IO::Socket(3p) Perl Programmers Reference Guide IO::Socket(3p) #
IO::Socket(3p) Perl Programmers Reference Guide IO::Socket(3p)
NNAAMMEE #
IO::Socket - Object interface to socket communications
SSYYNNOOPPSSIISS #
use strict;
use warnings;
use IO::Socket qw(AF_INET AF_UNIX);
# create a new AF_INET socket
my $sock = IO::Socket->new(Domain => AF_INET);
# which is the same as
$sock = IO::Socket::INET->new();
# create a new AF_UNIX socket
$sock = IO::Socket->new(Domain => AF_UNIX);
# which is the same as
$sock = IO::Socket::UNIX->new();
DDEESSCCRRIIPPTTIIOONN #
"IO::Socket" provides an object-oriented, IO::Handle-based interface to
creating and using sockets via Socket, which provides a near one-to-one
interface to the C socket library.
"IO::Socket" is a base class that really only defines methods for those
operations which are common to all types of sockets. Operations which are
specific to a particular socket domain have methods defined in subclasses
of "IO::Socket". See IO::Socket::INET, IO::Socket::UNIX, and
IO::Socket::IP for examples of such a subclass.
"IO::Socket" will export all functions (and constants) defined by Socket.
CCOONNSSTTRRUUCCTTOORR AARRGGUUMMEENNTTSS #
Given that "IO::Socket" doesn't have attributes in the traditional sense,
the following arguments, rather than attributes, can be passed into the
constructor.
Constructor arguments should be passed in "Key => 'Value'" pairs.
The only required argument is "Domain" in IO::Socket.
BBlloocckkiinngg my $sock = IO::Socket->new(…, Blocking => 1); $sock = IO::Socket->new(…, Blocking => 0);
If defined but false, the socket will be set to non-blocking mode. If not
specified it defaults to 1 (blocking mode).
DDoommaaiinn my $sock = IO::Socket->new(Domain => IO::Socket::AF_INET); $sock = IO::Socket->new(Domain => IO::Socket::AF_UNIX);
The socket domain will define which subclass of "IO::Socket" to use. The
two options available along with this distribution are "AF_INET" and
“AF_UNIX”. #
"AF_INET" is for the internet address family of sockets and is handled
via IO::Socket::INET. "AF_INET" sockets are bound to an internet address
and port.
"AF_UNIX" is for the unix domain socket and is handled via
IO::Socket::UNIX. "AF_UNIX" sockets are bound to the file system as their
address name space.
This argument is rreeqquuiirreedd. All other arguments are optional.
LLiisstteenn my $sock = IO::Socket->new(…, Listen => 5);
Listen should be an integer value or left unset.
If provided, this argument will place the socket into listening mode. New
connections can then be accepted using the "accept" in IO::Socket method.
The value given is used as the listen(2) queue size.
If the "Listen" argument is given, but false, the queue size will be set
to 5.
TTiimmeeoouutt my $sock = IO::Socket->new(…, Timeout => 5);
The timeout value, in seconds, for this socket connection. How exactly
this value is utilized is defined in the socket domain subclasses that
make use of the value.
TTyyppee my $sock = IO::Socket->new(…, Type => IO::Socket::SOCK_STREAM);
The socket type that will be used. These are usually "SOCK_STREAM",
"SOCK_DGRAM", or "SOCK_RAW". If this argument is left undefined an
attempt will be made to infer the type from the service name.
For example, you'll usually use "SOCK_STREAM" with a "tcp" connection and
"SOCK_DGRAM" with a "udp" connection.
CCOONNSSTTRRUUCCTTOORRSS #
"IO::Socket" extends the IO::Handle constructor.
nneeww my $sock = IO::Socket->new();
# get a new IO::Socket::INET instance
$sock = IO::Socket->new(Domain => IO::Socket::AF_INET);
# get a new IO::Socket::UNIX instance
$sock = IO::Socket->new(Domain => IO::Socket::AF_UNIX);
# Domain is the only required argument
$sock = IO::Socket->new(
Domain => IO::Socket::AF_INET, # AF_INET, AF_UNIX
Type => IO::Socket::SOCK_STREAM, # SOCK_STREAM, SOCK_DGRAM, ...
