Example of a simply UDP client

[jrfondren]

Sending and receiving UDP while accepting stdin, with just selectors:
    
    
    import std/[net, selectors, strformat, strutils]
    
    const
      cfgMaxPacket = 500
      cfgPort = 8800
      localhost = "127.0.0.1"
    
    let
      socket = newSocket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)
      events = newSelector[int]()
    
    socket.bindAddr(Port(cfgPort), localhost)
    events.registerHandle(socket.getFd, {Read}, 0)
    events.registerHandle(0, {Read}, 0) # stdin
    echo &"Listening to stdin and {localhost}:{cfgPort}"
    
    while true:
      for got in events.select(-1):
        if got.fd == cast[int](socket.getFd):
          var
            message, srcAddress = ""
            srcPort = Port(0)
          discard socket.recvFrom(message, cfgMaxPacket, srcAddress, srcPort)
          echo "got UDP: ", message.strip
        elif got.fd == 0:
          # send packet to ourselves
          try:
            socket.sendTo(localhost, Port(cfgPort), stdin.readLine())
          except EOFError:
            quit()
    
    
    Run

What you type interactively is sent and then received over UDP, and then 
printed. While you're doing this you can `nc -u 127.0.0.1 8800` in another 
window and send packets with netcat that'll be printed in the same manner.

The .strip is for the newlines that netcat will send.