.m.Lock()
+	defer i.m.Unlock()
+
+	i.clientFetchers = append(i.clientFetchers, f)
+}
+
+func (i *impl) FetchAllClients(ctx context.Context) []interface{} {
+	i.m.RLock()
+	defer i.m.RUnlock()
+
+	clients := make([]interface{}, 0, len(i.clientFetchers))
+	for _, f := range i.clientFetchers {
+		clients = append(clients, f(ctx))
+	}
+	return clients
+}

injection/clients_test.go

@@ -20,6 +20,7 @@ import (
 	"context"
 	"testing"
 
+	"github.com/google/go-cmp/cmp"
 	"k8s.io/client-go/rest"
 )
 
@@ -50,3 +51,35 @@ func TestRegisterClient(t *testing.T) {
 		t.Errorf("GetClients() = %d, wanted %d", want, got)
 	}
 }
+
+type fakeClient struct {
+	Name string
+}
+
+func TestRegisterClientFetcher(t *testing.T) {
+	i := &impl{}
+
+	fakeA := fakeClient{Name: "a"}
+	fetchA := func(ctx context.Context) interface{} {
+		return fakeA
+	}
+
+	fakeB := fakeClient{Name: "b"}
+	fetchB := func(ctx context.Context) interface{} {
+		return fakeB
+	}
+
+	ctx := context.Background()
+	if want, got := 0, len(i.FetchAllClients(ctx)); got != want {
+		t.Errorf("FetchAllClients() = %d, wanted %d", got, want)
+	}
+
+	i.RegisterClientFetcher(fetchA)
+	i.RegisterClientFetcher(fetchB)
+
+	got := i.FetchAllClients(ctx)
+	want := []interface{}{fakeA, fakeB}
+	if !cmp.Equal(got, want) {
+		t.Errorf("FetchAllClients() = %v, wanted %v", got, want)
+	}
+}

injection/interface.go

@@ -36,6 +36,13 @@ type Interface interface {
 	// GetClients fetches all of the registered client injectors.
 	GetClients() []ClientInjector
 
+	// RegisterClientFetcher registers a new callback that fetches a client from
+	// a given context.
+	RegisterClientFetcher(ClientFetcher)
+
+	// FetchAllClients returns all known clients from the given context.
+	FetchAllClients(context.Context) []interface{}
+
 	// RegisterInformerFactory registers a new injector callback for associating
 	// a new informer factory with a context.
 	RegisterInformerFactory(InformerFactoryInjector)
@@ -92,6 +99,7 @@ type impl struct {
 	m sync.RWMutex
 
 	clients           []ClientInjector
+	clientFetchers    []ClientFetcher
 	factories         []InformerFactoryInjector
 	informers         []InformerInjector
 	filteredInformers []FilteredInformersInjector