Proto => 'tcp', # 'tcp', 'udp', IPPROTO_TCP, IPPROTO_UDP
# and so on...
);
Creates an "IO::Socket", which is a reference to a newly created symbol
(see the Symbol package). "new" optionally takes arguments, these
arguments are defined in "CONSTRUCTOR ARGUMENTS" in IO::Socket.
Any of the "CONSTRUCTOR ARGUMENTS" in IO::Socket may be passed to the
constructor, but if any arguments are provided, then one of them must be
the "Domain" in IO::Socket argument. The "Domain" in IO::Socket argument
can, by default, be either "AF_INET" or "AF_UNIX". Other domains can be
used if a proper subclass for the domain family is registered. All other
arguments will be passed to the "configuration" method of the package for
that domain.
If the constructor fails it will return "undef" and set the $errstr
package variable to contain an error message.
$sock = IO::Socket->new(...)
or die "Cannot create socket - $IO::Socket::errstr\n";
For legacy reasons the error message is also set into the global $@
variable, and you may still find older code which looks here instead.
$sock = IO::Socket->new(...)
or die "Cannot create socket - $@\n";
MMEETTHHOODDSS #
"IO::Socket" inherits all methods from IO::Handle and implements the
following new ones.
aacccceepptt my $client_sock = $sock->accept(); my $inet_sock = $sock->accept(‘IO::Socket::INET’);
The accept method will perform the system call "accept" on the socket and
return a new object. The new object will be created in the same class as
the listen socket, unless a specific package name is specified. This
object can be used to communicate with the client that was trying to
connect.
This differs slightly from the "accept" function in perlfunc.
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.
aattmmaarrkk my $integer = $sock->atmark(); # read in some data on a given socket my $data; $sock->read($data, 1024) until $sock->atmark;
# or, export the function to use:
use IO::Socket 'sockatmark';
$sock->read($data, 1024) until sockatmark($sock);
True if the socket is currently positioned at the urgent data mark, false
otherwise. If your system doesn't yet implement "sockatmark" this will
throw an exception.
If your system does not support "sockatmark", the "use" declaration will
fail at compile time.
aauuttoofflluusshh # by default, autoflush will be turned on when referenced $sock->autoflush(); # turns on autoflush # turn off autoflush $sock->autoflush(0); # turn on autoflush $sock->autoflush(1);
This attribute isn't overridden from IO::Handle's implementation.
However, since we turn it on by default, it's worth mentioning here.
bbiinndd use Socket qw(pack_sockaddr_in); my $port = 3000; my $ip_address = ‘0.0.0.0’; my $packed_addr = pack_sockaddr_in($port, $ip_address); $sock->bind($packed_addr);
Binds a network address to a socket, just as bind(2) does. Returns true
if it succeeded, false otherwise. You should provide a packed address of
the appropriate type for the socket.
ccoonnnneecctteedd my $peer_addr = $sock->connected(); if ($peer_addr) { say “We’re connected to $peer_addr”; }
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 this method considers a half-open TCP socket to be "in a
connected state". Specifically, it does not distinguish between the
EESSTTAABBLLIISSHHEEDD and CCLLOOSSEE--WWAAIITT TCP states; it returns the peer address,
rather than "undef", in either case. Thus, in general, it 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
CCLLOOSSEE--WWAAIITT until the local application calls "shutdown" in IO::Socket or
"close". Only at that point does this function 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 that segment, the local TCP
transitions immediately to CCLLOOSSEEDD, and in that state, this method _w_i_l_l
return "undef".
ggeettssoocckkoopptt my $value = $sock->getsockopt(SOL_SOCKET, SO_REUSEADDR); my $buf = $socket->getsockopt(SOL_SOCKET, SO_RCVBUF); say “Receive buffer is $buf bytes”;
Get an option associated with the socket. Levels other than "SOL_SOCKET"
may be specified here. As a convenience, this method will unpack a byte
buffer of the correct size back into a number.
lliisstteenn $sock->listen(5);
Does the same thing that the listen(2) system call does. Returns true if
it succeeded, false otherwise. Listens to a socket with a given queue
size.
ppeeeerrnnaammee my $sockaddr_in = $sock->peername();
Returns the packed "sockaddr" address of the other end of the socket
connection. It calls "getpeername".
pprroottooccooll my $proto = $sock->protocol();
Returns the 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.
rreeccvv my $buffer = “”; my $length = 1024; my $flags = 0; # default. optional $sock->recv($buffer, $length); $sock->recv($buffer, $length, $flags);
Similar in functionality to "recv" in perlfunc.
