Code Snips

For a little while I’ve been playing with sockets in C now and have come up with the following succinct example of connecting.  Note that the connection is fairly flexible with regards to protocol and transport type.  It really is simply there to make the connection to somewhere else with as few questions asked.  It will involve DNS and service lookups if you provide names instead of the network address and port.  If you want to catch exceptions you need to clear the standard error variable and check it yourself after receiving a fail return value.  It won’t, or at least shouldn’t, report any exceptions because for my current purposes failures are not really exceptions just dead ends on some of many paths.  I tried to keep it simple too, have fun.

/* connect_to_socket
 *
 * connect to a socket using an initialised addrinfo structure,
 *
 * info is an initialised addrinfo structure
 * sock is a pointer to the location to store the socket descriptor when opened
 *
 * returns 0 if successful
 */
int connect_to_socket(const struct addrinfo *info, int* sock) {

    /* open socket */
    *sock = socket(info->ai_family, info->ai_socktype, info->ai_protocol);
    if (*sock < 1) return -1;

    /* connect to the server*/
    if (connect(*sock, info->ai_addr, info->ai_addrlen) == 0)
        return 0;

    /* clean up on failure */
    close(*sock);
    return -1;
}

/* connect_to_server
 *
 * connect to a server using the server name or adress and port or service name
 *
 * server is a string containing either the name or address of the server
 * port is a string containing either the service name or port number to use
 * sock is a pointer to the location to store the socket descriptor when opened
 *
 *  returns 0 if successful
 */
int connect_to_server(const char* server, const char* port, int* sock) {

    struct addrinfo hints, *info = NULL, *list = NULL;
    int e = 0;

    /* initialise the hints for retrieving the address details */
    memset(&hints, 0, sizeof (hints));
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_flags = AI_PASSIVE;
    hints.ai_protocol = 0;

    /* get the address if the server to connect to */
    e = getaddrinfo(server, port, &hints, &list);
    if (e != 0) return -1;

    /* connect to the first socket in the list */
    for (info = list; info != NULL; info = info->ai_next)
        if (connect_to_socket(info, sock) == 0)
            break;

    /* clean up and return */
    if (list != NULL) freeaddrinfo(list);
    if (sock > 0) return 0;
    else return -1;
}