<?php
/*
**	Copyright (C) 1995-2016 by the ITools Authors.
**	This file is part of ITools - the Internet Tools Library
**
**	ITools is free software; you can redistribute it and/or modify
**	it under the terms of the GNU General Public License as published by
**	the Free Software Foundation; either version 3 of the License, or
**	(at your option) any later version.
**
**	ITools is distributed in the hope that it will be useful,
**	but WITHOUT ANY WARRANTY; without even the implied warranty of
**	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
**	GNU General Public License for more details.
**
**	You should have received a copy of the GNU General Public License
**	along with this program.  If not, see <http://www.gnu.org/licenses/>.
**
**	url.class - URL parsing, retrieval and caching functions
*/

class it_url
{
	/* E.g. HTTP://falcon:joshua@www.Relog.CH.:80/default.asp */
	var $url;		/* E.g. http://www.relog.ch/ */
	var $protocol;		/* E.g. http */
	var $hostname;		/* E.g. relog.ch */
	var $realhostname;	/* E.g. www.relog.ch */
	var $port;		/* E.g. 80 */
	var $explicitport;	/* E.g. :80, explicitly set in rawurl */
	var $path;		/* E.g. / */
	var $rawurl;		/* E.g. HTTP://falcon:joshua@www.Relog.CH.:80/default.asp */
	var $user;		/* E.g. falcon */
	var $pass;		/* E.g. joshua */
	var $cookies;		/* key => values of cookies from server */
	var $headers;		/* Headers of page fetched by get() */
	var $data;		/* Data part, even if return code is not 200 */
	var $result;		/* Return code of get() */
	var $redir = 0;		/* Redirect count */
	var $header;    /* http header */
	var $errstr;    /* request error string */


/**
 * Constructor: canonicalize an URL
 * @param $url URL this object represents
 */
function it_url($url = null)
{
	$this->rawurl = $url;
	$comp = parse_url($url);
	$this->protocol = strtolower($comp['scheme']) ?: "http";
	$protoport = $this->protocol == 'https' ? 443 : 80;			# port according to protocol
	$this->port = intval($comp['port'] ?: $protoport);			# this is set even in default case
	$this->explicitport = $comp['port'] ? ':' . $comp['port'] : '';		# only set if explicitly specified in url, contains leading :
	$this->user = $comp['user'];
	$this->pass = $comp['pass'];
	$this->realhostname = strtolower($comp['host']);
	$this->hostname = preg_replace('/^www\./', '', $this->realhostname);
	$this->path = ltrim($comp['path'] . ($comp['query'] ? '?' . $comp['query'] : ''), '/');	# $this->path is named poorly, it includes path and query
	$this->url = "$this->protocol://$this->realhostname" . ($this->port != $protoport ? $this->explicitport : '') . "/$this->path";
	$this->realhostname = idn_to_ascii($this->realhostname) ?: $this->realhostname;		# punycode or original
}


/**
 * Check if a given url (currently http:port80-only) can be fetched
 * Note: Redirects are treated as succesful
 * $timeout Timeout for connection in seconds
 * @return true if url could be fetched
 */
function is_reachable($timeout = 5)
{
	$result = false;

	if ($fp = @fsockopen($this->realhostname, $this->port, $dummy_errno, $dummy_errstr, $timeout))
	{
		fputs($fp, "GET /$this->path HTTP/1.0\r\nHost: $this->realhostname\r\nUser-Agent: ITools\r\n\r\n");
		$line = fgets($fp, 128);
		fclose($fp);

