file length truncated

[mataspetrikas]

I'm trying to build an app that serves the same page no matter what url is called (except when loading assets). strangely, it load the html file correctly the first time, but it truncates the file on the consequent loads, thus breaking the HTML code.
here's my code:
https://gist.github.com/3728a339257fd70acc19

is there any additional setting needed?