add failover.sh and failover init script

update README

README.md

@@ -1,3 +1,16 @@
 # Basic Mwan
 
-init.d script for monitoring and adjusting route metrics of 2 WANs in a multi-WAN setup on OpenWRT. Used as a simple alternative to mwan3, where I just want failover and all traffic forwarded through wireguard vpn (mwan3 seems to struggle with this).
+init.d script for monitoring and adjusting route metrics of 2 WANs in a multi-WAN setup on OpenWRT.
+Used as a simple alternative to mwan3, where I just want failover and all traffic forwarded through wireguard vpn (mwan3 seems to struggle with this).
+
+```bash
+cp failover /etc/init.d/failover
+cp failover.sh /usr/bin/failover.sh
+chmod +x /etc/init.d/failover
+chmod +x /usr/bin/failover.sh
+/etc/init.d/failover enable
+/etc/init.d/failover start
+```
+
+The script uses logger to write to openwrt system log, which can be monitored using `logread`.
+It will log when it starts, when some pings fail, and when switching between WANs.

failover

@@ -0,0 +1,10 @@
+#!/bin/sh /etc/rc.common
+START=90
+start() {
+    /usr/bin/failover.sh &
+}
+
+stop() {
+    PID=`ps | awk '/failover.sh/ {print $1}'`
+    kill -9 $PID
+}

failover.sh

@@ -0,0 +1,103 @@
+#!/bin/bash
+
+INTERVAL=1
+PACKETS=1
+#reliable hosts for checking are cloudflare, quad9, hgoogle
+HOSTS=("1.1.1.1" "9.9.9.9" "8.8.8.8")
+WAN1=eth0
+WAN2=wwan0
+USINGWAN=eth0
+CHECKWAN=eth0
+COUNTER=0
+CHANGED=0
+
+function change_wan_metric() {
+	CHANGED=$SECONDS
+	local ROUTE=0
+	# 100 just in case this runs away for some reason
+	while [ $ROUTE -le 100 ]
+	do
+		local ROUTE_IFACE=`uci get network.@route[$ROUTE].interface`
+		if [ "$ROUTE_INTERFACE" == "uci: Entry not found" ]; then
+			break
+		elif [ "$ROUTE_INTERFACE" == "wan" ]; then
+			uci set network.@route[$ROUTE].metric='$1'
+			uci commit
+			reload_config
+			break
+		fi
+		let ROUTE++
+	done
+}
+
+function debug {
+	logger -t failover "`date`: pings:$PINGS, counter:$COUNTER, changed:$CHANGED, seconds:$SECONDS, usingwan:$USINGWAN, checkwan:$CHECKWAN"
+}
+
+logger -t failover "`date`: Failover script started."
+while sleep $INTERVAL
+do
+
+	if [ "$USINGWAN" == "$WAN2" ] && [ $(($SECONDS-$CHANGED)) -gt 300 ]; then
+		debug
+		# after 5 minutes on failover wan2, check main wan. if it fails counter will go to 1 but since
+		# wan2 is still fine it should reset to 0 next time and stay on wan2, until the check repeats and so on.
+		CHECKWAN=$WAN1
+		CHANGED=$SECONDS #and reset changed so it just tried once then returns to checking working wan
+	fi
+
+	PINGS=0
+	for (( c=0; c<${#HOSTS[@]}; c++ ))
+	do
+			RET=`ping -I $CHECKWAN -w 1 -W 1 -c $PACKETS ${HOSTS[c]} 2>/dev/null | awk '/received/ {print $4}'`
+			if [ "$RET" == "$PACKETS" ]; then
+				let PINGS++
+			fi
+	done
+
+	#debug if any pings fail, just for fun
+	if [ $PINGS -lt ${#HOSTS[@]} ]; then
+		debug
+	fi
+
+
+	# if all pings failed increase counter
+	if [ $PINGS -eq 0 ]; then
+		let COUNTER++
+	else
+		COUNTER=0
+	fi
+
+	# counter failed pings to all hosts multiple times, switch WAN
+	if [ $COUNTER -gt 3 ]; then
+		debug
+		# NOTE: if both wan fail, it will just switch back and forth. but not like it matters, neither would work anyway... lol
+		if [ "$USINGWAN" == "$WAN1" ]; then
+			#if failed and currently on wan, switch to wanb
+			change_wan_metric 2
+			USINGWAN=$WAN2
+			CHECKWAN=$USINGWAN
+			logger -t failover "`date`: Changed active WAN metric to 4G modem!"
+		elif [ "$USINGWAN" == "$WAN2" ]; then
+			#if failed and currently on wanb, switch back to wan
+			change_wan_metric 0
+			USINGWAN=$WAN1
+			CHECKWAN=$USINGWAN
+			logger -t failover "`date`: Changed active WAN metric to Cable connection!"
+		fi
+	elif [ $COUNTER -eq 0 ]; then
+	# counter is successful, if on wan2 and wan1 has recovered return to wan1
+		if [ "$CHECKWAN" == "$WAN1" ] && [ "$USINGWAN" == "$WAN2" ]; then
+			debug
+			#if failed and currently on wanb, switch back to wan
+			change_wan_metric 0
+			USINGWAN=$WAN1
+			CHECKWAN=$USINGWAN
+			logger -t failover "`date`: Changed active WAN metric to Cable connection!"
+		fi
+	fi
+
+	#set the checkwan back to the usingwan, in case it was set to the other wan for recovery check
+	CHECKWAN=$USINGWAN
+
+done;