Added a simple hash wrapper

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>

src/HashWrapper.php

@@ -0,0 +1,93 @@
+<?php
+/**
+ * @copyright Copyright (c) 2019, Roeland Jago Douma <roeland@famdouma.nl>
+ *
+ * @author Roeland Jago Douma <roeland@famdouma.nl>
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program 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 Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+namespace Icewind\Streams;
+
+/**
+ * Wrapper that calculates the hash on the stream on read
+ *
+ * The stream and hash should be passed in when wrapping the stream.
+ * On close the callback will be called with the calculated checksum.
+ *
+ * For supported hashes see: http://php.net/manual/en/function.hash-algos.php
+ */
+class HashWrapper extends Wrapper {
+
+	/**
+	 * @var callable
+	 */
+	private $callback;
+
+	/**
+	 * @var resource
+	 */
+	private $hashContext;
+
+	/**
+	 * Wraps a stream to make it seekable
+	 *
+	 * @param resource $source
+	 * @param string $hash
+	 * @param callable $callback
+	 * @return resource
+	 *
+	 * @throws \BadMethodCallException
+	 */
+	public static function wrap($source, $hash, $callback) {
+		$context = stream_context_create(array(
+			'hash' => array(
+				'source' => $source,
+				'hash' => $hash,
+				'callback' => $callback,
+			)
+		));
+		return self::wrapSource($source, $context);
+	}
+
+	public function dir_opendir($path, $options) {
+		return false;
+	}
+
+	public function stream_open($path, $mode, $options, &$opened_path) {
+		$context = $this->loadContext('callback');
+		$this->callback = $context['callback'];
+		$this->hashContext = hash_init($context['hash']);
+		return true;
+	}
+
+	public function stream_read($count) {
+		$data = parent::stream_read($count);
+		if ($this->hashContext !== false) {
+			hash_update($this->hashContext, $data);
+		}
+		return $data;
+	}
+
+	public function stream_close() {
+		$hash = hash_final($this->hashContext);
+		if ($this->hashContext !== false && is_callable($this->callback)) {
+			call_user_func($this->callback, $hash);
+		}
+		return parent::stream_close();
+	}
+}