cpan/Sys-Syslog/Syslog.pm

package Sys::Syslog;
use strict;
use warnings;
use warnings::register;
use Carp;
use Exporter        ();
use Fcntl           qw< O_WRONLY >;
use File::Basename;
use POSIX           qw< strftime setlocale LC_TIME >;
use Socket          qw< :all >;
require 5.005;


{   no strict 'vars';
    $VERSION = '0.32';
    @ISA     = qw< Exporter >;

    %EXPORT_TAGS = (
        standard => [qw(openlog syslog closelog setlogmask)],
        extended => [qw(setlogsock)],
        macros => [
            # levels
            qw(
                LOG_ALERT LOG_CRIT LOG_DEBUG LOG_EMERG LOG_ERR
                LOG_INFO LOG_NOTICE LOG_WARNING
            ),

            # standard facilities
            qw(
                LOG_AUTH LOG_AUTHPRIV LOG_CRON LOG_DAEMON LOG_FTP LOG_KERN
                LOG_LOCAL0 LOG_LOCAL1 LOG_LOCAL2 LOG_LOCAL3 LOG_LOCAL4
                LOG_LOCAL5 LOG_LOCAL6 LOG_LOCAL7 LOG_LPR LOG_MAIL LOG_NEWS
                LOG_SYSLOG LOG_USER LOG_UUCP
            ),
            # Mac OS X specific facilities
            qw( LOG_INSTALL LOG_LAUNCHD LOG_NETINFO LOG_RAS LOG_REMOTEAUTH ),
            # modern BSD specific facilities
            qw( LOG_CONSOLE LOG_NTP LOG_SECURITY ),
            # IRIX specific facilities
            qw( LOG_AUDIT LOG_LFMT ),

            # options
            qw(
                LOG_CONS LOG_PID LOG_NDELAY LOG_NOWAIT LOG_ODELAY LOG_PERROR
            ),

            # others macros
            qw(
                LOG_FACMASK LOG_NFACILITIES LOG_PRIMASK
                LOG_MASK LOG_UPTO
            ),
        ],
    );

    @EXPORT = (
        @{$EXPORT_TAGS{standard}},
    );

    @EXPORT_OK = (
        @{$EXPORT_TAGS{extended}},
        @{$EXPORT_TAGS{macros}},
    );

    eval {
        require XSLoader;
        XSLoader::load('Sys::Syslog', $VERSION);
        1
    } or do {
        require DynaLoader;
        push @ISA, 'DynaLoader';
        bootstrap Sys::Syslog $VERSION;
    };
}


#
# Public variables
#
use vars qw($host);             # host to send syslog messages to (see notes at end)

#
# Prototypes
#
sub silent_eval (&);

#
# Global variables
#
use vars qw($facility);
my $connected       = 0;        # flag to indicate if we're connected or not
my $syslog_send;                # coderef of the function used to send messages
my $syslog_path     = undef;    # syslog path for "stream" and "unix" mechanisms
my $syslog_xobj     = undef;    # if defined, holds the external object used to send messages
my $transmit_ok     = 0;        # flag to indicate if the last message was transmitted
my $sock_port       = undef;    # socket port
my $sock_timeout    = 0;        # socket timeout, see below
my $current_proto   = undef;    # current mechanism used to transmit messages
my $ident           = '';       # identifiant prepended to each message
$facility           = '';       # current facility
my $maskpri         = LOG_UPTO(&LOG_DEBUG);     # current log mask

my %options = (
    ndelay  => 0,
    noeol   => 0,
    nofatal => 0,
    nonul   => 0,
    nowait  => 0,
    perror  => 0,
    pid     => 0,
);

# Default is now to first use the native mechanism, so Perl programs
# behave like other normal Unix programs, then try other mechanisms.
my @connectMethods = qw(native tcp udp unix pipe stream console);
if ($^O eq "freebsd" or $^O eq "linux") {
    @connectMethods = grep { $_ ne 'udp' } @connectMethods;
}

# And on Win32 systems, we try to use the native mechanism for this
# platform, the events logger, available through Win32::EventLog.
EVENTLOG: {
    my $is_Win32 = $^O =~ /Win32/i;

    if (can_load("Sys::Syslog::Win32", $is_Win32)) {
        unshift @connectMethods, 'eventlog';
    }
}

my @defaultMethods = @connectMethods;
my @fallbackMethods = ();

# The timeout in connection_ok() was pushed up to 0.25 sec in
# Sys::Syslog v0.19 in order to address a heisenbug on MacOSX:
# http://london.pm.org/pipermail/london.pm/Week-of-Mon-20061211/005961.html
#
# However, this also had the effect of slowing this test for
# all other operating systems, which apparently impacted some
# users (cf. CPAN-RT #34753). So, in order to make everybody
# happy, the timeout is now zero by default on all systems
# except on OSX where it is set to 250 msec, and can be set
# with the infamous setlogsock() function.
#
# Update 2011-08: this issue is also been seen on multiprocessor
# Debian GNU/kFreeBSD systems. See http://bugs.debian.org/627821
# and https://rt.cpan.org/Ticket/Display.html?id=69997
# Also, lowering the delay to 1 ms, which should be enough.

$sock_timeout = 0.001 if $^O =~ /darwin|gnukfreebsd/;


# Perl 5.6.0's warnings.pm doesn't have warnings::warnif()
if (not defined &warnings::warnif) {
    *warnings::warnif = sub {
        goto &warnings::warn if warnings::enabled(__PACKAGE__)
    }
}

# coderef for a nicer handling of errors
my $err_sub = $options{nofatal} ? \&warnings::warnif : \&croak;


sub AUTOLOAD {
    # This AUTOLOAD is used to 'autoload' constants from the constant()
    # XS function.
    no strict 'vars';
    my $constname;
    ($constname = $AUTOLOAD) =~ s/.*:://;
    croak "Sys::Syslog::constant() not defined" if $constname eq 'constant';
    my ($error, $val) = constant($constname);
    croak $error if $error;
    no strict 'refs';
    *$AUTOLOAD = sub { $val };
    goto &$AUTOLOAD;
}


sub openlog {
    ($ident, my $logopt, $facility) = @_;

