http2: use nghttp2_session_upgrade2 than nghttp2_session_upgrade

[starrify]

I happen to notice from the upstream that nghttp2_session_upgrade may be considered deprecated:
https://github.com/nghttp2/nghttp2/blob/20079b4c2f688385ba9ecf723f958d0448894879/lib/includes/nghttp2/nghttp2.h#L3660-L3663

When searching for nghttp2_session_upgrade on GitHub, the only result returned is #521. Also there is no result when searching in the revision history. This may rule out the possibility that nghttp2_session_upgrade2 was once adapted but reverted due to some unexpected failure.

[bagder]

docs/INTERNALS.md says we support nghttp2 1.12.0 or later. Does this change then change our requirement? If so, maybe check for that function in the configure script to make sure a new enough lib is used?

[starrify]

Thanks a lot @bagder for the insight and the immediate response! Also my apologies for not having checked that early enough.

It's confirmed that nghttp2_session_upgrade2 exists in nghttp2 v1.12.0: https://github.com/nghttp2/nghttp2/blob/v1.12.0/lib/includes/nghttp2/nghttp2.h#L3364

Being initially introduced in 269a10008, that function is observed to have been available since nghttp2 v1.5.0.

No check for nghttp2_session_upgrade2 is added yet due to the above observations, plus that there is no current check for nghttp2_session_upgrade.

[bagder]

We already have a check for a function that was added in 1.12.0 (nghttp2_session_set_local_window_size) - that should be enough to make sure that nghttp2 is at least of that version.

[bagder]

Thanks!