		#debug("it_url::is_reachable($this->rawurl: $line");
		$result = preg_match("#^$this->protocol/[^ ]+ +[23]#i", $line);
	}

	return $result;
}

/**
 * Get simple URL with timeout and one retry. Can be called statically
 *
 * If the protocol is not http, only features of get_multi are supported.
 *
 * @param $p parameter array with the following keys
 * @param $p['url']          url to get, defaults to constructor URL
 * @param $p['headers']      optional associative array of HTTP headers to send
 * @param $p['safety']       set to 1 to generate an it::error in case of timeout
 * @param $p['it_error']     extra arguments given to it_error if safety is on an an error occurs
 * @param $p['timeout']      timeout per read in seconds, defaults to 5. fractions allowed. silent, see $p['safety']
 * @param $p['totaltimeout'] timeout for the whole function call
 * @param $p['maxlength']    maximum length of response
 * @param $p['filemtime']    Add HTTP header to only fetch when newer than this, otherwise return true instead of data
 * @param $p['data']         POST data array with key-value pairs
 * @param $p['files']        [fieldname => filename] of files to upload
 * @param $p['retries']      Number of retries if download fails, default 1
 * @param $p['retrysleep']   Number of seconds to wait before retry, fractions ok
 * @param $p['compression']  use compression (uses curl to do that)
 * @return contents of resulting page, considering redirects, excluding headers, or false on error
 */
function get($p=null, $timeout=5)
{
	if (!is_array($p))
		$p = array('url' => $p, 'timeout' => $timeout);
	$p += array('retries' => 1);

	if (($filter = EDC('req')) && ($filter == 1 || strstr($p['url'], "/$filter.")))
		ED($p['url']);

	if (isset($this) && $this instanceof it_url)
	{
		$url = $this;
		if ($p['url'])
			$this->it_url($p['url']);
	}
	else	# called statically
		$url = new it_url($p['url']);

	if ($url->protocol == 'http' && !$p['curl'] && !$p['files'] && !$p['compression'])	# only curl can do file upload or non-http protocols
		$result = $url->request($p);
	else
		$result = $url->request_curl($p);

	# Handle redirects (supports relative and global) but not for HTTP 201 Created because that can send the Location of the new resource
	if ($url->headers['Location'] && $url->result != 201 && preg_match('#^(https?://[^/]*)?(/)?(.*)$#i', $url->headers['Location'], $parts) && ($parts[1] != $url->url))
	{
		unset($p['url'], $p['headers']['Host']);
		$url->it_url($parts[1] ? $parts[1].$parts[2].$parts[3] : $url->protocol.'://'.$url->realhostname.($parts[2] ? $parts[2].$parts[3] : '/'.dirname($url->path).'/'.$parts[3]));
		if (++$url->redir <= 4)  /* Avoid infinite redirects */
			return $url->get($p);
	}

	if (!$result && $p['retries'] > 0 && $url->result < 400)
	{
		usleep($p['retrysleep']*1000000);
		$result = $url->get(array('retries' => $p['retries'] - 1) + $p);
	}

	if (($filter = EDC('res')) && strstr($p['url'], it::replace(array('1' => ":"), $filter)))
		ED($result);

	return $result;
}

function parse_http_header($header)
{
	foreach (explode("\n", trim($header)) as $line) {
		$line = trim($line);
		if (preg_match('#^(HTTP\S+)\s(\d+)#', $line, $parts)) # Parse result code
			$this->headers[$parts[1]] = $this->result = $parts[2];
		elseif (preg_match('#^([^:]+): (.*)$#', $line, $parts))
			$this->headers[$parts[1]] = $parts[2];
		if ($parts[1] == 'Set-Cookie' && preg_match('/^([^=]+)=([^;]*)/', $parts[2], $cookie))
			$this->cookies[$cookie[1]] = $cookie[2];
	}
}

static function _default_headers($url, $p)
{
	return [
		'Host' => $url->realhostname . $url->explicitport,
		'User-Agent' => "Mozilla/5.0 (compatible; MSIE 9.0; ITools)",
		'Accept-Language' => $p['headers']['Accept-Language'] ?: T_lang(), # can prevent loading of it_text
		'Referer' => it::match('([-\w]+\.\w+)$', $url->hostname) == it::match('([-\w]+\.\w+)$', $_SERVER['HTTP_HOST']) ? it_url::absolute(U($_GET)) : null,
		'X-Ultra-Https' => $_SERVER['HTTPS'],
	];
}

function request($p=array())
{
	$p += array('totaltimeout' => "999999", 'timeout' => 5);

