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<?php
/**
* Class CachedRemoteGetRequest.
*
* @package AmpProject\AmpWP
*/
namespace AmpProject\AmpWP\RemoteRequest;
use AmpProject\Exception\FailedToGetCachedResponse;
use AmpProject\Exception\FailedToGetFromRemoteUrl;
use AmpProject\RemoteGetRequest;
use AmpProject\RemoteRequest\RemoteGetRequestResponse;
use AmpProject\Response;
use DateTimeImmutable;
use DateTimeInterface;
/**
* Caching decorator for RemoteGetRequest implementations.
*
* Caching uses WordPress transients.
*
* @package AmpProject\AmpWP
* @since 2.0
* @internal
*/
final class CachedRemoteGetRequest implements RemoteGetRequest {
/**
* Prefix to use to identify transients.
*
* @var string
*/
const TRANSIENT_PREFIX = 'amp_remote_request_';
/**
* Cache control header directive name.
*
* @var string
*/
const CACHE_CONTROL = 'Cache-Control';
/**
* Remote request object to decorate with caching.
*
* @var RemoteGetRequest
*/
private $remote_request;
/**
* Cache expiration time in seconds.
*
* This will be used by default for successful requests when the 'cache-control: max-age' was not provided.
*
* @var int
*/
private $expiry;
/**
* Minimum cache expiration time in seconds.
*
* This will be used for failed requests, or for successful requests when the 'cache-control: max-age' is inferior.
* Caching will never expire quicker than this minimum.
*
* @var int
*/
private $min_expiry;
/**
* Whether to use Cache-Control headers to decide on expiry times if available.
*
* @var bool
*/
private $use_cache_control;
/**
* Instantiate a CachedRemoteGetRequest object.
*
* This is a decorator that can wrap around an existing remote request object to add a caching layer.
*
* @param RemoteGetRequest $remote_request Remote request object to decorate with caching.
* @param int|float $expiry Optional. Default cache expiry in seconds. Defaults to 30 days.
* @param int|float $min_expiry Optional. Default enforced minimum cache expiry in seconds. Defaults
* to 24 hours.
* @param bool $use_cache_control Optional. Use Cache-Control headers for expiry if available. Defaults
* to true.
*/
public function __construct(
RemoteGetRequest $remote_request,
$expiry = MONTH_IN_SECONDS,
$min_expiry = DAY_IN_SECONDS,
$use_cache_control = true
) {
$this->remote_request = $remote_request;
$this->expiry = (int) $expiry;
$this->min_expiry = (int) $min_expiry;
$this->use_cache_control = (bool) $use_cache_control;
}
/**
* Do a GET request to retrieve the contents of a remote URL.
*
* @todo Should this also respect additional Cache-Control directives like 'no-cache'?
*
* @param string $url URL to get.
* @param array $headers Optional. Associative array of headers to send with the request. Defaults to empty array.
* @return Response Response for the executed request.
* @throws FailedToGetCachedResponse If retrieving the contents from the URL failed.
*/
public function get( $url, $headers = [] ) {
$cache_key = self::TRANSIENT_PREFIX . md5( __CLASS__ . $url );
$cached_response = get_transient( $cache_key );
$headers = [];
if ( is_string( $cached_response ) ) {
if ( PHP_MAJOR_VERSION >= 7 ) {
$cached_response = unserialize( $cached_response, [ CachedResponse::class, DateTimeImmutable::class ] ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.serialize_unserialize,PHPCompatibility.FunctionUse.NewFunctionParameters.unserialize_optionsFound
} else {
// PHP 5.6 does not provide the second $options argument yet.
$cached_response = unserialize( $cached_response ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.serialize_unserialize
}
}
if ( ! $cached_response instanceof CachedResponse || $cached_response->is_expired() ) {
try {
$response = $this->remote_request->get( $url, $headers );
$status = $response->getStatusCode();
/** @var DateTimeImmutable $expiry */
$expiry = $this->get_expiry_time( $response );
$headers = $response->getHeaders();
$body = $response->getBody();
} catch ( FailedToGetFromRemoteUrl $exception ) {
$status = $exception->getStatusCode();
$expiry = new DateTimeImmutable( "+ {$this->min_expiry} seconds" );
$body = $exception->getMessage();
}
$cached_response = new CachedResponse( $body, $headers, $status, $expiry );
// Transient extend beyond cache expiry to allow for serving stale content.
// @TODO: We don't serve stale content atm, but rather synchronously refresh.
// See https://github.com/ampproject/amp-wp/issues/5477.
$transient_expiry = $expiry->modify( "+ {$this->expiry} seconds" );
set_transient( $cache_key, serialize( $cached_response ), $transient_expiry->getTimestamp() ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.serialize_serialize
}
if ( ! $cached_response->is_valid() ) {
throw new FailedToGetCachedResponse( $url );
}
return new RemoteGetRequestResponse( $cached_response->get_body(), $cached_response->get_headers(), $cached_response->get_status_code() );
}
/**
* Get the expiry time of the data to cache.
*
* This will use the cache-control header information in the provided response or fall back to the provided default
* expiry.
*
* @param Response $response Response object to get the expiry from.
* @return DateTimeInterface Expiry of the data.
*/
private function get_expiry_time( Response $response ) {
if ( $this->use_cache_control && $response->hasHeader( self::CACHE_CONTROL ) ) {
$expiry = max( $this->min_expiry, $this->get_max_age( $response->getHeader( self::CACHE_CONTROL ) ) );
return new DateTimeImmutable( "+ {$expiry} seconds" );
}
return new DateTimeImmutable( "+ {$this->expiry} seconds" );
}
/**
* Get the max age setting from one or more cache-control header strings.
*
* @param array|string $cache_control_strings One or more cache control header strings.
* @return int Value of the max-age cache directive. 0 if not found.
*/
private function get_max_age( $cache_control_strings ) {
$max_age = 0;
foreach ( (array) $cache_control_strings as $cache_control_string ) {
$cache_control_parts = array_map( 'trim', explode( ',', $cache_control_string ) );
foreach ( $cache_control_parts as $cache_control_part ) {
$cache_control_setting_parts = array_map( 'trim', explode( '=', $cache_control_part ) );
if ( count( $cache_control_setting_parts ) !== 2 ) {
continue;
}
if ( 'max-age' === $cache_control_setting_parts[0] ) {
$max_age = absint( $cache_control_setting_parts[1] );
}
}
}
return $max_age;
}
}