summaryrefslogtreecommitdiff
path: root/Master/tlpkg/tlperl/lib/IO/Socket.pm
blob: f10ac375328e07684badd2e892e6160eb4982dee (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919

# IO::Socket.pm
#
# 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.

package IO::Socket;

use 5.008_001;

use IO::Handle;
use Socket 1.3;
use Carp;
use strict;
use Exporter;
use Errno;

# legacy

require IO::Socket::INET;
require IO::Socket::UNIX if ($^O ne 'epoc' && $^O ne 'symbian');

our @ISA = qw(IO::Handle);

our $VERSION = "1.43";

our @EXPORT_OK = qw(sockatmark);

sub import {
    my $pkg = shift;
    if (@_ && $_[0] eq 'sockatmark') { # not very extensible but for now, fast
	Exporter::export_to_level('IO::Socket', 1, $pkg, 'sockatmark');
    } else {
	my $callpkg = caller;
	Exporter::export 'Socket', $callpkg, @_;
    }
}

sub new {
    my($class,%arg) = @_;
    my $sock = $class->SUPER::new();

    $sock->autoflush(1);

    ${*$sock}{'io_socket_timeout'} = delete $arg{Timeout};

    return scalar(%arg) ? $sock->configure(\%arg)
			: $sock;
}

my @domain2pkg;

sub register_domain {
    my($p,$d) = @_;
    $domain2pkg[$d] = $p;
}

sub configure {
    my($sock,$arg) = @_;
    my $domain = delete $arg->{Domain};

    croak 'IO::Socket: Cannot configure a generic socket'
	unless defined $domain;

    croak "IO::Socket: Unsupported socket domain"
	unless defined $domain2pkg[$domain];

    croak "IO::Socket: Cannot configure socket in domain '$domain'"
	unless ref($sock) eq "IO::Socket";

    bless($sock, $domain2pkg[$domain]);
    $sock->configure($arg);
}

sub socket {
    @_ == 4 or croak 'usage: $sock->socket(DOMAIN, TYPE, PROTOCOL)';
    my($sock,$domain,$type,$protocol) = @_;

    socket($sock,$domain,$type,$protocol) or
    	return undef;

    ${*$sock}{'io_socket_domain'} = $domain;
    ${*$sock}{'io_socket_type'}   = $type;

    # "A value of 0 for protocol will let the system select an
    # appropriate protocol"
    # so we need to look up what the system selected,
    # not cache PF_UNSPEC.
    ${*$sock}{'io_socket_proto'} = $protocol if $protocol;

    $sock;
}

sub socketpair {
    @_ == 4 || croak 'usage: IO::Socket->socketpair(DOMAIN, TYPE, PROTOCOL)';
    my($class,$domain,$type,$protocol) = @_;
    my $sock1 = $class->new();
    my $sock2 = $class->new();

    socketpair($sock1,$sock2,$domain,$type,$protocol) or
    	return ();

    ${*$sock1}{'io_socket_type'}  = ${*$sock2}{'io_socket_type'}  = $type;
    ${*$sock1}{'io_socket_proto'} = ${*$sock2}{'io_socket_proto'} = $protocol;

    ($sock1,$sock2);
}

sub connect {
    @_ == 2 or croak 'usage: $sock->connect(NAME)';
    my $sock = shift;
    my $addr = shift;
    my $timeout = ${*$sock}{'io_socket_timeout'};
    my $err;
    my $blocking;

    $blocking = $sock->blocking(0) if $timeout;
    if (!connect($sock, $addr)) {
	if (defined $timeout && ($!{EINPROGRESS} || $!{EWOULDBLOCK})) {
	    require IO::Select;

	    my $sel = new IO::Select $sock;

