/wp-content/plugins/jetpack/functions.photon.php

<?php

/**
 * Generates a Photon URL.
 *
 * @see http://developer.wordpress.com/docs/photon/
 *
 * @param string $image_url URL to the publicly accessible image you want to manipulate
 * @param array|string $args An array of arguments, i.e. array( 'w' => '300', 'resize' => array( 123, 456 ) ), or in string form (w=123&h=456)
 * @return string The raw final URL. You should run this through esc_url() before displaying it.
 */
function jetpack_photon_url( $image_url, $args = array(), $scheme = null ) {
	$image_url = trim( $image_url );

	if ( false !== apply_filters( 'jetpack_photon_skip_for_url', false, $image_url, $args, $scheme ) ) {
		return $image_url;
	}

	$image_url = apply_filters( 'jetpack_photon_pre_image_url', $image_url, $args,      $scheme );
	$args      = apply_filters( 'jetpack_photon_pre_args',      $args,      $image_url, $scheme );

	if ( empty( $image_url ) )
		return $image_url;

	$image_url_parts = @parse_url( $image_url );

	// Unable to parse
	if ( ! is_array( $image_url_parts ) || empty( $image_url_parts['host'] ) || empty( $image_url_parts['path'] ) )
		return $image_url;

	if ( is_array( $args ) ){
		// Convert values that are arrays into strings
		foreach ( $args as $arg => $value ) {
			if ( is_array( $value ) ) {
				$args[$arg] = implode( ',', $value );
			}
		}

		// Encode values
		// See http://core.trac.wordpress.org/ticket/17923
		$args = rawurlencode_deep( $args );
	}

	// You can't run a Photon URL through Photon again because query strings are stripped.
	// So if the image is already a Photon URL, append the new arguments to the existing URL.
	if ( in_array( $image_url_parts['host'], array( 'i0.wp.com', 'i1.wp.com', 'i2.wp.com' ) ) ) {
		$photon_url = add_query_arg( $args, $image_url );

		return jetpack_photon_url_scheme( $photon_url, $scheme );
	}

	// This setting is Photon Server dependent
	if ( ! apply_filters( 'jetpack_photon_any_extension_for_domain', false, $image_url_parts['host'] ) ) {
		// Photon doesn't support query strings so we ignore them and look only at the path.
		// However some source images are served via PHP so check the no-query-string extension.
		// For future proofing, this is a blacklist of common issues rather than a whitelist.
		$extension = pathinfo( $image_url_parts['path'], PATHINFO_EXTENSION );
		if ( empty( $extension ) || in_array( $extension, array( 'php' ) ) )
			return $image_url;
	}

	$image_host_path = $image_url_parts['host'] . $image_url_parts['path'];

	// Figure out which CDN subdomain to use
	srand( crc32( $image_host_path ) );
	$subdomain = rand( 0, 2 );
	srand();

	/**
	 * Filters the domain used by the Photon module.
	 *
	 * @since 3.4.2
	 *
	 * @param string http://i{$subdomain}.wp.com Domain used by Photon. $subdomain is a random number between 0 and 2.
	 * @param string $image_url URL of the image to be photonized.
	 */
	$photon_domain = apply_filters( 'jetpack_photon_domain', "http://i{$subdomain}.wp.com", $image_url );
	$photon_domain = trailingslashit( $photon_domain );
	$photon_url  = $photon_domain . $image_host_path;

	// This setting is Photon Server dependent
	if ( isset( $image_url_parts['query'] ) && apply_filters( 'jetpack_photon_add_query_string_to_domain', false, $image_url_parts['host'] ) ) {
		$photon_url .= '?q=' . rawurlencode( $image_url_parts['query'] );
	}

	if ( $args ) {
		if ( is_array( $args ) ) {
			$photon_url = add_query_arg( $args, $photon_url );
		} else {
			// You can pass a query string for complicated requests but where you still want CDN subdomain help, etc.
			$photon_url .= '?' . $args;
		}
	}

	return jetpack_photon_url_scheme( $photon_url, $scheme );
}
add_filter( 'jetpack_photon_url', 'jetpack_photon_url', 10, 3 );

/**
 * WordPress.com
 *
 * If a cropped WP.com-hosted image is the source image, have Photon replicate the crop.
 */
add_filter( 'jetpack_photon_pre_args', 'jetpack_photon_parse_wpcom_query_args', 10, 2 );

function jetpack_photon_parse_wpcom_query_args( $args, $image_url ) {
	$parsed_url = @parse_url( $image_url );

	if ( ! $parsed_url )
		return $args;

	$image_url_parts = wp_parse_args( $parsed_url, array(
		'host'  => '',
		'query' => ''
	) );

	if ( '.files.wordpress.com' != substr( $image_url_parts['host'], -20 ) )
		return $args;

	if ( empty( $image_url_parts['query'] ) )
		return $args;

	$wpcom_args = wp_parse_args( $image_url_parts['query'] );

	if ( empty( $wpcom_args['w'] ) || empty( $wpcom_args['h'] ) )
		return $args;

	// Keep the crop by using "resize"
	if ( ! empty( $wpcom_args['crop'] ) ) {
		if ( is_array( $args ) ) {
			$args = array_merge( array( 'resize' => array( $wpcom_args['w'], $wpcom_args['h'] ) ), $args );
		} else {
			$args = 'resize=' . rawurlencode( absint( $wpcom_args['w'] ) . ',' . absint( $wpcom_args['h'] ) ) . '&' . $args;
		}
	} else {
		if ( is_array( $args ) ) {
			$args = array_merge( array( 'fit' => array( $wpcom_args['w'], $wpcom_args['h'] ) ), $args );
		} else {
			$args = 'fit=' . rawurlencode( absint( $wpcom_args['w'] ) . ',' . absint( $wpcom_args['h'] ) ) . '&' . $args;
		}
	}

	return $args;
}


/**
 * Facebook
 */
add_filter( 'jetpack_photon_add_query_string_to_domain', 'jetpack_photon_allow_facebook_graph_domain', 10, 2 );
add_filter( 'jetpack_photon_any_extension_for_domain',   'jetpack_photon_allow_facebook_graph_domain', 10, 2 );

function jetpack_photon_url_scheme( $url, $scheme ) {
	if ( ! in_array( $scheme, array( 'http', 'https', 'network_path' ) ) ) {
		$scheme = is_ssl() ? 'https' : 'http';
	}

	if ( 'network_path' == $scheme ) {
		$scheme_slashes = '//';
	} else {
		$scheme_slashes = "$scheme://";
	}

	return preg_replace( '#^[a-z:]+//#i', $scheme_slashes, $url );
}

function jetpack_photon_allow_facebook_graph_domain( $allow = false, $domain ) {
	switch ( $domain ) {
	case 'graph.facebook.com' :
		return true;
	}

	return $allow;
}

add_filter( 'jetpack_photon_skip_for_url', 'jetpack_photon_banned_domains', 9, 4 );
function jetpack_photon_banned_domains( $skip, $image_url, $args, $scheme ) {
	$banned_domains = array(
		'http://chart.googleapis.com/',
		'https://chart.googleapis.com/',
		'http://chart.apis.google.com/',
	);

	foreach ( $banned_domains as $banned_domain ) {
		if ( wp_startswith( $image_url, $banned_domain ) )
			return true;
	}

	return $skip;
}