support buffers when mocking responses

[alexkolson]

👋 @yinzara

This would add support for the issue referenced in #218. This would be really useful for me and perhaps others as well! Let me know if this looks okay and/or if I should implement in a different way. Thanks!

[andreasg123]

To me, it looks like responseWrapper in src/index.js needs to be modified. That function creates a Response object via the constant ActualResponse that holds the JavaScript Response class. As the constructor for that class doesn't accept another Response object, the types of body and response in responseWrapper need to be checked to determine if that's already a Response object.

[alexkolson]

@andreasg123 Took another shot at it. What do you thnk?

[andreasg123]

It looks like this wasn't the correct place to check for Response after all. I believe that this change in normalizeResponse should do it:

          return resp instanceof ActualResponse
            ? resp
            : typeof resp === 'string'
            ? responseWrapper(resp, init)
            : responseWrapper(resp.body, responseInit(resp, init))

[alexkolson]

@andreasg123 Unfortunately if we swap out the check to go in normalizeResponse then it would have to be in two places no? Swapping the check to that location results in the test failing that checks that you can do:

fetchMock.mockResponse(new Response('foo'))

I am perhaps missing something and welcome your continued feedback. Sorry if I wasn't able to grasp what you were talking about on the first try!

[andreasg123]

@alexkolson, I'm concerned about these cases:

fetchMock.mockResponse(request => new Response('foo'));
fetchMock.mockResponse(request => Promise.resolve(new Response('foo')));

I don't think that those would work without the change that I suggested. For those examples, isFn(bodyOrFunction) in normalizeResponse would be true whereas your example wouldn't take that path.

[andreasg123]

As typeof resp === 'string' would be false, a new Response object would be constructed from resp.body, losing all the other information in the original Response object.