Receives a message on a socket. Attempts to receive $length characters of
data into $buffer from the specified socket. $buffer will be grown or
shrunk to the length actually read. Takes the same flags as the system
call of the same name. Returns the address of the sender if socket's
protocol supports this; returns an empty string otherwise. If there's an
error, returns "undef". This call is actually implemented in terms of the
recvfrom(2) system call.
Flags are ORed together values, such as "MSG_BCAST", "MSG_OOB",
"MSG_TRUNC". The default value for the flags is 0.
The cached value of "peername" in IO::Socket is updated with the result
of "recv".
NNoottee:: In Perl v5.30 and newer, if the socket has been marked as ":utf8",
"recv" will throw an exception. The ":encoding(...)" layer implicitly
introduces the ":utf8" layer. See "binmode" in perlfunc.
NNoottee:: In Perl versions older than v5.30, depending on the status of the
socket, either (8-bit) bytes or characters are received. By default all
sockets operate on bytes, but for example if the socket has been changed
using "binmode" in perlfunc to operate with the ":encoding(UTF-8)" I/O
layer (see the "open" in perlfunc pragma), the I/O will operate on
UTF8-encoded Unicode characters, not bytes. Similarly for the ":encoding"
layer: in that case pretty much any characters can be read.
sseenndd my $message = “Hello, world!”; my $flags = 0; # defaults to zero my $to = ‘0.0.0.0’; # optional destination my $sent = $sock->send($message); $sent = $sock->send($message, $flags); $sent = $sock->send($message, $flags, $to);
Similar in functionality to "send" in perlfunc.
Sends a message on a socket. Attempts to send the scalar message to the
socket. Takes the same flags as the system call of the same name. On
unconnected sockets, you must specify a destination to send to, in which
case it does a sendto(2) syscall. Returns the number of characters sent,
or "undef" on error. The sendmsg(2) syscall is currently unimplemented.
The "flags" option is optional and defaults to 0.
After a successful send with $to, further calls to "send" on an
unconnected socket without $to will send to the same address, and $to
will be used as the result of "peername" in IO::Socket.
NNoottee:: In Perl v5.30 and newer, if the socket has been marked as ":utf8",
"send" will throw an exception. The ":encoding(...)" layer implicitly
introduces the ":utf8" layer. See "binmode" in perlfunc.
NNoottee:: In Perl versions older than v5.30, depending on the status of the
socket, either (8-bit) bytes or characters are sent. By default all
sockets operate on bytes, but for example if the socket has been changed
using "binmode" in perlfunc to operate with the ":encoding(UTF-8)" I/O
layer (see the "open" in perlfunc pragma), the I/O will operate on
UTF8-encoded Unicode characters, not bytes. Similarly for the ":encoding"
layer: in that case pretty much any characters can be sent.
sseettssoocckkoopptt $sock->setsockopt(SOL_SOCKET, SO_REUSEADDR, 1); $sock->setsockopt(SOL_SOCKET, SO_RCVBUF, 64*1024);
Set option associated with the socket. Levels other than "SOL_SOCKET" may
be specified here. As a convenience, this method will convert a number
into a packed byte buffer.
sshhuuttddoowwnn $sock->shutdown(SHUT_RD); # we stopped reading data $sock->shutdown(SHUT_WR); # we stopped writing data $sock->shutdown(SHUT_RDWR); # we stopped using this socket
Shuts down a socket connection in the manner indicated by the value
passed in, which has the same interpretation as in the syscall of the
same name.
This is useful with sockets when you want to tell the other side you're
done writing but not done reading, or vice versa. It's also a more
insistent form of "close" because it also disables the file descriptor in
any forked copies in other processes.
