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#! /usr/bin/perl -w

# Copyright (C) 2015, 2017 Network Time Foundation
# Author: Harlan Stenn
#
# General cleanup and https support: Paul McMath
#
# Original shell version:
# Copyright (C) 2014 Timothe Litt litt at acm dot org
#
# This script may be freely copied, used and modified providing that
# this notice and the copyright statement are included in all copies
# and derivative works.  No warranty is offered, and use is entirely at
# your own risk.  Bugfixes and improvements would be appreciated by the
# author.

######## BEGIN #########
use strict;

# Core modules
use Digest::SHA qw(sha1_hex);
use File::Basename;
use File::Copy qw(move);
use File::Temp qw(tempfile);
use Getopt::Long qw(:config auto_help no_ignore_case bundling);
use Sys::Syslog qw(:standard :macros);

# External modules
use HTTP::Tiny 0.056;
use Net::SSLeay 1.49;
use IO::Socket::SSL 1.56;

my $VERSION = '1.004';

my $RUN_DIR = '/tmp';
my $RUN_UID = 0;
my $TMP_FILE;
my $TMP_FH;
my $FILE_MODE = 0644;

######## DEFAULT CONFIGURATION ##########
# LEAP FILE SRC URIS
#    HTTPS - (default)
#    	https://www.ietf.org/timezones/data/leap-seconds
#    HTTP - No TLS/SSL - (not recommended)
#	http://www.ietf.org/timezones/data/leap-seconds.list

my $LEAPSRC = 'https://www.ietf.org/timezones/data/leap-seconds.list';
my $LEAPFILE;

# How many times to try to download new file
my $MAXTRIES = 6;
my $INTERVAL = 10;

my $NTPCONF='/etc/ntp.conf';

# How long (in days) before expiration to get updated file
my $PREFETCH = 60;
my $EXPIRES;
my $FORCE;

# Output Flags
my $QUIET;
my $DEBUG;
my $SYSLOG;
my $TOTERM;
my $LOGFAC = 'LOG_USER';

######### PARSE/SET OPTIONS #########
my %SSL_OPTS;
my %SSL_ATTRS = (
    verify_SSL => 1,  
    SSL_options => \%SSL_OPTS,
);

our(%opt);

GetOptions(\%opt,	
	'C=s',
	'D=s',
	'e:60',
	'F',
	'f=s',
	'h|help',
	'i:10',
	'L=s',
	'l=s',
	'q',
	'r:6',
	's',
	't',
	'u=s',
	'v',
	);

$LOGFAC   = $opt{l} if defined $opt{l};
$LEAPSRC  = $opt{u} if defined $opt{u};
$LEAPFILE = $opt{L} if defined $opt{L};
$PREFETCH = $opt{e} if defined $opt{e};
$NTPCONF  = $opt{f} if defined $opt{f};
$MAXTRIES = $opt{r} if defined $opt{r};
$INTERVAL = $opt{i} if defined $opt{i};

$FORCE   = 1 if defined $opt{F};
$DEBUG	 = 1 if defined $opt{v};
$QUIET   = 1 if defined $opt{q};
$SYSLOG  = 1 if defined $opt{s};
$TOTERM  = 1 if defined $opt{t};

$SSL_OPTS{SSL_ca_file} = $opt{C} if (defined($opt{C}));
$SSL_OPTS{SSL_ca_path} = $opt{D} if (defined($opt{D}));

###############
## START MAIN
###############
my $PROG = basename($0);

# Logging - Default is to use syslog(3) if STDOUT isn't 
# connected to a tty.
if ($SYSLOG || !-t STDOUT) {
    $SYSLOG = 1;
    openlog($PROG, 'pid', $LOGFAC);
} 
else {
    $TOTERM = 1;
}

if (defined $opt{q} && defined $opt{v}) {
    log_fatal(LOG_ERR, '-q and -v options mutually exclusive');
}

if (defined $opt{L} && defined $opt{f}) {
    log_fatal(LOG_ERR, '-L and -f options mutually exclusive');
}

$SIG{INT} = \&signal_catcher;
$SIG{TERM} = \&signal_catcher;
$SIG{QUIT} = \&signal_catcher;

# Take some security precautions
close STDIN;

# Show help
if (defined $opt{h}) {
    show_help();
    exit 0;
}

if ($< != $RUN_UID) {
    log_fatal(LOG_ERR, 'User ' . getpwuid($<) . " (UID $<) tried to run $PROG");
}

chdir $RUN_DIR || log_fatal("Failed to change dir to $RUN_DIR");

# Parse ntp.conf for path to leapfile if not set by user
if (! $LEAPFILE) {

    open my $LF, '<', $NTPCONF || log_fatal(LOG_ERR, "Can't open <$NTPCONF>: $!");

    while (<$LF>) {
	chomp;
	$LEAPFILE = $1 if /^ *leapfile\s+"(\S+)"/;
    }
    close $LF;

    if (! $LEAPFILE) {
	log_fatal(LOG_ERR, "No leapfile directive in $NTPCONF; leapfile location not known"); 
    }
}

