plucky (3) IO::Socket::Multicast.3pm.gz

Provided by: libio-socket-multicast-perl_1.12-3build5_amd64 bug

NAME

       IO::Socket::Multicast - Send and receive multicast messages

SYNOPSIS

         use IO::Socket::Multicast;

         # create a new UDP socket ready to read datagrams on port 1100
         my $s = IO::Socket::Multicast->new(LocalPort=>1100);

         # Add a multicast group
         $s->mcast_add('225.0.1.1');

         # Add a multicast group to eth0 device
         $s->mcast_add('225.0.0.2','eth0');

         # now receive some multicast data
         $s->recv($data,1024);

         # Drop a multicast group
         $s->mcast_drop('225.0.0.1');

         # Set outgoing interface to eth0
         $s->mcast_if('eth0');

         # Set time to live on outgoing multicast packets
         $s->mcast_ttl(10);

         # Turn off loopbacking
         $s->mcast_loopback(0);

         # Multicast a message to group 225.0.0.1
         $s->mcast_send('hello world!','225.0.0.1:1200');
         $s->mcast_set('225.0.0.2:1200');
         $s->mcast_send('hello again!');

DESCRIPTION

       The IO::Socket::Multicast module subclasses IO::Socket::INET to enable you to manipulate multicast
       groups.  With this module (and an operating system that supports multicasting), you will be able to
       receive incoming multicast transmissions and generate your own outgoing multicast packets.

       This module requires IO::Interface version 0.94 or higher.

   INTRODUCTION
       Multicasting is designed for streaming multimedia applications and for conferencing systems in which one
       transmitting machines needs to distribute data to a large number of clients.

       IP addresses in the range 224.0.0.0 and 239.255.255.255 are reserved for multicasting.  These addresses
       do not correspond to individual machines, but to multicast groups.  Messages sent to these addresses will
       be delivered to a potentially large number of machines that have registered their interest in receiving
       transmissions on these groups.  They work like TV channels.  A program tunes in to a multicast group to
       receive transmissions to it, and tunes out when it no longer wishes to receive the transmissions.

       To receive transmissions from a multicast group, you will use IO::Socket::Multicast->new() to create a
       UDP socket and bind it to a local network port.  You will then subscribe one or more multicast groups
       using the mcast_add() method.  Subsequent calls to the standard recv() method will now receive messages
       incoming messages transmitted to the subscribed groups using the selected port number.

       To send transmissions to a multicast group, you can use the standard send() method to send messages to
       the multicast group and port of your choice.  The mcast_set() and mcast_send() methods are provided as
       convenience functions.  Mcast_set() will set a default multicast destination for messages which you then
       send with mcast_send().

       To set the number of hops (routers) that outgoing multicast messages will cross, call mcast_ttl().  To
       activate or deactivate the looping back of multicast messages (in which a copy of the transmitted
       messages is received by the local machine), call mcast_loopback().

   CONSTRUCTORS
       $socket = IO::Socket::Multicast->new([LocalPort=>$port,...])
           The new() method is the constructor for the IO::Socket::Multicast class.  It takes the same arguments
           as IO::Socket::INET, except that the Proto argument, rather than defaulting to "tcp", will default to
           "udp", which is more appropriate for multicasting.

           To create a UDP socket suitable for sending outgoing multicast messages, call new() without arguments
           (or with "Proto=>'udp'").  To create a UDP socket that can also receive incoming multicast
           transmissions on a specific port, call new() with the LocalPort argument.

           If you plan to run the client and server on the same machine, you may wish to set the IO::Socket
           ReuseAddr argument to a true value.  This allows multiple multicast sockets to bind to the same
           address.

   METHODS
       $success = $socket->mcast_add($multicast_address [,$interface])
           The mcast_add() method will add the provided multicast address to the list of subscribed multicast
           groups.  The address may be provided either as a dotted-quad decimal, or as a packed IP address (such
           as produced by the inet_aton() function).  On success, the method will return a true value.

           The optional $interface argument can be used to specify on which network interface to listen for
           incoming multicast messages.  If the IO::Interface module is installed, you may use the device name
           for the interface (e.g. "tu0").  Otherwise, you must use the IP address of the desired network
           interface.  Either dotted quad form or packed IP address is acceptable.  If no interface is
           specified, then the multicast group is joined on INADDR_ANY, meaning that multicast transmissions
           received on any of the host's network interfaces will be forwarded to the socket.

           Note that mcast_add() operates on the underlying interface(s) and not on the socket. If you have
           multiple sockets listening on a port, and you mcast_add() a group to one of those sockets,
           subsequently all the sockets will receive mcast messages on this group. To filter messages that can
           be received by a socket so that only those sent to a particular multicast address are received, pass
           the LocalAddr option to the socket at the time you create it:

             my $socket = IO::Socket::Multicast->new(LocalPort=>2000,
                                                     LocalAddr=>226.1.1.2',
                                                     ReuseAddr=>1);
             $socket->mcast_add('226.1.1.2');

           By combining this technique with IO::Select, you can write applications that listen to multiple
           multicast groups and distinguish which group a message was addressed to by identifying which socket
           it was received on.

