TCPSocket

Resolve host and return name and address information for it, similarly to gethostbyname(3). host can be a domain name or the presentation format of an address.

Returns an array of information similar to that found in a +struct hostent+:

- cannonical name: the cannonical name for host in the DNS, or a
  string representing the address
- aliases: an array of aliases for the canonical name, there may be no aliases
- address family: usually one of Socket::AF_INET or Socket::AF_INET6
- address: a string, the binary value of the +struct sockaddr+ for this name, in
  the indicated address family
- ...: if there are multiple addresses for this host,  a series of
  strings/+struct sockaddr+s may follow, not all necessarily in the same
  address family. Note that the fact that they may not be all in the same
  address family is a departure from the behaviour of gethostbyname(3).

Note: I believe that the fact that the multiple addresses returned are not necessarily in the same address family may be a bug, since if this function actually called gethostbyname(3), ALL the addresses returned in the trailing address list (h_addr_list from struct hostent) would be of the same address family! Examples from my system, OS X 10.3:

["localhost", [], 30, "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\001", "\177\000\000\001"]
  and
["ensemble.local", [], 30, "\376\200\000\004\000\000\000\000\002\003\223\377\376\255\010\214", "\300\250{\232" ]

Similar information can be returned by Socket.getaddrinfo if called as:

Socket.getaddrinfo(+host+, 0, Socket::AF_UNSPEC, Socket::SOCK_STREAM, nil, Socket::AI_CANONNAME)

Examples¶ ↑

Socket.gethostbyname "example.com"                                                           
=> ["example.com", [], 2, "\300\000\"\246"]

This name has no DNS aliases, and a single IPv4 address.

Socket.gethostbyname "smtp.telus.net"
=> ["smtp.svc.telus.net", ["smtp.telus.net"], 2, "\307\271\334\371"]

This name is an an alias so the canonical name is returned, as well as the alias and a single IPv4 address.

Socket.gethostbyname "localhost"
=> ["localhost", [], 30, "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\001", "\177\000\000\001"]

This machine has no aliases, returns an IPv6 address, and has an additional IPv4 address.

host can also be an IP address in presentation format, in which case a reverse lookup is done on the address:

Socket.gethostbyname("127.0.0.1")
=> ["localhost", [], 2, "\177\000\000\001"]

Socket.gethostbyname("192.0.34.166")
=> ["www.example.com", [], 2, "\300\000\"\246"]

See¶ ↑

See: Socket.getaddrinfo

 
               static VALUE
tcp_s_gethostbyname(obj, host)
    VALUE obj, host;
{
    rb_secure(3);
    return make_hostent(host, sock_addrinfo(host, Qnil, SOCK_STREAM, AI_CANONNAME), tcp_sockaddr);
}
            

Opens a TCP connection to remote_host on remote_port. If local_host and local_port are specified, then those parameters are used on the local end to establish the connection.

 
               static VALUE
tcp_init(argc, argv, sock)
     int argc;
     VALUE *argv;
     VALUE sock;
{
    VALUE remote_host, remote_serv;
    VALUE local_host, local_serv;

    rb_scan_args(argc, argv, "22", &remote_host, &remote_serv,
                        &local_host, &local_serv);

    return init_inetsock(sock, remote_host, remote_serv,
                        local_host, local_serv, INET_CLIENT);
}