#!/usr/bin/perl
# pssh
#       -- "persistent SSH" wrapper for autossh
#
# Copyright 2010 Greg Boyington.  All rights reserved.
#
# Redistribution and use in source and binary forms, with or without modification, are
# permitted provided that the following conditions are met:
#
#    1. Redistributions of source code must retain the above copyright notice, this list of
#       conditions and the following disclaimer.
#
#    2. Redistributions in binary form must reproduce the above copyright notice, this list
#       of conditions and the following disclaimer in the documentation and/or other materials
#       provided with the distribution.
#
# THIS SOFTWARE IS PROVIDED BY GREG BOYINGTON ``AS IS'' AND ANY EXPRESS OR IMPLIED
# WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
# FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> OR
# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
# SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
# ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
# NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
# ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#
# The views and conclusions contained in the software and documentation are those of the
# authors and should not be interpreted as representing official policies, either expressed
# or implied, of Greg Boyington.
#

use strict;
use IO::Socket::INET;

my $host = shift @ARGV or die "usage: $0 [user@]hostname [ SCREEN_LABEL ]\n";

my $autossh_path = 'autossh';

# the port range we should examine
my @port_range  = 20000 .. 30000;

# the IP we should try to bind to when checking for unused ports
my $bind_ip             = '127.0.0.1';

# map to corresponding AUTOSSH_* environment variables
my %config = (
        poll                    => undef,
        gatetime                => undef,
        logfile                 => undef,
        debug                   => undef,
        path                    => undef,
);
my ( $bind, $listen, $open );
while ( @port_range ) {
        $open=0;
        $bind   = shift @port_range;
        $listen = shift @port_range or last;
        for ( $bind, $listen ) {
                my $socket = IO::Socket::INET->new(
                        PeerAddr        => $bind_ip,
                        PeerPort        => $_,
                        Proto           => 'TCP',
                        Timeout         => 3
                );
                $open++ unless defined $socket;
                $socket=undef;
        }
        last if $open==2;
}
die "No available ports detected.\n" unless $open;

# use environment variables to configure autossh
$ENV{ 'AUTOSSH_'.$_ } = $config{ $_} foreach grep { defined $config{$_} } keys %config;

# use a unique label for this screen session
my $label = shift @ARGV || getpwuid( $> ) . $bind;

# invoke autossh
my $cmd = sprintf( q( %s -M %d -t %s "screen -e^Zz -D -R -S %s"), $autossh_path, $bind, $host, $label );
exec $cmd;

=head1  NAME

pssh - create a 'persistent' ssh connection with autossh and screen

=head1 SYNOPSIS

pssh user@hostname

=head1 DESCRIPTION

pssh is a small script that manages autossh and screen for "persistent" SSH sessions.  It searches a
given port range looking for two consecutive available ports, and passes them to autossh.  autossh
takes care of monitoring the SSH connection and reconnecting to the remote screen session as needed.

Screen sessions are labeled (via -S) with the effective username and the local port being used, so
one can correlate existing screen sessions on the remote host with the local autossh processes.  You
can force screen to reattach to an existing session by specifying the label when calling pssh:

pssh user@hostname joe20004

=head1 SEE ALSO

autossh, ssh

=head1 AUTHOR

pssh was written by Greg Boyington <greg@automagick.us>, inspired by the 'rscreen' script that ships
with autossh.

=head1 COPYRIGHT NOTICE

Copyright 2010 Greg Boyington.  All rights reserved.

pssh is distributed under the Simplified BSD License; see file header for details.

=cut