Allow html tags for survey solutions, add sanitizer

Resolves MS-500

client/src/components/content-blocks/Solution.vue

@@ -25,7 +25,7 @@
 </template>
 
 <script>
-  import {sanitize} from '@/helpers/text';
+  import {sanitizeAsHtml} from '@/helpers/text';
 
   export default {
     props: ['value'],
@@ -38,8 +38,8 @@
 
     computed: {
       sanitizedText() {
-        return sanitize(this.value.text);
-      }
+        return sanitizeAsHtml(this.value.text);
+      },
     },
 
     methods: {
@@ -81,6 +81,7 @@
 
       /deep/ ul {
         padding-left: $medium-spacing;
+
         > li {
           list-style: disc outside none;
           color: $color-silver-dark;

client/src/helpers/text.js

@@ -1,8 +1,52 @@
+// taken from https://gomakethings.com/how-to-sanitize-html-strings-with-vanilla-js-to-reduce-your-risk-of-xss-attacks/
+const getDocument = html => new DOMParser().parseFromString(html, 'text/html');
+
+const removeScripts = html => {
+  let scripts = html.querySelectorAll('script');
+  for (let script of scripts) {
+    script.remove();
+  }
+};
+
+// explicitly whitelist
+// todo: do we need more attributes whitelisted
+const isSafe = attr => {
+  return ['class'].includes(attr.name);
+};
+
+const removeAttributes = node => {
+  let attributes = [...node.attributes];
+  console.log(attributes);
+  for (const attr of attributes) {
+    if (isSafe(attr)) {
+      continue;
+    }
+    node.removeAttribute(attr.name);
+  }
+};
+
+const clean = node => {
+  let nodes = node.children;
+  for (let node of nodes) {
+    removeAttributes(node);
+    clean(node);
+  }
+};
+
 export const sanitize = html => {
-  let doc = new DOMParser().parseFromString(html, 'text/html');
+  let doc = getDocument(html);
   return doc.body.textContent || '';
 };
 
+export const sanitizeAsHtml = html => {
+  let doc = getDocument(html);
+  const body = doc.body || document.createElement('body');
+  removeScripts(body);
+  clean(body);
+  return body.innerHTML;
+};
+
+
 export const newLineToParagraph = (text) => {
   return text
     .split(/\n+/)