different requestHeaders between pretender / msw

[Techn1x]

Just wondering why we lowercase the requestHeaders here in our MSW interceptor?

mirage-msw/lib/msw-config.ts

Line 226 in 2c5e2d9

requestHeaders[k.toLowerCase()] = v;

Under pretender, they would come through exactly as they were requested

fetch('/my-url', { headers: { Authorization: 'valid', CrAzYkeY: true } })

It's of course an easy fix in my code, but it's a small hurdle to this mirage-msw package being a drop-in replacement for pretender

server.get('/my-url/**', function (_, request) {
-    return request.requestHeaders.Authorization === 'valid' && request.requestHeaders.CrAzYkeY
+    return request.requestHeaders.authorization === 'valid' && request.requestHeaders.crazykey
  })

[Techn1x]

Ok I've done a bit of digging and it looks as though, no matter how the headers are sent, they will always come through as lowercase when iterated over (at least, under chrome) and I suspect the toLowerCase() call is to make that consistent across browsers.

This makes sense since headers are intended to be case-insensitive.

We can see here that using the Headers.get() we can access with any sensitivity

But when iterating over, lowercase always comes through.

---

Closing this, since it looks like there's no way that mirage-msw could provide requestHeaders in the same case sensitivity as provided in the original request. Hopefully this issue can help others who stumble on it

[IanVS]

Thanks for following up. This is all pretty experimental, so let me know if you hit other snags while trying it out.