RFR: 8371471: HttpClient: Log HTTP/3 handshake failures if logging errors is enabled [v3]

[Jaikiran Pai]

On Fri, 7 Nov 2025 17:58:42 GMT, Daniel Fuchs <dfuchs at openjdk.org> wrote:

>> Oh sorry I meant to just remove this line. I thought it was better to not configure HTTP_3_URI_ONLY on the request in order to trigger the fallback on TCP. So something might actually respond. If something responds then we could get a response. On the other hand this might impacts other tests that might run on the machine...
>> hmmm... maybe I should fix that.
>
> The test now creates a TCP ServerSocket bound to the same port and which will close accepted connections. That should ensure safe fallback on TCP. If the ServerSocket cannot be created (address already in use) then the request will be configured with HTTP3_URI_ONLY to prevent fallback to TCP.

Hello Daniel, I think configuring the request to be just `HTTP3_URI_ONLY` and then verify that the request failed with this log message would be enough. But it's OK in the current proposed form too.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28196#discussion_r2509830160