simple waf for discuz to prevent duplicating post submit

we can also decode body to get formhash, which might be more percise as a hex key components

#how to in nginx.conf

• 1. set a lua shared DICT called waf inside nginx
• 2. initialize a variable called $postctl

set $postctl 10  <- 10 sec between posts

• 3. initialize access control

access_by_lua_file waf.lua;

#a reload is required each time you change $postctl value inside nginx.conf