> I'd rather see something where we can say "replace these things with newer > versions, fall back to v1 for the defaults".
I thought we would use something like: ``` url_handler(<<"_all_dbs">>, 2) -> fun handle_all_dbs_req/1; url_handler(<<"_all_dbs">>, _) -> fun chttpd_misc:handle_all_dbs_req/1; ``` On 2020/04/27 21:34:28, 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 > > > >
