IO::Socket(3pm) Perl Programmers Reference Guide IO::Socket(3pm)
NAME
IO::Socket - Object interface to socket communications
SYNOPSIS
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();
DESCRIPTION
"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.
CONSTRUCTOR ARGUMENTS
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.
Blocking
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).
Domain
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 required. All other arguments are optional.
Listen
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.
Timeout
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.
Type
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.
CONSTRUCTORS
"IO::Socket" extends the IO::Handle constructor.
new
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";
METHODS
"IO::Socket" inherits all methods from IO::Handle and implements the
following new ones.
accept
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.
atmark
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.
autoflush
# 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.
bind
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.
connected
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
ESTABLISHED and CLOSE-WAIT 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 CLOSE-WAIT 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 CLOSED, and in that state,
this method will return "undef".
getsockopt
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.
listen
$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.
peername
my $sockaddr_in = $sock->peername();
Returns the packed "sockaddr" address of the other end of the socket
connection. It calls "getpeername".
protocol
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.
recv
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".
Note: 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.
Note: 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.
send
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.
Note: 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.
Note: 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.
setsockopt
$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.
shutdown
$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.
sockdomain
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.
socket
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 = $sock->socket(AF_INET, SOCK_STREAM, 'tcp');
Opens a socket of the specified kind and returns it. Domain, type, and
protocol are specified the same as for the syscall of the same name.
socketpair
my ($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.
sockname
my $packed_addr = $sock->sockname();
Returns the packed "sockaddr" address of this end of the connection.
It's the same as getsockname(2).
sockopt
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.
socktype
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.
timeout
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.
EXAMPLES
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();
LIMITATIONS
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".
SEE ALSO
Socket(3), IO::Handle(3), IO::Socket::INET(3), IO::Socket::UNIX(3)
AUTHOR
Graham Barr. atmark() by Lincoln Stein. Currently maintained by the
Perl Porters. Please report all bugs to <perlbug@perl.org>.
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.
perl v5.34.0 2021-02-21 IO::Socket(3pm)
perl 5.34.0 - Generated Wed Mar 2 18:22:12 CST 2022