fetch with data URL throws error when used in SvelteKit

[danielniccoli]

Describe the bug

I have a web app that takes a zlib-compressed and base64-encoded blob as user input. I validate the data on the client, before sending it to the server, where it is validated again.

The validation happens by passing the base64-encoded blob to fetch() as a data URL, which returns a ReadableStream that is then deflated using a DecompressionStream. The validation function works in the browser and in node.js, which was a priority to not have nearly identical duplicate code.

Adding the function call on the server side (+page.server.ts) raises an exception.

Error: Cannot use relative URL (data:application/octet-stream;base64,eNrtfV1vXMm…) with global fetch — use `event.fetch` instead: https://kit.svelte.dev/docs/web-standards#fetch-apis
    at globalThis.fetch …

Svelte is mistakenly identifying a data URL as a relative URL.
And forcibly raising an error when global fetch() is used is a problem as well, because this prevents the use of functions that are designed to work in both environments, client and server.

Reproduction

Run this line in nodejs and in a +page.server.js file.

await fetch("data:application/octet-stream;base64,eNrtfV==")

Logs

No response

System Info

System:
    OS: Windows 10 10.0.22621
    CPU: (20) x64 13th Gen Intel(R) Core(TM) i5-13600K
    Memory: 16.37 GB / 31.75 GB
  Binaries:
    Node: 20.3.1 - C:\Program Files\nodejs\node.EXE
    Yarn: 1.22.19 - C:\Program Files\nodejs\yarn.CMD
    npm: 9.8.1 - ~\AppData\Roaming\npm\npm.CMD
    pnpm: 7.25.0 - C:\Program Files\nodejs\pnpm.CMD
  Browsers:
    Edge: Spartan (44.22621.2134.0), Chromium (116.0.1938.62)
    Internet Explorer: 11.0.22621.1
  npmPackages:
    svelte: ^4.0.5 => 4.2.0

Severity

blocking all usage of SvelteKit

Additional Information

No response

[danielniccoli]

#10656

[danielniccoli]

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