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I'm considering the tag implementation in neutron.
Although I proposed server returns 409 in tag existing case, on the 
basis of the above discussion, server should return the same response code.
I will change current implementation to returning 201.

Thanks,
Hirofumi

On 2016/02/27 2:24, Akihiro Motoki wrote:
> 2016-02-27 1:02 GMT+09:00 Sean Dague <sean at dague.net>:
>> On 02/26/2016 10:52 AM, Chris Dent wrote:
>>> On Fri, 26 Feb 2016, Jay Pipes wrote:
>>>> On 02/26/2016 09:02 AM, Akihiro Motoki wrote:
>>>>> We can create a tag by PUT'ing an individual tag:
>>>>> What status code should be returned if a requested tag already exists?
>>>>>
>>>>> PUT /servers/1234567890/tags/qux
>>>>>
>>>>> The guideline defines 201 (+ Location header) on success.
>>>>> In the current neutron implementation proposed, 409 is returned
>>>>> when a requested tag already exists.
>>>> 409 Conflict.
>>> /me gets some paint
>>>
>>> Stricly speaking, PUT should be idempotent so every time you put a
>>> qux tag on 123456789 it should return (the same) 2xx.
>>>
>>> In the real world things get messy and some implementations return
>>> 201 on create and some other 2xx when it is already there. It
>>> shouldn't be an error though.
>>>
>>> The time a 409 might be reasonable is if via a header, like an ETag,
>>> we have declared that qux must have a certain state before we accept
>>> a PUT of it.
>>>
>>> In some implementations things like 'Etag: 0' are used to say "Only
>>> let this PUT happen if it is a create." That's a bit of a hack but
>>> is useful.
>> Agree. PUT is an update. The should be no issue updating an existing
>> tag. That should be success
> Thanks. I agree PUT should be success in general.
> Honestly I am confused with a situation that a tag is created by PUT
> (not by POST)
> and applied the semantics around POST to PUT case.
>
>> Adding a tag should really be semantically:
>>
>> POST /servers/1234567890/tags
>>
>> to create tags and
>>
>> PUT /servers/1234567890/tags/qux to update them
> The above combination of POST and PUT is really easy to understand to me.
>
> Do we need to use POST to create a new tag,
> or can we keep using PUT to create a tag?
>
> If we keep using PUT, what status code should be returned?
> 201 Created is now returned for PUT operation.
> Is it okay to return 201 even when a tag already exists?
>
>> You should not PUT to any url that you can't GET. And it looks like GET
>> /servers/1234567890/tags/qux would be a 404 here.
> Yes, I totally agree.
>
> Akihiro
>
>>          -Sean
>>
>> --
>> Sean Dague
>> http://dague.net
>>
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