Question

I have a project that uses TCP sockets to communicate between a server and one client. As of now I have been doing this on one computer so I have just used local address of “127.0.0.1” for the address to bind and connect to on both sides and its worked fine. Now I have a second computer to act as a client, but I don’t know how to change the addresses accordingly. They are connected through a network that is not connected to the Internet. Before the code looked like this –

Server –

 struct addrinfo hints;
struct addrinfo *servinfo; //will point to the results

//store the connecting address and size
struct sockaddr_storage their_addr;
socklen_t their_addr_size;


memset(&hints, 0, sizeof hints); //make sure the struct is empty
hints.ai_family = AF_INET; //local address
hints.ai_socktype = SOCK_STREAM; //tcp
hints.ai_flags = AI_PASSIVE; //use local-host address

//get server info, put into servinfo
if ((status = getaddrinfo("127.0.0.1", port, &hints, &servinfo)) != 0) {
    fprintf(stderr, "getaddrinfo error: %s\n", gai_strerror(status));
    return false;
}

//make socket
fd = socket(servinfo->ai_family, servinfo->ai_socktype, servinfo->ai_protocol);
if (fd < 0) {
    printf("\nserver socket failure %m", errno);
    return false;
}

//allow reuse of port
int yes=1;
if (setsockopt(fd,SOL_SOCKET,SO_REUSEADDR,(char*) &yes,sizeof(int)) == -1) {
    perror("setsockopt");
    return false;
}

//unlink and bind
unlink("127.0.0.1");
if(bind (fd, servinfo->ai_addr, servinfo->ai_addrlen) < 0) {
    printf("\nBind error %m", errno);
    return false;
}

Client –

struct addrinfo hints;
struct addrinfo *servinfo; //will point to the results

memset(&hints, 0, sizeof hints); //make sure the struct is empty
hints.ai_family = AF_INET; //local address
hints.ai_socktype = SOCK_STREAM; //tcp
hints.ai_flags = AI_PASSIVE; //use local-host address

//get server info, put into servinfo
if ((status = getaddrinfo("127.0.0.1", port, &hints, &servinfo)) != 0) {
    fprintf(stderr, "getaddrinfo error: %s\n", gai_strerror(status));
    return false;
}

//make socket
fd = socket(servinfo->ai_family, servinfo->ai_socktype, servinfo->ai_protocol);
if (fd < 0) {
    printf("\nserver socket failure %m", errno);
    return false;
}

//connect
if(connect(fd, servinfo->ai_addr, servinfo->ai_addrlen) < 0) {
    printf("\nclient connection failure %m", errno);
    return false;
}

I know it should be simple, but I can’t figure out how to change the IPs to get them to work. I tried setting the server computer’s IP address in the quotes in these lines –
if ((status = getaddrinfo(“127.0.0.1”, port, &hints, &servinfo)) != 0)
and
unlink(“127.0.0.1”);

and then change the address in the client code to the client computer’s IP address in this line –
if ((status = getaddrinfo(“127.0.0.1”, port, &hints, &servinfo)) != 0)

Whenever I do that, it tells me connection refused. I have also tried doing the opposite way of putting the server’s address in the client’s line and client’s address in the server’s lines along with a few other attempts. At this point I feel like I am just guessing though. So can someone please help me understand how to change this from using the local address with one computer to connecting two computers? Any help is appreciated.

Answer 1

First, unlink("127.0.0.1"); is totally wrong here, don’t do that.

Then, you have two computers connected by some network. Both should have IP addresses. Replace 127.0.0.1 with the server‘s IP address in both client and the server. The server does not to have to know client’s address beforehand – it’ll get that information from the accept(2) call. The client needs server’s address to know where to connect. The server needs its own address for the bind(2) call.