    # default values
    $ident    ||= basename($0) || getlogin() || getpwuid($<) || 'syslog';
    $logopt   ||= '';
    $facility ||= LOG_USER();

    for my $opt (split /\b/, $logopt) {
        $options{$opt} = 1 if exists $options{$opt}
    }

    $err_sub = delete $options{nofatal} ? \&warnings::warnif : \&croak;
    return 1 unless $options{ndelay};
    connect_log();
}

sub closelog {
    disconnect_log() if $connected;
    $options{$_} = 0 for keys %options;
    $facility = $ident = "";
    $connected = 0;
    return 1
}

sub setlogmask {
    my $oldmask = $maskpri;
    $maskpri = shift unless $_[0] == 0;
    $oldmask;
}


my %mechanism = (
    console => {
        check   => sub { 1 },
    },
    eventlog => {
        check   => sub { return can_load("Win32::EventLog") },
        err_msg => "no Win32 API available",
    },
    inet => {
        check   => sub { 1 },
    },
    native => {
        check   => sub { 1 },
    },
    pipe => {
        check   => sub {
            ($syslog_path) = grep { defined && length && -p && -w _ }
                                $syslog_path, &_PATH_LOG, "/dev/log";
            return $syslog_path ? 1 : 0
        },
        err_msg => "path not available",
    },
    stream => {
        check   => sub {
            if (not defined $syslog_path) {
                my @try = qw(/dev/log /dev/conslog);
                unshift @try, &_PATH_LOG  if length &_PATH_LOG;
                ($syslog_path) = grep { -w } @try;
            }
            return defined $syslog_path && -w $syslog_path
        },
        err_msg => "could not find any writable device",
    },
    tcp => {
        check   => sub {
            return 1 if defined $sock_port;

            if (getservbyname('syslog', 'tcp') || getservbyname('syslogng', 'tcp')) {
                $host = $syslog_path;
                return 1
            }
            else {
                return
            }
        },
        err_msg => "TCP service unavailable",
    },
    udp => {
        check   => sub {
            return 1 if defined $sock_port;

            if (getservbyname('syslog', 'udp')) {
                $host = $syslog_path;
                return 1
            }
            else {
                return
            }
        },
        err_msg => "UDP service unavailable",
    },
    unix => {
        check   => sub {
            my @try = ($syslog_path, &_PATH_LOG);
            ($syslog_path) = grep { defined && length && -w } @try;
            return defined $syslog_path && -w $syslog_path
        },
        err_msg => "path not available",
    },
);

sub setlogsock {
    my %opt;

    # handle arguments
    # - old API: setlogsock($sock_type, $sock_path, $sock_timeout)
    # - new API: setlogsock(\%options)
    croak "setlogsock(): Invalid number of arguments"
        unless @_ >= 1 and @_ <= 3;

    if (my $ref = ref $_[0]) {
        if ($ref eq "HASH") {
            %opt = %{ $_[0] };
            croak "setlogsock(): No argument given" unless keys %opt;
        }
        elsif ($ref eq "ARRAY") {
            @opt{qw< type path timeout >} = @_;
        }
        else {
            croak "setlogsock(): Unexpected \L$ref\E reference"
        }
    }
    else {
        @opt{qw< type path timeout >} = @_;
    }

    # check socket type, remove invalid ones
    my $diag_invalid_type = "setlogsock(): Invalid type%s; must be one of "
                          . join ", ", map { "'$_'" } sort keys %mechanism;
    croak sprintf $diag_invalid_type, "" unless defined $opt{type};
    my @sock_types = ref $opt{type} eq "ARRAY" ? @{$opt{type}} : ($opt{type});
    my @tmp;

    for my $sock_type (@sock_types) {
        carp sprintf $diag_invalid_type, " '$sock_type'" and next
            unless exists $mechanism{$sock_type};
        push @tmp, "tcp", "udp" and next  if $sock_type eq "inet";
        push @tmp, $sock_type;
    }

    @sock_types = @tmp;

    # set global options
    $syslog_path  = $opt{path}    if defined $opt{path};
    $host         = $opt{host}    if defined $opt{host};
    $sock_timeout = $opt{timeout} if defined $opt{timeout};
    $sock_port    = $opt{port}    if defined $opt{port};

    disconnect_log() if $connected;
    $transmit_ok = 0;
    @fallbackMethods = ();
    @connectMethods = ();
    my $found = 0;

    # check each given mechanism and test if it can be used on the current system
    for my $sock_type (@sock_types) {
        if ( $mechanism{$sock_type}{check}->() ) {
            push @connectMethods, $sock_type;
            $found = 1;
        }
        else {
            warnings::warnif("setlogsock(): type='$sock_type': "
                           . $mechanism{$sock_type}{err_msg});
        }
    }

    # if no mechanism worked from the given ones, use the default ones
    @connectMethods = @defaultMethods unless @connectMethods;

    return $found;
}

sub syslog {
    my ($priority, $mask, @args) = @_;
    my ($message, $buf);
    my (@words, $num, $numpri, $numfac, $sum);
    my $failed = undef;
    my $fail_time = undef;
    my $error = $!;

    # if $ident is undefined, it means openlog() wasn't previously called
    # so do it now in order to have sensible defaults
    openlog() unless $ident;

    local $facility = $facility;    # may need to change temporarily.

    croak "syslog: expecting argument \$priority" unless defined $priority;
    croak "syslog: expecting argument \$format"   unless defined $mask;

    if ($priority =~ /^\d+$/) {
        $numpri = LOG_PRI($priority);
        $numfac = LOG_FAC($priority) << 3;
    }
    elsif ($priority =~ /^\w+/) {
        # Allow "level" or "level|facility".
        @words = split /\W+/, $priority, 2;

        undef $numpri;
        undef $numfac;

        for my $word (@words) {
            next if length $word == 0;

            # Translate word to number.
            $num = xlate($word);

            if ($num < 0) {
                croak "syslog: invalid level/facility: $word"
            }
            elsif ($num <= LOG_PRIMASK() and $word ne "kern") {
                croak "syslog: too many levels given: $word"
                    if defined $numpri;
                $numpri = $num;
            }
            else {
                croak "syslog: too many facilities given: $word"
                    if defined $numfac;
                $facility = $word if $word =~ /^[A-Za-z]/;
                $numfac = $num;
            }
        }
    }
    else {
        croak "syslog: invalid level/facility: $priority"
    }

    croak "syslog: level must be given" unless defined $numpri;

