Question

I have a root node(server) connected to many other nodes(clients) through TCP sockets. I want to send some data from server to client, but the data is different for each node and depends on the ip address of that node.

Thus I should have ip address of each node connected to server. How can I have that information?

Answer 1

As long as you have access to the list of file descriptors for the connected TCP sockets, it is easy to retrieve the addresses of the remote hosts. The key is the getpeername() system call, which allows you to find out the address of the remote end of a socket. Sample C code:

// This is ugly, but simpler than the alternative
union {
    struct sockaddr sa;
    struct sockaddr_in sa4;
    struct sockaddr_storage sas;
} address;
socklen_t size = sizeof(address);

// Assume the file descriptor is in the var 'fd':
if (getpeername(fd, &address.sa, &size) < 0) {
    // Deal with error here...
}

if (address.sa.family == AF_INET) {
    // IP address now in address.sa4.sin_addr, port in address.sa4.sin_port
} else {
    // Some other kind of socket...
}