/
mod.rs
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/
mod.rs
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// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! Utilities for random number generation
//!
//! The key functions are `random()` and `Rng::gen()`. These are polymorphic
//! and so can be used to generate any type that implements `Rand`. Type inference
//! means that often a simple call to `rand::random()` or `rng.gen()` will
//! suffice, but sometimes an annotation is required, e.g. `rand::random::<f64>()`.
//!
//! See the `distributions` submodule for sampling random numbers from
//! distributions like normal and exponential.
//!
//! # Thread-local RNG
//!
//! There is built-in support for a RNG associated with each thread stored
//! in thread-local storage. This RNG can be accessed via `thread_rng`, or
//! used implicitly via `random`. This RNG is normally randomly seeded
//! from an operating-system source of randomness, e.g. `/dev/urandom` on
//! Unix systems, and will automatically reseed itself from this source
//! after generating 32 KiB of random data.
//!
//! # Cryptographic security
//!
//! An application that requires an entropy source for cryptographic purposes
//! must use `OsRng`, which reads randomness from the source that the operating
//! system provides (e.g. `/dev/urandom` on Unixes or `CryptGenRandom()` on Windows).
//! The other random number generators provided by this module are not suitable
//! for such purposes.
//!
//! *Note*: many Unix systems provide `/dev/random` as well as `/dev/urandom`.
//! This module uses `/dev/urandom` for the following reasons:
//!
//! - On Linux, `/dev/random` may block if entropy pool is empty; `/dev/urandom` will not block.
//! This does not mean that `/dev/random` provides better output than
//! `/dev/urandom`; the kernel internally runs a cryptographically secure pseudorandom
//! number generator (CSPRNG) based on entropy pool for random number generation,
//! so the "quality" of `/dev/random` is not better than `/dev/urandom` in most cases.
//! However, this means that `/dev/urandom` can yield somewhat predictable randomness
//! if the entropy pool is very small, such as immediately after first booting.
//! Linux 3.17 added the `getrandom(2)` system call which solves the issue: it blocks if entropy
//! pool is not initialized yet, but it does not block once initialized.
//! `getrandom(2)` was based on `getentropy(2)`, an existing system call in OpenBSD.
//! `OsRng` tries to use `getrandom(2)` if available, and use `/dev/urandom` fallback if not.
//! If an application does not have `getrandom` and likely to be run soon after first booting,
//! or on a system with very few entropy sources, one should consider using `/dev/random` via
//! `ReaderRng`.
//! - On some systems (e.g. FreeBSD, OpenBSD and Mac OS X) there is no difference
//! between the two sources. (Also note that, on some systems e.g. FreeBSD, both `/dev/random`
//! and `/dev/urandom` may block once if the CSPRNG has not seeded yet.)
#![unstable(feature = "rand", issue = "0")]
use cell::RefCell;
use io;
use mem;
use rc::Rc;
use sys;
#[cfg(target_pointer_width = "32")]
use core_rand::IsaacRng as IsaacWordRng;
#[cfg(target_pointer_width = "64")]
use core_rand::Isaac64Rng as IsaacWordRng;
pub use core_rand::{Rand, Rng, SeedableRng};
pub use core_rand::{XorShiftRng, IsaacRng, Isaac64Rng};
pub use core_rand::reseeding;
pub mod reader;
/// The standard RNG. This is designed to be efficient on the current
/// platform.
#[derive(Copy, Clone)]
pub struct StdRng {
rng: IsaacWordRng,
}
impl StdRng {
/// Create a randomly seeded instance of `StdRng`.
///
/// This is a very expensive operation as it has to read
/// randomness from the operating system and use this in an
/// expensive seeding operation. If one is only generating a small
/// number of random numbers, or doesn't need the utmost speed for
/// generating each number, `thread_rng` and/or `random` may be more
/// appropriate.
///
/// Reading the randomness from the OS may fail, and any error is
/// propagated via the `io::Result` return value.
pub fn new() -> io::Result<StdRng> {
OsRng::new().map(|mut r| StdRng { rng: r.gen() })
}
}
impl Rng for StdRng {
#[inline]
fn next_u32(&mut self) -> u32 {
self.rng.next_u32()
}
#[inline]
fn next_u64(&mut self) -> u64 {
self.rng.next_u64()
}
}
impl<'a> SeedableRng<&'a [usize]> for StdRng {
fn reseed(&mut self, seed: &'a [usize]) {
// the internal RNG can just be seeded from the above
// randomness.
