perl-doc 5.26.1-6 / usr / share / perl / 5.26.1 / IO / Socket.pod

=head1 NAME

IO::Socket - Object interface to socket communications

=head1 SYNOPSIS

    use IO::Socket;

=head1 DESCRIPTION

C<IO::Socket> provides an object interface to creating and using sockets. It
is built upon the L<IO::Handle> interface and inherits all the methods defined
by L<IO::Handle>.

C<IO::Socket> only defines methods for those operations which are common to all
types of socket. Operations which are specified to a socket in a particular 
domain have methods defined in sub classes of C<IO::Socket>

C<IO::Socket> will export all functions (and constants) defined by L<Socket>.

=head1 CONSTRUCTOR

=over 4

=item new ( [ARGS] )

Creates an C<IO::Socket>, which is a reference to a
newly created symbol (see the C<Symbol> package). C<new>
optionally takes arguments, these arguments are in key-value pairs.
C<new> only looks for one key C<Domain> which tells new which domain
the socket will be in. All other arguments will be passed to the
configuration method of the package for that domain, See below.

 NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE

As of VERSION 1.18 all IO::Socket objects have autoflush turned on
by default. This was not the case with earlier releases.

 NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE NOTE

=back

=head1 METHODS

See L<perlfunc> for complete descriptions of each of the following
supported C<IO::Socket> methods, which are just front ends for the
corresponding built-in functions:

    socket
    socketpair
    bind
    listen
    accept
    send
    recv
    peername (getpeername)
    sockname (getsockname)
    shutdown

Some methods take slightly different arguments to those defined in L<perlfunc>
in attempt to make the interface more flexible. These are

=over 4

=item accept([PKG])

perform the system call C<accept> on the socket and return a new
object. The new object will be created in the same class as the listen
socket, unless C<PKG> is specified. This object can be used to
communicate with the client that was trying to connect.

In a scalar context the new socket is returned, or undef upon
failure. In a list context a two-element array is returned containing
the new socket and the peer address; the list will be empty upon
failure.

The timeout in the [PKG] can be specified as zero to effect a "poll",
but you shouldn't do that because a new IO::Select object will be
created behind the scenes just to do the single poll.  This is
horrendously inefficient.  Use rather true select() with a zero
timeout on the handle, or non-blocking IO.

=item socketpair(DOMAIN, TYPE, PROTOCOL)

Call C<socketpair> and return a list of two sockets created, or an
empty list on failure.

=back

Additional methods that are provided are:

=over 4

=item atmark

True if the socket is currently positioned at the urgent data mark,
false otherwise.

    use IO::Socket;

    my $sock = IO::Socket::INET->new('some_server');
    $sock->read($data, 1024) until $sock->atmark;

Note: this is a reasonably new addition to the family of socket
functions, so all systems may not support this yet.  If it is
unsupported by the system, an attempt to use this method will
abort the program.

The atmark() functionality is also exportable as sockatmark() function:

	use IO::Socket 'sockatmark';

This allows for a more traditional use of sockatmark() as a procedural
socket function.  If your system does not support sockatmark(), the
C<use> declaration will fail at compile time.

=item connected

If the socket is in a connected state, the peer address is returned. If the
socket is not in a connected state, undef is returned.

Note that connected() considers a half-open TCP socket to be "in a connected
state".  Specifically, connected() does not distinguish between the
B<ESTABLISHED> and B<CLOSE-WAIT> TCP states; it returns the peer address,
rather than undef, in either case.  Thus, in general, connected() cannot
be used to reliably learn whether the peer has initiated a graceful shutdown
because in most cases (see below) the local TCP state machine remains in
B<CLOSE-WAIT> until the local application calls shutdown() or close();
only at that point does connected() return undef.

The "in most cases" hedge is because local TCP state machine behavior may
depend on the peer's socket options. In particular, if the peer socket has
SO_LINGER enabled with a zero timeout, then the peer's close() will generate
a RST segment, upon receipt of which the local TCP transitions immediately to
B<CLOSED>, and in that state, connected() I<will> return undef.

=item protocol

Returns the numerical number for the protocol being used on the socket, if
known. If the protocol is unknown, as with an AF_UNIX socket, zero
is returned.

=item sockdomain

Returns the numerical number for the socket domain type. For example, for
an AF_INET socket the value of &AF_INET will be returned.

=item sockopt(OPT [, VAL])

Unified method to both set and get options in the SOL_SOCKET level. If called
with one argument then getsockopt is called, otherwise setsockopt is called.

=item getsockopt(LEVEL, OPT)

Get option associated with the socket. Other levels than SOL_SOCKET
may be specified here.

=item setsockopt(LEVEL, OPT, VAL)

Set option associated with the socket. Other levels than SOL_SOCKET
may be specified here.

=item socktype

Returns the numerical number for the socket type. For example, for
a SOCK_STREAM socket the value of &SOCK_STREAM will be returned.

=item timeout([VAL])

Set or get the timeout value (in seconds) associated with this socket.
If called without any arguments then the current setting is returned. If
called with an argument the current setting is changed and the previous
value returned.

=back

=head1 LIMITATIONS

On some systems, for an IO::Socket object created with new_from_fd(),
or created with accept() from such an object, the protocol(),
sockdomain() and socktype() methods may return undef.

=head1 SEE ALSO

L<Socket>, L<IO::Handle>, L<IO::Socket::INET>, L<IO::Socket::UNIX>

=head1 AUTHOR

Graham Barr.  atmark() by Lincoln Stein.  Currently maintained by the
Perl Porters.  Please report all bugs to <perlbug@perl.org>.

=head1 COPYRIGHT

Copyright (c) 1997-8 Graham Barr <gbarr@pobox.com>. All rights reserved.
This program is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.

The atmark() implementation: Copyright 2001, Lincoln Stein <lstein@cshl.org>.
This module is distributed under the same terms as Perl itself.
Feel free to use, modify and redistribute it as long as you retain
the correct attribution.

=cut