1// Copyright 2019 Developers of the Rand project.
2//
3// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
4// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
5// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
6// option. This file may not be copied, modified, or distributed
7// except according to those terms.
8
9//! Interface to the random number generator of the operating system.
10
11use crate::{TryCryptoRng, TryRngCore};
12
13/// An interface over the operating-system's random data source
14///
15/// This is a zero-sized struct. It can be freely constructed with just `OsRng`.
16///
17/// The implementation is provided by the [getrandom] crate. Refer to
18/// [getrandom] documentation for details.
19///
20/// This struct is available as `rand_core::OsRng` and as `rand::rngs::OsRng`.
21/// In both cases, this requires the crate feature `os_rng` or `std`
22/// (enabled by default in `rand` but not in `rand_core`).
23///
24/// # Blocking and error handling
25///
26/// It is possible that when used during early boot the first call to `OsRng`
27/// will block until the system's RNG is initialised. It is also possible
28/// (though highly unlikely) for `OsRng` to fail on some platforms, most
29/// likely due to system mis-configuration.
30///
31/// After the first successful call, it is highly unlikely that failures or
32/// significant delays will occur (although performance should be expected to
33/// be much slower than a user-space
34/// [PRNG](https://rust-random.github.io/book/guide-gen.html#pseudo-random-number-generators)).
35///
36/// # Usage example
37/// ```
38/// use rand_core::{TryRngCore, OsRng};
39///
40/// let mut key = [0u8; 16];
41/// OsRng.try_fill_bytes(&mut key).unwrap();
42/// let random_u64 = OsRng.try_next_u64().unwrap();
43/// ```
44///
45/// [getrandom]: https://crates.io/crates/getrandom
46#[derive(Clone, Copy, Debug, Default)]
47pub struct OsRng;
48
49/// Error type of [`OsRng`]
50#[derive(Clone, Copy, Debug, PartialEq, Eq)]
51pub struct OsError(getrandom::Error);
52
53impl core::fmt::Display for OsError {
54 #[inline]
55 fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
56 self.0.fmt(f)
57 }
58}
59
60// NOTE: this can use core::error::Error from rustc 1.81.0
61#[cfg(feature = "std")]
62impl std::error::Error for OsError {
63 #[inline]
64 fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
65 std::error::Error::source(&self.0)
66 }
67}
68
69impl OsError {
70 /// Extract the raw OS error code (if this error came from the OS)
71 ///
72 /// This method is identical to [`std::io::Error::raw_os_error()`][1], except
73 /// that it works in `no_std` contexts. If this method returns `None`, the
74 /// error value can still be formatted via the `Display` implementation.
75 ///
76 /// [1]: https://doc.rust-lang.org/std/io/struct.Error.html#method.raw_os_error
77 #[inline]
78 pub fn raw_os_error(self) -> Option<i32> {
79 self.0.raw_os_error()
80 }
81}
82
83impl TryRngCore for OsRng {
84 type Error = OsError;
85
86 #[inline]
87 fn try_next_u32(&mut self) -> Result<u32, Self::Error> {
88 getrandom::u32().map_err(op:OsError)
89 }
90
91 #[inline]
92 fn try_next_u64(&mut self) -> Result<u64, Self::Error> {
93 getrandom::u64().map_err(op:OsError)
94 }
95
96 #[inline]
97 fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Self::Error> {
98 getrandom::fill(dest).map_err(op:OsError)
99 }
100}
101
102impl TryCryptoRng for OsRng {}
103
104#[test]
105fn test_os_rng() {
106 let x = OsRng.try_next_u64().unwrap();
107 let y = OsRng.try_next_u64().unwrap();
108 assert!(x != 0);
109 assert!(x != y);
110}
111
112#[test]
113fn test_construction() {
114 assert!(OsRng.try_next_u64().unwrap() != 0);
115}
116