Do not advertise protobuf support

This fixes #150.

As the `Stack` struct does not support being serialized to protobuf, we
must not advertise that we support protobuf.

Signed-off-by: Christopher Crone <christopher.crone@docker.com>

internal/apiserver/apiserver.go

@@ -2,6 +2,8 @@ package apiserver
 
 import (
 	"net/http"
+	"reflect"
+	"unsafe"
 
 	"github.com/docker/compose-on-kubernetes/api/compose/v1alpha3"
 	"github.com/docker/compose-on-kubernetes/api/compose/v1beta1"
@@ -53,6 +55,25 @@ func init() {
 	if err := conversions.RegisterV1beta2Conversions(Scheme); err != nil {
 		panic(err)
 	}
+	// We do not support protobuf serialization as the `Stack` struct has
+	// fields with unsupported types (e.g.: map[string]*string). This causes
+	// issues like https://github.com/docker/compose-on-kubernetes/issues/150.
+	// The workaround is to remove protobuf from the advertised supported codecs.
+	removeProtobufMediaType(&Codecs)
+}
+
+// removeProtobufMediaType removes protobuf from the list of accepted media
+// types for the given CodecFactory.
+func removeProtobufMediaType(c *serializer.CodecFactory) {
+	codecsPtr := reflect.Indirect(reflect.ValueOf(c))
+	accepts := codecsPtr.FieldByName("accepts")
+	acceptsPtr := (*[]runtime.SerializerInfo)(unsafe.Pointer(accepts.UnsafeAddr()))
+	for i, v := range *acceptsPtr {
+		if v.MediaType == runtime.ContentTypeProtobuf {
+			*acceptsPtr = append((*acceptsPtr)[0:i], (*acceptsPtr)[i+1:]...)
+			break
+		}
+	}
 }
 
 // Config is the API server config

internal/apiserver/apiserver_test.go

@@ -1 +1,25 @@
 package apiserver
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/runtime/serializer"
+)
+
+func supportsProtobufCodec(c serializer.CodecFactory) bool {
+	for _, v := range c.SupportedMediaTypes() {
+		if v.MediaType == runtime.ContentTypeProtobuf {
+			return true
+		}
+	}
+	return false
+}
+
+func TestRemoveProtobuf(t *testing.T) {
+	codecs := serializer.NewCodecFactory(Scheme)
+	assert.True(t, supportsProtobufCodec(codecs))
+	removeProtobufMediaType(&codecs)
+	assert.False(t, supportsProtobufCodec(codecs))
+}