Matt Caswell

This should probably be backported to 3.0 and 1.1.1 but it won't cherry-pick cleanly there - so new PRs will be needed. I don't plan to merge this until #18132...

Let's check what the docs say for `SSL_pending`: ```` SSL_pending() returns the number of bytes which have been processed, buffered and are available inside ssl for immediate read. ```` https://www.openssl.org/docs/man3.0/man3/SSL_pending.html...

Pushed a fixup to address the CI failures

The CI failures in the "minimal" builds are due to #19622 and are not relevant for this PR.

> It should have a test.. Yes a test should be there for this. Perhaps in test/evp_extra_test.c

I've not reviewed this in detail but I have some initial comments on the overall structure and approach to this solution. Firstly we need to give some thought as to...

I would add that this is a substantial new feature so it would need to be discussed with OTC/OMC as to when/if this fits into our release plan.

Close/reopen to kick CLA bot

As an aside, if HPKE can be made to work within the bounds of our existing operations and their associated EVP APIs then it should be possible to write an...

> I think it makes sense to include HPKE a a feature for a crypto library anyway. Sure. I'm not suggesting we shouldn't look to include it in OpenSSL as...