Added code to correctly handle HEAD request

[dhoard]

Signed-off-by: Doug Hoard doug.hoard@gmail.com

[dhoard]

cc @fstab @tomwilkie

[fstab]

Thanks a lot for the PR. I tried to reproduce the bug, but I could not find a single Java version where the HEAD request doesn't work. Even with Azul's Java 6 it works. Moreover, the current implementation handles headers correctly, so if I run

curl -i --head -H 'Accept: application/openmetrics-text; version=1.0.0; charset=utf-8' http://localhost:9000/metrics

I get the correct Content-type and Content-length.

Are you aware of any Java version where HEAD requests don't work? I would only fix it if it is a real problem.

[fstab]

I just saw that #685 is linked here, I commented there as well.

[dhoard]

I updated the PR. The issue is around the generation of the warning message. I have updated #685 with specifics.

[fstab]

Ok, I see now what was the issue. Yes, it makes sense to fix this. The API of sun.net.httpserver.HttpExchangeImpl.sendResponseHeaders() is really strange, thanks for looking into it.