Returns 1 for success; on error, returns "undef" if the socket is not a
valid filehandle, or returns 0 and sets $! for any other failure.
ssoocckkddoommaaiinn my $domain = $sock->sockdomain();
Returns the number for the socket domain type. For example, for an
"AF_INET" socket the value of &AF_INET will be returned.
ssoocckkeett my $sock = IO::Socket->new(); # no values given # now let’s actually get a socket with the socket method # domain, type, and protocol are required $sock = $sock->socket(AF_INET, SOCK_STREAM, ’tcp’);
Opens a socket of the specified kind and returns it. Domain, type, and
protocol are specified the same as for the syscall of the same name.
ssoocckkeettppaaiirr my ($r, $w) = $sock->socketpair(AF_UNIX, SOCK_STREAM, PF_UNSPEC); ($r, $w) = IO::Socket::UNIX ->socketpair(AF_UNIX, SOCK_STREAM, PF_UNSPEC);
Will return a list of two sockets created (read and write), or an empty
list on failure.
Differs slightly from "socketpair" in perlfunc in that the argument list
is a bit simpler.
ssoocckknnaammee my $packed_addr = $sock->sockname();
Returns the packed "sockaddr" address of this end of the connection. It's
the same as getsockname(2).
ssoocckkoopptt my $value = $sock->sockopt(SO_REUSEADDR); $sock->sockopt(SO_REUSEADDR, 1);
Unified method to both set and get options in the "SOL_SOCKET" level. If
called with one argument then "getsockopt" in IO::Socket is called,
otherwise "setsockopt" in IO::Socket is called.
ssoocckkttyyppee my $type = $sock->socktype();
Returns the number for the socket type. For example, for a "SOCK_STREAM"
socket the value of &SOCK_STREAM will be returned.
ttiimmeeoouutt my $seconds = $sock->timeout(); my $old_val = $sock->timeout(5); # set new and return old value
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.
This method is available to all "IO::Socket" implementations but may or
may not be used by the individual domain subclasses.
EEXXAAMMPPLLEESS #
Let's create a TCP server on "localhost:3333".
use strict;
use warnings;
use feature 'say';
use IO::Socket qw(AF_INET AF_UNIX SOCK_STREAM SHUT_WR);
my $server = IO::Socket->new(
Domain => AF_INET,
Type => SOCK_STREAM,
Proto => 'tcp',
LocalHost => '0.0.0.0',
LocalPort => 3333,
ReusePort => 1,
Listen => 5,
) || die "Can't open socket: $IO::Socket::errstr";
say "Waiting on 3333";
while (1) {
# waiting for a new client connection
my $client = $server->accept();
# get information about a newly connected client
my $client_address = $client->peerhost();
my $client_port = $client->peerport();
say "Connection from $client_address:$client_port";
# read up to 1024 characters from the connected client
my $data = "";
$client->recv($data, 1024);
say "received data: $data";
# write response data to the connected client
$data = "ok";
$client->send($data);
# notify client that response has been sent
$client->shutdown(SHUT_WR);
}
$server->close();
A client for such a server could be
use strict;
use warnings;
use feature 'say';
use IO::Socket qw(AF_INET AF_UNIX SOCK_STREAM SHUT_WR);
my $client = IO::Socket->new(
Domain => AF_INET,
Type => SOCK_STREAM,
proto => 'tcp',
PeerPort => 3333,
PeerHost => '0.0.0.0',
) || die "Can't open socket: $IO::Socket::errstr";
say "Sending Hello World!";
my $size = $client->send("Hello World!");
say "Sent data of length: $size";
$client->shutdown(SHUT_WR);
my $buffer;
$client->recv($buffer, 1024);
say "Got back $buffer";
$client->close();
LLIIMMIITTAATTIIOONNSS #
On some systems, for an IO::Socket object created with "new_from_fd", or
created with "accept" in IO::Socket from such an object, the "protocol"
in IO::Socket, "sockdomain" in IO::Socket and "socktype" in IO::Socket
methods may return "undef".
SSEEEE AALLSSOO #
Socket, IO::Handle, IO::Socket::INET, IO::Socket::UNIX, IO::Socket::IP
AAUUTTHHOORR #
Graham Barr. aattmmaarrkk(()) by Lincoln Stein. Currently maintained by the
Perl 5 Porters. Please report all bugs at
<https://github.com/Perl/perl5/issues>.
CCOOPPYYRRIIGGHHTT #
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 aattmmaarrkk(()) 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.
perl v5.36.3 2023-02-15 IO::Socket(3p)