Middleware for Requests

Is your feature request related to a problem? Please describe. Middlewares would help in building dev tools/extend MSW without having to fork the repo.

Let’s say we want to “monitor” all the requests that are responded by the server. So that we can assert the requests made. Middleware/emitting responded event would help in building that.

Describe the solution you’d like Should be able to add “middleware” or event emitted.

server.middlewares(middleware)

Describe alternatives you’ve considered Right now to achieve this, we can add some logic to catch request in each handler.

let loginRequests = [];

server.use(
    rest.post('/login', (req, res, ctx) => {
        loginRequests.push(req);
        return res(ctx.json({ data: 'data'}));
    }),
);

But this would have to duplicated and we can’t reliably abstract this logic out.

[kettanaito]

@Secretmapper you can encapsulate this logic into a high-order resolver:

import { setupWorker, rest } from 'msw'

function withError(resolver) {
  return (req, res, ctx) => {
    // Customize the predicate and response error
    // according to your needs.
    if ('shouldError' in req.cookies) {
      return res(ctx.status(403))
    }

    return resolver(req, res, ctx)
  }
}

const worker = setupWorker(
  rest.get('/user', withError((req, res, ctx) => {
    return res(ctx.json({ success: true }))
  }))
)

worker.start()

[kettanaito]

We can establish an event-based API that could also support request start/finish notifications (#388) for users to execute their logic.

const worker = setupWorker(...)
worker.events.on('request-start', listener)
worker.events.on('request-end', listener)

You could then use this API in your tests to monitor all requests like so:

const loginRequests = []
const server = setupServer(...)

server.events.on('request-intercepted', (req) => {
  loginRequests.push(req)
})

Would this work for your use case?