Index: 10-patches.rb
===================================================================
diff --git a/trunk/config/initializers/10-patches.rb b/trunk/config/initializers/10-patches.rb
--- a/trunk/config/initializers/10-patches.rb	(revision 19981)
+++ b/trunk/config/initializers/10-patches.rb	(working copy)
@@ -213,3 +213,14 @@
     end
   end
 end
+
+# https://github.com/rack/rack/pull/1703
+require 'rack'
+module Rack
+  class RewindableInput
+    def size
+      make_rewindable unless @rewindable_io
+      @rewindable_io.size
+    end unless method_defined?(:size)
+  end
+end
\ No newline at end of file