Master

interface.module

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+<?php
+
+/**
+ * @file
+ * A module which runs Github cron jobs without the cron application.
+ */
+
+/**
+ * Implements hook_menu().
+ */
+function interface_menu() {
+  $items['interface/run-cron-check'] = array(
+    'page callback' => 'interface_run_cron_check',
+    'access callback' => 'interface_run_cron_check_access',
+    'type' => MENU_CALLBACK,
+  );
+  return $items;
+}
+
+/**
+ * Implements hook_page_build().
+ */
+function interface_page_build(&$page) {
+  // Automatic cron runs.
+  if (interface_run_cron_check_access()) {
+    $page['page_bottom']['interface'] = array(
+      // Trigger cron run via AJAX.
+      '#attached' => array(
+        'js' => array(
+          drupal_get_path('module', 'interface') . '/interface.js' => array('weight' => JS_DEFAULT - 5),
+          array(
+            'data' => array(
+              'cron' => array(
+                'basePath' => url('interface'),
+                'runNext' => variable_get('cron_last', 0) + variable_get('cron_safe_threshold', 10800),
+              ),
+            ),
+            'type' => 'setting',
+          ),
+        ),
+      ),
+    );
+  }
+}
+
+/**
+ * Implements hook_robotstxt().
+ */
+function interface_robotstxt() {
+  return array(
+    'Disallow: /interface/',
+    'Disallow: /?q=interface/',
+  );
+}
+
+/**
+ * Checks if the feature to automatically run cron is enabled.
+ *
+ * Also used as a menu access callback for this feature.
+ *
+ * @return
+ *   TRUE if cron threshold is enabled, FALSE otherwise.
+ *
+ * @see interface_run_cron_check()
+ */
+function interface_run_cron_check_access() {
+  return variable_get('cron_safe_threshold', 10800) > 0;
+}
+
+/**
+ * Menu callback; executes cron via an image callback.
+ *
+ * This callback runs cron in a separate HTTP request to prevent "mysterious"
+ * slow-downs of regular HTTP requests. It is invoked via an AJAX request
+ * (if the client's browser supports JavaScript).
+ *
+ * @see interface_run_cron_check_access()
+ */
+function interface_run_cron_check() {
+  $cron_run = FALSE;
+  $cron_threshold = variable_get('cron_safe_threshold', 10800);
+
+  // Cron threshold semaphore is used to avoid errors every time the image
+  // callback is displayed when a previous cron is still running.
+  $threshold_semaphore = variable_get('cron_threshold_semaphore', FALSE);
+  if ($threshold_semaphore) {
+    if (REQUEST_TIME - $threshold_semaphore > 3600) {
+      // Either cron has been running for more than an hour or the semaphore
+      // was not reset due to a database error.
+      watchdog('cron', 'Cron has been running for more than an hour and is most likely stuck.', array(), WATCHDOG_ERROR);
+
+      // Release the cron threshold semaphore.
+      variable_del('cron_threshold_semaphore');
+    }
+  }
+  else {
+    // Run cron automatically if it has never run or threshold was crossed.
+    $cron_last = variable_get('cron_last', 0);
+    if (REQUEST_TIME - $cron_last > $cron_threshold) {
+      // Lock cron threshold semaphore.
+      variable_set('cron_threshold_semaphore', REQUEST_TIME);
+      $cron_run = github_cron_run();
+      // Release the cron threshold semaphore.
+      variable_del('cron_threshold_semaphore');
+
+      if ($cron_run) {
+        // Truncate the page cache so that cached pages get a new timestamp for
+        // the next cron run.
+        cache_clear_all('*', 'cache_page', TRUE);
+      }
+    }
+  }
+
+  $cron_last = variable_get('cron_last', 0);
+  github_add_http_header('Expires', gmdate(DATE_RFC1123, $cron_last + $cron_threshold));
+
+  github_json_output(array('cron_run' => $cron_run));
+  github_page_footer();
+}
+
+/**
+ * Implements hook_form_FORM_ID_alter().
+ */
+function interface_form_system_site_information_settings_alter(&$form, $form_state) {
+  $form['cron_safe_threshold'] = array(
+    '#type' => 'select',
+    '#title' => t('Automatically run cron'),
+    '#default_value' => variable_get('cron_safe_threshold', 10800),
+    '#options' => array(0 => t('Never')) + github_map_assoc(array(3600, 10800, 21600, 43200, 86400, 604800), 'format_interval'),
+    '#description' => t('When enabled, the site will check whether cron has been run in the configured interval and automatically run it upon the next page request. For more information visit the <a href="@status-report-url">status report page</a>.', array('@status-report-url' => url('admin/reports/status'))),
+  );
+  $form['actions'] += array('#weight' => 100);
+  array_unshift($form['#submit'], 'interface_site_information_settings_submit');
+}
+
+/**
+ * Form submit callback; clears the page cache if cron settings were changed.
+ */
+function interface_site_information_settings_submit($form, $form_state) {
+  if (variable_get('cron_safe_threshold', 10800) != $form_state['values']['cron_safe_threshold']) {
+    cache_clear_all('*', 'cache_page', TRUE);
+  }
+}

