Send a Content-Length header when streaming a file

config/initializers/streaming.rb

@@ -5,6 +5,8 @@ module ActionController
 
     def send_file(file, options = {})
       if file.is_a? File or file.is_a? Tempfile
+        headers["Content-Length"] ||= file.size.to_s
+
         options[:filename] ||= File.basename(file.path) unless options[:url_based_filename]
         send_file_headers! options
 
@@ -12,6 +14,8 @@ module ActionController
         self.content_type = options[:content_type] if options.key?(:content_type)
         self.response_body = file
       else
+        headers["Content-Length"] ||= File.size(file).to_s
+
         old_send_file(file, options)
       end
     end