	    undef $!;
	    my($r,$w,$e) = IO::Select::select(undef,$sel,$sel,$timeout);
	    if(@$e[0]) {
		# Windows return from select after the timeout in case of
		# WSAECONNREFUSED(10061) if exception set is not used.
		# This behavior is different from Linux.
		# Using the exception
		# set we now emulate the behavior in Linux
		#    - Karthik Rajagopalan
		$err = $sock->getsockopt(SOL_SOCKET,SO_ERROR);
		$@ = "connect: $err";
	    }
	    elsif(!@$w[0]) {
		$err = $! || (exists &Errno::ETIMEDOUT ? &Errno::ETIMEDOUT : 1);
		$@ = "connect: timeout";
	    }
	    elsif (!connect($sock,$addr) &&
                not ($!{EISCONN} || ($^O eq 'MSWin32' &&
                ($! == (($] < 5.019004) ? 10022 : Errno::EINVAL))))
            ) {
		# Some systems refuse to re-connect() to
		# an already open socket and set errno to EISCONN.
		# Windows sets errno to WSAEINVAL (10022) (pre-5.19.4) or
		# EINVAL (22) (5.19.4 onwards).
		$err = $!;
		$@ = "connect: $!";
	    }
	}
        elsif ($blocking || !($!{EINPROGRESS} || $!{EWOULDBLOCK}))  {
	    $err = $!;
	    $@ = "connect: $!";
	}
    }

    $sock->blocking(1) if $blocking;

    $! = $err if $err;

    $err ? undef : $sock;
}

# Enable/disable blocking IO on sockets.
# Without args return the current status of blocking,
# with args change the mode as appropriate, returning the
# old setting, or in case of error during the mode change
# undef.

sub blocking {
    my $sock = shift;

    return $sock->SUPER::blocking(@_)
        if $^O ne 'MSWin32' && $^O ne 'VMS';

    # Windows handles blocking differently
    #
    # http://groups.google.co.uk/group/perl.perl5.porters/browse_thread/thread/b4e2b1d88280ddff/630b667a66e3509f?#630b667a66e3509f
    # http://msdn.microsoft.com/library/default.asp?url=/library/en-us/winsock/winsock/ioctlsocket_2.asp
    #
    # 0x8004667e is FIONBIO
    #
    # which is used to set blocking behaviour.

    # NOTE:
    # This is a little confusing, the perl keyword for this is
    # 'blocking' but the OS level behaviour is 'non-blocking', probably
    # because sockets are blocking by default.
    # Therefore internally we have to reverse the semantics.

    my $orig= !${*$sock}{io_sock_nonblocking};

    return $orig unless @_;

    my $block = shift;

    if ( !$block != !$orig ) {
        ${*$sock}{io_sock_nonblocking} = $block ? 0 : 1;
        ioctl($sock, 0x8004667e, pack("L!",${*$sock}{io_sock_nonblocking}))
            or return undef;
    }

    return $orig;
}


sub close {
    @_ == 1 or croak 'usage: $sock->close()';
    my $sock = shift;
    ${*$sock}{'io_socket_peername'} = undef;
    $sock->SUPER::close();
}

sub bind {
    @_ == 2 or croak 'usage: $sock->bind(NAME)';
    my $sock = shift;
    my $addr = shift;

    return bind($sock, $addr) ? $sock
			      : undef;
}

sub listen {
    @_ >= 1 && @_ <= 2 or croak 'usage: $sock->listen([QUEUE])';
    my($sock,$queue) = @_;
    $queue = 5
	unless $queue && $queue > 0;

    return listen($sock, $queue) ? $sock
				 : undef;
}

sub accept {
    @_ == 1 || @_ == 2 or croak 'usage $sock->accept([PKG])';
    my $sock = shift;
    my $pkg = shift || $sock;
    my $timeout = ${*$sock}{'io_socket_timeout'};
    my $new = $pkg->new(Timeout => $timeout);
    my $peer = undef;

    if(defined $timeout) {
	require IO::Select;

	my $sel = new IO::Select $sock;

	unless ($sel->can_read($timeout)) {
	    $@ = 'accept: timeout';
	    $! = (exists &Errno::ETIMEDOUT ? &Errno::ETIMEDOUT : 1);
	    return;
	}
    }

    $peer = accept($new,$sock)
	or return;

