[Web-SIG] WSGI Open Space @ PyCon.

[Mark Ramm]

My thought is that we should do a couple things to the wsgi standard,
and then anything like the lifecycle methods gets addresse,d it should
be pushed into a "container" standard or something.

I think Robert Brewer's WSGI Service Bus proposal that he made a
couple years ago at PyCon needs a new name, but it does provide a good
start on the lifecycle stuff.

As for WSGI itself, we should make a couple of smaller changes which I
think will likely be a bit easier to quantify and agree on. I'm sure
lots more folks from yesterday's discussion will chip in here, but
this is my take on the things we discussed.

1) We should drop the start_response callable, and return a three
member tupple from the wsgi callable:

   def wsgi2app(environ):
         ....
         return (status_code, headers, response_iterator)

2) We should turn wsgi.input into an iterator rather than a somewhat
file-like object.   WSGI middleware that reads part of the wsgi.input
iterator should make sure to restore it using itertools.chain or
replace it with whatever.  If there's a content length specified from
the server the middleware should be responsible for maintaining or
deleting that information as nessisary.   Content length of 0 is
allowed and means there's no data, whereas an unspecified or content
length, indicates that the value is unknown.  This will create a good
symmetry between the input and output methods, and seems like a good
comprimise between flexibility for middleware creators, and ease of
use for consumers.


3) The server should encode the headers and include explicit
information about the encoding in the wsgi environ variable.  So that
any assumptions about what they bytes in the headers represent is made
explicit.

I think we're all very sold on item 1, and items 2 and 3 require more
thinking, but seemed reasonable to those present at the discussion
this afternoon.    Hopefully we'll be meeting again on Saturday and
will be able to continue to think through this stuff and push this all
forward some more.

I'm sure there also be several other minor tweeks to the spec like:

* Not de-encoding encoded slashes in path strings, so that
applications can tell the difference between path separators and
encoded slashes.
* adding a "ClientWentAway" exception that indicates that wsgi.imput
has not been officially exausted, but that the client went away before
wsgi.input was fully populated.

I'm sure there are more.   It might also be interesting to look at
Rack and Jack the ruby and javascript implementations of the WSGI
idea:

http://jackjs.org/
http://rack.rubyforge.org/doc/files/SPEC.html

--Mark Ramm


On Fri, Mar 27, 2009 at 5:33 PM, Graham Dumpleton
<graham.dumpleton at gmail.com> wrote:
> 2009/3/28 Alan Kennedy <alan at xhaus.com>:
>> Dear all,
>>
>> For those of you at PyCon, there is a WSGI Open Space @ 5pm today (Friday).
>>
>> The sub-title of the open space is "Does WSGI need revision"?
>>
>> An example: Philip Jenvey (http://dunderboss.blogspot.com/) raised the
>> need for something akin to what Java folks call "Lifecycle methods",
>> so that WSGI apps can do initialization and finalization.
>>
>> http://java.sun.com/j2ee/tutorial/1_3-fcs/doc/Servlets4.html
>>
>> I'm sure there are plenty of other topics that could be discussed as well.
>>
>> See you @5pm.
>
> Please, whatever you do, do not go making anything like this, or even
> a standard request/response object a part of the WSGI standard.
>
> Create a new specification for this 'application level' stuff which is
> distinct from WSGI and leave WSGI as being the 'server gateway
> interface' as it is really meant to be.
>
> This should go as far as coming up with a better middleware
> abstraction for the application layer and discouraging people from
> using WSGI middleware as they exist now.
>
> All these new components, although the reference implementation may
> host on top of WSGI, should other wise hide WSGI thereby allowing them
> to be hosted on top of an alternate interface or a newer revision of
> WSGI, such as the minimal revision talked about for WSGI 2.0.
>
> If this stuff is all pushed into the WSGI specification then it will
> be a backward step as far as improving the situation for Python as far
> as web hosting availability.
>
> I have been trying to put together a blog entry saying just this and
> other things about the role of WSGI, but just haven't had the time.
> Since sprint almost starting, probably will not get a chance now.
>
> Graham
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-- 
Mark Ramm-Christensen
email: mark at compoundthinking dot com
blog: www.compoundthinking.com/blog