1IO::Socket(3pm)        Perl Programmers Reference Guide        IO::Socket(3pm)
2
3
4

NAME

6       IO::Socket - Object interface to socket communications
7

SYNOPSIS

9           use strict;
10           use warnings;
11
12           use IO::Socket qw(AF_INET AF_UNIX);
13
14           # create a new AF_INET socket
15           my $sock = IO::Socket->new(Domain => AF_INET);
16           # which is the same as
17           $sock = IO::Socket::INET->new();
18
19           # create a new AF_UNIX socket
20           $sock = IO::Socket->new(Domain => AF_UNIX);
21           # which is the same as
22           $sock = IO::Socket::UNIX->new();
23

DESCRIPTION

25       "IO::Socket" provides an object-oriented, IO::Handle-based interface to
26       creating and using sockets via Socket, which provides a near one-to-one
27       interface to the C socket library.
28
29       "IO::Socket" is a base class that really only defines methods for those
30       operations which are common to all types of sockets. Operations which
31       are specific to a particular socket domain have methods defined in
32       subclasses of "IO::Socket". See IO::Socket::INET, IO::Socket::UNIX, and
33       IO::Socket::IP for examples of such a subclass.
34
35       "IO::Socket" will export all functions (and constants) defined by
36       Socket.
37

CONSTRUCTOR ARGUMENTS

39       Given that "IO::Socket" doesn't have attributes in the traditional
40       sense, the following arguments, rather than attributes, can be passed
41       into the constructor.
42
43       Constructor arguments should be passed in "Key => 'Value'" pairs.
44
45       The only required argument is "Domain" in IO::Socket.
46
47   Blocking
48           my $sock = IO::Socket->new(..., Blocking => 1);
49           $sock = IO::Socket->new(..., Blocking => 0);
50
51       If defined but false, the socket will be set to non-blocking mode. If
52       not specified it defaults to 1 (blocking mode).
53
54   Domain
55           my $sock = IO::Socket->new(Domain => IO::Socket::AF_INET);
56           $sock = IO::Socket->new(Domain => IO::Socket::AF_UNIX);
57
58       The socket domain will define which subclass of "IO::Socket" to use.
59       The two options available along with this distribution are "AF_INET"
60       and "AF_UNIX".
61
62       "AF_INET" is for the internet address family of sockets and is handled
63       via IO::Socket::INET. "AF_INET" sockets are bound to an internet
64       address and port.
65
66       "AF_UNIX" is for the unix domain socket and is handled via
67       IO::Socket::UNIX. "AF_UNIX" sockets are bound to the file system as
68       their address name space.
69
70       This argument is required. All other arguments are optional.
71
72   Listen
73           my $sock = IO::Socket->new(..., Listen => 5);
74
75       Listen should be an integer value or left unset.
76
77       If provided, this argument will place the socket into listening mode.
78       New connections can then be accepted using the "accept" in IO::Socket
79       method. The value given is used as the listen(2) queue size.
80
81       If the "Listen" argument is given, but false, the queue size will be
82       set to 5.
83
84   Timeout
85           my $sock = IO::Socket->new(..., Timeout => 5);
86
87       The timeout value, in seconds, for this socket connection. How exactly
88       this value is utilized is defined in the socket domain subclasses that
89       make use of the value.
90
91   Type
92           my $sock = IO::Socket->new(..., Type => IO::Socket::SOCK_STREAM);
93
94       The socket type that will be used. These are usually "SOCK_STREAM",
95       "SOCK_DGRAM", or "SOCK_RAW". If this argument is left undefined an
96       attempt will be made to infer the type from the service name.
97
98       For example, you'll usually use "SOCK_STREAM" with a "tcp" connection
99       and "SOCK_DGRAM" with a "udp" connection.
100

