Vite strips base URL from request

[benmccann]

Describe the bug

Vite strips the base URL to avoid other middlewares from having to worry about the base URL:

vite/packages/vite/src/node/server/middlewares/base.ts

Line 20 in dfaeb2b

req.url = url.replace(devBase, '/')

Unfortunately, it doesn't really save us from having to worry about the base path and creates a number of broken / unexpected behaviors. E.g. our 404 messages print Not found: /whatever instead of Not found: /basepath/whatever.

While SvelteKit could change its own middleware, that's impossible off-the-shelf middlewares that users might. Some examples that are broken with Vite:

• https://expressjs.com/en/resources/middleware/morgan.html
• http://expressjs.com/en/resources/middleware/session.html (if cookie path is set)
• https://github.com/expressjs/express-paginate

SvelteKit does not use Vite's static asset serving because of this, but I'd love just use Vite's instead of recreating our own

Reproduction

vite/packages/vite/src/node/server/middlewares/base.ts

Line 20 in dfaeb2b

req.url = url.replace(devBase, '/')

System Info

`main`

Used Package Manager

npm

Logs

No response

Validations

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• The provided reproduction is a minimal reproducible example of the bug.

[benmccann]

We came up with an easy workaround for this: sveltejs/kit#7343

That's enough for SvelteKit. It could still cause problems for users if they have generic middlewares they want to use, but this is lower in priority now

[bluwy]

We discussed this briefly last meeting (I think Ben was there too) that reverting the req.url change would be a big breaking change to all downstream SSR frameworks, and something we're trying to avoid in Vite 4.

I didn't know of the req.originalUrl property but it feels like that is the solution if someone wants to access the original url. The express docs also mentions mutating req.url as a common pattern. So maybe we don't need to change this in Vite?

[benmccann]

I wouldn't object to closing this. In any case, it's low enough priority now that I'm not going to pursue it

[patak-dev]

About req.originalUrl, your original PR could have helped when using generic Vite middlewares, because we could tell people to use req.url (no base) or req.originalUrl as needed. The one you end up merging will make middlewares that expect no base fail. An option if you still want to continue this path is to still add a full URL and baseless URL helpers so middlewares can be more explicit. I'm a bit worried that SvelteKit and other projects will not be able to share plugins that use .configureServer and expect req.url to be baseless

[benmccann]

The one you end up merging will make middlewares that expect no base fail.

I had thought about that, but didn't think it'd be an issue as it'd only cause trouble if they come after the SvelteKit middleware and I believe none do, so it should be safe. We could restore the URL Vite provides at the end of processing if this turns out not to be the case.

[patak-dev]

If the SvelteKit middlewares are always expected to be last, then I think you could close this issue @benmccann, the PR you merged then looks good for now to me too 👍🏼