bpo-30622: Change NPN detection

[Sp1l]

This aligns the way NPN support is detected in the code. It now works the same way that ALPN support is detected and used.

https://bugs.python.org/issue30622

[the-knights-who-say-ni]

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[tiran]

Thanks! I have another NPN related fix in #5253. Are you ok if I merge your improvements with mine and give you credit for your work?

[Sp1l]

@tiran No problemo. Let me check #5253
You're OK with the general direction on the NPN feature detection?

[Sp1l]

@tiran Merged your changes into this PR.

CLA has been signed based on my bugs.python.org id 'spil'

[tiran]

Awesome! Thanks! 👍

• The-knights-who-say-ni don't see your CLI yet. It may take a day or two until it is processed by a human being.
• You have to regenerate the argument clinic, please run make clinic and push the modified header file.
• I'm currently travelling. Your fix may not land in 3.7.0-beta 1.

[tiran]

Please rebase your patch and simplify the check as explained.

[tiran]

I think it is safe to simplify the check even further. NPN is available if TLSEXT_TYPE_next_proto_neg and OPENSSL_NO_NEXTPROTONEG is not defined.

#ifdef OPENSSL_NO_NEXTPROTONEG
#  define HAVE_NPN 0
#elif defined(TLSEXT_TYPE_next_proto_neg)
#  define HAVE_NPN 1
#else
#  define HAVE_NPN 0
# endif

[bedevere-bot]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

[tiran]

I have resolved the merge conflict through GH ui. Tests are still failing because the clinic file is outdated.

[tiran]

Somehow I messed up your PR with Github's UI. Since 3.7.0b2 is immanent, I created PR #5859 and gave you credit as co-author.