random
Randomness without a hidden global generator.
Rng is a small seedable generator for work that must be reproducible and testable:
shuffle, sample and choose take it as an argument, so the same seed always gives
the same result. It is not for secrets: a 64-bit seed can be guessed.
Keys, tokens and anything an attacker must not predict come from the operating system, with
the random-entropy feature (not in default, it pulls the getrandom crate):
random_bytes, random_hex, random_alphanumeric and Rng::from_entropy. They
return an EntropyError when the system cannot provide bytes, and never fall back to
weaker randomness. They are not built for wasm32-unknown-unknown, which has no default
entropy source: pass bytes from the host (crypto.getRandomValues) to the pure constructors
of the id module instead.
Install
Section titled “Install”Cargo feature random (enabled by default). To compile only this module:
or in Cargo.toml:
Opt-in sub-feature random-entropy (adds the getrandom dependency): .
Import path: helpers4::random.
| Item | What it does |
|---|---|
choose | Picks one element at random, each with the same probability. |
random_alphanumeric | A random string of letters and digits (A-Za-z0-9) from the operating system’s random source, with every character equally likely. |
random_bytes | Random bytes from the operating system, suitable for keys, tokens and salts. |
random_hex | Random bytes from the operating system, written as lowercase hexadecimal: the usual form of a master key or a session token (random_hex(32) is a 256-bit key in 64 characters). |
Rng | A small, fast, seedable pseudo-random generator (SplitMix64): the same seed always gives the same sequence, on every platform. |
sample | Picks count different elements at random (without replacement), in random order. |
shuffle | Returns the elements in a random order (Fisher–Yates: every permutation is equally likely), leaving items as it is. |
Error types
Section titled “Error types”Documented on the page of the helper that returns them.
| Type | Returned by |
|---|---|
EntropyError | random_alphanumeric, random_bytes, random_hex, Rng |