-s $LEAPFILE || logger(LOG_DEBUG, "Leapfile $LEAPFILE is empty");

# Download new file if:
#   1. file doesn't exist
#   2. invoked w/ force flag (-F)
#   3. current file isn't valid
#   4. current file expired or expires soon

if ( !-e $LEAPFILE || $FORCE || ! verifySHA($LEAPFILE) || 
	( $EXPIRES lt ( $PREFETCH * 86400 + time() ) )) {

    for (my $try = 1; $try <= $MAXTRIES; $try++) {
	logger(LOG_DEBUG, "Attempting download from $LEAPSRC, try $try..");

	($TMP_FH, $TMP_FILE) = tempfile(UNLINK => 1, SUFFIX => '.list');

	if (retrieve_file($TMP_FH)) {

            if ( verifySHA($TMP_FILE) ) {
		move_file($TMP_FILE, $LEAPFILE);
		chmod $FILE_MODE, $LEAPFILE; 
		logger(LOG_INFO, "Installed new $LEAPFILE from $LEAPSRC");
	    }
	    else {
                logger(LOG_ERR, "Downloaded file $TMP_FILE rejected -- saved for diagnosis");
		move_file($TMP_FILE, 'leap-seconds.list_corrupt');
		exit 1;
            }
	    # Fall through
            exit 0;
	}

	# Failure
	unlink $TMP_FILE;
	logger(LOG_INFO, "Download failed. Waiting $INTERVAL minutes before retrying...");
        sleep $INTERVAL * 60 ;
    }

    # Failed and out of retries
    log_fatal(LOG_ERR, "Download from $LEAPSRC failed after $MAXTRIES attempts");
}

logger(LOG_INFO, "Not time to replace $LEAPFILE");

exit 0;

######## SUB ROUTINES #########
sub move_file {

    (my $src, my $dst) = @_;

    if ( move($src, $dst) ) {
	logger(LOG_DEBUG, "Moved $src to $dst");
    } 
    else {
	log_fatal(LOG_ERR, "Moving $src to $dst failed: $!");
    }
}

# Removes temp file if terminating signal recv'd
sub signal_catcher {
    my $signame = shift;

    close $TMP_FH;
    unlink $TMP_FILE;
    log_fatal(LOG_INFO, "Recv'd SIG${signame}. Terminating.");
}	    

sub log_fatal {
    my ($p, $msg) = @_;
    logger($p, $msg);
    exit 1;
}

sub logger {
    my ($p, $msg) = @_;

    # Suppress LOG_DEBUG msgs unless $DEBUG set
    return if (!$DEBUG && $p eq LOG_DEBUG);

    # Suppress all but LOG_ERR msgs if $QUIET set
    return if ($QUIET && $p ne LOG_ERR);

    if ($TOTERM) {
        if ($p eq LOG_ERR) {	# errors should go to STDERR
	    print STDERR "$msg\n";
	}
	else {
	    print STDOUT "$msg\n";
	}
    }

    if ($SYSLOG) {
	syslog($p, $msg)
    }
}

#################################
# Connect to server and retrieve file
#
# Since we make as many as $MAXTRIES attempts to connect to the remote
# server to download the file, the network socket should be closed after
# each attempt, rather than let it be reused (because it may be in some
# unknown state).
#
# HTTP::Tiny doesn't export a method to explicitly close a connected
# socket, therefore, we instantiate the lexically scoped $http object in
# a function; when the function returns, the object goes out of scope
# and is destroyed, closing the socket.
sub retrieve_file {

    my $fh = shift;
    my $http;

    if ($LEAPSRC =~ /^https\S+/) {
	$http = HTTP::Tiny->new(%SSL_ATTRS);
	(my $ok, my $why) = $http->can_ssl;
	log_fatal(LOG_ERR, "TLS/SSL config error: $why") if ! $ok;
    } 
    else {
	$http = HTTP::Tiny->new();
    }

    my $reply = $http->get($LEAPSRC);

    if ($reply->{success}) {
	logger(LOG_DEBUG, "Download of $LEAPSRC succeeded");
	print $fh $reply->{content} || 
	    log_fatal(LOG_ERR, "Couldn't write new file contents to temp file: $!");
	close $fh;
	return 1;
    } 
    else {
	close $fh;
	return 0;
    }
}

########################
# Validate a leap-seconds file checksum
#
# File format: (full description in file)
# Pound sign (#) marks comments, EXCEPT:
# 	#$ number : the NTP date of the last update
# 	#@ number : the NTP date that the file expires
# 	#h hex hex hex hex hex : the SHA-1 checksum of the data & dates, 
#	   excluding whitespace w/o leading zeroes
#
# Date (seconds since 1900) leaps : leaps is the # of seconds to add
#  for times >= Date 
# Date lines have comments.
#
# Returns:
#   0	Invalid Checksum/Expired
#   1	File is valid

sub verifySHA {

    my $file = shift;
    my $fh;
    my $data;
    my $FSHA;

    open $fh, '<', $file || log_fatal(LOG_ERR, "Can't open $file: $!");

