Fixed PHP warnings in upload.php

php/helper.php

@@ -0,0 +1,63 @@
+<?php
+/**
+ * helper.php, Kopano calender to ics im/exporter
+ *
+ * Author: Christoph Haas <christoph.h@sprinternet.at>
+ * Copyright (C) 2012-2016 Christoph Haas
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ */
+
+
+namespace calendarimporter;
+
+
+class Helper
+{
+    /**
+     * Generates a random string with variable length.
+     *
+     * @param $length the lenght of the generated string, defaults to 6
+     * @return string a random string
+     */
+    public static function randomstring($length = 6)
+    {
+        // $chars - all allowed charakters
+        $chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
+
+        srand((double)microtime() * 1000000);
+        $i = 0;
+        $pass = "";
+        while ($i < $length) {
+            $num = rand() % strlen($chars);
+            $tmp = substr($chars, $num, 1);
+            $pass = $pass . $tmp;
+            $i++;
+        }
+        return $pass;
+    }
+
+    /**
+     * respond/echo JSON
+     *
+     * @param $arr
+     * @return string JSON encoded string
+     */
+    public static function respondJSON($arr)
+    {
+        echo json_encode($arr);
+    }
+}