https://gist.github.com/1b5066eebac9467accabaec88e993f46
This implements the buffe encode/decode, though the streaming version is probably better.

The buttons that appear on the navigation view toolbar (the one with the back button) come from the view that's currently visible in the navigation view. That means you need to set the left_button_items of v, not nav. When you push/pop views on nav, the toolbar buttons change to those of the new top view.