Support the native "fetch" in Node.js 17

Environment

Name	Version
msw	0.38.1
node	17.5.0
OS	MacOS 12.0.1

Request handlers

import { setupServer } from 'msw/node'
import { rest } from 'msw'

const server = setupServer(
  rest.get('https://hello.world', (request, response, context) => {
    return response(
      context.status(200),
      context.json({ hello: 'world' }),
    )
  })
)

server.listen()

Actual request

const response = await fetch('https://hello.world')
const data = await response.json()

console.log(data)

Current behavior

Running the above setup using native fetch in node 17.5.0 (using the --experimental-fetch flag) does not work as expected. Requests are not intercepted, and origins (in this case https://hello.world) are hit.

Expected behavior

Intercepting requests, as usual. 😁

While this issue uses a “bug” template, I believe that msw simply does not support native node.js fetch yet. Are there any roadmaps I may watch to know if that’s already work-in-progress?

[cmolina]

@kettanaito you can see the PR where fetch was added: https://github.com/nodejs/node/pull/41749

[kettanaito]

Hey, @antoinerey. Thanks for reporting this.

Yeah, you’re right saying MSW does not have official support for native fetch in Node.js. Moreover, the latest official Node.js version we support is 12.22.0:

https://github.com/mswjs/msw/blob/1a7bc36d98e0fa0d0fa1c9da6d7dd40605f239ca/.nvmrc#L1

It doesn’t mean you can’t use the library with newer versions. It only means that our entire testing suite runs against the Node.js version specified in .nvmrc, which makes it the latest officially supported version.

Native fetch support

As with other requests in Node.js, supporting native fetch would imply analyzing how it works under the hood. Since it’s not being intercepted right now, I can assume that it doesn’t use http/https internally, and, perhaps, constructs a ClientRequest directly.

If anybody is willing to dive into the Node.js source and write a summary on how fetch is implemented there, they would be doing 50% of the work necessary to support it in MSW.