Feature gate: #![feature(random)]

This is a tracking issue for secure random data generation support in std.

Central to this feature is the RandomSource trait inside core::random, which generates random bytes. std also exposes the platform's secure random number generator via the DefaultRandomSource type. There is a Distribution<T> trait for distributions that can sample random values of a specific type, and a random function for convenience to allow things like random(1..=6).

Public API

// core::random

pub trait RandomSource {
    fn fill_bytes(&mut self, bytes: &mut [u8]);
}

pub trait Distribution<T> {
    fn sample(&self, source: &mut (impl RandomSource + ?Sized)) -> T;
}

impl Distribution<bool> for RangeFull { ... }
impl Distribution</* all integer types */> for /* all range types */ { ... }

// std::random (additionally)

pub struct DefaultRandomSource;

impl RandomSource for DefaultRandomSource { ... }

pub fn random<T>(dist: &(impl Distribution<T> + ?Sized)) -> T;

Steps / History

• ACP: Simple secure random number generation libs-team#393
• Implementation
  • std: implement the random feature (alternative version) #129201
  • API rework for Distribution<T> and new random
• Final comment period (FCP)¹
• Stabilization PR

Unresolved Questions

• Naming: the ACP used gen_bytes and DefaultRng, the implementation PR uses fill_bytes and DefaultRandomSource (see arguments pro gen_bytes and pro fill_bytes)
• Concerns listed at Simple secure random number generation libs-team#393 (comment) should be addressed