# Magnus High level Ruby bindings for Rust. Write Ruby extension gems in Rust, or call Ruby code from a Rust binary. [API Docs] | [GitHub] | [crates.io] [API Docs]: https://docs.rs/magnus/latest/magnus/ [GitHub]: https://github.com/matsadler/magnus [crates.io]: https://crates.io/crates/magnus [Getting Started] | [Type Conversions] | [Safety] | [Compatibility] [Getting Started]: #getting-started [Type Conversions]: #type-conversions [Safety]: #safety [Compatibility]: #compatibility ## Examples ### Defining Methods Using Magnus, regular Rust functions can be bound to Ruby as methods with automatic type conversion. Callers passing the wrong arguments or incompatible types will get the same kind of `ArgumentError` or `TypeError` they are used to seeing from Ruby's built in methods. Defining a function (with no Ruby `self` argument): ```rust fn fib(n: usize) -> usize { match n { 0 => 0, 1 | 2 => 1, _ => fib(n - 1) + fib(n - 2), } } #[magnus::init] fn init(ruby: &magnus::Ruby) -> Result<(), Error> { ruby.define_global_function("fib", magnus::function!(fib, 1)); Ok(()) } ``` Defining a method (with a Ruby `self` argument): ```rust fn is_blank(rb_self: String) -> bool { !rb_self.contains(|c: char| !c.is_whitespace()) } #[magnus::init] fn init(ruby: &magnus::Ruby) -> Result<(), Error> { // returns the existing class if already defined let class = ruby.define_class("String", ruby.class_object())?; // 0 as self doesn't count against the number of arguments class.define_method("blank?", magnus::method!(is_blank, 0))?; Ok(()) } ``` ### Calling Ruby Methods Some Ruby methods have direct counterparts in Ruby's C API and therefore in Magnus. Ruby's `Object#frozen?` method is available as `magnus::ReprValue::check_frozen`, or `Array#[]` becomes `magnus::RArray::aref`. Other Ruby methods that are defined only in Ruby must be called with `magnus::ReprValue::funcall`. All of Magnus' Ruby wrapper types implement the `ReprValue` trait, so `funcall` can be used on all of them. ```rust let s: String = value.funcall("test", ())?; // 0 arguments let x: bool = value.funcall("example", ("foo",))?; // 1 argument let i: i64 = value.funcall("other", (42, false))?; // 2 arguments, etc ``` `funcall` will convert return types, returning `Err(magnus::Error)` if the type conversion fails or the method call raised an error. To skip type conversion make sure the return type is `magnus::Value`. ### Wrapping Rust Types in Ruby Objects Rust structs and enums can be wrapped in Ruby objects so they can be returned to Ruby. Types can opt-in to this with the `magnus::wrap` macro (or by implementing `magnus::TypedData`). Whenever a compatible type is returned to Ruby it will be wrapped in the specified class, and whenever it is passed back to Rust it will be unwrapped to a reference. ```rust use magnus::{function, method, prelude::*, Error, Ruby}; #[magnus::wrap(class = "Point")] struct Point { x: isize, y: isize, } impl Point { fn new(x: isize, y: isize) -> Self { Self { x, y } } fn x(&self) -> isize { self.x } fn y(&self) -> isize { self.y } fn distance(&self, other: &Point) -> f64 { (((other.x - self.x).pow(2) + (other.y - self.y).pow(2)) as f64).sqrt() } } #[magnus::init] fn init(ruby: &Ruby) -> Result<(), Error> { let class = ruby.define_class("Point", ruby.class_object())?; class.define_singleton_method("new", function!(Point::new, 2))?; class.define_method("x", method!(Point::x, 0))?; class.define_method("y", method!(Point::y, 0))?; class.define_method("distance", method!(Point::distance, 1))?; Ok(()) } ``` The newtype pattern and `RefCell` can be used if mutability is required: ```rust struct Point { x: isize, y: isize, } #[magnus::wrap(class = "Point")] struct MutPoint(std::cell::RefCell); impl MutPoint { fn set_x(&self, i: isize) { self.0.borrow_mut().x = i; } } ``` To allow wrapped types to be subclassed they must implement `Default`, and define and alloc func and an initialize method: ``` rust #[derive(Default)] struct Point { x: isize, y: isize, } #[derive(Default)] #[wrap(class = "Point")] struct MutPoint(RefCell); impl MutPoint { fn initialize(&self, x: isize, y: isize) { let mut this = self.0.borrow_mut(); this.x = x; this.y = y; } } #[magnus::init] fn init(ruby: &Ruby) -> Result<(), Error> { let class = ruby.define_class("Point", ruby.class_object()).unwrap(); class.define_alloc_func::(); class.define_method("initialize", method!