<?php
/**
 * Class HTTP_Encoder 
 * @package Minify
 * @subpackage HTTP
 */
 
/**
 * Encode and send gzipped/deflated content
 *
 * The "Vary: Accept-Encoding" header is sent. If the client allows encoding, 
 * Content-Encoding and Content-Length are added.
 *
 * <code>
 * // Send a CSS file, compressed if possible
 * $he = new HTTP_Encoder(array(
 * 'content' => file_get_contents($cssFile)
 * ,'type' => 'text/css'
 * ));
 * $he->encode();
 * $he->sendAll();
 * </code>
 *
 * <code>
 * // Shortcut to encoding output
 * header('Content-Type: text/css'); // needed if not HTML
 * HTTP_Encoder::output($css);
 * </code>
 * 
 * <code>
 * // Just sniff for the accepted encoding
 * $encoding = HTTP_Encoder::getAcceptedEncoding();
 * </code>
 *
 * For more control over headers, use getHeaders() and getData() and send your
 * own output.
 * 
 * Note: If you don't need header mgmt, use PHP's native gzencode, gzdeflate, 
 * and gzcompress functions for gzip, deflate, and compress-encoding
 * respectively.
 * 
 * @package Minify
 * @subpackage HTTP
 * @author Stephen Clay <steve@mrclay.org>
 */
class HTTP_Encoder {

 /**
 * Should the encoder allow HTTP encoding to IE6? 
 * 
 * If you have many IE6 users and the bandwidth savings is worth troubling 
 * some of them, set this to true.
 * 
 * By default, encoding is only offered to IE7+. When this is true,
 * getAcceptedEncoding() will return an encoding for IE6 if its user agent
 * string contains "SV1". This has been documented in many places as "safe",
 * but there seem to be remaining, intermittent encoding bugs in patched 
 * IE6 on the wild web.
 * 
 * @var bool
 */
 public static $encodeToIe6 = true;
 
 
 /**
 * Default compression level for zlib operations
 * 
 * This level is used if encode() is not given a $compressionLevel
 * 
 * @var int
 */
 public static $compressionLevel = 6;
 

 /**
 * Get an HTTP Encoder object
 * 
 * @param array $spec options
 * 
 * 'content': (string required) content to be encoded
 * 
 * 'type': (string) if set, the Content-Type header will have this value.
 * 
 * 'method: (string) only set this if you are forcing a particular encoding
 * method. If not set, the best method will be chosen by getAcceptedEncoding()
 * The available methods are 'gzip', 'deflate', 'compress', and '' (no
 * encoding)
 */
 public function __construct($spec) 
 {
 $this->_useMbStrlen = (function_exists('mb_strlen')
 && (ini_get('mbstring.func_overload') !== '')
 && ((int)ini_get('mbstring.func_overload') & 2));
 $this->_content = $spec['content'];
 $this->_headers['Content-Length'] = $this->_useMbStrlen
 ? (string)mb_strlen($this->_content, '8bit')
 : (string)strlen($this->_content);
 if (isset($spec['type'])) {
 $this->_headers['Content-Type'] = $spec['type'];
 }
 if (isset($spec['method'])
 && in_array($spec['method'], array('gzip', 'deflate', 'compress', '')))
 {
 $this->_encodeMethod = array($spec['method'], $spec['method']);
 } else {
 $this->_encodeMethod = self::getAcceptedEncoding();
 }
 }

 /**
 * Get content in current form
 * 
 * Call after encode() for encoded content.
 * 
 * @return string
 */
 public function getContent() 
 {
 return $this->_content;
 }
 
 /**
 * Get array of output headers to be sent
 * 
 * E.g.
 * <code>
 * array(
 * 'Content-Length' => '615'
 * ,'Content-Encoding' => 'x-gzip'
 * ,'Vary' => 'Accept-Encoding'
 * )
 * </code>
 *
 * @return array 
 */
 public function getHeaders()
 {
 return $this->_headers;
 }

 /**
 * Send output headers
 * 
 * You must call this before headers are sent and it probably cannot be
 * used in conjunction with zlib output buffering / mod_gzip. Errors are
 * not handled purposefully.
 * 
 * @see getHeaders()
 */
 public function sendHeaders()
 {
 foreach ($this->_headers as $name => $val) {
 header($name . ': ' . $val);
 }
 }
 
 /**
 * Send output headers and content
 * 
 * A shortcut for sendHeaders() and echo getContent()
 *
 * You must call this before headers are sent and it probably cannot be
 * used in conjunction with zlib output buffering / mod_gzip. Errors are
 * not handled purposefully.
 */
 public function sendAll()
 {
 $this->sendHeaders();
 echo $this->_content;
 }

