1Net::Daemon(3) User Contributed Perl Documentation Net::Daemon(3)
2
6 Net::Daemon - Perl extension for portable daemons
7
9 # Create a subclass of Net::Daemon
10 require Net::Daemon;
11 package MyDaemon;
12 @MyDaemon::ISA = qw(Net::Daemon);
13 sub Run ($) {
15 # This function does the real work; it is invoked whenever a
16 # new connection is made.
17 }
18
20 Net::Daemon is an abstract base class for implementing portable server
21 applications in a very simple way. The module is designed for Perl
22 5.005 and threads, but can work with fork() and Perl 5.004.
23 The Net::Daemon class offers methods for the most common tasks a daemon
25 needs: Starting up, logging, accepting clients, authorization,
26 restricting its own environment for security and doing the true work.
27 You only have to override those methods that aren't appropriate for
28 you, but typically inheriting will safe you a lot of work anyways.
29 Constructors
31 $server = Net::Daemon->new($attr, $options);
32 $connection = $server->Clone($socket);
34 Two constructors are available: The new method is called upon startup
36 and creates an object that will basically act as an anchor over the
37 complete program. It supports command line parsing via Getopt::Long
38 (3).
39 Arguments of new are $attr, an hash ref of attributes (see below) and
41 $options an array ref of options, typically command line arguments (for
42 example \@ARGV) that will be passed to Getopt::Long::GetOptions.
43 The second constructor is Clone: It is called whenever a client
45 connects. It receives the main server object as input and returns a new
46 object. This new object will be passed to the methods that finally do
47 the true work of communicating with the client. Communication occurs
48 over the socket $socket, Clone's argument.
49 Possible object attributes and the corresponding command line arguments
51 are:
52 catchint (--nocatchint)
54 On some systems, in particular Solaris, the functions accept(),
55 read() and so on are not safe against interrupts by signals. For
56 example, if the user raises a USR1 signal (as typically used to
57 reread config files), then the function returns an error EINTR. If
58 the catchint option is on (by default it is, use --nocatchint to
59 turn this off), then the package will ignore EINTR errors whereever
60 possible.
61 chroot (--chroot=dir)
63 (UNIX only) After doing a bind(), change root directory to the
64 given directory by doing a chroot(). This is usefull for security
65 operations, but it restricts programming a lot. For example, you
66 typically have to load external Perl extensions before doing a
67 chroot(), or you need to create hard links to Unix sockets. This is
68 typically done in the config file, see the --configfile option. See
69 also the --group and --user options.
70 If you don't know chroot(), think of an FTP server where you can
72 see a certain directory tree only after logging in.
73 clients
75 An array ref with a list of clients. Clients are hash refs, the
76 attributes accept (0 for denying access and 1 for permitting) and
77 mask, a Perl regular expression for the clients IP number or its
78 host name. See "Access control" below.
79 configfile (--configfile=file)
81 Net::Daemon supports the use of config files. These files are
82 assumed to contain a single hash ref that overrides the arguments
83 of the new method. However, command line arguments in turn take
84 precedence over the config file. See the "Config File" section
85 below for details on the config file.
86 debug (--debug)
88 Turn debugging mode on. Mainly this asserts that logging messages
89 of level "debug" are created.
90 facility (--facility=mode)
92 (UNIX only) Facility to use for Sys::Syslog (3). The default is
93 daemon.
94 group (--group=gid)
96 After doing a bind(), change the real and effective GID to the
97 given. This is usefull, if you want your server to bind to a
98 privileged port (<1024), but don't want the server to execute as
99 root. See also the --user option.
100 GID's can be passed as group names or numeric values.
102 localaddr (--localaddr=ip)
104 By default a daemon is listening to any IP number that a machine
105 has. This attribute allows to restrict the server to the given IP
106 number.
107 localpath (--localpath=path)
109 If you want to restrict your server to local services only, you'll
110 prefer using Unix sockets, if available. In that case you can use
111 this option for setting the path of the Unix socket being created.
