XMPP and Metadata

I'm slowly building my own XMPP client, one key thing I'm running into trouble with is there seems to be no standard library for End to End Encryption other than Signal's own, I don't want to have to relicense my entire project for one dependency, I would rather keep my project Apache licensed. The other problem is voice and video options seem to be married to some Java specific library (Jingle) which is fine if you're using Java, but I'm not, seems nobody has implemented a solution to this in other languages that I'm interested in as well.

For the End to End I could try my best to implement it using existing libraries as pieces I can use, but I'm not comfortable doing that.

I always liked XMPP and SIP as messaging protocols. So easy to read and understand and implement. Both are extensible and can be made secure.

Watch the most popular clients[1] gain traction as countries (e.g. UK) pass laws mandating that tech companies backdoor their apps/encryption.

[1] Conversations for Android and Gajim for Debian.