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`](https://github.com/rust-fuzz/cargo-fuzz) or
[AFL](https://github.com/rust-fuzz/afl.rs), 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`!**](https://docs.rs/arbitrary)
## 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