#!/bin/sh
#
# capture.sh, Copyright © 2011 Matteo Cypriani <mcy@lm7.fr>
#
########################################################################
# This program is licensed under the terms of the Expat license.
#
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
# IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
# CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
# TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
# SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
########################################################################
#
# Captures a few packets on a Wi-Fi interface, using Tcpdump, and
# writes them to a Pcap file along with some information about the
# system. A tarball containing all these files is finally created.

#set -x
set -e


## Parameters (tune them if you want) ##

# Number of packet to capture:
NB_PKT=10
# Maximal time of a capture on a given channel:
TIMEOUT=15
# Temporary directory:
TMP=/tmp
# Name of the capture file:
FILE=capture.pcap
# First channel to scan:
CHANNEL=1


## Functions ##

# Displays the message in argument on the error output and exits
error()
{
	echo "$1" >&2
	clean
	exit 1
}

# Deletes the temporary files
clean()
{
	rm -fr "$DESTDIR"
}

# Verifies the presence of the needed programs
check_dependencies()
{
	which tcpdump >/dev/null \
		|| error "tcpdump is required to run this program!"

	if [ "$OS" = Linux ] ; then
		[ -x /sbin/iwconfig ] \
			|| error "iwconfig is required to run this program on Linux!"
	fi
}

# Switches the capture interface to monitor mode, on the channel in
# argument
iface_set_channel()
{
	echo "Setting interface $IFACE on channel $1..."
	case $OS in
		Linux)
			iface_down
			iwconfig $IFACE mode managed
			iface_up
			iwconfig $IFACE channel $1
			;;
		NetBSD | OpenBSD)
			iface_down
			ifconfig $IFACE media autoselect chan $1
			iface_up
			;;
		*)
			error "Your OS is not supported."
			;;
	esac \
		&& echo "Channel set." \
		|| error "Cannot set the channel!"

	iface_monitor
}

# Switches the capture interface to monitor mode
iface_monitor()
{
	iface_down

	echo -n "Switching interface $IFACE to monitor mode... "
	case $OS in
		Linux)
			iwconfig $IFACE mode monitor
			;;
		NetBSD | OpenBSD)
			ifconfig $IFACE media autoselect mediaopt monitor
			;;
		*)
			error "Your OS is not supported."
			;;
	esac \
		&& echo "OK." \
		|| error "Cannot switch the interface to monitor mode!"

	iface_up
}

# Shuts down the capture interface
iface_down()
{
	echo -n "Shuting down interface $IFACE... "
	ifconfig $IFACE down && echo "OK." \
		|| error "Cannot shut down the interface!"
}

# Turns on the capture interface
iface_up()
{
	echo -n "Turning up interface $IFACE... "
	ifconfig $IFACE up && echo "OK." \
		|| error "Cannot turn the interface up!"
}

# Invokes tcpdump and displays the number of packets captured
invoke_tcpdump()
{
	NCAP=$(tcpdump -i $IFACE -c $NB_PKT -w "$FILE" 2>&1 \
		| sed -nr 's/([[:digit:]]+) packets received by filter$/\1/p')
	[ "$NCAP" = "" ] \
		&& error "Error parsing the tcpdump messages! (NCAP=\"$NCAP\")"
	echo $NCAP
}

# Waits for a number of seconds, then kills any tcpdump process
wait_tcpdump()
{
	sleep $1
	echo "$1 seconds passed, killing all tcpdump processes..."
	pkill tcpdump
}

# Gets some information about the running system
gather_system_information()
{
	echo -n "Gathering system information... "
	# Kernel & other information:
	uname -a >"$DESTDIR"/uname-a
	# Wi-Fi interface information:
	ifconfig $IFACE >"$DESTDIR"/ifconfig_$IFACE
	# PCI devices:
	which lspci >/dev/null \
		&& lspci >"$DESTDIR"/lspci \
		|| echo "lspci not available! Please install pciutils. "
	# Loaded kernel modules & USB devices:
	case $OS in
		Linux)
			lsmod >"$DESTDIR"/lsmod
			which lsusb >/dev/null \
				&& lsusb >"$DESTDIR"/lsusb \
				|| echo "lsusb not available! Please install usbutils. "
			;;
		NetBSD | OpenBSD)
			modstat >"$DESTDIR"/modstat
			which usbstats >/dev/null \
				&& usbstats >"$DESTDIR"/usbstats \
				|| echo "usbstats not available! Please install usbutil. "
			;;
		DragonFly)
			kldstat >"$DESTDIR"/kldstat
			which usbstats >/dev/null \
				&& usbstats >"$DESTDIR"/usbstats \
				|| echo "usbstats not available! Please install usbutil. "
			;;
	esac
	echo "OK."
}

# Compresses the destination directory to a tarball
create_archive()
{
	TARBALL="${DESTDIR}.tar.gz"
	DIR=`basename "$DESTDIR"`
	tar -C "$TMP" -czf "$TARBALL" "$DIR"
	echo "Archive \"$TARBALL\" created."
}


## Main program ##

[ $# -eq 1 ] \
	|| error "Usage: $0 <wifi_interface>"

# Interface to capture from:
IFACE=$1
# Machine information:
OS=`uname`
OS_RELEASE=`uname -r`
HOSTNAME=`uname -n`
# Current date:
DATE=`date +%FT%H%M%S`
# Temporary destination directory:
DESTDIR=$(mktemp -d \
	"$TMP"/capture_${OS}-${OS_RELEASE}_${IFACE}_${HOSTNAME}_${DATE}_XXX)
# Update capture file with full path:
FILE="$DESTDIR/$FILE"

check_dependencies

echo "Trying to capture $NB_PKT packets..."
CAPTURED=0
while [ $CAPTURED -eq 0 -a $CHANNEL -le 14 ] ; do
	echo
	iface_set_channel $CHANNEL
	wait_tcpdump $TIMEOUT &
	CAPTURED=$(invoke_tcpdump)
	[ $CAPTURED -eq 0 ] \
		&& echo "No packet captured on channel $CHANNEL." \
		|| echo "$CAPTURED packets captured on channel $CHANNEL."
	CHANNEL=`expr $CHANNEL + 1`
done

echo
[ $CAPTURED -gt 0 ] \
	&& echo "Capture file \"$FILE\" created." \
	|| error "Failed to capture any packet!"

gather_system_information
create_archive
clean

echo
echo "You can now shut down the interface $IFACE if you want:"
echo "	ifconfig $IFACE down"