    # don't log if priority is below mask level
    return 0 unless LOG_MASK($numpri) & $maskpri;

    if (not defined $numfac) {  # Facility not specified in this call.
	$facility = 'user' unless $facility;
	$numfac = xlate($facility);
    }

    connect_log() unless $connected;

    if ($mask =~ /%m/) {
        # escape percent signs for sprintf()
        $error =~ s/%/%%/g if @args;
        # replace %m with $error, if preceded by an even number of percent signs
        $mask =~ s/(?<!%)((?:%%)*)%m/$1$error/g;
    }

    $mask .= "\n" unless $mask =~ /\n$/;
    $message = @args ? sprintf($mask, @args) : $mask;

    if ($current_proto eq 'native') {
        $buf = $message;
    }
    elsif ($current_proto eq 'eventlog') {
        $buf = $message;
    }
    else {
        my $whoami = $ident;
        $whoami .= "[$$]" if $options{pid};

        $sum = $numpri + $numfac;
        my $oldlocale = setlocale(LC_TIME);
        setlocale(LC_TIME, 'C');
        my $timestamp = strftime "%b %d %H:%M:%S", localtime;
        setlocale(LC_TIME, $oldlocale);

        # construct the stream that will be transmitted
        $buf = "<$sum>$timestamp $whoami: $message";

        # add (or not) a newline
        $buf .= "\n" if !$options{noeol} and rindex($buf, "\n") == -1;

        # add (or not) a NUL character
        $buf .= "\0" if !$options{nonul};
    }

    # handle PERROR option
    # "native" mechanism already handles it by itself
    if ($options{perror} and $current_proto ne 'native') {
        my $whoami = $ident;
        $whoami .= "[$$]" if $options{pid};
        print STDERR "$whoami: $message\n";
    }

    # it's possible that we'll get an error from sending
    # (e.g. if method is UDP and there is no UDP listener,
    # then we'll get ECONNREFUSED on the send). So what we
    # want to do at this point is to fallback onto a different
    # connection method.
    while (scalar @fallbackMethods || $syslog_send) {
	if ($failed && (time - $fail_time) > 60) {
	    # it's been a while... maybe things have been fixed
	    @fallbackMethods = ();
	    disconnect_log();
	    $transmit_ok = 0; # make it look like a fresh attempt
	    connect_log();
        }

	if ($connected && !connection_ok()) {
	    # Something was OK, but has now broken. Remember coz we'll
	    # want to go back to what used to be OK.
	    $failed = $current_proto unless $failed;
	    $fail_time = time;
	    disconnect_log();
	}

	connect_log() unless $connected;
	$failed = undef if ($current_proto && $failed && $current_proto eq $failed);

	if ($syslog_send) {
            if ($syslog_send->($buf, $numpri, $numfac)) {
		$transmit_ok++;
		return 1;
	    }
	    # typically doesn't happen, since errors are rare from write().
	    disconnect_log();
	}
    }
    # could not send, could not fallback onto a working
    # connection method. Lose.
    return 0;
}

sub _syslog_send_console {
    my ($buf) = @_;

    # The console print is a method which could block
    # so we do it in a child process and always return success
    # to the caller.
    if (my $pid = fork) {

	if ($options{nowait}) {
	    return 1;
	} else {
	    if (waitpid($pid, 0) >= 0) {
	    	return ($? >> 8);
	    } else {
		# it's possible that the caller has other
		# plans for SIGCHLD, so let's not interfere
		return 1;
	    }
	}
    } else {
        if (open(CONS, ">/dev/console")) {
	    my $ret = print CONS $buf . "\r";  # XXX: should this be \x0A ?
	    POSIX::_exit $ret if defined $pid;
	    close CONS;
	}

	POSIX::_exit if defined $pid;
    }
}

sub _syslog_send_stream {
    my ($buf) = @_;
    # XXX: this only works if the OS stream implementation makes a write
    # look like a putmsg() with simple header. For instance it works on
    # Solaris 8 but not Solaris 7.
    # To be correct, it should use a STREAMS API, but perl doesn't have one.
    return syswrite(SYSLOG, $buf, length($buf));
}

sub _syslog_send_pipe {
    my ($buf) = @_;
    return print SYSLOG $buf;
}

sub _syslog_send_socket {
    my ($buf) = @_;
    return syswrite(SYSLOG, $buf, length($buf));
    #return send(SYSLOG, $buf, 0);
}

sub _syslog_send_native {
    my ($buf, $numpri, $numfac) = @_;
    syslog_xs($numpri|$numfac, $buf);
    return 1;
}


# xlate()
# -----
# private function to translate names to numeric values
#
sub xlate {
    my ($name) = @_;

    return $name+0 if $name =~ /^\s*\d+\s*$/;
    $name = uc $name;
    $name = "LOG_$name" unless $name =~ /^LOG_/;

    # ExtUtils::Constant 0.20 introduced a new way to implement
    # constants, called ProxySubs.  When it was used to generate
    # the C code, the constant() function no longer returns the
    # correct value.  Therefore, we first try a direct call to
    # constant(), and if the value is an error we try to call the
    # constant by its full name.
    my $value = constant($name);

    if (index($value, "not a valid") >= 0) {
        $name = "Sys::Syslog::$name";
        $value = eval { no strict "refs"; &$name };
        $value = $@ unless defined $value;
    }

    $value = -1 if index($value, "not a valid") >= 0;

    return defined $value ? $value : -1;
}


# connect_log()
# -----------
# This function acts as a kind of front-end: it tries to connect to
# a syslog service using the selected methods, trying each one in the
# selected order.
#
sub connect_log {
    @fallbackMethods = @connectMethods unless scalar @fallbackMethods;

    if ($transmit_ok && $current_proto) {
        # Retry what we were on, because it has worked in the past.
	unshift(@fallbackMethods, $current_proto);
    }

    $connected = 0;
    my @errs = ();
    my $proto = undef;

    while ($proto = shift @fallbackMethods) {
	no strict 'refs';
	my $fn = "connect_$proto";
	$connected = &$fn(\@errs) if defined &$fn;
	last if $connected;
    }

