From 0ce1010d26e4c22cda2f3576ea45e3564119d004 Mon Sep 17 00:00:00 2001
From: Christian Schneider
Date: Fri, 31 Jul 2009 17:12:13 +0000
Subject: New version of get_cache (using If-Not-Modified-Since support in get)

---
 it_url.class | 212 ++++++++++++++++++++++++++++++++++++-----------------------
 1 file changed, 129 insertions(+), 83 deletions(-)

diff --git a/it_url.class b/it_url.class
index 063aed0..7035291 100644
--- a/it_url.class
+++ b/it_url.class
@@ -225,6 +225,7 @@ function is_reachable($timeout = 5)
  * @param $p['url']: url to get, defaults to constructor URL
  * @param $p['timeout']: timeout per read in seconds, defaults to 5. fractions allowed
  * @param $p['totaltimeout']: timeout for the whole function call
+ * @param $p['filemtime']: Add HTTP header to only fetch when newer than this, otherwise return true instead of data
  * @param $p['data']: POST data array with key-value pairs
  * @return contents of resulting page, considering redirects, excluding headers, or false on error
  */
@@ -260,6 +261,9 @@ function get($p=null, $timeout=5)
 				'Accept-Language' => T_lang(),
 			);
 
+			if (is_int($p['filemtime']))
+				$p['headers']['If-Modified-Since'] = date("r", $p['filemtime']);
+
 			if ($datalen = strlen($data))
 			{
 				$method = "POST";
@@ -297,7 +301,7 @@ function get($p=null, $timeout=5)
 
 			if ($url->result)
 			{
-				if ($url->headers['Transfer-Encoding'] == "chunked")	# Bogus HTTP/1.1 chunked answer from server (e.g. Wordpress/Apach2/PHP5)
+				if ($url->headers['Transfer-Encoding'] == "chunked")	# Bogus HTTP/1.1 chunked answer from server (e.g. Wordpress/Apache2/PHP5)
 				{
 					while ($len = hexdec(fgets($fp)))
 					{
@@ -315,7 +319,9 @@ function get($p=null, $timeout=5)
 						$url->data .= @fread($fp, 20480);
 				}
 
-				if ($url->result < 400)
+				if ($p['filemtime'] && ($url->result == 304))
+					$result = true;	# Not modified, success but no data
+				else if ($url->result < 400)
 					$result =& $url->data;
 			}
 
@@ -375,93 +381,83 @@ 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
+	$path = it_url::get_cache_filename($p);	# Must be before changing cachedir below
 	$p['cachedir'] = it_url::get_cache_dir($p);
 
 	@mkdir($p['cachedir']);
 	@mkdir(dirname($path));
-	$age = file_exists($path) ? (time() - @filemtime($path)) : 0;
-
-	# expire forgotten locks
-	$lockmtime = @filemtime("$path.lock");
-	if ($lockmtime && time()-$lockmtime > 30)
-		@unlink("$path.lock");
 
-	if ($p['keepfailed'] && ($age>$p['maxage']) && ($dummy = @fopen("$path.lock", EDC('nocache') ? "w" : "x"))) # update our copy if we get the lock
-	{ 
-		# my job to refresh the cache entry
-		fclose($dummy);
-
-		# Touch existing file to prevent locking other getters
-		touch($path);
+	if ($filemtime = 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', "refresh", $p['url'], $path);
-		if (($result = it_url::get($p)))
-			it_url::_atomicwrite($path, $result);
-		else 
-			touch($path);
+			EDC('getcache', "new", $filemtime, $p['url'], $path);
+			if ($result = it_url::get($p + array('filemtime' => EDC('nocache') ? null : $filemtime)))	# => true means not modified (no new data fetched)
+				$newfile = it_url::_atomicwrite($path, $result);
+			else if (!$p['keepfailed'])
+				@unlink($path);	# Expired and failed to get
 
-		if ($p['safety'] == 1 && !$result)
+			it_url::_unlock($path, $lock);
+		}
+		else
 		{
-			$parts = @parse_url($p['url']);
-			it::error($p['it_error'] + array('title'=>"get_cache: download failures on {$p['url']}", 'id'=>$parts['host'])); # send err only if multi failure
+			# Wait for file currently being transferred
+			EDC('getcache', "wait", $p['url'], $path);
+			$result = it_url::_waitforlock($path, $p);
 		}
-		@unlink("$path.lock");
-	}
-
-	# Remove ancient lock or cached file if it is too old
-	if (!$p['keepfailed'])
-		it_url::_expire($path, $p['maxage']);
-
-	if ($dummy = @fopen($path, EDC('nocache') ? "w" : "x")) # succeeds if file is missing (or we are in nocache mode)
-	{
-		# fill cache myself
-		fclose($dummy);
-		EDC('getcache', "new", $p['url'], $path);
-		$result = it_url::_atomicwrite($path, it_url::get($p));
 	}
 	else
 	{
-		# get file from cache, potentially waiting if file is currently being transferred
-		EDC('getcache', "old", $p['url'], $path);
-		$result = it_url::_waitforpath($p + array('path' => $path));
+		# Get file from cache
+		EDC('getcache', "cached", $p['url'], $path);
+		$result = true;	# Up to date
 	}
 
 	if ($result && $p['preprocess'])
 	{
 		$srcpath = $path;
 		$path .= substr(md5(serialize($p['preprocess'])), 0, 2);
-		it_url::_expire($path, $p['maxage']);
 
