Fix raw_post empty bug when when Transfer-Encoding: chunked

[pedro108]

Motivation / Background

This PR fixes the issue with request.raw_post property being empty for chunked requests. (Transfer-Encoding header present and without a Content-Length value). It was inspired from this previous PR, but without the need of doing a second rewind of the request body.

A similar fix was done on Puma webserver, but with this fix, raw_post will work as expected for any Rack based http server.

Detail

This pull request changes ActionDispatch::Request#raw_post and ActionDispatch::Request#content_length methods, to take into account the presence of Transfer-Encoding header or not.

According to HTTP/1.1 RFC, when Transfer-Encoding is present, a sender must not send a Content-Length header field on a request, so because of that we can't rely on that field when reading the raw request body stream and calculating its content length for the upstream app.

So what this change does is to read the entire requests's body_stream for raw_post instead of using content_length as its length when Transfer-Encoding header is present.

And it uses the raw_post#bytesize value to calculate the request's content_length instead of reading this value from the Content-Length header, when Transfer-Encoding header is present.

Additional information

To test this case an integration railties test http_request_test.rb was used, in order for it to be similar to real use cases.

It is also recommended to test this change manually with a real Rails app running on different Rack servers (e.g. Puma, Unicorn, Webrick or Thin)

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• Tests are added or updated if you fix a bug or add a feature.

[etiennebarrie]

I'm not on the team so take these with a grain of salt, but this is my feedback.