	$url = $this;
	if ($p['url'])
		$this->it_url($p['url']);

	$url->result = $result = false;
	unset($url->data);
	$url->headers = $url->cookies = array();
	$p['timeout'] = min($p['timeout'], $p['totaltimeout']);	# No operation may be longer than totaltimeout
	$endtime = time() + $p['totaltimeout'];

	if ($fp = @fsockopen($url->realhostname, $url->port, $dummy_errno, $errstr, $p['timeout']))
	{
		# urlencode data pairs if is array
		$data = is_array($p['data']) ? it_url::params($p['data']) : $p['data'];

		$p['headers'] = (array)$p['headers'] + self::_default_headers($url, $p);

		if (is_int($p['filemtime']))
			$p['headers']['If-Modified-Since'] = date("r", $p['filemtime']);

		if ($datalen = strlen($data))
		{
			$method = $p['method'] ?: "POST";
			$p['headers'] += array(
				'Content-Type' => "application/x-www-form-urlencoded",
				'Content-Length' => $datalen,
			);
		}
		else
			$method = $p['method'] ?: "GET";

		if ($url->user || $url->pass)
			$p['headers'] += array('Authorization' => 'Basic ' . base64_encode($url->user . ':' . $url->pass));

		foreach ($p['headers'] as $header => $value) {
			if ($value !== null)
				$headers .= "$header: $value\r\n";
		}

		stream_set_timeout($fp, intval($p['timeout']), intval(($p['timeout']*1000000)%1000000));
		@fputs($fp, "$method /$url->path HTTP/1.0\r\n$headers\r\n$data");

		$url->header = '';
		while (!feof($fp) && ($origline = @fgets($fp, 10240)) && (trim($origline)) && (time() < $endtime))
		{
			$url->header .= $origline;
			$origline = '';
		}
		$url->header .= $origline;
		$this->parse_http_header($url->header);

		if ($url->result)
		{
			if ($url->headers['Transfer-Encoding'] == "chunked")	# Bogus HTTP/1.1 chunked answer from server (e.g. Wordpress/Apache2/PHP5)
			{
				while (($len = hexdec(fgets($fp))) && (!$p['maxlength'] || strlen($url->data) + $len <= $p['maxlength']))
				{
					$chunk = "";

					while (!feof($fp) && (strlen($chunk) < $len) && (time() < $endtime))
						$chunk .= @fread($fp, $len - strlen($chunk));

					$url->data .= $chunk;
				}
			}
			else
			{
				while (!feof($fp) && (time() < $endtime) && (!$p['maxlength'] || strlen($url->data) <= $p['maxlength']))
					$url->data .= @fread($fp, 20480);
			}

			if ($p['filemtime'] && ($url->result == 304))
				$result = true;	# Not modified, success but no data
			else if ($url->result < 400)
				$result =& $url->data;
		}

		@fclose($fp);
	} else
		$this->errstr = $errstr;

	if (time() >= $endtime) {
		$result = $this->result = false;
		$errstr = $this->errstr = "totaltimeout (" . $p['totaltimeout'] . ") reached";
	}

	if ($p['maxlength'] && (strlen($this->data) + $len > $p['maxlength'])) {
		$result = $this->result = false;
		$errstr = $this->errstr = "maxlength reached";
	}

	if ($result === false && $p['safety'] == 1)
		it::error(array('title' => "problem (timeout?) getting $url->url " . $errstr) + (array)$p['it_error']);

	return $result;
}

static function curl_opts($p=array())
{
	$p += array('totaltimeout' => "999999", 'timeout' => 5);

	foreach ($p['headers'] as $header => $value)
		$headers[] = "$header: $value";

	if ($p['maxlength']) {
		$maxlength = $p['maxlength'];
		$add = array(
			#CURLOPT_BUFFERSIZE       => 1024 * 1024 * 10,
			CURLOPT_NOPROGRESS       => false,
			CURLOPT_PROGRESSFUNCTION => function ($dummy0, $dummy1, $size, $dummy2, $dummy3) use ($maxlength) { return $size < $maxlength ? 0 : 1; },
		);
	}

