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

* move opentelemetry into trace package, and refactoring

* rename rewritten package names

core/trace/opentelemetry/message.go

@@ -0,0 +1,38 @@
+package opentelemetry
+
+import (
+	"context"
+
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/trace"
+	"google.golang.org/protobuf/proto"
+)
+
+const messageEvent = "message"
+
+var (
+	// MessageSent is the type of sent messages.
+	MessageSent = messageType(RPCMessageTypeSent)
+	// MessageReceived is the type of received messages.
+	MessageReceived = messageType(RPCMessageTypeReceived)
+)
+
+type messageType attribute.KeyValue
+
+// Event adds an event of the messageType to the span associated with the
+// passed context with id and size (if message is a proto message).
+func (m messageType) Event(ctx context.Context, id int, message interface{}) {
+	span := trace.SpanFromContext(ctx)
+	if p, ok := message.(proto.Message); ok {
+		span.AddEvent(messageEvent, trace.WithAttributes(
+			attribute.KeyValue(m),
+			RPCMessageIDKey.Int(id),
+			RPCMessageUncompressedSizeKey.Int(proto.Size(p)),
+		))
+	} else {
+		span.AddEvent(messageEvent, trace.WithAttributes(
+			attribute.KeyValue(m),
+			RPCMessageIDKey.Int(id),
+		))
+	}
+}