adapter-node fails and logs a 404 when it encounters an asset with a protocol-relative url

Describe the bug

When an asset has an url starting with “//”, adapter-node fails and logs a 404 error.

Logs Server logs:

> Using @sveltejs/adapter-node
> 404 //localhost/svelte-welcome.png (linked from /)
Error: 404 //localhost/svelte-welcome.png (linked from /)

(more details in the “Stacktrace” part)

To Reproduce

An example is here: https://github.com/SiegfriedEhret/svelte-404-repro

Here we go for the steps:

Run the following:

npm init svelte@next my-app
cd my-app
npm install
npm i -D @sveltejs/adapter-node@next

Follow the docs to update the svelte config and add the adapter:

// svelte.config.js
import adapter from '@sveltejs/adapter-node';

export default {
	kit: {
		adapter: adapter({
			// default options are shown
			out: 'build'
		})
	}
};

(⚠️ this is the important part) Modify src/routes/index.svelte and replace:

<img src="svelte-welcome.png" alt="Welcome" />

With:

<img src="//localhost/svelte-welcome.png" alt="Welcome" />

Run:

npm run build

And that is where the 404 is logged.

Expected behavior

First, I’d love to see a warning instead of an error. Then, if we have a warning, it should not stop on the first relevant asset (it currently does).

Stacktraces If you have a stack trace to include, we recommend putting inside a <details> block for the sake of the thread’s readability:

Stack trace

❯ npm run build

> ~TODO~@0.0.1 build
> svelte-kit build

vite v2.3.3 building for production...
✓ 34 modules transformed.
.svelte-kit/output/client/_app/assets/svelte-logo.87df40b8.svg                           1.85kb
.svelte-kit/output/client/_app/assets/fira-mono-cyrillic-400-normal.046b609f.woff2       9.08kb
.svelte-kit/output/client/_app/assets/fira-mono-greek-ext-400-normal.8659ae46.woff2      7.85kb
.svelte-kit/output/client/_app/assets/fira-mono-greek-400-normal.1f8b3a07.woff2          10.48kb
.svelte-kit/output/client/_app/assets/fira-mono-cyrillic-ext-400-normal.b3140dd3.woff2   16.11kb
.svelte-kit/output/client/_app/assets/fira-mono-latin-ext-400-normal.b6331a25.woff2      11.84kb
.svelte-kit/output/client/_app/assets/fira-mono-latin-400-normal.a2f9dbe8.woff2          16.44kb
.svelte-kit/output/client/_app/assets/fira-mono-all-400-normal.0d19eb5d.woff             75.54kb
.svelte-kit/output/client/_app/manifest.json                                             2.43kb
.svelte-kit/output/client/_app/error.svelte-9614ef2b.js                                  1.19kb / brotli: 0.57kb
.svelte-kit/output/client/_app/pages/index.svelte-cc0dcee2.js                            4.07kb / brotli: 1.45kb
.svelte-kit/output/client/_app/pages/__layout.svelte-176944a0.js                         4.62kb / brotli: 1.51kb
.svelte-kit/output/client/_app/pages/about.svelte-f4f53345.js                            2.39kb / brotli: 0.90kb
.svelte-kit/output/client/_app/assets/start-a8cd1609.css                                 0.16kb / brotli: 0.10kb
.svelte-kit/output/client/_app/pages/todos/index.svelte-d3b5a46f.js                      6.12kb / brotli: 2.11kb
.svelte-kit/output/client/_app/assets/pages/__layout.svelte-d4883a00.css                 5.04kb / brotli: 1.35kb
.svelte-kit/output/client/_app/assets/pages/about.svelte-4db5be0d.css                    0.11kb / brotli: 0.07kb
.svelte-kit/output/client/_app/assets/pages/index.svelte-078f1a0b.css                    1.35kb / brotli: 0.36kb
.svelte-kit/output/client/_app/assets/pages/todos/index.svelte-ef0435f2.css              3.71kb / brotli: 0.86kb
.svelte-kit/output/client/_app/chunks/vendor-2f7c43bc.js                                 11.48kb / brotli: 4.54kb
.svelte-kit/output/client/_app/start-b2a68348.js                                         17.76kb / brotli: 5.62kb
vite v2.3.3 building SSR bundle for production...
transforming (22) .svelte-kit/build/runtime/app/env.js"scale" is imported from external module "svelte/transition" but never used in "src/routes/todos/index.svelte".
"flip" is imported from external module "svelte/animate" but never used in "src/routes/todos/index.svelte".
✓ 27 modules transformed.
.svelte-kit/output/server/app.js   64.27kb