(MutPoint::initialize, 2))?; Ok(()) } ``` ## Getting Started ### Writing an extension gem (calling Rust from Ruby) Ruby extensions must be built as dynamic system libraries, this can be done by setting the `crate-type` attribute in your `Cargo.toml`. **`Cargo.toml`** ```toml [lib] crate-type = ["cdylib"] [dependencies] magnus = "0.7" ``` When Ruby loads your extension it calls an 'init' function defined in your extension. In this function you will need to define your Ruby classes and bind Rust functions to Ruby methods. Use the `#[magnus::init]` attribute to mark your init function so it can be correctly exposed to Ruby. **`src/lib.rs`** ```rust use magnus::{function, Error, Ruby}; fn distance(a: (f64, f64), b: (f64, f64)) -> f64 { ((b.0 - a.0).powi(2) + (b.1 - a.1).powi(2)).sqrt() } #[magnus::init] fn init(ruby: &Ruby) -> Result<(), Error> { ruby.define_global_function("distance", function!(distance, 2)); } ``` If you wish to package your extension as a Gem, we recommend using the [`rb_sys` gem] to build along with `rake-compiler`. These tools will automatically build your Rust extension as a dynamic library, and then package it as a gem. *Note*: The newest version of rubygems does have beta support for compiling Rust, so in the future the `rb_sys` gem won't be necessary. **`my_example_gem.gemspec`** ```ruby spec.extensions = ["ext/my_example_gem/extconf.rb"] # needed until rubygems supports Rust support is out of beta spec.add_dependency "rb_sys", "~> 0.9.39" # only needed when developing or packaging your gem spec.add_development_dependency "rake-compiler", "~> 1.2.0" ``` Then, we add an `extconf.rb` file to the `ext` directory. Ruby will execute this file during the compilation process, and it will generate a `Makefile` in the `ext` directory. See the [`rb_sys` gem] for more information. **`ext/my_example_gem/extconf.rb`** ```ruby require "mkmf" require "rb_sys/mkmf" create_rust_makefile("my_example_gem/my_example_gem") ``` See the [`rust_blank`] example for examples if `extconf.rb` and `Rakefile`. Running `rake compile` will place the extension at `lib/my_example_gem/my_example_gem.so` (or `.bundle` on macOS), which you'd load from Ruby like so: **`lib/my_example_gem.rb`** ```ruby require_relative "my_example_gem/my_example_gem" ``` For a more detailed example (including cross-compilation and more), see the [`rb-sys` example project]. Although the code in `lib.rs` does not feature magnus, but it will compile and run properly. [`rb_sys` gem]: https://github.com/oxidize-rb/rb-sys/tree/main/gem [`rake-compiler`]: https://github.com/rake-compiler/rake-compiler [`rust_blank`]: https://github.com/matsadler/magnus/tree/main/examples/rust_blank/ext/rust_blank [`rb-sys` example project]: https://github.com/oxidize-rb/rb-sys/tree/main/examples/rust_reverse ### Embedding Ruby in Rust To call Ruby from a Rust program, enable the `embed` feature: **`Cargo.toml`** ```toml [dependencies] magnus = { version = "0.7", features = ["embed"] } ``` This enables linking to Ruby and gives access to the `embed` module. `magnus::embed::init` must be called before calling Ruby and the value it returns must not be dropped until you are done with Ruby. `init` can not be called more than once. **`src/main.rs`** ```rust use magnus::eval; fn main() { magnus::Ruby::init(|ruby| { let val: f64 = eval!(ruby, "a + rand", a = 1)?; println!