RFR: 8350279: HttpClient: Add a new HttpResponse method to identify connections [v4]

[Jaikiran Pai]

On Fri, 4 Apr 2025 13:10:56 GMT, Volkan Yazici <vyazici at openjdk.org> wrote:

>> @jaikiran, what you're suggesting makes sense. I'm still exploring the interplay between the connection label and HTTP/3 server pushes. I will return back to your suggestion soon.
>
>> In this proposed form, no two connections in two different HttpClient instances will ever have the same `connectionLabel`.
> 
> Yes, but this is neither required by the connection label contract. That is, the contract doesn't say that they must have overlapping connection labels. It only states connection labels are unique-per-client. Our implementation is more stricter than that: unique-per-VM, but that is just an implementation detail.
> 
>> I think this counter should probably be present on the `HttpClientImpl` as an instance field.
> 
> I've given this approach an attempt. Though I find it difficult to reason about in the code that a counter _only_ `HttpConnection` uses is situated in `HttpClientImpl`, just to make two `HttpConnection`s from different `HttpClientImpl`s share the connection label.
> 
> I also agree with @dfuch that having a unique-per-VM connection label helps with troubleshooting too.
> 
> @jaikiran, unless you're strongly opinionated about this, I prefer to leave the connection label counter in `HttpConnection`. How shall we proceed?

I don't have a strong opinion nor can I think of any issues this current JVM level counter might cause. If necessary, we can reconsider this if/when any issue shows up, without impacting the specification of `HttpResponse.connectionLabel()`. The current form looks good to me.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24154#discussion_r2030809033