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 <paul.joseph.da...@gmail.com> 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 <iil...@apache.org> 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 <iil...@apache.org> 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 >>>
