[Web-SIG] PEP 444 (aka Web3)

Ian Bicking ianb at colorstudy.com
Fri Sep 17 19:02:52 CEST 2010

On Fri, Sep 17, 2010 at 9:43 AM, And Clover <and-py at doxdesk.com> wrote:

> On 09/17/2010 02:03 PM, Armin Ronacher wrote:
>  In case we change the spec as Ian mentioned above, I am all for
>> a "wsgi.guessed_encoding" = True flag or something like that.
> Yes, I'd like to see that. I believe going with *only* a
> raw-or-reconstructed path_info, rather than having both path_info and
> PATH_INFO, is probably best, for the middleware-dupication reasons PJE
> mentioned.
> A more in-depth possibility might be:
> wsgi.path_accuracy =
>    0: script_name/path_info have been crudely reconstructed from
>    SCRIPT_NAME/PATH_INFO from an unknown source. Beware!
>    If there is to be backwards compatibility with WSGI1, this
>    would be seen as the 'default value' given a missing path_accuracy.
>    1: script_name/path_info have been reconstructed, but it is known
>    that path_info is accurate, other than %2F and non-ASCII issues.
>    That is, it's known that the path doesn't come from IIS's broken
>    PATH_INFO, or the IIS error has been detected and compensated for.
>    2: script_name/path_info have been reconstructed using known-good
>    encodings for the env. The only way in which they may differ from
>    the original request path is that a slash might originally have
>    been a %2F. (This is good enough for the vast majority of
>    applications.)
>    3: script_name/path_info come directly from the request path
>    without any intervening mangling.

path_accuracy is certainly a better name than encoding; nothing here
actually relates to encoding (except insofar as attempts to encode or
reencode values corrupts the path).  Personally I wouldn't want to split it
up this much, I'd rather a simple flag to indicate something was guessed,
vs. an accurate request.  The only real value I see in it is to help people
debug problems.  Maybe.  I'm not sure it's that realistic to imagine this
will be noticed by people deploying software and encountering problems.  A
helpful application could use it to warn the deployer of potential problems.

It seems that it would be possible to create a WSGI application and client
library that together can detect and help resolve these issues.  E.g., the
application always returns the values of script_name, path_info, and
query_string, and the client fires off a bunch of different requests to see
how it gets interpreted.  It could suggest corrections until everything

I would really like to see concerns over bad gateways not be used to keep
valuable information out of the spec.  We want people to use well-configured
gateways that accurately represent requests.  There are limits, e.g., in
environments where information is lost.  The only really problematic example
is losing the distinction between %2f and /, and I think it's reasonable to
suggest that applications should avoid making that distinction in the path
if they want to be easily deployed in different environments.

Ian Bicking  |  http://blog.ianbicking.org
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