Introduce ObjectConvertor for conversion to known API versions

Will allow clients to transform internal objects to a version
suitable for external output.

pkg/conversion/scheme.go

@@ -211,6 +211,46 @@ func (s *Scheme) Convert(in, out interface{}) error {
 	return s.converter.Convert(in, out, 0, s.generateConvertMeta(inVersion, outVersion))
 }
 
+// ConvertToVersion attempts to convert an input object to its matching Kind in another
+// version within this scheme. Will return an error if the provided version does not
+// contain the inKind (or a mapping by name defined with AddKnownTypeWithName).
+func (s *Scheme) ConvertToVersion(in interface{}, outVersion string) (interface{}, error) {
+	t := reflect.TypeOf(in)
+	if t.Kind() != reflect.Ptr {
+		return nil, fmt.Errorf("only pointer types may be converted: %v", t)
+	}
+	t = t.Elem()
+	if t.Kind() != reflect.Struct {
+		return nil, fmt.Errorf("only pointers to struct types may be converted: %v", t)
+	}
+
+	kinds, ok := s.typeToKind[t]
+	if !ok {
+		return nil, fmt.Errorf("%v cannot be converted into version %q", t, outVersion)
+	}
+	outKind := kinds[0]
+
+	inVersion, _, err := s.ObjectVersionAndKind(in)
+	if err != nil {
+		return nil, err
+	}
+
+	out, err := s.NewObject(outVersion, outKind)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := s.converter.Convert(in, out, 0, s.generateConvertMeta(inVersion, outVersion)); err != nil {
+		return nil, err
+	}
+
+	if err := s.SetVersionAndKind(outVersion, outKind, out); err != nil {
+		return nil, err
+	}
+
+	return out, nil
+}
+
 // generateConvertMeta constructs the meta value we pass to Convert.
 func (s *Scheme) generateConvertMeta(srcVersion, destVersion string) *Meta {
 	return &Meta{

pkg/conversion/scheme_test.go

@@ -240,6 +240,45 @@ func TestMultipleNames(t *testing.T) {
 	}
 }
 
+func TestKnownTypes(t *testing.T) {
+	s := GetTestScheme()
+	if len(s.KnownTypes("v2")) != 0 {
+		t.Errorf("should have no known types for v2")
+	}
+
+	types := s.KnownTypes("v1")
+	for _, s := range []string{"TestType1", "TestType2", "TestType3", "ExternalInternalSame"} {
+		if _, ok := types[s]; !ok {
+			t.Errorf("missing type %q", s)
+		}
+	}
+}
+
+func TestConvertToVersion(t *testing.T) {
+	s := GetTestScheme()
+	tt := &TestType1{A: "I'm not a pointer object"}
+	other, err := s.ConvertToVersion(tt, "v1")
+	if err != nil {
+		t.Fatalf("Failure: %v", err)
+	}
+	converted, ok := other.(*ExternalTestType1)
+	if !ok {
+		t.Fatalf("Got wrong type")
+	}
+	if tt.A != converted.A {
+		t.Fatalf("Failed to convert object correctly: %#v", converted)
+	}
+}
+
+func TestConvertToVersionErr(t *testing.T) {
+	s := GetTestScheme()
+	tt := TestType1{A: "I'm not a pointer object"}
+	_, err := s.ConvertToVersion(tt, "v1")
+	if err == nil {
+		t.Fatalf("unexpected non-error")
+	}
+}
+
 func TestEncode_NonPtr(t *testing.T) {
 	s := GetTestScheme()
 	tt := TestType1{A: "I'm not a pointer object"}

pkg/runtime/interfaces.go

@@ -33,6 +33,11 @@ type Codec interface {
 	Encoder
 }
 
+// ObjectConvertor converts an object to a different version.
+type ObjectConvertor interface {
+	ConvertToVersion(in Object, outVersion string) (out Object, err error)
+}
+
 // ObjectTyper contains methods for extracting the APIVersion and Kind
 // of objects.
 type ObjectTyper interface {

pkg/runtime/scheme.go

@@ -17,6 +17,7 @@ limitations under the License.
 package runtime
 
 import (
+	"fmt"
 	"reflect"
 
 	"github.com/GoogleCloudPlatform/kubernetes/pkg/conversion"
@@ -223,6 +224,23 @@ func (s *Scheme) Convert(in, out interface{}) error {
 	return s.raw.Convert(in, out)
 }
 
+// ConvertToVersion attempts to convert an input object to its matching Kind in another
+// version within this scheme. Will return an error if the provided version does not
+// contain the inKind (or a mapping by name defined with AddKnownTypeWithName). Will also
+// return an error if the conversion does not result in a valid Object being
+// returned.
+func (s *Scheme) ConvertToVersion(in Object, outVersion string) (Object, error) {
+	unknown, err := s.raw.ConvertToVersion(in, outVersion)
+	if err != nil {
+		return nil, err
+	}
+	obj, ok := unknown.(Object)
+	if !ok {
+		return nil, fmt.Errorf("the provided object cannot be converted to a runtime.Object: %#v", unknown)
+	}
+	return obj, nil
+}
+
 // EncodeToVersion turns the given api object into an appropriate JSON string.
 // Will return an error if the object doesn't have an embedded TypeMeta.
 // Obj may be a pointer to a struct, or a struct. If a struct, a copy