Issue #3231996: Ensure file system is writeable

src/Validator/WriteableFileSystemValidator.php

+<?php
+
+namespace Drupal\automatic_updates\Validator;
+
+use Drupal\automatic_updates\AutomaticUpdatesEvents;
+use Drupal\automatic_updates\Event\UpdateEvent;
+use Drupal\automatic_updates\PathLocator;
+use Drupal\automatic_updates\Validation\ValidationResult;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+
+/**
+ * Validates that important file system paths are writable.
+ */
+class WriteableFileSystemValidator implements EventSubscriberInterface {
+
+  use StringTranslationTrait;
+
+  /**
+   * The path locator service.
+   *
+   * @var \Drupal\automatic_updates\PathLocator
+   */
+  protected $pathLocator;
+
+  /**
+   * Constructs a WriteableFileSystemValidator object.
+   *
+   * @param \Drupal\automatic_updates\PathLocator $path_locator
+   *   The path locator service.
+   */
+  public function __construct(PathLocator $path_locator) {
+    $this->pathLocator = $path_locator;
+  }
+
+  /**
+   * Validates that the file system is writable.
+   *
+   * @param \Drupal\automatic_updates\Event\UpdateEvent $event
+   *   The event object.
+   */
+  public function checkPermissions(UpdateEvent $event): void {
+    $dir = $this->pathLocator->getProjectRoot();
+    $message = $this->t('The project directory "@dir" is not writable.', [
+      '@dir' => $dir,
+    ]);
+    $this->checkPath($dir, $event, $message);
+
+    $dir = $this->pathLocator->getVendorDirectory();
+    $message = $this->t('The vendor directory "@dir" is not writable.', [
+      '@dir' => $dir,
+    ]);
+    $this->checkPath($dir, $event, $message);
+  }
+
+  /**
+   * Checks that a path is writable, and flags an error if it's not.
+   *
+   * @param string $path
+   *   The path to check.
+   * @param \Drupal\automatic_updates\Event\UpdateEvent $event
+   *   The event object.
+   * @param \Drupal\Core\StringTranslation\TranslatableMarkup $error_message
+   *   The translated error message if the path is not writeable.
+   */
+  protected function checkPath(string $path, UpdateEvent $event, TranslatableMarkup $error_message): void {
+    if (is_writable($path)) {
+      return;
+    }
+    $result = ValidationResult::createError([$error_message]);
+    $event->addValidationResult($result);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getSubscribedEvents() {
+    return [
+      AutomaticUpdatesEvents::READINESS_CHECK => 'checkPermissions',
+    ];
+  }
+
+}