("{}", val); Ok(()) }).unwrap(); } ``` ## Type Conversions Magnus will automatically convert between Rust and Ruby types, including converting Ruby exceptions to Rust `Result`s and vice versa. These conversions follow the pattern set by Ruby's core and standard libraries, where many conversions will delegate to a `#to_` method if the object is not of the requested type, but does implement the `#to_` method. Below are tables outlining many common conversions. See the Magnus api documentation for the full list of types. ### Rust functions accepting values from Ruby See `magnus::TryConvert` for more details. | Rust function argument | accepted from Ruby | | -------------------------------------------------------------------- | --------------------------------------- | | `i8`,`i16`,`i32`,`i64`,`isize`, `magnus::Integer` | `Integer`, `#to_int` | | `u8`,`u16`,`u32`,`u64`,`usize` | `Integer`, `#to_int` | | `f32`,`f64`, `magnus::Float` | `Float`, `Numeric` | | `String`, `PathBuf`, `char`, `magnus::RString`, `bytes::Bytes`\*\*\* | `String`, `#to_str` | | `magnus::Symbol` | `Symbol`, `#to_sym` | | `bool` | any object | | `magnus::Range` | `Range` | | `magnus::Encoding`, `magnus::RbEncoding` | `Encoding`, encoding name as a string | | `Option` | `T` or `nil` | | `(T, U)`, `(T, U, V)`, etc | `[T, U]`, `[T, U, V]`, etc, `#to_ary` | | `[T; N]` | `[T]`, `#to_ary` | | `magnus::RArray` | `Array`, `#to_ary` | | `magnus::RHash` | `Hash`, `#to_hash` | | `std::time::SystemTime`, `magnus::Time` | `Time` | | `magnus::Value` | any object | | `Vec`\* | `[T]`, `#to_ary` | | `HashMap`\* | `{K => V}`, `#to_hash` | | `&T`, `typed_data::Obj` where `T: TypedData`\*\* | instance of `::class()` | \* when converting to `Vec` and `HashMap` the types of `T`/`K`,`V` must be native Rust types. \*\* see the `wrap` macro. \*\*\* when the `bytes` feature is enabled ### Rust returning / passing values to Ruby See `magnus::IntoValue` for more details, plus `magnus::method::ReturnValue` and `magnus::ArgList` for some additional details. | returned from Rust / calling Ruby from Rust | received in Ruby | | -------------------------------------------------- | --------------------------------------- | | `i8`,`i16`,`i32`,`i64`,`isize` | `Integer` | | `u8`,`u16`,`u32`,`u64`,`usize` | `Integer` | | `f32`, `f64` | `Float` | | `String`, `&str`, `char`, `&Path`, `PathBuf` | `String` | | `bool` | `true`/`false` | | `()` | `nil` | | `Range`, `RangeFrom`, `RangeTo`, `RangeInclusive` | `Range` | | `Option` | `T` or `nil` | | `Result` (return only) | `T` or raises error | | `(T, U)`, `(T, U, V)`, etc, `[T; N]`, `Vec` | `Array` | | `HashMap` | `Hash` | | `std::time::SystemTime` | `Time` | | `T`, `typed_data::Obj` where `T: TypedData`\*\* | instance of `::class()` | \*\* see the `wrap` macro. ### Conversions via Serde Rust types can also be converted to Ruby, and vice versa, using [Serde] with the [`serde_magnus`] crate. [Serde]: https://github.com/serde-rs/serde [`serde_magnus`]: https://github.com/OneSignal/serde-magnus ### Manual Conversions There may be cases where you want to bypass the automatic type conversions, to do this use the type `magnus::Value` and then manually convert or type check from there. For example, if you wanted to ensure your function is always passed a UTF-8 encoded String so you can take a reference without allocating you could do the following: ```rust fn example(ruby: &Ruby, val: magnus::Value) -> Result<(), magnus::Error> { // checks value is a String, does not call #to_str let r_string = RString::from_value(val) .ok_or_else(|| magnus::Error::new(ruby.exception_type_error(), "expected string"))?; // error on encodings that would otherwise need converting to utf-8 if !r_string.is_utf8_compatible_encoding() { return Err(magnus::Error::new( ruby.exception_encoding_error(), "string must be utf-8", )); } // RString::as_str is unsafe as it's possible for Ruby to invalidate the // str as we hold a reference to it. The easiest way to ensure the &str // stays valid is to avoid any other calls to Ruby for the life of the // reference (the rest of the unsafe block). unsafe { let s = r_string.as_str()?; // ... } Ok(()) } ``` ## Safety When