gethostbyname

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