=head1 NAME

 Daemon::Generic - framework to provide start/stop/reload for a daemon

=head1 SYNOPSIS

 use Daemon::Generic;

 sub gd_run { ... stuff }

 newdaemon();

=head1 DESCRIPTION

Daemon::Generic provides a framework for starting, stopping,
reconfiguring daemon-like programs.  The framework provides
for standard commands that work for as init.d files and 
as apachectl-like commands.

Programs that use Daemon::Generic subclass Daemon::Generic
to override its behavior.  Almost everything that 
Genric::Daemon does can be overridden as needed.

=head1 EXAMPLE USAGE OUTPUT

Unless overridden, the usage output for your program will 
look something like this:

 Usage: $progname [ -c file ] [ -f ] { start | stop | reload | restart | help | version | check }
  -c		Specify configuration file (defaults to $configfile)
  -f		Run in the foreground (don't detach)
  start		Starts a new $progname if there isn't one running already
  stop		Stops a running $progname
  reload	Causes a running $progname to reload it's config file.  Starts
 		a new one if none is running.
  restart	Stops a running $progname if one is running.  Starts a new one.
  check		Check the configuration file and report the daemon state
  help		Display this usage info
  version	Display the version of $progname

=head1 CONSTRUCTION

To hand control over to C<Daemon::Generic>, call C<newdaemon()>.
Control will be handed back through method calls to functions you
define.

Your C<@ISA> will be modified to include C<Daemon::Generic> if 
if it isn't already there.  

These are the arguments to C<newdaemon()>.
Defaults are in (parenthesis).

=over 15

=item progname

(C<$0>) The name of this program.  This will be used for 
logging and for naming the PID file.

=item configfile

(C</etc/$progname.conf>) The location of the configuration
file for this daemon.

=item pidbase

(/var/run/$progname) We include the configuration file name
as part of the pid file in case there are multiple instances
of this daemon.  The pidbase is the part of the PID file
that does not include the configuration file name.

=item pidfile

(C<$pidbase.$configfile.pid>) The location of the
process id file.  

=item foreground

(C<0>) Do not detach/daemon and run in the foreground instead.

=item debug

(C<0>) Turn on debugging. 

=item no_srand

(C<0>) Normall srand() is called.  If no_srand is set then
srand() won't be called.

=item options

() Additional arguments for L<Getopt::Long::GetOptions> which
is used to parse C<@ARGV>.  Alternatively: define C<&gd_more_opt()>.

=item minimum_args

(C<1>) Minimum number of @ARGV arguments after flags have been
processed.

=item maximum_args

(C<1>) Maximum number of @ARGV arguments after flags have been
processed.

=item version

(C<$pkg::VERSION>) The version number of the daemon.

=item logpriority

Used for C<logger -p>.

=back

=head1 MUST-OVERRIDE CALLBACK METHODS

The package that subclasses Daemon::Generic must provide the following
callback methods.

=over 15

=item gd_run()

This is where you put your main program.

It is okay to change userid/group as the first action of gd_run().

=back

=head1 MAY-OVERRIDE CALLBACK METHODS

The package that subclasses Daemon::Generic does not have to override these
methods but it may want to.

=over 15

=item gd_preconfig()

C<gd_preconfig()> is called to parse the configuration file 
(C<$self-E<gt>{configfile}>).  Preconfig is called on all invocations
of the daemon (C<daemon reload>, C<daemon check>, C<daemon stop>, etc).
It shouldn't start anything but it can and should verify that
the config file is fine.

The return value should be a hash.  With one exception, the return
value is only used by C<gd_postconfig()>.  The exception is that 
C<gd_preconfig()> may return a revised PID file location (key C<pidfile>).

Most uses of Daemon::Generic should define C<gd_preconfig>.

=item gd_postconfig(%config)

Postconfig() is called only when the daemon is actually starting up.
(Or on reconfigs).  It is passed the return value from C<gd_preconfig>.

