#!/bin/sh

# Sets up a tunnel from the local host A to a remote host B and rewrites
# .ssh/config on B to be able to access A from B.  This is useful if, for
# instance, A is a laptop hosting some services via SSH.  These services
# will be accessible via the same hostname, even if A moves from place to
# place (no need to modify svn+ssh URL's and so on).

# If $HOST is hostname.tld, the .ssh/config on B should have:
#   Host hostname.tld
#     HostKeyAlias hostname.tld
#     Hostname anything
#     Port any-number
# The Hostname and Port lines will be rewritten by this script.

# Arguments:
#   $1: remote host B.
#   $2: free port on B used for the tunnel.

if [ $# -ne 2 ]; then
  echo "Usage: $0 <host> <port>" >&2
  exit 1
fi

ssh -f -N -R ${2}:localhost:22 $1
ssh $1 "perl -pi -e '/^Host\s+(.*)/ and \$host = \$1;
                     \$host eq \"$HOST\" or next;
                     s/^(\s*Hostname)\s.*/\1 localhost/;
                     s/^(\s*Port)\s.*/\1 $2/' .ssh/config"

# $Id: ssh-forward 38408 2010-08-03 17:11:27Z vinc17/xvii $