Re: Socket client and server talking to each other on same system?

[Scott Klement <rpg400-l@xxxxxxxxxxxxxxxx>]

Hi Jerry,

> I have a socket server program supporting multiple connections. I
> want to be able to gracefully shut down the server program. So I
> thought I'd use a socket client to connect to the server program and
> through a socket connection tell the server program to end.

Be careful of this!  Make sure that the application is only available 
inside a trusted network, or that the server only accepts "shutdown" 
requests after verifying that the command came from within the same system.

Otherwise you run the risk of a hacker (or disgruntled employee) writing 
a program to continually send the "Shut down" message to prevent your 
application from working.


> In my client program, when I perform the gethostbyname function, it 
> returns a null. So I deduced that it can't resolve since the
> communication is 'redunant' (for lack of a better term), since the
> client and server are already 'connnected' by virtue of their
> existence on the same system.

Nope, I don't agree with your conclusion.  My programs are able to look 
up the local computer's domain name without error.   You can also look 
up the name 'localhost' which is the conventional name for IP address 
127.0.0.1, connecting to that IP address should always connect to a 
program on the same host.  (That IP address is a special value just for 
that purpose.)

If your client program has no need to ever connect to a different 
computer, you can also use the special value INADDR_LOOPBACK when you 
build your sockaddr data structure for the connect API.  For example:

     D connto          ds                  likeds(sockaddr_in)

         connto = *allx'00';
         connto.sin_family = AF_INET;
         connto.sin_port   = <whatever the port number is>
         connto.sin_addr   = INADDR_LOOPBACK;

         rc = connect(mySock: %addr(connto): %size(connto));

The idea is that INADDR_LOOPBACK will always connect to the same 
computer.  But, gethostbyname() should work... either by using a name 
that can be found in DNS (or the host table) that matches your current 
computer, or by using the special value 'localhost' (which is in the 
host table by default)

> So the question is can I use a socket client connection to tell my
> server program to shutdown when both programs are on the same system?

Yeah, that should be no problem at all.