recvfrom_nonblock

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 first element of the results, mesg, is the data received. The second element, sender_addrinfo, contains protocol-specific address information of the sender.

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

Parameters

• maxlen - the maximum number of bytes to receive from the socket

• flags - zero or more of the MSG_ options

• outbuf - destination String buffer

• opts - keyword hash, supporting `exception: false`

Example

# In one file, start this first
require 'socket'
include Socket::Constants
socket = Socket.new(AF_INET, SOCK_STREAM, 0)
sockaddr = Socket.sockaddr_in(2200, 'localhost')
socket.bind(sockaddr)
socket.listen(5)
client, client_addrinfo = socket.accept
begin # emulate blocking recvfrom
  pair = client.recvfrom_nonblock(20)
rescue IO::WaitReadable
  IO.select([client])
  retry
end
data = pair[0].chomp
puts "I only received 20 bytes '#{data}'"
sleep 1
socket.close

# In another file, start this second
require 'socket'
include Socket::Constants
socket = Socket.new(AF_INET, SOCK_STREAM, 0)
sockaddr = Socket.sockaddr_in(2200, 'localhost')
socket.connect(sockaddr)
socket.puts "Watch this get cut short!"
socket.close

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

Socket#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