#!/usr/bin/perl
use strict;

#This script should run and either reconfigure teh box for dual homing (if needed) or do nothing (if already done)
#
#Broadly
# /etc/iproute2/rt_tables 
# - needs entries for each interface
#
#/sbin/ip route add default via (default gateway for eth0) table eth0
#/sbin/ip route add default via (default gateway for eth1) table eth1
#/sbin/ip rule add from (ip of eth0) table eth0
#/sbin/ip rule add from (ip of eth1) table eth1
#/sbin/ip rule add iif eth0 table eth0
#/sbin/ip rule add iif eth1 table eth1
#/sbin/ip rule add oif eth0 table eth0
#/sbin/ip rule add oif eth1 table eth1

my $logLevel = 5;

my $IP = "/sbin/ip";

# First enumerate interfaces

sub execute($) {
    my ($cmd) = @_;
    print("RUNNING: $cmd\n") if ($logLevel >= 1);
    open(RUN, "$cmd 2>&1|");
    while (<RUN>) {
        chomp;
        debug($_);
    }
    close(RUN);
}
sub warning($) {
    my ($msg) = @_;
    print("WARNING: $msg\n") if ($logLevel >= 3);
}
    
sub summ($) {
    my ($msg) = @_;
    print("SUMM: $msg\n") if ($logLevel >= 2);
}
sub info($) {
    my ($msg) = @_;
    print("INFO: $msg\n") if ($logLevel >= 4);
}
sub debug($) {
    my ($msg) = @_;
    print("DEBUG: $msg\n") if ($logLevel >= 5);
}

my $ints = {};

my $cmd = "$IP -o a";
open(C, "$cmd|");
while (<C>) {
    next unless /: ([^ ]+) +inet ([0-9.]+)\/([0-9]+) /;
    my ($int, $ip, $subnet) = ($1, $2, $3);
    next if ($int =~ /^lo/);
    info("$ip /$subnet on $int");
    $ints->{$int}->{ip} = $ip;
    $ints->{$int}->{subnet} = $subnet;
}
close(C);

# Check tables
open(RT, "/etc/iproute2/rt_tables");
my $tables = {};
while (<RT>) {
    chomp;
    s/#.*//;
    next unless /./;
    my ($num, $int) = split(/[	 ]+/g);
    debug("Table $int = table $num");
    $tables->{byint}->{$int} = $num;
    $tables->{bynum}->{$num} = $int;
}
close(RT);


foreach my $int (sort keys %{$ints}) {
    if (!defined($tables->{byint}->{$int})) {
        for (my $i = 201; $i < 250; $i++) {
            if (!defined($tables->{bynum}->{$i})) {
                debug("ADD $int to tables as $i");
                open(RT, ">>/etc/iproute2/rt_tables");
                print(RT "$i	$int\n");
                close(RT);
                $tables->{bynum}->{$i} = $int;
                last;
            }
        }
    }
}


# 32763:	from all oif eno2 lookup eno2 
# 32764:	from all iif eno2 lookup eno2 
# 32765:	from 192.168.26.101 lookup eno2 

my $rule;

open(RULE, "$IP rule|");
while (<RULE>) {
    chomp;
    debug("RULE: $_");
    if (/from all (.if) ([^ ]*) lookup ([^ ]*)/) {
        my $xif = $1; my $int = $2; my $tab = $3;
        info("$xif rule for $int $tab exists");
        $rule->{$xif}->{$tab} = $int;
    }
    if (/from ([0-9.]*) lookup ([^ ]*)/) {
        my $ip = $1; my $tab = $2;
        info("IP rule for $ip via $tab exists");
        $rule->{ip}->{$ip} = $tab;
    }
}
close(RULE);

# Add rules for interfaces->table mapping *if the rules don't exist*
#/sbin/ip rule add from (ip of eth0) table eth0
#/sbin/ip rule add iif eth0 table eth0
#/sbin/ip rule add oif eth0 table eth0


foreach my $int (sort keys %{$tables->{byint}}) {
    my $ip = $ints->{$int}->{ip};
    if ($ip =~ /[0-9]/) {
        if ($rule->{ip}->{$ip} eq $int) {
            info("# ip $ip table $int exists");
        } else {
            execute("$IP rule add from $ip table $int");
        }
        if ($rule->{iif}->{$int} eq $int) {
            info("# iif $int table $int exists");
        } else {
            execute("$IP rule add iif $int table $int");
        }
        if ($rule->{oif}->{$int} eq $int) {
            info("# oif $int table $int exists");
        } else {
            execute("$IP rule add oif $int table $int");
        }
    }
}
# Add default gateway to tables
#/sbin/ip route add default via (default gateway for eth0) table eth0

