wpcom_file_get_contents()

file_get_contents.php

/*
 * Fetch a remote URL and cache the result for a certain period of time
 * See http://lobby.vip.wordpress.com/best-practices/fetching-remote-data/ for more details
 *
 * This function originally used file_get_contents(), hence the function name.
 * While it no longer does, it still operates the same as the basic PHP function.
 *
 * We strongly recommend not using a $timeout value of more than 3 seconds as this
 * function makes blocking requests (stops page generation and waits for the response).
 */
function wpcom_vip_file_get_contents( $url, $timeout = 3, $cache_time = 900, $extra_args = array() ) {
	global $blog_id;

	$extra_args_defaults = array(
		'obey_cache_control_header' => true, // Uses the "cache-control" "max-age" value if greater than $cache_time
		'http_api_args' => array(), // See http://codex.wordpress.org/Function_API/wp_remote_get
	);

	$extra_args = wp_parse_args( $extra_args, $extra_args_defaults );

	$cache_key       = md5( serialize( array_merge( $extra_args, array( 'url' => $url ) ) ) );
	$backup_key      = $cache_key . '_backup';
	$disable_get_key = $cache_key . '_disable';
	$cache_group     = 'wpcom_vip_file_get_contents';

	// Temporary legacy keys to prevent mass cache misses during our key switch
	$old_cache_key       = md5( $url );
	$old_backup_key      = 'backup:' . $old_cache_key;
	$old_disable_get_key = 'disable:' . $old_cache_key;

	// Let's see if we have an existing cache already
	// Empty strings are okay, false means no cache
	if ( false !== $cache = wp_cache_get( $cache_key, $cache_group) )
		return $cache;

	// Legacy
	if ( false !== $cache = wp_cache_get( $old_cache_key, $cache_group) )
		return $cache;

	// The timeout can be 1 to 10 seconds, we strongly recommend no more than 3 seconds
	$timeout = min( 10, max( 1, (int) $timeout ) );

	if ( $timeout > 3 )
		_doing_it_wrong( __FUNCTION__, 'Using a timeout value of over 3 seconds is strongly discouraged because users have to wait for the remote request to finish before the rest of their page loads.', null );

	$server_up = true;
	$response = false;
	$content = false;

	// Check to see if previous attempts have failed
	if ( false !== wp_cache_get( $disable_get_key, $cache_group ) ) {
		$server_up = false;
	}
	// Legacy
	elseif ( false !== wp_cache_get( $old_disable_get_key, $cache_group ) ) {
		$server_up = false;
	}
	// Otherwise make the remote request
	else {
		$http_api_args = (array) $extra_args['http_api_args'];
		$http_api_args['timeout'] = $timeout;
		$response = wp_remote_get( $url, $http_api_args );
	}

	// Was the request successful?
	if ( $server_up && ! is_wp_error( $response ) && 200 == wp_remote_retrieve_response_code( $response ) ) {
		$content = wp_remote_retrieve_body( $response );

		$cache_header = wp_remote_retrieve_header( $response, 'cache-control' );
		if ( is_array( $cache_header ) )
			$cache_header = array_shift( $cache_header );

		// Obey the cache time header unless an arg is passed saying not to
		if ( $extra_args['obey_cache_control_header'] && $cache_header ) {
			$cache_header = trim( $cache_header );
			// When multiple cache-control directives are returned, they are comma separated
			foreach ( explode( ',', $cache_header ) as $cache_control ) {
				// In this scenario, only look for the max-age directive
				if( 'max-age' == substr( trim( $cache_control ), 0, 7 ) )
					list( $cache_header_type, $cache_header_time ) = explode( '=', trim( $cache_control ) );
			}
			// If the max-age directive was found and had a value set that is greater than our cache time
			if ( isset( $cache_header_type ) && isset( $cache_header_time ) && $cache_header_time > $cache_time )
				$cache_time = (int) $cache_header_time; // Casting to an int will strip "must-revalidate", etc.
		}

		// The cache time shouldn't be less than a minute
		// Please try and keep this as high as possible though
		// It'll make your site faster if you do
		$cache_time = (int) $cache_time;
		if ( $cache_time < 60 )
			$cache_time = 60;

		// Cache the result
		wp_cache_set( $cache_key, $content, $cache_group, $cache_time );

		// Additionally cache the result with no expiry as a backup content source
		wp_cache_set( $backup_key, $content, $cache_group );

		// So we can hook in other places and do stuff
		do_action( 'wpcom_vip_remote_request_success', $url, $response );
	}
	// Okay, it wasn't successful. Perhaps we have a backup result from earlier.
	elseif ( $content = wp_cache_get( $backup_key, $cache_group ) ) {
		// If a remote request failed, log why it did
		if ( $response && ! is_wp_error( $response ) ) {
			error_log( "wpcom_vip_file_get_contents: Blog ID {$blog_id}: Failure for $url and the result was: " . maybe_serialize( $response['headers'] ) . ' ' . maybe_serialize( $response['response'] ) );
		} elseif ( $response ) { // is WP_Error object
			error_log( "wpcom_vip_file_get_contents: Blog ID {$blog_id}: Failure for $url and the result was: " . maybe_serialize( $response ) );
		}
	}
	// Legacy
	elseif ( $content = wp_cache_get( $old_backup_key, $cache_group ) ) {
		// If a remote request failed, log why it did
		if ( $response && ! is_wp_error( $response ) ) {
			error_log( "wpcom_vip_file_get_contents: Blog ID {$blog_id}: Failure for $url and the result was: " . maybe_serialize( $response['headers'] ) . ' ' . maybe_serialize( $response['response'] ) );
		} elseif ( $response ) { // is WP_Error object
			error_log( "wpcom_vip_file_get_contents: Blog ID {$blog_id}: Failure for $url and the result was: " . maybe_serialize( $response ) );
		}
	}
	// We were unable to fetch any content, so don't try again for another 60 seconds
	elseif ( $response ) {
		wp_cache_set( $disable_get_key, 1, $cache_group, 60 );

		// If a remote request failed, log why it did
		if ( $response && ! is_wp_error( $response ) ) {
			error_log( "wpcom_vip_file_get_contents: Blog ID {$blog_id}: Failure for $url and the result was: " . maybe_serialize( $response['headers'] ) . ' ' . maybe_serialize( $response['response'] ) );
		} elseif ( $response ) { // is WP_Error object
			error_log( "wpcom_vip_file_get_contents: Blog ID {$blog_id}: Failure for $url and the result was: " . maybe_serialize( $response ) );
		}
		// So we can hook in other places and do stuff
		do_action( 'wpcom_vip_remote_request_error', $url, $response );
	}

	return $content;
}