=item gd_setup_signals()

Set things up so that SIGHUP calls gd_reconfig_event() and
SIGINT calls gd_quit_event().  It will call these at any time
so if you want to delay signal delivery or something you should 
override this method.

=item gd_getopt()

This is invoked to parse the command line.  Useful things to modify are:

=over 20

=item $self->{configfile}

The location of the configuration file to be parsed by C<gd_preconfig()>.

=item $self->{foreground}

Run in the foreground (don't daemonize).

=item $self->{debug}

Use it yourself.

=back

The supplied C<gd_getopt()> method uses L<Getopt::Long>.

=item gd_parse_argv()

Parse any additional command line arguments beyond what C<gd_getopt()>
handled.

C<$ARGV[0]> needs to be left alone if it is one of the following
standard items:

=over 10

=item start

Start up a new daemon.

=item stop

Stop the running daemon.

=item restart

Stop the running daemon, start a new one.

=item reload

Send a signal to the running daemon, asking
it to reconfigure itself.

=item check

Just check the configuration file. 

=item help

Print the help screen (probably usage()).

=item version

Display the daemon's version.

=back

There is no default C<gd_parse_argv()>.

=item gd_check($pidfile, $pid)

Normal behavior: return.  Define additional checks to run when
the C<check> command is given.  A C<$pid> will only be supplied
if there is a daemon running.

=item gd_version()

Normal behavior: display a version message and exit.

=item gd_help()

Normal behavior: call C<gd_usage()>.

=item gd_commands_more()

Used by C<gd_usage()>: provide information on additional commands
beyond C<start>, C<stop>, C<reload>, etc.  Return is an array of
key value pairs.  

 sub gd_commands_more 
 {
	return (
		savestate => 'Tell xyz server to save its state',
		reset     => 'Tell xyz servr to reset',
	);
 }

=item gd_flags_more

Like C<gd_commands_more()> but defines additional command line flags.
There should also be a C<gd_more_opt()> or an C<options> argument to
C<new()>.

=item gd_positional_more

Like C<gd_commands_more()> but defines positional arguments.

=item gd_usage()

Display a usage message.  
The return value from C<gd_usage()> is the exit code for the program.

=item gd_more_opt()

() Additional arguments for L<Getopt::Long::GetOptions> which
is used to parse C<@ARGV>.  Alternatively: pass C<options> to C<new()>.

=item gd_pidfile()

Figure out the PID file should be. 

=item gd_error()

Print out an error (call die?)

=item gd_other_cmd()

Called C<$ARGV[0]> isn't one of the commands that Daemon::Generic knows
by default.  Default behavior: call C<gd_usage()> and C<exit(1)>. 

=item gd_daemonize()

Normal behavior: C<fork()>, C<fork()>, detach from tty.

=item gd_redirect_output()

This is a mis-named method.  Sorry.  This directs C<STDOUT>/C<STDERR>/C<STDIN>
to C</dev/null> as part of daemonizing.  Used by C<gd_daemonize()>.

=item gd_reopen_output()

After daemonizing, output file descriptors are be re-established.
Normal behavior: redirect C<STDOUT> and C<STDERR> to 
C<logger -t $progname[$$]>.  Used by C<gd_daemonize()>.

=item gd_logname()

Normal behavior: C<$progname[$$]>.  Used by C<gd_redirect_output()>.

=item gd_reconfig_event()

Normal behavior: call C<gd_postconfig(gd_preconfig))>.  
Only referenced by C<gd_setup_signals()>.

=item gd_quit_event()

Normal behavior: exit. 
Only referenced by C<gd_setup_signals()>.

=item gd_kill_groups()

Return true if gd_kill should kill process groups ($pid) instead of just
the one daemon ($pid).  Default is false.

