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MAN page from CentOS 8 perl-IO-1.40-452.module_el8.4.0+646+45e06e4a.x86_64.rpm

IO::Socket

Section: Perl Programmers Reference Guide (3pm)
Updated: 2021-01-20
Index 

NAME

IO::Socket - Object interface to socket communications 

SYNOPSIS

    use IO::Socket;
 

DESCRIPTION

"IO::Socket" provides an object interface to creating and using sockets. Itis built upon the IO::Handle interface and inherits all the methods definedby IO::Handle.

"IO::Socket" only defines methods for those operations which are common to alltypes of socket. Operations which are specified to a socket in a particular domain have methods defined in sub classes of "IO::Socket"

"IO::Socket" will export all functions (and constants) defined by Socket. 

CONSTRUCTOR

new ( [ARGS] )
Creates an "IO::Socket", which is a reference to anewly created symbol (see the "Symbol" package). "new"optionally takes arguments, these arguments are in key-value pairs."new" only looks for one key "Domain" which tells new which domainthe socket will be in. All other arguments will be passed to theconfiguration 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 onby default. This was not the case with earlier releases.

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

 

METHODS

See perlfunc for complete descriptions of each of the followingsupported "IO::Socket" methods, which are just front ends for thecorresponding built-in functions:

    socket    socketpair    bind    listen    accept    sockname (getsockname)    shutdown

Some methods take slightly different arguments to those defined in perlfuncin attempt to make the interface more flexible. These are

accept([PKG])
perform the system call "accept" on the socket and return a newobject. The new object will be created in the same class as the listensocket, unless "PKG" is specified. This object can be used tocommunicate with the client that was trying to connect.

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

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 becreated behind the scenes just to do the single poll. This ishorrendously inefficient. Use rather true select() with a zerotimeout on the handle, or non-blocking IO.

socketpair(DOMAIN, TYPE, PROTOCOL)
Call "socketpair" and return a list of two sockets created, or anempty list on failure.

Additional methods that are provided are:

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 socketfunctions, so all systems may not support this yet. If it isunsupported by the system, an attempt to use this method willabort 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 proceduralsocket function. If your system does not support sockatmark(), the"use" declaration will fail at compile time.

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

Note that connected() considers a half-open TCP socket to be ``in a connectedstate''. Specifically, connected() does not distinguish between theESTABLISHED and CLOSE-WAIT TCP states; it returns the peer address,rather than undef, in either case. Thus, in general, connected() cannotbe used to reliably learn whether the peer has initiated a graceful shutdownbecause in most cases (see below) the local TCP state machine remains inCLOSE-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 maydepend on the peer's socket options. In particular, if the peer socket hasSO_LINGER enabled with a zero timeout, then the peer's close() will generatea RST segment, upon receipt of which the local TCP transitions immediately toCLOSED, and in that state, connected() will return undef.

send(MSG, [, FLAGS [, TO ] ])
Like the built-in send(), except that:
*
"FLAGS" is optional and defaults to 0, and
*
after a successful send with "TO", further calls to send() on anunconnected socket without "TO" will send to the same address, and"TO" will be used as the result of peername().
recv(BUF, LEN, [,FLAGS])
Like the built-in recv(), except that:
*
"FLAGS" is optional and defaults to 0, and
*
the cached value returned by peername() is updated with the result ofrecv().
peername
Returns the cached peername, possibly set by recv() or send() above.If not otherwise set returns (and caches) the result of getpeername().
protocol
Returns the numerical number for the protocol being used on the socket, ifknown. If the protocol is unknown, as with an AF_UNIX socket, zerois returned.
sockdomain
Returns the numerical number for the socket domain type. For example, foran AF_INET socket the value of &AF_INET will be returned.
sockopt(OPT [, VAL])
Unified method to both set and get options in the SOL_SOCKET level. If calledwith one argument then getsockopt is called, otherwise setsockopt is called.
getsockopt(LEVEL, OPT)
Get option associated with the socket. Other levels than SOL_SOCKETmay be specified here.
setsockopt(LEVEL, OPT, VAL)
Set option associated with the socket. Other levels than SOL_SOCKETmay be specified here.
socktype
Returns the numerical number for the socket type. For example, fora SOCK_STREAM socket the value of &SOCK_STREAM will be returned.
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. Ifcalled with an argument the current setting is changed and the previousvalue returned.
 

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. 

SEE ALSO

Socket, IO::Handle, IO::Socket::INET, IO::Socket::UNIX 

AUTHOR

Graham Barr. atmark() by Lincoln Stein. Currently maintained by thePerl Porters. Please report all bugs to <perlbugAATTperl.org>. 

COPYRIGHT

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

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


 

Index

NAME
SYNOPSIS
DESCRIPTION
CONSTRUCTOR
METHODS
LIMITATIONS
SEE ALSO
AUTHOR
COPYRIGHT

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