[openstack-dev] [api] [all] To changes-since or not to changes-since
Ian Cordasco
ian.cordasco at RACKSPACE.COM
Fri Jun 19 19:39:45 UTC 2015
On 6/19/15, 14:26, "Kevin L. Mitchell" <kevin.mitchell at rackspace.com>
wrote:
>On Fri, 2015-06-19 at 10:07 +0100, Chris Dent wrote:
>> * Are there additional relevant pros and cons for the two proposals?
>> * Are there additional proposals which can address the shortcomings
>> in either?
>
>On the latter question, would using the If-Modified-Since header[1] make
>any sense as a possible solution? That at least would be a standard
>HTTP convention for this sort of thing, and tends to match up with the
>semantics of a changes-since query parameter.
First, please use the updated RFC references
(https://tools.ietf.org/html/rfc7232#section-3.3)
If-Modified-Since does not. That's meant for entire resources. In other
words, let's say you're listing images in Glance and you do
GET /v2/images
And your response has
HTTP/1.1 200 OK
Last-Modified: some_last_modified_value
In the headers, when you do
GET /v2/images
If-Modified-Since: some_last_modified_value
Then you should either get a:
HTTP/1.1 204 No Content
Or
HTTP/1.1 200 OK
Last-Modified: new_last_modified_value
(all of the images you saw before)
In other words, If-Modified-Since is meant purely for the state of the
resource. It's main purpose is when used in conjunction with caching.
That said, changes-since is more of a "delta". If you need an analogy,
think of it as an equivalent to
$ git log 2015.1.0..stable/kilo
It's just the deltas after a certain timestamp.
Cheers,
Ian
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