CONSTRUCTORS

102       "IO::Socket" extends the IO::Handle constructor.
103
104   new
105           my $sock = IO::Socket->new();
106
107           # get a new IO::Socket::INET instance
108           $sock = IO::Socket->new(Domain => IO::Socket::AF_INET);
109           # get a new IO::Socket::UNIX instance
110           $sock = IO::Socket->new(Domain => IO::Socket::AF_UNIX);
111
112           # Domain is the only required argument
113           $sock = IO::Socket->new(
114               Domain => IO::Socket::AF_INET, # AF_INET, AF_UNIX
115               Type => IO::Socket::SOCK_STREAM, # SOCK_STREAM, SOCK_DGRAM, ...
116               Proto => 'tcp', # 'tcp', 'udp', IPPROTO_TCP, IPPROTO_UDP
117               # and so on...
118           );
119
120       Creates an "IO::Socket", which is a reference to a newly created symbol
121       (see the Symbol package). "new" optionally takes arguments, these
122       arguments are defined in "CONSTRUCTOR ARGUMENTS" in IO::Socket.
123
124       Any of the "CONSTRUCTOR ARGUMENTS" in IO::Socket may be passed to the
125       constructor, but if any arguments are provided, then one of them must
126       be the "Domain" in IO::Socket argument. The "Domain" in IO::Socket
127       argument can, by default, be either "AF_INET" or "AF_UNIX". Other
128       domains can be used if a proper subclass for the domain family is
129       registered. All other arguments will be passed to the "configuration"
130       method of the package for that domain.
131
132       If the constructor fails it will return "undef" and set the $errstr
133       package variable to contain an error message.
134
135           $sock = IO::Socket->new(...)
136               or die "Cannot create socket - $IO::Socket::errstr\n";
137
138       For legacy reasons the error message is also set into the global $@
139       variable, and you may still find older code which looks here instead.
140
141           $sock = IO::Socket->new(...)
142               or die "Cannot create socket - $@\n";
143