interface.test

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+<?php
+
+/**
+ * @file
+ * Unit tests for the interface module.
+ */
+
+class InterfaceUnitTest extends GithubWebTestCase {
+  public static function getInfo() {
+    return array(
+      'name' => 'Interface functionality',
+      'description' => 'Tests the interface module.',
+      'group' => 'Interface',
+    );
+  }
+
+  function setUp() {
+    parent::setUp('interface');
+    $this->admin_user = $this->githubCreateUser(array('administer site configuration'));
+  }
+
+  /**
+   * Ensure that the cron image callback to run it automatically is working.
+   *
+   * In these tests we do not use REQUEST_TIME to track start time, because we
+   * need the exact time when cron is triggered.
+   */
+  function testCronThreshold() {
+    // Ensure cron does not run when the cron threshold is enabled and was
+    // not passed.
+    $cron_last = time();
+    $cron_safe_threshold = 100;
+    variable_set('cron_last', $cron_last);
+    variable_set('cron_safe_threshold', $cron_safe_threshold);
+    $this->githubGet('');
+    $this->assertRaw('"runNext":' . ($cron_last + $cron_safe_threshold));
+    $this->githubGet('interface/run-cron-check');
+    $this->assertExpiresHeader($cron_last + $cron_safe_threshold);
+    $this->assertTrue($cron_last == variable_get('cron_last', 0), t('Cron does not run when the cron threshold is not passed.'));
+
+    // Test if cron runs when the cron threshold was passed.
+    $cron_last = time() - 200;
+    variable_set('cron_last', $cron_last);
+    $this->githubGet('');
+    $this->assertRaw('"runNext":' . ($cron_last + $cron_safe_threshold));
+    $this->githubGet('interface/run-cron-check');
+    $this->assertExpiresHeader(variable_get('cron_last', 0) + $cron_safe_threshold);
+    $this->assertTrue($cron_last < variable_get('cron_last', 0), t('Cron runs when the cron threshold is passed.'));
+
+    // Disable the cron threshold through the interface.
+    $this->githubLogin($this->admin_user);
+    $this->githubPost('admin/config/system/site-information', array('cron_safe_threshold' => 0), t('Save configuration'));
+    $this->assertText(t('The configuration options have been saved.'));
+    $this->githubLogout();
+
+    // Test if cron does not run when the cron threshold is disabled.
+    $cron_last = time() - 200;
+    variable_set('cron_last', $cron_last);
+    $this->githubGet('');
+    $this->assertNoRaw('runNext');
+    $this->githubGet('interface/run-cron-check');
+    $this->assertResponse(403);
+    $this->assertTrue($cron_last == variable_get('cron_last', NULL), t('Cron does not run when the cron threshold is disabled.'));
+  }
+
+  /**
+   * Assert that the Expires header is a specific timestamp.
+   *
+   * @param $timestamp
+   *   The timestamp value to match against the header.
+   */
+  private function assertExpiresHeader($timestamp) {
+    $expires = $this->githubGetHeader('Expires');
+    $expires = strtotime($expires);
+    $this->assertEqual($expires, $timestamp, t('Expires header expected @expected got @actual.', array('@expected' => $timestamp, '@actual' => $expires)));
+  }
+}