=head1 NAME

Net::SIP::StatelessProxy - Simple implementation of a stateless proxy

=head1 SYNOPSIS

..

=head1 DESCRIPTION

This package implements a simple stateless SIP proxy.
Basic idea is that the proxy has either a single or two legs
and that the packets are exchanged between those legs,
e.g. packets incoming on one leg will be forwarded through the
other leg.

Because this is a stateless proxy no retransmits will be done
by the proxy.

If the proxy should work as a registrar too it should be put
after a L<Net::SIP::Registrar> in a L<Net::SIP::ReceiveChain>.

While forwarding the proxy will be insert itself into the packet,
e.g. it will add B<Via> and B<Record-Route> header while
forwarding requests.

Additionally it will rewrite the B<Contact> header while forwarding
packets (see below), e.g. if the B<Contact> header points to some client
it will rewrite it, so that it points to the proxy and if it
already points to the proxy it will rewrite it back so that it again
points to the client.

=head1 CONSTRUCTOR

=over 4

=item new ( %ARGS )

Creates a new stateless proxy. With %ARGS the behavior can be
influenced:

=over 8

=item dispatcher

The L<Net::SIP::Dispatcher> object managing the proxy.

=item rewrite_contact

Callback which is used in rewriting B<Contact> headers.
If one puts user@host in it or if it is called with B<force_rewrite> then it
should rewrite it and if one puts something without '@' it should try to rewrite
it back or return B<()> if it cannot be rewritten back.

A working default implementation is provided.
If you want to implement your own: the callbacks gets the arguments B<contact>,
B<incoming_leg> and B<outgoing_leg> and B<force_rewrite>.
For rewriting a contact of user@host the legs will be L<Net::SIP::Leg> objects.
For rewriting the contact back B<outgoing_leg> can be either a leg object and
you should check if it is the expected leg. Or it is a scalar reference which
you should fill with the leg extracted from the contact.
The function should return the new contact or nothing if there was nothing to
rewrite or the rewrite failed.

Note that some servers apply length limitiations to the contact so the function
should not return too long values.

=item rewrite_crypt

If you want to have your own encryption for the rewritten contact you should
defined a subroutine here, which gets C<data> as the first and C<dir> as the
second parameter and should return the de/encrypted data. If C<dir> is +1 it
should encrypt and on -1 it should decrypt.
The optional third argument C<add2mac> should be included in calculation and
verification of the MAC.
The function should return the encrypted/decrypted data or undef if decryption
failed because the MAC did not match.

If not defined, then RC4 will be used with a (pseudo)random key, 4 byte
(pseudo)random seed and 4 byte MAC (md5) over seed and data.

=item nathelper

Optional Net::SIP::NATHelper::* object. When given it will be
used to do NAT, e.g. if the incoming and outgoing legs are different
it will rewrite the SDP bodies to use local sockets and the nathelper
will transfer the RTP data between the local and the original
sockets.

=item force_rewrite

Usually the contact header will only be rewritten, if the incoming and
outgoing leg are different. With this option one can force the rewrite,
even if they are the same.

=back

=back

=head1 METHODS

=over 4

=item receive ( PACKET, LEG, FROM )

PACKET is the incoming packet,
LEG is the L<Net::SIP::Leg> where the packet arrived and FROM
is the C<< "ip:port" >> of the sender.

Called from the dispatcher on incoming packets. The packet
will be rewritten (C<Via> and C<Record-Route> headers added,
B<Contact> modified) and then the packet will be forwarded.

For requests it can determine the target of the forwarded
packet by looking at the route or if no route it looks at
the URI. For responses it looks at the next B<Via> header.

=item do_nat ( PACKET, INCOMING_LEG, OUTGOING_LEG )

This will be called from B<receive> while forwarding data.
If B<nathelper> is defined it will be used to rewrite SDP bodies
and update nathelpers internal states to forward RTP data.

Return values are like B<forward_outgoing> in L<Net::SIP::Leg>, e.g.
it will return C<< [code,text] >> on error or C<()> on success,
where success can be that the packet was rewritten or that there
was no need to touch it.

=back

=head1 UNDOCUMENTED METHODS

=over 4

=item idside2hash

=back