=head1 NAME

Net::SIP::Leg - Wrapper around Socket for sending and receiving SIP packets

=head1 SYNOPSIS

  my $leg = Net::SIP::Leg->new( addr => '192.168.0.2' );
  $leg->deliver( $packet, '192.168.0.5:5060' );

=head1 DESCRIPTION

A B<Leg> wraps the socket which is used to send and receive packets.
It provides ways to strip B<Via> header from incoming packets, to
add B<Via> header to outgoing packets and to add B<Record-Route> header
while forwarding.

It's usually not used directly, but from L<Net::SIP::Dispatcher>.

=head1 CONSTRUCTOR

=over 4

=item new ( %ARGS )

The constructor creates a new object based on the hash %ARGS.
The following keys are used from %ARGS:

=over 8

=item sock

The socket as IO::Socket::INET object. C<addr>, C<port> and C<proto>
will be determined from this object and not from %ARGS.

=item addr

The local address of the socket. If this is given but no port it
will extract port from addr, if it's in the format C<< host:port >>.

=item port

The port of the socket. Defaults to 5060.

=item proto

The connection protocol, e.g. 'tcp' or 'udp'. Defaults to 'udp'.

=item contact

Optional contact information which will be added as B<Record-route> header
to outgoing requests and used within Contact header for 200 Responses to 
INVITE. If not given it will be created based on C<addr>, C<port>
and C<proto>.

=back

If no socket is given with C<sock> it will be created based on C<addr>, C<port>
and C<proto>. If this fails the constructur will C<< die() >>.

The constructor will creeate a uniq branch tag for this leg.

=back

=head1 METHODS

=over 4

=item forward_incoming ( PACKET )

Modifies the L<Net::SIP::Packet> PACKET in-place for forwarding, e.g
strips top B<Via> header in responses, adds B<received> parameter to
top B<Via> header in requests, handles the difference between forwarding
of requests to strict or loose routes and inserts B<Record-Route>
header in requests.

=item forward_outgoing ( PACKET, LEG_IN )

Similar to B<forward_incoming>, but will be called on the outgoing
leg. LEG_IN is the L<Net::SIP::Leg>, where the packet came in (and where
B<forward_incoming> was called). Will add B<Record-Route> header and
remove itself from B<Route>.

=item deliver ( PACKET, ADDR, [ CALLBACK ] )

Delivers L<Net::SIP::Packet> PACKET through the leg C<$self> to ADDR, which
is C<< "ip:port" >>.
Usually this method will be call from within L<Net::SIP::Dispatcher>.

If the packet was received by the other end (which is
only possible to say if a reliable protocol, e.g. 'tcp' was used) it will
call CALLBACK if provided. See B<invoke_callback> in L<Net::SIP::Util> for
the format of callbacks. If the packet could not be delivered CALLBACK
will be invoked with the appropriate errno (C<$!>).

While delivering requests it adds a B<Via> header.

=item receive

Reads a packet from the socket and returns the L<Net::SIP::Packet> PACKET
and the senders ADDR as C<< "ip:port" >>. If reading failed will return C<()>.

=item check_via ( PACKET )

Returns TRUE if the top B<Via> header in the L<Net::SIP::Packet> PACKET contains
the B<branch>-tag from C<$self>, otherwise FALSE. Used to check if the response
came in through the same leg the response was send.

=item add_via ( PACKET )

Adds itself to PACKET as B<Via> header.

=item can_deliver_to ( ADDR|%SPEC )

Returns TRUE if the leg can deliver address specified by ADDR or %SPEC.
ADDR is a hostname which can be prefixed by the protocol ( e.g. C<udp:host> )
and postfixed by the port ( C<host:port>, C<tcp:host:port>,... ).

If the caller has 'proto','addr' and 'port' already as seperate items
it can call the method with %SPEC instead.

Right now it has now way to check if the leg can deliver to a specific
host because it has no access to the routing information of the underlying
OS, so that only proto will be checked.

=item fd

Returns socket of leg. In some special environments (like tests) there might
be legs, which don't have a socket associated. In this case you need to call
B<receive> from L<Net::SIP::Dispatcher> yourself, because it cannot be
called automatically once it receives data on the socket.

=item dump

Returns string containing information about the leg.
Used for debugging.

=back