setsockopt

Sets a socket option. These are protocol and system specific, see your local system documentation for details.

Parameters

• level is an integer, usually one of the SOL_ constants such as Socket::SOL_SOCKET, or a protocol level. A string or symbol of the name, possibly without prefix, is also accepted.

• optname is an integer, usually one of the SO_ constants, such as Socket::SO_REUSEADDR. A string or symbol of the name, possibly without prefix, is also accepted.

• optval is the value of the option, it is passed to the underlying setsockopt() as a pointer to a certain number of bytes. How this is done depends on the type:

  • Fixnum: value is assigned to an int, and a pointer to the int is passed, with length of sizeof(int).

  • true or false: 1 or 0 (respectively) is assigned to an int, and the int is passed as for a Fixnum. Note that false must be passed, not nil.

  • String: the string's data and length is passed to the socket.

• socketoption is an instance of Socket::Option

Examples

Some socket options are integers with boolean values, in this case setsockopt could be called like this:

sock.setsockopt(:SOCKET, :REUSEADDR, true)
sock.setsockopt(Socket::SOL_SOCKET,Socket::SO_REUSEADDR, true)
sock.setsockopt(Socket::Option.bool(:INET, :SOCKET, :REUSEADDR, true))

Some socket options are integers with numeric values, in this case setsockopt could be called like this:

sock.setsockopt(:IP, :TTL, 255)
sock.setsockopt(Socket::IPPROTO_IP, Socket::IP_TTL, 255)
sock.setsockopt(Socket::Option.int(:INET, :IP, :TTL, 255))

Option values may be structs. Passing them can be complex as it involves examining your system headers to determine the correct definition. An example is an ip_mreq, which may be defined in your system headers as:

struct ip_mreq {
  struct  in_addr imr_multiaddr;
  struct  in_addr imr_interface;
};

In this case setsockopt could be called like this:

optval = IPAddr.new("224.0.0.251").hton +
         IPAddr.new(Socket::INADDR_ANY, Socket::AF_INET).hton
sock.setsockopt(Socket::IPPROTO_IP, Socket::IP_ADD_MEMBERSHIP, optval)