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<?php |
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/* |
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* Copyright 2012 Google Inc. |
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* |
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* Licensed under the Apache License, Version 2.0 (the "License"); |
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* you may not use this file except in compliance with the License. |
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* You may obtain a copy of the License at |
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* |
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* http://www.apache.org/licenses/LICENSE-2.0 |
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* |
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* Unless required by applicable law or agreed to in writing, software |
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* distributed under the License is distributed on an "AS IS" BASIS, |
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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* See the License for the specific language governing permissions and |
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* limitations under the License. |
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*/ |
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if (!class_exists('Google_Client')) { |
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require_once dirname(__FILE__) . '/../autoload.php'; |
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} |
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/** |
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* Implement the caching directives specified in rfc2616. This |
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* implementation is guided by the guidance offered in rfc2616-sec13. |
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*/ |
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class Google_Http_CacheParser |
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{ |
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public static $CACHEABLE_HTTP_METHODS = array('GET', 'HEAD'); |
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public static $CACHEABLE_STATUS_CODES = array('200', '203', '300', '301'); |
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/** |
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* Check if an HTTP request can be cached by a private local cache. |
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* |
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* @static |
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* @param Google_Http_Request $resp |
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* @return bool True if the request is cacheable. |
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* False if the request is uncacheable. |
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*/ |
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public static function isRequestCacheable(Google_Http_Request $resp) |
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{ |
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$method = $resp->getRequestMethod(); |
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if (! in_array($method, self::$CACHEABLE_HTTP_METHODS)) { |
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return false; |
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} |
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// Don't cache authorized requests/responses. |
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// [rfc2616-14.8] When a shared cache receives a request containing an |
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// Authorization field, it MUST NOT return the corresponding response |
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// as a reply to any other request... |
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if ($resp->getRequestHeader("authorization")) { |
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return false; |
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} |
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return true; |
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} |
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/** |
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* Check if an HTTP response can be cached by a private local cache. |
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* |
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* @static |
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* @param Google_Http_Request $resp |
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* @return bool True if the response is cacheable. |
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* False if the response is un-cacheable. |
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*/ |
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public static function isResponseCacheable(Google_Http_Request $resp) |
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{ |
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// First, check if the HTTP request was cacheable before inspecting the |
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// HTTP response. |
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if (false == self::isRequestCacheable($resp)) { |
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return false; |
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} |
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$code = $resp->getResponseHttpCode(); |
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if (! in_array($code, self::$CACHEABLE_STATUS_CODES)) { |
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return false; |
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} |
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// The resource is uncacheable if the resource is already expired and |
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// the resource doesn't have an ETag for revalidation. |
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$etag = $resp->getResponseHeader("etag"); |
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if (self::isExpired($resp) && $etag == false) { |
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return false; |
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} |
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// [rfc2616-14.9.2] If [no-store is] sent in a response, a cache MUST NOT |
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// store any part of either this response or the request that elicited it. |
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$cacheControl = $resp->getParsedCacheControl(); |
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if (isset($cacheControl['no-store'])) { |
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return false; |
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} |
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// Pragma: no-cache is an http request directive, but is occasionally |
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// used as a response header incorrectly. |
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$pragma = $resp->getResponseHeader('pragma'); |
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if ($pragma == 'no-cache' || strpos($pragma, 'no-cache') !== false) { |
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return false; |
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} |
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// [rfc2616-14.44] Vary: * is extremely difficult to cache. "It implies that |
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// a cache cannot determine from the request headers of a subsequent request |
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// whether this response is the appropriate representation." |
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// Given this, we deem responses with the Vary header as uncacheable. |
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$vary = $resp->getResponseHeader('vary'); |
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if ($vary) { |
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return false; |
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} |
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return true; |
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} |
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/** |
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* @static |
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* @param Google_Http_Request $resp |
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* @return bool True if the HTTP response is considered to be expired. |
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* False if it is considered to be fresh. |
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*/ |
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public static function isExpired(Google_Http_Request $resp) |
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{ |
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// HTTP/1.1 clients and caches MUST treat other invalid date formats, |
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// especially including the value “0”, as in the past. |
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$parsedExpires = false; |
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$responseHeaders = $resp->getResponseHeaders(); |
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if (isset($responseHeaders['expires'])) { |
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$rawExpires = $responseHeaders['expires']; |
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// Check for a malformed expires header first. |
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if (empty($rawExpires) || (is_numeric($rawExpires) && $rawExpires <= 0)) { |
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return true; |
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} |
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// See if we can parse the expires header. |
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$parsedExpires = strtotime($rawExpires); |
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if (false == $parsedExpires || $parsedExpires <= 0) { |
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return true; |
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} |
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} |
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// Calculate the freshness of an http response. |
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$freshnessLifetime = false; |
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$cacheControl = $resp->getParsedCacheControl(); |
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if (isset($cacheControl['max-age'])) { |
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$freshnessLifetime = $cacheControl['max-age']; |
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} |
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$rawDate = $resp->getResponseHeader('date'); |
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$parsedDate = strtotime($rawDate); |
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if (empty($rawDate) || false == $parsedDate) { |
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// We can't default this to now, as that means future cache reads |
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// will always pass with the logic below, so we will require a |
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// date be injected if not supplied. |
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throw new Google_Exception("All cacheable requests must have creation dates."); |
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} |
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if (false == $freshnessLifetime && isset($responseHeaders['expires'])) { |
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$freshnessLifetime = $parsedExpires - $parsedDate; |
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} |
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if (false == $freshnessLifetime) { |
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return true; |
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} |
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// Calculate the age of an http response. |
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$age = max(0, time() - $parsedDate); |
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if (isset($responseHeaders['age'])) { |
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$age = max($age, strtotime($responseHeaders['age'])); |
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} |
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return $freshnessLifetime <= $age; |
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} |
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/** |
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* Determine if a cache entry should be revalidated with by the origin. |
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* |
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* @param Google_Http_Request $response |
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* @return bool True if the entry is expired, else return false. |
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*/ |
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public static function mustRevalidate(Google_Http_Request $response) |
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{ |
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// [13.3] When a cache has a stale entry that it would like to use as a |
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// response to a client's request, it first has to check with the origin |
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// server to see if its cached entry is still usable. |
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return self::isExpired($response); |
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} |
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} |
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When comparing two booleans, it is generally considered safer to use the strict comparison operator.