udp_server.rb

require "socket"

LISTEN_ADDR = "::"
LISTEN_PORT = 12345
MSG_LENGTH  = 256
FLAGS       = 0

# Create socket and bind it to the listen on all addresses and the given port
server_socket = UDPSocket.new :INET6
server_socket.bind(LISTEN_ADDR, LISTEN_PORT)

loop do
  # Listen for messages of up to specified length
  message, client = server_socket.recvfrom(MSG_LENGTH)

  # Extract client information given as array and log connection
  addr_info = Addrinfo.new(client)
  puts "Client connected from #{addr_info.ip_address} using " +
    "#{addr_info.ipv6_v4mapped? ? "IPv4" : "IPv6"}"

  # Write back to client with AddressFamily and reversed original message
  server_socket.send("[#{addr_info.ipv6_v4mapped? ? "IPv4" : "IPv6"}]" +
                     " #{message.chomp.reverse}",
                     FLAGS, addr_info.ip_address, addr_info.ip_port)
end