How do I create a TCP server that will accept only one connection at a time? [closed]

Question

I'm writing a client-server pair in C++ using Linux sockets. I want the server to listen for a connection, and while one client is connected the server should reject any other clients that try to connect.

I tried implementing this by setting the backlog parameter in the listen function to 0 and to 1 and neither one of those values seems to work. The first client connects as expected, but any subsequent clients just block while the first client finishes. What's really confusing to me is that they don't block on connecting to the server, they block on the first read.

I used the code here to get started writing my client and server. Does anyone know what I need to change to get the server to accept only one client connection, and drop any subsequent connection attempts?

Answer 1

When you accept a connection, a new socket gets created. The old one is still used to listen for future connections.

Since you want to only allow 1 connection at a time, you could just accept the connections, and then close the new accepted socket if you detect you are already processing another.

Is there a net difference that you are looking for compared to closing the new accepted socket right after the accept? The client will know as soon as it tries to use its socket (or right away if it is already waiting on the server with a read call) with a last error of: server actively closed the connection.

Answer 2

Just don't fork() after accept().

This pseudo-C-code will only accept one client at once.

while(1) {
    listen()
    accept()
    *do something with the connection*
    close()
}