luci/modules/luci-mod-network/root/usr/libexec/luci-peeraddr

#!/bin/sh

NL="
"

function ifaces_by_device() {
	ubus call network.interface dump 2>/dev/null | \
		jsonfilter -e "@.interface[@.device='$1' || @.l3_device='$1'].interface"
}

function device_by_addr() {
	set -- $(ip route get "$1" ${2:+from "$2"} 2>/dev/null)
	echo "$5"
}

for inbound_device in $(device_by_addr "$REMOTE_ADDR" "$SERVER_ADDR"); do
	inbound_devices="$inbound_device"
	inbound_interfaces=""

	for iface in $(ifaces_by_device "$inbound_device"); do
		inbound_interfaces="${inbound_interfaces:+$inbound_interfaces$NL}$iface"

		for peeraddr in $(uci get "network.$iface.peeraddr"); do
			for ipaddr in $(resolveip -t 1 "$peeraddr" 2>/dev/null); do
				for peerdev in $(device_by_addr "$ipaddr"); do
					for iface in $(ifaces_by_device "$peerdev"); do
						inbound_devices="${inbound_devices:+$inbound_devices$NL}$peerdev"
						inbound_interfaces="${inbound_interfaces:+$inbound_interfaces$NL}$iface"
					done
				done
			done
		done
	done
done

inbound_devices="$(echo "$inbound_devices" | sort -u | sed ':a;N;$!ba;s/\n/", "/g')"
inbound_interfaces="$(echo "$inbound_interfaces" | sort -u | sed ':a;N;$!ba;s/\n/", "/g')"

cat <<JSON
{
	"remote_addr": "$REMOTE_ADDR",
	"server_addr": "$SERVER_ADDR",
	"inbound_devices": [ ${inbound_devices:+\"$inbound_devices\"} ],
	"inbound_interfaces": [ ${inbound_interfaces:+\"$inbound_interfaces\"} ]
}
JSON