Implement a more comprehensive way to get connection information

[mtrudel]

DO NOT MERGE (YET). Presented for feedback on the API ergonomics. Once we get alignment on the approach here, I'll get corresponding PRs queued up for Bandit and Plug.Cowboy to go out at the same time.

Scope of changes:

• Add c:Plug.Conn.Adapter.get_connection_data/1
• Remove c:Plug.Conn.Adapter.get_peer_data/1 from Adapter behaviour
• Add Plug.Conn.get_connection_data/1
• Implement Plug.Conn.get_peer_data in terms of get_connection_data/1

[mtrudel]

Hrm. Looking into the work required to implement this in Cowboy, it's not insignificant. Cowboy easily provides all of the existing info in peer_data, but basically nothing else (I suspect that this is probably why the existing Plug.Conn.Adapter contract looks the way it does). It'd be a whole set of kinda subtle PRs all the way up to Ranch to get this information sourced, for what amounts to a pretty niche use case. Not entirely sure this is a good use of effort, TBH.

WDYT?

[ns-blee]

Out of curiosity here... It is not possible to do an adapter check, return nil if Cowboy, and the value if Bandit? Or is the expectation that it will remain agnostic? If so, is there not some way to expose the methods and allow the user to do the adapter check, if needed, though implied? Without access I will be forced to use a proxy and handle TLS termination there so I can inject the values in the stream...