	# file upload
	foreach ((array)$p['files'] as $field => $filename)
		$p['data'][$field] = new CURLFile($filename, mime_content_type($filename));

	if ($p['data'])
		$add[CURLOPT_POSTFIELDS] = $p['data'];

	if ($p['compression'])
		$add[CURLOPT_ENCODING] = "";

	return (array)$add + array(
		CURLOPT_HEADER => false,
		CURLOPT_RETURNTRANSFER => true,
		CURLOPT_TIMEOUT => $p['totaltimeout'],
		CURLOPT_LOW_SPEED_LIMIT => 5,
		CURLOPT_LOW_SPEED_TIME => $p['timeout'],
		CURLOPT_FOLLOWLOCATION => false,
		CURLOPT_HTTPHEADER => $headers,
		CURLOPT_CUSTOMREQUEST => $p['method'] ?: null,
		CURLOPT_SAFE_UPLOAD => true,	# disable special meaning of @value in POST forms (security)

		CURLOPT_CAPATH         => '/etc/ssl/certs/',
		CURLOPT_SSL_VERIFYPEER => !$p['allow_insecure_ssl'],
		CURLOPT_SSL_VERIFYHOST => $p['allow_insecure_ssl'] ? 0 : 2,

		CURLINFO_HEADER_OUT => 1,
	);
}

/*
 * drop in replacement for request using curl
 *
 * todo:
 * @param $p['filemtime']    Add HTTP header to only fetch when newer than this, otherwise return true instead of data
 * @param $p['data']         POST data array with key-value pairs
 * @param $p['files']        [fieldname => filename] of files to upload
 * @param $p['method']       different HTTP method
*/

function request_curl($p=array())
{
	$url = $this;
	if ($p['url'])
		$this->it_url($p['url']);

	$url->headers = array();
	$p['headers'] = (array)$p['headers'] + self::_default_headers($url, $p);
	$opts = array(CURLOPT_FOLLOWLOCATION => false, CURLOPT_HEADER => 1) + self::curl_opts($p);

	$curl = curl_init($url->rawurl);
	curl_setopt_array($curl, $opts);

	$got = curl_exec($curl);

	EDC('curlinfo', curl_getinfo($curl));

	if ($got) {
		list($url->header, $url->data) = explode("\r\n\r\n", $got, 2);
		while (preg_match('#^(HTTP\S+)\s100\sContinue$#', $url->header))
			list($url->header, $url->data) = explode("\r\n\r\n", $url->data, 2);
		$url->header .= "\r\n\r\n";

		$url->parse_http_header($url->header);

		if ($p['maxlength'] && (strlen($this->data) > $p['maxlength'])) {
			$result = $this->result = false;
			$errstr = $this->errstr = "maxlength reached";
		} else
			$result =& $url->data;
	} else {
		$result = $this->result = false;
		$errstr = $this->errstr = curl_error($curl);
	}

	if ($got === false && $p['safety'] == 1)
		it::error(array('title' => "problem getting $url->url with curl: " . curl_error($curl)) + (array)$p['it_error']);

	return $result;
}


/**
 * Get multiple URL in parallel with timeout. Needs to be called statically
 * @param $p parameter array with the following keys (same as it_url::get)
 * @param $p['urls']: array of urls to get
 * @param $p['timeout']: timeout per read in seconds, defaults to 5. (TODO: fractions allowed?)
 * @param $p['totaltimeout']: timeout for the whole function call
 * @param $p['headers']: optional array of HTTP headers to send
 * @return array of contents (or false for errors like timesou) of resulting page using same
 *         keys as the urls input array, considering redirects, excluding headers
 */
function get_multi($p=null)
{
	$p += array('retries' => 1);

