asynchronous WSGI implementation

Hi.

I have started to write an asynchronous WSGI implementation for
Twisted Web.

The code is available from a Mercurial repository:
http://hg.mperillo.ath.cx/twisted/twsgi/

The WSGI application is executed in the main Twisted thread, and the
application will be able to directly use Twisted features.

The reason I'm doing this is because I have written a WSGI
implementation for Nginx:
http://hg.mperillo.ath.cx/nginx/ngx_http_wsgi_module

and I would like to have a *similar* implementation written in pure
Python, for testing purpose.


I have some questions:

* What's the use of

     __metaclass__ = type

   in twisted.web.wsgi ?

* Is request.content always buffered (in memory or temporary file)?

* In my ngx_http_wsgi_module, when the yielded string can not be sent to
  the client (because OS buffer is full), I suspend the execution of the
  application, and resume it when the socket is ready.

  I want to do the same with Twisted, and the way to go is to be a
  push producer.

  However I don't know how to implement and use the IPushProducer
  interface for _WSGIResponse.


By the way: it seems that the WSGI implementation in Twisted Web has
some bugs:

* close method of the application iterator is not called in case of
  errors

* _sendResponseHeaders does not check if start_response has been called



Thanks  Manlio