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Differences Between: [Versions 400 and 402] [Versions 400 and 403]

   1  <?php
   2  /*
   3   * Copyright 2012 Google Inc.
   4   *
   5   * Licensed under the Apache License, Version 2.0 (the "License");
   6   * you may not use this file except in compliance with the License.
   7   * You may obtain a copy of the License at
   8   *
   9   *     http://www.apache.org/licenses/LICENSE-2.0
  10   *
  11   * Unless required by applicable law or agreed to in writing, software
  12   * distributed under the License is distributed on an "AS IS" BASIS,
  13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14   * See the License for the specific language governing permissions and
  15   * limitations under the License.
  16   */
  17  
  18  if (!class_exists('Google_Client')) {
  19    require_once dirname(__FILE__) . '/../autoload.php';
  20  }
  21  
  22  /**
  23   * Implement the caching directives specified in rfc2616. This
  24   * implementation is guided by the guidance offered in rfc2616-sec13.
  25   */
  26  class Google_Http_CacheParser
  27  {
  28    public static $CACHEABLE_HTTP_METHODS = array('GET', 'HEAD');
  29    public static $CACHEABLE_STATUS_CODES = array('200', '203', '300', '301');
  30  
  31    /**
  32     * Check if an HTTP request can be cached by a private local cache.
  33     *
  34     * @static
  35     * @param Google_Http_Request $resp
  36     * @return bool True if the request is cacheable.
  37     * False if the request is uncacheable.
  38     */
  39    public static function isRequestCacheable(Google_Http_Request $resp)
  40    {
  41      $method = $resp->getRequestMethod();
  42      if (! in_array($method, self::$CACHEABLE_HTTP_METHODS)) {
  43        return false;
  44      }
  45  
  46      // Don't cache authorized requests/responses.
  47      // [rfc2616-14.8] When a shared cache receives a request containing an
  48      // Authorization field, it MUST NOT return the corresponding response
  49      // as a reply to any other request...
  50      if ($resp->getRequestHeader("authorization")) {
  51        return false;
  52      }
  53  
  54      return true;
  55    }
  56  
  57    /**
  58     * Check if an HTTP response can be cached by a private local cache.
  59     *
  60     * @static
  61     * @param Google_Http_Request $resp
  62     * @return bool True if the response is cacheable.
  63     * False if the response is un-cacheable.
  64     */
  65    public static function isResponseCacheable(Google_Http_Request $resp)
  66    {
  67      // First, check if the HTTP request was cacheable before inspecting the
  68      // HTTP response.
  69      if (false == self::isRequestCacheable($resp)) {
  70        return false;
  71      }
  72  
  73      $code = $resp->getResponseHttpCode();
  74      if (! in_array($code, self::$CACHEABLE_STATUS_CODES)) {
  75        return false;
  76      }
  77  
  78      // The resource is uncacheable if the resource is already expired and
  79      // the resource doesn't have an ETag for revalidation.
  80      $etag = $resp->getResponseHeader("etag");
  81      if (self::isExpired($resp) && $etag == false) {
  82        return false;
  83      }
  84  
  85      // [rfc2616-14.9.2]  If [no-store is] sent in a response, a cache MUST NOT
  86      // store any part of either this response or the request that elicited it.
  87      $cacheControl = $resp->getParsedCacheControl();
  88      if (isset($cacheControl['no-store'])) {
  89        return false;
  90      }
  91  
  92      // Pragma: no-cache is an http request directive, but is occasionally
  93      // used as a response header incorrectly.
  94      $pragma = $resp->getResponseHeader('pragma');
  95      if ($pragma == 'no-cache' || strpos($pragma, 'no-cache') !== false) {
  96        return false;
  97      }
  98  
  99      // [rfc2616-14.44] Vary: * is extremely difficult to cache. "It implies that
 100      // a cache cannot determine from the request headers of a subsequent request
 101      // whether this response is the appropriate representation."
 102      // Given this, we deem responses with the Vary header as uncacheable.
 103      $vary = $resp->getResponseHeader('vary');
 104      if ($vary) {
 105        return false;
 106      }
 107  
 108      return true;
 109    }
 110  
 111    /**
 112     * @static
 113     * @param Google_Http_Request $resp
 114     * @return bool True if the HTTP response is considered to be expired.
 115     * False if it is considered to be fresh.
 116     */
 117    public static function isExpired(Google_Http_Request $resp)
 118    {
 119      // HTTP/1.1 clients and caches MUST treat other invalid date formats,
 120      // especially including the value “0”, as in the past.
 121      $parsedExpires = false;
 122      $responseHeaders = $resp->getResponseHeaders();
 123  
 124      if (isset($responseHeaders['expires'])) {
 125        $rawExpires = $responseHeaders['expires'];
 126        // Check for a malformed expires header first.
 127        if (empty($rawExpires) || (is_numeric($rawExpires) && $rawExpires <= 0)) {
 128          return true;
 129        }
 130  
 131        // See if we can parse the expires header.
 132        $parsedExpires = strtotime($rawExpires);
 133        if (false == $parsedExpires || $parsedExpires <= 0) {
 134          return true;
 135        }
 136      }
 137  
 138      // Calculate the freshness of an http response.
 139      $freshnessLifetime = false;
 140      $cacheControl = $resp->getParsedCacheControl();
 141      if (isset($cacheControl['max-age'])) {
 142        $freshnessLifetime = $cacheControl['max-age'];
 143      }
 144  
 145      $rawDate = $resp->getResponseHeader('date');
 146      $parsedDate = strtotime($rawDate);
 147  
 148      if (empty($rawDate) || false == $parsedDate) {
 149        // We can't default this to now, as that means future cache reads
 150        // will always pass with the logic below, so we will require a
 151        // date be injected if not supplied.
 152        throw new Google_Exception("All cacheable requests must have creation dates.");
 153      }
 154  
 155      if (false == $freshnessLifetime && isset($responseHeaders['expires'])) {
 156        $freshnessLifetime = $parsedExpires - $parsedDate;
 157      }
 158  
 159      if (false == $freshnessLifetime) {
 160        return true;
 161      }
 162  
 163      // Calculate the age of an http response.
 164      $age = max(0, time() - $parsedDate);
 165      if (isset($responseHeaders['age'])) {
 166        $age = max($age, strtotime($responseHeaders['age']));
 167      }
 168  
 169      return $freshnessLifetime <= $age;
 170    }
 171  
 172    /**
 173     * Determine if a cache entry should be revalidated with by the origin.
 174     *
 175     * @param Google_Http_Request $response
 176     * @return bool True if the entry is expired, else return false.
 177     */
 178    public static function mustRevalidate(Google_Http_Request $response)
 179    {
 180      // [13.3] When a cache has a stale entry that it would like to use as a
 181      // response to a client's request, it first has to check with the origin
 182      // server to see if its cached entry is still usable.
 183      return self::isExpired($response);
 184    }
 185  }