	$url = new it_url;
	$p['headers'] = (array)$p['headers'] + array_diff_key(self::_default_headers($url, $p), ['Host' => null]);

	$opts = array(CURLOPT_FOLLOWLOCATION => true) + self::curl_opts($p);

	$mh = curl_multi_init();

	$urls = array();
	foreach ($p['urls'] as $key => $url)
		$urls[$key] = is_array($url) ? $url : array('url' => $url);

	foreach ($urls as $key => $url)
	{
		$handle = curl_init();
		curl_setopt($handle, CURLOPT_URL, it::replace([ '^//' => "http://" ], $url['url']));
		curl_setopt_array($handle, $opts);
		curl_multi_add_handle($mh, $handle);
		$keys[$handle] = $key;
		$handles[$key] = $handle;
	}

	$start = microtime(true);

	# curl_multi loop copied from example at http://php.net/manual/en/function.curl-multi-exec.php
	$active = null;
	do {
		$mrc = curl_multi_exec($mh, $active);
	} while ($mrc == CURLM_CALL_MULTI_PERFORM);

	$timeout = 0.001;	# Very short timeout to work around problem with first select call on cURL 7.25.0
	while (!$abort && $active && $mrc == CURLM_OK)
	{
		if (curl_multi_select($mh, $timeout) == -1)
			usleep($timeout * 1000000);
		do {
			$mrc = curl_multi_exec($mh, $active);

			while (($info = curl_multi_info_read($mh)) !== false)
			{
				if ($info['msg'] == CURLMSG_DONE)
				{
					$key = $keys[$info['handle']];
					EDC('reqtimings', $key, $info['result'], (microtime(true) - $start) * 1000);
					if ($info['result'] == CURLE_OK)
						$results_unordered[$key] = curl_multi_getcontent($info['handle']);
					else
						$results_unordered[$key] = false;
					if (($handler = $urls[$keys[$info['handle']]]['handler']))
						$abort = $handler($info['result'], $results_unordered[$key]);
				}
			}
		} while ($mrc == CURLM_CALL_MULTI_PERFORM);
		$timeout = 0.1;	# Longer delay to avoid busy loop but shorter than default of 1s in case we stil hit cURL 7.25.0 problem
	}

	$results = array();
	foreach ($handles as $key => $handle) {
		curl_multi_remove_handle($mh, $handle);
		curl_close($handle);
		$results[$key] = $results_unordered[$key];
	}
	curl_multi_close($mh);
	return $results;
}

/**
 * Construct a local directory name to cache an URL. Named args:
 * @param $p['cachedir']    directory to store cache files in, defaults to $ULTRAHOME/var/urlcache
 * @param $p['id']          If you need more than one type of cache (e.g. different maxage) you can specify an id
 */
static function get_cache_dir($p)
{
	$p += array('cachedir' => $GLOBALS['ULTRAHOME'] . "/var/urlcache", 'id' => "default");
	return rtrim($p['cachedir'] . "/" . $p['id'], "/");
}


/**
 * Construct a local file name to cache an URL. Named args:
 * @param $p['url'] remote url to get
 * @param $p['cachedir']    directory to store cache files in, @see get_cache_dir
 * @param $p['data']        POST data array with key-value pairs
 * @param $p['id']          If you need more than one type of cache (e.g. different maxage) you can specify an id
 */
static function get_cache_filename($p)
{
	if (!is_array($p))
		$p = array('url'=>$p);

	$p['cachedir'] = it_url::get_cache_dir($p);
	$filename = md5(T_lang() . $p['url'] . ($p['headers'] ? serialize($p['headers']) : "") . ($p['data'] ? serialize($p['data']) : ""));

