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+<?php
+/**
+ * Class HTTP_ConditionalGet
+ * @package Minify
+ * @subpackage HTTP
+ */
+
+/**
+ * Implement conditional GET via a timestamp or hash of content
+ *
+ * E.g. Content from DB with update time:
+ * <code>
+ * list($updateTime, $content) = getDbUpdateAndContent();
+ * $cg = new HTTP_ConditionalGet(array(
+ * 'lastModifiedTime' => $updateTime
+ * ,'isPublic' => true
+ * ));
+ * $cg->sendHeaders();
+ * if ($cg->cacheIsValid) {
+ * exit();
+ * }
+ * echo $content;
+ * </code>
+ *
+ * E.g. Shortcut for the above
+ * <code>
+ * HTTP_ConditionalGet::check($updateTime, true); // exits if client has cache
+ * echo $content;
+ * </code>
+ *
+ * E.g. Content from DB with no update time:
+ * <code>
+ * $content = getContentFromDB();
+ * $cg = new HTTP_ConditionalGet(array(
+ * 'contentHash' => md5($content)
+ * ));
+ * $cg->sendHeaders();
+ * if ($cg->cacheIsValid) {
+ * exit();
+ * }
+ * echo $content;
+ * </code>
+ *
+ * E.g. Static content with some static includes:
+ * <code>
+ * // before content
+ * $cg = new HTTP_ConditionalGet(array(
+ * 'lastUpdateTime' => max(
+ * filemtime(__FILE__)
+ * ,filemtime('/path/to/header.inc')
+ * ,filemtime('/path/to/footer.inc')
+ * )
+ * ));
+ * $cg->sendHeaders();
+ * if ($cg->cacheIsValid) {
+ * exit();
+ * }
+ * </code>
+ * @package Minify
+ * @subpackage HTTP
+ * @author Stephen Clay <steve@mrclay.org>
+ */
+class HTTP_ConditionalGet {
+
+ /**
+ * Does the client have a valid copy of the requested resource?
+ *
+ * You'll want to check this after instantiating the object. If true, do
+ * not send content, just call sendHeaders() if you haven't already.
+ *
+ * @var bool
+ */
+ public $cacheIsValid = null;
+
+ /**
+ * @param array $spec options
+ *
+ * 'isPublic': (bool) if true, the Cache-Control header will contain
+ * "public", allowing proxies to cache the content. Otherwise "private" will
+ * be sent, allowing only browser caching. (default false)
+ *
+ * 'lastModifiedTime': (int) if given, both ETag AND Last-Modified headers
+ * will be sent with content. This is recommended.
+ *
+ * 'encoding': (string) if set, the header "Vary: Accept-Encoding" will
+ * always be sent and a truncated version of the encoding will be appended
+ * to the ETag. E.g. "pub123456;gz". This will also trigger a more lenient
+ * checking of the client's If-None-Match header, as the encoding portion of
+ * the ETag will be stripped before comparison.
+ *
+ * 'contentHash': (string) if given, only the ETag header can be sent with
+ * content (only HTTP1.1 clients can conditionally GET). The given string
+ * should be short with no quote characters and always change when the
+ * resource changes (recommend md5()). This is not needed/used if
+ * lastModifiedTime is given.
+ *
+ * 'eTag': (string) if given, this will be used as the ETag header rather
+ * than values based on lastModifiedTime or contentHash. Also the encoding
+ * string will not be appended to the given value as described above.
+ *
+ * 'invalidate': (bool) if true, the client cache will be considered invalid
+ * without testing. Effectively this disables conditional GET.
+ * (default false)
+ *
+ * 'maxAge': (int) if given, this will set the Cache-Control max-age in
+ * seconds, and also set the Expires header to the equivalent GMT date.
+ * After the max-age period has passed, the browser will again send a
+ * conditional GET to revalidate its cache.
