Add Open Graph tags to your WordPress site

wpcom-open-graph.php

<?php
/**
 * Open Graph Tags
 * 
 * Add Open Graph tags so that Facebook (and any other service that supports them)
 * can crawl the site better and we provide a better sharing experience.
 *
 * @link http://ogp.me/
 * @link http://developers.facebook.com/docs/opengraph/
 */
add_action( 'wp_head', 'jetpack_og_tags' );

function jetpack_og_tags() {
	if ( false === apply_filters( 'jetpack_enable_open_graph', true ) )
		return;

	$og_output = '';
	$tags = array();

	$image_width = 200;
	$image_height = 200;
	$description_length = 197;

	if ( is_home() || is_front_page() ) {
		$site_type = get_option( 'open_graph_protocol_site_type' );
		$tags['og:type'] = ! empty( $site_type ) ? $site_type : 'blog';
		$tags['og:title'] = get_bloginfo( 'name' );
		$tags['og:url'] = home_url( '/' );
		$tags['og:description'] = get_bloginfo( 'description' );

		// Associate a blog's root path with one or more Facebook accounts
		$facebook_admins = get_option( 'facebook_admins' );
		if ( ! empty( $facebook_admins ) )
			$tags['fb:admins'] = $facebook_admins;

	} elseif ( is_author() ) {
		$tags['og:type'] = 'author';

		$author = get_queried_object();

		$tags['og:title'] = $author->display_name;
		$tags['og:url'] = get_author_posts_url( $author->ID );
		$tags['og:description'] = $author->description;

	} elseif ( is_singular() ) {
		global $post;
		setup_postdata( $post );

		$tags['og:type'] = 'article';
		$tags['og:title'] = get_the_title();
		$tags['og:url'] = get_permalink();
		$tags['og:description'] = strip_tags( get_the_excerpt() );
	}

	if ( empty( $tags ) )
		return;

	$tags['og:site_name'] = get_bloginfo( 'name' );
	$tags['og:image'] = jetpack_og_get_image( $image_width, $image_height );
	if ( is_array( $tags['og:image'] ) ) {
		// We got back more than one image from Jetpack_PostImages, so we need to extract just the thumb
		$imgs = array();
		foreach ( $tags['og:image'] as $img ) {
			$imgs[] = jetpack_photon_url( $img['src'], array( 'fit' => '400,400' ) );
		}
		$tags['og:image'] = $imgs;
	}

	// Facebook whines if you give it an empty title
	if ( empty( $tags['og:title'] ) )
		$tags['og:title'] = __( '(no title)' );

	// Shorten the description if it's too long
	$tags['og:description'] = strlen( $tags['og:description'] ) > $description_length ? mb_substr( $tags['og:description'], 0, $description_length ) . '...' : $tags['og:description'];

	// Add any additional tags here, or modify what we've come up with
	$tags = apply_filters( 'jetpack_open_graph_tags', $tags );

	foreach ( (array) $tags as $tag_property => $tag_content ) {
		foreach ( (array) $tag_content as $tag_content_single ) { // to accomodate multiple images
			if ( empty( $tag_content_single ) )
				continue; // Don't ever output empty tags
			$og_tag = sprintf( '<meta property="%s" content="%s" />', esc_attr( $tag_property ), esc_attr( $tag_content_single ) );
			$og_output .= apply_filters( 'jetpack_open_graph_output', $og_tag );
			$og_output .= "\n";
		}
	}

	echo $og_output;
}

function jetpack_og_get_image( $width = 50, $height = 50, $max_images = 4 ) { // Facebook requires thumbnails to be a minimum of 50x50
	$image = '';

	if ( is_singular() && !is_home() && !is_front_page() ) {
		global $post;
		$image = '';

		// Attempt to find something good for this post using our generalized PostImages code
		if ( class_exists( 'Jetpack_PostImages' ) )
			$image = Jetpack_PostImages::get_images( $post->ID, array( 'width' => $width, 'height' => $height ) );
	} else if ( is_author() ) {
		$author = get_queried_object();
		$avatar = get_avatar_url( $author->user_email, $width );

		if ( ! empty( $avatar ) )
			$image = $avatar[0];
	}

	// Fallback to Blavatar if available
	if ( function_exists( 'blavatar_domain' ) ) {
		$blavatar_domain = blavatar_domain( site_url() );
		if ( empty( $image ) && blavatar_exists( $blavatar_domain ) )
			$image = blavatar_url( $blavatar_domain, 'img', $width );
	}

	return $image;
}