Support for TLS SNI

[cknowles]

The compose.io implementation of RabbitMQ needs SNI on the TLS connection in order to verify correctly, at least on their very latest implementation. I was looking through the bunny docs and code but didn't spot any support for it. Is there any? If not I may submit the change for review.

The openssl equivalent would be along the lines of adding servername:
openssl s_client -connect HOST:PORT -servername HOST

It's undocumented but Ruby seems to support this via hostname on the SSL socket:

socket = OpenSSL::SSL::SSLSocket.new(tcp_client, ssl_context)
socket.hostname = 'HOST'
socket.connect

[michaelklishin]

@c-knowles thanks. Do you know what's the earliest Ruby version to provide OpenSSL::SSL::SSLSocket#hostname?

[michaelklishin]

Three Bunny classes that are relevant if you are to consider a PR:

• Bunny::Transport
• Bunny::Socket for MRI
• Bunny::Socket for JRuby (JRuby support for Bunny is a "best effort" kind of feature since there's a dedicated JRuby client, March Hare)

Thank you.

[cknowles]

Not sure about the versions yet, I do know it seems to have been in there since at least 2015. So if there is no support yet or planned I will likely have a go at a pull request soon, doesn't look like the changes would be that big.

[michaelklishin]

We can always set that field only if the socket object responds to :hostname.

[cknowles]

According to ruby/openssl#81 on the hostname setting:

Yes, it is part of the public API, since Ruby 1.9.2 (note it requires OpenSSL >= 0.9.8f).

RDoc comment was fixed some time ago, and OpenSSL::SSL::SSLSocket#hostname= 
now shows up in the latest HTML generated from the master branch:

http://ruby.github.io/openssl/OpenSSL/SSL/SSLSocket.html#method-i-hostname-3D