iss1171 - Add validation of metadata for length and broken JSON.

Author: EJMFarrow

lang/en/qtype_stack.php

@@ -440,6 +440,8 @@
 $string['makemecreator'] = 'Make me the creator';
 $string['validateandclose'] = 'Validate and close';
 $string['JSONmetadata'] = 'JSON metadata';
+$string['JSONtoolong'] = 'There is too much metadata. Metadata should be under 32000 bytes.';
+$string['JSONbroken'] = 'Metadata is invalid JSON.';
 $string['metadataexplanation'] = 'STACK metadata is stored as a JSON object. You can edit metadata in the inputs above or directly edit the JSON below and then click \'Update inputs from JSON\'. On closing this metadata window, the inputs will be validated and, if this is successful you will be returned to the main question edit form. You will still need to save the question as normal to save the metadata.';
 $string['scope'] = 'Scope';
 $string['property'] = 'Property';

questiontype.php

@@ -2412,6 +2412,14 @@ public function validate_fromform($fromform, $errors, $question = null) {
             $fromform['questiondescription']['text']
         );
 
+        $errors['metadata_text'] = [];
+        if (mb_strlen($fromform['metadata']) > 32000) {
+            $errors['metadata_text'][] = stack_string('JSONtoolong');
+        }
+        if ($fromform['metadata'] && !json_decode($fromform['metadata'])) {
+            $errors['metadata_text'][] = stack_string('JSONbroken');
+        }
+
         // 2) Validate all inputs.
         $stackinputfactory = new stack_input_factory();
         foreach ($inputs as $inputname => $counts) {