Rails5 fix format in uploads actions

app/controllers/concerns/uploads_actions.rb

 module UploadsActions
+  extend ActiveSupport::Concern
+
   include Gitlab::Utils::StrongMemoize
   include SendFileUpload
 
   UPLOAD_MOUNTS = %w(avatar attachment file logo header_logo favicon).freeze
 
+  included do
+    prepend_before_action :set_html_format, only: :show
+  end
+
   def create
     link_to_file = UploadService.new(model, params[:file], uploader_class).execute
 
@@ -41,6 +47,13 @@ module UploadsActions
 
   private
 
+  # Explicitly set the format.
+  # Otherwise rails 5 will set it from a file extension.
+  # See https://github.com/rails/rails/commit/84e8accd6fb83031e4c27e44925d7596655285f7#diff-2b8f2fbb113b55ca8e16001c393da8f1
+  def set_html_format
+    request.format = :html
+  end
+
   def uploader_class
     raise NotImplementedError
   end

changelogs/unreleased/rails5-fix-46276.yml

+---
+title: Rails5 fix format in uploads actions
+merge_request: 19907
+author: Jasper Maes
+type: fixed