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.

Needs the random-entropy feature. Bytes that would favor some characters are discarded rather than folded with a modulo (256 is not a multiple of 62), so a 20-character result carries 20 × log2(62) ≈ 119 bits of randomness.

Import

use helpers4::random::random_alphanumeric;

Cargo feature random (enabled by default). To compile only this module:

cargo add helpers4 --no-default-features --features random

or in Cargo.toml:

[dependencies]
helpers4 = { version = "0.0.9", default-features = false, features = ["random"] }

Signature

pub fn random_alphanumeric(len: usize) -> Result<String, EntropyError>

Parameters

Parameter	Type	Description
len	usize	The number of characters.

Returns

Result<String, EntropyError> — A string of len characters, or an EntropyError.

Errors

Returns an EntropyError when the operating system cannot provide random bytes.

Examples

use helpers4::random::random_alphanumeric;

let token = random_alphanumeric(24)?;
assert_eq!(token.len(), 24);
assert!(token.chars().all(|c| c.is_ascii_alphanumeric()));

Error type: EntropyError

The operating system could not provide random bytes.

Rare, but possible (no entropy source at boot, a sandbox that blocks the system call, an unsupported platform). The functions that return it never fall back to weaker randomness: a key or a token made from predictable bytes is worse than no key.

use helpers4::random::EntropyError;

pub struct EntropyError(getrandom::Error) { /* private fields */ }

Examples

use helpers4::random::random_bytes;

match random_bytes(16) {
    Ok(bytes) => assert_eq!(bytes.len(), 16),
    Err(error) => eprintln!("no randomness available: {error}"),
}

Source

src/random/random_alphanumeric.rs