Gets a socket option. These are protocol and system specific, see your local sytem documentation for details. The option is returned as a String with the data being the binary value of the socket option.

Parameters

• level is an integer, usually one of the SOL_ constants such as Socket::SOL_SOCKET, or a protocol level.
• optname is an integer, usually one of the SO_ constants, such as Socket::SO_REUSEADDR.

Examples

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

  optval = sock.getsockopt(Socket::SOL_SOCKET,Socket::SO_REUSEADDR)
  optval = optval.unpack "i"
  reuseaddr = optval[0] == 0 ? false : true

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

  optval = sock.getsockopt(Socket::IPPROTO_IP, Socket::IP_TTL)
  ipttl = optval.unpack("i")[0]

Option values may be structs. Decoding them can be complex as it involves examining your system headers to determine the correct definition. An example is a +struct linger+, which may be defined in your system headers as:

  struct linger {
    int l_onoff;
    int l_linger;
  };

In this case getsockopt could be called like this:

  optval =  sock.getsockopt(Socket::SOL_SOCKET, Socket::SO_LINGER)
  onoff, linger = optval.unpack "ii"

Receives up to maxlen bytes from socket using recvfrom(2) after O_NONBLOCK is set for the underlying file descriptor. flags is zero or more of the MSG_ options. The result, mesg, is the data received.

When recvfrom(2) returns 0, Socket#recv_nonblock returns an empty string as data. The meaning depends on the socket: EOF on TCP, empty packet on UDP, etc.

Parameters

• maxlen - the number of bytes to receive from the socket
• flags - zero or more of the MSG_ options

Example

     serv = TCPServer.new("127.0.0.1", 0)
     af, port, host, addr = serv.addr
     c = TCPSocket.new(addr, port)
     s = serv.accept
     c.send "aaa", 0
     IO.select([s])
     p s.recv_nonblock(10) #=> "aaa"

Refer to Socket#recvfrom for the exceptions that may be thrown if the call to recv_nonblock fails.

BasicSocket#recv_nonblock may raise any error corresponding to recvfrom(2) failure, including Errno::EWOULDBLOCK.

See

• Socket#recvfrom

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

Parameters

• level is an integer, usually one of the SOL_ constants such as Socket::SOL_SOCKET, or a protocol level.
• optname is an integer, usually one of the SO_ constants, such as Socket::SO_REUSEADDR.
• 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.

Examples

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

  sock.setsockopt(Socket::SOL_SOCKET,Socket::SO_REUSEADDR, true)

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

  sock.setsockopt(Socket::IPPROTO_IP, Socket::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") + Socket::INADDR_ANY
  sock.setsockopt(Socket::IPPROTO_IP, Socket::IP_ADD_MEMBERSHIP, optval)