    ${*$new}{$_} = ${*$sock}{$_} for qw( io_socket_domain io_socket_type io_socket_proto );

    return wantarray ? ($new, $peer)
    	      	     : $new;
}

sub sockname {
    @_ == 1 or croak 'usage: $sock->sockname()';
    getsockname($_[0]);
}

sub peername {
    @_ == 1 or croak 'usage: $sock->peername()';
    my($sock) = @_;
    ${*$sock}{'io_socket_peername'} ||= getpeername($sock);
}

sub connected {
    @_ == 1 or croak 'usage: $sock->connected()';
    my($sock) = @_;
    getpeername($sock);
}

sub send {
    @_ >= 2 && @_ <= 4 or croak 'usage: $sock->send(BUF, [FLAGS, [TO]])';
    my $sock  = $_[0];
    my $flags = $_[2] || 0;
    my $peer;

    if ($_[3]) {
        # the caller explicitly requested a TO, so use it
        # this is non-portable for "connected" UDP sockets
        $peer = $_[3];
    }
    elsif (!defined getpeername($sock)) {
        # we're not connected, so we require a peer from somewhere
        $peer = $sock->peername;

	croak 'send: Cannot determine peer address'
	    unless(defined $peer);
    }

    my $r = $peer
      ? send($sock, $_[1], $flags, $peer)
      : send($sock, $_[1], $flags);

    # remember who we send to, if it was successful
    ${*$sock}{'io_socket_peername'} = $peer
	if(@_ == 4 && defined $r);

    $r;
}

sub recv {
    @_ == 3 || @_ == 4 or croak 'usage: $sock->recv(BUF, LEN [, FLAGS])';
    my $sock  = $_[0];
    my $len   = $_[2];
    my $flags = $_[3] || 0;

    # remember who we recv'd from
    ${*$sock}{'io_socket_peername'} = recv($sock, $_[1]='', $len, $flags);
}

sub shutdown {
    @_ == 2 or croak 'usage: $sock->shutdown(HOW)';
    my($sock, $how) = @_;
    ${*$sock}{'io_socket_peername'} = undef;
    shutdown($sock, $how);
}

sub setsockopt {
    @_ == 4 or croak '$sock->setsockopt(LEVEL, OPTNAME, OPTVAL)';
    setsockopt($_[0],$_[1],$_[2],$_[3]);
}

my $intsize = length(pack("i",0));

sub getsockopt {
    @_ == 3 or croak '$sock->getsockopt(LEVEL, OPTNAME)';
    my $r = getsockopt($_[0],$_[1],$_[2]);
    # Just a guess
    $r = unpack("i", $r)
	if(defined $r && length($r) == $intsize);
    $r;
}

sub sockopt {
    my $sock = shift;
    @_ == 1 ? $sock->getsockopt(SOL_SOCKET,@_)
	    : $sock->setsockopt(SOL_SOCKET,@_);
}

sub atmark {
    @_ == 1 or croak 'usage: $sock->atmark()';
    my($sock) = @_;
    sockatmark($sock);
}

sub timeout {
    @_ == 1 || @_ == 2 or croak 'usage: $sock->timeout([VALUE])';
    my($sock,$val) = @_;
    my $r = ${*$sock}{'io_socket_timeout'};

    ${*$sock}{'io_socket_timeout'} = defined $val ? 0 + $val : $val
	if(@_ == 2);

    $r;
}

sub sockdomain {
    @_ == 1 or croak 'usage: $sock->sockdomain()';
    my $sock = shift;
    if (!defined(${*$sock}{'io_socket_domain'})) {
	my $addr = $sock->sockname();
	${*$sock}{'io_socket_domain'} = sockaddr_family($addr)
	    if (defined($addr));
    }
    ${*$sock}{'io_socket_domain'};
}

sub socktype {
    @_ == 1 or croak 'usage: $sock->socktype()';
    my $sock = shift;
    ${*$sock}{'io_socket_type'} = $sock->sockopt(Socket::SO_TYPE)
	if (!defined(${*$sock}{'io_socket_type'}) && defined(eval{Socket::SO_TYPE}));
    ${*$sock}{'io_socket_type'}
}

sub protocol {
    @_ == 1 or croak 'usage: $sock->protocol()';
    my($sock) = @_;
    ${*$sock}{'io_socket_proto'} = $sock->sockopt(Socket::SO_PROTOCOL)
	if (!defined(${*$sock}{'io_socket_proto'}) && defined(eval{Socket::SO_PROTOCOL}));
    ${*$sock}{'io_socket_proto'};
}

1;

__END__

=head1 NAME

IO::Socket - Object interface to socket communications

=head1 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();

=head1 DESCRIPTION

C<IO::Socket> provides an object-oriented, L<IO::Handle>-based interface to
creating and using sockets via L<Socket>, which provides a near one-to-one
interface to the C socket library.