# Gateway could be in /etc/network/interfaces
# Or could be in dhcp lease table

my $inInt = "";
my $nextInterfaceDefault = 0;
my $gw = {};

# choose desired default interface
my $desiredDefaultInterface = "";

open(INT, "/etc/network/interfaces");
while (<INT>) {
    if (/# The primary network interface/) {
        debug("Will choose the next interface for default gateway if possible");
        $nextInterfaceDefault = 1;
    }
    if (/iface ([^ ]+) inet dhcp/) {
        $inInt = $1;
        $gw->{$inInt} = "dhcp";
        if ($nextInterfaceDefault) { 
            $desiredDefaultInterface = $inInt;
            $nextInterfaceDefault = 0;
        }
        $inInt = "";
    } elsif (/iface ([^ ]+) inet static/) {
        $inInt = $1;
        if ($nextInterfaceDefault) { 
            $desiredDefaultInterface = $inInt;
            $nextInterfaceDefault = 0;
        }
    }
    if (/gateway ([^\s]+)/) {
        $gw->{$inInt} = $1;
    }
}
close(INT);

foreach my $int (sort keys %{$tables->{byint}}) {
    my $ip = $ints->{$int}->{ip};
    my $gwip = $gw->{$int};
    if ($ip =~ /[0-9]/) {
        if ($gwip eq "dhcp") {
            if (-f "/var/lib/dhcp/dhclient.$int.leases") {
                open(L, "/var/lib/dhcp/dhclient.$int.leases");
                while(<L>) {
		    # Remove commented lines
		    s/#.*//;
                    if (/option routers ([0-9.]+)/) {
                        $gwip = $1;
                    }
                }
                close(L);
            } else {
                warning("Can't find DHCP lease for $int")
            }
        }
        info ("Int $int IP $ip GW=$gwip");
        if ($gwip =~ /[0-9]/) {
            #/sbin/ip route add default via (default gateway for eth0) table eth0
            # If route isn't right, delete it
            my $routeOK = 0;
            open(RT, "$IP route list table $int|");
            while(<RT>) {
                chomp;
                if (/default via $gwip dev $int/) {
                    $routeOK = 1;
                    info("Route for $int via $gwip is OK");
                }
            }
            close(RT);
            if ($routeOK == 0) {
                execute("$IP route del default table $int");
                execute("$IP route add default via $gwip table $int");
            }
        } else {
            warning("Can't find gateway for $int / $ip");
        }
    } else {
        if ($int =~ /[0-9]/) {
            # real interface
            info("$int doesn't have an IP");
        } else {
            debug("$int doesn't have an IP");
        }
    }
}

# Fianlly summarise the current state
open(RT, "$IP route list|");
while(<RT>) {
    if (/default via ([0-9.]+) dev ([^ ]+)/) {
        my $defgw = $1;
        my $defint = $2;
        my $ip = $ints->{$defint}->{ip};
        if ($desiredDefaultInterface =~ /../) {
            debug("We'd like to use $desiredDefaultInterface as default gateway for non tabled packets");
            if ($defint eq $desiredDefaultInterface) {
                debug("And we are using $defint as default gateay!");
            } else {
        	my $newgw = $gw->{$desiredDefaultInterface};
                info("Replacing default gateway with '$desiredDefaultInterface' $newgw");
                execute("$IP route change default via $newgw");
            }
        }
        summ("DFLT: Default gateway via $defgw on $defint/$ip");
    } elsif (/([0-9.]+) dev ([^ ]+) .*src ([0-9.]+)/) {
        my ($net, $int, $ip) = ($1, $2, $3);
        summ("DFLT: Directly connected $net on $int/$ip");
    }
}
close(RT);
foreach my $tab (sort keys %{$tables->{byint}}) {
    next unless defined($ints->{$tab}->{ip});
    open(RT, "$IP route list table $tab|");
    while(<RT>) {
        if (/default via ([0-9.]+) dev ([^ ]+)/) {
            my $defgw = $1;
            my $defint = $2;
            my $ip = $ints->{$defint}->{ip};
            summ("$tab: Gateway via $defgw on $defint/$ip");
        } elsif (/([0-9.]+) dev ([^ ]+) .*src ([0-9.]+)/) {
            my ($net, $int, $ip) = ($1, $2, $3);
            summ("$tab: Directly connected $net on $int/$ip");
        }
    }
    close(RT);
}