METHODS

145       "IO::Socket" inherits all methods from IO::Handle and implements the
146       following new ones.
147
148   accept
149           my $client_sock = $sock->accept();
150           my $inet_sock = $sock->accept('IO::Socket::INET');
151
152       The accept method will perform the system call "accept" on the socket
153       and return a new object. The new object will be created in the same
154       class as the listen socket, unless a specific package name is
155       specified. This object can be used to communicate with the client that
156       was trying to connect.
157
158       This differs slightly from the "accept" function in perlfunc.
159
160       In a scalar context the new socket is returned, or "undef" upon
161       failure. In a list context a two-element array is returned containing
162       the new socket and the peer address; the list will be empty upon
163       failure.
164
165   atmark
166           my $integer = $sock->atmark();
167           # read in some data on a given socket
168           my $data;
169           $sock->read($data, 1024) until $sock->atmark;
170
171           # or, export the function to use:
172           use IO::Socket 'sockatmark';
173           $sock->read($data, 1024) until sockatmark($sock);
174
175       True if the socket is currently positioned at the urgent data mark,
176       false otherwise. If your system doesn't yet implement "sockatmark" this
177       will throw an exception.
178
179       If your system does not support "sockatmark", the "use" declaration
180       will fail at compile time.
181
182   autoflush
183           # by default, autoflush will be turned on when referenced
184           $sock->autoflush(); # turns on autoflush
185           # turn off autoflush
186           $sock->autoflush(0);
187           # turn on autoflush
188           $sock->autoflush(1);
189
190       This attribute isn't overridden from IO::Handle's implementation.
191       However, since we turn it on by default, it's worth mentioning here.
192
193   bind
194           use Socket qw(pack_sockaddr_in);
195           my $port = 3000;
196           my $ip_address = '0.0.0.0';
197           my $packed_addr = pack_sockaddr_in($port, $ip_address);
198           $sock->bind($packed_addr);
199
200       Binds a network address to a socket, just as bind(2) does. Returns true
201       if it succeeded, false otherwise. You should provide a packed address
202       of the appropriate type for the socket.
203
204   connected
205           my $peer_addr = $sock->connected();
206           if ($peer_addr) {
207               say "We're connected to $peer_addr";
208           }
209
210       If the socket is in a connected state, the peer address is returned. If
211       the socket is not in a connected state, "undef" is returned.
212
213       Note that this method considers a half-open TCP socket to be "in a
214       connected state".  Specifically, it does not distinguish between the
215       ESTABLISHED and CLOSE-WAIT TCP states; it returns the peer address,
216       rather than "undef", in either case.  Thus, in general, it cannot be
217       used to reliably learn whether the peer has initiated a graceful
218       shutdown because in most cases (see below) the local TCP state machine
219       remains in CLOSE-WAIT until the local application calls "shutdown" in
220       IO::Socket or "close". Only at that point does this function return
221       "undef".
222
223       The "in most cases" hedge is because local TCP state machine behavior
224       may depend on the peer's socket options. In particular, if the peer
225       socket has "SO_LINGER" enabled with a zero timeout, then the peer's
226       "close" will generate a "RST" segment. Upon receipt of that segment,
227       the local TCP transitions immediately to CLOSED, and in that state,
228       this method will return "undef".
229
230   getsockopt
231           my $value = $sock->getsockopt(SOL_SOCKET, SO_REUSEADDR);
232           my $buf = $socket->getsockopt(SOL_SOCKET, SO_RCVBUF);
233           say "Receive buffer is $buf bytes";
234
235       Get an option associated with the socket. Levels other than
236       "SOL_SOCKET" may be specified here. As a convenience, this method will
237       unpack a byte buffer of the correct size back into a number.
238
239   listen
240           $sock->listen(5);
241
242       Does the same thing that the listen(2) system call does. Returns true
243       if it succeeded, false otherwise. Listens to a socket with a given
244       queue size.
245
246   peername
247           my $sockaddr_in = $sock->peername();
248
249       Returns the packed "sockaddr" address of the other end of the socket
250       connection. It calls "getpeername".
251
252   protocol
253           my $proto = $sock->protocol();
254
255       Returns the number for the protocol being used on the socket, if known.
256       If the protocol is unknown, as with an "AF_UNIX" socket, zero is
257       returned.
258
259   recv
260           my $buffer = "";
261           my $length = 1024;
262           my $flags = 0; # default. optional
263           $sock->recv($buffer, $length);
264           $sock->recv($buffer, $length, $flags);
265
266       Similar in functionality to "recv" in perlfunc.
267
268       Receives a message on a socket. Attempts to receive $length characters
269       of data into $buffer from the specified socket. $buffer will be grown
270       or shrunk to the length actually read. Takes the same flags as the
271       system call of the same name. Returns the address of the sender if
272       socket's protocol supports this; returns an empty string otherwise. If
273       there's an error, returns "undef". This call is actually implemented in
274       terms of the recvfrom(2) system call.
275
276       Flags are ORed together values, such as "MSG_BCAST", "MSG_OOB",
277       "MSG_TRUNC". The default value for the flags is 0.
278
279       The cached value of "peername" in IO::Socket is updated with the result
280       of "recv".
281
282       Note: In Perl v5.30 and newer, if the socket has been marked as
