Add support for reversible suspensions through ActivityPub (#14989)

app/services/suspend_account_service.rb

@@ -1,10 +1,14 @@
 # frozen_string_literal: true
 
 class SuspendAccountService < BaseService
+  include Payloadable
+
   def call(account)
     @account = account
 
     suspend!
+    reject_remote_follows!
+    distribute_update_actor!
     unmerge_from_home_timelines!
     unmerge_from_list_timelines!
     privatize_media_attachments!
@@ -16,6 +20,31 @@ class SuspendAccountService < BaseService
     @account.suspend! unless @account.suspended?
   end
 
+  def reject_remote_follows!
+    return if @account.local? || !@account.activitypub?
+
+    # When suspending a remote account, the account obviously doesn't
+    # actually become suspended on its origin server, i.e. unlike a
+    # locally suspended account it continues to have access to its home
+    # feed and other content. To prevent it from being able to continue
+    # to access toots it would receive because it follows local accounts,
+    # we have to force it to unfollow them. Unfortunately, there is no
+    # counterpart to this operation, i.e. you can't then force a remote
+    # account to re-follow you, so this part is not reversible.
+
+    follows = Follow.where(account: @account).to_a
+
+    ActivityPub::DeliveryWorker.push_bulk(follows) do |follow|
+      [Oj.dump(serialize_payload(follow, ActivityPub::RejectFollowSerializer)), follow.target_account_id, @account.inbox_url]
+    end
+
+    follows.in_batches.destroy_all
+  end
+
+  def distribute_update_actor!
+    ActivityPub::UpdateDistributionWorker.perform_async(@account.id) if @account.local?
+  end
+
   def unmerge_from_home_timelines!
     @account.followers_for_local_distribution.find_each do |follower|
       FeedManager.instance.unmerge_from_home(@account, follower)