Nginx Lua generic redirect caching

nginx.conf

#user  nobody;
worker_processes  auto;

#error_log  logs/error.log;
#error_log  logs/error.log  notice;
#error_log  logs/error.log  info;

#pid        logs/nginx.pid;


events {
    worker_connections  1024;
}


http {
    include       mime.types;
    default_type  application/octet-stream;

    #log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
    #                  '$status $body_bytes_sent "$http_referer" '
    #                  '"$http_user_agent" "$http_x_forwarded_for"';

    #access_log  logs/access.log  main;

    sendfile        on;
    #tcp_nopush     on;

    #keepalive_timeout  0;
    keepalive_timeout  65;

    gzip  on;

    lua_shared_dict redirects 50m;
    server {
        listen       80;
        server_name  localhost;
         location / {
             access_by_lua_block {
                 local redir = ngx.shared.redirects
                 local args = ngx.var.args
                 -- section/id/slug
                 -- section/subsection/id/slug
                 m, err = ngx.re.match(ngx.var.uri, "(.*/)+([0-9]*)/.+")
                 if err then
                     ngx.log(ngx.ERR, "error: ", err)
                     return
                 end
                 if not m then
                   return
                 end
                 if redir:get(m[2]) then
                   -- We have cached state about this article ID
                   if redir:get(m[2]) == ngx.var.uri then
                     -- URL is already canonical
                     return
                   else
                     -- URL not canonical, redirect user
                     if args then
                       return ngx.redirect(redir:get(m[2]) .. "?" .. args)
                     else
                       return ngx.redirect(redir:get(m[2]))
                     end
                   end
                 else
                   -- We don't know about this URL, find out!
                   ngx.req.read_body()
                   res = ngx.location.capture(ngx.var.uri)
                   if res.status == 301 then
                     redir:set(m[2], res.header['Location'])
                     ngx.redirect(res.header['Location'])
                   else
                     redir:set(m[2], ngx.var.uri)
                   end
                 end
                 }
            #Not redirecting, proxy
            proxy_pass http://backend;
         }
    }
}