Add ActivityPub inbox (#4216)

* Add ActivityPub inbox

* Handle ActivityPub deletes

* Handle ActivityPub creates

* Handle ActivityPub announces

* Stubs for handling all activities that need to be handled

* Add ActivityPub actor resolving

* Handle conversation URI passing in ActivityPub

* Handle content language in ActivityPub

* Send accept header when fetching actor, handle JSON parse errors

* Test for ActivityPub::FetchRemoteAccountService

* Handle public key and icon/image when embedded/as array/as resolvable URI

* Implement ActivityPub::FetchRemoteStatusService

* Add stubs for more interactions

* Undo activities implemented

* Handle out of order activities

* Hook up ActivityPub to ResolveRemoteAccountService, handle
Update Account activities

* Add fragment IDs to all transient activity serializers

* Add tests and fixes

* Add stubs for missing tests

* Add more tests

* Add more tests

app/serializers/activitypub/actor_serializer.rb

@@ -5,10 +5,27 @@ class ActivityPub::ActorSerializer < ActiveModel::Serializer
 
   attributes :id, :type, :following, :followers,
              :inbox, :outbox, :preferred_username,
-             :name, :summary, :icon, :image
+             :name, :summary, :url
 
   has_one :public_key, serializer: ActivityPub::PublicKeySerializer
 
+  class ImageSerializer < ActiveModel::Serializer
+    include RoutingHelper
+
+    attributes :type, :url
+
+    def type
+      'Image'
+    end
+
+    def url
+      full_asset_url(object.url(:original))
+    end
+  end
+
+  has_one :icon,  serializer: ImageSerializer, if: :avatar_exists?
+  has_one :image, serializer: ImageSerializer, if: :header_exists?
+
   def id
     account_url(object)
   end
@@ -26,7 +43,7 @@ class ActivityPub::ActorSerializer < ActiveModel::Serializer
   end
 
   def inbox
-    nil
+    account_inbox_url(object)
   end
 
   def outbox
@@ -46,14 +63,26 @@ class ActivityPub::ActorSerializer < ActiveModel::Serializer
   end
 
   def icon
-    full_asset_url(object.avatar.url(:original))
+    object.avatar
   end
 
   def image
-    full_asset_url(object.header.url(:original))
+    object.header
   end
 
   def public_key
     object
   end
+
+  def url
+    short_account_url(object)
+  end
+
+  def avatar_exists?
+    object.avatar.exists?
+  end
+
+  def header_exists?
+    object.header.exists?
+  end
 end