Monky Python has asked for the wisdom of the Perl Monks concerning the following question:

tried to read data from a multicast port but I don't get any data.
The connection is established and the program seems to wait for data, but even if another process
sends some data to this address nothing happens.
I already checked with some Java and a C program that the server process is working correctly.
Any ideas?

my $udpcon  =  "227.50.49.48:9897";

my $sock1 = IO::Socket::INET->new(Proto=>'udp',PeerAddr=>$udpcon);
die "Can't bind to $udpcon: $!\n" unless $sock1;

my $data;
my $len;

print "waiting for data on $udpcon ...\n";

while (1) {
  $len = recv($sock1, $data, 10, 0);
  print $len."\n";

}

Replies are listed 'Best First'.
Re: reading from multicast socket
by rasta (Hermit) on Nov 12, 2002 at 08:56 UTC
    There are a few mistakes in your code:

    1. You should specify local port and SO_BROADCAST flag
    2. Use $@ to output error message from new()
    3. recv returns the addres of sender

    So, here is my code:
    my $sock1 = IO::Socket::INET->new(
    LocalPort  => 9897,
    PeerAddr  => inet_ntoa(INADDR_BROADCAST), # you may use '127.0.0.1
+' for local host
    Proto     => 'udp',
    LocalAddr => '127.0.0.1',
    Broadcast => 1 );

die "Can't bind to $udpcon: $@\n" unless $sock1;

my $data;
my $addr;

print "waiting for data on $udpcon ...\n";

while (1) {
  $addr = recv($sock1, $data, 10, 0);
}

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Re: reading from multicast socket
by Chief of Chaos (Friar) on Nov 12, 2002 at 10:58 UTC
    Hi Monky,
    it is possible to use the 'IO::Socket::Multicast'-module.
    This may be a little bit easier.

    e.g.:
     #!/usr/bin/perl
 # client

 use strict;
 use IO::Socket::Multicast;

 use constant GROUP => '227.50.49.48';
 use constant PORT  => '9897';

 my $sock = IO::Socket::INET->new(Proto=>'udp',LocalPort=>PORT);
 $sock->mcast_add(GROUP) || die "Couldn't set group: $!\n";

 while (1) {
   my $data;
   next unless $sock->recv($data,1024);
   print $data;
 }

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Re: reading from multicast socket
by amphiplex (Monk) on Nov 12, 2002 at 08:57 UTC
    Hi !

    shouldn't you be using LocalAddr instead of RemoteAddr ?

    ---- amphiplex

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