recv_nonblock

        # BasicSocket.recv_nonblock

(from ruby core)
---
    basicsocket.recv_nonblock(maxlen [, flags [, buf [, options ]]]) => mesg

---

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
*   `buf` - destination String buffer
*   `options` - keyword hash, supporting `exception: false`


### 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
    begin # emulate blocking recv.
      p s.recv_nonblock(10) #=> "aaa"
    rescue IO::WaitReadable
      IO.select([s])
      retry
    end

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.

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 recv_nonblock.

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

### See
*   Socket#recvfrom