Issue #3231996: Ensure file system is writeable

src/Validator/WritableFileSystemValidator.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\File\Exception\FileException;
+use Drupal\Core\File\FileSystemInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+
+/**
+ * Validates that important file system paths are writable.
+ */
+class WritableFileSystemValidator implements EventSubscriberInterface {
+
+  use StringTranslationTrait;
+
+  /**
+   * The path locator service.
+   *
+   * @var \Drupal\automatic_updates\PathLocator
+   */
+  protected $pathLocator;
+
+  /**
+   * The file system service.
+   *
+   * @var \Drupal\Core\File\FileSystemInterface
+   */
+  protected $fileSystem;
+
+  /**
+   * Constructs a WriteableFileSystemValidator object.
+   *
+   * @param \Drupal\automatic_updates\PathLocator $path_locator
+   *   The path locator service.
+   * @param \Drupal\Core\File\FileSystemInterface $file_system
+   *   The file system service.
+   */
+  public function __construct(PathLocator $path_locator, FileSystemInterface $file_system) {
+    $this->pathLocator = $path_locator;
+    $this->fileSystem = $file_system;
+  }
+
+  /**
+   * Validates that the file system is writable.
+   *
+   * @param \Drupal\automatic_updates\Event\UpdateEvent $event
+   *   The event object.
+   */
+  public function checkPermissions(UpdateEvent $event): void {
+    $dir = implode(DIRECTORY_SEPARATOR, [
+      $this->pathLocator->getProjectRoot(),
+      $this->pathLocator->getWebRoot(),
+    ]);
+    $message = $this->t('The Drupal directory "@dir" is not writable.', [
+      '@dir' => $dir,
+    ]);
+    $this->checkPath($dir, 'core/core.api.php', $event, $message);
+
+    $dir = $this->pathLocator->getVendorDirectory();
+    $message = $this->t('The vendor directory "@dir" is not writable.', [
+      '@dir' => $dir,
+    ]);
+    $this->checkPath($dir, 'composer/LICENSE', $event, $message);
+  }
+
+  /**
+   * Tests that a path is writable by writing and deleting a temporary file.
+   *
+   * @param string $path_to_check
+   *   The path (directory) to test.
+   * @param string $file_to_copy
+   *   The path of the file, relative to $path_to_check, which should be copied
+   *   temporarily.
+   * @param \Drupal\automatic_updates\Event\UpdateEvent $event
+   *   The event object.
+   * @param \Drupal\Core\StringTranslation\TranslatableMarkup $summary
+   *   The error summary if the path is not writable.
+   */
+  protected function checkPath(string $path_to_check, string $file_to_copy, UpdateEvent $event, TranslatableMarkup $summary): void {
+    $source = $path_to_check . DIRECTORY_SEPARATOR . $file_to_copy;
+    $destination = uniqid($source);
+
+    try {
+      // If we can copy the file and then delete the copy, the file system is
+      // writable.
+      $this->fileSystem->copy($source, $destination, FileSystemInterface::EXISTS_REPLACE);
+      $this->fileSystem->delete($destination);
+    }
+    catch (FileException $e) {
+      $message = $e->getMessage();
+      $result = ValidationResult::createError([$message], $summary);
+      $event->addValidationResult($result);
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getSubscribedEvents() {
+    return [
+      AutomaticUpdatesEvents::READINESS_CHECK => 'checkPermissions',
+    ];
+  }
+
+}