    $transmit_ok = 0;
    if ($connected) {
	$current_proto = $proto;
        my ($old) = select(SYSLOG); $| = 1; select($old);
    } else {
	@fallbackMethods = ();
        $err_sub->(join "\n\t- ", "no connection to syslog available", @errs);
        return undef;
    }
}

sub connect_tcp {
    my ($errs) = @_;

    my $proto = getprotobyname('tcp');
    if (!defined $proto) {
	push @$errs, "getprotobyname failed for tcp";
	return 0;
    }

    my $port = $sock_port || getservbyname('syslog', 'tcp');
    $port = getservbyname('syslogng', 'tcp') unless defined $port;
    if (!defined $port) {
	push @$errs, "getservbyname failed for syslog/tcp and syslogng/tcp";
	return 0;
    }

    my $addr;
    if (defined $host) {
        $addr = inet_aton($host);
        if (!$addr) {
	    push @$errs, "can't lookup $host";
	    return 0;
	}
    } else {
        $addr = INADDR_LOOPBACK;
    }
    $addr = sockaddr_in($port, $addr);

    if (!socket(SYSLOG, AF_INET, SOCK_STREAM, $proto)) {
	push @$errs, "tcp socket: $!";
	return 0;
    }

    setsockopt(SYSLOG, SOL_SOCKET, SO_KEEPALIVE, 1);
    if (silent_eval { IPPROTO_TCP() }) {
        # These constants don't exist in 5.005. They were added in 1999
        setsockopt(SYSLOG, IPPROTO_TCP(), TCP_NODELAY(), 1);
    }
    if (!connect(SYSLOG, $addr)) {
	push @$errs, "tcp connect: $!";
	return 0;
    }

    $syslog_send = \&_syslog_send_socket;

    return 1;
}

sub connect_udp {
    my ($errs) = @_;

    my $proto = getprotobyname('udp');
    if (!defined $proto) {
	push @$errs, "getprotobyname failed for udp";
	return 0;
    }

    my $port = $sock_port || getservbyname('syslog', 'udp');
    if (!defined $port) {
	push @$errs, "getservbyname failed for syslog/udp";
	return 0;
    }

    my $addr;
    if (defined $host) {
        $addr = inet_aton($host);
        if (!$addr) {
	    push @$errs, "can't lookup $host";
	    return 0;
	}
    } else {
        $addr = INADDR_LOOPBACK;
    }
    $addr = sockaddr_in($port, $addr);

    if (!socket(SYSLOG, AF_INET, SOCK_DGRAM, $proto)) {
	push @$errs, "udp socket: $!";
	return 0;
    }
    if (!connect(SYSLOG, $addr)) {
	push @$errs, "udp connect: $!";
	return 0;
    }

    # We want to check that the UDP connect worked. However the only
    # way to do that is to send a message and see if an ICMP is returned
    _syslog_send_socket("");
    if (!connection_ok()) {
	push @$errs, "udp connect: nobody listening";
	return 0;
    }

    $syslog_send = \&_syslog_send_socket;

    return 1;
}

sub connect_stream {
    my ($errs) = @_;
    # might want syslog_path to be variable based on syslog.h (if only
    # it were in there!)
    $syslog_path = '/dev/conslog' unless defined $syslog_path;
    if (!-w $syslog_path) {
	push @$errs, "stream $syslog_path is not writable";
	return 0;
    }
    if (!sysopen(SYSLOG, $syslog_path, O_WRONLY, 0400)) {
	push @$errs, "stream can't open $syslog_path: $!";
	return 0;
    }
    $syslog_send = \&_syslog_send_stream;
    return 1;
}

sub connect_pipe {
    my ($errs) = @_;

    $syslog_path ||= &_PATH_LOG || "/dev/log";

    if (not -w $syslog_path) {
        push @$errs, "$syslog_path is not writable";
        return 0;
    }

    if (not open(SYSLOG, ">$syslog_path")) {
        push @$errs, "can't write to $syslog_path: $!";
        return 0;
    }

    $syslog_send = \&_syslog_send_pipe;

    return 1;
}

sub connect_unix {
    my ($errs) = @_;

    $syslog_path ||= _PATH_LOG() if length _PATH_LOG();

    if (not defined $syslog_path) {
        push @$errs, "_PATH_LOG not available in syslog.h and no user-supplied socket path";
	return 0;
    }

    if (not (-S $syslog_path or -c _)) {
        push @$errs, "$syslog_path is not a socket";
	return 0;
    }

    my $addr = sockaddr_un($syslog_path);
    if (!$addr) {
	push @$errs, "can't locate $syslog_path";
	return 0;
    }
    if (!socket(SYSLOG, AF_UNIX, SOCK_STREAM, 0)) {
        push @$errs, "unix stream socket: $!";
	return 0;
    }

    if (!connect(SYSLOG, $addr)) {
        if (!socket(SYSLOG, AF_UNIX, SOCK_DGRAM, 0)) {
	    push @$errs, "unix dgram socket: $!";
	    return 0;
	}
        if (!connect(SYSLOG, $addr)) {
	    push @$errs, "unix dgram connect: $!";
	    return 0;
	}
    }

    $syslog_send = \&_syslog_send_socket;

    return 1;
}

sub connect_native {
    my ($errs) = @_;
    my $logopt = 0;

    # reconstruct the numeric equivalent of the options
    for my $opt (keys %options) {
        $logopt += xlate($opt) if $options{$opt}
    }

    openlog_xs($ident, $logopt, xlate($facility));
    $syslog_send = \&_syslog_send_native;

    return 1;
}

sub connect_eventlog {
    my ($errs) = @_;

    $syslog_xobj = Sys::Syslog::Win32::_install();
    $syslog_send = \&Sys::Syslog::Win32::_syslog_send;

    return 1;
}

sub connect_console {
    my ($errs) = @_;
    if (!-w '/dev/console') {
	push @$errs, "console is not writable";
	return 0;
    }
    $syslog_send = \&_syslog_send_console;
    return 1;
}

