3 * Class HTTP_ConditionalGet
9 * Implement conditional GET via a timestamp or hash of content
11 * E.g. Content from DB with update time:
13 * list($updateTime, $content) = getDbUpdateAndContent();
14 * $cg = new HTTP_ConditionalGet(array(
15 * 'lastModifiedTime' => $updateTime
19 * if ($cg->cacheIsValid) {
25 * E.g. Shortcut for the above
27 * HTTP_ConditionalGet::check($updateTime, true); // exits if client has cache
31 * E.g. Content from DB with no update time:
33 * $content = getContentFromDB();
34 * $cg = new HTTP_ConditionalGet(array(
35 * 'contentHash' => md5($content)
38 * if ($cg->cacheIsValid) {
44 * E.g. Static content with some static includes:
47 * $cg = new HTTP_ConditionalGet(array(
48 * 'lastUpdateTime' => max(
50 * ,filemtime('/path/to/header.inc')
51 * ,filemtime('/path/to/footer.inc')
55 * if ($cg->cacheIsValid) {
61 * @author Stephen Clay <steve@mrclay.org>
63 class HTTP_ConditionalGet {
66 * Does the client have a valid copy of the requested resource?
68 * You'll want to check this after instantiating the object. If true, do
69 * not send content, just call sendHeaders() if you haven't already.
73 public $cacheIsValid = null;
76 * @param array $spec options
78 * 'isPublic': (bool) if true, the Cache-Control header will contain
79 * "public", allowing proxies to cache the content. Otherwise "private" will
80 * be sent, allowing only browser caching. (default false)
82 * 'lastModifiedTime': (int) if given, both ETag AND Last-Modified headers
83 * will be sent with content. This is recommended.
85 * 'encoding': (string) if set, the header "Vary: Accept-Encoding" will
86 * always be sent and a truncated version of the encoding will be appended
87 * to the ETag. E.g. "pub123456;gz". This will also trigger a more lenient
88 * checking of the client's If-None-Match header, as the encoding portion of
89 * the ETag will be stripped before comparison.
91 * 'contentHash': (string) if given, only the ETag header can be sent with
92 * content (only HTTP1.1 clients can conditionally GET). The given string
93 * should be short with no quote characters and always change when the
94 * resource changes (recommend md5()). This is not needed/used if
95 * lastModifiedTime is given.
97 * 'eTag': (string) if given, this will be used as the ETag header rather
98 * than values based on lastModifiedTime or contentHash. Also the encoding
99 * string will not be appended to the given value as described above.
101 * 'invalidate': (bool) if true, the client cache will be considered invalid
102 * without testing. Effectively this disables conditional GET.
105 * 'maxAge': (int) if given, this will set the Cache-Control max-age in
106 * seconds, and also set the Expires header to the equivalent GMT date.
107 * After the max-age period has passed, the browser will again send a
108 * conditional GET to revalidate its cache.
112 public function __construct($spec)
114 $scope = (isset($spec['isPublic']) && $spec['isPublic'])
118 // backwards compatibility (can be removed later)
119 if (isset($spec['setExpires'])
120 && is_numeric($spec['setExpires'])
121 && ! isset($spec['maxAge'])) {
122 $spec['maxAge'] = $spec['setExpires'] - $_SERVER['REQUEST_TIME'];
124 if (isset($spec['maxAge'])) {
125 $maxAge = $spec['maxAge'];
126 $this->_headers['Expires'] = self::gmtDate(
127 $_SERVER['REQUEST_TIME'] + $spec['maxAge']
131 if (isset($spec['encoding'])) {
132 $this->_stripEtag = true;
133 $this->_headers['Vary'] = 'Accept-Encoding';
134 if ('' !== $spec['encoding']) {
135 if (0 === strpos($spec['encoding'], 'x-')) {
136 $spec['encoding'] = substr($spec['encoding'], 2);
138 $etagAppend = ';' . substr($spec['encoding'], 0, 2);
141 if (isset($spec['lastModifiedTime'])) {
142 $this->_setLastModified($spec['lastModifiedTime']);
143 if (isset($spec['eTag'])) { // Use it
144 $this->_setEtag($spec['eTag'], $scope);
145 } else { // base both headers on time
146 $this->_setEtag($spec['lastModifiedTime'] . $etagAppend, $scope);
148 } elseif (isset($spec['eTag'])) { // Use it
149 $this->_setEtag($spec['eTag'], $scope);
150 } elseif (isset($spec['contentHash'])) { // Use the hash as the ETag
151 $this->_setEtag($spec['contentHash'] . $etagAppend, $scope);
153 $this->_headers['Cache-Control'] = "max-age={$maxAge}, {$scope}";
154 // invalidate cache if disabled, otherwise check
155 $this->cacheIsValid = (isset($spec['invalidate']) && $spec['invalidate'])
157 : $this->_isCacheValid();
161 * Get array of output headers to be sent
163 * In the case of 304 responses, this array will only contain the response
164 * code header: array('_responseCode' => 'HTTP/1.0 304 Not Modified')
166 * Otherwise something like:
169 * 'Cache-Control' => 'max-age=0, public'
170 * ,'ETag' => '"foobar"'
176 public function getHeaders()
178 return $this->_headers;
182 * Set the Content-Length header in bytes
184 * With most PHP configs, as long as you don't flush() output, this method
185 * is not needed and PHP will buffer all output and set Content-Length for
186 * you. Otherwise you'll want to call this to let the client know up front.
