diff --git a/examples/login/client.lua b/examples/login/client.lua
index 2dfdf25b..4180e7a7 100644
--- a/examples/login/client.lua
+++ b/examples/login/client.lua
@@ -2,7 +2,10 @@ package.cpath = "luaclib/?.so"
 
 local socket = require "clientsocket"
 local crypt = require "crypt"
-local bit32 = require "bit32"
+
+if _VERSION ~= "Lua 5.3" then
+	error "Use lua 5.3"
+end
 
 local fd = assert(socket.connect("127.0.0.1", 8001))
 
@@ -93,26 +96,14 @@ print("login ok, subid=", subid)
 
 local function send_request(v, session)
 	local size = #v + 4
-	local package = string.char(bit32.extract(size,8,8))..
-		string.char(bit32.extract(size,0,8))..
-		v..
-		string.char(bit32.extract(session,24,8))..
-		string.char(bit32.extract(session,16,8))..
-		string.char(bit32.extract(session,8,8))..
-		string.char(bit32.extract(session,0,8))
-
+	local package = string.pack(">I2", size)..v..string.pack(">I4", session)
 	socket.send(fd, package)
 	return v, session
 end
 
 local function recv_response(v)
-	local content = v:sub(1,-6)
-	local ok = v:sub(-5,-5):byte()
-	local session = 0
-	for i=-4,-1 do
-		local c = v:byte(i)
-		session = session + bit32.lshift(c,(-1-i) * 8)
-	end
+	local size = #v - 5
+	local content, ok, session = string.unpack("c"..tostring(size).."B>I4", v)
 	return ok ~=0 , content, session
 end
 
@@ -132,11 +123,7 @@ end
 local readpackage = unpack_f(unpack_package)
 
 local function send_package(fd, pack)
-	local size = #pack
-	local package = string.char(bit32.extract(size,8,8))..
-		string.char(bit32.extract(size,0,8))..
-		pack
-
+	local package = string.pack(">s2", pack)
 	socket.send(fd, package)
 end