How to break a event flow form an Observer and redirect to the same page in Magento 2?

Question

How can I break a flow when some condition is true? Let's say the customer is writing a review for the product https://url/review/product/post/id/2/ and when the user presses the save butto some condition should be tested and if true the save process should not continue, and the user should be redirected to the same page with a error message ('your message could not be saved ....'.

For the moment I have the following code inside the observer:

public function execute(Observer $observer)
    {

        if($sometest === true){
            $this->messageManager->addError(__("you have an error in your string"));
        }
        //Avoid save and redirect to the same page
    }

What should I use in order to break the save process and redirect the user to the same page?

Answer 1

Edited:

I am not sure why review_controller_product_init_before . It is very strange to me. I have tried with redirection using Magento\Framework\Controller\ResultFactory and want to failed.

So, for your case, you can use direct using

observer over controller_action_predispatch_review_product_post

OR, You can create redirection using plugin over Magento\Review\Controller\Product\Post:execute

I have chosen the observer for your requirement.

Observer Class look Like:

<?php

namespace {VendorName}\{ModuelName}\Observer;

use Magento\Framework\Event\Observer;
use Magento\Framework\Event\ObserverInterface;

class RedirectfromPostObserver implements ObserverInterface {

    /**
     * @var \Magento\Framework\App\ActionFlag
     */
    private $actionFlag;

    /**
     * @var \Magento\Framework\App\Action\Context
     */
    private $context;

    /**
     * @var \Magento\Framework\App\Response\RedirectInterface
     */
    private $redirect;

    /**
     * @var \Magento\Framework\Message\ManagerInterface
     */
    private $manager;

    public function __construct(
            \Magento\Framework\App\Response\RedirectInterface $redirect,
            \Magento\Framework\Message\ManagerInterface $manager,
            \Magento\Framework\App\ActionFlag $actionFlag
    ) {

        $this->redirect = $redirect;
        $this->manager = $manager;
        $this->actionFlag = $actionFlag;
    }

    public function execute(Observer $observer) {

        $controllerAction = $observer->getEvent()->getControllerAction();
        $currentActionName = $controllerAction->getRequest()->getActionName();
        $nickname = $controllerAction->getRequest()->getParam('nickname', false);
        $title = $controllerAction->getRequest()->getParam('title', false);
        $detail = $controllerAction->getRequest()->getParam('detail', false);
        $ratings = $controllerAction->getRequest()->getParam('ratings', false);

        $sometest = true;
        if ($sometest === true) {
            $this->manager->addErrorMessage(__("you have an error in your string %1", 
                    $controllerAction->getRequest()->getParam('nickname')));
            $controllerAction->getResponse()->setRedirect($this->redirect->getRefererUrl());
            $this->actionFlag->set('', \Magento\Framework\App\Action\Action::FLAG_NO_DISPATCH, true);
            $this->redirect->redirect($controllerAction->getResponse(), $this->redirect->getRefererUrl());
        }
    }

}