mlua

Guided Tour

A fork of rlua 0.15 which provides a high level interface between Rust and Lua. Unlike rlua , mlua supports Lua 5.1 (including LuaJIT), 5.2 and 5.3. The mlua goal is to be an easy to use, practical and flexible API between Rust and Lua but not always 100% safe due to the Lua VM nature. Also, mlua provides a way to write native lua modules in Rust.

Usage

Choosing Lua version

The following features could be used to choose Lua version: lua53 (default), lua52, lua51 and luajit.

By default mlua uses pkg-config tool to find lua includes and lib. In most cases it works as desired, although sometimes could be more preferable to use a custom lua library. To achieve this, mlua supports LUA_INC, LUA_LIB, LUA_LIB_NAME and LUA_LINK environment variables. LUA_LINK is optional and may be dylib (a dynamic library) or static (a static library, .a archive).

An example how to use them:

my_project $ LUA_INC=$HOME/tmp/lua-5.2.4/src LUA_LIB=$HOME/tmp/lua-5.2.4/src LUA_LIB_NAME=lua LUA_LINK=static cargo build

mlua also supports vendored lua/luajit using the auxilary crates lua-src and luajit-src. Just enable the vendored feature and cargo will automatically build and link specified lua/luajit version. This is the easiest way to get started with mlua.

Standalone mode

Add to Cargo.toml :

[dependencies]
mlua = "0.2"

main.rs

use mlua::prelude::*;

fn main() -> LuaResult<()> {
    let lua = Lua::new();

    let map_table = lua.create_table()?;
    map_table.set(1, "one")?;
    map_table.set("two", 2)?;

    lua.globals().set("map_table", map_table)?;

    lua.load("for k,v in pairs(map_table) do print(k,v) end").exec()?;

    Ok(())
}

Module mode

Add to Cargo.toml :

[lib]
crate-type = ["cdylib"]

[dependencies]
mlua = "0.2"
mlua_derive = "0.2"

lib.rs :

#[macro_use]
extern crate mlua_derive;
use mlua::prelude::*;

fn hello(_: &Lua, name: String) -> LuaResult<()> {
    println!("hello, {}!", name);
    Ok(())
}

#[lua_module]
fn my_module(lua: &Lua) -> LuaResult<LuaTable> {
    let exports = lua.create_table()?;
    exports.set("hello", lua.create_function(hello)?)?;
    Ok(exports)
}

And then (macos example):

$ cargo build
$ ln -s ./target/debug/libmy_module.dylib ./my_module.so
$ lua5.3 -e 'require("my_module").hello("world")'
hello, world!

Safety

One of the mlua goals is to provide safe API between Rust and Lua. Every place where the Lua C API may trigger an error longjmp in any way is protected by lua_pcall , and the user of the library is protected from directly interacting with unsafe things like the Lua stack, and there is overhead associated with this safety.

Unfortunately, mlua does not provide absolute safety even without using unsafe . This library contains a huge amount of unsafe code. There are almost certainly bugs still lurking in this library! It is surprisingly, fiendishly difficult to use the Lua C API without the potential for unsafety.

Panic handling

mlua wraps panics that are generated inside Rust callbacks in a regular Lua error. Panics could be resumed then by propagating the Lua error to Rust code.

For example:

let lua = Lua::new();
let f = lua.create_function(|_, ()| -> LuaResult<()> {
    panic!("test panic");
})?;
lua.globals().set("rust_func", f)?;

let _ = lua.load(r#"
    local status, err = pcall(rust_func)
    print(err) -- prints: test panic
    error(err) -- propagate panic
"#).exec();

unreachable!()

mlua should also be panic safe in another way as well, which is that any Lua instances or handles remains usable after a user generated panic, and such panics should not break internal invariants or leak Lua stack space. This is mostly important to safely use mlua types in Drop impls, as you should not be using panics for general error handling.

Below is a list of mlua behaviors that should be considered a bug. If you encounter them, a bug report would be very welcome:

• If your program panics with a message that contains the string "mlua internal error", this is a bug.

• The above is true even for the internal panic about running out of stack space! There are a few ways to generate normal script errors by running out of stack, but if you encounter a panic based on running out of stack, this is a bug.

• Lua C API errors are handled by lonjmp. All instances where the Lua C API would otherwise longjmp over calling stack frames should be guarded against, except in internal callbacks where this is intentional. If you detect that mlua is triggering a longjmp over your Rust stack frames, this is a bug!

• If you detect that, after catching a panic or during a Drop triggered from a panic, a Lua or handle method is triggering other bugs or there is a Lua stack space leak, this is a bug. mlua instances are supposed to remain fully usable in the face of user generated panics. This guarantee does not extend to panics marked with "mlua internal error" simply because that is already indicative of a separate bug.

License

This project is licensed under the MIT license