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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 $spec options
*
* 'isPublic': (bool) if false, the Cache-Control header will contain
* "private", allowing only browser caching. (default false)
*
* 'lastModifiedTime': (int) if given, both ETag AND Last-Modified headers
* will be sent with content. This is recommended.
*
* 'encoding': (string) if set, the header "Vary: Accept-Encoding" will
* always be sent and a truncated version of the encoding will be appended
* to the ETag. E.g. "pub123456;gz". This will also trigger a more lenient
* checking of the client's If-None-Match header, as the encoding portion of
* the ETag will be stripped before comparison.
*
* 'contentHash': (string) if given, only the ETag header can be sent with
* content (only HTTP1.1 clients can conditionally GET). The given string
* should be short with no quote characters and always change when the
* resource changes (recommend md5()). This is not needed/used if
* lastModifiedTime is given.
*
* 'eTag': (string) if given, this will be used as the ETag header rather
* than values based on lastModifiedTime or contentHash. Also the encoding
* string will not be appended to the given value as described above.
*
* 'invalidate': (bool) if true, the client cache will be considered invalid
* without testing. Effectively this disables conditional GET.
* (default false)
*
* 'maxAge': (int) if given, this will set the Cache-Control max-age in
* seconds, and also set the Expires header to the equivalent GMT date.
* After the max-age period has passed, the browser will again send a
* conditional GET to revalidate its cache.
*/
public function __construct($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;
if ('' !== $spec['encoding']) {
$this->_headers['Vary'] = 'Accept-Encoding';
if (0 === strpos($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);
}
$privacy = ($scope === 'private')
? ', private'
: '';
$this->_headers['Cache-Control'] = "max-age={$maxAge}{$privacy}";
// 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)) {
// FastCGI environments require 3rd arg to header() to be set
list(, $code) = explode(' ', $headers['_responseCode'], 3);
header($headers['_responseCode'], true, $code);
unset($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 $options (default empty) additional options for constructor
*/
public static function check($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;
/**
* @param string $hash
*
* @param string $scope
*/
protected function _setEtag($hash, $scope)
{
$this->_etag = '"' . substr($scope, 0, 3) . $hash . '"';
$this->_headers['ETag'] = $this->_etag;
}
/**
* @param int $time
*/
protected function _setLastModified($time)
{
$this->_lmTime = (int)$time;
$this->_headers['Last-Modified'] = self::gmtDate($time);
}
/**
* Determine validity of client cache and queue 304 header if valid
*
* @return bool
*/
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 $isValid;
}
/**
* @return bool
*/
protected function resourceMatchedEtag()
{
if (!isset($_SERVER['HTTP_IF_NONE_MATCH'])) {
return false;
}
$clientEtagList = PHP_VERSION_ID < 50400 && get_magic_quotes_gpc()
? stripslashes($_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;
}
/**
* @param string $etag
*
* @return string
*/
protected function normalizeEtag($etag)
{
$etag = trim($etag);
return $this->_stripEtag
? preg_replace('/;\\w\\w"$/', '"', $etag)
: $etag;
}
/**
* @return bool
*/
protected function resourceNotModified()
{
if (!isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) {
return false;
}
// strip off IE's extra data (semicolon)
list($ifModifiedSince) = explode(';', $_SERVER['HTTP_IF_MODIFIED_SINCE'], 2);
$date = new DateTime($ifModifiedSince, new DateTimeZone('UTC'));
if ($date->getTimestamp() >= $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;
}
}