112 This option implies --proto=unix.
113 localport (--localport=port)
115 This attribute sets the port on which the daemon is listening. It
116 must be given somehow, as there's no default.
117 logfile (--logfile=file)
119 By default logging messages will be written to the syslog (Unix) or
120 to the event log (Windows NT). On other operating systems you need
121 to specify a log file. The special value "STDERR" forces logging to
122 stderr.
123 loop-child (--loop-child)
125 This option forces creation of a new child for loops. (See the
126 loop-timeout option.) By default the loops are serialized.
127 loop-timeout (--loop-timeout=secs)
129 Some servers need to take an action from time to time. For example
130 the Net::Daemon::Spooler attempts to empty its spooling queue every
131 5 minutes. If this option is set to a positive value (zero being
132 the default), then the server will call its Loop method every
133 "loop-timeout" seconds.
134 Don't trust too much on the precision of the interval: It depends
136 on a number of factors, in particular the execution time of the
137 Loop() method. The loop is implemented by using the select
138 function. If you need an exact interval, you should better try to
139 use the alarm() function and a signal handler. (And don't forget to
140 look at the catchint option!)
141 It is recommended to use the loop-child option in conjunction with
143 loop-timeout.
144 mode (--mode=modename)
146 The Net::Daemon server can run in three different modes, depending
147 on the environment.
148 If you are running Perl 5.005 and did compile it for threads, then
150 the server will create a new thread for each connection. The thread
151 will execute the server's Run() method and then terminate. This
152 mode is the default, you can force it with "--mode=ithreads" or
153 "--mode=threads".
154 If threads are not available, but you have a working fork(), then
156 the server will behave similar by creating a new process for each
157 connection. This mode will be used automatically in the absence of
158 threads or if you use the "--mode=fork" option.
159 Finally there's a single-connection mode: If the server has
161 accepted a connection, he will enter the Run() method. No other
162 connections are accepted until the Run() method returns. This
163 operation mode is useful if you have neither threads nor fork(),
164 for example on the Macintosh. For debugging purposes you can force
165 this mode with "--mode=single".
166 When running in mode single, you can still handle multiple clients
168 at a time by preforking multiple child processes. The number of
169 childs is configured with the option "--childs".
170 childs
172 Use this parameter to let Net::Daemon run in prefork mode, which
173 means it forks the number of childs processes you give with this
174 parameter, and all child handle connections concurrently. The
175 difference to fork mode is, that the child processes continue to
176 run after a connection has terminated and are able to accept a new
177 connection. This is useful for caching inside the childs process
178 (e.g. DBI::ProxyServer connect_cached attribute)
179 options
181 Array ref of Command line options that have been passed to the
182 server object via the new method.
183 parent
185 When creating an object with Clone the original object becomes the
186 parent of the new object. Objects created with new usually don't
187 have a parent, thus this attribute is not set.
188 pidfile (--pidfile=file)
190 (UNIX only) If this option is present, a PID file will be created
191 at the given location.
192 proto (--proto=proto)
194 The transport layer to use, by default tcp or unix for a Unix
195 socket. It is not yet possible to combine both.
196 socket
198 The socket that is connected to the client; passed as $client
199 argument to the Clone method. If the server object was created with
200 new, this attribute can be undef, as long as the Bind method isn't
201 called. Sockets are assumed to be IO::Socket objects.
202 user (--user=uid)
204 After doing a bind(), change the real and effective UID to the
205 given. This is usefull, if you want your server to bind to a
206 privileged port (<1024), but don't want the server to execute as
207 root. See also the --group and the --chroot options.
208 UID's can be passed as group names or numeric values.
210 version (--version)
212 Supresses startup of the server; instead the version string will be
213 printed and the program exits immediately.
214 Note that most of these attributes (facility, mode, localaddr,
216 localport, pidfile, version) are meaningfull only at startup. If you
217 set them later, they will be simply ignored. As almost all attributes
218 have appropriate defaults, you will typically use the localport
219 attribute only.
