runner

#!/usr/bin/perl

# This is a runner script managing an application's lifecycle by executing the following actions:
# start, stop, show. It invokes a "daemonize" script as a part of the "start" action

use strict;
use warnings;
use Data::Dumper;

=pod
    Slurps an entire file into a string
    IN:  file name
    OUT: entire file as a string
=cut

sub read_file_contents {
    my $file = shift;
    if (-e $file) {
        open my $fh, '<', $file;
        local $/ = undef;
        my $content = <$fh>;
        return $content;
    }
}

=pod
    Reads an app-specific configuration file
    IN:  configuration file name
    OUT: file content
=cut

sub read_config {
    my $file = shift;
    our $CONFIG;
    if (-e $file) {
        do $file;
    }
    return $CONFIG // {};
}

=pod
    Sends a signal to a process or a process group
    IN:  signal (a string literal or an integer), pid of the process /group to kill,
         a flag indicating that the signal should be sent to a process group
    OUT: signal sending result
=cut

sub send_signal {
    my ($signal, $pid, $kill_group) = @_;
    $signal = "-$signal" if $kill_group;
    return kill $signal, $pid;
}

=pod
    Starts a controlled process
    IN:  app name, app command name, startup mode, pid file name, log file name, force start flag
=cut

sub start {
    my ($app, $appcmd, $mode, $pidfile, $log, $forcestart) = @_;
    unless ($forcestart) {
        print "Starting $app...\n";
        if (-e $pidfile) {
            my $pid = read_file_contents($pidfile);
            print "Sorry, $app is already running, PID = $pid.\nIf you consider this a mistake, please delete the pidfile $pidfile\n";
            return;
        }
        print "Type 'daemonizer $app show' to get its PID and references to other commands.\n";
    } else {
        print "Forcibly starting $app... An existing pidfile won't be respected, so duplicate instances can emerge!\n";
    }
    # Start a new instance in foreground or background mode
    if ($mode eq 'fg') {
        exec "$ENV{DAEMONIZER_APPSCRIPTS_DIR}/$app" or die "Cannot exec '$ENV{DAEMONIZER_APPSCRIPTS_DIR}/$app'!";
    } elsif ($mode eq 'background') {
        exec "daemonize '$appcmd' $log" or die "Cannot exec 'daemonize '$appcmd' $log'!";
    } else {
        die "Unknown deamonizer mode: $mode";
    }
}

=pod
    Stops a controlled process
    IN:  app name, pid file name
=cut

sub stop {
    my ($app, $pidfile, $config) = @_;
    # Stop an instance
    print "Stopping $app...\n";
    my $pid = read_file_contents($pidfile);
    if ($pid) {
        my $timeout = 10;
        my $seconds_passed = 0;
        my $stop_signal = $config->{stop_signal} // 'TERM';
        my $kill_group  = $config->{kill_group}  // 0;
        print "Attempting to stop the $app (pid = $pid) with signal $stop_signal...\n";
        send_signal($stop_signal, $pid, $kill_group);

        for (1..$timeout) {
            # If a process is dead, stop checking
            last unless send_signal('ZERO', $pid, $kill_group);
            print "The process with PID $pid is still alive, waiting for 1 more second...\n";
            $seconds_passed++;
            sleep 1;
        }

        if ($seconds_passed == $timeout) {
            $stop_signal = 'KILL';
            print "$timeout-second timeout has expired, forcibly killing $pid with $stop_signal.\n";
            send_signal($stop_signal, $pid, $kill_group)
        } else {
            print "The process with PID $pid voluntarily exited after $seconds_passed seconds of waiting.\n";
        }

        unlink "$pidfile";
        print "Done\n";
    } else {
        print "$app seems to be stopped already!\n";
    }
}

=pod
    Prints a controlled process' pid information
    IN:  app name, log file name, process pid file name
=cut

sub show {
    my ($app, $log, $pidfile) = @_;
    my $parsable = $ENV{DAEMONIZER_PARSABLE_OUTPUT};
    # Show a PID of the running instance
    my $pid = read_file_contents($pidfile);
    if ($pid) {
        if ($parsable) {
            print $pid;
        } else {
            print "$app is running, PID = $pid\n";
            print "pid file: $pidfile. Remove it if you believe this is not true\n";
            print "log file: $log. Type 'daemonizer $app showlog' to see its contents'\n";
        }
    } else {
        unless ($parsable) {
            print "$app is NOT running\n";
        }
    }
}

=pod
    Prints a controlled process' log content
    IN:  log file name, pid file name
=cut

sub showlog {
    my ($log, $pidfile) = @_;
    my $log_contents = read_file_contents($log);
    unless (-e $pidfile) {
        print "[!] daemonizer: PID file doesn't exist. You are reading a log of a defunct process.\n\n";
    }
    print ">>> Log file start <<<\n\n";
    print $log_contents;
    print "\n>>> Log file end <<<\n";
}

my ($appcmd, $mode) = @ARGV;
die "Application command line is not specified!" unless $appcmd;
$mode //= 'background';
my ($app, $cmd) = $appcmd =~ /^([^ ]+) +(.+)$/;
die "Application command line is malformed, must contain <app> <cmd>!" if !$app or !$cmd;
die "Essential environment variables DAEMONIZER_PIDFILE_DIR and DAEMONIZER_LOGFILE_DIR are not set!" if !$ENV{DAEMONIZER_PIDFILE_DIR} or !$ENV{DAEMONIZER_LOGFILE_DIR};
my $pidfile = "$ENV{DAEMONIZER_PIDFILE_DIR}/$app.pid";
my $log = "$ENV{DAEMONIZER_LOGFILE_DIR}/$app.log";

die "Sorry, the startup script '$ENV{DAEMONIZER_APPSCRIPTS_DIR}/$app' does not exist!" unless -e "$ENV{DAEMONIZER_APPSCRIPTS_DIR}/$app";

# "core" is a special case which allows to invoke commands internal to daemonizer
# For example, you can check the list of startup scripts or pidfiles
if ($app eq 'core') {
    exec "$ENV{DAEMONIZER_APPSCRIPTS_DIR}/$app $cmd" or die "Cannot exec '$ENV{DAEMONIZER_APPSCRIPTS_DIR}/$app $cmd'!";
}

my $config = read_config("$ENV{DAEMONIZER_APPSCRIPTS_DIR}/$app.conf");

if ($cmd eq 'start') {
    my $forcestart = 0;
    start($app, $appcmd, $mode, $pidfile, $log, $forcestart);
} elsif ($cmd eq 'forcestart') {
    my $forcestart = 1;
    start($app, $appcmd, $mode, $pidfile, $log, $forcestart);
} elsif ($cmd eq 'stop') {
    stop($app, $pidfile, $config);
} elsif ($cmd eq 'restart') {
    stop($app, $pidfile);
    start($app, $appcmd, $mode, $pidfile, $log);
} elsif ($cmd eq 'show') {
    show($app, $log, $pidfile);
} elsif ($cmd eq 'showlog') {
    showlog($log, $pidfile);
} elsif ($cmd ne '') {
    exec "$ENV{DAEMONIZER_APPSCRIPTS_DIR}/$app $cmd" or die "Cannot exec '$ENV{DAEMONIZER_APPSCRIPTS_DIR}/$app $cmd'";
} else {
    die "A command must be specified!";
}