< Object

Class Socket provides access to the underlying operating system socket implementations. It can be used to provide more operating system specific functionality than the protocol-specific socket classes but at the expense of greater complexity. In particular, the class handles addresses using +struct sockaddr+ structures packed into Ruby strings, which can be a joy to manipulate.

Exception Handling

Ruby‘s implementation of Socket causes an exception to be raised based on the error generated by the system dependent implementation. This is why the methods are documented in a way that isolate Unix-based system exceptions from Windows based exceptions. If more information on particular exception is needed please refer to the Unix manual pages or the Windows WinSock reference.

Documentation by

  • Zach Dennis
  • Sam Roberts
  • Programming Ruby from The Pragmatic Bookshelf.

Much material in this documentation is taken with permission from Programming Ruby from The Pragmatic Bookshelf.


Method Alias Description
initialize → original_resolv_initialize



Visibility Signature
public gethostbyname (p1)
public new (host, serv, *rest)
public new (...)

Class Method Detail

Socket.gethostbyname(host) => hostent

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"]
  ["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)


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

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

  Socket.gethostbyname ""
  => ["", [""], 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:

  => ["localhost", [], 2, "\177\000\000\001"]

  => ["", [], 2, "\300\000\"\246"]


See: Socket.getaddrinfo

new(host, serv, *rest), remote_port, local_host=nil, local_port=nil)

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.