[Python-Dev] wsgi validator with asynchronous handlers/servers

[Benjamin Peterson]

Hi,
The people who best understand WSGI are to be found on the Web-SIG:
http://mail.python.org/mailman/listinfo/web-sig

2013/3/23 Luca Sbardella <luca.sbardella at gmail.com>:
> Hi,
>
> I have an asynchronous wsgi application handler which yields empty bytes
> before it is ready to yield the response body and, importantly, to call
> start_response.
>
> Something like this:
>
> def wsgi_handler(environ, start_response):
>         body = generate_body(environ)
>         body = maybe_async(body)
>         while is_async(body):
>             yield b''
>         start_response(...)
>         ...
>
> I started using wsgiref.validator recently, nice little gem in the standard
> lib, and I discovered that the above handler does not validate! Disaster.
> Reading pep 3333
>
> "the application must invoke the start_response() callable before the
> iterable yields its first body bytestring, so that the server can send the
> headers before any body content. However, this invocation may be performed
> by the iterable's first iteration, so servers must not assume that
> start_response() has been called before they begin iterating over the
> iterable."
>
> The pseudocode above does yields bytes before start_response, but they are
> not *body* bytes, they are empty bytes so that the asynchronous wsgi server
> releases the eventloop and call back at the next eventloop iteration.
>
> I'm I misinterpreting the pep, or the wsgi validator should be fixed
> accordingly?
>
> Regards,
> Luca
>
>
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-- 
Regards,
Benjamin