API Route always returns 404 on Vercel depending on trailingSlash

[florian-lefebvre]

Astro Info

Astro                    v3.6.1
Node                     v18.14.1
System                   Windows (x64)
Package Manager          yarn
Output                   hybrid
Adapter                  @astrojs/vercel/serverless
Integrations             none

If this issue only occurs in one browser, which browser is a problem?

No response

Describe the Bug

When setting trailingSlash in both astro and vercel configs, I think there is some conflict that causes API routes to always be 404.

What's the expected result?

The route /api/test/ should return some json. Here is the deployment: https://astro-vercel-endpoint-issue.vercel.app/api/test/

Link to Minimal Reproducible Example

https://github.com/florian-lefebvre/astro-vercel-endpoint-issue

Participation

• I am willing to submit a pull request for this issue.

[lilnasy]

Does not just affect vercel. The combination of base and trailingSlash is sufficient to break routing.

defineConfig({
    base: "/",
    trailingSlash: "always"
})

[lilnasy]

i am not sure if base: "/" even makes sense
i think the fix would be to error when base ends in slash or ignore base's trailing slash 💀

[florian-lefebvre]

I thought / would kinda mean root but yeah, I guess we should always strip base's trailing slash

[florian-lefebvre]

I checked and removing base does not solve the issue

[matthewp]

Is output: 'hybrid' required to see this problem @florian-lefebvre ?

[lilnasy]

This issue is that astro's trailingSlash never acts on API routes. They are always served without it. When you enable vercel's trailingSlash, it redirects from /api/test (which astro could have served) to /api/test/ (which astro currently does not; bug).

We could make trailingSlash: "always" apply to API routes but that would be a breaking change because currently it only works without them. Since the option is for SEO use-cases, API routes have some wiggle room - we could ignore the trailing slash in all cases.

[MadSpindel]

I think I've a similar issue with /_image and Vercel. If I enable trailingSlash: true in vercel.json, all images stop working on SSR pages, since Vercel is changing the /_image URL to /_image/. And it looks like trailingSlash: 'always' doesn't affect the /_image endpoint?