====== 2021-01-25 - the flask path ======

every now and then i use [[wp>Flask (web framework)|Flask]] to get some [[wp>REST]] service up and running in no time. recently i had an interesting case, as API i exposed was in a form ''/api/1/branch/<brn>/stuff'', where ''brn'' was a [[wp>Version control system|VCS]] branch name, that the API referred to. after some time, one of the project teams started to send out their branches data. branches however were in the form ''feature/foo-bar''... and boom -- API returned an error, that path does not exist. so the obvious solution was to URL-encode it, i.e. ''feature%2Ffoo-bar''... and the same! it turned out that Flask is kind enough to parse URL-encoded data for you. convenient. unless it is not sth that you want... :/

the answer is "parameter types". when you normally type in route in flask, it looks like this:
<code python>
@app.route("/api/1/branch/<brn>/stuff")
def handle_stuff(brn):
    foobar(brn)
</code>
you are implicitly getting ''string'' parameter type. this is where (and why) Flask URL-decides ''%2F'' into ''/''.

there are however other types, like ''int'' and ''path''. in particular ''path'' can handle ''%2F'' properly. so the "correct" code is:
<code python>
@app.route("/api/1/branch/<path:brn>/stuff")
def handle_stuff(brn):
    foobar(brn)
</code>
now users can send out ''feature%2Ffoo-bar'' and a proper function will get called, with ''brn'' set to ''feature/foo-bar'', as expected.

it took me a bit of searching. the main problem was that i was looking for ways to "disable URL-encoding in flask" (and similar) and there i got bunch of "can't do", "won't work" and rally nasty hacks in the implementation of a backend. in the end, the solution turned out to be trivial... once you know what are you looking for. it would be nice if it was more explicit in a documentation (FAQ maybe?).