mastodon: prefer media_attachments.remote_url when available

...since it may be more long-lived than `url` for remote statuses. fixes snarfed/bridgy#1675

README.md

@@ -346,6 +346,7 @@ Changelog
 * `mastodon`:
   * `get_activities` bug fix: use query params for `/api/v1/notifications` API call, not JSON body.
   * Convert HTTP 200 responses with `error` JSON field (eg from Sharkey) to 400/401 exceptions.
+  * Prefer `media_attachments.remote_url` when available since it may be more long-lived than `url` for remote statuses ([bridgy#1675](https://github.com/snarfed/bridgy/issues/1675)).
 * `microformats2`:
   * `object_to_json` bug fix: handle singular `inReplyTo`.
 * `nostr:`

granary/mastodon.py

@@ -375,7 +375,7 @@ def status_to_object(self, status):
         'objectType': MEDIA_TYPES.get(type),
         'displayName': desc,
       }
-      url = media.get('url')
+      url = media.get('remote_url') or media.get('url')
       if type == 'image':
         att['image'] = {
           'url': url,

granary/tests/test_mastodon.py

@@ -203,8 +203,9 @@ def tag_uri(name):
 }, {
   'id': '444',
   'type': 'gifv',
-  'url': 'http://foo.com/video.mp4',
+  'url': 'http://use/remote/url/instead',
   'preview_url': 'http://foo.com/poster.png',
+  'remote_url': 'http://foo.com/video.mp4',
   'description': 'a fun video',
   'meta': {
      'width': 640,