-		if ($dummy = @fopen($path, EDC('nocache') ? "w" : "x")) # in nocache mode, always succeed
+		if ($filemtime = $newfile ? true : it_url::_expired($path, $p['maxage']))	# Outdated(non-zero int) or non-existant(true)?
 		{
-			fclose($dummy);
-			EDC('getcache', "process", $p['url'], $path);
-			$dstpath = "$path.preprocesstmp";
+			if ($result === true && $filemtime !== true)	# Source not modified, destination exists => touch
+			{
+				EDC('getcache', "processtouch", $p['url'], $path);
+				touch($path);
+			}
+			else if ($lock = it_url::_lock($path))
+			{
+				# Touch existing file to prevent locking other getters while refreshing
+				if ($filemtime !== true)
+					touch($path);
 
-			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);
+				EDC('getcache', "processnew", $p['url'], $path);
+				$dstpath = "$path.preprocesstmp";
 
-			if (!@filesize($dstpath) || !@rename($dstpath, $path))
-			{
-				@unlink($dstpath);
-				@unlink($path);
-				$result = false;
+				if (is_array($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);
+					@unlink($path);
+				}
+
+				it_url::_unlock($path, $lock);
 			}
 			else
-				$result = $path;
-
-			if ($result)
 			{
-				EDC('getcache', "processold", $p['url'], $path);
-				touch($result, @filemtime($srcpath));	# Ensure processed is never newer than src
+				# Wait for file currently being processed
+				EDC('getcache', "processwait", $p['url'], $path);
+				$result = it_url::_waitforlock($path, $p);
 			}
 		}
-		else
-			$result = it_url::_waitforpath($p + array('path' => $path));
-
 	}
 
 	# cache cleanup at night
@@ -472,38 +468,98 @@ function get_cache($p = array())
 		exec("nohup bash -c 'cd {$p['cachedir']} && sleep 10 && find ?? -mmin +$maxagemin -print0 | xargs -0 -r rm' </dev/null >/dev/null 2>&1 &");
 	}
 
+	EDC('getcache', $result, $path);
+	return $result ? $path : false;
+}
+
+/**
+ * Check whether file at given path is older than maxage
+ * @param $path File to check
+ * @param $maxage Maximum age of file in seconds
+ * @return Not expired: false | Non-existant file: true | Timestamp of expired file
+ */
+function _expired($path, $maxage)
+{
+	if ($result = EDC('nocache') ? false : @filemtime($path))
+	{
+		if (time() - $result > $maxage)
+			EDC('getcache', "expired", $path);
+		else
+			$result = false;
+	}
+	else	# File does not exists yet
+		$result = true;
+
 	return $result;
 }
 
-function _waitforpath($p)
+/**
+ * Acquire lock for a given file
+ * @param $path File to lock
+ * @return Lock handle if successfully locked file
+ */
+function _lock($path)
+{
+	# expire forgotten locks
+	if (($mtime = @filemtime("$path.lock")) && (time() - $mtime > 30))
+		@unlink("$path.lock");
+
+	return @fopen("$path.lock", EDC('nocache') ? "w" : "x");
+}
+
+/**
+ * Release lock on a file
+ * @param $path File to unlock
+ * @param $lock Handle to lock acquird by _lock
+ */
+function _unlock($path, $lock)
+{
+	fclose($lock);
+	@unlink("$path.lock");
+}
+
+/**
+ * Wait for lock on a file to be released
+ * @param $path File to wait for lock
+ * @param $p Wait parameters, see @get_cache
+ * @return Whether lock was released within timeout
+ */
+function _waitforlock($path, $p)
 {
-	$p += array('sleeptime' => 0.1); # seconds to wait per pass
+	$sleeptime = 0.1; # seconds to wait per pass
 
 	# wait until cache is ready, then read from cache
-	for ($maxpasses = $p['timeout'] / $p['sleeptime'], $passes = 0; (($size = @filesize($p['path'])) === 0) && ($passes < $maxpasses); ++$passes)
+	for ($maxpasses = $p['timeout'] / $sleeptime, $passes = 0; ($result = file_exists("$path.lock")) && ($passes < $maxpasses); ++$passes)
 	{
-		usleep($p['sleeptime'] * 1000000);
+		usleep($sleeptime * 1000000);
 		clearstatcache();
 	}
 
-	if ($size)
-		$result = $p['path'];
-	else if ($p['safety'] == 1)
+	if ($result && $p['safety'] == 1)
 		it::error(($passes < $maxpasses ? "error getting url" : "timeout") . " in it_url::get_cache(): url={$p['url']}, passes=$passes, maxpasses=$maxpasses, path={$p['path']}");
 
-	return $result;
+	return !$result;
 }
 
+/**
+ * Write data to tmp file and atomically rename it to destination
+ * @param $path Destination file to write data to
+ * @param $data Data to write | true to just touch file
+ * @return True if data was written to file
+ */
 function _atomicwrite($path, $data)
 {
-	if ($data !== false)
+	$result = false;
+
+	if ($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($tmpname, 0664);
-		rename($tmpname, $path);
-		$result = $path;
+		$result = rename($tmpname, $path);
 	}
 	else
 		@unlink($path);
@@ -511,16 +567,6 @@ function _atomicwrite($path, $data)
 	return $result;
 }
 
-function _expire($path, $maxage)
-{
-	# Remove ancient lock or cached file if it is too old
-	if (file_exists($path) && (((@filesize($path) == 0) && (time() - @filemtime($path)) > 30) || (time() - @filemtime($path) > $maxage)))
-	{
-		EDC('getcache', "expire", $path);
-		@unlink($path);
-	}
-}
-
 /**
  * Make an URL absolute by using host an 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
-- 
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