feat: add support for read in edge environments

[vnphanquang]

This PR helps with the cloudflare part of #12446. Added a test case and I also tested in a project bootstrapped with create cloudflare@latest. Hope i didn't miss anything 🤞.

Thanks all.

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🦋 Changeset detected

Latest commit: de885af

The changes in this PR will be included in the next version bump.

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Name	Type
@sveltejs/adapter-cloudflare	Minor
@sveltejs/kit	Minor

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-13859-svelte.vercel.app/

[vnphanquang]

Not sure why that particular firefox CI test failed but it did pass on my local machine (pnpm test:cross-platform:build). Let me know, thanks!

[eltigerchino]

We could save some space by testing with a .txt file instead. The .txt file has to be imported with the ?url query so that Vite doesn't inline it. For example:

import textFile from './myFile.txt?url';

[vnphanquang]

Thanks, happy to adjust. I also wanted to test the content-type header in the response. My expectation was that read should automatically return the correct mime type given the asset, without the need to do so explicitly in the caller. Do you know if that's always the case or worth testing here? I guess with a txt we can still test with "text/plain".

Let me know

[eltigerchino]

Oh I'm not actually sure. I would think that it doesn't automatically return the correct mime type but I'd have to check if that's something Cloudflare is doing or if it happens in Node as well.

[vnphanquang]

Just gave it a quick test with adapter-node. content-type is correctly returned from the built server, but not during development. Here's a test repo if you want to take a look.

Anyway, let's simplify to txt for now. Having correct mime is nice but it seems out of scope for this particular PR.

[eltigerchino]

It's probably because during development, read uses a different implementation (it assumes we're always running in a Node.js environment). I could be wrong about this though and maybe it's something else. Are you using vite preview or node build?

kit/packages/kit/src/exports/vite/dev/index.js

Lines 550 to 556 in 6261a87

	read: (file) => {
	if (file in manifest._.server_assets) {
	return fs.readFileSync(from_fs(file));
	}
	return fs.readFileSync(path.join(svelte_config.kit.files.assets, file));
	},

kit/packages/kit/src/exports/vite/preview/index.js

Lines 203 to 209 in 6261a87

	read: (file) => {
	if (file in manifest._.server_assets) {
	return fs.readFileSync(join(dir, file));
	}
	return fs.readFileSync(join(svelte_config.kit.files.assets, file));
	},

kit/packages/adapter-node/src/handler.js

Line 39 in 6261a87

read: (file) => createReadableStream(`${asset_dir}/${file}`)

This could be an issue once dev runs things in a Cloudflare or Netlify environment etc. based on the adapter.

[vnphanquang]

I ran pnpm build followed by node build/index.js

[eltigerchino]

Ah alright. That definitely uses a different implementation, although I don't see how createReadableStream and readFileSync would differ much. Maybe it's how files are served in the Node adapter itself (which is different from vite dev and vite preview).

[vnphanquang]

Yeah I have no clue either. Something to investigate more if I can find some time. For now I'll try to get this PR done first. I guess users can always explicitly set content-type if they find it inconsistent.

[vnphanquang]

moved to txt via 9a525d6.

[eltigerchino]

Thanks for this PR! Is there any chance you could continue the work from #11674 so that it's implemented in the Netlify and Vercel adapters too? I think if the reusable fetchFile function could allow passing a fetch function to it, we could pass env.ASSETS.fetch in the case of the Cloudflare adapter and it would just work.

Not sure why that particular firefox CI test failed but it did pass on my local machine (pnpm test:cross-platform:build). Let me know, thanks!

I re-ran the test in CI and it passes. Probably just a flaky test that failed.

[vnphanquang]

Ah yes. Sorry I missed Rich's PR in my search. Will look into it. Thanks for the input!

[vnphanquang]

@eltigerchino extracted into a streamFileContent function via 6da55ed. A couple of things:

• added some unit tests; I don't think they are strictly necessary but nice to have anyway,
• exported this util via @sveltejs/kit/adapter, as I think kit is already a peer-dependency for all adapters anyway,
• settled with this name rather than fetchFile since I feel like fetch would indicate a returned Response.

Also, I haven't added read for netlify & vercel yet, since edge environment can't be easily tested locally for them as far as I know (vercel requires connecting to a cloud project, and netlify docs says edge functions don't work locally).

I can spawn up some projects in netlify & vercel and do some manual tests, but I feel like i shouldn't block progress here. How about I do that in a separate PR?

Thanks

[eltigerchino]

Thank you!

Also, I haven't added read for netlify & vercel yet, since edge environment can't be easily tested locally for them as far as I know (vercel requires connecting to a cloud project, and netlify docs says edge functions don't work locally).

I can spawn up some projects in netlify & vercel and do some manual tests, but I feel like i shouldn't block progress here. How about I do that in a separate PR?

Yeah, manual testing for those are fine. There is no local environment for Vercel and like you said, Netlify's edge doesn't work locally.