From b701dfbf57f433c99eff1a30acc2d2c395fee8e7 Mon Sep 17 00:00:00 2001
From: Ryan Barrett <git@ryanb.org>
Date: Wed, 21 Dec 2022 14:49:22 -0800
Subject: [PATCH] unfollow via 410, in progress

---
 tests/test_webmention.py | 32 ++++++++++++++++++++++++++++
 webmention.py            | 45 +++++++++++++++++++++++++++++++++++++---
 2 files changed, 74 insertions(+), 3 deletions(-)

diff --git a/tests/test_webmention.py b/tests/test_webmention.py
index 9cf4e85..34988d7 100644
--- a/tests/test_webmention.py
+++ b/tests/test_webmention.py
@@ -888,6 +888,38 @@ class WebmentionTest(testutil.TestCase):
         self.assert_equals('a', followers[0].src)
         self.assert_equals('https://foo.com/about-me', followers[0].dest)
 
+    def test_activitypub_unfollow(self, mock_get, mock_post):
+        Activity.get_or_create('http://a/follow', 'https://foo.com/about-me',
+                               status='complete')
+        Follower.get_or_create('https://foo.com/about-me', 'a')
+
+        self.follow.status_code = 410
+        mock_get.side_effect = [self.follow, self.actor]
+        mock_post.return_value = requests_response('abc xyz')
+
+        got = self.client.post('/webmention', data={
+            'source': 'http://a/follow',
+            'target': 'https://fed.brid.gy/',
+        })
+        self.assertEqual(200, got.status_code)
+
+        args, kwargs = mock_post.call_args
+        self.assert_equals(('https://foo.com/inbox',), args)
+        self.assert_equals({
+            '@context': 'https://www.w3.org/ns/activitystreams',
+            'type': 'Undo',
+            'object': self.follow_as2,
+        }, json_loads(kwargs['data']))
+
+        activity = Activity.get_by_id('http://a/follow#deleted http://followee/')
+        self.assertEqual(['a'], activity.domain)
+        self.assertEqual('out', activity.direction)
+        self.assertEqual('activitypub', activity.protocol)
+        self.assertEqual('complete', activity.status)
+        self.assertIsNone(activity.source_mf2)
+
+        self.assertEqual(0, Follower.query().count())
+
     def test_activitypub_error_fragment_missing(self, mock_get, mock_post):
         mock_get.side_effect = [self.follow_fragment]
 
diff --git a/webmention.py b/webmention.py
index 25efe7d..f6c1fcf 100644
--- a/webmention.py
+++ b/webmention.py
@@ -50,13 +50,24 @@ class Webmention(View):
 
         # fetch source page
         source = flask_util.get_required_param('source')
-        logger.info(f'webmention from {util.domain_from_link(source, minimize=False)}')
+        self.source_domain = util.domain_from_link(source, minimize=False)
+        logger.info(f'webmention from {self.source_domain}')
         try:
-            source_resp = util.requests_get(source, gateway=True)
+            source_resp = util.requests_get(source)
+            source_resp.raise_for_status()
         except ValueError as e:
             error(f'Bad source URL: {source}: {e}')
+        except BaseException as e:
+            status, body = util.interpret_http_exception(e)
+            if status == '410':
+                if self.try_activitypub_unfollow(source_resp.url or source):
+                    return 'OK'
+                else:
+                    error(f"410 HTTP response is only supported for unfollow; couldn't find a matching follow post to unfollow")
+            else:
+                error(f'Could not fetch source URL {source}: {e}', status=502)
+
         self.source_url = source_resp.url or source
-        self.source_domain = urllib.parse.urlparse(self.source_url).netloc.split(':')[0]
         fragment = urllib.parse.urlparse(self.source_url).fragment
         self.source_mf2 = util.parse_mf2(source_resp, id=fragment)
 
@@ -129,6 +140,7 @@ class Webmention(View):
                                 items[0].get('properties')
                             ).get('content')
 
+
                     orig_content = content(json_loads(activity.source_mf2))
                     new_content = content(self.source_mf2)
                     if orig_content and new_content and orig_content == new_content:
@@ -166,6 +178,33 @@ class Webmention(View):
         else:
             return str(error)
 
+    def try_activitypub_unfollow(self, follow_url):
+        """Attempts ActivityPub Undo Follow.
+
+        Args:
+          follow_url: str
+
+        Returns: boolean, whether we successfully unfollowed
+        """
+        logging.info(f'Attempting to undo follow {follow_url}')
+        for activity in Activity.query().filter(
+                Activity.key > Key('Response', follow_url + ' '),
+                Activity.key < Key('Response', follow_url + chr(ord(' ') + 1))):
+            if activity.status == 'complete':
+                logging.info(f'Found follow activity {activity.key}')
+                follower = Follower.get_by_id(
+                    Follower._id(activity.target(), self.source_domain))
+                if follower:
+                    logging.info(f'Deactivating existing Follower {follower.key}')
+                    follower.status = 'inactive'
+                    follower.put()
+                    STATE: construct Activity here, send AP Undo
+                    {
+                        '@context': 'https://www.w3.org/ns/activitystreams',
+                        'type': 'Undo',
+                    })
+                    return True
+
     def _activitypub_targets(self):
         """
         Returns: list of (Activity, string inbox URL)