MDL-33338 recognising the mimetype for uploaded files

- when file is uploaded in php, the tmpname does not have initial extension and mimetype recognition by extension fails
- another issue is that import form for questions fails with fatal error when it should just say that field is required

lib/filestorage/file_storage.php

@@ -1028,7 +1028,7 @@ public function create_file_from_pathname($filerecord, $pathname) {
 
         $newrecord->timecreated  = $filerecord->timecreated;
         $newrecord->timemodified = $filerecord->timemodified;
-        $newrecord->mimetype     = empty($filerecord->mimetype) ? $this->mimetype($pathname) : $filerecord->mimetype;
+        $newrecord->mimetype     = empty($filerecord->mimetype) ? $this->mimetype($pathname, $filerecord->filename) : $filerecord->mimetype;
         $newrecord->userid       = empty($filerecord->userid) ? null : $filerecord->userid;
         $newrecord->source       = empty($filerecord->source) ? null : $filerecord->source;
         $newrecord->author       = empty($filerecord->author) ? null : $filerecord->author;
@@ -1154,7 +1154,7 @@ public function create_file_from_string($filerecord, $content) {
         list($newrecord->contenthash, $newrecord->filesize, $newfile) = $this->add_string_to_pool($content);
         $filepathname = $this->path_from_hash($newrecord->contenthash) . '/' . $newrecord->contenthash;
         // get mimetype by magic bytes
-        $newrecord->mimetype = empty($filerecord->mimetype) ? $this->mimetype($filepathname) : $filerecord->mimetype;
+        $newrecord->mimetype = empty($filerecord->mimetype) ? $this->mimetype($filepathname, $filerecord->filename) : $filerecord->mimetype;
 
         $newrecord->pathnamehash = $this->get_pathname_hash($newrecord->contextid, $newrecord->component, $newrecord->filearea, $newrecord->itemid, $newrecord->filepath, $newrecord->filename);
 
@@ -1801,11 +1801,15 @@ public function import_external_file($storedfile) {
      * If file has a known extension, we return the mimetype based on extension.
      * Otherwise (when possible) we try to get the mimetype from file contents.
      *
-     * @param string $pathname
+     * @param string $pathname full path to the file
+     * @param string $filename correct file name with extension, if omitted will be taken from $path
      * @return string
      */
-    public static function mimetype($pathname) {
-        $type = mimeinfo('type', $pathname);
+    public static function mimetype($pathname, $filename = null) {
+        if (empty($filename)) {
+            $filename = $pathname;
+        }
+        $type = mimeinfo('type', $filename);
         if ($type === 'document/unknown' && class_exists('finfo') && file_exists($pathname)) {
             $finfo = new finfo(FILEINFO_MIME_TYPE);
             $type = mimeinfo_from_type('type', $finfo->file($pathname));

question/import_form.php

@@ -122,6 +122,11 @@ protected function validate_uploaded_file($data, $errors) {
             return $errors;
         }
 
+        if (empty($data['format'])) {
+            $errors['format'] = get_string('required');
+            return $errors;
+        }
+
         $formatfile = 'format/' . $data['format'] . '/format.php';
         if (!is_readable($formatfile)) {
             throw new moodle_exception('formatnotfound', 'question', '', $data['format']);