self.rng.reseed(unsafe {mem::transmute(seed)})
}
fn from_seed(seed: &'a [usize]) -> StdRng {
StdRng { rng: SeedableRng::from_seed(unsafe {mem::transmute(seed)}) }
}
}
/// Controls how the thread-local RNG is reseeded.
struct ThreadRngReseeder;
impl reseeding::Reseeder<StdRng> for ThreadRngReseeder {
fn reseed(&mut self, rng: &mut StdRng) {
*rng = match StdRng::new() {
Ok(r) => r,
Err(e) => panic!("could not reseed thread_rng: {}", e)
}
}
}
const THREAD_RNG_RESEED_THRESHOLD: usize = 32_768;
type ThreadRngInner = reseeding::ReseedingRng<StdRng, ThreadRngReseeder>;
/// The thread-local RNG.
#[derive(Clone)]
pub struct ThreadRng {
rng: Rc<RefCell<ThreadRngInner>>,
}
/// Retrieve the lazily-initialized thread-local random number
/// generator, seeded by the system. Intended to be used in method
/// chaining style, e.g. `thread_rng().gen::<isize>()`.
///
/// The RNG provided will reseed itself from the operating system
/// after generating a certain amount of randomness.
///
/// The internal RNG used is platform and architecture dependent, even
/// if the operating system random number generator is rigged to give
/// the same sequence always. If absolute consistency is required,
/// explicitly select an RNG, e.g. `IsaacRng` or `Isaac64Rng`.
pub fn thread_rng() -> ThreadRng {
// used to make space in TLS for a random number generator
thread_local!(static THREAD_RNG_KEY: Rc<RefCell<ThreadRngInner>> = {
let r = match StdRng::new() {
Ok(r) => r,
Err(e) => panic!("could not initialize thread_rng: {}", e)
};
let rng = reseeding::ReseedingRng::new(r,
THREAD_RNG_RESEED_THRESHOLD,
ThreadRngReseeder);
Rc::new(RefCell::new(rng))
});
ThreadRng { rng: THREAD_RNG_KEY.with(|t| t.clone()) }
}
impl Rng for ThreadRng {
fn next_u32(&mut self) -> u32 {
self.rng.borrow_mut().next_u32()
}
fn next_u64(&mut self) -> u64 {
self.rng.borrow_mut().next_u64()
}
#[inline]
fn fill_bytes(&mut self, bytes: &mut [u8]) {
self.rng.borrow_mut().fill_bytes(bytes)
}
}
/// A random number generator that retrieves randomness straight from
/// the operating system. Platform sources:
///
/// - Unix-like systems (Linux, Android, Mac OSX): read directly from
/// `/dev/urandom`, or from `getrandom(2)` system call if available.
/// - Windows: calls `CryptGenRandom`, using the default cryptographic
/// service provider with the `PROV_RSA_FULL` type.
/// - iOS: calls SecRandomCopyBytes as /dev/(u)random is sandboxed.
/// - OpenBSD: uses the `getentropy(2)` system call.
///
/// This does not block.
pub struct OsRng(sys::rand::OsRng);
impl OsRng {
/// Create a new `OsRng`.
pub fn new() -> io::Result<OsRng> {
sys::rand::OsRng::new().map(OsRng)
}
}
impl Rng for OsRng {
#[inline]
fn next_u32(&mut self) -> u32 {
self.0.next_u32()
}
#[inline]
fn next_u64(&mut self) -> u64 {
self.0.next_u64()
}
#[inline]
fn fill_bytes(&mut self, bytes: &mut [u8]) {
self.0.fill_bytes(bytes)
}
}
#[cfg(test)]
mod tests {
use sync::mpsc::channel;
use rand::Rng;
use super::OsRng;
use thread;
#[test]
fn test_os_rng() {
let mut r = OsRng::new().unwrap();
r.next_u32();
r.next_u64();
let mut v = [0; 1000];
r.fill_bytes(&mut v);
}
#[test]
fn test_os_rng_tasks() {
let mut txs = vec!();
for _ in 0..20 {
let (tx, rx) = channel();
txs.push(tx);
thread::spawn(move|| {
// wait until all the threads are ready to go.
rx.recv().unwrap();
// deschedule to attempt to interleave things as much
// as possible (XXX: is this a good test?)
let mut r = OsRng::new().unwrap();
thread::yield_now();
let mut v = [0; 1000];
for _ in 0..100 {
r.next_u32();
thread::yield_now();
r.next_u64();
thread::yield_now();
r.fill_bytes(&mut v);
thread::yield_now();
}
});
}
// start all the threads
for tx in &txs {
tx.send(()).unwrap();
}
}
}