+ *
+ * @return null
+ */
+ public function __construct($spec)
+ {
+ $scope = (isset($spec['isPublic']) && $spec['isPublic'])
+ ? 'public'
+ : 'private';
+ $maxAge = 0;
+ // backwards compatibility (can be removed later)
+ if (isset($spec['setExpires'])
+ && is_numeric($spec['setExpires'])
+ && ! isset($spec['maxAge'])) {
+ $spec['maxAge'] = $spec['setExpires'] - $_SERVER['REQUEST_TIME'];
+ }
+ if (isset($spec['maxAge'])) {
+ $maxAge = $spec['maxAge'];
+ $this->_headers['Expires'] = self::gmtDate(
+ $_SERVER['REQUEST_TIME'] + $spec['maxAge']
+ );
+ }
+ $etagAppend = '';
+ if (isset($spec['encoding'])) {
+ $this->_stripEtag = true;
+ $this->_headers['Vary'] = 'Accept-Encoding';
+ if ('' !== $spec['encoding']) {
+ if (0 === strpos($spec['encoding'], 'x-')) {
+ $spec['encoding'] = substr($spec['encoding'], 2);
+ }
+ $etagAppend = ';' . substr($spec['encoding'], 0, 2);
+ }
+ }
+ if (isset($spec['lastModifiedTime'])) {
+ $this->_setLastModified($spec['lastModifiedTime']);
+ if (isset($spec['eTag'])) { // Use it
+ $this->_setEtag($spec['eTag'], $scope);
+ } else { // base both headers on time
+ $this->_setEtag($spec['lastModifiedTime'] . $etagAppend, $scope);
+ }
+ } elseif (isset($spec['eTag'])) { // Use it
+ $this->_setEtag($spec['eTag'], $scope);
+ } elseif (isset($spec['contentHash'])) { // Use the hash as the ETag
+ $this->_setEtag($spec['contentHash'] . $etagAppend, $scope);
+ }
+ $this->_headers['Cache-Control'] = "max-age={$maxAge}, {$scope}";
+ // invalidate cache if disabled, otherwise check
+ $this->cacheIsValid = (isset($spec['invalidate']) && $spec['invalidate'])
+ ? false
+ : $this->_isCacheValid();
+ }
+
+ /**
+ * Get array of output headers to be sent
+ *
+ * In the case of 304 responses, this array will only contain the response
+ * code header: array('_responseCode' => 'HTTP/1.0 304 Not Modified')
+ *
+ * Otherwise something like:
+ * <code>
+ * array(
+ * 'Cache-Control' => 'max-age=0, public'
+ * ,'ETag' => '"foobar"'
+ * )
+ * </code>
+ *
+ * @return array
+ */
+ public function getHeaders()
+ {
+ return $this->_headers;
+ }
+
+ /**
+ * Set the Content-Length header in bytes
+ *
+ * With most PHP configs, as long as you don't flush() output, this method
+ * is not needed and PHP will buffer all output and set Content-Length for
+ * you. Otherwise you'll want to call this to let the client know up front.
+ *
+ * @param int $bytes
+ *
+ * @return int copy of input $bytes
+ */
+ public function setContentLength($bytes)
+ {
+ return $this->_headers['Content-Length'] = $bytes;
+ }
+
+ /**
+ * Send headers
+ *
+ * @see getHeaders()
+ *
+ * Note this doesn't "clear" the headers. Calling sendHeaders() will
+ * call header() again (but probably have not effect) and getHeaders() will
+ * still return the headers.
+ *
+ * @return null
+ */
+ public function sendHeaders()
+ {
+ $headers = $this->_headers;
+ if (array_key_exists('_responseCode', $headers)) {
+ header($headers['_responseCode']);
+ unset($headers['_responseCode']);
+ }
+ foreach ($headers as $name => $val) {
+ header($name . ': ' . $val);
+ }
+ }
+
+ /**
+ * Exit if the client's cache is valid for this resource
+ *
+ * This is a convenience method for common use of the class
+ *
+ * @param int $lastModifiedTime if given, both ETag AND Last-Modified headers
+ * will be sent with content. This is recommended.
+ *
+ * @param bool $isPublic (default false) if true, the Cache-Control header
+ * will contain "public", allowing proxies to cache the content. Otherwise
+ * "private" will be sent, allowing only browser caching.
