mirror of
https://github.com/dongdigua/dongdigua.github.io
synced 2024-11-23 23:53:10 +08:00
68 lines
2.7 KiB
Org Mode
68 lines
2.7 KiB
Org Mode
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#+TITLE: Run a Lua Demo
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#+DATE: <2023-07-25 二>
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#+OPTIONS: \n:nil
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Lua is everywhere.
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Neovim uses lua, Vis uses lua; when I visited [[./internet_collections.org::#lantian][Lantian]]'s website[fn:1], it's running [[https://openresty.org/][OpenResty]];
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when I'm [[https://bookfere.com/post/970.html][jailbreaking]] Kindle, it uses a lua script and [[https://github.com/koreader/koreader][Koreader]] uses lua.
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So I want to learn a little lua, just enough to handle daily tasks.
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I visited lua.org and found the [[https://www.lua.org/cgi-bin/demo][demo]]. The idea of knowing how it works immediately came to my mind.
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By searching on DDG[fn:2] I fount it have a hidden demo program called demo,
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it's just the script for running demo (talk about that later why I'm sure about it).
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I copied it and added the essential html in the print block,
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put it on the server, use [[https://man.openbsd.org/slowcgi.8][slowcgi(8)]] to serve it with [[https://man.openbsd.org/httpd.8][httpd(8)]].
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Then I got "No such file or directory".
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I carefully checked the path and permission, but the error still exists
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Finally StackOverflow taught me that the execution environment should also
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be located in the chroot environment. For security, chroot is needed.
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Well, just [[https://blog.syndcat.com/?p=181][statically]] link lua[fn:3].
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#+BEGIN_SRC makefile
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MYLDFLAGS= -static
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#+END_SRC
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It runs well, but the =-- continue HTML began in shell script= line
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indicates it's not the only file in the CGI application.
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I found the rest of them at [[https://web.tecgraf.puc-rio.br/~lhf/ftp/lua/#demo]] from [[http://lua-users.org/lists/lua-l/][lua-l]] mailing list.
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It contains 3 files
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#+BEGIN_EXAMPLE
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demo the CGI script
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demo.html the HTML page
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demo.lua the Lua program that runs user programs
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#+END_EXAMPLE
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The shell script takes =QUERY_STRING= and replace textarea with =$QUERY_STRING.lua=.
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So demo?demo just prints the demo.lua itself in the same directory.
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I thought my single-file solution is better because it don't need to fork twice and perform file IO,
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and it can be even better.
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I added resource limit according to [[https://www.lua.org/pil/][PIL]] chapter 25 "SandBoxing"
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#+BEGIN_SRC lua
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local steplimit = 100
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local memlimit = 100
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local count = 0
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local function step ()
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count = count + 1
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if collectgarbage("count") > memlimit then
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error("DoSer uses too much memory")
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end
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if count > steplimit then
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error("DoSer uses too much CPU")
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end
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end
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debug.sethook(step, "", 100)
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#+END_SRC
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source code: https://github.com/dongdigua/demo.lua
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* Footnotes
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[fn:1] I found his page all empty so I sent him an email, he quickly fixed it.
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[fn:2] DuckDuckGo, not DongDiGua
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[fn:3] If =make freebsd= don't work, try =make generic=
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