Expose headers from native client request after request is committed

[sokomishalov]

Fixes issues like that, when public API does not expose headers that have been set by connector implementation.

[rstoyanchev]

The change might not be implemented in exactly this way. For example we don't use protected fields.

Rather than providing a solution, please update the description of the pull request in order to describe the actual problem, and not just reference some external issue which requires additional context.

[sokomishalov]

@rstoyanchev Fair enough
The problem is that ClientHttpRequest::getHeaders contain only headers that have been applied via WebClient API and don't contain headers applied by an underlying connector, (i.e. "user-agent").
Regarding implementation with restriction on protected fields - should this logic be duplicated to the ReactorClientHttpRequest?

[rstoyanchev]

Thanks for elaborating.

We have a NettyHeadersAdapter that's used to expose the underlying headers on the response. We can enable the same on the request side. So, rather than exposing all the protected fields, I would suggest a protected initReadOnlyHeaders method that can be overridden in sub-classes. For Reactor Netty, it would be:

@Override
protected HttpHeaders initReadOnlyHeaders() {
	return HttpHeaders.readOnlyHttpHeaders(new NettyHeadersAdapter(request.requestHeaders()));
}

Let me know if you plan to update the PR, or otherwise I'll take it from here.

[sokomishalov]

@rstoyanchev totally makes sense, I've reworked it according to your recommendations (netty, apache http 5, jetty).
p.s. I've noticed you marked these changes to the 6.x milestone - is there any chance this enhancement to be backported on 5.x ?