11.3. Example of Listener written in Lua

-- This program will register a menu that will open a window with a count of occurrences
-- of every address in the capture

do
	local function menuable_tap()
		-- Declare the window we will use
		local tw = TextWindow.new("Address Counter")

		-- This will contain a hash of counters of appearances of a certain address
		local ips = {}

		-- this is our tap
		local tap = Listener.new();

		function remove()
			-- this way we remove the listener that otherwise will remain running indefinitely
			tap:remove();
		end

		-- we tell the window to call the remove() function when closed
		tw:set_atclose(remove)

		-- this function will be called once for each packet
		function tap.packet(pinfo,tvb)
			local src = ips[tostring(pinfo.src)] or 0
			local dst = ips[tostring(pinfo.dst)] or 0

			ips[tostring(pinfo.src)] = src + 1
			ips[tostring(pinfo.dst)] = dst + 1
		end

		-- this function will be called once every few seconds to update our window
		function tap.draw(t)
			tw:clear()
			for ip,num in pairs(ips) do
				tw:append(ip .. "\t" .. num .. "\n");
			end
		end

		-- this function will be called whenever a reset is needed
		-- e.g. when reloading the capture file
		function tap.reset()
			tw:clear()
			ips = {}
		end
	end

	-- using this function we register our function
	-- to be called when the user selects the Tools->Test->Packets menu
	register_menu("Test/Packets", menuable_tap, MENU_TOOLS_UNSORTED)
end