#! /usr/bin/perl
# Copyright (C) 2012 Sergey Poznyakoff <gray@gnu.org>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3, or (at your option)
# any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

use strict;
use Getopt::Long qw(:config gnu_getopt no_ignore_case);
use Socket;
use Digest::MD5;
use Net::DNS;
use Net::CIDR;
use Pod::Usage;
use Pod::Man;
use POSIX qw(strftime);

# Global vars
my $sys_config_file = "/etc/axfr2acl.conf"; # Configuration file name
my $descr = "create a BIND-style ACL containing all A records from a zone";
my $script;        # This script name.
my %debug_level = ( 'GENERAL' => 0, 'DNS' => 0);
my @netlist;
my @oldlist;

# Options:
my $debug;         # Debug mode indicator.
my $logfile;       # Name of the logfile.
my $dry_run;       # Dry-run mode.
my $help;          # Show help and exit.
my $man;           # Show man and exit.
my @zones;
my $outfile = "netlist";
my $aclname;       # Name of a bind-style ACL
my $comment;       # Initial comment line
my $update;
my %oldserial;     # Old serial numbers  
my %serial;        # Zone serial numbers

# "Initial" are networks supplied by "--add-network" and "--from-file" options.
my $initnetctx;    # MD5 context for tracking changes in initial networks
my $oldsig;        # Old MD5 signature of the initial networks
my $netsig;        # Current MD5 signature of the initial networks

# Return codes:
#  0 - OK, nothing changed
#  1 - OK, list updated
#  2 - General error
#  3 - Usage error

#############

sub logit {
    print LOG "@_\n";
}

sub loginit {
    if ($logfile and (!-e $logfile or -w $logfile)) {
	print STDERR "$script: logging to $logfile\n";
	open(LOG, ">$logfile");
    } else {
	open(LOG, ">&STDERR");
    }
}

sub logdone {
}

sub abend($) {
    my $msg = shift;
    logit($msg);
    debug('GENERAL', 1, "ABEND");
    logdone();
    exit(2);
}

sub debug {
    my $category = shift;
    my $level = shift;
    #    print STDERR "$category: $debug_level{$category} >= $level\n";
    if ($debug_level{$category} >= $level) {
	print LOG "$script: DEBUG[$category]: @_\n";
    }
}

sub read_config_file($) {
    my $config_file = shift;
    print STDERR "reading $config_file\n" if ($debug);
    open(FILE, "<", $config_file) or die("cannot open $config_file: $!");
    while (<FILE>) {
	chomp;
	s/^\s+//;
	s/\s+$//;
	s/\s+=\s+/=/;
        s/#.*//;
	next if ($_ eq "");
	unshift(@ARGV, "--$_");
    }
}

sub note_init_network($) {
    my $cidr = shift;
    $initnetctx->add($cidr);
}

sub networks_from_file($) {
    my ($file) = @_;
    open(FILE, "<", $file)
	or abend("Cannot open file $file for reading");
    while (<FILE>) {
	chomp;
	s/^\s+//;
	s/\s+$//;
	s/;$//;
	s/#.*//;
	next if ($_ eq "");
	note_init_network($_);
	@netlist = Net::CIDR::cidradd($_,@netlist);
    }
    close(FILE);
}

sub read_acl($) {
    my ($file) = @_;
    open(FILE, "<", $file) or return;
    my $line=1;
    my $zone;
    my $sn;
    while (<FILE>) {
	chomp;
	s/^\s+//;
	s/\s+$//;
	s/;$//;
	if (($zone, $sn) = ($_ =~ /^#serial\s+(\S+)\s+([0-9]+)/)) {
	    $oldserial{$zone} = $sn;
	    next;
        }
	if (($sn) = ($_ =~ /^#netsig\s+(\S+)/)) {
            $oldsig = $sn;
	}
	s/#.*//;
	next if ($_ eq "");
	next if /^acl/;
	next if /}/;
        abend("$file:$line: invalid CIDR: $_") unless (Net::CIDR::cidrvalidate($_));
	@oldlist = Net::CIDR::cidradd($_,@oldlist);
        $line++;
    }
    @oldlist = sort @oldlist;
    close(FILE);
}

###########
($script = $0) =~ s/.*\///;

my $home;

eval {
    my @ar = getpwuid($<);
    $home = $ar[7];
};

if ($ENV{'AXFR2ACL_CONF'}) {
    read_config_file($ENV{'AXFR2ACL_CONF'});
} elsif (-e "$home/.axfr2acl.conf") {
    read_config_file("$home/.axfr2acl.conf");
} elsif (-e "$sys_config_file") {
    read_config_file("$sys_config_file");
}

$initnetctx = Digest::MD5->new;

