Handle multiple headers with the same name

[kettanaito]

https://github.com/kettanaito/msw/blob/fb1e53cf9cb719ea03c7a3f964461cfb84aa54e2/mockServiceWorker.js#L59-L65

Need to ensure multiple headers with the same name can be handled by MockServiceWorker.

This may also mean to adjust the current algorithm for handling headers between client/sw.

Surface

• Adjust serialization/deserialization of headers in MSW and interceptRequest
• Adjust public API of context.set() to support setting of multiple headers with the same name
• Add tests

[kettanaito]

Noting down our productive discussion with @redraushan below.

Data structure

I suggest to store the multiple headers in a list of tuples:

// mockServiceWorker.js
// This would need to be constructed dynamically from "req.headers"
const headers = [['name', 'value'], ['name', 'value']]

Current implementation mirrors the req.headers into a new object instance:

https://github.com/open-draft/msw/blob/6b4242845bb6d301252fbd41c0f4818ce4883e5b/mockServiceWorker.js#L62-L65

De-serialization

When accepted from the MSW on the client side in interceptRequest(), the custom reviver function during JSON parsing should be adjusted to handle the list of tuples. Now it passes the object to new Headers() right away.

https://github.com/open-draft/msw/blob/6b4242845bb6d301252fbd41c0f4818ce4883e5b/src/utils/interceptRequest.ts#L15-L17

[kettanaito]

I was going through the open issues and this is one of the most needed things at the moment. I was wondering if you have the time/desire to implement this, @hehehai? Feel free to say no, I'd try to do this some time next week in that case.

[redraushan]

@kettanaito this was the issue that I discussed with you, it’s my bad I literally forgot to implement the changes. If anyone is not taking in 2-3 days, it’s mine 😅

[hehehai]

@kettanaito I'm sorry, I don't have any ideas at the moment😐