toggle-pi-ap-mode

#!/bin/sh

# toggle-pi-ap-mode - toggle on or off the Access Point mode of a Raspberry Pi
# 
# Copyright 2013 by David Lindes.  All rights reserved.
# See the accompanying LICENSE file for license information.
#
# This script is based on the setup described in the instructions here:
# http://learn.adafruit.com/setting-up-a-raspberry-pi-as-a-wifi-access-point
# This script assumes you've already followed these, plus a few extras (see
# next comment), to set things up.

# Of course, one thing the above-referenced instructions didn't have us do is
# create interfaces files for both versions, which we need, to easily toggle
# back and forth.  I'm creating my own little pseudo-standard here for how this
# should be done, and this is the check for making sure it's set up (with info
# on how to set it up, if not):
INTERFACES=/etc/network/interfaces
validate_interfaces() {
    if [ -f ${INTERFACES}.ap -a -f ${INTERFACES}.normal ]
    then
    	:
    else
	cat >&2 << EOF
Sorry, looks like you need to set up your interfaces files for this script.

Please copy $INTERFACES to ${INTERFACES}.ap and ${INTERFACES}.normal,
and then edit them as follows:

${INTERFACES}.ap should have the instructions for the access-point version, perhaps like:

    iface wlan0 inet static
      address 192.168.42.1
      netmask 255.255.255.0
    up iptables-restore < /etc/iptables.ipv4.nat

${INTERFACES}.normal should have the normal instructions, perhaps like:

    iface wlan0 inet manual
    wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf
    iface default inet dhcp

(In both cases, there will be other lines above that.)
EOF
    	exit 1
    fi
}

# function to make sure we have sudo access without a password.  User is
# expected to run sudo -v before running this script, or else to run this
# script under sudo.  We do this to ensure trust that we're not stealing the
# password.  (I have a tendency not to trust password prompts I don't know I
# asked for, or which exact command is being run that causes the prompt.)
validate_sudo() {
    if sudo -n -v
    then
	:
    else
	echo "Please run sudo -v first, to establish password readiness."
	exit 1
    fi
}

# toggle in the appropriate interfaces file.  Note that we potentially destroy
# the extant copy!  - we'll back it up at least once.
toggle_interfaces_file() {
    case "$1" in
	ap|normal)
	    # first, check to see if we need a backup:

	    if [ $1 = normal ] && diff ${INTERFACES} ${INTERFACES}.ap >/dev/null
	    then
	    	: # we're switching away from ap, and same, so all good.
	    elif [ $1 = ap ] && diff ${INTERFACES} ${INTERFACES}.normal >/dev/null
	    then
	    	:
	    else
		# if we don't have a backup, just make it:
		if [ ! -f ${INTERFACES}.bak ]
		then
		    sudo cp ${INTERFACES} ${INTERFACES}.bak
		# otherwise, we check it...  and we let this diff output show:
		elif diff -u ${INTERFACES}.bak ${INTERFACES}
		then
		    # do nothing if it's the same:
		    :
		else
		    # otherwise let the user decide whether to over-write, having seen the diff:
		    sudo cp -i ${INTERFACES} ${INTERFACES}.bak
		    # but bail if we didn't copy:
		    if diff ${INTERFACES} ${INTERFACES}.bak >/dev/null
		    then
		    	:
		    else
			echo "Sorry, don't know how to back up your $INTERFACES file.  Please do so, and try again." >&2
		    	exit 1
		    fi
		fi
	    fi

            # finally, put the appropriate mode-based file into place:
	    sudo cp -f ${INTERFACES}.$1 ${INTERFACES}
	    ;;
	*)
	    # shouldn't ever happen, but just in case:
	    echo "Error: unknown target mode $1 for toggle_interfaces_file" >&2
	    exit 1
    esac
}

# (Attempt to...) Figure out what mode we're currently in:
current_mode() {
    # just some very primitive checks, for now:
    # TODO: more elaborate checks?

    # if we have a start script for hostapd, assume ap mode:
    if [ -f /etc/rc2.d/S01hostapd ]
    then
	echo "ap"
    # or if our interfaces file is the same as the normal one, assume that:
    elif diff $INTERFACES $INTERFACES.normal >/dev/null 2>&1
    then
    	echo "normal"
    # otherwise, we don't really know:
    else
	echo "unknown-TBD"
    fi
}


# Target mode is whatever the other mode is:
target_mode() {
    case "`current_mode`" in
	ap)
	    echo "normal"
	    ;;
	normal)
	    echo "ap"
	    ;;
	*)
	    echo "unknown"
	    ;;
    esac
}

# some mode settings are speciic enough to separate them out:
set_ap_mode() {
    sudo update-rc.d hostapd enable
    sudo update-rc.d isc-dhcp-server enable
    sudo service hostapd start
    sudo service isc-dhcp-server start
}
set_normal_mode() {
    sudo service hostapd stop
    sudo service isc-dhcp-server stop
    sudo update-rc.d hostapd disable
    sudo update-rc.d isc-dhcp-server disable
}

# some are common to both:
set_mode() {
    case "$1" in
	ap|normal)
	    validate_interfaces
	    validate_sudo
	    echo "==> Switching into $1 mode."
	    sudo ifdown wlan0
	    toggle_interfaces_file $1
	    set_${1}_mode
	    sudo /etc/init.d/networking reload

	    # I'm not sure why I need this, but I seem to:
	    sleep 1
	    sudo ifdown wlan0
	    sleep 1
	    sudo ifup wlan0
	    sleep 1

	    echo "==> Should now be in $1 mode."
	    ;;
	*)
	    echo "Unknown mode to set: $1.  Try '$0 ap' or '$0 normal' to get into a known state." >&2
	    exit 1
	    ;;
    esac
}

case "${1:-`target_mode`}" in
    on|ap)
	set_mode ap
	;;
    off|normal)
	set_mode normal
	;;
    state|status)
    	echo "Currently estimated to be in: `current_mode` mode."
	;;
    *)
	echo "Don't know which mode you want (current mode is `current_mode`).  Try '$0 ap' or '$0 normal'"
	;;
esac