#!/bin/sh
#
# /opt/tether/tether.sh
#
# Written by jschan @ http://talk.maemo.org
#
# Code snippets and inspiration from:
#   - http://wiki.maemo.org/DbusScripts
#   - http://talk.maemo.org/showthread.php?t=58570
#   - http://code.google.com/p/n900ipv6/source/browse/share/pan
#
# Enables tethering over USB network and Bluetooth PAN.
#
# usage: ./tether.sh start|stop [internal_interface]
#
# Examples:
#   - "./tether.sh start" - Enables tethering on a single PAN client when an Internet connection is active
#   - "./tether.sh stop" - Disables tethering on a single PAN client (assumes the client is on bnep0)
#   - "./tether.sh start bnep1" - Enables tethering on a 2nd PAN client when an Internet connection is active
#   - "./tether.sh stop bnep1" - Disables tethering on the 2nd PAN client, without interfering with the 1st
#
# Notes:
#   - Tested to work with multiple Bluetooth PAN clients including a WiFi-only XOOM
#   - Tested to work in conjuction with a dbus-scripts to automate tethering setups
#   - Doesn't currently have support for multiple concurrent Internet interfaces
#     such as an IPv4 grps connection and a seperate IPv6 grps connection.
#   - IPv6 isn't supported yet... (Waiting for T-Mobile IPv6 activation)
#

# You will want to customize the IAP ID value below
#   - DEFAULT_IAP_ID: This a code uniquely identifying the default GPRS connection to use if you aren't currently connected.
#     It can be obtained with the following command: gconftool -R /system/osso/connectivity/IAP
#     Find lines which matches /system/osso/connectivity/IAP/<IAP_ID> for the GRPS connection you use for Internet connectivity.
#     See http://wiki.maemo.org/Phone_control#Connect_to_specific_saved_connection for more information.
DEFAULT_IAP_ID="efc9b252-9bf3-4aa7-a023-348c2d46f101"
DEFAULT_INTERFACE="bnep0"
PAN_NETWORK_PREFIX="10.20"
USB_NETWORK_PREFIX="10.30"
INTERFACE_OCTET="88"
DHCP_MIN_IP_OCTET="100"
DHCP_MAX_IP_OCTET="127"
DHCP_MAX_LEASE_TIME="1h"
PRIMARY_DNS="8.8.8.8"
SECONDARY_DNS="8.8.4.4"

if [ $# -lt 1 ] || [ $# -gt 2 ]; then
	echo "usage: $0 start|stop [internal_interface]"
	exit 1
fi

if [ -z "$2" ]; then
	INTERFACE="$DEFAULT_INTERFACE"
else
	INTERFACE="$2"
fi

print_message () {
	echo "$(date) $*"
       	run-standalone.sh dbus-send \
		--type=method_call \
		--dest=org.freedesktop.Notifications \
		/org/freedesktop/Notifications \
		org.freedesktop.Notifications.SystemNoteInfoprint \
		string:"$*"
}

connect_default_access_point () {
	print_message "Establishing Default Connection"
	dbus-send \
		--system \
		--type=method_call \
		--print-reply \
		--dest=com.nokia.icd \
		/com/nokia/icd \
		com.nokia.icd.connect \
		string:$DEFAULT_IAP_ID uint32:0
	#sleep 2
}
#set -x

INTERFACE_TYPE="$(echo $INTERFACE | sed 's/\([a-z]*\)[0-9]*/\1/')"
INTERFACE_NUMBER="$(echo $INTERFACE | sed 's/[a-z]*\([0-9]*\)/\1/')"

case $INTERFACE_TYPE in
	bnep )
		NETWORK_PREFIX="$PAN_NETWORK_PREFIX.$INTERFACE_NUMBER"
	;;
	usb )
		NETWORK_PREFIX="$USB_NETWORK_PREFIX.$INTERFACE_NUMBER"
	;;
	* )
		# Notify no active Internet connection
		print_message "Unsupported interface type: $INTERFACE_TYPE"
		exit 1
	;;
esac

INTERFACE_IP="$NETWORK_PREFIX.$INTERFACE_OCTET"
NETMASK="255.255.255.0"
EXTERNAL_INTERFACE="$(ifconfig | awk '/(gprs|wlan)/ {print $1}' | head -1)"

