recvfrom_nonblock

        # UDPSocket.recvfrom_nonblock

(from ruby core)
---
    udpsocket.recvfrom_nonblock(maxlen [, flags[, outbuf [, options]]]) => [mesg, sender_inet_addr]

---

Receives up to *maxlen* bytes from `udpsocket` using recvfrom(2) after
O_NONBLOCK is set for the underlying file descriptor. *flags* is zero or
more of the `MSG_` options. The first element of the results, *mesg*, is
the data received. The second element, *sender_inet_addr*, is an array
to represent the sender address.

When recvfrom(2) returns 0, Socket#recvfrom_nonblock returns an empty
string as data. It means an empty packet.

### Parameters
*   `maxlen` - the number of bytes to receive from the socket
*   `flags` - zero or more of the `MSG_` options
*   `outbuf` - destination String buffer
*   `options` - keyword hash, supporting `exception: false`


### Example
    require 'socket'
    s1 = UDPSocket.new
    s1.bind("127.0.0.1", 0)
    s2 = UDPSocket.new
    s2.bind("127.0.0.1", 0)
    s2.connect(*s1.addr.values_at(3,1))
    s1.connect(*s2.addr.values_at(3,1))
    s1.send "aaa", 0
    begin # emulate blocking recvfrom
      p s2.recvfrom_nonblock(10)  #=> ["aaa", ["AF_INET", 33302, "localhost.localdomain", "127.0.0.1"]]
    rescue IO::WaitReadable
      IO.select([s2])
      retry
    end

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

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

If the exception is Errno::EWOULDBLOCK or Errno::EAGAIN, it is extended
by IO::WaitReadable. So IO::WaitReadable can be used to rescue the
exceptions for retrying recvfrom_nonblock.

By specifying a keyword argument *exception* to `false`, you can
indicate that recvfrom_nonblock should not raise an IO::WaitReadable
exception, but return the symbol `:wait_readable` instead.

### See
*   Socket#recvfrom