func (e *EngineHandler) invokeCall(ctx context.Context, gclient *grpc.ClientConn, target, serviceName, methodName, data string) (*ResultModel, error) {
	if serviceName == "" || methodName == "" {
		return nil, errors.New("serverName or methodName is null")
	}

	if gclient == nil && target == "" {
		return nil, errors.New("target addr is null")
	}

	if ctx == nil {
		ctx = e.ctx
	}

	var (
		err       error
		cc        *grpc.ClientConn
		connErr   error
		refClient *grpcreflect.Client

		addlHeaders multiString
		rpcHeaders  multiString
		reflHeaders multiString

		descSource DescriptorSource
	)

	descSource = descSourceController.descSource

	// parse proto by grpc reflet api
	if descSourceController.descMode == ProtoReflectMode {
		md := MetadataFromHeaders(append(addlHeaders, reflHeaders...))
		refCtx := metadata.NewOutgoingContext(e.ctx, md)
		cc, connErr = e.DoConnect(target)
		if connErr != nil {
			return nil, connErr
		}

		refClient = grpcreflect.NewClient(refCtx, reflectpb.NewServerReflectionClient(cc))
		descSource = DescriptorSourceFromServer(e.ctx, refClient)
	}

	if gclient == nil {
		cc, connErr = e.DoConnect(target)
		if connErr != nil {
			return nil, connErr
		}
	} else {
		cc = gclient
	}

	var inData io.Reader
	inData = strings.NewReader(data)
	rf, err := RequestParserFor(descSource, inData)
	if err != nil {
		return nil, errors.New("request parse and format failed")
	}

	result, err := e.invokeCtl.InvokeRPC(e.ctx, descSource, cc, serviceName, methodName,
		append(addlHeaders, rpcHeaders...),
		rf.Next,
	)
	return result, err
}