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107 lines
5.1 KiB
Rust
107 lines
5.1 KiB
Rust
//! Random value generation.
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//!
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//! The [`Random`] trait allows generating a random value for a type using a
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//! given [`RandomSource`].
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#[unstable(feature = "random", issue = "130703")]
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pub use core::random::*;
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use crate::sys::random as sys;
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/// The default random source.
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///
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/// This asks the system for random data suitable for cryptographic purposes
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/// such as key generation. If security is a concern, consult the platform
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/// documentation below for the specific guarantees your target provides.
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///
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/// The high quality of randomness provided by this source means it can be quite
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/// slow on some targets. If you need a large quantity of random numbers and
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/// security is not a concern, consider using an alternative random number
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/// generator (potentially seeded from this one).
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///
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/// # Underlying sources
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///
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/// Platform | Source
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/// -----------------------|---------------------------------------------------------------
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/// Linux | [`getrandom`] or [`/dev/urandom`] after polling `/dev/random`
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/// Windows | [`ProcessPrng`](https://learn.microsoft.com/en-us/windows/win32/seccng/processprng)
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/// Apple | `CCRandomGenerateBytes`
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/// DragonFly | [`arc4random_buf`](https://man.dragonflybsd.org/?command=arc4random)
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/// ESP-IDF | [`esp_fill_random`](https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/system/random.html#_CPPv415esp_fill_randomPv6size_t)
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/// FreeBSD | [`arc4random_buf`](https://man.freebsd.org/cgi/man.cgi?query=arc4random)
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/// Fuchsia | [`cprng_draw`](https://fuchsia.dev/reference/syscalls/cprng_draw)
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/// Haiku | `arc4random_buf`
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/// Illumos | [`arc4random_buf`](https://www.illumos.org/man/3C/arc4random)
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/// NetBSD | [`arc4random_buf`](https://man.netbsd.org/arc4random.3)
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/// OpenBSD | [`arc4random_buf`](https://man.openbsd.org/arc4random.3)
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/// Solaris | [`arc4random_buf`](https://docs.oracle.com/cd/E88353_01/html/E37843/arc4random-3c.html)
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/// Vita | `arc4random_buf`
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/// Hermit | `read_entropy`
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/// Horizon, Cygwin | `getrandom`
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/// AIX, Hurd, L4Re, QNX | `/dev/urandom`
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/// Redox | `/scheme/rand`
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/// RTEMS | [`arc4random_buf`](https://docs.rtems.org/branches/master/bsp-howto/getentropy.html)
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/// SGX | [`rdrand`](https://en.wikipedia.org/wiki/RDRAND)
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/// SOLID | `SOLID_RNG_SampleRandomBytes`
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/// TEEOS | `TEE_GenerateRandom`
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/// UEFI | [`EFI_RNG_PROTOCOL`](https://uefi.org/specs/UEFI/2.10/37_Secure_Technologies.html#random-number-generator-protocol)
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/// VxWorks | `randABytes` after waiting for `randSecure` to become ready
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/// WASI | [`random_get`](https://github.com/WebAssembly/WASI/blob/main/legacy/preview1/docs.md#-random_getbuf-pointeru8-buf_len-size---result-errno)
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/// ZKVM | `sys_rand`
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///
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/// Note that the sources used might change over time.
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///
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/// Consult the documentation for the underlying operations on your supported
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/// targets to determine whether they provide any particular desired properties,
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/// such as support for reseeding on VM fork operations.
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///
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/// [`getrandom`]: https://www.man7.org/linux/man-pages/man2/getrandom.2.html
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/// [`/dev/urandom`]: https://www.man7.org/linux/man-pages/man4/random.4.html
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#[derive(Default, Debug, Clone, Copy)]
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#[unstable(feature = "random", issue = "130703")]
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pub struct DefaultRandomSource;
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#[unstable(feature = "random", issue = "130703")]
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impl RandomSource for DefaultRandomSource {
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fn fill_bytes(&mut self, bytes: &mut [u8]) {
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sys::fill_bytes(bytes)
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}
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}
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/// Generates a random value with the default random source.
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///
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/// This is a convenience function for `T::random(&mut DefaultRandomSource)` and
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/// will sample according to the same distribution as the underlying [`Random`]
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/// trait implementation. See [`DefaultRandomSource`] for more information about
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/// how randomness is sourced.
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///
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/// **Warning:** Be careful when manipulating random values! The
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/// [`random`](Random::random) method on integers samples them with a uniform
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/// distribution, so a value of 1 is just as likely as [`i32::MAX`]. By using
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/// modulo operations, some of the resulting values can become more likely than
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/// others. Use audited crates when in doubt.
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///
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/// # Examples
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///
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/// Generating a [version 4/variant 1 UUID] represented as text:
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/// ```
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/// #![feature(random)]
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///
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/// use std::random::random;
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///
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/// let bits: u128 = random();
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/// let g1 = (bits >> 96) as u32;
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/// let g2 = (bits >> 80) as u16;
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/// let g3 = (0x4000 | (bits >> 64) & 0x0fff) as u16;
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/// let g4 = (0x8000 | (bits >> 48) & 0x3fff) as u16;
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/// let g5 = (bits & 0xffffffffffff) as u64;
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/// let uuid = format!("{g1:08x}-{g2:04x}-{g3:04x}-{g4:04x}-{g5:012x}");
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/// println!("{uuid}");
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/// ```
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///
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/// [version 4/variant 1 UUID]: https://en.wikipedia.org/wiki/Universally_unique_identifier#Version_4_(random)
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#[unstable(feature = "random", issue = "130703")]
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pub fn random<T: Random>() -> T {
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T::random(&mut DefaultRandomSource)
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}
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