handle followers

app/lib/activity_log_audience_helper.rb

@@ -19,7 +19,9 @@ class ActivityLogAudienceHelper
       if match = activity_log_event.path.match(Regexp.new("https://#{domain}/users/([^/]*)/inbox"))
         return [match.captures[0]]
       elsif activity_log_event.path == "https://#{domain}/inbox"
-        return ['to', 'bto', 'cc', 'bcc'].map { |target| actors(activity_log_event.data[target]) }.flatten
+        return ['to', 'bto', 'cc', 'bcc']
+          .map { |target| actors(activity_log_event.data[target]) }
+          .flatten
       end
 
       return []
@@ -41,10 +43,17 @@ class ActivityLogAudienceHelper
       string_or_array.map do |string|
         if match = string.match(Regexp.new("https://#{domain}/users/([^/]*)"))
           match.captures[0]
+        elsif string.ends_with?("/followers")
+          Account
+            .joins(
+              "JOIN follows ON follows.account_id = accounts.id
+                JOIN accounts AS followed ON follows.target_account_id = followed.id
+                WHERE followed.followers_url = '#{string}'")
+            .map { |account| account.username }
         else
           nil
         end
-      end.compact
+      end.flatten.compact
     end
   end
 end

spec/fixtures/activity_log_events/inbound-with-follower-recipients.json

@@ -0,0 +1,25 @@
+{
+  "timestamp":"2022-12-08T17:12:38Z",
+  "type": "inbound",
+  "path": "https://example.com/inbox",
+  "data": {
+    "@context": "https://www.w3.org/ns/activitystreams",
+    "actor": "https://other.org/users/bob/",
+    "id": "https://other.org/users/bob/statuses/109473290785654613/activity",
+    "object": {
+      "attributedTo": "https://other.org/users/bob/",
+      "content": "A post to selected audiences",
+      "id": "https://other.org/users/bob/statuses/109473290785654613",
+      "to": [
+        "https://www.w3.org/ns/activitystreams#Public",
+        "https://other.org/users/bob/followers"
+      ],
+      "type": "Note"
+    },
+    "to": [
+      "https://www.w3.org/ns/activitystreams#Public",
+      "https://other.org/users/bob/followers"
+    ],
+    "type": "Create"
+  }
+}

spec/lib/activity_log_audience_helper_spec.rb

@@ -59,6 +59,20 @@ RSpec.describe ActivityLogAudienceHelper do
           'one-bcc'
         ])
       end
+
+      it 'returns followers from to, bto, cc, bcc if sent to public inbox' do
+        Rails.configuration.x.web_domain = 'example.com'
+        inbound_event = activity_log_event_fixture('inbound-with-follower-recipients.json')
+
+        bob = Fabricate(:account, username: 'bob', followers_url: 'https://other.org/users/bob/followers')
+        Fabricate(:account, username: 'first_follower').follow!(bob)
+        Fabricate(:account, username: 'second_follower').follow!(bob)
+
+        expect(ActivityLogAudienceHelper.audience(inbound_event)).to match_array([
+          'first_follower',
+          'second_follower',
+        ])
+      end
     end
   end
 end