	return $p['cachedir'] . "/" . substr($filename, 0, 2) . "/$filename";
}


/**
 * Store contents of url in a file and return file name. Threadsafe: Provides locking. Called statically.
 * Requires webserver writeable directory in $p['cachdedir']. Params in associative array p:
 * @param $p['id']          RECOMMENDED: If you need more than one type of cache (e.g. different maxage) you should specify an id
 * @param $p['url']         url to get
 * @param $p['headers']     optional array of HTTP headers to send
 * @param $p['cachedir']    directory to store cache files in, @see get_cache_dir
 * @param $p['timeout']     timeout in seconds, default 10. fractions allowed
 * @param $p['maxage']      maximum age of cache entries in seconds, default 86400
 * @param $p['cleanbefore'] maximum daytime when attempting cleanup, default 7200
 * @param $p['preprocess']  callback function (or array for methods) to change received file or array('function' => ..., 'in' => $src, 'out' => $dst, ...) with callback function plus args
 * @param $p['safety']      value 0 means dont generate alert, value 1 means generate alerts on timeouts and failures
 * @param $p['keepfailed']  keep old versions of files if download fails (sending alerts conservatively)
 * @param $p['returnheaders'] Return array($path, $headers) instead of simply $path
 * @param $p['it_error']    parameters for it::error()
 * @return Cache filename or false if fetch failed
 */
function get_cache($p = array())
{
	$p += array('timeout' => 10, 'maxage' => 86400, 'cleanbefore' => 7200, 'safety' => 1, 'it_error' => array());
	$p['totaltimeout'] = $p['timeout'];
	$path = it_url::get_cache_filename($p);	# Must be before changing cachedir below
	$p['cachedir'] = it_url::get_cache_dir($p);

	@mkdir($p['cachedir']);
	@mkdir(dirname($path));

	if (!is_writable(dirname($path)))
		it::error(dirname($path) . " not writable");

	if ($filemtime = it_url::_expired($path, $p['maxage']))	# Outdated(non-zero int) or non-existant(true)?
	{
		$fileexists = $filemtime !== true;

		if ($lock = it_url::_lock($path))
		{
			# Touch existing file to prevent locking other getters while refreshing
			if ($fileexists)
				touch($path);

			EDC('getcache', "new", $filemtime, $p['url'], $path);
			$url = new it_url;
			if ($result = $url->get(array('safety' => 0) + $p + array('filemtime' => EDC('nocache') ? null : $filemtime)))	# => true means not modified (no new data fetched)
			{
				$newfile = it_url::_atomicwrite($path, $result);
				if ($p['returnheaders'])
					file_put_contents("$path.headers", '<?php return ' . var_export($url->headers, true) . ";\n");
			}
			else if ($p['keepfailed'])
				$result = $fileexists;
			else
				@unlink($path);	# Expired and failed to get

			it_url::_unlock($path, $lock);
		}
		else
		{
			# Wait for file currently being transferred
			EDC('getcache', "wait", $p['url'], $path);
			$result = it_url::_waitforlockedfile($path, $p);

			# If file could no be fetched by other thread but exists and we are in keepfailed mode then return old file
			if (!$result && $p['keepfailed'])
				$result = $fileexists;

		}
	}
	else
	{
		# Get file from cache
		EDC('getcache', "cached", $p['url'], $path);
		$result = true;	# Up to date
	}

	# Read headers before $path is modified for preprocessing
	if ($p['returnheaders'])
		$headers = @include("$path.headers");

	if ($result && $p['preprocess'])
	{
		$srcpath = $path;
		$path .= substr(md5(serialize($p['preprocess'])), 0, 2);

		if ($filemtime = $newfile ? true : it_url::_expired($path, $p['maxage']))	# Outdated(non-zero int) or non-existant(true)?
		{
			if ($lock = it_url::_lock($path))
			{
				# Touch existing file to prevent locking other getters while refreshing
				if ($filemtime !== true)
					touch($path);

				EDC('getcache', "processnew", $p['url'], $path);
				$dstpath = "$path.preprocesstmp";

				if (is_array($p['preprocess']) && $p['preprocess']['function'])	# Needs is_array as it can be a string where dereferencing gives first character!
					call_user_func($p['preprocess']['function'], array('in' => $srcpath, 'out' => $dstpath) + $p['preprocess']);
				else
					call_user_func($p['preprocess'], $srcpath, $dstpath);

				if (!($result = @filesize($dstpath) && @rename($dstpath, $path)))
				{
					@unlink($dstpath);
					if (!$p['keepfailed'])
						@unlink($path);
					$result = file_exists($path);
				}

