MSW seems to "trap" all websocket requests even when the URL doesn't match the ws.link(url) definition.

[simondell]

Hi folks,

My app includes this in its MSW handlers configuration:

const mockSocket = ws.link(`ws://localhost:3000/someResource/:resourceId/updates`);

export const handlers = [
    http.get('http://localhost:3000/someEndpoint', () => {}),

    mockSocket.addEventListener('connection', ({ client, params }) => {
        console.log(`[MSW] Client connected for resource ${params.resourceId}`);

        client.addEventListener('close', () => {
            console.log(
                `[MSW] Client disconnected from resource ${params.resourceId}`,
            );
        });
    }),
]

And elsewhere I have this:

const wsUrl = `wss://our-testing-domain.cloud.foo`;
const socket = new WebSocket(wsUrl);

So, with this setup, I would expect MSW would not trap my websocket connection attempts. This is intentional because I'm doing some early stage configuration to prove I can talk to the socket. I'm doing it from my local dev environment so that I don't have to wait for remote deployments every time I change some code, so I want to (temporarily) have the real URL in my local build (but keeping all the other MSW handlers mocking HTTP requests).

But, the browser console makes it seem as if MSW is successfully catching the WS connection request.

If I replace the URL in the MSW config ws.link(nonsense:/made.up.domain);`... then it still traps the connection and appears to make and maintain the mock socket connection.

The docs say:

A link preconfigures the interceptor to match WebSocket connections that match the provided predicate (e.g. URL).

... but this doesn't seem to be the case. It seems like the predicate is interpreted as "is it a valid URL", rather than "is this the url".

Is this intentional? Have I misunderstood the API?

[kettanaito]

Hi, @simondell. Thanks for raising this.

MSW patches the global.WebSocket class itself in order to know when connections are made and then see if they match your URLs from ws.link(). Not sure if that's the behavior you're referring to, but this one is intentional for there's no other way to spy on the connections to occasionally mock them.

That being said, MSW guarantees that connections not matching your ws.link() predicate should work as they normally do. E.g. you must not see a log message in the console about an intercepted WebSocket connection that doesn't match your predicate. If that happens, that is a bug and I would kindly ask you to create a minimal reproduction repo and share it with me. Then, I'd be able to fix it. Thanks.