Add ActivityPub actor representing the entire server (mastodon#11321)

* Add support for an instance actor

* Skip username validation for local Application accounts

* Add migration script to create instance actor

* Make Codeclimate happy

* Switch to id -99 for instance actor

* Remove unused `icon` and `image` attributes from instance actor

* Use if/elsif/else instead of return + ternary operator

* Add instance actor to fresh installs

* Use instance actor as instance representative

Use instance actor for forwarding reports, relay operations, and spam
auto-reporting.

* Seed database in test environment

* Fix single-user mode

* Fix tests

* Fix specs to accomodate for an extra `Account`

* Auto-reject follows on instance actor

Following an instance actor might make sense, but we are not handling that
right now, so auto-reject.

* Fix webfinger lookup and serialization for instance actor

* Rename instance actor

* Make it clear in the HTML view that the instance actor should not be blocked

* Raise cache time for instance actor as there's no dynamic content

* Re-use /about/more with a flash message for instance actor profile

Author: ClearlyClaire

app/controllers/about_controller.rb

@@ -11,7 +11,9 @@ class AboutController < ApplicationController
 
   def show; end
 
-  def more; end
+  def more
+    flash.now[:notice] = I18n.t('about.instance_actor_flash') if params[:instance_actor]
+  end
 
   def terms; end
 

app/controllers/application_controller.rb

@@ -91,7 +91,7 @@ def not_acceptable
   end
 
   def single_user_mode?
-    @single_user_mode ||= Rails.configuration.x.single_user_mode && Account.exists?
+    @single_user_mode ||= Rails.configuration.x.single_user_mode && Account.where('id > 0').exists?
   end
 
   def use_seamless_external_login?

app/controllers/home_controller.rb

@@ -58,7 +58,7 @@ def default_redirect_path
     if request.path.start_with?('/web')
       new_user_session_path
     elsif single_user_mode?
-      short_account_path(Account.local.without_suspended.first)
+      short_account_path(Account.local.without_suspended.where('id > 0').first)
     else
       about_path
     end

app/controllers/instance_actors_controller.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+class InstanceActorsController < ApplicationController
+  include AccountControllerConcern
+
+  def show
+    expires_in 10.minutes, public: true
+    render json: @account, content_type: 'application/activity+json', serializer: ActivityPub::ActorSerializer, adapter: ActivityPub::Adapter, fields: restrict_fields_to
+  end
+
+  private
+
+  def set_account
+    @account = Account.find(-99)
+  end
+
+  def restrict_fields_to
+    %i(id type preferred_username inbox public_key endpoints url manually_approves_followers)
+  end
+end

app/javascript/styles/mastodon/containers.scss

@@ -145,6 +145,10 @@
     min-height: 100%;
   }
 
+  .flash-message {
+    margin-bottom: 10px;
+  }
+
   @media screen and (max-width: 738px) {
     grid-template-columns: minmax(0, 50%) minmax(0, 50%);
 

app/lib/activitypub/activity/follow.rb

@@ -8,7 +8,7 @@ def perform
 
     return if target_account.nil? || !target_account.local? || delete_arrived_first?(@json['id']) || @account.requested?(target_account)
 
-    if target_account.blocking?(@account) || target_account.domain_blocking?(@account.domain) || target_account.moved?
+    if target_account.blocking?(@account) || target_account.domain_blocking?(@account.domain) || target_account.moved? || target_account.instance_actor?
       reject_follow_request!(target_account)
       return
     end

app/lib/activitypub/tag_manager.rb

@@ -17,7 +17,7 @@ def url_for(target)
 
     case target.object_type
     when :person
-      short_account_url(target)
+      target.instance_actor? ? about_more_url(instance_actor: true) : short_account_url(target)
     when :note, :comment, :activity
       return activity_account_status_url(target.account, target) if target.reblog?
       short_account_status_url(target.account, target)
@@ -29,7 +29,7 @@ def uri_for(target)
 
     case target.object_type
     when :person
-      account_url(target)
+      target.instance_actor? ? instance_actor_url : account_url(target)
     when :note, :comment, :activity
       return activity_account_status_url(target.account, target) if target.reblog?
       account_status_url(target.account, target)
@@ -119,6 +119,7 @@ def local_uri?(uri)
 
   def uri_to_local_id(uri, param = :id)
     path_params = Rails.application.routes.recognize_path(uri)
+    path_params[:username] = Rails.configuration.x.local_domain if path_params[:controller] == 'instance_actors'
     path_params[param]
   end
 

app/lib/webfinger_resource.rb

@@ -23,11 +23,17 @@ def username
   def username_from_url
     if account_show_page?
       path_params[:username]
+    elsif instance_actor_page?
+      Rails.configuration.x.local_domain
     else
       raise ActiveRecord::RecordNotFound
     end
   end
 
+  def instance_actor_page?
+    path_params[:controller] == 'instance_actors'
+  end
+
   def account_show_page?
     path_params[:controller] == 'accounts' && path_params[:action] == 'show'
   end

app/models/account.rb

@@ -78,7 +78,7 @@ class Account < ApplicationRecord
   validates :username, format: { with: /\A#{USERNAME_RE}\z/i }, if: -> { !local? && will_save_change_to_username? }
 
   # Local user validations
-  validates :username, format: { with: /\A[a-z0-9_]+\z/i }, length: { maximum: 128 }, if: -> { local? && will_save_change_to_username? }
+  validates :username, format: { with: /\A[a-z0-9_]+\z/i }, length: { maximum: 128 }, if: -> { local? && will_save_change_to_username? && actor_type != 'Application' }
   validates_with UniqueUsernameValidator, if: -> { local? && will_save_change_to_username? }
   validates_with UnreservedUsernameValidator, if: -> { local? && will_save_change_to_username? }
   validates :display_name, length: { maximum: 128 }, if: -> { local? && will_save_change_to_display_name? }
@@ -140,6 +140,10 @@ def bot?
     %w(Application Service).include? actor_type
   end
 
+  def instance_actor?
+    id == -99
+  end
+
   alias bot bot?
 
   def bot=(val)
@@ -499,7 +503,7 @@ def prepare_username
   end
 
   def generate_keys
-    return unless local? && !Rails.env.test?
+    return unless local? && private_key.blank? && public_key.blank?
 
     keypair = OpenSSL::PKey::RSA.new(2048)
     self.private_key = keypair.to_pem

app/models/concerns/account_finder_concern.rb

@@ -13,7 +13,7 @@ def find_remote!(username, domain)
     end
 
     def representative
-      find_local(Setting.site_contact_username.strip.gsub(/\A@/, '')) || Account.local.without_suspended.first
+      Account.find(-99)
     end
 
     def find_local(username)