wp_remote_get_with_cache – Fetches remote data with dual-layer caching

wp_remote_get_with_cache.php

<?php

/**
 * Fetches remote data with dual-layer caching.
 *
 * Uses wp_remote_get to fetch remote data. The data is cached twice: it's
 * stored in a transient and an option. The transient is used as the main cache
 * but if the transient has expired and the remote site doesn't respond, 
 * backup data from the option is returned.
 *
 * @param string $url      The URL of the remote resource.
 * @param string $key      The name of the option and the transient.
 * @param array  $args     Argument array that is passed on to wp_remote_get().
 * Default empty array.
 * @param int    $expiry   The expiration length of the transient, default
 * DAY_IN_SECONDS.
 * @param string $callback A callback function that is applied to the data
 * before it's saved in the transient and option. Default null.
 *
 * @see wp_remote_get()
 *
 * @return string The remote data set, JSON encoded.
 */
function wp_remote_get_with_cache( $url, $key, $args = array(), $expiry = DAY_IN_SECONDS, $callback = null ) {
	$data = get_transient( $key );
	if ( $data ) {
		// Data found in cache, return that.
		return json_decode( $data );
	}

	$response = wp_remote_get( $url, $args );
	if ( ! is_array( $response ) ) {
		// Couldn't get the remote data, set the transient for an hour to avoid
		// bothering the server and return backup data.
		$json_encoded_data = json_decode( get_option( $key ) );
		set_transient( $key, $json_encoded_data, HOUR_IN_SECONDS );
		return $json_encoded_data;
	}

	$fetched_data = $response['body'];
	if ( is_callable( $callback ) ) {
		$fetched_data = call_user_func( $callback, $fetched_data );
	}

	$json_encoded_data = wp_json_encode( $fetched_data );
	set_transient( $key, $json_encoded_data, $expiry );
	update_option( $key, $json_encoded_data );

	return $fetched_data;
}