From ef87bb0719579d55a692992e1843f20e57f209d6 Mon Sep 17 00:00:00 2001
From: Owen Jacobson <owen@grimoire.ca>
Date: Mon, 21 Apr 2025 22:00:09 -0400
Subject: Add the following attributes to all markdown-generated links:

* `target="_blank"`: when Pilcrow is running in a browser, clicking a link should not replace Pilcrow with the target of the link. Pilcrow is "app-like" enough that opening links in a new tab _by default_, without user intervention, is likely more appropriate.

* `rel="noreferrer"`, which (A) stops most UAs from setting a referrer header when following those links, and (B) also implies `noopener`, preventing the link target from using `window.opener` from reaching back into Pilcrow's DOM.

I briefly experimented with DOMPurify's `RETURN_DOM_FRAGMENT` mode, which would have made the tests somewhat easier to write, but I wasn't able to find a good way to integrate the returned `DocumentFragment` objects with Svelte components, so HTML-as-strings it is. Sigh.
---
 ui/lib/markdown.js | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

(limited to 'ui/lib/markdown.js')

diff --git a/ui/lib/markdown.js b/ui/lib/markdown.js
index 2e73309..c4f2803 100644
--- a/ui/lib/markdown.js
+++ b/ui/lib/markdown.js
@@ -1,6 +1,26 @@
 import { marked } from 'marked';
 import DOMPurify from 'dompurify';
 
+const extension = {
+  useNewRenderer: true,
+  renderer: {
+    link({ title, href, tokens }) {
+      const titleAttr = title ? ` title="${title}"` : ``;
+      const text = this.parser.parseInline(tokens);
+      return `<a 
+        target="_blank"
+        rel="noreferrer"
+        ${titleAttr}
+        href="${href}">${text}</a>`;
+    }
+  }
+};
+
+marked.use(extension);
+
 export function render(body) {
-  return DOMPurify.sanitize(marked.parse(body, { breaks: true }));
+  const rendered = marked.parse(body, { breaks: true });
+  return DOMPurify.sanitize(rendered, {
+    ADD_ATTR: ['target']
+  });
 }
-- 
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