Adding Facebook OG Tags to in Your Drupal 7 Theme Layer

A demonstration of how to add Facebook OG tags into a Drupal 7 site using template.php in the theme layer.

Some other items demonstrated here include:

• How to get the absolute URL to the current page.
• How to get the absolute URL to a file from a stream URI, e.g., public://somefile.png.
• How to trim a string to the first line in PHP.
• How to add items to the HTML head with drupal_add_html_head(). Hint, it involves an unwieldy array.

<?php
/*
 * This demonstrates a means of injecting Facebook OG tags into your
 * HTML header using template.php in your theme rather than a module.
 *
 */

/**
 * Implements hook_preprocess_page() for the following reasons:
 *  - We want to inject Facebook OG tags into our HTML head.
 *
 */
function MYTHEME_preprocess_page(&$vars,$hook) {
  _MYTHEME_facebook_og_meta($vars);

}

/**
 * Inject Facebook OG meta tags into head.
 * @return Void
 */
function _MYTHEME_facebook_og_meta(&$vars) {
  $site_name = t('Your Site Name');
  $title = t('Default Title');
  $description = t('A default page description');
  // Get the absolute URL to the current page. 
  $path = isset($_GET['q']) ? $_GET['q'] : '<front>';
  $url = url($path, array('absolute' => TRUE));
  $default_image = 'http://example.com/sites/default/files/default_fb_image.jpg';
  $facebook_image = $default_image;

  // Here we get node specific information. Update field names and such for site as needed.
  if ($vars['node']) {
    $node = node_load($vars['node']->nid);
    // Title
    $title = (!empty($node->title)) ? t($node->title) : "";
    // Description
    if (!empty($node->field_summary[LANGUAGE_NONE][0]['safe_value'])) {
      $cleaned = _MYTHEME_cleanup_summary($node->field_summary[LANGUAGE_NONE][0]['value']);
      $description = t($cleaned);
    }
    // Image
    if (!empty($node->field_my_image[LANGUAGE_NONE][0])) {
      $facebook_image = file_create_url($node->field_my_image[LANGUAGE_NONE][0]['uri']);
    }
  }

  $og_meta['og_site_name'] = array(
    '#type' => 'html_tag',
    '#tag' => 'meta',
    '#attributes' => array(
      'property' => 'og:site_name',
      'content' => $site_name,
    )
  );

  $og_meta['og_type'] = array(
    '#type' => 'html_tag',
    '#tag' => 'meta',
    '#attributes' => array(
      'property' => 'og:type',
      'content' => 'website',
    )
  );

  $og_meta['og_url'] = array(
    '#type' => 'html_tag',
    '#tag' => 'meta',
    '#attributes' => array(
      'property' => 'og:url',
      'content' => $url,
    )
  );

  $og_meta['og_title'] = array(
    '#type' => 'html_tag',
    '#tag' => 'meta',
    '#attributes' => array(
      'property' => 'og:title',
      'content' => $title,
    )
  );

  $og_meta['og_description'] = array(
    '#type' => 'html_tag',
    '#tag' => 'meta',
    '#attributes' => array(
      'property' => 'og:description',
      'content' => $description,
    )
  );

  $og_meta['og_image'] = array(
    '#type' => 'html_tag',
    '#tag' => 'meta',
    '#attributes' => array(
      'property' => 'og:image',
      'content' => $facebook_image,
    )
  );

  foreach($og_meta as $k => $v) {
    drupal_add_html_head($v, $k);
  }

}

/**
 * Cleans up summary text for use in meta tags. All tags will be stripped along
 * with '&nbsp;', and text will be trimmed at the first linefeed.
 *
 * @param string $text
 * @return string
 */
function _MYTHEME_cleanup_summary($text="") {
  $text = strip_tags($text);
  $text = str_ireplace('&nbsp;', ' ', $text);
  $text = strtok($text, PHP_EOL);
  return $text;
}