2.7 KiB
Run a Lua Demo
Lua is everywhere. Neovim uses lua, Vis uses lua; when I visited Lantian's website1, it's running OpenResty; when I'm jailbreaking Kindle, it uses a lua script and Koreader uses lua.
So I want to learn a little lua, just enough to handle daily tasks.
I visited lua.org and found the demo. The idea of knowing how it works immediately came to my mind. By searching on DDG2 I fount it have a hidden demo program called demo, it's just the script for running demo (talk about that later why I'm sure about it).
I copied it and added the essential html in the print block, put it on the server, use slowcgi(8) to serve it with httpd(8). Then I got "No such file or directory". I carefully checked the path and permission, but the error still exists
Finally StackOverflow taught me that the execution environment should also be located in the chroot environment. For security, chroot is needed. Well, just statically link lua3.
MYLDFLAGS= -static
It runs well, but the -- continue HTML began in shell script line
indicates it's not the only file in the CGI application.
I found the rest of them at https://web.tecgraf.puc-rio.br/~lhf/ftp/lua/#demo from lua-l mailing list.
It contains 3 files
demo the CGI script
demo.html the HTML page
demo.lua the Lua program that runs user programs
The shell script takes QUERY_STRING and replace textarea with $QUERY_STRING.lua.
So demo?demo just prints the demo.lua itself in the same directory.
I thought my single-file solution is better because it don't need to fork twice and perform file IO, and it can be even better.
I added resource limit according to PIL chapter 25 "SandBoxing"
local steplimit = 100
local memlimit = 100
local count = 0
local function step ()
count = count + 1
if collectgarbage("count") > memlimit then
error("DoSer uses too much memory")
end
if count > steplimit then
error("DoSer uses too much CPU")
end
end
debug.sethook(step, "", 100)source code: https://github.com/dongdigua/demo.lua