Question

I would like to be able to loop through a list which is a result of the getaddrinfo() function and call connect() using every element of that list until connect() is successful. Unfortunately, even when I specify the AI_ALL | AI_V4MAPPED flags, and an AF_INET6 family, the results are mixed. The first part of the list contains sockaddr_in6 structures, and the second part sockaddr_in structures, so i can’t use them with an AF_INET6 socket.

I know i can create two sockets. I would like to know whether it’s possible to do it with just the AF_INET6 socket.

Here’s the operating system:

> uname -a
> Linux debian 2.6.32-5-amd64 #1 SMP Wed Jan 12 03:40:32 UTC 2011 x86_64 GNU/Linux

Answer 1

You don’t have to worry if it’s an AF_INET or AF_INET6 socket you are creating.
Simply pass the data from the getaddrinfo() call to the socket() call.

e.g.

/* returns -1 on error, or a connected socket descriptor*/
int opensock(const char *hostname, const char *service)
{
    struct addrinfo hint, *host, *res = NULL;
    int tcp_sd = -1, error;

    memset(&hint, '\0', sizeof(hint));
    hint.ai_socktype = SOCK_STREAM;
    hint.ai_family = PF_UNSPEC;
    error = getaddrinfo(hostname, service, &hint, &res);
    if(error){
        syslog(LOG_DEBUG,"getaddrinfo failed. Cant find host %s: %m",hostname);
        return tcp_sd;
    }
    for (host = res; host; host = host->ai_next) {
        tcp_sd = socket(host->ai_family, host->ai_socktype, host->ai_protocol);
        if (tcp_sd < 0) {
            continue;
        }

        if (connect(tcp_sd, host->ai_addr, host->ai_addrlen) < 0) {
            close(tcp_sd);
            tcp_sd = -1;
            continue;
        }

        break;      /* okay we got one */
    }

    freeaddrinfo(res);

    return tcp_sd;
}