Axios fails to follow redirects from MSW mocked responses

[a11rew]

Prerequisites

• I confirm my issue is not in the opened issues
• I confirm the Frequently Asked Questions didn't contain the answer to my issue

Environment check

• I'm using the latest msw version
• I'm using Node.js version 18 or higher

Node.js version

v20.12.2

Other versions

msw - 2.3.1
axios - 1.7.2

Reproduction repository

https://codesandbox.io/p/devbox/axios-follow-redirects-issue-9qn7z9

Reproduction steps

1. Setup a http.get response handler that responds with a redirect (HttpResponse.redirect or new Response with 3xx code and Location header)
2. Make a GET request to the URL specified in the handler

Current behavior

The request fails with this error message originating from the follow-redirects library Axios uses

Error [ERR_FR_REDIRECTION_FAILURE]: Redirected request failed: Cannot read properties of undefined (reading 'getHeader')

The stack trace points to this line in the follow-redirects lib
https://github.com/follow-redirects/follow-redirects/blob/35a517c5861d79dc8bff7db8626013d20b711b06/index.js#L422

response.req.getHeader is undefined in the IncomingMessage/response follow-redirects receives when the response is mocked using MSW. This does not happen when the requests returning redirects are not intercepted with MSW.

Expected behavior

Axios should be able to follow redirects normally like it does when responses are not mocked with MSW.

[kettanaito]

Hi, @a11rew. Thanks for reporting this.

We have a test for follow-redirects here but, apparently, it misses something. One difference I can spot is that in our tests the original server responds with a redirect, while in your use case the mock does that. Perhaps that's the culprit.

Would you have some time to add a new test case to the test I've linked above? Something like

interceptor.on('request', ({ request }) => {
  request.respondWith(new Response(null, {
    status: 300,
    headers: { Location: '/new/url' }
  }))
})

[a11rew]

Added the failing test case in this PR mswjs/interceptors#581 @kettanaito. I'd be open to contributing a fix for this, any pointers on where I should be looking?

[kettanaito]

Could be potentially fixed by mswjs/interceptors#626. Afaik, Axios uses XHR by default, so we need to look into whether XHR follows redirects to distinguish if that's a request client behavior or Axios' behavior.

[kettanaito]

Released: v2.4.4 🎉

This has been released in v2.4.4!

• 📄 Release notes
• 📦 npm package

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