# To test if the connection is still good, we need to check if any
# errors are present on the connection. The errors will not be raised
# by a write. Instead, sockets are made readable and the next read
# would cause the error to be returned. Unfortunately the syslog
# 'protocol' never provides anything for us to read. But with
# judicious use of select(), we can see if it would be readable...
sub connection_ok {
    return 1 if defined $current_proto and (
        $current_proto eq 'native' or $current_proto eq 'console'
        or $current_proto eq 'eventlog'
    );

    my $rin = '';
    vec($rin, fileno(SYSLOG), 1) = 1;
    my $ret = select $rin, undef, $rin, $sock_timeout;
    return ($ret ? 0 : 1);
}

sub disconnect_log {
    $connected = 0;
    $syslog_send = undef;

    if (defined $current_proto and $current_proto eq 'native') {
        closelog_xs();
        unshift @fallbackMethods, $current_proto;
        $current_proto = undef;
        return 1;
    }
    elsif (defined $current_proto and $current_proto eq 'eventlog') {
        $syslog_xobj->Close();
        unshift @fallbackMethods, $current_proto;
        $current_proto = undef;
        return 1;
    }

    return close SYSLOG;
}


#
# Wrappers around eval() that makes sure that nobody, and I say NOBODY,
# ever knows that I wanted to test if something was here or not.
# It is needed because some applications are trying to be too smart,
# do it wrong, and it ends up in EPIC FAIL.
# Yes I'm speaking of YOU, SpamAssassin.
#
sub silent_eval (&) {
    local($SIG{__DIE__}, $SIG{__WARN__}, $@);
    return eval { $_[0]->() }
}

sub can_load {
    my ($module, $verbose) = @_;
    local($SIG{__DIE__}, $SIG{__WARN__}, $@);
    my $loaded = eval "use $module; 1";
    warn $@ if not $loaded and $verbose;
    return $loaded
}


"Eighth Rule: read the documentation."

__END__

=head1 NAME

Sys::Syslog - Perl interface to the UNIX syslog(3) calls

=head1 VERSION

This is the documentation of version 0.32

=head1 SYNOPSIS

    use Sys::Syslog;                        # all except setlogsock()
    use Sys::Syslog qw(:standard :macros);  # standard functions & macros

    openlog($ident, $logopt, $facility);    # don't forget this
    syslog($priority, $format, @args);
    $oldmask = setlogmask($mask_priority);
    closelog();


=head1 DESCRIPTION

C<Sys::Syslog> is an interface to the UNIX C<syslog(3)> program.
Call C<syslog()> with a string priority and a list of C<printf()> args
just like C<syslog(3)>.


=head1 EXPORTS

C<Sys::Syslog> exports the following C<Exporter> tags:

=over 4

=item *

C<:standard> exports the standard C<syslog(3)> functions:

    openlog closelog setlogmask syslog

=item *

C<:extended> exports the Perl specific functions for C<syslog(3)>:

    setlogsock

=item *

C<:macros> exports the symbols corresponding to most of your C<syslog(3)>
macros and the C<LOG_UPTO()> and C<LOG_MASK()> functions.
See L<"CONSTANTS"> for the supported constants and their meaning.

=back

By default, C<Sys::Syslog> exports the symbols from the C<:standard> tag.


=head1 FUNCTIONS

=over 4

=item B<openlog($ident, $logopt, $facility)>

Opens the syslog.
C<$ident> is prepended to every message.  C<$logopt> contains zero or
more of the options detailed below.  C<$facility> specifies the part
of the system to report about, for example C<LOG_USER> or C<LOG_LOCAL0>:
see L<"Facilities"> for a list of well-known facilities, and your
C<syslog(3)> documentation for the facilities available in your system.
Check L<"SEE ALSO"> for useful links. Facility can be given as a string
or a numeric macro.

This function will croak if it can't connect to the syslog daemon.

Note that C<openlog()> now takes three arguments, just like C<openlog(3)>.

B<You should use C<openlog()> before calling C<syslog()>.>

B<Options>

=over 4

=item *

C<cons> - This option is ignored, since the failover mechanism will drop
down to the console automatically if all other media fail.

=item *

C<ndelay> - Open the connection immediately (normally, the connection is
opened when the first message is logged).

=item *

C<noeol> - When set to true, no end of line character (C<\n>) will be
appended to the message. This can be useful for some buggy syslog daemons.

=item *

C<nofatal> - When set to true, C<openlog()> and C<syslog()> will only
emit warnings instead of dying if the connection to the syslog can't
be established.

=item *

C<nonul> - When set to true, no C<NUL> character (C<\0>) will be
appended to the message. This can be useful for some buggy syslog daemons.

=item *

C<nowait> - Don't wait for child processes that may have been created
while logging the message.  (The GNU C library does not create a child
process, so this option has no effect on Linux.)

=item *

C<perror> - Write the message to standard error output as well to the
system log (added in C<Sys::Syslo> 0.22).

=item *

C<pid> - Include PID with each message.

=back

B<Examples>

Open the syslog with options C<ndelay> and C<pid>, and with facility C<LOCAL0>:

    openlog($name, "ndelay,pid", "local0");

Same thing, but this time using the macro corresponding to C<LOCAL0>:

    openlog($name, "ndelay,pid", LOG_LOCAL0);


=item B<syslog($priority, $message)>

=item B<syslog($priority, $format, @args)>

If C<$priority> permits, logs C<$message> or C<sprintf($format, @args)>
with the addition that C<%m> in $message or C<$format> is replaced with
C<"$!"> (the latest error message).

C<$priority> can specify a level, or a level and a facility.  Levels and
facilities can be given as strings or as macros.  When using the C<eventlog>
mechanism, priorities C<DEBUG> and C<INFO> are mapped to event type
C<informational>, C<NOTICE> and C<WARNING> to C<warning> and C<ERR> to
C<EMERG> to C<error>.

If you didn't use C<openlog()> before using C<syslog()>, C<syslog()> will
try to guess the C<$ident> by extracting the shortest prefix of
C<$format> that ends in a C<":">.

B<Examples>

    # informational level
    syslog("info", $message);
    syslog(LOG_INFO, $message);

    # information level, Local0 facility
    syslog("info|local0", $message);
    syslog(LOG_INFO|LOG_LOCAL0, $message);

=over 4

=item B<Note>

C<Sys::Syslog> version v0.07 and older passed the C<$message> as the
formatting string to C<sprintf()> even when no formatting arguments
were provided.  If the code calling C<syslog()> might execute with
older versions of this module, make sure to call the function as
C<syslog($priority, "%s", $message)> instead of C<syslog($priority,
$message)>.  This protects against hostile formatting sequences that
might show up if $message contains tainted data.

