Use runtime.SerializerInfo in place of internal "serializerType".

CodecFactory construction uses an unexported struct type named "serializerType" to hold serializer
definitions. There are few differences between it and runtime.SerializerInfo, and they do not appear
to be used anymore. For example, serializerType includes an unused FileExtensions field, and has
distinct ContentType (singular) and AcceptContentTypes (plural) fields instead of
runtime.SerializeInfo's singular MediaType. All remaining uses of serializerType set
AcceptContentTypes to a single-entry slice whose element is equal to its ContentType field.

During construction of a CodecFactory, all serializerType values were already being mechanically
translated into runtime.SerializerInfo values.

Moving to an exported type for serializer definitions makes it easier to expose an option to allow
callers to register their own serializer definitions, which in turn makes it possible to
conditionally include new serializers at runtime (especially behind feature gates).

Author: benluddy

staging/src/k8s.io/apimachinery/pkg/runtime/serializer/codec_factory.go

@@ -17,9 +17,6 @@ limitations under the License.
 package serializer
 
 import (
-	"mime"
-	"strings"
-
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/runtime/schema"
 	"k8s.io/apimachinery/pkg/runtime/serializer/json"
@@ -28,41 +25,26 @@ import (
 	"k8s.io/apimachinery/pkg/runtime/serializer/versioning"
 )
 
-// serializerExtensions are for serializers that are conditionally compiled in
-var serializerExtensions = []func(*runtime.Scheme) (serializerType, bool){}
-
-type serializerType struct {
-	AcceptContentTypes []string
-	ContentType        string
-	FileExtensions     []string
-	// EncodesAsText should be true if this content type can be represented safely in UTF-8
-	EncodesAsText bool
-
-	Serializer       runtime.Serializer
-	PrettySerializer runtime.Serializer
-	StrictSerializer runtime.Serializer
-
-	AcceptStreamContentTypes []string
-	StreamContentType        string
-
-	Framer           runtime.Framer
-	StreamSerializer runtime.Serializer
-}
-
-func newSerializersForScheme(scheme *runtime.Scheme, mf json.MetaFactory, options CodecFactoryOptions) []serializerType {
+func newSerializersForScheme(scheme *runtime.Scheme, mf json.MetaFactory, options CodecFactoryOptions) []runtime.SerializerInfo {
 	jsonSerializer := json.NewSerializerWithOptions(
 		mf, scheme, scheme,
 		json.SerializerOptions{Yaml: false, Pretty: false, Strict: options.Strict},
 	)
-	jsonSerializerType := serializerType{
-		AcceptContentTypes: []string{runtime.ContentTypeJSON},
-		ContentType:        runtime.ContentTypeJSON,
-		FileExtensions:     []string{"json"},
-		EncodesAsText:      true,
-		Serializer:         jsonSerializer,
-
-		Framer:           json.Framer,
-		StreamSerializer: jsonSerializer,
+	jsonSerializerType := runtime.SerializerInfo{
+		MediaType:        runtime.ContentTypeJSON,
+		MediaTypeType:    "application",
+		MediaTypeSubType: "json",
+		EncodesAsText:    true,
+		Serializer:       jsonSerializer,
+		StrictSerializer: json.NewSerializerWithOptions(
+			mf, scheme, scheme,
+			json.SerializerOptions{Yaml: false, Pretty: false, Strict: true},
+		),
+		StreamSerializer: &runtime.StreamSerializerInfo{
+			EncodesAsText: true,
+			Serializer:    jsonSerializer,
+			Framer:        json.Framer,
+		},
 	}
 	if options.Pretty {
 		jsonSerializerType.PrettySerializer = json.NewSerializerWithOptions(
@@ -71,12 +53,6 @@ func newSerializersForScheme(scheme *runtime.Scheme, mf json.MetaFactory, option
 		)
 	}
 
-	strictJSONSerializer := json.NewSerializerWithOptions(
-		mf, scheme, scheme,
-		json.SerializerOptions{Yaml: false, Pretty: false, Strict: true},
-	)
-	jsonSerializerType.StrictSerializer = strictJSONSerializer
-
 	yamlSerializer := json.NewSerializerWithOptions(
 		mf, scheme, scheme,
 		json.SerializerOptions{Yaml: true, Pretty: false, Strict: options.Strict},
@@ -88,35 +64,31 @@ func newSerializersForScheme(scheme *runtime.Scheme, mf json.MetaFactory, option
 	protoSerializer := protobuf.NewSerializer(scheme, scheme)
 	protoRawSerializer := protobuf.NewRawSerializer(scheme, scheme)
 
