Fix #1972, fix #1870 - Fix special characters in XML, add tests (#1988)

Also improve efficiency of the mastodon:maintenance:add_static_avatars task

app/lib/atom_serializer.rb

@@ -3,13 +3,11 @@
 class AtomSerializer
   include RoutingHelper
 
-  INVALID_XML_CHARS = /[^\u0009\u000a\u000d\u0020-\uD7FF\uE000-\uFFFD\u10000-\u10FFFF]/
-
   class << self
     def render(element)
       document = Ox::Document.new(version: '1.0')
       document << element
-      ('<?xml version="1.0"?>' + Ox.dump(element)).force_encoding('UTF-8')
+      ('<?xml version="1.0"?>' + Ox.dump(element, effort: :tolerant)).force_encoding('UTF-8')
     end
   end
 
@@ -319,7 +317,7 @@ class AtomSerializer
   end
 
   def sanitize_str(raw_str)
-    raw_str.to_s.gsub(INVALID_XML_CHARS, '')
+    raw_str.to_s
   end
 
   def add_namespaces(parent)

app/views/api/v1/statuses/_media.rabl

 attributes :id, :remote_url, :type
 
-node(:url)         { |media| media.file.blank? ? media.remote_url : full_asset_url(media.file.url(:original)) }
-node(:preview_url) { |media| media.file.blank? ? media.remote_url : full_asset_url(media.file.url(:small)) }
+node(:url)         { |media| full_asset_url(media.file.url(:original)) }
+node(:preview_url) { |media| full_asset_url(media.file.url(:small)) }
 node(:text_url)    { |media| media.local? ? medium_url(media) : nil }

lib/tasks/mastodon.rake

@@ -145,8 +145,8 @@ namespace :mastodon do
 
       Account.unscoped.where(avatar_content_type: 'image/gif').or(Account.unscoped.where(header_content_type: 'image/gif')).find_each do |account|
         begin
-          account.avatar.reprocess!
-          account.header.reprocess!
+          account.avatar.reprocess! if account.avatar_content_type == 'image/gif' && !account.avatar.exists?(:static)
+          account.header.reprocess! if account.header_content_type == 'image/gif' && !account.header.exists?(:static)
         rescue StandardError => e
           Rails.logger.error "Error while generating static avatars/headers for account #{account.id}: #{e}"
           next