#!/bin/sh -
#
#  $Id: ssh-tunnel,v 1.2 2005/01/27 05:36:46 dgregor Exp $
#
# Copyright (c) 2000-2004 Daniel J. Gregor, Jr.
# All rights reserved.
# 
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
# 
#    - Redistributions of source code must retain the above copyright
#      notice, this list of conditions and the following disclaimer.
#    - 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 THE COPYRIGHT HOLDER AND CONTRIBUTORS
# "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 THE
# COPYRIGHT HOLDERS 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.
#
#
#
# This script is a tool for people who need to setup SSH[1] sessions through
# which they tunnel other traffic, but want to keep the original "tunnel"
# session tucked away.  It uses GNU Screen[2] to setup a single virtual
# terminal for each tunnel session.  On the remote end, it executes a script
# called nothing[3], which is used to keep the session alive by sending a
# null character or the date every sixty seconds (useful to keep firewall
# and NAT session timeouts from occurring).  The details of configuring
# the tunnels[4] in SSH for are left to the user.
#
# References:
# [1]	OpenSSH:
#	http://www.openssh.org/
#
# [2]	GNU Screen:
#	http://www.gnu.org/software/screen/
#
# [3]	"nothing" script:
#	http://www.gregor.com/download/scripts/nothing
#
# [4]	ssh_config man page:
#	http://www.openbsd.org/cgi-bin/man.cgi?query=ssh_config
#
#
# How to install:
#
# 1) Put this script in your path somewhere.  I'm a fan of $HOME/bin.
#
# 2) Create an entry in your $HOME/.ssh/ssh_config directory for the
#    tunnel session.  I usually name it something like "<host>-forward".
#    This is what you put in the "Host" specification.  E.g.:
#	Host loginserver-forward
#	  Hostname loginserver.example.com
#	  LocalForward ... ...:...
#	  ...
#    See [4] for details on configuring tunnels.
#
# 3) Create a symblic link from ssh-tunnel to the name that you used above
#    for the SSH configuration.  E.g.:
#	cd $HOME/bin
#	ln -s ssh-tunnel loginserver-forward
#
# 4) Grab the nothing script from [3] and install it on the remote server.
#    If you put the nothing script somewhere other than the home directory
#    remote server, edit this script and fix the "remote_nothing" variable.
#
#
# To use:
#
# Just type "<host>-forward" or whatever you called the SSH session.  E.g.:
#	loginserver-forward
#
# See the man page for "screen" for details on its escape character and
# how to change it.  To disconnect from screen, you use "CTRL-A d" (that's
# Control-A and then the "d" character) by default.  To reconnect, just
# execute the command for the session again as you had done so before.
#

remote_nothing="./nothing"

us="`basename $0`"

if [ $# -gt 0 -a x"$1" = x"-c" ]; then
	while [ 1 ]; do
		echo -e "Connect? (Y/n): \c"
		read answer
		if [ x"$answer" = x"n" -o x"$answer" = x"N" ]; then
			exit 0
		fi
		ssh $us $remote_nothing -d
	done
else
	screen -r -d $us || screen -S $us $0 -c
fi