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Lua binding for libcrun

Bare libcrun interface for Lua.

There are some problems still and the API is a subject to change.

LuaRocks build

To build luacrun luarocks package, you must have:

  • Dependencies for building libcrun
  • Lua 5.4 and its development files
  • LuaRocks 3.x
  • sed, git and zip

Started by ./configure:

./autogen.sh && ./configure --with-lua-bindings

This is only to enable the option to build source rocks. The options to build the rocks is hard-coded at "lua/luacrun.rockspec".

Create the source rock:

make dist-luarock

You can find the new rock file as luacrun-x.x.x-xx.src.rock.

If you want the binary rock, use luarocks:

luarocks build <the-rock-file-name> --pack-binary-rock

Regular build

Requirements:

  • Dependencies for building libcrun
  • Lua 5.4 and its development files

You can still build this module for regular directory structure, like:

./autogen.sh && ./configure --with-lua-bindings --disable-libcrun --disable-crun --enable-shared

The options here for ./configure will affect the final output.

make && make install

Usage

See luacrun.d.tl.

Interpreter may restart?

Related issue: #695: [Python bindings] Python interpreter restarts (?) after first import of python_crun

The lua interpreter may restart at the first open of the library (may not happen if statically linked into your program). It's side effect of a protection (click for the code) to avoid attacks like CVE-2019-5736.

To ease the hurt, always place the require call at the start of your program:

-- entry point module for luabundler
require "luacrun"

return function(...) -- the entry point
    print("Hello World!")
end

It's not required to use the library at the moment. Since it is cached, the require() will not open the library again.

If the entry point is at the C-side, you may use the luaL_requiref to open the library instead of require() call in Lua code.

#include <lua.h>
#include <lauxlib.h>

extern int luaopen_luacrun(lua_State *S);

int main(int argc, char *argv[]) {
    lua_State *S = luaL_newstate();
    // Open the library before any actual logic,
    // to make sure users will not notice the program have actually started twice
    luaL_requiref(S, "luacrun", &luaopen_luacrun, false);
    lua_pop(S, 1);
    // ...your code
}

The protection might cause another problem in REPL:

$ lua
Lua 5.4.4  Copyright (C) 1994-2022 Lua.org, PUC-Rio
> luacrun = require "luacrun"
Lua 5.4.4  Copyright (C) 1994-2022 Lua.org, PUC-Rio
> luacrun
nil
>

When you call require "luacrun" at the first time, the REPL restarted and the state have been reset.

The workaround is require "luacrun" again and you get the library this time. The protection will not apply again if it's already applied.

$ lua
Lua 5.4.4  Copyright (C) 1994-2022 Lua.org, PUC-Rio
> luacrun = require "luacrun"
Lua 5.4.4  Copyright (C) 1994-2022 Lua.org, PUC-Rio
> luacrun
nil
> luacrun = require "luacrun"
> luacrun
table: 0x561edad470d0
>

It's safe to use luacrun in multi-state usage, the program restarts only once.

Test

You need busted and below dependencies to run tests:

luarocks install busted dkjson luaposix

The tests assume environment variable INIT exists. It's the init program compiled in tests.

INIT=$(pwd)/tests/init lua_modules/bin/busted lua

Additional Build Options

  • --with-lua-bindings enables the building options about the lua binding
  • --enable-lua-path-guessing/--disable-lua-path-guessing enable or disable the lua module path guessing. If disabled, the install path for this module will be set to libdir.