Avoid hard crash if user searches when Solr stopped

Question

I use search_api_solr with a server-based Solr installation. Works fine. For reasons I won't explain, the Solr service is stopped sometimes. If a user does a search while Solr is stopped, they crash with "The website encountered an unexpected error."

The error log says "Drupal\search_api_solr\SearchApiSolrException: An error occurred while trying to search with Solr: Solr endpoint http://localhost:8983/ unreachable or returned unexpected response code "0"." No surprise, since the service is stopped.

How can I trap this error and display a "Search isn't working" page instead of crashing? Seems like there should be a way to intercept it, but I haven't figured it out.

Answer 1

Based on the comment by @4k4 and post at https://drupal.stackexchange.com/a/235942/70681 and further reading, I used my existing custom module (rsc) to solve the problem as follows:

In modules/custom/rsc/rsc.services.yml

services:
  rsc.event.SolrException:
    class: Drupal\rsc\EventSubscriber\rscSolrException
    tags:
      - { name: event_subscriber }

In modules/custom/rsc/src/EventSubscriber/rscSolrException.php

<?php
namespace Drupal\rsc\EventSubscriber;

use Drupal\search_api_solr\SearchApiSolrException;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpKernel\Event\GetResponseForExceptionEvent;
use Symfony\Component\HttpKernel\KernelEvents;
use Symfony\Component\HttpFoundation\RedirectResponse;

class rscSolrException implements EventSubscriberInterface {

  public static function getSubscribedEvents() {
    $events[KernelEvents::EXCEPTION][] = ['onException', 60];
    return $events;
  }

  public function onException(GetResponseForExceptionEvent $event) {
    $exception = $event->getException();
    if ($exception instanceof SearchApiSolrException) {
      $event->setResponse(new RedirectResponse('/search-not-working'));
    }
  }
}

When a Solr exception occurs, users are redirected to the search-not-working page instead of to "The website encountered an unexpected error." Much nicer.