C socket get IP address from filedescriptor returned from accept

Question

I know this question seems typical and multiple times answered but I think if you read the details it is not so common (I did not find it).

The poin

Answer 1

Statefull connection is uniquely identified by two end points Peer(address:port)<=>My(address:port). Both getpeername() and getsockname() are needed to get this information.

Answer 2

Ok. Thanks to @alk and @rileyberton I found the correct method to use, the getpeername:

int sockfd;

void main(void) {
    //[...]
    struct sockaddr_in clientaddr;
    socklen_t clientaddr_size = sizeof(clientaddr);
    int newfd = accept(sockfd, (struct sockaddr *)&clientaddr, &clientaddr_size);
    //fork() and other code
    foo(newfd);
    //[...]
}
void foo(int newfd) {
    //[...]
    struct sockaddr_in addr;
    socklen_t addr_size = sizeof(struct sockaddr_in);
    int res = getpeername(newfd, (struct sockaddr *)&addr, &addr_size);
    char *clientip = new char[20];
    strcpy(clientip, inet_ntoa(addr.sin_addr));
    //[...]
}

So now in a different process I can get the IP address (in the "string" clientip) of the client that originated the connection only carrying the file descriptor newfd obtained with the accept method.

Answer 3

You would use getsockname() (http://linux.die.net/man/2/getsockname) to get the IP of the bound socket.

Also answered before, here: C - Public IP from file descriptor