Worker instantiation from URLs

[guybedford]

When creating workers from within modules, we don't have __filename or __dirname so rather have to rely on import.meta.url, something like:

import { Worker } from 'worker_threads';
import { fileURLToPath } from 'url';
new Worker(fileURLToPath(import.meta.url));

To avoid the fileURLToPath call being necessary here, should we consider supporting URLs as input into new Worker?

[devsnek]

IIRC we have prior art on accepting file urls for various APIs, but i don't remember which ones.

[addaleax]

IIRC we have prior art on accepting file urls for various APIs, but i don't remember which ones.

The initial URL support for the fs module supported this, but it was later withdrawn from the PR because a) it could invalidate previously existing security checks when reading from paths that are partially user-controlled and b) file URLs are, sadly, also valid paths for files in directories named file:.

I think a) is not a large concern here.

[guybedford]

b) has typically been also seen as a backwards-incompatible change. Perhaps to implement it that way upfront now though would be permissible.

Then, if users really need a directory named file: they can convert the path into a URL.

[coreyfarrell]

Support for new Worker(import.meta) would eliminate ambiguity. Just a thought, not suggesting it's a good idea.

That said a filename matching /^file:/ or /^data:/ is very edge case for this API, does anyone even use new Worker(pathRelativeToCWD)? The documentation only suggests new Worker(__filename) which would never result in a filename that is ambiguous to URL's. new Worker('./other-file.js') would be unreliable as it would be based on process.cwd(), instead new Worker(require.resolve('./other-file.js')) or new Worker(new URL('./other-file.js', import.meta.url).href) would be needed. I'd go as far as saying that passing a relative path to this API should be an error.

[targos]

does anyone even use new Worker(pathRelativeToCWD) ?

I used it multiple times. It is convenient in apps to always use new Worker('./src/workers/myworker.js') from anywhere in the hierarchy and as not necessarily unreliable. My apps are always started with their root as working directory.

[jasnell]

Just having something like the following would work...

new Worker(new URL(import.meta.url));

[Jamesernator]

^ This approach is how fs accepts URLs, it just accepts URL objects, strings are always treated as paths.