fix pdf export cache directory (#650)

src/Utils/MPdfConverter.php

@@ -0,0 +1,41 @@
+<?php
+
+/*
+ * This file is part of the Kimai time-tracking app.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace App\Utils;
+
+use App\Constants;
+use Mpdf\Mpdf;
+use Mpdf\Output\Destination;
+
+class MPdfConverter implements HtmlToPdfConverter
+{
+    /**
+     * @var string
+     */
+    private $cacheDirectory;
+
+    public function __construct(string $cacheDirectory)
+    {
+        $this->cacheDirectory = $cacheDirectory;
+    }
+
+    /**
+     * @param string $html
+     * @return mixed|string
+     * @throws \Mpdf\MpdfException
+     */
+    public function convertToPdf(string $html)
+    {
+        $mpdf = new Mpdf([['tempDir' => $this->cacheDirectory]]);
+        $mpdf->creator = Constants::SOFTWARE;
+        $mpdf->WriteHTML($html);
+
+        return $mpdf->Output('', Destination::STRING_RETURN);
+    }
+}