Fixed #34028 -- Allow usage of script prefix in middleware init

[sarahboyce]

Ticket: https://code.djangoproject.com/ticket/34028

An issue people seem to be having is that Whitenoise wants to access the script prefix in the middleware initialisation (see here). This is giving an unexpected result.

I believe this kind of relates to this ticket: https://code.djangoproject.com/ticket/16734 and this PR: #5470

I'm not sure why this set_prefix=False option was created, @claudep I know this is quite a long time ago, but maybe you can add some context?

If we agree with this change, it means all internal usages of set_prefix are removed which probably means it makes sense to depreciate it 🤔 I'm not sure, I've never depreciated anything

Note: asgi is also doing the sameset_prefix=False - I can remove from there also just not comfortable writing anything async so might need help with the test case

[felixxm]

We don't have a request here, so script_prefix would be wrong in most of cases. ticket-16734 was about setting script prefix when we are outside of the request-response cycle e.g. in management command. As far as I'm aware, this cannot be done properly because script_prefix can change even between requests and should only be used dynamically. Maybe we should "wontfix" this ticket 🤔 (\cc @apollo13).

[sarahboyce]

If we end up going for a won't fix, I can try and raise a pr to whitenoise to help resolve it on their side (I think they just need to move the logic from the middleware init)
We could also add a note in the get_script_prefix() docs warning against using it outside the request response cycle - or maybe the ticket itself is enough documentation

[apollo13]

The way I see it we should do the following: There is a real need to have some kind of URL outside the request cycle (sending emails which need to create a link etc). For constructing a correct MEDIA_URL / STATIC_URL we wanted to use the script prefix to allow for more dynamic changes (ie allow a user to move to a subpath without having to change multiple variables). Since this is all not workable I am really starting to lean towards introducing a setting (yes!) called BASE_URL that can be set to https://mysite.com/subpath. This would allow for a) generating URLs outside a request context and b) allow us to mostly ignore script prefix. We could also use a relative STATIC_URL and append it to BASE_URL. This way there would be just one setting that requires changing and many projects hopefully would make that configurable via env vars etc.

[sarahboyce]

Sounds good to me 👍
Would that suggestion need discussing in a wider group or do you think we can reuse the existing ticket or would it be cleaner to open a new one with the suggested feature? 🤔

We could also add a note in the get_script_prefix() docs warning against using it outside the request response cycle

I will close this PR once I've sorted my todo list 👍 do we think this would add value?

[apollo13]

I guess a new ticket that links to the existing ticket(s) would make more sense. We certainly need to explain what BASE_URL would fix and how the migration to it would look like.

We could also add a note in the get_script_prefix() docs warning against using it outside the request response cycle

I will close this PR once I've sorted my todo list +1 do we think this would add value?

Not to sure, get_script_prefix is used so deep inside in Django that it is not really in control of the enduser?

[sarahboyce]

Not to sure, get_script_prefix is used so deep inside in Django that it is not really in control of the enduser?

It's a documented utility function which people could use and I guess the reason the ticket was raised initially was because of how an external package (whitenoise) was using it. Still think documentation is a balance thing and it currently reads well so I will leave it alone.

I raised a ticket https://code.djangoproject.com/ticket/34461
@apollo13 please feel free to update the title and description as you see fit 👍

Also @felixxm I'll let you decide if to accept the new ticket and close the older one 👍

[apollo13]

Mhm fair, I was only thinking of Django's use of the script prefix which can already cause problems in other areas (static url comes to mind). So yes, a docs amendment can probably indeed help :)

Thanks for the ticket!

[sarahboyce]

As discussed, not the right approach 👍