GetOptions("help|h" => \$help,
	   "man" => \$man,
	   "dry-run|n" => \$dry_run,
           "debug|d:s" => sub {
	       if (!$_[1]) {
		   foreach my $key (keys %debug_level) {
		       $debug_level{$key} = 1;
		   }
	       } elsif ($_[1] =~ /^[0-9]+/) {
		   foreach my $key (keys %debug_level) {
		       $debug_level{$key} = $_[1];
		   }
	       } else {
		   foreach my $cat (split(/,/, $_[1])) {
		       my @s = split(/[:=]/, $cat, 2);
		       $s[0] =~ tr/[a-z]/[A-Z]/;
		       if (defined($debug_level{$s[0]})) {
			   $debug_level{$s[0]} =
			       ($#s == 1) ? $s[1] : 1;
		       } else {
			   abend("no such category: $s[0]");
		       }
		   }
	       }
	   },
           "log-file|l=s" => \$logfile,
	   "outfile|o=s" => \$outfile,
	   "acl=s" => \$aclname,
	   "comment=s" => \$comment,
	   "add-network=s" => sub {
	       foreach my $cidr (split(/,/, $_[1])) {
		   note_init_network($cidr);
		   @netlist = Net::CIDR::cidradd($cidr,@netlist);
	       }
	   },
	   "from-file|T=s" => sub {
	       networks_from_file($_[1]);
	   },
	   "zones|z=s" => sub {
	       foreach my $rs (split(/,/, $_[1])) {
		   push(@zones,$rs);
	       }
	   },
	   "update|u" => \$update
    ) or exit(3);

pod2usage(-message => "$script: $descr", -exitstatus => 0) if $help;
pod2usage(-exitstatus => 0, -verbose => 2) if $man;

loginit();
debug('GENERAL', 1, "startup");

abend("No zones given") if ($#zones == -1);

$netsig = $initnetctx->b64digest;
read_acl($outfile) if ($update);

# Determine initial update status:
# The output needs to be updated if either the --update flag is *not*
# given (i.e. the user wants unconditional update), or if the MD5 signatures
# of added network differ.
#
# The initial update status will be corrected in the loop below, based on the
# SOA of the networks involved.
#
my $need_update = !$update;
if (!$need_update) {
    $need_update = $netsig ne $oldsig;
    debug('GENERAL', 1,
	  "update forced because initial networks changed") if ($need_update);
}

# Create resolvers and collect serial numbers
my %resolver;

foreach my $zone (@zones) {
    my $res  = Net::DNS::Resolver->new;
    debug('DNS', 1, "querying SOA for $zone");
    my $query = $res->query($zone, "SOA");
    unless ($query) {
	print STDERR "$script: cannot get SOA of $zone: " . $res->errorstring . "\n";
	next;
    }
    $resolver{$zone} = $res;
    my $rr = (grep { $_->type eq 'SOA' } $query->answer)[0];
    debug('DNS', 2, "zone $zone serial ".$rr->serial);
    $need_update = 1
	if ($update && (!defined($oldserial{$zone}) ||
			$oldserial{$zone} < $rr->serial));
    delete $oldserial{$zone};
    $serial{$zone} = $rr->serial;
}

if ($update and keys(%oldserial)) {
    debug('GENERAL', 1, "some zones removed: forcing update");
    $need_update = 1;
}

if ($need_update) {
    foreach my $zone (@zones) {
	my $res;
	my $rr;

	$res = $resolver{$zone};
	next unless ($res);
	
	debug('DNS', 1, "querying NSs for $zone");
	my $query = $res->query($zone, "NS");
	unless ($query) {
	    print STDERR "$script: cannot get NS records for $zone: " .
		          $res->errorstring . "\n";
	    next;
	}

	foreach $rr (grep { $_->type eq 'NS' } $query->answer) {
	    $res->nameservers($rr->nsdname);
	    debug('DNS', 2, "$zone NS ". $rr->nsdname);
	}

	debug('DNS', 1, "Transferring $zone");
	my @records = grep { $_->type eq 'A' } $res->axfr($zone);
	debug('DNS', 1, "Got $#records records");
	
	foreach my $rr (@records) {
	    @netlist = Net::CIDR::cidradd($rr->address,@netlist);
	}
    }
}

if (!$need_update) {
    debug('GENERAL', 1, "shutdown: list unchanged");
    logdone();
    exit(1);
}    

if ($update) {
    my %oldset = map { $_ => $_ } @oldlist;
    $update = 0;
    foreach my $net (sort @netlist) {
	if (!$oldset{$net}) {
	    $update = 1;
	    last;
	} else {
	    delete $oldset{$net};
	}
    }
    unless ($update or keys(%oldset) > 0) {
	if ($need_update && !$dry_run) {
	    debug('GENERAL', 1, "list unchanged; proceeding to save serials");
	} else {
	    debug('GENERAL', 1, "shutdown: list unchanged");
	    logdone();
	    exit(1);
	}
    }
}

if ($dry_run) {
    print join("\n",@netlist)."\n";
} else {
    my $file;
    my $indent = "";

    debug('GENERAL',1,"writing output file $outfile");
    
    open($file, ">", $outfile) or
	abend("cannot open $outfile for writing: $!");
    if ($comment) {
	foreach my $line (split(/\n/, $comment)) {
	    print $file "# $line\n";
	}
    }
    print $file strftime "# network list created by $script on %c\n",
          localtime;
    foreach my $zone (keys %serial) {
	print $file "#serial $zone $serial{$zone}\n";
    }
    print $file "#netsig $netsig\n" if ($netsig);
    
    if (defined($aclname)) {
	print $file "acl $aclname {\n";
	$indent = "\t";
    }
    foreach my $cidr (@netlist) {
	print $file "${indent}${cidr};\n";
    }
    print $file "};\n" if (defined($aclname));
    close($file);
}

debug('GENERAL', 1, "shutdown");
logdone();