-	serializers := []serializerType{
+	serializers := []runtime.SerializerInfo{
 		jsonSerializerType,
 		{
-			AcceptContentTypes: []string{runtime.ContentTypeYAML},
-			ContentType:        runtime.ContentTypeYAML,
-			FileExtensions:     []string{"yaml"},
-			EncodesAsText:      true,
-			Serializer:         yamlSerializer,
-			StrictSerializer:   strictYAMLSerializer,
+			MediaType:        runtime.ContentTypeYAML,
+			MediaTypeType:    "application",
+			MediaTypeSubType: "yaml",
+			EncodesAsText:    true,
+			Serializer:       yamlSerializer,
+			StrictSerializer: strictYAMLSerializer,
 		},
 		{
-			AcceptContentTypes: []string{runtime.ContentTypeProtobuf},
-			ContentType:        runtime.ContentTypeProtobuf,
-			FileExtensions:     []string{"pb"},
-			Serializer:         protoSerializer,
+			MediaType:        runtime.ContentTypeProtobuf,
+			MediaTypeType:    "application",
+			MediaTypeSubType: "vnd.kubernetes.protobuf",
+			Serializer:       protoSerializer,
 			// note, strict decoding is unsupported for protobuf,
 			// fall back to regular serializing
 			StrictSerializer: protoSerializer,
-
-			Framer:           protobuf.LengthDelimitedFramer,
-			StreamSerializer: protoRawSerializer,
+			StreamSerializer: &runtime.StreamSerializerInfo{
+				Serializer: protoRawSerializer,
+				Framer:     protobuf.LengthDelimitedFramer,
+			},
 		},
 	}
 
-	for _, fn := range serializerExtensions {
-		if serializer, ok := fn(scheme); ok {
-			serializers = append(serializers, serializer)
-		}
-	}
 	return serializers
 }
 
@@ -184,46 +156,28 @@ func NewCodecFactory(scheme *runtime.Scheme, mutators ...CodecFactoryOptionsMuta
 }
 
 // newCodecFactory is a helper for testing that allows a different metafactory to be specified.
-func newCodecFactory(scheme *runtime.Scheme, serializers []serializerType) CodecFactory {
+func newCodecFactory(scheme *runtime.Scheme, serializers []runtime.SerializerInfo) CodecFactory {
 	decoders := make([]runtime.Decoder, 0, len(serializers))
 	var accepts []runtime.SerializerInfo
 	alreadyAccepted := make(map[string]struct{})
 
 	var legacySerializer runtime.Serializer
 	for _, d := range serializers {
 		decoders = append(decoders, d.Serializer)
-		for _, mediaType := range d.AcceptContentTypes {
-			if _, ok := alreadyAccepted[mediaType]; ok {
-				continue
-			}
-			alreadyAccepted[mediaType] = struct{}{}
-			info := runtime.SerializerInfo{
-				MediaType:        d.ContentType,
-				EncodesAsText:    d.EncodesAsText,
-				Serializer:       d.Serializer,
-				PrettySerializer: d.PrettySerializer,
-				StrictSerializer: d.StrictSerializer,
-			}
-
-			mediaType, _, err := mime.ParseMediaType(info.MediaType)
-			if err != nil {
-				panic(err)
-			}
-			parts := strings.SplitN(mediaType, "/", 2)
-			info.MediaTypeType = parts[0]
-			info.MediaTypeSubType = parts[1]
-
-			if d.StreamSerializer != nil {
-				info.StreamSerializer = &runtime.StreamSerializerInfo{
-					Serializer:    d.StreamSerializer,
-					EncodesAsText: d.EncodesAsText,
-					Framer:        d.Framer,
-				}
-			}
-			accepts = append(accepts, info)
-			if mediaType == runtime.ContentTypeJSON {
-				legacySerializer = d.Serializer
-			}
+		if _, ok := alreadyAccepted[d.MediaType]; ok {
+			continue
+		}
+		alreadyAccepted[d.MediaType] = struct{}{}
+
+		acceptedSerializerShallowCopy := d
+		if d.StreamSerializer != nil {
+			cloned := *d.StreamSerializer
+			acceptedSerializerShallowCopy.StreamSerializer = &cloned
+		}
+		accepts = append(accepts, acceptedSerializerShallowCopy)
+
+		if d.MediaType == runtime.ContentTypeJSON {
+			legacySerializer = d.Serializer
 		}
 	}
 	if legacySerializer == nil {