190 * @return int copy of input $bytes
192 public function setContentLength($bytes)
194 return $this->_headers['Content-Length'] = $bytes;
202 * Note this doesn't "clear" the headers. Calling sendHeaders() will
203 * call header() again (but probably have not effect) and getHeaders() will
204 * still return the headers.
208 public function sendHeaders()
210 $headers = $this->_headers;
211 if (array_key_exists('_responseCode', $headers)) {
212 header($headers['_responseCode']);
213 unset($headers['_responseCode']);
215 foreach ($headers as $name => $val) {
216 header($name . ': ' . $val);
221 * Exit if the client's cache is valid for this resource
223 * This is a convenience method for common use of the class
225 * @param int $lastModifiedTime if given, both ETag AND Last-Modified headers
226 * will be sent with content. This is recommended.
228 * @param bool $isPublic (default false) if true, the Cache-Control header
229 * will contain "public", allowing proxies to cache the content. Otherwise
230 * "private" will be sent, allowing only browser caching.
232 * @param array $options (default empty) additional options for constructor
236 public static function check($lastModifiedTime = null, $isPublic = false, $options = array())
238 if (null !== $lastModifiedTime) {
239 $options['lastModifiedTime'] = (int)$lastModifiedTime;
241 $options['isPublic'] = (bool)$isPublic;
242 $cg = new HTTP_ConditionalGet($options);
244 if ($cg->cacheIsValid) {
251 * Get a GMT formatted date for use in HTTP headers
254 * header('Expires: ' . HTTP_ConditionalGet::gmtdate($time));
257 * @param int $time unix timestamp
261 public static function gmtDate($time)
263 return gmdate('D, d M Y H:i:s \G\M\T', $time);
266 protected $_headers = array();
267 protected $_lmTime = null;
268 protected $_etag = null;
269 protected $_stripEtag = false;
271 protected function _setEtag($hash, $scope)
273 $this->_etag = '"' . substr($scope, 0, 3) . $hash . '"';
274 $this->_headers['ETag'] = $this->_etag;
277 protected function _setLastModified($time)
279 $this->_lmTime = (int)$time;
280 $this->_headers['Last-Modified'] = self::gmtDate($time);
284 * Determine validity of client cache and queue 304 header if valid
286 protected function _isCacheValid()
288 if (null === $this->_etag) {
289 // lmTime is copied to ETag, so this condition implies that the
290 // server sent neither ETag nor Last-Modified, so the client can't
291 // possibly has a valid cache.
294 $isValid = ($this->resourceMatchedEtag() || $this->resourceNotModified());
296 $this->_headers['_responseCode'] = 'HTTP/1.0 304 Not Modified';
301 protected function resourceMatchedEtag()
303 if (!isset($_SERVER['HTTP_IF_NONE_MATCH'])) {
306 $clientEtagList = get_magic_quotes_gpc()
307 ? stripslashes($_SERVER['HTTP_IF_NONE_MATCH'])
308 : $_SERVER['HTTP_IF_NONE_MATCH'];
309 $clientEtags = explode(',', $clientEtagList);
311 $compareTo = $this->normalizeEtag($this->_etag);
312 foreach ($clientEtags as $clientEtag) {
313 if ($this->normalizeEtag($clientEtag) === $compareTo) {
314 // respond with the client's matched ETag, even if it's not what
315 // we would've sent by default
316 $this->_headers['ETag'] = trim($clientEtag);
323 protected function normalizeEtag($etag) {
325 return $this->_stripEtag
326 ? preg_replace('/;\\w\\w"$/', '"', $etag)
330 protected function resourceNotModified()
332 if (!isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) {
335 $ifModifiedSince = $_SERVER['HTTP_IF_MODIFIED_SINCE'];
336 if (false !== ($semicolon = strrpos($ifModifiedSince, ';'))) {
337 // IE has tacked on extra data to this header, strip it
338 $ifModifiedSince = substr($ifModifiedSince, 0, $semicolon);
340 if ($ifModifiedSince == self::gmtDate($this->_lmTime)) {
341 // Apache 2.2's behavior. If there was no ETag match, send the
342 // non-encoded version of the ETag value.
343 $this->_headers['ETag'] = $this->normalizeEtag($this->_etag);