220 Command Line Parsing
222 my $optionsAvailable = Net::Daemon->Options();
223 print Net::Daemon->Version(), "\n";
225 Net::Daemon->Usage();
227 The Options method returns a hash ref of possible command line options.
229 The keys are option names, the values are again hash refs with the
230 following keys:
231 template
233 An option template that can be passed to Getopt::Long::GetOptions.
234 description
236 A description of this option, as used in Usage
237 The Usage method prints a list of all possible options and returns. It
239 uses the Version method for printing program name and version.
240 Config File
242 If the config file option is set in the command line options or in the
243 in the "new" args, then the method
244 $server->ReadConfigFile($file, $options, $args)
246 is invoked. By default the config file is expected to contain Perl
248 source that returns a hash ref of options. These options override the
249 "new" args and will in turn be overwritten by the command line options,
250 as present in the $options hash ref.
251 A typical config file might look as follows, we use the
253 DBI::ProxyServer as an example:
254 # Load external modules; this is not required unless you use
256 # the chroot() option.
257 #require DBD::mysql;
258 #require DBD::CSV;
259 {
261 # 'chroot' => '/var/dbiproxy',
262 'facility' => 'daemon',
263 'pidfile' => '/var/dbiproxy/dbiproxy.pid',
264 'user' => 'nobody',
265 'group' => 'nobody',
266 'localport' => '1003',
267 'mode' => 'fork'
268 # Access control
270 'clients' => [
271 # Accept the local
272 {
273 'mask' => '^192\.168\.1\.\d+$',
274 'accept' => 1
275 },
276 # Accept myhost.company.com
277 {
278 'mask' => '^myhost\.company\.com$',
279 'accept' => 1
280 }
281 # Deny everything else
282 {
283 'mask' => '.*',
284 'accept' => 0
285 }
286 ]
287 }
288 Access control
290 The Net::Daemon package supports a host based access control scheme. By
291 default access is open for anyone. However, if you create an attribute
292 $self->{'clients'}, typically in the config file, then access control
293 is disabled by default. For any connection the client list is
294 processed: The clients attribute is an array ref to a list of hash
295 refs. Any of the hash refs may contain arbitrary attributes, including
296 the following:
297 mask A Perl regular expression that has to match the clients IP
299 number or its host name. The list is processed from the left to
300 the right, whenever a 'mask' attribute matches, then the
301 related hash ref is choosen as client and processing the client
302 list stops.
303 accept This may be set to true or false (default when omitting the
305 attribute), the former means accepting the client.
306 Event logging
308 $server->Log($level, $format, @args);
309 $server->Debug($format, @args);
310 $server->Error($format, @args);
311 $server->Fatal($format, @args);
312 The Log method is an interface to Sys::Syslog (3) or Win32::EventLog
314 (3). It's arguments are $level, a syslog level like debug, notice or
315 err, a format string in the style of printf and the format strings
316 arguments.
317 The Debug and Error methods are shorthands for calling Log with a level
319 of debug and err, respectively. The Fatal method is like Error, except
320 it additionally throws the given message as exception.
321 See Net::Daemon::Log(3) for details.
323 Flow of control
325 $server->Bind();
326 # The following inside Bind():
327 if ($connection->Accept()) {
328 $connection->Run();
329 } else {
330 $connection->Log('err', 'Connection refused');
331 }
332 The Bind method is called by the application when the server should
334 start. Typically this can be done right after creating the server
335 object $server. Bind usually never returns, except in case of errors.
336 When a client connects, the server uses Clone to derive a connection
338 object $connection from the server object. A new thread or process is
339 created that uses the connection object to call your classes Accept
340 method. This method is intended for host authorization and should
341 return either FALSE (refuse the client) or TRUE (accept the client).
342 If the client is accepted, the Run method is called which does the true
344 work. The connection is closed when Run returns and the corresponding
345 thread or process exits.
