adapter-node doesn't work correctly with paths.base

[vekunz]

Describe the bug

Basically, we have this svelte.config.js.

import adapter from '@sveltejs/adapter-node';

const config = {
    kit: {
        adapter: adapter(),
        paths: {
            base: '/basepath'
        },
    }
};
export default config;

When we now run svelte-kit build, it produces this folder structure (partly):

build
    client
        _app
            ...
    server
        ...
    static
        ...

the problem now is that the browser is not able to fetch the files in client and static. The node server returns status code 404 for these files.

The browser requests the files like this: http://localhost:3000/basepath/_app/....

If we manually modify the folder structure to this (manually add a basepath folder in client and static) it works fine.

build
    client
        basepath
            _app
                ...
    server
        ...
    static
        basepath
            ...

It seems that the adapter-node forgets to take paths.base into account for the static files.

By the way: If I start the build with svelte-kit preview, it works fine. Just starting it with node build does not work.

Reproduction

I created a simple demo app based on the npm init svelte@next command.

https://github.com/vekunz/svelte-paths-base-demo

Logs

basepath:1 GET http://localhost:3000/basepath 404 (Not Found)
basepath:9 GET http://localhost:3000/basepath/_app/assets/pages/__layout.svelte-ace81755.css net::ERR_ABORTED 404 (Not Found)
basepath:10 GET http://localhost:3000/basepath/_app/start-5dffe62e.js net::ERR_ABORTED 404 (Not Found)
basepath:19 GET http://localhost:3000/basepath/_app/assets/svelte-logo-87df40b8.svg 404 (Not Found)
basepath:13 GET http://localhost:3000/basepath/_app/error.svelte-bf7b1a86.js net::ERR_ABORTED 404 (Not Found)
basepath:11 GET http://localhost:3000/basepath/_app/chunks/vendor-ee294e9e.js net::ERR_ABORTED 404 (Not Found)
basepath:12 GET http://localhost:3000/basepath/_app/pages/__layout.svelte-1bb88ece.js net::ERR_ABORTED 404 (Not Found)

System Info

System:
    OS: Windows 10 10.0.18363
    CPU: (12) x64 Intel(R) Core(TM) i7-9850H CPU @ 2.60GHz
    Memory: 16.61 GB / 31.79 GB
  Binaries:
    Node: 14.18.1 - C:\Program Files\nodejs\node.EXE
    npm: 6.14.15 - C:\Program Files\nodejs\npm.CMD
  Browsers:
    Chrome: 97.0.4692.99
    Edge: Spartan (44.18362.1593.0)
    Internet Explorer: 11.0.18362.1766
  npmPackages:
    @sveltejs/adapter-auto: next => 1.0.0-next.17
    @sveltejs/adapter-node: ^1.0.0-next.67 => 1.0.0-next.67
    @sveltejs/kit: next => 1.0.0-next.260
    svelte: ^3.46.0 => 3.46.4

Severity

blocking all usage of SvelteKit

Additional Information

It seems that in my example app moving the static files in a basepath subdirectory does not work also.

[joelhickok]

Same issue. Software is not usable for now.

[yannp00]

Similar issues with adapter-static - see #3620 Incorrect build path for prerendered endpoints when setting a basepath

[bundabrg]

I actually question the reason for hard-coding the base path in a folder structure like this. If I run the app behind a reverse proxy I'd like to dynamically provide the prefix its listening to (through the x-forwaded-prefix header for example).

The workaround of fixing the build folder seems to solve the issue for the moment however

[bundabrg]

I've had a closer look at how the copy occurs. If you're simply wanting to copy to the correct folders then a small modification of the following to include the base could be done.

kit/packages/adapter-node/index.js

Lines 33 to 36 in 3d728d2

	builder.log.minor('Copying assets');
	builder.writeClient(`${out}/client`);
	builder.writeServer(`${out}/server`);
	builder.writeStatic(`${out}/static`);

This is probably the easiest way to solve both the static and node adapters though presumably the static adapter would place it in the root (as you would copy it into the correct base subfolder when deploying it, so the problem is actually the reverse of the node adapter) whereas the node adapter one needs to EITHER translate base on the fly (which means it could support an environment variable defining the base at runtime, which is supported by the override method exported from Server allowing you to override this at runtime, I think) OR it can just serve it from the hard coded compile time base folder. I don't really know which way is preferred so can't provide a PR and may need some discussion.

[joelhickok]

Instead of having to modify the source code as @bundabrg mentions, I am just using an npm deploy script to copy my node-adaptor build directory to a production directory, and move the problem directories to restructure at the same time. This has caused me to temporarily forget about this issue.

[bundabrg]

I personally think that this is actually part of a bigger issue and simply copying to the correct folder whilst a quick fix is not a "good fix". I've added changes to my branch that does the quick fix but I don't like it.

When generating a static site we ultimately will be placing it either in the correct folder OR preferably behind a load-balancing reverse proxy that strips off the prefix and have it served from the root. So the prefix should not exist in the build folder at all but the code will need to know to add the prefix when referring to assets.

When generating a dynamic site it can be passed environment variables (or perhaps read a config file) where it gets its base prefix. In the same way the site could exist behind a reverse proxy that strips off the prefix OR it'll handle the prefix itself. It matters not as this is an implementation detail of the adapter. The code needs to know to add the prefix when referring to assets and presumably when doing SSR fetching it'll need to know to add/remove the prefix as necessary.

adapter-node uses Polka to serve its assets, executed with the following code:

const server = polka().use(
	// https://github.com/lukeed/polka/issues/173
	// @ts-ignore - nothing we can do about so just ignore it
	compression$1({ threshold: 0 }),
	handler
);

handler is provided as:

const handler = sequence(
	[
		serve(path.join(__dirname, '/client'), 31536000, true),
		serve(path.join(__dirname, '/static'), 0),
		serve(path.join(__dirname, '/prerendered'), 0),
		ssr
	].filter(Boolean)
);

The issue is that ssr will strip off base from the beginning of the URL but the three serve calls do not. The ssr function IMHO should not be doing this and instead everything should be mounted at the polka().use() call, something like this:

const server = polka().use(
        BASE_PATH,
	// https://github.com/lukeed/polka/issues/173
	// @ts-ignore - nothing we can do about so just ignore it
	compression$1({ threshold: 0 }),
	handler
);

where BASE_PATH would be set either by reading the config file or come in from an environment variable.

This way if I have a reverse proxy that strips prefixes I can have BASE_PATH set to '' but pass the actual base through a header like X-Forwarded-Prefix for when building URL's.

If I don't strip the prefix, then I can set BASE_PATH to the prefix so its handled inside Polka instead but otherwise the rest of the code remains the same.

Anyway, that's my 2c.

[j6b72]

This bug still exists in the current version. The workaround of moving both the client/_app folder and the contents of the client/static folder to the right place works though.

[shot-codes]

As already mentioned, there is a related issue with the static adapter - #4528. The workaround of adjusting the directories didn't work for me but I found a workaround with the following.

<script>
  import { base } from '$app/paths';
</script>

<a href="{base}/">Home</a>
<a href="{base}/about">About</a>

[jcallaha]

@TheFoolishPupil - I tried your trick but I get links like /%7Bbase%7D/about - may be because I'm using a component to render nav and it is passed an array with href properties? If I switch to ${base}/about it works in dev but gets lost when I run preview or build (using static adapter)