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 ':all';
require 5.005;

{ no strict 'vars';
$VERSION = '0.27';
@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 transmited
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,
nofatal => 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 ($^O =~ /^(freebsd|linux)$/) {
@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")) {
unshift @connectMethods, 'eventlog';
}
elsif ($is_Win32) {
warn $@;
}
}

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.
$sock_timeout = 0.25 if $^O =~ /darwin/;

# 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 {
$facility = $ident = '';
disconnect_log();
}

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

sub setlogsock {
my ($setsock, $setpath, $settime) = @_;

# check arguments
my $diag_invalid_arg
= "Invalid argument passed to setlogsock; must be 'stream', 'pipe', "
. "'unix', 'native', 'eventlog', 'tcp', 'udp' or 'inet'";
croak $diag_invalid_arg unless defined $setsock;
croak "Invalid number of arguments" unless @_ >= 1 and @_ <= 3;

$syslog_path = $setpath if defined $setpath;
$sock_timeout = $settime if defined $settime;

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

if (ref $setsock eq 'ARRAY') {
@connectMethods = @$setsock;

} elsif (lc $setsock eq 'stream') {
if (not defined $syslog_path) {
my @try = qw(/dev/log /dev/conslog);

if (length &_PATH_LOG) { # Undefined _PATH_LOG is "".
unshift @try, &_PATH_LOG;
}

for my $try (@try) {
if (-w $try) {
$syslog_path = $try;
last;
}
}

if (not defined $syslog_path) {
warnings::warnif "stream passed to setlogsock, but could not find any device";
return undef
}
}

if (not -w $syslog_path) {
warnings::warnif "stream passed to setlogsock, but $syslog_path is not writable";
return undef;
} else {
@connectMethods = qw(stream);
}

} elsif (lc $setsock eq 'unix') {
if (length _PATH_LOG() || (defined $syslog_path && -w $syslog_path)) {
$syslog_path = _PATH_LOG() unless defined $syslog_path;
@connectMethods = qw(unix);
} else {
warnings::warnif 'unix passed to setlogsock, but path not available';
return undef;
}

} elsif (lc $setsock eq 'pipe') {
for my $path ($syslog_path, &_PATH_LOG, "/dev/log") {
next unless defined $path and length $path and -p $path and -w _;
$syslog_path = $path;
last
}

if (not $syslog_path) {
warnings::warnif "pipe passed to setlogsock, but path not available";
return undef
}

@connectMethods = qw(pipe);

} elsif (lc $setsock eq 'native') {
@connectMethods = qw(native);

} elsif (lc $setsock eq 'eventlog') {
if (can_load("Win32::EventLog")) {
@connectMethods = qw(eventlog);
} else {
warnings::warnif "eventlog passed to setlogsock, but no Win32 API available";
$@ = "";
return undef;
}

} elsif (lc $setsock eq 'tcp') {
if (getservbyname('syslog', 'tcp') || getservbyname('syslogng', 'tcp')) {
@connectMethods = qw(tcp);
$host = $syslog_path;
} else {
warnings::warnif "tcp passed to setlogsock, but tcp service unavailable";
return undef;
}

} elsif (lc $setsock eq 'udp') {
if (getservbyname('syslog', 'udp')) {
@connectMethods = qw(udp);
$host = $syslog_path;
} else {
warnings::warnif "udp passed to setlogsock, but udp service unavailable";
return undef;
}

} elsif (lc $setsock eq 'inet') {
@connectMethods = ( 'tcp', 'udp' );

} elsif (lc $setsock eq 'console') {
@connectMethods = qw(console);

} else {
croak $diag_invalid_arg
}

return 1;
}

sub syslog {
my $priority = shift;
my $mask = shift;
my ($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;

croak "syslog: invalid level/facility: $priority" if $priority =~ /^-\d+$/;
@words = split(/\W+/, $priority, 2); # Allow "level" or "level|facility".
undef $numpri;
undef $numfac;