346 Error Handling
348 All methods are supposed to throw Perl exceptions in case of errors.
349
351 All methods are working with lexically scoped data and handle data
352 only, the exception being the OpenLog method which is invoked before
353 threading starts. Thus you are safe as long as you don't share handles
354 between threads. I strongly recommend that your application behaves
355 similar. (This doesn't apply to mode 'ithreads'.)
356
358 As an example we'll write a simple calculator server. After connecting
359 to this server you may type expressions, one per line. The server
360 evaluates the expressions and prints the result. (Note this is an
361 example, in real life we'd never implement such a security hole. :-)
362 For the purpose of example we add a command line option --base that
364 takes 'hex', 'oct' or 'dec' as values: The servers output will use the
365 given base.
366 # -*- perl -*-
368 #
369 # Calculator server
370 #
371 use strict;
372 require Net::Daemon;
374 package Calculator;
376 our $VERSION = '0.01';
378 our @ISA = qw(Net::Daemon); # to inherit from Net::Daemon
379 sub Version ($) { 'Calculator Example Server, 0.01'; }
381 # Add a command line option "--base"
383 sub Options ($) {
384 my($self) = @_;
385 my($options) = $self->SUPER::Options();
386 $options->{'base'} = { 'template' => 'base=s',
387 'description' => '--base '
388 . 'dec (default), hex or oct'
389 };
390 $options;
391 }
392 # Treat command line option in the constructor
394 sub new ($$;$) {
395 my($class, $attr, $args) = @_;
396 my($self) = $class->SUPER::new($attr, $args);
397 if ($self->{'parent'}) {
398 # Called via Clone()
399 $self->{'base'} = $self->{'parent'}->{'base'};
400 } else {
401 # Initial call
402 if ($self->{'options'} && $self->{'options'}->{'base'}) {
403 $self->{'base'} = $self->{'options'}->{'base'}
404 }
405 }
406 if (!$self->{'base'}) {
407 $self->{'base'} = 'dec';
408 }
409 $self;
410 }
411 sub Run ($) {
413 my($self) = @_;
414 my($line, $sock);
415 $sock = $self->{'socket'};
416 while (1) {
417 if (!defined($line = $sock->getline())) {
418 if ($sock->error()) {
419 $self->Error("Client connection error %s",
420 $sock->error());
421 }
422 $sock->close();
423 return;
424 }
425 $line =~ s/\s+$//; # Remove CRLF
426 my($result) = eval $line;
427 my($rc);
428 if ($self->{'base'} eq 'hex') {
429 $rc = printf $sock ("%x\n", $result);
430 } elsif ($self->{'base'} eq 'oct') {
431 $rc = printf $sock ("%o\n", $result);
432 } else {
433 $rc = printf $sock ("%d\n", $result);
434 }
435 if (!$rc) {
436 $self->Error("Client connection error %s",
437 $sock->error());
438 $sock->close();
439 return;
440 }
441 }
442 }
443 package main;
445 my $server = Calculator->new({'pidfile' => 'none',
447 'localport' => 2000}, \@ARGV);
448 $server->Bind();
449
451 Most, or even any, known problems are related to the Sys::Syslog module
452 which is by default used for logging events under Unix. I'll quote some
453 examples:
454 Usage: Sys::Syslog::_PATH_LOG at ...
456 This problem is treated in perl bug 20000712.003. A workaround is
457 changing line 277 of Syslog.pm to
458 my $syslog = &_PATH_LOG() || croak "_PATH_LOG not found in syslog.ph";
460
462 Net::Daemon is Copyright (C) 1998, Jochen Wiedmann
463 Am Eisteich 9
464 72555 Metzingen
465 Germany
466 Phone: +49 7123 14887
468 Email: joe@ispsoft.de
469 All rights reserved.
471 You may distribute this package under the terms of either the GNU
473 General Public License or the Artistic License, as specified in the
474 Perl README file.
475
477 RPC::pServer(3), Netserver::Generic(3), Net::Daemon::Log(3),
478 Net::Daemon::Test(3)
479perl v5.38.0 2023-07-21 Net::Daemon(3)