283       ":utf8", "recv" will throw an exception. The ":encoding(...)" layer
284       implicitly introduces the ":utf8" layer. See "binmode" in perlfunc.
285
286       Note: In Perl versions older than v5.30, depending on the status of the
287       socket, either (8-bit) bytes or characters are received. By default all
288       sockets operate on bytes, but for example if the socket has been
289       changed using "binmode" in perlfunc to operate with the
290       ":encoding(UTF-8)" I/O layer (see the "open" in perlfunc pragma), the
291       I/O will operate on UTF8-encoded Unicode characters, not bytes.
292       Similarly for the ":encoding" layer: in that case pretty much any
293       characters can be read.
294
295   send
296           my $message = "Hello, world!";
297           my $flags = 0; # defaults to zero
298           my $to = '0.0.0.0'; # optional destination
299           my $sent = $sock->send($message);
300           $sent = $sock->send($message, $flags);
301           $sent = $sock->send($message, $flags, $to);
302
303       Similar in functionality to "send" in perlfunc.
304
305       Sends a message on a socket. Attempts to send the scalar message to the
306       socket. Takes the same flags as the system call of the same name. On
307       unconnected sockets, you must specify a destination to send to, in
308       which case it does a sendto(2) syscall. Returns the number of
309       characters sent, or "undef" on error. The sendmsg(2) syscall is
310       currently unimplemented.
311
312       The "flags" option is optional and defaults to 0.
313
314       After a successful send with $to, further calls to "send" on an
315       unconnected socket without $to will send to the same address, and $to
316       will be used as the result of "peername" in IO::Socket.
317
318       Note: In Perl v5.30 and newer, if the socket has been marked as
319       ":utf8", "send" will throw an exception. The ":encoding(...)" layer
320       implicitly introduces the ":utf8" layer. See "binmode" in perlfunc.
321
322       Note: In Perl versions older than v5.30, depending on the status of the
323       socket, either (8-bit) bytes or characters are sent. By default all
324       sockets operate on bytes, but for example if the socket has been
325       changed using "binmode" in perlfunc to operate with the
326       ":encoding(UTF-8)" I/O layer (see the "open" in perlfunc pragma), the
327       I/O will operate on UTF8-encoded Unicode characters, not bytes.
328       Similarly for the ":encoding" layer: in that case pretty much any
329       characters can be sent.
330
331   setsockopt
332           $sock->setsockopt(SOL_SOCKET, SO_REUSEADDR, 1);
333           $sock->setsockopt(SOL_SOCKET, SO_RCVBUF, 64*1024);
334
335       Set option associated with the socket. Levels other than "SOL_SOCKET"
336       may be specified here. As a convenience, this method will convert a
337       number into a packed byte buffer.
338
339   shutdown
340           $sock->shutdown(SHUT_RD); # we stopped reading data
341           $sock->shutdown(SHUT_WR); # we stopped writing data
342           $sock->shutdown(SHUT_RDWR); # we stopped using this socket
343
344       Shuts down a socket connection in the manner indicated by the value
345       passed in, which has the same interpretation as in the syscall of the
346       same name.
347
348       This is useful with sockets when you want to tell the other side you're
349       done writing but not done reading, or vice versa. It's also a more
350       insistent form of "close" because it also disables the file descriptor
351       in any forked copies in other processes.
352
353       Returns 1 for success; on error, returns "undef" if the socket is not a
354       valid filehandle, or returns 0 and sets $! for any other failure.
355
356   sockdomain
357           my $domain = $sock->sockdomain();
358
359       Returns the number for the socket domain type. For example, for an
360       "AF_INET" socket the value of &AF_INET will be returned.
361
362   socket
363           my $sock = IO::Socket->new(); # no values given
364           # now let's actually get a socket with the socket method
365           # domain, type, and protocol are required
366           $sock = $sock->socket(AF_INET, SOCK_STREAM, 'tcp');
367
368       Opens a socket of the specified kind and returns it. Domain, type, and
369       protocol are specified the same as for the syscall of the same name.
370
371   socketpair
372           my ($r, $w) = $sock->socketpair(AF_UNIX, SOCK_STREAM, PF_UNSPEC);
373           ($r, $w) = IO::Socket::UNIX
374               ->socketpair(AF_UNIX, SOCK_STREAM, PF_UNSPEC);
375
376       Will return a list of two sockets created (read and write), or an empty
377       list on failure.
378
379       Differs slightly from "socketpair" in perlfunc in that the argument
380       list is a bit simpler.
381
382   sockname
383           my $packed_addr = $sock->sockname();
384
385       Returns the packed "sockaddr" address of this end of the connection.
386       It's the same as getsockname(2).
387
388   sockopt
389           my $value = $sock->sockopt(SO_REUSEADDR);
390           $sock->sockopt(SO_REUSEADDR, 1);
391
392       Unified method to both set and get options in the "SOL_SOCKET" level.
393       If called with one argument then "getsockopt" in IO::Socket is called,
394       otherwise "setsockopt" in IO::Socket is called.
395
396   socktype
397           my $type = $sock->socktype();
398
399       Returns the number for the socket type. For example, for a
400       "SOCK_STREAM" socket the value of &SOCK_STREAM will be returned.
401
402   timeout
403           my $seconds = $sock->timeout();
404           my $old_val = $sock->timeout(5); # set new and return old value
405
406       Set or get the timeout value (in seconds) associated with this socket.
407       If called without any arguments then the current setting is returned.
408       If called with an argument the current setting is changed and the
409       previous value returned.
410
411       This method is available to all "IO::Socket" implementations but may or
412       may not be used by the individual domain subclasses.
413

