#!/bin/bash
#
#	audiodata_sense v0.1 - detects incoming audio data from the 'Net
#	Written by Robert Pectol
#	rob@pectol.com
#	http://rob.pectol.com/irlp/
#
#	This script returns a, "1" if there is audio data coming in from the
#	'Net when it is executed, else it returns a , "0".
#
#	* NOTE *
#	This script requires that your /etc/sudoers file contains the following
#	line:
#
#		repeater ALL= NOPASSWD: /sbin/iptables
#
#	This MUST be accomplished by editing /etc/sudoers with the, 'visudo'
#	command as user, root.
#
##############################################################################

# establish packet marking for incoming audio data only
if ! ( sudo /sbin/iptables -t mangle --list -nv | grep '0x2' > /dev/null 2>&1 ); then
	sudo /sbin/iptables -t mangle -A INPUT -p udp --dport 2074:2093 -m length --length 128:640 -j MARK --set-mark 2
fi

# reset the packet counters and inspect the number of marked packets between intervals and see if they are different
sudo /sbin/iptables -t mangle --zero
pass=0
firstvalue=0
secondvalue=0
while [[ "$pass" -lt "3" && "$secondvalue" == "$firstvalue" ]]; do
	let firstvalue=`sudo /sbin/iptables -t mangle --list -nv | grep '0x2' | awk '{$1=$1;print}' | cut -d ' ' -f1`
	usleep 80000
	let secondvalue=`sudo /sbin/iptables -t mangle --list -nv | grep '0x2' | awk '{$1=$1;print}' | cut -d ' ' -f1`
	pass=$(($pass + 1))
done

# set the activity flag based upon the inspected packet counts
if [ "$secondvalue" -gt "$firstvalue" ]; then
	data_in=1
else
	data_in=0
fi

# return the flag value
echo $data_in
exit 0