###########

__END__
=head1 NAME

axfr2acl - create a BIND ACL containing "A" records from a set of zones

=head1 SYNOPSIS

axfr2acl [I<options>]
    
=head1 DESCRIPTION

B<Axfr2acl> collects all B<A> records from a set of supplied DNS zones
and writes out a DNS ACL containing all of them.  If possible, the
addresses are compressed into CIDRs.  The resulting list is sorted
lexicographically.

The resulting ACL is normally written to a file, either as a list of CIDRs
or as a BIND B<acl> statement, if the ACL name is given.  In both cases, the
file is sutable for inclusion in the BIND configuration file.  If the file
already exists when the command is invoked, its contents is recorded and
is used subsequently to determine whether it has changed.  The utility will
actually modify the output file only if the constructed list differs from
the one it contained initially.  It will also avoid running zone transfers
if the serial records of all involved zones did not change since the last
run.

The program exits with code 0 if the file is up to date, 1 if it has
successfully updated the file, 2 if some error ocurred and 3 if the
command line usage was incorrect.    
    
=head1 OPTIONS

The following option control the output:
    
=over 4

=item B<--acl>=I<name>

Format output as a B<bind> ACL statement with the given I<name>.

=item B<--comment>=I<string>

Print I<string> as the heading comment to the output.  The argument can
consist of multiple lines.  A C<#> sign will be printed before each of
them.

=item B<--outfile>=I<FILE>, B<-o> I<FILE>

Write the result to I<FILE>, instead of the default C<netlist>.

=back

The following options control the selection of DNS zones and initial
contents of the output list:

=over 4

=item B<--add-network>=I<arg>

Add given CIDRs to the output list.  Argument is a comma-separated list
of CIDRs.

=item B<--from-file>=I<FILE>, B<-T> I<FILE>

Populate the output list with CIDRs read from I<FILE>.  The file must
list each CIDR on a separate line.  Empty lines and comments (introduced
by C<#> sign) are ignored.

=item B<--zones>=I<zonelist>, B<-z> I<zonelist>

Defines a list of zones to query.  I<Zonelist> is a comma-separated list
of zone names.

=back

Options controlling log and debug output:

=over 4

=item B<--log-file>=I<FILE>, B<-l> I<FILE>

Write diagnostic output to I<FILE>, instead of standard error.

=item B<--debug>[=I<spec>[,I<spec>...]], B<-d>[I<spec>[,I<spec>...]]

Set debugging level.  I<Spec> is either B<category> or B<category>=B<level>,
B<category> is a debugging category name and B<level> is a decimal
verbosity level.  Valid categories are: C<GENERAL> and C<DNS>.

=item B<--dry-run>, B<-n>

Don't create output file.  Instead print the result on the standard
output.    

=back

Informational options:

=over 4

=item B<--help>, B<-h>

Shows a terse help summary and exit.

=item B<--man>

Prints the manual page and exits.

=back

=head1 CONFIGURATION

The program reads its configuration from one of the following locations:

=over 4

=item B<a.> The file name given by C<AXFR2ACL_CONF> environment variable (if set)

=item B<b.> B<~>/.axfr2acl.conf

=item B<c.> /etc/axfr2acl.conf

=back

The first existing file from this list is used.  It is an error, if the
B<$AXFR2ACL_CONF> variable is set, but points to a file that does not exist.
It is not an error, if B<$AXFR2ACL_CONF> is not set and neither of the two
remaining files exist.  It is, however, an error if any of these file exists,
but is not readable.

The configuration file uses a usual UNIX configuration format.  Empty
lines and UNIX comments are ignored.  Each non-empty line is either an
option name, or option assignment, i.e. B<opt>=B<val>, with any amount of
optional whitespace around the equals sign.  Valid option names are
the same as the long command line options, but without the leading B<-->.
For example:

  zones = example.net,example.com
  acl = mynets
  add-network = 10.0.0.0/8
  outfile = networks.inc

=head1 ENVIRONMENT

=over 4

=item AXFR2ACL_CONF

The name of the configuration file to read, instead of the default
F</etc/axfr2acl.conf>.

=back

=head1 SEE ALSO

B<rpsl2acl>(1).

=head1 AUTHOR

Sergey Poznyakoff <gray@gnu.org>

=cut