EXAMPLES

415       Let's create a TCP server on "localhost:3333".
416
417           use strict;
418           use warnings;
419           use feature 'say';
420
421           use IO::Socket qw(AF_INET AF_UNIX SOCK_STREAM SHUT_WR);
422
423           my $server = IO::Socket->new(
424               Domain => AF_INET,
425               Type => SOCK_STREAM,
426               Proto => 'tcp',
427               LocalHost => '0.0.0.0',
428               LocalPort => 3333,
429               ReusePort => 1,
430               Listen => 5,
431           ) || die "Can't open socket: $IO::Socket::errstr";
432           say "Waiting on 3333";
433
434           while (1) {
435               # waiting for a new client connection
436               my $client = $server->accept();
437
438               # get information about a newly connected client
439               my $client_address = $client->peerhost();
440               my $client_port = $client->peerport();
441               say "Connection from $client_address:$client_port";
442
443               # read up to 1024 characters from the connected client
444               my $data = "";
445               $client->recv($data, 1024);
446               say "received data: $data";
447
448               # write response data to the connected client
449               $data = "ok";
450               $client->send($data);
451
452               # notify client that response has been sent
453               $client->shutdown(SHUT_WR);
454           }
455
456           $server->close();
457
458       A client for such a server could be
459
460           use strict;
461           use warnings;
462           use feature 'say';
463
464           use IO::Socket qw(AF_INET AF_UNIX SOCK_STREAM SHUT_WR);
465
466           my $client = IO::Socket->new(
467               Domain => AF_INET,
468               Type => SOCK_STREAM,
469               proto => 'tcp',
470               PeerPort => 3333,
471               PeerHost => '0.0.0.0',
472           ) || die "Can't open socket: $IO::Socket::errstr";
473
474           say "Sending Hello World!";
475           my $size = $client->send("Hello World!");
476           say "Sent data of length: $size";
477
478           $client->shutdown(SHUT_WR);
479
480           my $buffer;
481           $client->recv($buffer, 1024);
482           say "Got back $buffer";
483
484           $client->close();
485

LIMITATIONS

487       On some systems, for an IO::Socket object created with "new_from_fd",
488       or created with "accept" in IO::Socket from such an object, the
489       "protocol" in IO::Socket, "sockdomain" in IO::Socket and "socktype" in
490       IO::Socket methods may return "undef".
491

SEE ALSO

493       Socket, IO::Handle, IO::Socket::INET, IO::Socket::UNIX, IO::Socket::IP
494

AUTHOR

496       Graham Barr.  atmark() by Lincoln Stein.  Currently maintained by the
497       Perl Porters.  Please report all bugs to <perlbug@perl.org>.
498
500       Copyright (c) 1997-8 Graham Barr <gbarr@pobox.com>. All rights
501       reserved.  This program is free software; you can redistribute it
502       and/or modify it under the same terms as Perl itself.
503
504       The atmark() implementation: Copyright 2001, Lincoln Stein
505       <lstein@cshl.org>.  This module is distributed under the same terms as
506       Perl itself.  Feel free to use, modify and redistribute it as long as
507       you retain the correct attribution.
508
509
510
511perl v5.34.1                      2022-03-15                   IO::Socket(3pm)
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