SSL_CTX_set_alpn_select_cb and Other OpenSSL API ALPN Functions + Their Callbacks

[Osman Zakir <osmanzakir90@xxxxxxxxxxx>]

Hi again.

I don't understand how to write the callback functions some of the OpenSSL ALPN functions expect, and the manual really isn't helping there either, so I'd like some help.  

I have a HTTP/2 upgrade request inside the ClientHello and it's causing my server app to give an error about an unknown protocol.  That's why I want to do this.  I understand that I need to call the ALPN functions somewhere in the function I'm using to run the server.  I'm already using TLS for HTTPS, so I have to use ALPN.  Please help me out here.  Thanks.