    # Remove comments, except those that are markers for last update,
    # expires and hash
    while (<$fh>) {
	if (/^#\$/) {
	    s/^..//;
	    $data .= $_;
	}
	elsif (/^#\@/) {
	    s/^..//;
	    $data .= $_;
	    s/\s+//g;
	    $EXPIRES = $_ - 2208988800;
	}
	elsif (/^#h\s+([[:xdigit:]]+)\s+([[:xdigit:]]+)\s+([[:xdigit:]]+)\s+([[:xdigit:]]+)\s+([[:xdigit:]]+)/) {
	    chomp;
	    $FSHA = sprintf("%08s%08s%08s%08s%08s", $1, $2, $3, $4, $5);
	}
	elsif (/^#/) {
	    # ignore it
	}
	elsif (/^\d/) {
	    s/#.*$//;
	    $data .= $_;
	} 
	else {
	    chomp;
	    print "Unexpected line: <$_>\n";
	}
    }
    close $fh;

    if ( $EXPIRES < time() ) {
        logger(LOG_DEBUG, 'File expired on ' . gmtime($EXPIRES));
        return 0;
    }

    if (! $FSHA) {
	logger(LOG_NOTICE, "no checksum record found in file");
	return 0;
    }

    # Remove all white space
    $data =~ s/\s//g;

    # Compute the SHA hash of the data, removing the marker and filename
    # Computed in binary mode, which shouldn't matter since whitespace has been removed
    my $DSHA = sha1_hex($data);

    if ($FSHA eq $DSHA) {
	logger(LOG_DEBUG, "Checksum of $file validated");
	return 1;
    } 
    else {
        logger(LOG_NOTICE, "Checksum of $file is invalid EXPECTED: $FSHA COMPUTED: $DSHA");
        return 0;
    }
}

sub show_help {
print <<EOF

Usage: $PROG [options]

Verifies and if necessary, updates leap-second definition file

All arguments are optional:  Default (or current value) shown:
    -C    Absolute path to CA Cert (see SSL/TLS Considerations)
    -D    Path to a CAdir (see SSL/TLS Considerations)
    -e    Specify how long (in days) before expiration the file is to be
    	  refreshed.  Note that larger values imply more frequent refreshes.
          $PREFETCH
    -F    Force update even if current file is OK and not close to expiring.
    -f    Absolute path ntp.conf file (default /etc/ntp.conf)
          $NTPCONF
    -h    show help
    -i    Specify number of minutes between retries
          $INTERVAL
    -L    Absolute path to leapfile on the local system
	  (overrides value in ntp.conf)
    -l    Specify the syslog(3) facility for logging
          $LOGFAC
    -q    Only report errors (cannot be used with -v)
    -r    Specify number of attempts to retrieve file
          $MAXTRIES
    -s    Send output to syslog(3) - implied if STDOUT has no tty or redirected
    -t    Send output to terminal - implied if STDOUT attached to terminal
    -u    Specify the URL of the master copy to download
          $LEAPSRC
    -v    Verbose - show debug messages (cannot be used with -q)

The following options are not (yet) implemented in the perl version:
    -4    Use only IPv4
    -6    Use only IPv6
    -c    Command to restart NTP after installing a new file
          <none> - ntpd checks file daily
    -p 4|6
          Prefer IPv4 or IPv6 (as specified) addresses, but use either

$PROG will validate the file currently on the local system.

Ordinarily, the leapfile is found using the 'leapfile' directive in
$NTPCONF.  However, an alternate location can be specified on the
command line with the -L flag.

If the leapfile does not exist, is not valid, has expired, or is
expiring soon, a new copy will be downloaded.  If the new copy is
valid, it is installed.

If the current file is acceptable, no download or restart occurs.

This can be run as a cron job.  As the file is rarely updated, and
leap seconds are announced at least one month in advance (usually
longer), it need not be run more frequently than about once every
three weeks.

SSL/TLS Considerations
-----------------------
The perl modules can usually locate the CA certificate used to verify
the peer's identity.

On BSDs, the default is typically the file /etc/ssl/certs.pem.  On
Linux, the location is typically a path to a CAdir - a directory of
symlinks named according to a hash of the certificates' subject names.

The -C or -D options are available to pass in a location if no CA cert
is found in the default location.

External Dependencies
---------------------
The following perl modules are required:
HTTP::Tiny 	- version >= 0.056
IO::Socket::SSL - version >= 1.56
NET::SSLeay 	- version >= 1.49

Version: $VERSION

EOF
}