From 94cf3abd97350d5aa857722827157e4a9515d9a2 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Tim=20D=C3=BCsterhus?= <duesterhus@woltlab.com>
Date: Mon, 8 Sep 2014 17:53:32 +0200
Subject: [PATCH] Add AtomicWriter.class.php

---
 .../lib/system/io/AtomicWriter.class.php      | 119 ++++++++++++++++++
 1 file changed, 119 insertions(+)
 create mode 100644 wcfsetup/install/files/lib/system/io/AtomicWriter.class.php

diff --git a/wcfsetup/install/files/lib/system/io/AtomicWriter.class.php b/wcfsetup/install/files/lib/system/io/AtomicWriter.class.php
new file mode 100644
index 0000000000..9fecdac719
--- /dev/null
+++ b/wcfsetup/install/files/lib/system/io/AtomicWriter.class.php
@@ -0,0 +1,119 @@
+<?php
+namespace wcf\system\io;
+use wcf\system\exception\SystemException;
+use wcf\util\FileUtil;
+
+/**
+ * AtomicWriter performs an atomic write operation to the given file.
+ * Nothing is written to the actual file, until you explicitly call 'flush',
+ * simply closing the file will discard any written data.
+ * 
+ * Only a single 'flush' is supported, the AtomicWriter will be unusable after
+ * the data was flushed.
+ * 
+ * Note: The AtomicWriter only supports a small number of whitelisted (write) operations.
+ *
+ * @author	Tim Duesterhus
+ * @copyright	2001-2014 WoltLab GmbH
+ * @license	GNU Lesser General Public License <http://opensource.org/licenses/lgpl-license.php>
+ * @package	com.woltlab.wcf
+ * @subpackage	system.io
+ * @category	Community Framework
+ */
+class AtomicWriter extends File {
+	/**
+	 * The file the data should be flushed into.
+	 * @var	string
+	 */
+	protected $targetFilename = '';
+	
+	/**
+	 * AtomicWriter will be unusable, once this flag is true.
+	 * @var	boolean
+	 */
+	protected $isFlushed = false;
+	
+	/**
+	 * Opens a new file. The file is always opened in binary mode.
+	 * 
+	 * @param	string		$filename
+	 */
+	public function __construct($filename) {
+		$this->targetFilename = $filename;
+		
+		$i = 0;
+		while (true) {
+			try {
+				parent::__construct(FileUtil::getTemporaryFilename('atomic_'), 'xb');
+				break;
+			}
+			catch (SystemException $e) {
+				// allow at most 5 failures
+				if (++$i == 5) {
+					throw $e;
+				}
+			}
+		}
+		
+		if (!flock($this->resource, LOCK_EX)) throw new SystemException('Could not get lock on temporary file');
+	}
+	
+	/**
+	 * @see	\wcf\system\io\AtomicWriter::close()
+	 */
+	public function __destruct() {
+		$this->close();
+	}
+	
+	/**
+	 * Closes the file, while discarding any written data, noop if the
+	 * file is already closed or flushed.
+	 */
+	public function close() {
+		if (!$this->isFlushed) {
+			$this->isFlushed = true;
+			
+			flock($this->resource, LOCK_UN);
+			fclose($this->resource);
+			@unlink($this->filename);
+		}
+	}
+	
+	/**
+	 * Persists the written data into the target file. The flush is atomic
+	 * if the underlying storage supports an atomic rename.
+	 */
+	public function flush() {
+		$this->isFlushed = true;
+		
+		fflush($this->resource);
+		flock($this->resource, LOCK_UN);
+		fclose($this->resource);
+		
+		rename($this->filename, $this->targetFilename);
+	}
+	
+	/**
+	 * @see	\wcf\system\io\File::__call($function, $arguments)
+	 */
+	public function __call($function, $arguments) {
+		if ($this->isFlushed) {
+			throw new SystemException('AtomicWriter for '.$this->targetFilename.' was already flushed.');
+		}
+		
+		switch ($function) {
+			case 'write':
+			case 'puts':
+			case 'seek':
+			case 'tell':
+			case 'rewind':
+			case 'truncate':
+				// these are fine
+			break;
+			default:
+				throw new SystemException("AtomicWriter does not allow '".$function."'");
+		}
+		
+		return parent::__call($function, $arguments);
+	}
+}
-- 
2.20.1