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Re: URI Template -04 Implementation Notes

From: Mike Burrows <mjb@asplake.co.uk>
Date: Wed, 2 Jun 2010 11:49:37 +0100
Message-ID: <AANLkTinANl9TRnoTl7N-v6OVmh2kwZz1zoOouA0OwXhC@mail.gmail.com>
To: Joe Gregorio <joe@bitworking.org>
Cc: URI <uri@w3.org>
Further to point 5, these are the actual expansions given by my
implementation:

x{empty_list=_}y -> x_y (was: xy)
x{empty_keys=_}y -> x_y (was: xy)
x{;name=none} -> x;Fred,Wilma,Pebbles (was: x;name=Fred,Wilma,Pebbles)
x{;favs=none} -> x;color,red,volume,high (was: x;favs=color,red,volume,high)
x{;empty_list=none} -> x;none (was: x;empty_list=none)
x{;empty_keys=none} -> x;none (was: x;empty_keys=none)

Mike
mjb@asplake.co.uk
http://positiveincline.com
http://twitter.com/asplake


On 2 June 2010 11:18, Mike Burrows <mjb@asplake.co.uk> wrote:

> On 2 June 2010 05:00, Joe Gregorio <joe@bitworking.org> wrote:
>
>> I've committed an incomplete implementation of the -04 spec
>> in Python to svn along with test cases taken from the spec.
>>
>>   http://code.google.com/p/uri-templates/source/detail?r=57
>>
>> The tests themselves are taken directly from the spec and
>> are stored in a JSON file, to make it easier to reuse them.
>> (Well, almost taken verbatim from the spec, below I list
>> the cases that were either inconsistent or looked wrong
>> and how I changed them.) The code does not implement
>> 'partial' modifiers.
>>
>
> Cool (the JSON part especially).
>
>
>> Here are my notes:
>>
>> 1. The spec is fiddly, by which I mean that while the rules
>>   for handling semicolon, query parameter, path and label
>>   expansions all make sense on their own, they are all
>>   slightly different from each other. It makes for a lot
>>   more code than I expected, and is fairly tedious to implement.
>>   I'm not sure that the amount of complexity is warranted.
>>
>
>>
>   To simplify I would like to see label and semicolon path
>>   style expansions dropped. I also believe the '+' modifier could
>>   be dropped without loss of generality.
>>
>
>
> Please don't drop label expansion.  I added this to Routes (as used by
> Pylons) and it enables applications to simplify their routing quite
> significantly.  It's the optionality that makes them not redundant (unless
> you want to revive the prefix operator!).  I'm not bothered by the other
> features, but are there more consistent ways of specifying them?
>
> But yes, it was fiddly and annoying.
>
>
>
>> 2. From the spec, this rule isn't consistent:
>>      ["{?x,y,empty}", "?x=1024&y=768&empty="],
>>
>
>
> Yes, it seems we have both concluded that the trailing '=' above is needed
> (missing in the spec).
>
>
>
>> 3. One of these is inconsistent
>>     ["X{.empty}", "X."],
>>     ["x{?empty_list}", "x"],
>>
>
>
> My implementation manages both of these.  Perhaps (it was a while ago) it
> was at the cost of a special case in the code though.  What would you change
> them to?
>
>
>
>> 4. Also inconsistent
>>     ["{;list}", ";val1,val2,val3"],
>>     ["x{;name=none}", "x;name=Fred,Wilma,Pebbles"],
>>
>
>
> Yes, I disabled the latter test.
>
>
>
>> 5. I tried working through the empty and default cases
>>    (section 2.5) but came across so many cases that
>>    seemed to disagree with previous examples or the wording
>>    of the spec that I began to suspect the section was incomplete.
>>    Here is the list of test cases I had collected and believe are wrong,
>>    before I stopped:
>>
>>     ["x{empty_list=_}y", "xy"],
>>     ["x{empty_list+=_}y", "xempty_list._y"],
>>     ["x{empty_keys=_}y", "xy"],
>>     ["x{empty_keys+=_}y", "xempty_keys._y"],
>>     ["x{?empty}", "x?empty="],
>>     ["x{?empty=none}", "x?empty="],
>>     ["x{?empty_list*=none}", "x?none"],
>>     ["x{?empty_list+=none}", "x?empty_list.none"],
>>     ["x{?empty_keys*=none}", "x?none"],
>>     ["x{?empty_keys+=none}", "x?empty_keys.none"],
>>
>>  I believe many of these cases with defaults are ones that Mike Burrows
>>  raised earlier.
>>
>
>
> I pass several of those; I got away with disabling out just these tests:
>
>
>     ('x{empty_list=_}y',       'xy'),
>     ('x{empty_keys=_}y',       'xy'),
>     ('x{;name=none}',          'x;name=Fred,Wilma,Pebbles'),
>     ('x{;favs=none}',          'x;favs=color,red,volume,high'),
>     ('x{;empty_list=none}',    'x;empty_list=none'),
>     ('x{;empty_keys=none}',    'x;empty_keys=none'),
>
>
>
>> 6. I've come across yet another case where going in reverse, from a
>> template
>>   to matching, would be useful. How about carving out () at the end of
>>   an expression as a place where a regex could be stored for applications
>>   that want to use a template for matching against incoming requests, but
>>   just state that the allowed regex's and matching algorithms are outside
>>   the scope of the current spec?
>>
>
>
> That could be done without changing the spec at this stage.  Routes (for
> example) has a syntax that allows a regex to be embedded - e.g.
> "{foo:[a-z]+}" - but it's usually much better to provide these as separate
> parameters to the route definition.  Implementers are free to do something
> similar now with the URI Template spec as it stands, and meanwhile the spec
> can progress towards approval.
>
> It should be sufficient for servers to be able to generate URI Templates
> from their native formats (this is what described_routes does with templates
> from Routes or Rails); in the worst case they can be maintained separately.
> So far I've manage to avoid doing anything that will encourage clients to
> parse URIs.
>
> In summary, there are only a few broken tests, the complexity is slightly
> annoying but still manageable (assuming the broken tests can be fixed to
> something sensible), and I for one would still press on towards approval.
> Meanwhile, feel free to get what you can from
>
>
> http://bitbucket.org/asplake/described_routes/src/tip/described_routes/uri_template.py
>
> http://bitbucket.org/asplake/described_routes/src/tip/tests/test_uri_template.py
>
> When the spec is stable it would be nice to release either package (I
> really don't mind whose) to pypi.
>
>
>>  Thanks,
>>   -joe
>>
>>
> Regards,
>
> Mike
> mjb@asplake.co.uk
> http://positiveincline.com
> http://twitter.com/asplake
>
>
Received on Wednesday, 2 June 2010 12:30:23 UTC

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