add stream wrapper to calculate hash on write

src/ReadHashWrapper.php

@@ -0,0 +1,40 @@
+<?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 ReadHashWrapper extends HashWrapper {
+	public function stream_read($count) {
+		$data = parent::stream_read($count);
+		$this->updateHash($data);
+		return $data;
+	}
+}