Limit the number of people that can be followed from one account (#8807)

Configurable soft limit of 7,500, and above that, configurable
ratio of 1.1 * followers, controlled by:

- MAX_FOLLOWS_THRESHOLD
- MAX_FOLLOWS_RATIO

Fix #2311

1 files changed, 27 insertions, 0 deletions

diff --git a/app/validators/follow_limit_validator.rb b/app/validators/follow_limit_validator.rb
new file mode 100644
index 000000000..eb083ed85
--- /dev/null
+++ b/app/validators/follow_limit_validator.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+class FollowLimitValidator < ActiveModel::Validator
+  LIMIT = ENV.fetch('MAX_FOLLOWS_THRESHOLD', 7_500).to_i
+  RATIO = ENV.fetch('MAX_FOLLOWS_RATIO', 1.1).to_f
+
+  def validate(follow)
+    return if follow.account.nil? || !follow.account.local?
+    follow.errors.add(:base, I18n.t('users.follow_limit_reached', limit: self.class.limit_for_account(follow.account))) if limit_reached?(follow.account)
+  end
+
+  class << self
+    def limit_for_account(account)
+      if account.following_count < LIMIT
+        LIMIT
+      else
+        account.followers_count * RATIO
+      end
+    end
+  end
+
+  private
+
+  def limit_reached?(account)
+    account.following_count >= self.class.limit_for_account(account)
+  end
+end