C Server connect to Client - c

Question

I'm trying to make a Server/Client with push notifications.
First of all the Client connects with Server and then Server saves IP address and port of the client. At some point server needs to connect with client to send a notification.
This is how Server saves Client IP address and port after the accept of the first connection:
char client_ip[INET_ADDRSTRLEN];
int port_c;
// Socket, ..., bind, listen, accept
// Gets Client IP address
struct sockaddr_in* pV4Addr = (struct sockaddr_in*)&cli_addr;
struct in_addr ipAddr = pV4Addr->sin_addr;
inet_ntop( AF_INET, &ipAddr, client_ip, INET_ADDRSTRLEN );
printf("Client ip: %s\n", client_ip);
// Gets Client Port Number
port_c = (int) ntohs(cli_addr.sin_port);
printf("Client port is: %d\n", (int) ntohs(cli_addr.sin_port));
// [ ... ]
// Time to send notification to client
bzero((char *) &cli_addr, sizeof(cli_addr));
// Setting IP address and port
cli_addr.sin_family = AF_INET;
bcopy(client_ip, (char *)&cli_addr.sin_addr.s_addr, strlen(client_ip));
cli_addr.sin_port = htons(port_c);
// Create socket
sockfd = socket(AF_INET, SOCK_STREAM, 0);
// Bind socket to the local address
if(bind(sockfd, (struct sockaddr *) &cli_addr, sizeof(cli_addr)) < 0)
error("Error bind");
if (connect(sockfd, (struct sockaddr *)&cli_addr, sizeof(cli_addr)) < 0)
error("ERROR connecting");
I get bind error: Can't assign requested address.
And I am not sure how to code Client after the first connection. It would be listening and accepting the connection but if I do in the Client's code
cli_addr.sin_family = AF_INET;
cli_addr.sin_addr.s_addr = INADDR_ANY;
cli_addr.sin_port = htons(port_client);
Will the IP address be the same as the first connection?
If someone has another solution or better, please share it.

Answer 1

You are trying to bind the server socket to a client IP. That cannot work. You can only bind a socket to a local address. You must use bind for incomming connections, not for outgoing ones.
If you want your server to respond to a request from the client, simply use the socket returned by accept(), then send() using this socket.
You server code should look like this:
SOCKET sock_server = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
struct sockaddr_in sock_local_addr;
memset(&sock_local_addr, 0, sizeof(sock_local_addr));
sock_local_addr.sin_family = AF_INET;
sock_local_addr.sin_port = htons(SERVER_PORT);
sock_local_addr.sin_addr.s_addr = INADDR_ANY;
bind(sock_server, (const struct sockaddr *)&sock_local_addr, sizeof(sock_local_addr)); // bind server socket to any network interface of the server
listen(sock_server, 10);
struct sockaddr_in client_addr;
SOCKLEN_T client_addr_size = sizeof(client_addr);
SOCKET sock_client = accept(sock_server, (struct sockaddr *)&client_addr, &client_addr_size); // accept incomming connection; this will block until a client connects
recv_size = recv(sock_client, buf_in, sizeof(buf_in), 0); // receive data from client
send(sock_client, buf_out, sizeof(buf_out), 0); // send data back to client (buf_out is buffer containing the data to be sent)
shutdown(sock_client, SHUT_RDWR); // shutdown connection with client