=item gd_kill($pid)

Used by the C<stop> and C<restart> commands to get rid of
the old daemon.
Normal behavior: send a SIGINT.  
Check to see if process C<$pid> has died.  If it has not, keep checking
and if it's still alive.  After 
C<$Daemon::Generic::force_quit_delay> seconds,
send a SIGTERM.  Keep checking.  After another
C<$Daemon::Generic::force_quit_delay> seconds,
send a SIGKILL (-9).  Keep checking.  After 
C<$Daemon::Generic::force_quit_delay * 4> seconds or 60 seconds
(whichever is smaller), give up and exit(1).

=item gd_install

Installs the daemon so that it runs automatically at next
reboot.  Currently done with a symlink to C<$0> and 
C</usr/sbin/update-rc.d>.  Please send patches for other 
methods!

=item gd_can_install

Returns a function to do an C<gd_install> if installation
is possible.  Returns C<0> otherwise.

=item gd_install_pre($method)

Normal behavior: return.  Called just before doing an installation.
The method indicates the installation method (currently always
C<update-rc.d>.)

=item gd_install_post($method)

Normal behavior: return.  Called just after doing an installation.

=item gd_uninstall

Will remove the daemon from the automatic startup regime.

=item gd_can_uninstall

Returns a function to do the work for C<gd_uninstall> if it's
possible.  C<0> otherwise.

=item gd_uninstall_pre($method)

Normal behavior: return.  Called just before doing an un-installation.
The method indicates the installation method (currently always
C<update-rc.d>.)

=item gd_install_post($method)

Normal behavior: return.  Called just after doing an un-installation.

=back

=head1 MEMBER DATA

Since you need to subclass Daemon::Generic, you need to know
what the internal data structures for Daemon::Generic are.  
With two exceptions, all of the member data items begin with 
the prefix C<gd_>.

=over 15

=item configfile

The location of the configuration file.  (Not used by
Daemon::Generic).

=item debug

Display debugging?  (Not used by Daemon::Generic)

=item gd_args

The original C<%args> passed to C<new>.

=item gd_progname

The process name.  (defaults to $0)

=item gd_pidfile

The location of the process ID file.

=item gd_logpriority

Used for C<logger -p>.

=item gd_foreground

Are we running in the foreground?

=back

=head1 EXAMPLE PROGRAM

 my $sleeptime = 1;

 newdaemon(
	progname	=> 'ticktockd',
	pidfile		=> '/var/run/ticktockd.pid',
	configfile	=> '/etc/ticktockd.conf',
 );

 sub gd_preconfig
 {
	my ($self) = @_;
	open(CONFIG, "<$self->{configfile}") or die;
	while(<CONFIG>) {
		$sleeptime = $1 if /^sleeptime\s+(\d+)/;
	}
	close(CONFIG);
	return ();
 }

 sub gd_run
 {
	while(1) {
		sleep($sleeptime);
		print scalar(localtime(time))."\n";
	}
 }

=head1 SEE ALSO

With a while(1) and delayed signal delivery: L<Daemon::Generic::While1>.

With L<Event>: L<Daemon::Generic::Event>.

With L<AnyEvent>: L<Daemon::Generic::AnyEvent>.

Modules that use Daemon::Generic:
L<SyslogScan::Daemon>;
L<IO::Event> (rinetd.pl)

Other modules that do similar things: 
L<Net::Daemon>,
L<Net::Server>,
L<Net::Server::Daemonize>, 
L<NetServer::Generic>,
L<Proc::Application::Daemon>,
L<Proc::Daemon>,
L<Proc::Forking>.

=head1 LICENSE

Copyright (C) 2006-2010 David Muir Sharnoff <cpan@dave.sharnoff.org>.
Copyright (C) 2011 Google, Inc.
This module may be used and distributed on the same terms
as Perl itself.

=head1 PACKAGERS

Daemon::Generic is packaged for Fedora by Emmanuel Seyman <emmanuel.seyman@club-internet.fr>.