Rustler

Documentation | Getting Started | Example

Rustler is a library for writing Erlang NIFs in safe Rust code. That means there should be no ways to crash the BEAM (Erlang VM). The library provides facilities for generating the boilerplate for interacting with the BEAM, handles encoding and decoding of Erlang terms, and catches rust panics before they unwind into C.

The library provides functionality for both Erlang and Elixir, however Elixir is favored as of now.

Features:

Safety - The code you write in a Rust NIF should never be able to crash the BEAM.
Interop - Decoding and encoding rust values into Erlang terms is as easy as a function call.
Type composition - Making a Rust struct encodable and decodable to Erlang or Elixir can be done with a single attribute.
Resource objects - Enables you to safely pass a reference to a Rust struct into Erlang code. The struct will be automatically dropped when it's no longer referenced.

Getting started

The easiest way of getting started is the rustler elixir library.

Add the rustler elixir library as a dependency of your project.
Run mix rustler.new to generate a new NIF in your project. Follow the instructions.

NOTE: If you have previously used Rustler, you need to run mix archive.uninstall rustler_installer.ez to remove it before generating the NIF.

How it looks like

This is the code for a minimal NIF that adds two numbers and returns the result.

#[macro_use] extern crate rustler;
#[macro_use] extern crate lazy_static;

use rustler::{Env, Term, NifResult, Encoder};

mod atoms {
    rustler_atoms! {
        atom ok;
    }
}

rustler_export_nifs!(
    "Elixir.TestNifModule",
    [("add", 2, add)],
    None
);

fn add<'a>(env: Env<'a>, args: &[Term<'a>]) -> NifResult<Term<'a>> {
    let num1: i64 = args[0].decode()?;
    let num2: i64 = args[1].decode()?;

    Ok((atoms::ok(), num1 + num2).encode(env))
}

Supported nif_version

Rustler uses erlang:system_info(nif_version) to detect the supported NIF version of the Erlang/OTP system for which the NIF is to be compiled. It is possible to restrict the NIF version to an older version if the NIF is to be compiled for an older version of Erlang. For example, if the target NIF version should be 2.7 (Erlang/OTP 17.3), this can be defined using an environment variable:

RUSTLER_NIF_VERSION=2.7 mix compile

Building a binary on OSX

When running cargo build on OSX you may run into a linker error similar to this Issue. This linker error is occuring because Erlang has chosen to go with a flat namespace on OSX instead of the 2 layer namespace the OSX dynamic linker expects, for more information you read the this comment on a similar issue. To avoid this you need to pass some arguments to rustc. This can be done by adding cargo config.

$ mkdir .cargo
$ touch .cargo/config

and add the following to the the config file

[target.x86_64-apple-darwin]
rustflags = [
    "-C", "link-arg=-undefined",
    "-C", "link-arg=dynamic_lookup",

Community

You can find us in #rustler on freenode or the elixir-lang slack.

License

Licensed under either of

Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

KevinCybura/rustler