#552478 by pwolanin, samj, dropcube, and sun: Improve link/header API and...

#552478 by pwolanin, samj, dropcube, and sun: Improve link/header API and support on node/comment pages rel=canonical and rel=shortlink standards.

CHANGELOG.txt

@@ -149,6 +149,12 @@ Drupal 7.0, xxxx-xx-xx (development version)
     * Modules can specify how their data structure maps to RDF.
     * Added support for RDFa export of nodes, comments, terms, users, etc. and
       their fields.
+- Search engine optimization and web linking:
+    * Added a rel="canonical" link on node and comment pages to prevent
+      duplicate content indexing by search engines.
+    * Added a default rel="shortlink" link on node and comment pages that
+      advertises a short link as an alternative URL to third-party services.
+    * Meta information is now alterable by all modules before rendering.
 - Field API:
     * Custom data fields may be attached to nodes, users, comments and taxonomy
       terms.

includes/batch.inc

@@ -215,7 +215,14 @@ function _batch_progress_page_nojs() {
   $batch['url_options']['query']['op'] = $new_op;
 
   $url = url($batch['url'], $batch['url_options']);
-  drupal_add_html_head('<meta http-equiv="Refresh" content="0; URL=' . $url . '">');
+  $element = array(
+    '#tag' => 'meta',
+    '#attributes' => array(
+      'http-equiv' => 'Refresh',
+      'content' => '0; URL=' . $url,
+    ),
+  );
+  drupal_add_html_head($element, 'batch_progress_meta_refresh');
 
   return theme('progress_bar', array('percent' => $percentage, 'message' => $message));
 }

includes/theme.inc

@@ -1878,6 +1878,48 @@ function theme_feed_icon($variables) {
   }
 }
 
+/**
+ * Generate the output for a generic HTML tag with attributes.
+ *
+ * This theme function should be used for tags appearing in the HTML HEAD of a
+ * document (specified via the #tag property in the passed $element):
+ *
+ * @param $variables
+ *   An associative array containing:
+ *   - element: An associative array describing the tag:
+ *     - #tag: The tag name to output.  Typical tags added to the HTML HEAD:
+ *       - meta: To provide meta information, such as a page refresh.
+ *       - link: To refer to stylesheets and other contextual information.
+ *       - script: To load JavaScript.
+ *     - #attributes: (optional) An array of HTML attributes to apply to the
+ *       tag.
+ *     - #value: (optional) A string containing tag content, such as inline CSS.
+ *     - #value_prefix: (optional) A string to prepend to #value, e.g. a CDATA
+ *       wrapper prefix.
+ *     - #value_suffix: (optional) A string to append to #value, e.g. a CDATA
+ *       wrapper suffix.
+ *
+ * @ingroup themeable
+ */
+function theme_html_tag($variables) {
+  $element = $variables['element'];
+  if (!isset($element['#value'])) {
+    return '<' . $element['#tag'] . drupal_attributes($element['#attributes']) . " />\n";
+  }
+  else {
+    $output = '<' . $element['#tag'] . drupal_attributes($element['#attributes']) . '>';
+    if (isset($element['#value_prefix'])) {
+      $output .= $element['#value_prefix'];
+    }
+    $output .= $element['#value'];
+    if (isset($element['#value_suffix'])) {
+      $output .= $element['#value_suffix'];
+    }
+    $output .= '</' . $element['#tag'] . ">\n";
+    return $output;
+  }
+}
+
 /**
  * Returns code that emits the 'more' link used on blocks.
  *
@@ -2181,7 +2223,7 @@ function template_preprocess_html(&$variables) {
   if (theme_get_setting('toggle_favicon')) {
     $favicon = theme_get_setting('favicon');
     $type = theme_get_setting('favicon_mimetype');
-    drupal_add_html_head('<link rel="shortcut icon" href="' . check_url($favicon) . '" type="' . check_plain($type) . '" />');
+    drupal_add_html_head_link(array('rel' => 'shortcut icon', 'href' => check_url($favicon), 'type' => $type));
   }
 
   // Construct page title.
@@ -2350,7 +2392,7 @@ function template_preprocess_maintenance_page(&$variables) {
   if (theme_get_setting('toggle_favicon')) {
     $favicon = theme_get_setting('favicon');
     $type = theme_get_setting('favicon_mimetype');
-    drupal_add_html_head('<link rel="shortcut icon" href="' . check_url($favicon) . '" type="' . check_plain($type) . '" />');
+    drupal_add_html_head_link(array('rel' => 'shortcut icon', 'href' => check_url($favicon), 'type' => $type));
   }
 
   global $theme;

modules/book/book.module

@@ -940,21 +940,21 @@ function template_preprocess_book_navigation(&$variables) {
 
     if ($prev = book_prev($book_link)) {
       $prev_href = url($prev['href']);
-      drupal_add_link(array('rel' => 'prev', 'href' => $prev_href));
+      drupal_add_html_head_link(array('rel' => 'prev', 'href' => $prev_href));
       $variables['prev_url'] = $prev_href;
       $variables['prev_title'] = check_plain($prev['title']);
     }
 