+ *
+ * @param array $options (default empty) additional options for constructor
+ *
+ * @return null
+ */
+ public static function check($lastModifiedTime = null, $isPublic = false, $options = array())
+ {
+ if (null !== $lastModifiedTime) {
+ $options['lastModifiedTime'] = (int)$lastModifiedTime;
+ }
+ $options['isPublic'] = (bool)$isPublic;
+ $cg = new HTTP_ConditionalGet($options);
+ $cg->sendHeaders();
+ if ($cg->cacheIsValid) {
+ exit();
+ }
+ }
+
+
+ /**
+ * Get a GMT formatted date for use in HTTP headers
+ *
+ * <code>
+ * header('Expires: ' . HTTP_ConditionalGet::gmtdate($time));
+ * </code>
+ *
+ * @param int $time unix timestamp
+ *
+ * @return string
+ */
+ public static function gmtDate($time)
+ {
+ return gmdate('D, d M Y H:i:s \G\M\T', $time);
+ }
+
+ protected $_headers = array();
+ protected $_lmTime = null;
+ protected $_etag = null;
+ protected $_stripEtag = false;
+
+ protected function _setEtag($hash, $scope)
+ {
+ $this->_etag = '"' . substr($scope, 0, 3) . $hash . '"';
+ $this->_headers['ETag'] = $this->_etag;
+ }
+
+ protected function _setLastModified($time)
+ {
+ $this->_lmTime = (int)$time;
+ $this->_headers['Last-Modified'] = self::gmtDate($time);
+ }
+
+ /**
+ * Determine validity of client cache and queue 304 header if valid
+ */
+ protected function _isCacheValid()
+ {
+ if (null === $this->_etag) {
+ // lmTime is copied to ETag, so this condition implies that the
+ // server sent neither ETag nor Last-Modified, so the client can't
+ // possibly has a valid cache.
+ return false;
+ }
+ $isValid = ($this->resourceMatchedEtag() || $this->resourceNotModified());
+ if ($isValid) {
+ $this->_headers['_responseCode'] = 'HTTP/1.0 304 Not Modified';
+ }
+ return $isValid;
+ }
+
+ protected function resourceMatchedEtag()
+ {
+ if (!isset($_SERVER['HTTP_IF_NONE_MATCH'])) {
+ return false;
+ }
+ $clientEtagList = get_magic_quotes_gpc()
+ ? stripslashes($_SERVER['HTTP_IF_NONE_MATCH'])
+ : $_SERVER['HTTP_IF_NONE_MATCH'];
+ $clientEtags = explode(',', $clientEtagList);
+
+ $compareTo = $this->normalizeEtag($this->_etag);
+ foreach ($clientEtags as $clientEtag) {
+ if ($this->normalizeEtag($clientEtag) === $compareTo) {
+ // respond with the client's matched ETag, even if it's not what
+ // we would've sent by default
+ $this->_headers['ETag'] = trim($clientEtag);
+ return true;
+ }
+ }
+ return false;
+ }
+
+ protected function normalizeEtag($etag) {
+ $etag = trim($etag);
+ return $this->_stripEtag
+ ? preg_replace('/;\\w\\w"$/', '"', $etag)
+ : $etag;
+ }
+
+ protected function resourceNotModified()
+ {
+ if (!isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) {
+ return false;
+ }
+ $ifModifiedSince = $_SERVER['HTTP_IF_MODIFIED_SINCE'];
+ if (false !== ($semicolon = strrpos($ifModifiedSince, ';'))) {
+ // IE has tacked on extra data to this header, strip it
+ $ifModifiedSince = substr($ifModifiedSince, 0, $semicolon);
+ }
+ if ($ifModifiedSince == self::gmtDate($this->_lmTime)) {
+ // Apache 2.2's behavior. If there was no ETag match, send the
+ // non-encoded version of the ETag value.
+ $this->_headers['ETag'] = $this->normalizeEtag($this->_etag);
+ return true;
+ }
+ return false;
+ }
+}
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