#!/usr/bin/perl -w

use strict;

use File::Spec::Functions;
use File::Temp;
use FindBin;

my $SERVER = catfile($FindBin::Bin, 'mosh-server.real');
my $SHELL = catfile($FindBin::Bin, 'mosh-session');

sub check_max_logins {
    open LIMITS, '<', '/etc/security/limits.conf' or return;
    my $max;
    while (<LIMITS>) {
        $max = $1 if m/
            ^ \s* \* \s* hard \s* maxlogins \s* (\d+) \s* $
        /x;
    }
    close LIMITS;
    defined $max or return;
    open W, '-|', 'w', '-hs', '--', $ENV{'USER'} or return;
    my $cur = 0;
    $cur++ while (<W>);
    close W;
    $cur >= $max - 1 and $cur >= 3 or return;

    print STDERR <<EOF;
$0: error: too many logins.

Hey!  I know it isn't really any of my business, but I couldn't help
but notice that you are logged in to this server $cur times out of a
maximum $max.  To stop you from using up all of your simultaneous
logins and locking yourself out of this server entirely, I'm going to
exit.  You can thank me later.

RIGHT NOW:
You should log in to this server with ssh.  Then you should clean up
your disconnected mosh-server processes to reduce your login count.
If all of your mosh sessions are disconnected, you can do this with:
  pkill -u $ENV{'USER'} mosh-server
You will then be able to safely continue using mosh.

IN THE FUTURE:
If you are using screen or tmux inside mosh, the easiest way to avoid
this problem is to attach your screen or tmux directly from the mosh
command line with -d:
  mosh HOSTNAME -- screen -dr
  mosh HOSTNAME -- tmux attach -d
Then when you reattach from another session, the previous screen or
tmux client will exit, and because there's no shell between it and the
corresponding mosh-server, the mosh-server will exit too.

Have a nice day!

$0: exiting.
EOF
    exit -1;
}

check_max_logins;

sub finish {
    if ( not grep { $_ eq "--" } @ARGV ) {
      push @ARGV, '--', $SHELL;
    }

    $ENV{ 'MOSH_SERVER_NETWORK_TMOUT' } = q{1209600}; # 14-day timeout per 2/15/2017 jweiss request

    exec 'pagsh', '-c', 'aklog; exec "$@"', '--', $SERVER, @ARGV;
    die;
}

if ( not defined $ENV{ 'KRB5CCNAME' } ) {
  $ENV{ 'KRB5CCNAME' } = 'FILE:/tmp/krb5cc_' . $>;
}

my $filename;

if ( $ENV{ 'KRB5CCNAME' } =~ m{^FILE:(.*)} ) {
  $filename = $1;
} else {
  finish;
}

# Read ticket credentials
my $credentials;
{
  open CREDENTIALS, $filename or finish;
  local $/ = undef;
  $credentials = <CREDENTIALS>;
  close CREDENTIALS or die;
}

# Write it to a temp file
File::Temp->safe_level( File::Temp::HIGH );
my $new_credentials = File::Temp->new( UNLINK => 0,
				       TEMPLATE => '/tmp/krb5cc-mosh_' . $> . '_XXXXXX' );
my $new_filename = $new_credentials->filename;
print $new_credentials $credentials or die "print: $!\n";
close $new_credentials or die "close: $!\n";

$ENV{ 'KRB5CCNAME' } = 'FILE:' . $new_filename;
finish;