				$cachemiss = 1;
				it_url::_unlock($path, $lock);
			}
			else
			{
				# Wait for file currently being processed
				EDC('getcache', "processwait", $p['url'], $path);
				$result = it_url::_waitforlockedfile($path, $p);
			}
		}
	}

	# cache cleanup at night
	if (date('H') >= 1 && (date('H')*3600 + date('i')*60 < $p['cleanbefore']) && (time()-@filemtime($p['cachedir'] . "/cleaned") > 80000))
	{
		touch($p['cachedir'] . "/cleaned");
		$maxagemin = intval($p['maxage']/60);
		exec("nohup bash -c 'cd {$p['cachedir']} && for i in ??; do sleep 20; ionice -c 3 find \$i -mmin +$maxagemin -delete; done' </dev/null >/dev/null 2>&1 &");
	}

	if (EDC('getcachelog'))
		it::log('debug', 'getcachelog', "miss=" . intval($cachemiss), $p['url']);

	### EDC('getcache', $result, $path); # too verbose
	return $result ? ($p['returnheaders'] ? array($path, $headers) : $path) : false;
}

/**
 * Fetch a file, cache it and return contents
 * @param see it_url::get_cache()
 */
function get_cache_contents($p)
{
	return ($fn = self::get_cache($p)) ? file_get_contents($fn) : ($p['safety'] === 0 ? null : it::error(array('title' => "failed getting " . it_url::absolute($p['url']), 'body' => var_export($p, true))));
}

/**
 * Check whether file at given path is older than maxage
 * @param $path File to check
 * @param $maxage Maximum age of file in seconds
 * @return Not expired: false | Non-existant file: true | Timestamp of expired file
 */
static function _expired($path, $maxage)
{
	if ($result = EDC('nocache') ? false : @filemtime($path))
	{
		if (time() - $result > $maxage)
			EDC('getcache', "expired", $maxage, $path);
		else
			$result = false;
	}
	else	# File does not exists yet
		$result = true;

	return $result;
}

/**
 * Acquire lock for a given file
 * @param $path File to lock
 * @return Lock handle if successfully locked file
 */
static function _lock($path)
{
	$force = EDC('nocache') || (($mtime = @filemtime("$path.lock")) && (time() - $mtime > 30)); # expire forgotten locks
	return @fopen("$path.lock", $force ? "w" : "x");
}

/**
 * Release lock on a file
 * @param $path File to unlock
 * @param $lock Handle to lock acquird by _lock
 */
static function _unlock($path, $lock)
{
	fclose($lock);
	@unlink("$path.lock");
}

/**
 * Wait for file which is currently locked
 * @param $path File to wait for
 * @param $p Wait parameters, see @get_cache
 * @return Whether lock was released within timeout and file is still there
 */
static function _waitforlockedfile($path, $p)
{
	$sleeptime = 0.1; # seconds to wait per pass

	# wait until cache is ready, then read from cache
	for ($maxpasses = $p['timeout'] / $sleeptime, $passes = 0; ($lockedbyother = file_exists("$path.lock")) && ($passes < $maxpasses); ++$passes)
	{
		usleep($sleeptime * 1000000);
		clearstatcache();
	}

	if ($lockedbyother && $p['safety'] == 1)
		it::error(($passes < $maxpasses ? "error getting url" : "timeout") . " in it_url::get_cache(): url={$p['url']}, passes=$passes, maxpasses=$maxpasses, path={$p['path']}");

	return !$lockedbyother && file_exists($path);
}

/**
 * Write data to tmp file and atomically rename it to destination
 * @param $path Destination file to write data to
 * @param $data Data to write | true to just touch file
 * @return True if data was written to file
 */
static function _atomicwrite($path, $data)
{
	$result = false;

