Fix custom gogo codec to allow OTLP data (#3719)

Signed-off-by: Yuri Shkuro <github@ysh.us>

pkg/gogocodec/codec.go

@@ -20,20 +20,23 @@ import (
 
 	gogoproto "github.com/gogo/protobuf/proto"
 	"google.golang.org/grpc/encoding"
-	"google.golang.org/protobuf/proto"
+	"google.golang.org/grpc/encoding/proto"
 )
 
 const jaegerProtoGenPkgPath = "github.com/jaegertracing/jaeger/proto-gen"
 const jaegerModelPkgPath = "github.com/jaegertracing/jaeger/model"
 
+var defaultCodec encoding.Codec
+
 func init() {
+	defaultCodec = encoding.GetCodec(proto.Name)
+	defaultCodec.Name() // ensure it's not nil
 	encoding.RegisterCodec(newCodec())
 }
 
 // gogoCodec forces the use of gogo proto marshalling/unmarshalling for
 // Jaeger proto types (package jaeger/gen-proto).
-type gogoCodec struct {
-}
+type gogoCodec struct{}
 
 var _ encoding.Codec = (*gogoCodec)(nil)
 
@@ -43,7 +46,7 @@ func newCodec() *gogoCodec {
 
 // Name implements encoding.Codec
 func (c *gogoCodec) Name() string {
-	return "proto"
+	return proto.Name
 }
 
 // Marshal implements encoding.Codec
@@ -54,7 +57,7 @@ func (c *gogoCodec) Marshal(v interface{}) ([]byte, error) {
 	if useGogo(elem) {
 		return gogoproto.Marshal(v.(gogoproto.Message))
 	}
-	return proto.Marshal(v.(proto.Message))
+	return defaultCodec.Marshal(v)
 }
 
 // Unmarshal implements encoding.Codec
@@ -65,7 +68,7 @@ func (c *gogoCodec) Unmarshal(data []byte, v interface{}) error {
 	if useGogo(elem) {
 		return gogoproto.Unmarshal(data, v.(gogoproto.Message))
 	}
-	return proto.Unmarshal(data, v.(proto.Message))
+	return defaultCodec.Unmarshal(data, v)
 }
 
 func useGogo(t reflect.Type) bool {