refactoring tracing interceptors. (#1009)

* refactor tracing interceptors

* add stream tracing interceptor

zrpc/internal/serverinterceptors/tracinginterceptor.go

@@ -27,3 +27,23 @@ func UnaryTracingInterceptor(serviceName string) grpc.UnaryServerInterceptor {
 		return handler(ctx, req)
 	}
 }
+
+func StreamTracingInterceptor(serviceName string) grpc.StreamServerInterceptor {
+	return func(srv interface{}, ss grpc.ServerStream, info *grpc.StreamServerInfo,
+		handler grpc.StreamHandler) error {
+		ctx := ss.Context()
+		md, ok := metadata.FromIncomingContext(ctx)
+		if !ok {
+			return handler(srv, ss)
+		}
+
+		carrier, err := trace.Extract(trace.GrpcFormat, md)
+		if err != nil {
+			return handler(srv, ss)
+		}
+
+		ctx, span := trace.StartServerSpan(ctx, carrier, serviceName, info.FullMethod)
+		defer span.Finish()
+		return handler(srv, ss)
+	}
+}