=head1 NAME

Net::SIP::Packet - handling of SIP packets

=head1 SYNOPSIS

  use Net::SIP::Packet;
  use Net::SIP::Request;
  use Net::SIP::Response;
  my $pkt = eval { Net::SIP::Packet->new( $sip_string ) }
    or die "invalid SIP packet";
  $pkt->get_header( 'call-id' ) || die "no call-id";
  $pkt->set_header( via => \@via );
  print $pkt->as_string;

=head1 DESCRIPTION

This module implements the parsing, manipulation and creation of SIP
packets according to RFC3261.

NET::SIP::Packet's objects can be created by parsing a string containing
the SIP packet or by constructing it from parts, e.g. header keys and
values, body, method+URI (requests) or code+text (responses).

All parts can be manipulated and finally the string representation of
the manipulated packet can be (re)created.

For dealing with requests and responses directly usually the subclasses
L<Net::SIP::Request> or L<Net::SIP::Response> will be used instead.

=head1 EXAMPLES

  # create packet from string
  my $invite = Net::SIP::Packet->new(  <<'EOS' );
  INVITE sip:you@example.com SIP/2.0
  From: <sip:me@example.com>
  To: <sip:you@example.com>
  ...
  EOS

  # show and manipulate some header
  print "callid=".$invite->get_header( 'call-id' )."\n";
  print "route=".join( ",", $invite->get_header( 'route' ))."\n";
  $invite->set_header( 'via' => [ $via1,$via2,.. ] );

  # get resulting string representation
  print $invite->as_string;

  # create packet from parts
  my $resp = Net::SIP::Packet->new(
	200, 'Ok',
	{ to => '<sip:you@example.com>', from => '<sip:me@example.com>',.. }
	Net::SIP::SDP->new(...)
  );

  # and get the packet as string
  print $resp->as_string;

=head1 CONSTRUCTOR

=over 4

=item new ( STRING | @PARTS | HASH )

This is the default constructor. Depending on the number of arguments branches
into B<new_from_string> or B<new_from_parts> or just creates the object directly
from the given HASH.

=item new_from_string ( STRING )

Interprets STRING as a SIP request or response and creates L<Net::SIP::Request>
or L<Net::SIP::Response> object accordingly (these classes must have been
loaded already).
Will die() if it cannot parse the string as a SIP packet.

=item new_from_parts ( CODE|METHOD, TEXT|URI, \%HEADER|\@HEADER, [ BODY ] )

If CODE|METHOD is numeric a L<Net::SIP::Response> object will be created with
the response code CODE and the text TEXT.
Otherwise a L<Net::SIP::Request> object will be created with the method METHOD
and the uri URI.
Note that the Request or Response class need to be loaded already.

Header data can be given as a hash %HEADER or array @HEADER reference.
In case of a hash the key is the SIP field name and the value as either a string
or a \@list of strings. The fields on the resulting SIP packet
will be sorted by name of the fields and fields with multiple values will be
created as seperat lines.

If the header is given as an array the elements of the array are C<< [ key => value ] >>
pairs where the keys are the field names and the values are strings or \@list of
strings. Each pair will result in a single line in the SIP header.
If the value was a list reference the values in the list will be concatened by ','.
The order of the fields in the resulting SIP packet will be the same as in
the array.

The BODY is optional and can be given either as a string or as an reference to an
object which has a method B<as_string>, like L<Net::SIP::SDP>. If the BODY is an
object which has a method B<content_type> it will set the C<content-type> header
of the SIP object based on the result of C<< BODY->content_type >> unless a
C<content-type> header was explicitly given.

=item _new_request | _new_response

These work like C<new> but assign the new object to the subclasses
C<Net::SIP::Request> resp. C<Net::SIP:.Response>. They are not intended to be
used directly but only for redefining for using different subclasses when
subclassing C<Net::SIP::Packet>.

=back

=head1 METHODS

=over 4

=item is_request

Returns TRUE if the SIP packet is a request, otherwise FALSE.

=item is_response

Returns TRUE if the SIP packet is a response, otherwise FALSE.

=item tid

Returns a transaction ID created from the sequence number in
the C<CSeq> header and the C<Call-Id> header.
All packets with the same tid belong to the same transaction.

=item cseq

Returns C<CSeq> header. Short for C<< $self->get_header( 'cseq' ) >>.

=item callid

Returns C<Call-Id> header. Short for C<< $self->get_header( 'call-id' ) >>.

=item get_header ( [ NAME ] )

If NAME is given it returns the SIP header for NAME. If no header
exists returns (). If there is only one value for the header returns
this value. In case of multiple values it returns a @list of all
values, but if C<wantarray> says, that the caller expects only a
single value it will C<croak()>.

If no NAME is given it will return a reference to a hash which contains
all fields and has the format described in B<new_from_parts>.

=item add_header ( NAME, VAL )

Adds the header at the end of the SIP header.
VAL can be a string or a reference to a list of strings.

=item insert_header ( NAME, VAL )

Like B<add_header>, but the lines will be added on top of the header.

=item del_header ( NAME )

Delete all lines from header where the field name is NAME.

=item set_header ( NAME, VAL )

Replaces an existing header, like B<del_header> followed by B<add_header>.

=item set_body ( VAL )

Sets body to VAL, which can be string or object. The handling for body
objects see B<new_from_parts>.

=item as_string

Returns string representation of SIP packet.

=item dump ( [ LEVEL ] )

Returns dump of packet as string for debugging. The higher LEVEL
is the more details one gets. At the moment a LEVEL of 0 gets
a one-line summary and the rest the result from B<as_string>.

=item as_parts

Returns Array with CODE|METHOD, TEXT|URI, \@HEADER and BODY like used
in B<new_from_parts>.

=item sdp_body

Returns body as L<Net::SIP::SDP> object if there is a body and the
content-type is 'application/sdp' or empty.

If body contains invalid SDP it raises an exception (e.g. die()).

=back

=head2 UNDOCUMENTED METHODS

=over 4

=item get_header_hashval ( [ NAME ] )

=item scan_header ( @ARG )

=item clone

=back