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

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

if ($num < 0) {
croak "syslog: invalid level/facility: $word"
}
elsif ($num <= &LOG_PRIMASK) {
croak "syslog: too many levels given: $word" if defined $numpri;
$numpri = $num;
return 0 unless LOG_MASK($numpri) & $maskpri;
}
else {
croak "syslog: too many facilities given: $word" if defined $numfac;
$facility = $word;
$numfac = $num;
}
}

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

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

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

# See CPAN-RT#24431. Opened on Apple Radar as bug #4944407 on 2007.01.21
# Supposedly resolved on Leopard.
chomp $message if $^O =~ /darwin/;

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 %e %T", localtime;
setlocale(LC_TIME, $oldlocale);
$buf = "<$sum>$timestamp $whoami: $message\0";
}

# handle PERROR option
# "native" mechanism already handles it by itself
if ($options{perror} and $current_proto ne 'native') {
chomp $message;
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 ($buf) = @_;
chop($buf); # delete the NUL from the end
# 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 ?
exit $ret if defined $pid;
close CONS;
}
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, $numpri) = @_;
syslog_xs($numpri, $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 $tcp = getprotobyname('tcp');
if (!defined $tcp) {
push @$errs, "getprotobyname failed for tcp";
return 0;
}

my $syslog = getservbyname('syslog', 'tcp');
$syslog = getservbyname('syslogng', 'tcp') unless defined $syslog;
if (!defined $syslog) {
push @$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;
}
$addr = sockaddr_in($syslog, $addr);

if (!socket(SYSLOG, AF_INET, SOCK_STREAM, $tcp)) {
push @$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 $udp = getprotobyname('udp');
if (!defined $udp) {
push @$errs, "getprotobyname failed for udp";
return 0;
}

my $syslog = getservbyname('syslog', 'udp');
if (!defined $syslog) {
push @$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;
}
$addr = sockaddr_in($syslog, $addr);

if (!socket(SYSLOG, AF_INET, SOCK_DGRAM, $udp)) {
push @$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();
return 1;
}
elsif (defined $current_proto and $current_proto eq 'eventlog') {
$syslog_xobj->Close();
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 {
local($SIG{__DIE__}, $SIG{__WARN__}, $@);
return eval "use $_[0]; 1"
}


"Eighth Rule: read the documentation."

__END__

=head1 NAME

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

=head1 VERSION

Version 0.27

=head1 SYNOPSIS

use Sys::Syslog; # all except setlogsock(), or:
use Sys::Syslog qw(:DEFAULT setlogsock); # default set, plus setlogsock()
use Sys::Syslog qw(:standard :macros); # standard functions, plus 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)>.

You can find a kind of FAQ in L<"THE RULES OF SYS::SYSLOG">. Please read
it before coding, and again before asking questions.


=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<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<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.

=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<WARNIN> 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>

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

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

=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($sock_type)>

=item B<setlogsock($sock_type, $stream_location)> (added in Perl 5.004_02)

=item B<setlogsock($sock_type, $stream_location, $sock_timeout)> (added in 0.25)

Sets the socket type to be used for the next call to
C<openlog()> or C<syslog()> and returns true on success,
C<undef> on failure. 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. If defined, the second parameter is used as a hostname to connect to.

=item *

C<"udp"> - connect to a UDP socket, on the C<syslog/udp> service.
If defined, the second parameter is used as a hostname to connect to,
and the third parameter as the timeout used to check for UDP response.

=item *

C<"inet"> - connect to an INET socket, either TCP or UDP, tried in that
order. If defined, the second parameter is used as a hostname to connect to.

=item *

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

=item *

C<"stream"> - connect to the stream indicated by the pathname provided as
the optional second parameter, or, if omitted, to F</dev/conslog>.
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 pathname provided as
the optional second parameter, 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).

=item *

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

=back

A reference to an array can also be passed as the first parameter.
When this calling method is used, the array should contain a list of
mechanisms which are attempted in order.

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");

Select 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 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/NoAuth/Bugs.html?Dist=Sys-Syslog>

=item * Search CPAN

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

=item * Kobes' CPAN Search

L<http://cpan.uwinnipeg.ca/dist/Sys-Syslog>

=item * Perl Documentation

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

=back


=head1 COPYRIGHT

Copyright (C) 1990-2008 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.tpc.int/tpc/server/UNIX/>
- 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