C<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
C<IO::Socket>. See L<IO::Socket::INET>, L<IO::Socket::UNIX>, and
L<IO::Socket::IP> for examples of such a subclass.

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

=head1 CONSTRUCTOR ARGUMENTS

Given that C<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 C<< Key => 'Value' >> pairs.

The only required argument is L<IO::Socket/"Domain">.

=head2 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 C<1> (blocking mode).

=head2 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 C<IO::Socket> to use. The two
options available along with this distribution are C<AF_INET> and C<AF_UNIX>.

C<AF_INET> is for the internet address family of sockets and is handled via
L<IO::Socket::INET>. C<AF_INET> sockets are bound to an internet address and
port.

C<AF_UNIX> is for the unix domain socket and is handled via
L<IO::Socket::UNIX>. C<AF_UNIX> sockets are bound to the file system as their
address name space.

This argument is B<required>. All other arguments are optional.

=head2 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 L<IO::Socket/"accept"> method. The
value given is used as the C<listen(2)> queue size.

If the C<Listen> argument is given, but false, the queue size will be set to
5.

=head2 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.

=head2 Type

    my $sock = IO::Socket->new(..., Type => IO::Socket::SOCK_STREAM);

The socket type that will be used. These are usually C<SOCK_STREAM>,
C<SOCK_DGRAM>, or C<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 C<SOCK_STREAM> with a C<tcp> connection and
C<SOCK_DGRAM> with a C<udp> connection.

=head1 CONSTRUCTORS

C<IO::Socket> extends the L<IO::Handle> constructor.

=head2 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 C<IO::Socket>, which is a reference to a newly created symbol (see
the L<Symbol> package). C<new> optionally takes arguments, these arguments
are defined in L<IO::Socket/"CONSTRUCTOR ARGUMENTS">.

Any of the L<IO::Socket/"CONSTRUCTOR ARGUMENTS"> may be passed to the
constructor, but if any arguments are provided, then one of them must be
the L<IO::Socket/"Domain"> argument. The L<IO::Socket/"Domain"> argument can,
by default, be either C<AF_INET> or C<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 C<configuration> method of the package for that domain.

=head1 METHODS

C<IO::Socket> inherits all methods from L<IO::Handle> and implements the
following new ones.

=head2 accept

    my $client_sock = $sock->accept();
    my $inet_sock = $sock->accept('IO::Socket::INET');

The accept method will 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 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 C<accept> function in L<perlfunc>.

In a scalar context the new socket is returned, or C<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.

=head2 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 C<sockatmark> this will throw
an exception.

If your system does not support C<sockatmark>, the C<use> declaration will
fail at compile time.

=head2 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 L<IO::Handle>'s implementation. However,
since we turn it on by default, it's worth mentioning here.

=head2 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 C<bind(2)> does. Returns true if
it succeeded, false otherwise. You should provide a packed address of the
appropriate type for the socket.

=head2 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, C<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
B<ESTABLISHED> and B<CLOSE-WAIT> TCP states; it returns the peer address,
rather than C<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
B<CLOSE-WAIT> until the local application calls L<IO::Socket/"shutdown"> or
C<close>. Only at that point does this function return C<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
C<SO_LINGER> enabled with a zero timeout, then the peer's C<close> will
generate a C<RST> segment. Upon receipt of that segment, the local TCP
transitions immediately to B<CLOSED>, and in that state, this method I<will>
return C<undef>.

=head2 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 C<SOL_SOCKET>
may be specified here. As a convenience, this method will unpack a byte buffer
of the correct size back into a number.

=head2 listen

    $sock->listen(5);

Does the same thing that the C<listen(2)> system call does. Returns true if it
succeeded, false otherwise. Listens to a socket with a given queue size.