=back


=item B<setlogmask($mask_priority)>

Sets the log mask for the current process to C<$mask_priority> and
returns the old mask.  If the mask argument is 0, the current log mask
is not modified.  See L<"Levels"> for the list of available levels.
You can use the C<LOG_UPTO()> function to allow all levels up to a
given priority (but it only accept the numeric macros as arguments).

B<Examples>

Only log errors:

    setlogmask( LOG_MASK(LOG_ERR) );

Log everything except informational messages:

    setlogmask( ~(LOG_MASK(LOG_INFO)) );

Log critical messages, errors and warnings:

    setlogmask( LOG_MASK(LOG_CRIT)
              | LOG_MASK(LOG_ERR)
              | LOG_MASK(LOG_WARNING) );

Log all messages up to debug:

    setlogmask( LOG_UPTO(LOG_DEBUG) );


=item B<setlogsock()>

Sets the socket type and options to be used for the next call to C<openlog()>
or C<syslog()>.  Returns true on success, C<undef> on failure.

Being Perl-specific, this function has evolved along time.  It can currently
be called as follow:

=over

=item *

C<setlogsock($sock_type)>

=item *

C<setlogsock($sock_type, $stream_location)> (added in Perl 5.004_02)

=item *

C<setlogsock($sock_type, $stream_location, $sock_timeout)> (added in
C<Sys::Syslog> 0.25)

=item *

C<setlogsock(\%options)> (added in C<Sys::Syslog> 0.28)

=back

The available options are:

=over

=item *

C<type> - equivalent to C<$sock_type>, selects the socket type (or
"mechanism").  An array reference can be passed to specify several
mechanisms to try, in the given order.

=item *

C<path> - equivalent to C<$stream_location>, sets the stream location.
Defaults to standard Unix location, or C<_PATH_LOG>.

=item *

C<timeout> - equivalent to C<$sock_timeout>, sets the socket timeout
in seconds.  Defaults to 0 on all systems except S<Mac OS X> where it
is set to 0.25 sec.

=item *

C<host> - sets the hostname to send the messages to.  Defaults to
the local host.

=item *

C<port> - sets the TCP or UDP port to connect to.  Defaults to the
first standard syslog port available on the system.

=back


The available mechanisms are:

=over

=item *

C<"native"> - use the native C functions from your C<syslog(3)> library
(added in C<Sys::Syslog> 0.15).

=item *

C<"eventlog"> - send messages to the Win32 events logger (Win32 only;
added in C<Sys::Syslog> 0.19).

=item *

C<"tcp"> - connect to a TCP socket, on the C<syslog/tcp> or C<syslogng/tcp>
service.  See also the C<host>, C<port> and C<timeout> options.

=item *

C<"udp"> - connect to a UDP socket, on the C<syslog/udp> service.
See also the C<host>, C<port> and C<timeout> options.

=item *

C<"inet"> - connect to an INET socket, either TCP or UDP, tried in that
order.  See also the C<host>, C<port> and C<timeout> options.

=item *

C<"unix"> - connect to a UNIX domain socket (in some systems a character
special device).  The name of that socket is given by the C<path> option
or, if omitted, the value returned by the C<_PATH_LOG> macro (if your
system defines it), F</dev/log> or F</dev/conslog>, whichever is writable.

=item *

C<"stream"> - connect to the stream indicated by the C<path> option, or,
if omitted, the value returned by the C<_PATH_LOG> macro (if your system
defines it), F</dev/log> or F</dev/conslog>, whichever is writable.  For
example Solaris and IRIX system may prefer C<"stream"> instead of C<"unix">.

=item *

C<"pipe"> - connect to the named pipe indicated by the C<path> option,
or, if omitted, to the value returned by the C<_PATH_LOG> macro (if your
system defines it), or F</dev/log> (added in C<Sys::Syslog> 0.21).
HP-UX is a system which uses such a named pipe.

=item *

C<"console"> - send messages directly to the console, as for the C<"cons">
option of C<openlog()>.

=back

The default is to try C<native>, C<tcp>, C<udp>, C<unix>, C<pipe>, C<stream>,
C<console>.
Under systems with the Win32 API, C<eventlog> will be added as the first
mechanism to try if C<Win32::EventLog> is available.

Giving an invalid value for C<$sock_type> will C<croak>.

B<Examples>

Select the UDP socket mechanism:

    setlogsock("udp");

Send messages using the TCP socket mechanism on a custom port:

    setlogsock({ type => "tcp", port => 2486 });

Send messages to a remote host using the TCP socket mechanism:

    setlogsock({ type => "tcp", host => $loghost });

Try the native, UDP socket then UNIX domain socket mechanisms:

    setlogsock(["native", "udp", "unix"]);

=over

=item B<Note>

Now that the "native" mechanism is supported by C<Sys::Syslog> and selected
by default, the use of the C<setlogsock()> function is discouraged because
other mechanisms are less portable across operating systems.  Authors of
modules and programs that use this function, especially its cargo-cult form
C<setlogsock("unix")>, are advised to remove any occurence of it unless they
specifically want to use a given mechanism (like TCP or UDP to connect to
a remote host).

=back

=item B<closelog()>

Closes the log file and returns true on success.

=back


=head1 THE RULES OF SYS::SYSLOG

I<The First Rule of Sys::Syslog is:>
You do not call C<setlogsock>.

I<The Second Rule of Sys::Syslog is:>
You B<do not> call C<setlogsock>.

I<The Third Rule of Sys::Syslog is:>
The program crashes, C<die>s, calls C<closelog>, the log is over.

I<The Fourth Rule of Sys::Syslog is:>
One facility, one priority.

I<The Fifth Rule of Sys::Syslog is:>
One log at a time.

I<The Sixth Rule of Sys::Syslog is:>
No C<syslog> before C<openlog>.

I<The Seventh Rule of Sys::Syslog is:>
Logs will go on as long as they have to.

I<The Eighth, and Final Rule of Sys::Syslog is:>
If this is your first use of Sys::Syslog, you must read the doc.


