Uncaught (in promise) Error: Unable to fetch protocol negotiation info: URL returned [201]

Search terms you've used

Based on firefox devtools console output

Uncaught (in promise) Error: Unable to fetch protocol negotiation info: <redacted URL> returned [201]

Bug description

When using WebsocketNotification and calling .connect(), negotiation fails.
The server responds with "201 Created", but execution of the client library stops there.

Debugging in Browser shows me the following Request payload for POSTing to e.g. https://solid.mydomain.com/storage/:

{"protocols":["ws"],"features":[]}

Uncaught (in promise) Error: Unable to fetch protocol negotiation info: https://solid.mydomain.com/storage returned [201] 

To Reproduce

1. Use Community Solid Server 7 as your POD software
2. Set up a webid profile
3. Try to subscribe to any SolidDataset location
4. Check server response to be HTTP 201 instead of HTTP 200 (I don't know what the solid spec says should be the right code)

Minimal reproduction

      const resourceUrl = new URL('https://solid.mydomain.com/storage/')
      const websocket = new WebsocketNotification(resourceUrl.href, {
        // fetch is an authenticated instance
        fetch,
      })
      websocket.connect()

Expected result

Do not fail on HTTP Status code 201

Actual result

Fails on HTTP Status code 201

Environment

$ npx envinfo --system --npmPackages --binaries --npmGlobalPackages --browsers
  System:
    ...
  Binaries:
    Node: 20.11.0 - ~/.nvm/versions/node/v20.11.0/bin/node
    npm: 10.2.4 - ~/.nvm/versions/node/v20.11.0/bin/npm
    bun: 1.0.25 - ~/.bun/bin/bun
  npmPackages:
    @hexagon6/svelte-solid-store: ^0.3.2 => 0.3.2 
    @hexagon6/svelte-solid-webid-check: ^0.4.0 => 0.4.0 
    @histoire/plugin-svelte: ^0.17.9 => 0.17.9 
    @inrupt/solid-client: ^1.27.0 => 1.30.2 
    @inrupt/solid-client-authn-browser: ^1.15.0 => 1.17.5 
    @inrupt/solid-client-authn-node: ^1.15.0 => 1.17.5 
    @inrupt/solid-client-notifications: ^2.0.0 => 2.0.0 
    @inrupt/vocab-common-rdf: ^1.0.5 => 1.0.5 
    @inrupt/vocab-solid: ^1.0.4 => 1.0.4 
    @lukeapage/pretty-quick: ^4.0.1 => 4.0.1 
    @playwright/test: ~1.32 => 1.32.3 
    @sveltejs/adapter-auto: ^3.1.1 => 3.1.1 
    @sveltejs/adapter-static: ^3.0.1 => 3.0.1 
    @sveltejs/kit: ^2.5.0 => 2.5.0 
    @types/cookie: ^0.5.1 => 0.5.4 
    ava: ^5.1.0 => 5.3.1 
    buffer: ^6.0.3 => 6.0.3 
    eslint: ^8.27.0 => 8.54.0 
    eslint-config-prettier: ^9.0.0 => 9.0.0 
    eslint-plugin-fp: ^2.3.0 => 2.3.0 
    eslint-plugin-svelte: ^2.32.4 => 2.35.0 
    esm-module-alias: ^2.0.2 => 2.1.0 
    histoire: ^0.17.9 => 0.17.9 
    husky: ^8.0.3 => 8.0.3 
    localforage: ^1.10.0 => 1.10.0 
    node-stdlib-browser: ^1.2.0 => 1.2.0 
    prettier: ^3.0.3 => 3.1.0 
    prettier-plugin-svelte: ^3.0.3 => 3.1.1 
    ramda: ^0.29.0 => 0.29.1 
    svelte: ^4.2.9 => 4.2.9 
    svelte-check: ^3.6.3 => 3.6.3 
    typescript: ^5.3.3 => 5.3.3 
    uuid: ^9.0.0 => 9.0.1 
    vite: ^5.0.0 => 5.0.12 
  npmGlobalPackages:
    corepack: 0.23.0
    npm: 10.2.4

Additional information

Start at the WebsocketNotification.connect() entry point and inspect how the protocol-negotiation response status is handled. Reproduce the request against Community Solid Server 7 using the provided minimal example and confirm the expected behavior for HTTP 201; done means negotiation no longer fails for that response.