     if ($book_link['plid'] && $parent = book_link_load($book_link['plid'])) {
       $parent_href = url($parent['href']);
-      drupal_add_link(array('rel' => 'up', 'href' => $parent_href));
+      drupal_add_html_head_link(array('rel' => 'up', 'href' => $parent_href));
       $variables['parent_url'] = $parent_href;
       $variables['parent_title'] = check_plain($parent['title']);
     }
 
     if ($next = book_next($book_link)) {
       $next_href = url($next['href']);
-      drupal_add_link(array('rel' => 'next', 'href' => $next_href));
+      drupal_add_html_head_link(array('rel' => 'next', 'href' => $next_href));
       $variables['next_url'] = $next_href;
       $variables['next_title'] = check_plain($next['title']);
     }

modules/comment/comment.module

@@ -362,9 +362,6 @@ function comment_permalink($comment) {
     $_GET['q'] = 'node/' . $node->nid;
     $_GET['page'] = $page;
 
-    // Set the node path as the canonical URL to prevent duplicate content.
-    drupal_add_link(array('rel' => 'canonical', 'href' => url('node/' . $node->nid)));
-
     // Return the node view, this will show the correct comment in context.
     return menu_execute_active_handler('node/' . $node->nid, FALSE);
   }

modules/node/node.module

@@ -2152,6 +2152,10 @@ function node_page_view(stdClass $node) {
   if (isset($return['nodes'][$node->nid]['title'])) {
     drupal_set_title($return['nodes'][$node->nid]['title']['items'][0]['#item']['value']);
   }
+  // Set the node path as the canonical URL to prevent duplicate content.
+  drupal_add_html_head_link(array('rel' => 'canonical', 'href' => url('node/' . $node->nid)), TRUE);
+  // Set the non-aliased path as a default shortlink.
+  drupal_add_html_head_link(array('rel' => 'shortlink', 'href' => url('node/' . $node->nid, array('alias' => TRUE))), TRUE);
   return $return;
 }
 

modules/openid/tests/openid_test.module

@@ -97,7 +97,14 @@ function openid_test_yadis_x_xrds_location() {
  * Menu callback; regular HTML page with <meta> element.
  */
 function openid_test_yadis_http_equiv() {
-  drupal_add_html_head('<meta http-equiv="X-XRDS-Location" content="' . url('openid-test/yadis/xrds', array('absolute' => TRUE)) . '" />');
+  $element = array(
+    '#tag' => 'meta',
+    '#attributes' => array(
+      'http-equiv' => 'X-XRDS-Location',
+      'content' => url('openid-test/yadis/xrds', array('absolute' => TRUE)),
+    ),
+  );
+  drupal_add_html_head($element, 'openid_test_yadis_http_equiv');
   return t('This page includes a &lt;meta equiv=...&gt; element containing the URL of an XRDS document.');
 }
 
@@ -105,7 +112,7 @@ function openid_test_yadis_http_equiv() {
  * Menu callback; regular HTML page with OpenID 1.0 <link> element.
  */
 function openid_test_html_openid1() {
-  drupal_add_html_head('<link rel="openid.server" href="' . url('openid-test/endpoint', array('absolute' => TRUE)) . '" />');
+  drupal_add_html_head_link(array('rel' => 'openid.server', 'href' => url('openid-test/endpoint', array('absolute' => TRUE))));
   return t('This page includes a &lt;link rel=...&gt; element containing the URL of an OpenID Provider Endpoint.');
 }
 
@@ -113,7 +120,7 @@ function openid_test_html_openid1() {
  * Menu callback; regular HTML page with OpenID 2.0 <link> element.
  */
 function openid_test_html_openid2() {
-  drupal_add_html_head('<link rel="openid2.provider" href="' . url('openid-test/endpoint', array('absolute' => TRUE)) . '" />');
+  drupal_add_html_head_link(array('rel' => 'openid2.provider', 'href' => url('openid-test/endpoint', array('absolute' => TRUE))));
   return t('This page includes a &lt;link rel=...&gt; element containing the URL of an OpenID Provider Endpoint.');
 }
 

modules/rdf/rdf.module

@@ -384,10 +384,17 @@ function rdf_preprocess_node(&$variables) {
   // In full node mode, the title is not displayed by node.tpl.php so it is
   // added in the head tag of the HTML page.
   if ($variables['page']) {
-    $title_attributes['property'] = empty($variables['node']->rdf_mapping['title']['predicates']) ? NULL : $variables['node']->rdf_mapping['title']['predicates'];
-    $title_attributes['content'] = $variables['node_title'];
-    $title_attributes['about'] = $variables['node_url'];
-    drupal_add_html_head('<meta' . drupal_attributes($title_attributes) . ' />');
+    $element = array(
+      '#tag' => 'meta',
+      '#attributes' => array(
+        'content' => $variables['node_title'],
+        'about' => $variables['node_url'],
+      ),
+    );
+    if (!empty($variables['node']->rdf_mapping['title']['predicates'])) {
+      $element['#attributes']['property'] = $variables['node']->rdf_mapping['title']['predicates'];
+    }
+    drupal_add_html_head($element, 'rdf_node');
   }
 