=head1 EXAMPLES

An example:

    openlog($program, 'cons,pid', 'user');
    syslog('info', '%s', 'this is another test');
    syslog('mail|warning', 'this is a better test: %d', time);
    closelog();

    syslog('debug', 'this is the last test');

Another example:

    openlog("$program $$", 'ndelay', 'user');
    syslog('notice', 'fooprogram: this is really done');

Example of use of C<%m>:

    $! = 55;
    syslog('info', 'problem was %m');   # %m == $! in syslog(3)

Log to UDP port on C<$remotehost> instead of logging locally:

    setlogsock("udp", $remotehost);
    openlog($program, 'ndelay', 'user');
    syslog('info', 'something happened over here');


=head1 CONSTANTS

=head2 Facilities

=over 4

=item *

C<LOG_AUDIT> - audit daemon (IRIX); falls back to C<LOG_AUTH>

=item *

C<LOG_AUTH> - security/authorization messages

=item *

C<LOG_AUTHPRIV> - security/authorization messages (private)

=item *

C<LOG_CONSOLE> - C</dev/console> output (FreeBSD); falls back to C<LOG_USER>

=item *

C<LOG_CRON> - clock daemons (B<cron> and B<at>)

=item *

C<LOG_DAEMON> - system daemons without separate facility value

=item *

C<LOG_FTP> - FTP daemon

=item *

C<LOG_KERN> - kernel messages

=item *

C<LOG_INSTALL> - installer subsystem (Mac OS X); falls back to C<LOG_USER>

=item *

C<LOG_LAUNCHD> - launchd - general bootstrap daemon (Mac OS X);
falls back to C<LOG_DAEMON>

=item *

C<LOG_LFMT> - logalert facility; falls back to C<LOG_USER>

=item *

C<LOG_LOCAL0> through C<LOG_LOCAL7> - reserved for local use

=item *

C<LOG_LPR> - line printer subsystem

=item *

C<LOG_MAIL> - mail subsystem

=item *

C<LOG_NETINFO> - NetInfo subsystem (Mac OS X); falls back to C<LOG_DAEMON>

=item *

C<LOG_NEWS> - USENET news subsystem

=item *

C<LOG_NTP> - NTP subsystem (FreeBSD, NetBSD); falls back to C<LOG_DAEMON>

=item *

C<LOG_RAS> - Remote Access Service (VPN / PPP) (Mac OS X);
falls back to C<LOG_AUTH>

=item *

C<LOG_REMOTEAUTH> - remote authentication/authorization (Mac OS X);
falls back to C<LOG_AUTH>

=item *

C<LOG_SECURITY> - security subsystems (firewalling, etc.) (FreeBSD);
falls back to C<LOG_AUTH>

=item *

C<LOG_SYSLOG> - messages generated internally by B<syslogd>

=item *

C<LOG_USER> (default) - generic user-level messages

=item *

C<LOG_UUCP> - UUCP subsystem

=back


=head2 Levels

=over 4

=item *

C<LOG_EMERG> - system is unusable

=item *

C<LOG_ALERT> - action must be taken immediately

=item *

C<LOG_CRIT> - critical conditions

=item *

C<LOG_ERR> - error conditions

=item *

C<LOG_WARNING> - warning conditions

=item *

C<LOG_NOTICE> - normal, but significant, condition

=item *

C<LOG_INFO> - informational message

=item *

C<LOG_DEBUG> - debug-level message

=back


=head1 DIAGNOSTICS

=over

=item C<Invalid argument passed to setlogsock>

B<(F)> You gave C<setlogsock()> an invalid value for C<$sock_type>.

=item C<eventlog passed to setlogsock, but no Win32 API available>

B<(W)> You asked C<setlogsock()> to use the Win32 event logger but the
operating system running the program isn't Win32 or does not provides Win32
compatible facilities.

=item C<no connection to syslog available>

B<(F)> C<syslog()> failed to connect to the specified socket.

=item C<stream passed to setlogsock, but %s is not writable>

B<(W)> You asked C<setlogsock()> to use a stream socket, but the given
path is not writable.

=item C<stream passed to setlogsock, but could not find any device>

B<(W)> You asked C<setlogsock()> to use a stream socket, but didn't
provide a path, and C<Sys::Syslog> was unable to find an appropriate one.

=item C<tcp passed to setlogsock, but tcp service unavailable>

B<(W)> You asked C<setlogsock()> to use a TCP socket, but the service
is not available on the system.

=item C<syslog: expecting argument %s>

B<(F)> You forgot to give C<syslog()> the indicated argument.

=item C<syslog: invalid level/facility: %s>

B<(F)> You specified an invalid level or facility.

=item C<syslog: too many levels given: %s>

B<(F)> You specified too many levels.

=item C<syslog: too many facilities given: %s>

B<(F)> You specified too many facilities.

=item C<syslog: level must be given>

B<(F)> You forgot to specify a level.

=item C<udp passed to setlogsock, but udp service unavailable>

B<(W)> You asked C<setlogsock()> to use a UDP socket, but the service
is not available on the system.

=item C<unix passed to setlogsock, but path not available>

B<(W)> You asked C<setlogsock()> to use a UNIX socket, but C<Sys::Syslog>
was unable to find an appropriate an appropriate device.

=back


=head1 HISTORY

C<Sys::Syslog> is a core module, part of the standard Perl distribution
since 1990.  At this time, modules as we know them didn't exist, the
Perl library was a collection of F<.pl> files, and the one for sending
syslog messages with was simply F<lib/syslog.pl>, included with Perl 3.0.
It was converted as a module with Perl 5.0, but had a version number
only starting with Perl 5.6.  Here is a small table with the matching
Perl and C<Sys::Syslog> versions.

