code: func RegisterGraphQLService(stack *node.Node, endpoint string, cors, vhosts []string, timeouts rpc.HTTPTimeouts) error {
  	return stack.Register(func(ctx *node.ServiceContext) (node.Service, error) {
  		var ethereum *eth.Ethereum
  		if err := ctx.Service(&ethereum); err != nil {
  			return nil, err
  		}
  		return NewService(ethereum.APIBackend, endpoint, cors, vhosts, timeouts)
  	})
  }
docs: // RegisterGraphQLService is a utility function to construct a new service and register it against a node.