#!/bin/bash
#
# wshare v1.0 - gui agnostic sharing of your network connections 
#
#     Copyright (C) 2008  Stefan Marsiske
# 
#    This program is free software: you can redistribute it and/or modify
#    it under the terms of the GNU General Public License as published by
#    the Free Software Foundation, either version 3 of the License, or
#    (at your option) any later version.
#
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.
#
#    You should have received a copy of the GNU General Public License
#    along with this program.  If not, see <http://www.gnu.org/licenses/>.

# default config
#------------------
### Common settings

# set internal network, over which the external is shared
# try to automatically select the first wireless device from /proc/net/wireless
innet=$(head -3 /proc/net/wireless 2>/dev/null | tail -1 | cut -f1 -d: | tr -d " ")
# if automatic detection fails, use ath0 as default
innet=${innet:-ath0}
# set the essid of the shared network master
essid=wshared

#------------------
### Master settings

# specify the subnet of the internal network 
# this must be in the /24 range currently...
# so only specify networks with 3 of four octets
subnet=10.17.17

# specify which network to share, this is the device that connects to the
# internet
exnet=ppp0

# specify Master IP address
ownip=10.17.17.1

#------------------
# none of the files below might exist, so we route any error messages to our
# logging daemon /dev/null
# global config
[[ -r /etc/wshare.conf ]] && . /etc/wshare.conf 2>/dev/null
# personal config
[[ -r $HOME/.wshare.conf ]] && . $HOME/.wshare.conf 2>/dev/null
# testing config, same dir as script, shmagic.
[[ -r ${0%%wshare}wshare.conf ]] && . ${0%%wshare}wshare.conf 2>/dev/null

# default behaviour
client=true

usage="${0##*/} [-m] \
      [-e <essid:wshared>] \
      [-n subnet <10.17.17>] \
      [-o <exnet:ppp0>] \
      [-i <innet:eth0>] \
      [-a <self.address:subnet.1>] \
      [-k <key:unset>]"

# only root can do this
[[ $(id -u) -ne 0 ]] && { 
   echo $usage
   echo "error: please run ${0##*/} as root"
   exit 1;
}

while getopts ?m:e:n:o:i:a: opt; do
   case $opt in
      m) client=false;;
      e) essid=$OPTARG;;
      n) subnet=$OPTARG;;
      o) exnet=$OPTARG;;
      i) innet=$OPTARG;;
      a) ownip=$OPTARG;;
      k) key=$OPTARG;;
      ?|h) echo $usage; exit;;
   esac
done
shift `expr $OPTIND - 1`

# switch MODE
echo switching ${innet} to mode: ad-hoc
if [[ ${innet} == "ath0" ]]; then
   wlanconfig ${innet} destroy || exit 1
   # madwifi calls the mode adhoc, not ad-hoc...
   wlanconfig ath0 create wlandev wifi0 wlanmode adhoc
else
   iwconfig ${innet} mode ad-hoc || exit 1
fi

# set ESSID
# TBA clients in ad-hoc and essid? necessary?
echo setting essid: ${essid}
iwconfig ${innet} essid ${essid} || exit 1

# set encryption KEY
if [[ -n "${key}" ]]; then
   echo setting encryption key: ${key}
   iwconfig ${innet} key ${key} || exit 1
fi

if $client; then
   ifconfig ${innet} up || exit 1
   dhclient ${innet} || exit 1
else
   # start shared network
   echo starting ${innet} @ ${ownip}
   ifconfig ${innet} up ${ownip} || exit 1

   # NET shared network to external network
   echo enabling nat of ${innet} to ${exnet}
   iptables --table nat --flush || exit 1
   # Delete all chains that are not in default filter and nat table
   iptables --table nat --delete-chain || exit 1
   # Set up IP FORWARDing and Masquerading
   iptables --table nat --append POSTROUTING --out-interface ${exnet} -j MASQUERADE || exit 1
   iptables --append FORWARD --in-interface ${innet} -j ACCEPT || exit 1
   # Enables packet forwarding by kernel 
   echo 1 > /proc/sys/net/ipv4/ip_forward || exit 1

   # set up DHCP server for wshared
   echo setting up dhcp server for ${subnet}.0 @ ${innet}
   dhcpcfg=/tmp/dhcp-wshare-$$-${RANDOM}
   cat >${dhcpcfg} <<EOF
ddns-update-style none;
default-lease-time 600;
max-lease-time 7200;
log-facility local7;

option routers ${subnet}.1;
option domain-name-servers $(grep '^nameserver ' /etc/resolv.conf | sed -e 's/^nameserver[      ]*\(.*\)/\1/' |  sed -e "s/$/, /" | tr -d "\n" | sed "s/, $/\n/") ;

subnet ${subnet}.0 netmask 255.255.255.0 {
    range ${subnet}.2 ${subnet}.253;
}
EOF

   # serve IP addresses
   echo running dhcp server
   dhcpd3 -cf ${dhcpcfg} -pf ${dhcpcfg}.pid ${innet} || exit 1
fi