From a19b7fbe9efe56b8d9f45bba371c7383b751987f Mon Sep 17 00:00:00 2001
From: Alex Gleason <alex@alexgleason.me>
Date: Sat, 7 Sep 2024 13:07:47 -0500
Subject: [PATCH] Fetch link previews with facebookexternalhit instead of
 WhatsApp/2 by default, make it configurable

---
 src/config.ts       | 4 ++++
 src/utils/unfurl.ts | 6 +++++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/config.ts b/src/config.ts
index 0cb71509..7954e744 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -258,6 +258,10 @@ class Conf {
       'i',
     );
   }
+  /** User-Agent to use when fetching link previews. Pretend to be Facebook by default. */
+  static get fetchUserAgent(): string {
+    return Deno.env.get('DITTO_FETCH_USER_AGENT') ?? 'facebookexternalhit';
+  }
   /** Path to the custom policy module. Must be an absolute path, https:, npm:, or jsr: URI. */
   static get policy(): string {
     return Deno.env.get('DITTO_POLICY') || new URL('../data/policy.ts', import.meta.url).pathname;
diff --git a/src/utils/unfurl.ts b/src/utils/unfurl.ts
index a0ab1d7b..8123c423 100644
--- a/src/utils/unfurl.ts
+++ b/src/utils/unfurl.ts
@@ -3,6 +3,7 @@ import Debug from '@soapbox/stickynotes/debug';
 import DOMPurify from 'isomorphic-dompurify';
 import { unfurl } from 'unfurl.js';
 
+import { Conf } from '@/config.ts';
 import { PreviewCard } from '@/entities/PreviewCard.ts';
 import { Time } from '@/utils/time.ts';
 import { fetchWorker } from '@/workers/fetch.ts';
@@ -15,7 +16,10 @@ async function unfurlCard(url: string, signal: AbortSignal): Promise<PreviewCard
     const result = await unfurl(url, {
       fetch: (url) =>
         fetchWorker(url, {
-          headers: { 'User-Agent': 'WhatsApp/2' },
+          headers: {
+            'Accept': 'text/html, application/xhtml+xml',
+            'User-Agent': Conf.fetchUserAgent,
+          },
           signal,
         }),
     });