   // Adds RDFa markup for the date.

modules/simpletest/tests/browser_test.module

@@ -57,7 +57,14 @@ function browser_test_print_post_form_submit($form, &$form_state) {
 function browser_test_refresh_meta() {
   if (!isset($_GET['refresh'])) {
     $url = url('browser_test/refresh/meta', array('absolute' => TRUE, 'query' => array('refresh' => 'true')));
-    drupal_add_html_head('<meta http-equiv="Refresh" content="0; URL=' . $url . '">');
+    $element = array(
+      '#tag' => 'meta',
+      '#attributes' => array(
+        'http-equiv' => 'Refresh',
+        'content' => '0; URL=' . $url,
+      ),
+    );
+    drupal_add_html_head($element, 'browser_test_refresh_meta');
     return '';
   }
   echo 'Refresh successful';

modules/simpletest/tests/common.test

@@ -530,7 +530,7 @@ class CascadingStylesheetsTestCase extends DrupalWebTestCase {
     $css_preprocessed = '<style type="text/css">' . drupal_load_stylesheet_content($css, TRUE) . '</style>';
     drupal_add_css($css, 'inline');
     $styles = drupal_get_css();
-    $this->assertEqual($styles, "\n" . $css_preprocessed, t('Rendering preprocessed inline CSS adds it to the page.'));
+    $this->assertEqual($styles, "\n" . $css_preprocessed . "\n", t('Rendering preprocessed inline CSS adds it to the page.'));
   }
 
   /**

modules/system/system.api.php

@@ -2281,6 +2281,27 @@ function hook_drupal_goto_alter(&$path, &$options, &$http_response_code) {
   $http_response_code = 500;
 }
 
+/**
+ * Alter XHTML HEAD tags before they are rendered by drupal_get_html_head().
+ *
+ * Elements available to be altered are only those added using
+ * drupal_add_html_head_link() or drupal_add_html_head(). CSS and JS files
+ * are handled using drupal_add_css() and drupal_add_js(), so the head links
+ * for those files will not appear in the $head_elements array.
+ *
+ * @param $head_elements
+ *   An array of renderable elements. Generally the values of the #attributes
+ *   array will be the most likely target for changes.
+ */
+function hook_html_head_alter(&$head_elements) {
+  foreach($head_elements as $key => $element) {
+    if (isset($element['#attributes']['rel']) && $element['#attributes']['rel'] == 'canonical') {
+      // I want a custom canonical url.
+      $head_elements[$key]['#attributes']['href'] = mymodule_canonical_url();
+    }
+  }
+}
+
 /**
  * Alter the full list of installation tasks.
  *

modules/system/system.module

@@ -179,12 +179,6 @@ function system_theme() {
     'system_powered_by' => array(
       'variables' => array(),
     ),
-    'meta_generator_html' => array(
-      'variables' => array('version' => NULL),
-    ),
-    'meta_generator_header' => array(
-      'variables' => array('version' => NULL),
-    ),
     'system_compact_link' => array(
       'variables' => array(),
     ),
@@ -318,6 +312,12 @@ function system_element_info() {
     '#ajax_commands' => array(),
   );
 
+  $types['html_tag'] = array(
+    '#theme' => 'html_tag',
+    '#attributes' => array(),
+    '#value' => NULL,
+  );
+
   // Input elements.
   $types['submit'] = array(
     '#input' => TRUE,
@@ -1717,22 +1717,6 @@ function system_init() {
   }
 }
 
-/**
- * Implement MODULE_preprocess_HOOK().
- */
-function system_preprocess_page(&$variables) {
-  // Get the major version
-  list($version, ) = explode('.', VERSION);
-
-  // Emit the META tag in the HTML HEAD section
-  theme('meta_generator_html', array('version' => $version));
-
-  // Emit the HTTP Header too
-  theme('meta_generator_header', array('version' => $version));
-
-  $variables['head'] = drupal_get_html_head();
-}
-
 /**
  * Implement hook_form_FORM_ID_alter().
  */
@@ -2973,24 +2957,6 @@ function theme_system_compact_link() {
   return $output;
 }
 
-/**
- * Send Drupal and the major version number in the META GENERATOR HTML.
- *
- * @ingroup themeable
- */
-function theme_meta_generator_html($variables) {
-  drupal_add_html_head('<meta name="Generator" content="Drupal ' . $variables['version'] . ' (http://drupal.org)" />');
-}
-
-/**
- * Send Drupal and the major version number in the HTTP headers.
- *
- * @ingroup themeable
- */
-function theme_meta_generator_header($variables) {
-  drupal_add_http_header('X-Generator', 'Drupal ' . $variables['version'] . ' (http://drupal.org)');
-}
-
 /**
  * Implement hook_image_toolkits().
  */