Provide a more descriptive error on fetching "file" scheme

[kettanaito]

This would solve...

The current error is cryptic, to say the least:

undici/lib/web/fetch/index.js

Line 945 in 68107da

return Promise.resolve(makeNetworkError('not implemented... yet...'))

The implementation should look like...

makeNetworkError('Failed to fetch the "file" URL scheme: not implemented')

Additional context

There's an existing better error for an unsupported URL schemes, like about:

undici/lib/web/fetch/index.js

Line 786 in 68107da

return Promise.resolve(makeNetworkError('about scheme is not supported'))

I'd still like to have it mention "fetch" at least somewhere so it's clear where the issue originates from.

[kettanaito]

The comment above the network error also mentions that file fetching is left as an exercise for the reader. Is there a workaround for this, somehow?

I'm stumbling upon this through another library so I have no control over that fetch request. Can I "teach" Undici to fetch files? Can I override this behavior in any way, not being in charge of that request-issuing library? (it loads a WASM)

[mcollina]

Thanks for reporting! Would you like to send a Pull Request to address this issue? Remember to add unit tests.

[KhafraDev]

Can I "teach" Undici to fetch files? Can I override this behavior in any way, not being in charge of that request-issuing library?

We've decided in previous discussions not to support fetching file urls, it cannot be changed. Realistically, there isn't a good way for us to satisfy security requirements and user requirements.