DHCP_MIN_IP="$NETWORK_PREFIX.$DHCP_MIN_IP_OCTET"
DHCP_MAX_IP="$NETWORK_PREFIX.$DHCP_MAX_IP_OCTET"
DHCP_GATEWAY="$INTERFACE_IP"

DNSMASQ_PID_NAME="dnsmasq.$INTERFACE"
DNSMASQ_PID_FILE="/var/run/$DNSMASQ_PID_NAME.pid"

if [ "$1" == "start" ]; then
	INTERFACE_EXISTANCE_CHECK="$(ifconfig -a | grep $INTERFACE | awk '{print $1}')"
	if [ -z "$INTERFACE_EXISTANCE_CHECK" ]; then
		# Notify no active Internet connection
		print_message "$INTERFACE does not exist"
		exit 1
	fi

	if [ -z "$EXTERNAL_INTERFACE" ]; then
		connect_default_access_point
		EXTERNAL_INTERFACE="$(ifconfig | awk '/(gprs|wlan)/ {print $1}' | head -1)"

		if [ -z "$EXTERNAL_INTERFACE" ]; then
			# Notify no active Internet connection
			print_message "Unable to establish tether for $INTERFACE"
			exit 1
		fi
	fi

	# Setup interface
	ifconfig $INTERFACE down 2> /dev/null
	ifconfig $INTERFACE up
	ifconfig $INTERFACE $INTERFACE_IP netmask $NETMASK

	# Load modules
	modprobe ipt_MASQUERADE

	# flush old iptables rules
	iptables --flush
	iptables --table nat --flush

	# Setup NAT
	iptables --out-interface $EXTERNAL_INTERFACE \
		--table nat \
		--append POSTROUTING \
                --jump MASQUERADE

	# Enable IP forwarding
	echo 1 > /proc/sys/net/ipv4/ip_forward
	echo 1 > /proc/sys/net/ipv4/conf/$INTERFACE/forwarding
	echo 1 > /proc/sys/net/ipv4/conf/$EXTERNAL_INTERFACE/forwarding

	# Setup DNS and DHCP
	start-stop-daemon \
		--exec /usr/sbin/dnsmasq \
		--pidfile $DNSMASQ_PID_FILE \
		--verbose \
		--start -- \
			--interface=$INTERFACE \
			--listen-address=$INTERFACE_IP \
			--except-interface=lo \
			--bind-interfaces \
			--pid-file=$DNSMASQ_PID_FILE \
			--dhcp-range=$DHCP_MIN_IP,$DHCP_MAX_IP,$DHCP_MAX_LEASE_TIME \
			--dhcp-option=1,$NETMASK \
			--dhcp-option=3,$DHCP_GATEWAY \
			--dhcp-option=6,$PRIMARY_DNS,$SECONDARY_DNS

	# Notify user bluetooth tethering is active
	print_message "Tethering from $INTERFACE to $EXTERNAL_INTERFACE activated"

elif [ "$1" == "stop" ]; then

	start-stop-daemon \
		--exec /usr/sbin/dnsmasq \
		--pidfile $DNSMASQ_PID_FILE \
		--verbose \
		--stop

	# Bring down the interface
	ifconfig $INTERFACE down 2> /dev/null

	# Disable IP forwarding for tethered interface
	if [ -f "/proc/sys/net/ipv4/conf/$INTERFACE/forwarding" ]; then
		echo 0 > /proc/sys/net/ipv4/conf/$INTERFACE/forwarding 2> /dev/null
	fi

	# Notify user bluetooth tethering is inactive
	print_message "Tethering from $INTERFACE to $EXTERNAL_INTERFACE deactivated"

	# Disable external interface IP forwarding if appropriate
	DNSMASQ_CHECK="$(ps -eaf | grep 'dnsmasq' | grep -v -e '127\.0\.0\.1' -e 'grep')"
	if [ -z "$DNSMASQ_CHECK" ]; then
		echo "$(date) No more clients tethered--disabling all forwarding"
		echo 0 > /proc/sys/net/ipv4/conf/$EXTERNAL_INTERFACE/forwarding
		echo 0 > /proc/sys/net/ipv4/ip_forward
	fi

else

	echo "unknown argument: $1"
	echo "usage: $0 start|stop [internal_interface]"
	exit 1

fi