> application/couchdb needs registering, which is a faff, and isn't appropriate
> imo as we have many different formats of request and response, which a
> content-type ought to capture.
I could be wrong but `application/couchdb;
_v={version_number},application/json` should fall back to json if client don't
understand `application/couchdb` (different alternatives separated by comma).
> We could sink a lot of time into declaring content types for the all_docs
> response, the changes response, etc, or do something like like Accept:
> application/json; couch_version=2,
If fallback to json works (and my reading of the spec tells me that it should)
then we just prepend existent Content-Type with `application/couchdb;
_v={version_number},`
On 2020/04/27 22:44:03, Robert Samuel Newson <[email protected]> wrote:
> As a general direction, I like it, but the specific example of accept/content
> doesn't sit right with me.
>
> application/couchdb needs registering, which is a faff, and isn't appropriate
> imo as we have many different formats of request and response, which a
> content-type ought to capture. From the post I linked, it's the ".v2+json"
> bit that matters. We could sink a lot of time into declaring content types
> for the all_docs response, the changes response, etc, or do something like
> like Accept: application/json; couch_version=2, or simply omit this option
> and just have the path option, the query parameter option and the custom
> header option.
>
> B.
>
> > On 27 Apr 2020, at 22:34, Paul Davis <[email protected]> wrote:
> >
> > Overall this looks quite good to me. The only thing I'd say is that we
> > should set our version much earlier so we can eventually rely on this
> > for selecting an entirely independent implementation. Though that's
> > not very pressing as once we have the concept embedded we can extend
> > it as needed.
> >
> > For this approach the only thing that concerns me is the way
> > versioning is applied to individual URL handlers. I'd rather see
> > something where we can say "replace these things with newer versions,
> > fall back to v1 for the defaults". Though I couldn't figure out a very
> > clean way to do that. The only thing I came up with was to have a
> > chttpd_handlers_v2.erl service that's called and then
> > chttpd_httpd_handlers_v2.erl that instead of defaulting to `no_match`
> > would just forward to `chttpd_httpd_handlers:url_handler(Req)` or w/e
> > it would be. But to be honest, I'm not super fond of that approach.
> >
> > On Mon, Apr 27, 2020 at 2:41 PM Ilya Khlopotov <[email protected]> wrote:
> >>
> >> I've implemented a PoC for versioned API
> >> https://github.com/apache/couchdb/pull/2832. The code is very ugly but it
> >> demonstrates how it could work.
> >>
> >> Best regards,
> >> iilyak
> >>
> >> On 2020/04/27 14:55:10, Ilya Khlopotov <[email protected]> wrote:
> >>> Hello,
> >>>
> >>> The topic of API versioning was brought in the [Streaming API in CouchDB
> >>> 4.0](https://lists.apache.org/thread.html/ra8d16937cca332207d772844d2789f932fbc4572443a354391663b9c%40%3Cdev.couchdb.apache.org%3E)
> >>> thread. The tread proposes to add new API endpoints to introduce a
> >>> response structure change. The alternative approach could be to implement
> >>> proper support for different API versions.
> >>>
> >>> It would benefit CouchDB project if we would have support for API
> >>> versioning. Adding new endpoint is easy but it is very hard to deprecate
> >>> or change the old ones. With proper API versioning we can avoid the need
> >>> to rewrite all client applications at the same time.
> >>>
> >>> rnewson mentioned a good blog post about API versioning
> >>> (https://www.troyhunt.com/your-api-versioning-is-wrong-which-is/). The
> >>> main idea of the blog post is. There is no perfect solution it would be
> >>> the best to support all options so the user can choose which one to use.
> >>>
> >>> In that spirit I propose to implement four different ways of specifying
> >>> the API version (per endpoint):
> >>>
> >>> - Path based - `/_v{version_number}/{db}/_all_docs`
> >>> - Query parameter based - `/{db}/_all_docs?_v={version_number}`
> >>> - Accept / Content-Type headers in the form of `application/couchdb;
> >>> _v={version_number},application/json`
> >>> - Custom header - X-Couch-API: v2
> >>>
> >>> The server would include response version in two places:
> >>> - Custom header - `X-Couch-API: v2`
> >>> - `Content-type: application/couchdb;
> >>> _v={version_number},application/json`
> >>>
> >>> Implementation wise it would go as follows:
> >>> 1) we teach chttpd how to extract version (we set version to `1` if it is
> >>> not specified)
> >>> 2) we change arity of chttpd_handlers:url_handler/2 to pass API version
> >>> 3) we would update functions in chttpd_httpd_handlers.erl to match on API
> >>> version
> >>> ```
> >>> url_handler(<<"_all_dbs">>, 1) -> fun
> >>> chttpd_misc:handle_all_dbs_req/1;
> >>> url_handler(<<"_all_dbs">>, 2) -> fun
> >>> chttpd_misc_v2:handle_all_dbs_req/1;
> >>> ...
> >>> db_handler(<<"_design">>, 1) -> fun chttpd_db:handle_design_req/2;
> >>> db_handler(<<"_design">>, 2) -> fun
> >>> chttpd_db_v2:handle_design_req/2;
> >>> ...
> >>> design_handler(<<"_view">>, 1) -> fun chttpd_view:handle_view_req/3;
> >>> design_handler(<<"_view">>, 2) -> fun
> >>> chttpd_view_v2:handle_view_req/3;
> >>> ```
> >>> 4) Modify chttpd:send_response to set response version (pass additional
> >>> argument)
> >>>
> >>> I don't expect the implementation to exceed 20 lines of code (not
> >>> counting changes in arity of functions in chttpd_httpd_handlers).
> >>>
> >>> Best regards,
> >>> iilyak
> >>>
>
>
