`Arbitrary`

The trait for generating structured data from arbitrary, unstructured input.

About

The Arbitrary crate lets you construct arbitrary instances of a type.

This crate is primarily intended to be combined with a fuzzer like libFuzzer and cargo-fuzz or AFL, and to help you turn the raw, untyped byte buffers that they produce into well-typed, valid, structured values. This allows you to combine structure-aware test case generation with coverage-guided, mutation-based fuzzers.

Documentation

Read the API documentation on docs.rs!

Example

Say you're writing a color conversion library, and you have an Rgb struct to represent RGB colors. You might want to implement Arbitrary for Rgb so that you could take arbitrary Rgb instances in a test function that asserts some property (for example, asserting that RGB converted to HSL and converted back to RGB always ends up exactly where we started).

Automatically Deriving `Arbitrary`

Automatically deriving the Arbitrary trait is the recommended way to implement Arbitrary for your types.

Automatically deriving Arbitrary requires you to enable the "derive" cargo feature:

# Cargo.toml

[dependencies]
arbitrary = { version = "1", features = ["derive"] }

And then you can simply add #[derive(Arbitrary)] annotations to your types:

// rgb.rs

use arbitrary::Arbitrary;

#[derive(Arbitrary)]
pub struct Rgb {
    pub r: u8,
    pub g: u8,
    pub b: u8,
}

Customizing single fields

This can be particular handy if your structure uses a type that does not implement Arbitrary or you want to have more customization for particular fields.

#[derive(Arbitrary)]
pub struct Rgba {
    // set `r` to Default::default()
    #[arbitrary(default)]
    pub r: u8,

    // set `g` to 255
    #[arbitrary(value = 255)]
    pub g: u8,

    // Generate `b` with a custom function of type
    //
    //    fn(&mut Unstructured) -> arbitrary::Result<T>
    //
    // where `T` is the field's type.
    #[arbitrary(with = arbitrary_b)]
    pub b: u8,

    // Generate `a` with a custom closure (shortuct to avoid a custom function)
    #[arbitrary(with = |u: &mut Unstructured| u.int_in_range(0..=64))]
    pub a: u8,
}

fn arbitrary_b(u: &mut Unstructured) -> arbitrary::Result<u8> {
    u.int_in_range(64..=128)
}

Implementing `Arbitrary` By Hand

Alternatively, you can write an Arbitrary implementation by hand:

// rgb.rs

use arbitrary::{Arbitrary, Result, Unstructured};

#[derive(Copy, Clone, Debug)]
pub struct Rgb {
    pub r: u8,
    pub g: u8,
    pub b: u8,
}

impl<'a> Arbitrary<'a> for Rgb {
    fn arbitrary(u: &mut Unstructured<'a>) -> Result<Self> {
        let r = u8::arbitrary(u)?;
        let g = u8::arbitrary(u)?;
        let b = u8::arbitrary(u)?;
        Ok(Rgb { r, g, b })
    }
}

License

Licensed under dual MIT or Apache-2.0 at your choice.

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

krtab/arbitrary

Arbitrary