=head1 NAME

Socket, sockaddr_in, sockaddr_un, inet_aton, inet_ntoa - load the C socket.h defines and structure manipulators 

=head1 SYNOPSIS

    use Socket;

    $proto = getprotobyname('udp');
    socket(Socket_Handle, PF_INET, SOCK_DGRAM, $proto);
    $iaddr = gethostbyname('hishost.com');
    $port = getservbyname('time', 'udp');
    $sin = sockaddr_in($port, $iaddr);
    send(Socket_Handle, 0, 0, $sin);

    $proto = getprotobyname('tcp');
    socket(Socket_Handle, PF_INET, SOCK_STREAM, $proto);
    $port = getservbyname('smtp', 'tcp');
    $sin = sockaddr_in($port,inet_aton("127.1"));
    $sin = sockaddr_in(7,inet_aton("localhost"));
    $sin = sockaddr_in(7,INADDR_LOOPBACK);
    connect(Socket_Handle,$sin);

    ($port, $iaddr) = sockaddr_in(getpeername(Socket_Handle));
    $peer_host = gethostbyaddr($iaddr, AF_INET);
    $peer_addr = inet_ntoa($iaddr);

    $proto = getprotobyname('tcp');
    socket(Socket_Handle, PF_UNIX, SOCK_STREAM, $proto);
    unlink('/var/run/usock');
    $sun = sockaddr_un('/var/run/usock');
    connect(Socket_Handle,$sun);

=head1 DESCRIPTION

This module is just a translation of the C F<socket.h> file.
Unlike the old mechanism of requiring a translated F<socket.ph>
file, this uses the B<h2xs> program (see the Perl source distribution)
and your native C compiler.  This means that it has a 
far more likely chance of getting the numbers right.  This includes
all of the commonly used pound-defines like AF_INET, SOCK_STREAM, etc.

Also, some common socket "newline" constants are provided: the
constants C<CR>, C<LF>, and C<CRLF>, as well as C<$CR>, C<$LF>, and
C<$CRLF>, which map to C<\015>, C<\012>, and C<\015\012>.  If you do
not want to use the literal characters in your programs, then use
the constants provided here.  They are not exported by default, but can
be imported individually, and with the C<:crlf> export tag:

    use Socket qw(:DEFAULT :crlf);

In addition, some structure manipulation functions are available:

=over 4

=item inet_aton HOSTNAME

Takes a string giving the name of a host, and translates that to an
opaque string (if programming in C, struct in_addr). Takes arguments
of both the 'rtfm.mit.edu' type and '18.181.0.24'. If the host name
cannot be resolved, returns undef.  For multi-homed hosts (hosts with
more than one address), the first address found is returned.

For portability do not assume that the result of inet_aton() is 32
bits wide, in other words, that it would contain only the IPv4 address
in network order.

=item inet_ntoa IP_ADDRESS

Takes a string (an opaque string as returned by inet_aton(),
or a v-string representing the four octets of the IPv4 address in
network order) and translates it into a string of the form 'd.d.d.d'
where the 'd's are numbers less than 256 (the normal human-readable
four dotted number notation for Internet addresses).

=item INADDR_ANY

Note: does not return a number, but a packed string.

Returns the 4-byte wildcard ip address which specifies any
of the hosts ip addresses.  (A particular machine can have
more than one ip address, each address corresponding to
a particular network interface. This wildcard address
allows you to bind to all of them simultaneously.)
Normally equivalent to inet_aton('0.0.0.0').

=item INADDR_BROADCAST

Note: does not return a number, but a packed string.

Returns the 4-byte 'this-lan' ip broadcast address.
This can be useful for some protocols to solicit information
from all servers on the same LAN cable.
Normally equivalent to inet_aton('255.255.255.255').

=item INADDR_LOOPBACK

Note - does not return a number.

Returns the 4-byte loopback address.  Normally equivalent
to inet_aton('localhost').

=item INADDR_NONE

Note - does not return a number.

Returns the 4-byte 'invalid' ip address.  Normally equivalent
to inet_aton('255.255.255.255').

=item sockaddr_family SOCKADDR

Takes a sockaddr structure (as returned by pack_sockaddr_in(),
pack_sockaddr_un() or the perl builtin functions getsockname() and
getpeername()) and returns the address family tag.  It will match the
constant AF_INET for a sockaddr_in and AF_UNIX for a sockaddr_un.  It
can be used to figure out what unpacker to use for a sockaddr of
unknown type.

=item sockaddr_in PORT, ADDRESS

=item sockaddr_in SOCKADDR_IN

In a list context, unpacks its SOCKADDR_IN argument and returns an array
consisting of (PORT, ADDRESS).  In a scalar context, packs its (PORT,
ADDRESS) arguments as a SOCKADDR_IN and returns it.  If this is confusing,
use pack_sockaddr_in() and unpack_sockaddr_in() explicitly.

=item pack_sockaddr_in PORT, IP_ADDRESS

Takes two arguments, a port number and an opaque string, IP_ADDRESS
(as returned by inet_aton(), or a v-string).  Returns the sockaddr_in
structure with those arguments packed in with AF_INET filled in.  For
Internet domain sockets, this structure is normally what you need for
the arguments in bind(), connect(), and send(), and is also returned
by getpeername(), getsockname() and recv().

=item unpack_sockaddr_in SOCKADDR_IN

Takes a sockaddr_in structure (as returned by pack_sockaddr_in()) and
returns an array of two elements: the port and an opaque string
representing the IP address (you can use inet_ntoa() to convert the
address to the four-dotted numeric format).  Will croak if the
structure does not have AF_INET in the right place.

=item sockaddr_un PATHNAME

=item sockaddr_un SOCKADDR_UN

In a list context, unpacks its SOCKADDR_UN argument and returns an array
consisting of (PATHNAME).  In a scalar context, packs its PATHNAME
arguments as a SOCKADDR_UN and returns it.  If this is confusing, use
pack_sockaddr_un() and unpack_sockaddr_un() explicitly.
These are only supported if your system has E<lt>F<sys/un.h>E<gt>.

=item pack_sockaddr_un PATH

Takes one argument, a pathname. Returns the sockaddr_un structure with
that path packed in with AF_UNIX filled in. For unix domain sockets, this
structure is normally what you need for the arguments in bind(),
connect(), and send(), and is also returned by getpeername(),
getsockname() and recv().

=item unpack_sockaddr_un SOCKADDR_UN

Takes a sockaddr_un structure (as returned by pack_sockaddr_un())
and returns the pathname.  Will croak if the structure does not
have AF_UNIX in the right place.

=back

=cut
