luci/applications/luci-splash/root/usr/bin/luci-splashd

#!/usr/bin/lua

require("socket")
require("luci.ip")
require("luci.model.uci")

local uci = luci.model.uci.cursor_state()
uci:load("network")

local server = socket.bind("0.0.0.0", arg[1] or 8082)
server:settimeout(0, "t")

while true do
	local client = server:accept()
	
	if client then
		client:settimeout(1)
		local srv
		local ip = luci.ip.IPv4(client:getpeername())
		uci:foreach("network", "interface",
			function (section)
			    if section.ipaddr then
			        local net = luci.ip.IPv4(section.ipaddr, section.netmask)
			        if ip and net and net:contains(ip) then
			            srv = section.ipaddr
			            return
			        end
			    end
			end)

		client:receive()
		client:send("HTTP/1.0 302 Found\r\nLocation: http://" .. srv ..
		 (arg[2] or "/luci/splash") .. "\r\n\r\n")
		client:close() 
	else
		socket.sleep(0.1)
	end
end