=head2 peername

    my $sockaddr_in = $sock->peername();

Returns the packed C<sockaddr> address of the other end of the socket
connection. It calls C<getpeername>.


=head2 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 C<AF_UNIX> socket, zero
is returned.

=head2 recv

    my $buffer = "";
    my $length = 1024;
    my $flags = 0; # default. optional
    $sock->recv($buffer, $length);
    $sock->recv($buffer, $length, $flags);

Similar in functionality to L<perlfunc/recv>.

Receives a message on a socket. Attempts to receive C<$length> characters of
data into C<$buffer> from the specified socket. C<$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
C<undef>. This call is actually implemented in terms of the C<recvfrom(2)>
system call.

Flags are ORed together values, such as C<MSG_BCAST>, C<MSG_OOB>,
C<MSG_TRUNC>. The default value for the flags is C<0>.

The cached value of L<IO::Socket/"peername"> is updated with the result of
C<recv>.

B<Note:> In Perl v5.30 and newer, if the socket has been marked as C<:utf8>,
C<recv> will throw an exception. The C<:encoding(...)> layer implicitly
introduces the C<:utf8> layer. See L<perlfunc/binmode>.

B<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 L<perlfunc/binmode> to operate with the C<:encoding(UTF-8)> I/O layer
(see the L<perlfunc/open> pragma), the I/O will operate on UTF8-encoded
Unicode characters, not bytes. Similarly for the C<:encoding> layer: in
that case pretty much any characters can be read.

=head2 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 L<perlfunc/send>.

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 C<sendto(2)> syscall. Returns the number of characters sent, or
C<undef> on error. The C<sendmsg(2)> syscall is currently unimplemented.

The C<flags> option is optional and defaults to C<0>.

After a successful send with C<$to>, further calls to C<send> on an
unconnected socket without C<$to> will send to the same address, and C<$to>
will be used as the result of L<IO::Socket/"peername">.

B<Note:> In Perl v5.30 and newer, if the socket has been marked as C<:utf8>,
C<send> will throw an exception. The C<:encoding(...)> layer implicitly
introduces the C<:utf8> layer. See L<perlfunc/binmode>.

B<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 L<perlfunc/binmode> to operate with the C<:encoding(UTF-8)> I/O layer
(see the L<perlfunc/open> pragma), the I/O will operate on UTF8-encoded
Unicode characters, not bytes. Similarly for the C<:encoding> layer: in
that case pretty much any characters can be sent.

=head2 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 C<SOL_SOCKET>
may be specified here. As a convenience, this method will convert a number
into a packed byte buffer.

=head2 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 C<close> because it also disables the file descriptor in any
forked copies in other processes.

Returns C<1> for success; on error, returns C<undef> if the socket is
not a valid filehandle, or returns C<0> and sets C<$!> for any other failure.

=head2 sockdomain

    my $domain = $sock->sockdomain();

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

=head2 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.

=head2 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 C<socketpair> in L<perlfunc> in that the argument list
is a bit simpler.

=head2 sockname

    my $packed_addr = $sock->sockname();

Returns the packed C<sockaddr> address of this end of the connection. It's the
same as C<getsockname(2)>.

=head2 sockopt

    my $value = $sock->sockopt(SO_REUSEADDR);
    $sock->sockopt(SO_REUSEADDR, 1);

Unified method to both set and get options in the C<SOL_SOCKET> level. If
called with one argument then L<IO::Socket/"getsockopt"> is called, otherwise
L<IO::Socket/"setsockopt"> is called.

=head2 socktype

    my $type = $sock->socktype();

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

=head2 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 C<IO::Socket> implementations but may or may
not be used by the individual domain subclasses.

=head1 EXAMPLES

Let's create a TCP server on C<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: $@";
    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: $@";

    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();


=head1 LIMITATIONS

On some systems, for an IO::Socket object created with C<new_from_fd>,
or created with L<IO::Socket/"accept"> from such an object, the
L<IO::Socket/"protocol">, L<IO::Socket/"sockdomain"> and
L<IO::Socket/"socktype"> methods may return C<undef>.

=head1 SEE ALSO

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

=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