what is the sock fd in this code?
int listen_soc = socket(AF_INET, SOCK_STREAM, 0);
if (listen_soc == -1) {
    perror("server: socket");
    exit(1);
}

struct sockaddr_in server;
server.sin_family = AF_INET;
server.sin_port = htons(54321);
memset(&server.sin_zero, 0, 8);
server.sin_addr.s_addr = INADDR_ANY;

if (bind(listen_soc, (struct sockaddr *)&server, sizeof(struct sockaddr_in)) == -1) {
    perror("server: bind");
    close(listen_soc);
    exit(1);
}

if (listen(listen_soc, 5) < 0) {
    perror("listen");
    exit(1);
}

struct sockaddr_in client_addr;
unsigned int client_len = sizeof(struct sockaddr_in);
client_addr.sin_family = AF_INET;

int client_socket = accept(listen_soc, (struct sockaddr *)&client_addr, &client_len);
if (client_socket == -1) {
    perror("accept");
    return -1;
}

write(client_socket, "Welcome to FriendMe!\nPlease type a command:\n> ", 49);

char line[INPUT_BUFFER_SIZE];
read(client_socket, line, INPUT_BUFFER_SIZE);
line[INPUT_BUFFER_SIZE - 1] = '\0';
printf("reading line");
