Ruby TCPSocket Server - Can I tell to what host a client was connecting?

Question

I have a ruby server based on TCPSocket (non-HTTP).

I have 2 different domains, both pointing with an A-Record to my servers IP Address (the same one). So, there are clients connecting to one of those domains. Is it possible to tell which domain a client was connecting to?

I saw that this is possible in other protocols, but I'm not sure if this is based on manually added headers or really extracted from the basic tcp/ip connection. E.g. in PHP there is $_SERVER["HTTP_HOST"] which shows to which domain a client was connecting.

Answer 1

At the TCP socket level, the only things that are known are the source and destination IP addresses (and ports) of the connection. How the IP address was resolved via DNS is not possible to know at this layer. Even though HTTP works on top of TCP, HTTP servers have to look at the HTTP headers from the client to know which domain they are making a request to. (That's how the HTTP_HOST value gets filled in.)

One possible solution is to configure your server to have an additional IP address. This can be by assigning an additional IP address to the NIC or adding an additional NIC. Then have each domain use a different IP address. Otherwise, this is not possible and you may want to consider your application protocol on top of TCP to convey this information.