move opentelemetry into trace package, and refactoring (#996)

* move opentelemetry into trace package, and refactoring

* rename rewritten package names

core/trace/opentelemetry/serverstream.go

@@ -0,0 +1,47 @@
+package opentelemetry
+
+import (
+	"context"
+
+	"google.golang.org/grpc"
+)
+
+// serverStream wraps around the embedded grpc.ServerStream, and intercepts the RecvMsg and
+// SendMsg method call.
+type serverStream struct {
+	grpc.ServerStream
+	ctx context.Context
+
+	receivedMessageID int
+	sentMessageID     int
+}
+
+func (w *serverStream) Context() context.Context {
+	return w.ctx
+}
+
+func (w *serverStream) RecvMsg(m interface{}) error {
+	err := w.ServerStream.RecvMsg(m)
+	if err == nil {
+		w.receivedMessageID++
+		MessageReceived.Event(w.Context(), w.receivedMessageID, m)
+	}
+
+	return err
+}
+
+func (w *serverStream) SendMsg(m interface{}) error {
+	err := w.ServerStream.SendMsg(m)
+	w.sentMessageID++
+	MessageSent.Event(w.Context(), w.sentMessageID, m)
+
+	return err
+}
+
+// WrapServerStream wraps the given grpc.ServerStream with the given context.
+func WrapServerStream(ctx context.Context, ss grpc.ServerStream) *serverStream {
+	return &serverStream{
+		ServerStream: ss,
+		ctx:          ctx,
+	}
+}