	if ($data === true)	# Not modified, no new data, just update timestamp
		touch($path);
	else if ($data !== false)
	{
		$tmpname = tempnam(dirname($path), "writetmp");
		fputs($cachetmp = fopen($tmpname, "w"), $data);
		fclose($cachetmp);
		chmod($tmpname, 0664);
		$result = rename($tmpname, $path);
	}
	else
		@unlink($path);

	return $result;
}

/**
 * Make an URL absolute by using host and protocol from current Apache request (but not port number)
 * @param $url Optional URL ( foo.html, /foo.html, //host/bar.html, http://host/bar.html ), default self
 * @param $proto_force Optional protocol to enforce, default protocol of current request or http if in script context
 * @return absolute version of URL ( http[s]://host/bar.html )
 */
static function absolute($url = null, $proto_force = null)
{
	if (!isset($url))
		$url = $_SERVER['PHP_SELF'];

	if (list($proto_url, $urltmp) = it::match('^(\w+):(.*)$', $url))
	{
		$url = $urltmp;
		$proto = $proto_force ?: $proto_url;
	}
	else
		$proto = $proto_force ?: (isset($_SERVER['HTTPS']) ? 'https' : 'http');

	if (!preg_match('#^//#', $url))
	{
		$dir = preg_replace('#/[^/]*$#', '/', $_SERVER['PHP_SELF']);
		$url = preg_match('#^/#', $url) ? $url : "$dir$url";
		$url = "//" . $_SERVER['HTTP_HOST'] . $url;
	}

	return "$proto:$url";
}

/**
 * Craft a valid redirect URL, send Location: header and terminate execution
 * @param $url  Optional URL ( foo.html, /foo.html, //host/bar.html, http://host/bar.html ), default self
 * @param $type Type of redirect, "temporary" or "permanent", default temporary
 * @return This method never returns.
 */
function redirect($url = null, $type = "temporary")
{
	$codes = array('permanent' => 301, 'temporary' => 303);	# NOTE: HTTP 303 is called "See Other", rather than Temporary (which would be HTTP 307), but is the behaviour one usually wants for temporary redirects
	if (!($code = $codes[$type]) || !$url)
		it::fatal("invalid redirect type or missing redirect url");

	$url = preg_replace("/[\r\n].*/", '', it_url::absolute($url));	# Security: cut after CR/LF

	if (EDC('noredir')) {
		if (!function_exists('a'))
			new it_html();
		echo a(array('href' => $url), Q($url)) . Q(" (HTTP/1.1 $code, $type redirect)") . br() . Q("Trace: " . it_debug::backtrace());
	}
	else
		header('Location: ' . it_untaint($url, TC_SELF), true, $code);
	exit;
}

/**
 * Urlencode but leave some chars
 */
static function encode($str)
{
	return strtr(urlencode($str), array("%2C"=>",", "%28"=>"(", "%29"=>")"));
}

/**
 * Create GET request from params, optionally only using given fields
 * @param $params Array to take values from, usually $_GET. Values of zero length are ignored.
 * @param $keys Keys to use; default: all
 */
static function params($params, $keys = null)
{
	return join("&", it_url::_params($params, $keys));
}

static function _params($params, $keys = null)
{
	$result = array();

	if (!isset($keys))
		$keys = array_keys($params);

	foreach ($keys as $key)
	{
		if (is_array($params[$key]))
		{
			foreach (it_url::_params($params[$key]) as $value)
			{
				if (strlen($value))
					$result[] = it::replace(array('^([^=\[]*)' => $key . '[$1]'), $value);
			}
		}
		else if (strlen($params[$key]))
			$result[] = urlencode($key) . "=" . it_url::encode($params[$key]);
	}

	return $result;
}

/**
 * Convert url into array with base url in $result[0] and GET params
 */
static function parse($url)
{
	list($path, $query) = explode("?", $url, 2);
	parse_str((string)$query, $params);
	return (array)$path + (array)$params;
}

}

?>