Remote console access protocol (as alternative for legacy RCON protocol)

[SNMetamorph]

We definitely need to have two-way remote connection with dedicated servers. My suggestion is to use VConsole protocol from Source 2, this is simple binary protocol, based on TCP. Though it does not have any encryption, but I think this should not be a problem as usually you don't need to pass remote connection directly over the Internet, usually VPN or SSH forwarding are involved in such contexts. Also, there is already some clients for this protocol, which will be helpful during testing.

Why we shouldn't use RCON anymore:

• Works on same port as game protocol, therefore it's pretty problematic to filter RCON packets on firewall
• Based on raw UDP, not even Netchan. Vulnerable to packet loss and data corruption
• Does not have three-way handshake check (aka "challenge") which makes it vulnerable to source IP spoofing.

[a1batross]

Some time ago I had an idea of implementing ssh protocol for that.

Though that would be definitely an overkill, it's still a widely adopted standard with tons of clients. And it's actually secure.

[SNMetamorph]

Some time ago I had an idea of implementing ssh protocol for that.

Though that would be definitely an overkill, it's still a widely adopted standard with tons of clients. And it's actually secure.

Yeah. Practically, SSH fits our requirements, but technically it is pretty complex protocol, which requires security updates, managing SSH keys and so on.

[a1batross]

Forcing people to learn how to manage their SSH keys sounds like a good opportunity to me. :)

[a1batross]

There are also libraries that implement the protocol: https://www.libssh.org/. Written in C even.

[a1batross]

Oh, I remember now why I didn't considered actually implementing SSH.

As it wouldn't be any different than running engine in screen session

[stevenlafl]

For clarity:

1. Do we want to keep the old RCON compatibility present? Maybe an rcon_protocol CVar to switch.
2. We are not doing SSH then, and instead doing VConsole?

If we choose to keep backward compatibility, then the client will need a detection mechanism unless they too should use rcon_protocol. That would allow us to set it to:

# rcon_protocol
"0" - autodetect on client, RCON on server.
"1" - RCON
"2" - VConsole

Autodetection is probably relatively easy, favoring TCP first as it gets a guaranteed response within a short timeout period.

For bonus points, perhaps subsequent requests could automatically use what that specific server's protocol ultimately resolved to, so as to not waste idle time. Could be as simple as setting rcon_protocol in the client and then resetting it when connecting to any other server unless rcon_address is non-empty.

[SNMetamorph]

https://github.com/stevenlafl/metamod-vconsole