Fixed win10 cannot handle EventSource Response

[max918]

This PR contains a:

• bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

on Window 10, browsers would not process (or cannot handle) the EventSource's HTTP response if the response is without 'Content-Length'. It cause the client.js cannot be notified to update frontend changes.

But hot-middleware is using the streaming data approach to achieve eventsource. So, adding the Response Header 'Content-Length: -1' can solve the problem.

The fix is already tested on Chrome browser of window 10 (64 bit) and Mac OS.

#101

Breaking Changes

Additional Info

[jsf-clabot]

All committers have signed the CLA.

[alexander-akait]

Can you create minimum reproducible test repo, adding this header is breaking change and break logic for other types

[thfai2000]

@max918
It may be a better way for developer to pass additional headers instead of strictly changing the 'Content-Length'.

// add below code at Line 92 of middleware.js
Object.assign(headers, opts.additionalHeaders || {});

So that you can pass 'Content-Length' in the middleware configuration for your needs

{
  "additionalHeaders": {
    "Content-Length": -1
  }
}