[ruby-talk:18925] RE: IP multicast with UDPSocket

 
Something I threw together a few weeks ago. It has only been tested using
Ruby 1.7.1 on Win32, but It should work on the other platforms as well. You
may have to take out the definition of the constants since they should
already be defined in socket.c. There are some some differences in the C
headers #defines of these constants, but I did not have time to look into
this and fix it on Windows. 
 
enjoy...
 
- Will
 
<SNIP filename='multicast.rb' >

require 'socket'
 
#struct ip_mreq {
#        struct in_addr  imr_multiaddr;  /* IP multicast address of group */
#        struct in_addr  imr_interface;  /* local IP address of interface */
#};
 

class MulticastSocket < UDPSocket
 
 # Some constants that are not set in Win32 version of socket.c
 IPPROTO_IP = 0
 IPPROTO_UDP = 17
 IP_DROP_MEMBERSHIP = 6
 
 def convAddr(a)
  h = nil
  case a
  when String
   h = a.split('.').collect! { |b| b.to_i }.pack('CCCC')
 
  when Array
   h = a.pack('CCCC')
 
  else
   raise "Bad address"
  end
  h
 end
 private :convAddr
 
 def addMembership(mcaddr)
  mreq = convAddr(mcaddr) + Socket.gethostbyname(Socket.gethostname)[3]
  setsockopt(IPPROTO_IP, Socket::IP_ADD_MEMBERSHIP, mreq)
 end
 
 def dropMembership(mcaddr)
  mreq = convAddr(mcaddr) + Socket.gethostbyname(Socket.gethostname)[3]
  setsockopt(IPPROTO_IP, IP_DROP_MEMBERSHIP, mreq)
 end
 
 def setMCTTL(ttl)
  setsockopt(IPPROTO_IP, Socket::IP_MULTICAST_TTL, ttl)
 end
 
 def setMCLoop(loop)
  setsockopt(IPPROTO_IP, Socket::IP_MULTICAST_LOOP, loop)
 end
 
 def setMCInterface(int)
  host = Socket.gethostbyname(int)[3]
  setsockopt(IPPROTO_IP, Socket::IP_MULTICAST_IF, host)
 end
 
end
 
if $0 == __FILE__
 
 $port = 1900
 $addr = '239.192.0.1'
 
 sock = MulticastSocket.open
 sock.bind(Socket.gethostname, $port)
 sock.addMembership($addr)
  
 thread = Thread.start do
  2.times { p sock.recvfrom(8000) }
 end
 
 sock.send('Hello', 0, $addr, $port)
 sock.send('There', 0, $addr, $port)
 
 thread.join
 sock.dropMembership($addr)
end
 

</SNIP>

-----Original Message-----
From: Nat Pryce [mailto:[e-mail]]
Sent: Tuesday, July 31, 2001 5:09 AM
To: [e-mail]
Subject: [ruby-talk:18883] IP multicast with UDPSocket


Does anyone have example code for joining/leaving multicast groups using the
UDPSocket?
 
Also, how is it possible to write this in a platform independent manner?  As
far as I can tell, the API for setting socket options seems to be completely
platform dependent.  It is also hard to code to, because you have to build
strings of binary data that contain valid C structures used by the OS APIs.
Would there be interest in code to replace or wrap setsockopt/getsockopt
with methods and attribute accessors?  
 
For example:
 
socket = UDPSocket.new
socket.add_membership "240.212.100.200"  # or whatever a valid IP group
number is
socket.ip_multicast_ttl = Socket::TTL_LOCAL_NETWORK
socket.ip_multicast_loopback = false
socket.sol_reuse_address = true
socket.bind( 15630 )
 
Or:
 
socket = TCPSocket.new( 'www.b13media.com', 80 )
socket.sol_sndbuf = 512
socket.sol_rcvbuf = 4096
 
Would this be a useful RCR?
 
Cheers,
    Nat.