MaraDNS snapshot update: Deadwood now has TCP support

I have added TCP load balancing support to Deadwood. Let me clarify that: Deadwood now compiles two programs, DwMain, which is the UDP DNS load balancer, and DwTcp, which is currently a general-purpose simple TCP load balancer.

What DwTcp does is quite simple: It listens on a user-settable port (53, or DNS, by default). When a client connects to it, DwTcp connects to the upstream TCP server on a user-settable port (again, 53 by default) and any data the client sends over TCP is sent, unchanged, to the upstream server, and any data upstream sends over TCP is sent, unchanged, back to the client.

DwTcp is currently not DNS-specific. It could be used as a HTTP or even SMTP load balancer. The main problem with DwTcp is, when used as a load balancer, is that the servers behind DwTcp will not be able to determine the IP connections come from--they will see the DwTcp server's IP, and DwTcp does not log connections.

My plan is to integrate the TCP code back in to DwMain, making DwMain both a TCP and UDP DNS load balancer. I have written the DwTcp code in a manner that should not make this too difficult to do.

I also plan on making the TCP code do some useful DNS-specific things. One useful feature, for example, would be to look at the incoming TCP packet. If the request is not an AXFR or IXFR request, send the question over UDP and, if the UDP reply is not truncated, convert the UDP reply back in to a TCP reply. If the packet is truncated, try again over TCP.

However, other things are more important. I am currently working on Winsock support and getting the code to run as a native Windows binary with MinGW32. Both the UDP and TCP code compile in Windows, but the socket() call fails in the TCP code. Since I didn't have Winsock documentation at home, I couldn't resolve the issue.

After finishing that, I want to add ip-based ACL support which will allow the load balancers to restrict the range of IP addresses that can connect to the load balancer.