 /**
 * Determine the client's best encoding method from the HTTP Accept-Encoding 
 * header.
 * 
 * If no Accept-Encoding header is set, or the browser is IE before v6 SP2,
 * this will return ('', ''), the "identity" encoding.
 * 
 * A syntax-aware scan is done of the Accept-Encoding, so the method must
 * be non 0. The methods are favored in order of gzip, deflate, then 
 * compress. Deflate is always smallest and generally faster, but is 
 * rarely sent by servers, so client support could be buggier.
 * 
 * @param bool $allowCompress allow the older compress encoding
 * 
 * @param bool $allowDeflate allow the more recent deflate encoding
 * 
 * @return array two values, 1st is the actual encoding method, 2nd is the
 * alias of that method to use in the Content-Encoding header (some browsers
 * call gzip "x-gzip" etc.)
 */
 public static function getAcceptedEncoding($allowCompress = true, $allowDeflate = true)
 {
 // @link http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html
 
 if (! isset($_SERVER['HTTP_ACCEPT_ENCODING'])
 || self::isBuggyIe())
 {
 return array('', '');
 }
 $ae = $_SERVER['HTTP_ACCEPT_ENCODING'];
 // gzip checks (quick)
 if (0 === strpos($ae, 'gzip,') // most browsers
 || 0 === strpos($ae, 'deflate, gzip,') // opera
 ) {
 return array('gzip', 'gzip');
 }
 // gzip checks (slow)
 if (preg_match(
 '@(?:^|,)\\s*((?:x-)?gzip)\\s*(?:$|,|;\\s*q=(?:0\\.|1))@'
 ,$ae
 ,$m)) {
 return array('gzip', $m[1]);
 }
 if ($allowDeflate) {
 // deflate checks 
 $aeRev = strrev($ae);
 if (0 === strpos($aeRev, 'etalfed ,') // ie, webkit
 || 0 === strpos($aeRev, 'etalfed,') // gecko
 || 0 === strpos($ae, 'deflate,') // opera
 // slow parsing
 || preg_match(
 '@(?:^|,)\\s*deflate\\s*(?:$|,|;\\s*q=(?:0\\.|1))@', $ae)) {
 return array('deflate', 'deflate');
 }
 }
 if ($allowCompress && preg_match(
 '@(?:^|,)\\s*((?:x-)?compress)\\s*(?:$|,|;\\s*q=(?:0\\.|1))@'
 ,$ae
 ,$m)) {
 return array('compress', $m[1]);
 }
 return array('', '');
 }

 /**
 * Encode (compress) the content
 * 
 * If the encode method is '' (none) or compression level is 0, or the 'zlib'
 * extension isn't loaded, we return false.
 * 
 * Then the appropriate gz_* function is called to compress the content. If
 * this fails, false is returned.
 * 
 * The header "Vary: Accept-Encoding" is added. If encoding is successful, 
 * the Content-Length header is updated, and Content-Encoding is also added.
 * 
 * @param int $compressionLevel given to zlib functions. If not given, the
 * class default will be used.
 * 
 * @return bool success true if the content was actually compressed
 */
 public function encode($compressionLevel = null)
 {
 if (! self::isBuggyIe()) {
 $this->_headers['Vary'] = 'Accept-Encoding';
 }
 if (null === $compressionLevel) {
 $compressionLevel = self::$compressionLevel;
 }
 if ('' === $this->_encodeMethod[0]
 || ($compressionLevel == 0)
 || !extension_loaded('zlib'))
 {
 return false;
 }
 if ($this->_encodeMethod[0] === 'deflate') {
 $encoded = gzdeflate($this->_content, $compressionLevel);
 } elseif ($this->_encodeMethod[0] === 'gzip') {
 $encoded = gzencode($this->_content, $compressionLevel);
 } else {
 $encoded = gzcompress($this->_content, $compressionLevel);
 }
 if (false === $encoded) {
 return false;
 }
 $this->_headers['Content-Length'] = $this->_useMbStrlen
 ? (string)mb_strlen($encoded, '8bit')
 : (string)strlen($encoded);
 $this->_headers['Content-Encoding'] = $this->_encodeMethod[1];
 $this->_content = $encoded;
 return true;
 }
 
 /**
 * Encode and send appropriate headers and content
 *
 * This is a convenience method for common use of the class
 * 
 * @param string $content
 * 
 * @param int $compressionLevel given to zlib functions. If not given, the
 * class default will be used.
 * 
 * @return bool success true if the content was actually compressed
 */
 public static function output($content, $compressionLevel = null)
 {
 if (null === $compressionLevel) {
 $compressionLevel = self::$compressionLevel;
 }
 $he = new HTTP_Encoder(array('content' => $content));
 $ret = $he->encode($compressionLevel);
 $he->sendAll();
 return $ret;
 }

 /**
 * Is the browser an IE version earlier than 6 SP2?
 *
 * @return bool
 */
 public static function isBuggyIe()
 {
 if (empty($_SERVER['HTTP_USER_AGENT'])) {
 return false;
 }
 $ua = $_SERVER['HTTP_USER_AGENT'];
 // quick escape for non-IEs
 if (0 !== strpos($ua, 'Mozilla/4.0 (compatible; MSIE ')
 || false !== strpos($ua, 'Opera')) {
 return false;
 }
 // no regex = faaast
 $version = (float)substr($ua, 30);
 return self::$encodeToIe6
 ? ($version < 6 || ($version == 6 && false === strpos($ua, 'SV1')))
 : ($version < 7);
 }
 
 protected $_content = '';
 protected $_headers = array();
 protected $_encodeMethod = array('', '');
 protected $_useMbStrlen = false;
}