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<h1><code>Arbitrary</code></h1>
<p><strong>The trait for generating structured data from arbitrary, unstructured input.</strong></p>
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## 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
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
## 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:
```toml
# Cargo.toml
[dependencies]
arbitrary = { version = "1", features = ["derive"] }
```
And then you can simply add `#[derive(Arbitrary)]` annotations to your types:
```rust
// 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.
```rust
#[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:
```rust
// 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.