Run npm run preview to preview your production build locally.

> Using @sveltejs/adapter-node
> 404 //localhost/svelte-welcome.png (linked from /)
Error: 404 //localhost/svelte-welcome.png (linked from /)
    at error (file:///Users/siegfried/dev/my-app/node_modules/@sveltejs/kit/dist/chunks/index5.js:93:11)
    at visit (file:///Users/siegfried/dev/my-app/node_modules/@sveltejs/kit/dist/chunks/index5.js:160:5)
    at async visit (file:///Users/siegfried/dev/my-app/node_modules/@sveltejs/kit/dist/chunks/index5.js:220:6)
    at async prerender (file:///Users/siegfried/dev/my-app/node_modules/@sveltejs/kit/dist/chunks/index5.js:229:5)
    at async Object.prerender (file:///Users/siegfried/dev/my-app/node_modules/@sveltejs/kit/dist/chunks/index5.js:296:5)
    at async adapt (file:///Users/siegfried/dev/my-app/node_modules/@sveltejs/adapter-node/index.js:28:4)
    at async adapt (file:///Users/siegfried/dev/my-app/node_modules/@sveltejs/kit/dist/chunks/index5.js:322:2)
    at async file:///Users/siegfried/dev/my-app/node_modules/@sveltejs/kit/dist/cli.js:616:5

Information about your SvelteKit Installation:

Diagnostics

• The output of npx envinfo --system --npmPackages svelte,@sveltejs/kit,vite --binaries --browsers

  System:
    OS: macOS 11.3.1
    CPU: (8) x64 Intel(R) Core(TM) i5-1030NG7 CPU @ 1.10GHz
    Memory: 20.20 MB / 16.00 GB
    Shell: 3.2.2 - /usr/local/bin/fish
  Binaries:
    Node: 16.1.0 - ~/.asdf/installs/nodejs/16.1.0/bin/node
    npm: 7.14.0 - ~/.asdf/installs/nodejs/16.1.0/.npm/bin/npm
  Browsers:
    Firefox Developer Edition: 89.0
    Safari: 14.1
  npmPackages:
    @sveltejs/kit: next => 1.0.0-next.109
    svelte: ^3.34.0 => 3.38.2

• Your browser

Firefox 89.0b15

• Your adapter (e.g. Node, static, Vercel, Begin, etc…)

Node

Severity

On the protocol-relative url, here are 2 interesting readings:

• https://en.wikipedia.org/wiki/Wikipedia:Protocol-relative_URL
• https://www.paulirish.com/2010/the-protocol-relative-url/

Even if discouraged, it is still around.

In the end, not severe. I just have to go through all my content to force https 😅!

[babichjacob]

This is a (potential) issue with the prerendering functionality, so it’s best represented by the static adapter label. (Maybe we can change that)

@babichjacob You are right, it should be //domain.tld/svelte-welcome.png. I have updated the issue description and the example repository. Thank you.

Could I perhaps argue that protocol-aware links aren’t really useful anymore, or at least not in a modern framework like SvelteKit given previous decisions about what legacy things not to support? HTTPS should be an always thing now—I think. So write your links with the appropriate https:// prefix and in its current state the prerenderer will recognize them as external rather than erroring about not being able to find them internally.

[SiegfriedEhret]

Hello, I just tried again and it is working. Aaaand maybe it was a problem between keyboard and chair after all, because the //localhost/... could not work, I needed //localhost:3000/.... Sorry! xoxo