       $success = $socket->mcast_drop($multicast_address)
           This reverses the action of mcast_add(), removing the indicated multicast address from the list of
           subscribed groups.

       $loopback = $socket->mcast_loopback
       $previous = $socket->mcast_loopback($new)
           The mcast_loopback() method controls whether the socket will receive its own multicast transmissions
           (default yes).  Called without arguments, the method returns the current state of the loopback flag.
           Called with a boolean argument, the method will set the loopback flag, and return its previous value.

       $ttl = $socket->mcast_ttl
       $previous = $socket->mcast_ttl($new)
           The mcast_ttl() method examines or sets the time to live (TTL) for outgoing multicast messages.  The
           TTL controls the numbers of routers the packet can cross before being expired.  The default TTL is 1,
           meaning that the message is confined to the local area network.  Values between 0 and 255 are valid.

           Called without arguments, this method returns the socket's current TTL.  Called with a value, this
           method sets the TTL and returns its previous value.

       $interface = $socket->mcast_if
       $previous = $socket->mcast_if($new)
           By default, the OS will pick the network interface to use for outgoing multicasts automatically.  You
           can control this process by using the mcast_if() method to set the outgoing network interface
           explicitly.  Called without arguments, returns the current interface.  Called with the name of an
           interface, sets the outgoing interface and returns its previous value.

           You can use the device name for the interface (e.g. "tu0") if the IO::Interface module is present.
           Otherwise, you must use the interface's dotted IP address.

           NOTE: To set the interface used for incoming multicasts, use the mcast_add() method.

       $dest = $socket->mcast_dest
       $previous = $socket->mcast_dest($new)
           The mcast_dest() method is a convenience function that allows you to set the default destination
           group for outgoing multicasts.  Called without arguments, returns the current destination as a packed
           binary sockaddr_in data structure.  Called with a new destination address, the method sets the
           default destination and returns the previous one, if any.

           Destination addresses may be provided as packed sockaddr_in structures, or in the form
           "XX.XX.XX.XX:YY" where the first part is the IP address, and the second the port number.

       $bytes = $socket->mcast_send($data [,$dest])
           Mcast_send() is a convenience function that simplifies the sending of multicast messages.  $data is
           the message contents, and $dest is an optional destination group.  You can use either the dotted IP
           form of the destination address and its port number, or a packed sockaddr_in structure.  If the
           destination is not supplied, it will default to the most recent value set in mcast_dest() or a
           previous call to mcast_send().

           The method returns the number of bytes successfully queued for delivery.

           As a side-effect, the method will call mcast_dest() to remember the destination address.

           Example:

             $socket->mcast_send('Hi there group members!','225.0.1.1:1900') || die;
             $socket->mcast_send("How's the weather?") || die;

           Note that you may still call IO::Socket::Multicast->new() with a PeerAddr, and IO::Socket::INET will
           perform a connect(), creating a default destination for calls to send().

EXAMPLE

       The following is an example of a multicast server.  Every 10 seconds it transmits the current time and
       the list of logged-in users to the local network using multicast group 226.1.1.2, port 2000 (these are
       chosen arbitrarily).

        #!/usr/bin/perl
        # server
        use strict;
        use IO::Socket::Multicast;

        use constant DESTINATION => '226.1.1.2:2000';
        my $sock = IO::Socket::Multicast->new(Proto=>'udp',PeerAddr=>DESTINATION);

        while (1) {
          my $message = localtime;
          $message .= "\n" . `who`;
          $sock->send($message) || die "Couldn't send: $!";
        } continue {
          sleep 10;
        }

       This is the corresponding client.  It listens for transmissions on group 226.1.1.2, port 2000, and echoes
       the messages to standard output.

        #!/usr/bin/perl
        # client

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

        use constant GROUP => '226.1.1.2';
        use constant PORT  => '2000';

        my $sock = IO::Socket::Multicast->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;
        }

   EXPORT
       None by default.  However, if you wish to call mcast_add(), mcast_drop(), mcast_if(), mcast_loopback(),
       mcast_ttl, mcast_dest() and mcast_send() as functions you may import them explicitly on the use line or
       by importing the tag ":functions".

   BUGS
       The mcast_if(), mcast_ttl() and mcast_loopback() methods will cause a crash on versions of Linux earlier
       than 2.2.0 because of a kernel bug in the implementation of the multicast socket options.

AUTHOR

       Lincoln Stein, lstein@cshl.org.

       This module is distributed under the same terms as Perl itself.

SEE ALSO

       perl(1), IO::Socket(3), IO::Socket::INET(3).