broadcast

A while back I asked:

> 2. One thing I need to do is implement a discovery protocol, involving a
> UDP broadcast. I don't see a way to set SO_BROADCAST on the underlying
> socket. Is there any way to do that?

Francis replied:

> For UDP broadcasts, just sent the packet to a target address of
> 255.255.255.255 to get a broadcast on your local lan.



I wrote test code (see below) to try this.

Using the Ruby UDPSocket class:

bc_sock ==>
"hello sock world" -> 255.255.255.255">1392255.255.255.255
sent

... and the server (running separately) gets it:

serv ==>
udp server  1392
129.196.215.84">1628129.196.215.84 -> "hello sock world"
goodbye

But using EM, it doesn't get to the server:


bc_evma ==>
"hello evma world" -> 255.255.255.255">1392255.255.255.255
sent

serv ==>
udp server  1392



I assume that the difference is that I set the SO_BROADCAST option in the
Socket-based code. So I reiterate my original question: is there a way to
set the SO_BROADCAST option on the underlying UDP socket resulting from
EM::open_datagram_socket?


Thanks,

Mark Z.


------------------ Test Code ----------------------
require "socket"
require "eventmachine"

PORT = 1392
BROADCAST = "255.255.255.255"

# Broadcast using UDPSocket.
def bc_sock( broadcast_addr = BROADCAST )
  s = UDPSocket.new
  s.setsockopt( Socket::SOL_SOCKET, Socket::SO_BROADCAST, 1 )
  msg = "hello sock world"
  puts "#{msg.inspect} -> ##{broadcast_addr}"
  s.send( msg, 0, broadcast_addr, PORT )
  s.close
  puts "sent"
end

# Broadcast using EM, datagram socket, and send_datagram.
def bc_evma( broadcast_addr = BROADCAST )
  msg = "hello evma world"
  puts "#{msg.inspect} -> ##{broadcast_addr}"
  EM::run {
    conn = EM::open_datagram_socket( "", 0, Client )
    conn.send_datagram( msg, broadcast_addr, PORT )
    conn.close_connection_after_writing
  }
end

module Client
  def unbind
    puts "sent"
    EM::stop_event_loop
  end
end

# Server that receives a datagram and quits.
def serv
  s = UDPSocket.new
  s.bind( "", PORT )
  puts "udp server  %d" % [PORT]

  msg, sender = s.recvfrom(64)
  puts "#{sender[1]}#{sender[3]} -> #{msg.inspect}"

  s.close
  puts "goodbye"

end