using Magnus, in Rust code, Ruby objects must be kept on the stack. If objects are moved to the heap the Ruby GC can not reach them, and they may be garbage collected. This could lead to memory safety issues. It is not possible to enforce this rule in Rust's type system or via the borrow checker, users of Magnus must maintain this rule manually. An example of something that breaks this rule would be storing a Ruby object in a Rust heap allocated data structure, such as `Vec`, `HashMap`, or `Box`. This must be avoided at all costs. While it would be possible to mark any functions that could expose this unsafty as `unsafe`, that would mean that almost every interaction with Ruby would be `unsafe`. This would leave no way to differentiate the *really* unsafe functions that need much more care to use. Other than this, Magnus strives to match Rust's usual safety guaranties for users of the library. Magnus itself contains a large amount of code marked with the `unsafe` keyword, it is impossible to interact with Ruby's C-api without this, but users of Magnus should be able to do most things without needing to use `unsafe`. ## Compatibility Ruby versions 3.0, 3.1, 3.2, and 3.3 are fully supported. Magnus currently works with, and is still tested against, Ruby 2.7, but as this version of the language is no longer supported by the Ruby developers it is not recommended and future support in Magnus is not guaranteed. Ruby bindings will be generated at compile time, this may require libclang to be installed. The Minimum supported Rust version is currently Rust 1.61. Support for statically linking Ruby is provided via the lower-level [rb-sys] crate, and can be enabled by adding the following to your `Cargo.toml`: ```toml # * should select the same version used by Magnus rb-sys = { version = "*", default-features = false, features = ["ruby-static"] } ``` Cross-compilation is supported by rb-sys [for the platforms listed here][plat]. Magnus is not tested on 32 bit systems. Efforts are made to ensure it compiles. Patches are welcome. [plat]: https://github.com/oxidize-rb/rb-sys#supported-platforms ## Crates that work with Magnus ### rb-sys Magnus uses [rb-sys] to provide the low-level bindings to Ruby. The `rb-sys` feature enables the [`rb_sys`][rb_sys_module] module for advanced interoperability with rb-sys, allows you to access low-level Ruby APIs which Magnus does not expose. [rb-sys]: https://github.com/oxidize-rb/rb-sys/tree/main/crates/rb-sys [rb_sys_module]: https://docs.rs/magnus/latest/magnus/rb_sys/index.html ### `serde_magnus` [`serde_magnus`] integrates [Serde] and Magnus for seamless serialisation and deserialisation of Rust to Ruby data structures and vice versa. ## Users * [`halton`](https://github.com/matsadler/halton-rb) a Ruby gem providing a highly optimised method for generating Halton sequences. Please open a [pull request](https://github.com/matsadler/magnus/pulls) if you'd like your project listed here. ## Troubleshooting ### Issues with static linking If you encounter an error such as `symbol not found in flat namespace '_rb_ext_ractor_safe'` when embedding static Ruby, you will need to instruct Cargo not to strip code that it thinks is dead. In you the same directory as your `Cargo.toml` file, create a `.cargo/config.toml` file with the following contents: ```toml [build] # Without this flag, when linking static libruby, the linker removes symbols # (such as `_rb_ext_ractor_safe`) which it thinks are dead code... but they are # not, and they need to be included for the `embed` feature to work with static # Ruby. rustflags = ["-C", "link-dead-code=on"] ``` ## Naming Magnus is named after *Magnus the Red* a character from the Warhammer 40,000 universe. A sorcerer who believed he could tame the psychic energy of the Warp. Ultimately, his hubris lead to his fall to Chaos, but let's hope using this library turns out better for you. ## License This project is licensed under the MIT license, see LICENSE.