recvfrom_nonblock

Receives up to maxlen bytes from udpsocket using recvfrom(2) after O_NONBLOCK is set for the underlying file descriptor. If maxlen is omitted, its default value is 65536. 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

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::AGAIN, it is extended by IO::WaitReadable. So IO::WaitReadable can be used to rescue the exceptions for retrying recvfrom_nonblock.

See

• Socket#recvfrom

static VALUE
udp_recvfrom_nonblock(int argc, VALUE *argv, VALUE sock)
{
    return rsock_s_recvfrom_nonblock(sock, argc, argv, RECV_IP);
}

require 'socket'

PORT = 5500

socket = UDPSocket.new
socket.bind('', PORT)

for i in 1..10
IO.select([socket])
p socket.recvfrom_nonblock(4096)
end

echo "Hello APIdock" | nc -vv -u 127.0.0.1 5500

["X", ["AF_INET", 61755, "localhost", "127.0.0.1"]]
["X", ["AF_INET", 61755, "localhost", "127.0.0.1"]]
["X", ["AF_INET", 61755, "localhost", "127.0.0.1"]]
["X", ["AF_INET", 61755, "localhost", "127.0.0.1"]]
["Hello APIdock\