[Web-SIG] some questions about start_response implementation

[Manlio Perillo]

Phillip J. Eby ha scritto:
> At 05:52 PM 10/15/2007 +0200, Manlio Perillo wrote:
>> Hi.
>>
>> I'm implementing the start_response callable for Nginx mod_wsgi and I
>> have a few questions.
>>
>> 1) From the WSGI PEP it seems that an implementation is allowed to
>>     *always* raise an exception when start_response is called with a not
>>     null exc_info.
>>
>>     Is this true?
> 
> Yes - as long as it's the exc_info passed in, i.e.:

It seems that WSGI *does not* requires the application to raise the 
exc_info passed.

> 
>     try:
>         raise exc_info[0], exc_info[1], exc_info[2]
>     finally:
>         del exc_info
> 
> (this pattern of raising prevents the possibility of a reference cycle 
> passing through the current stack location, keeping lots of objects 
> around longer than necessary)

Is this a concern for an implementation in C, too?

> 
> 
> 
>> 2) What happens if an application call start_response with an incorrect
>>     status line or headers?
>>
>>     Should an implementation consider the function "called", so that an
>>     application can call it a second time, *without* the exc_info
>>     parameter?
> 
> Interesting point.  I think it would be compliant either way, though.
> 
> (I'm skipping your third question because it doesn't matter how many 
> frameworks use exc_info; if you're implementing WSGI 1.0 you have to 
> support it.)
> 

Well, I'm asking because in the current implementation I always raise an 
exception, thus not allowing an application to "change its mind".

Its not a big problem to improve the code, but I can delay it if not 
really required.



Thanks and regards   Manlio Perillo