    Sys::Syslog     Perl
    -----------     ----
       undef        5.0.0 ~ 5.5.4
       0.01         5.6.*
       0.03         5.8.0
       0.04         5.8.1, 5.8.2, 5.8.3
       0.05         5.8.4, 5.8.5, 5.8.6
       0.06         5.8.7
       0.13         5.8.8
       0.22         5.10.0
       0.27         5.8.9, 5.10.1 ~ 5.14.2
       0.29         5.16.0, 5.16.1


=head1 SEE ALSO

=head2 Manual Pages

L<syslog(3)>

SUSv3 issue 6, IEEE Std 1003.1, 2004 edition,
L<http://www.opengroup.org/onlinepubs/000095399/basedefs/syslog.h.html>

GNU C Library documentation on syslog,
L<http://www.gnu.org/software/libc/manual/html_node/Syslog.html>

Solaris 10 documentation on syslog,
L<http://docs.sun.com/app/docs/doc/816-5168/syslog-3c?a=view>

Mac OS X documentation on syslog,
L<http://developer.apple.com/documentation/Darwin/Reference/ManPages/man3/syslog.3.html>

IRIX 6.5 documentation on syslog,
L<http://techpubs.sgi.com/library/tpl/cgi-bin/getdoc.cgi?coll=0650&db=man&fname=3c+syslog>

AIX 5L 5.3 documentation on syslog,
L<http://publib.boulder.ibm.com/infocenter/pseries/v5r3/index.jsp?topic=/com.ibm.aix.basetechref/doc/basetrf2/syslog.htm>

HP-UX 11i documentation on syslog,
L<http://docs.hp.com/en/B2355-60130/syslog.3C.html>

Tru64 5.1 documentation on syslog,
L<http://h30097.www3.hp.com/docs/base_doc/DOCUMENTATION/V51_HTML/MAN/MAN3/0193____.HTM>

Stratus VOS 15.1,
L<http://stratadoc.stratus.com/vos/15.1.1/r502-01/wwhelp/wwhimpl/js/html/wwhelp.htm?context=r502-01&file=ch5r502-01bi.html>

=head2 RFCs

I<RFC 3164 - The BSD syslog Protocol>, L<http://www.faqs.org/rfcs/rfc3164.html>
-- Please note that this is an informational RFC, and therefore does not
specify a standard of any kind.

I<RFC 3195 - Reliable Delivery for syslog>, L<http://www.faqs.org/rfcs/rfc3195.html>

=head2 Articles

I<Syslogging with Perl>, L<http://lexington.pm.org/meetings/022001.html>

=head2 Event Log

Windows Event Log,
L<http://msdn.microsoft.com/library/default.asp?url=/library/en-us/wes/wes/windows_event_log.asp>


=head1 AUTHORS & ACKNOWLEDGEMENTS

Tom Christiansen E<lt>F<tchrist (at) perl.com>E<gt> and Larry Wall
E<lt>F<larry (at) wall.org>E<gt>.

UNIX domain sockets added by Sean Robinson
E<lt>F<robinson_s (at) sc.maricopa.edu>E<gt> with support from Tim Bunce
E<lt>F<Tim.Bunce (at) ig.co.uk>E<gt> and the C<perl5-porters> mailing list.

Dependency on F<syslog.ph> replaced with XS code by Tom Hughes
E<lt>F<tom (at) compton.nu>E<gt>.

Code for C<constant()>s regenerated by Nicholas Clark E<lt>F<nick (at) ccl4.org>E<gt>.

Failover to different communication modes by Nick Williams
E<lt>F<Nick.Williams (at) morganstanley.com>E<gt>.

Extracted from core distribution for publishing on the CPAN by
SE<eacute>bastien Aperghis-Tramoni E<lt>sebastien (at) aperghis.netE<gt>.

XS code for using native C functions borrowed from C<L<Unix::Syslog>>,
written by Marcus Harnisch E<lt>F<marcus.harnisch (at) gmx.net>E<gt>.

Yves Orton suggested and helped for making C<Sys::Syslog> use the native
event logger under Win32 systems.

Jerry D. Hedden and Reini Urban provided greatly appreciated help to
debug and polish C<Sys::Syslog> under Cygwin.


=head1 BUGS

Please report any bugs or feature requests to
C<bug-sys-syslog (at) rt.cpan.org>, or through the web interface at
L<http://rt.cpan.org/Public/Dist/Display.html?Name=Sys-Syslog>.
I will be notified, and then you'll automatically be notified of progress on
your bug as I make changes.


=head1 SUPPORT

You can find documentation for this module with the perldoc command.

    perldoc Sys::Syslog

You can also look for information at:

=over 4

=item * AnnoCPAN: Annotated CPAN documentation

L<http://annocpan.org/dist/Sys-Syslog>

=item * CPAN Ratings

L<http://cpanratings.perl.org/d/Sys-Syslog>

=item * RT: CPAN's request tracker

L<http://rt.cpan.org/Dist/Display.html?Queue=Sys-Syslog>

=item * Search CPAN

L<http://search.cpan.org/dist/Sys-Syslog/>

=item * MetaCPAN

L<https://metacpan.org/module/Sys::Syslog>

=item * Perl Documentation

L<http://perldoc.perl.org/Sys/Syslog.html>

=back


=head1 COPYRIGHT

Copyright (C) 1990-2012 by Larry Wall and others.


=head1 LICENSE

This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.

=cut

=begin comment

Notes for the future maintainer (even if it's still me..)
- - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Using Google Code Search, I search who on Earth was relying on $host being
public. It found 5 hits:

* First was inside Indigo Star Perl2exe documentation. Just an old version
of Sys::Syslog.


* One real hit was inside DalWeathDB, a weather related program. It simply
does a

    $Sys::Syslog::host = '127.0.0.1';

- L<http://www.gallistel.net/nparker/weather/code/>


* Two hits were in TPC, a fax server thingy. It does a

    $Sys::Syslog::host = $TPC::LOGHOST;

but also has this strange piece of code:

    # work around perl5.003 bug
    sub Sys::Syslog::hostname {}

I don't know what bug the author referred to.

- L<http://www.tpc.int/>
- L<ftp://ftp-usa.tpc.int/pub/tpc/server/UNIX/>


* Last hit was in Filefix, which seems to be a FIDOnet mail program (!).
This one does not use $host, but has the following piece of code:

    sub Sys::Syslog::hostname
    {
        use Sys::Hostname;
        return hostname;
    }

I guess this was a more elaborate form of the previous bit, maybe because
of a bug in Sys::Syslog back then?

- L<ftp://ftp.kiae.su/pub/unix/fido/>


Links
-----
Linux Fast-STREAMS
- L<http://www.openss7.org/streams.html>

II12021: SYSLOGD HOWTO TCPIPINFO (z/OS, OS/390, MVS)
- L<http://www-1.ibm.com/support/docview.wss?uid=isg1II12021>

Getting the most out of the Event Viewer
- L<http://www.codeproject.com/dotnet/evtvwr.asp?print=true>

Log events to the Windows NT Event Log with JNI
- L<http://www.javaworld.com/javaworld/jw-09-2001/jw-0928-ntmessages.html>

=end comment