Regression bug with configuredRedirects: local relative redirects are being interpreted as external urls

[lfilho]

Astro Info

Astro                    v5.6.1
Node                     v23.7.0
System                   macOS (arm64)
Package Manager          unknown
Output                   static
Adapter                  none
Integrations             @astrojs/react
                         @astrojs/sitemap
                         @astrojs/tailwind

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

No response

Describe the Bug

Hi! Just upagraded to 5.6 after a while, and saw that this line here introduced a regression bug, described below.

Basically, I have a complicated but necessary logic that configures a redirect during compile time, in looks like this:

    redirects: {
        '/cv/pdf': pdfRelativePath,
    },

where pdfRelativePath is the result of a function doing that complex compile time calculation I mentioned. The path needs to be relative so it can work both for localhost and production, so it starts with ../. But as you can see on the line I mentioned above, if it doesn't see a value starting with /, it thinks it's an external URL, and then it fails with [UnsupportedExternalRedirect] An external redirect must start with http or https, and must be a valid URL. since it doesn't start with http nor https.

So could we change the conditional to also support relative paths again?

What's the expected result?

Local relative paths should work as before 😊

Link to Minimal Reproducible Example

https://stackblitz.com/edit/github-mstiazbh?file=astro.config.mjs

Participation

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

[ematipico]

I think it's a bit of a gray area here. I believe we never documented local redirects that don't start with a leading slash. Is there a place somewhere we document this behaviour @lfilho?

[ematipico]

Had a chat with team, and yeah it's a bug 🐛

I will make sure to update the docs too, to document this

[lfilho]

Great, thank you, Emanuele. If you think it's an easy thing for novice contributor (I'm rusty!) to fix, I'd be happy to give it try

[ematipico]

It should be relatively easy. The code that does the check is here:

astro/packages/astro/src/core/routing/manifest/create.ts

Lines 360 to 366 in 29ab38e

	// URLs that don't start with leading slash should be considered external
	if (!destination.startsWith('/')) {
	// check if the link starts with http or https; if not, log a warning
	if (!/^https?:\/\//.test(destination) && !URL.canParse(destination)) {
	throw new AstroError(UnsupportedExternalRedirect);
	}
	}

The new code should be like this:

• use URL.canParse at the beginning of the check
• if it parses, check if it's https or HTTP. If not, throw the error
• remove the destination.startsWith('/')

Then add a new test in redirects.test.js