Lower case request headers

[aaronatbissell]

Issue #, if available:
Fixes:
#347

Possibly fixes:
#654

Description of changes:
When a request comes in as an API Gateway V1 request, the request headers get passed down as-is. If we are trying to make the req object look like a Node.js HTTP request object, then it should probably include the logic to lower-case all the HTTP headers. Even though we are satisfying the shape of an HTTP object, we aren't satisfying the behavior.

https://nodejs.org/api/http.html#messageheaders

Checklist

• Tests have been added and are passing
• Documentation has been updated

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[kibiz0r]

Another possible solution is to change the implementation of ServerlessRequest so that it preserves more of the behavior of its base class http.IncomingMessage.

Right now, it uses Object.assign({ headers }), which overwrites the .headers accessor defined in nodejs.

This would probably work:

Object.assign(this, { ip: remoteAddress, complete: true, httpVersion: '1.1', httpVersionMajor: '1', httpVersionMinor: '1', method, rawHeaders: Object.entries(headers).flat(), body, url }) 

Then it's not the responsibility of the event source to abide by the lowercase rules, and any future changes to the nodejs implementation will be respected without having to duplicate the behavior in this package.

[brettstack]

@kibiz0r this is a great suggestion. Could you submit a PR for this?

[kibiz0r]

@brettstack Actual implementation turned out to be a little bit different, because the .headers accessor only works right when this[kHeadersCount] is set, and that only gets assigned when the stream handler calls _addHeaderLines()

[github-actions]

🎉 This issue has been resolved in version 4.14.2 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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