/rust/registry/src/index.crates.io-1949cf8c6b5b557f/getrandom-0.2.16/src/lib.rs

Source
//! Interface to the operating system's random number generator.
//!
//! # Supported targets
//!
//! | Target            | Target Triple      | Implementation
//! | ----------------- | ------------------ | --------------
//! | Linux, Android    | `*‑linux‑*`        | [`getrandom`][1] system call if available, otherwise [`/dev/urandom`][2] after successfully polling `/dev/random`
//! | Windows           | `*‑windows‑*`      | [`BCryptGenRandom`]
//! | macOS             | `*‑apple‑darwin`   | [`getentropy`][3]
//! | iOS, tvOS, watchOS | `*‑apple‑ios`, `*-apple-tvos`, `*-apple-watchos` | [`CCRandomGenerateBytes`]
//! | FreeBSD           | `*‑freebsd`        | [`getrandom`][5]
//! | OpenBSD           | `*‑openbsd`        | [`getentropy`][7]
//! | NetBSD            | `*‑netbsd`         | [`getrandom`][16] if available, otherwise [`kern.arandom`][8]
//! | Dragonfly BSD     | `*‑dragonfly`      | [`getrandom`][9]
//! | Solaris           | `*‑solaris`        | [`getrandom`][11] (with `GRND_RANDOM`)
//! | illumos           | `*‑illumos`        | [`getrandom`][12]
//! | Fuchsia OS        | `*‑fuchsia`        | [`cprng_draw`]
//! | Redox             | `*‑redox`          | `/dev/urandom`
//! | Haiku             | `*‑haiku`          | `/dev/urandom` (identical to `/dev/random`)
//! | Hermit            | `*-hermit`         | [`sys_read_entropy`]
//! | Hurd              | `*-hurd-*`         | [`getrandom`][17]
//! | SGX               | `x86_64‑*‑sgx`     | [`RDRAND`]
//! | VxWorks           | `*‑wrs‑vxworks‑*`  | `randABytes` after checking entropy pool initialization with `randSecure`
//! | ESP-IDF           | `*‑espidf`         | [`esp_fill_random`]
//! | Emscripten        | `*‑emscripten`     | [`getentropy`][13]
//! | WASI              | `wasm32‑wasi`      | [`random_get`]
//! | Web Browser and Node.js | `wasm*‑*‑unknown` | [`Crypto.getRandomValues`] if available, then [`crypto.randomFillSync`] if on Node.js, see [WebAssembly support]
//! | SOLID             | `*-kmc-solid_*`    | `SOLID_RNG_SampleRandomBytes`
//! | Nintendo 3DS      | `*-nintendo-3ds`   | [`getrandom`][18]
//! | PS Vita           | `*-vita-*`         | [`getentropy`][13]
//! | QNX Neutrino      | `*‑nto-qnx*`       | [`/dev/urandom`][14] (identical to `/dev/random`)
//! | AIX               | `*-ibm-aix`        | [`/dev/urandom`][15]
//! | Cygwin            | `*-cygwin`         | [`getrandom`][19] (based on [`RtlGenRandom`])
//!
//! Pull Requests that add support for new targets to `getrandom` are always welcome.
//!
//! ## Unsupported targets
//!
//! By default, `getrandom` will not compile on unsupported targets, but certain
//! features allow a user to select a "fallback" implementation if no supported
//! implementation exists.
//!
//! All of the below mechanisms only affect unsupported
//! targets. Supported targets will _always_ use their supported implementations.
//! This prevents a crate from overriding a secure source of randomness
//! (either accidentally or intentionally).
//!
//! ## `/dev/urandom` fallback on Linux and Android
//!
//! On Linux targets the fallback is present only if either `target_env` is `musl`,
//! or `target_arch` is one of the following: `aarch64`, `arm`, `powerpc`, `powerpc64`,
//! `s390x`, `x86`, `x86_64`. Other supported targets [require][platform-support]
//! kernel versions which support `getrandom` system call, so fallback is not needed.
//!
//! On Android targets the fallback is present only for the following `target_arch`es:
//! `aarch64`, `arm`, `x86`, `x86_64`. Other `target_arch`es (e.g. RISC-V) require
//! sufficiently high API levels.
//!
//! The fallback can be disabled by enabling the `linux_disable_fallback` crate feature.
//! Note that doing so will bump minimum supported Linux kernel version to 3.17 and
//! Android API level to 23 (Marshmallow).
//!
//! ### RDRAND on x86
//!
//! *If the `rdrand` Cargo feature is enabled*, `getrandom` will fallback to using
//! the [`RDRAND`] instruction to get randomness on `no_std` `x86`/`x86_64`
//! targets. This feature has no effect on other CPU architectures.
//!
//! ### WebAssembly support
//!
//! This crate fully supports the
//! [`wasm32-wasi`](https://github.com/CraneStation/wasi) and
//! [`wasm32-unknown-emscripten`](https://www.hellorust.com/setup/emscripten/)
//! targets. However, the `wasm32-unknown-unknown` target (i.e. the target used
//! by `wasm-pack`) is not automatically
//! supported since, from the target name alone, we cannot deduce which
//! JavaScript interface is in use (or if JavaScript is available at all).
//!
//! Instead, *if the `js` Cargo feature is enabled*, this crate will assume
//! that you are building for an environment containing JavaScript, and will
//! call the appropriate methods. Both web browser (main window and Web Workers)
//! and Node.js environments are supported, invoking the methods
//! [described above](#supported-targets) using the [`wasm-bindgen`] toolchain.
//!
//! To enable the `js` Cargo feature, add the following to the `dependencies`
//! section in your `Cargo.toml` file:
//! ```toml
//! [dependencies]
//! getrandom = { version = "0.2", features = ["js"] }
//! ```
//!
//! This can be done even if `getrandom` is not a direct dependency. Cargo
//! allows crates to enable features for indirect dependencies.
//!
//! This feature should only be enabled for binary, test, or benchmark crates.
//! Library crates should generally not enable this feature, leaving such a
//! decision to *users* of their library. Also, libraries should not introduce
//! their own `js` features *just* to enable `getrandom`'s `js` feature.
//!
//! This feature has no effect on targets other than `wasm32-unknown-unknown`.
//!
//! #### Node.js ES module support
//!
//! Node.js supports both [CommonJS modules] and [ES modules]. Due to
//! limitations in wasm-bindgen's [`module`] support, we cannot directly
//! support ES Modules running on Node.js. However, on Node v15 and later, the
//! module author can add a simple shim to support the Web Cryptography API:
//! ```js
//! import { webcrypto } from 'node:crypto'
//! globalThis.crypto = webcrypto
//! ```
//! This crate will then use the provided `webcrypto` implementation.
//!
//! ### Platform Support
//! This crate generally supports the same operating system and platform versions
//! that the Rust standard library does. Additional targets may be supported using
//! pluggable custom implementations.
//!
//! This means that as Rust drops support for old versions of operating systems
//! (such as old Linux kernel versions, Android API levels, etc) in stable releases,
//! `getrandom` may create new patch releases (`0.N.x`) that remove support for
//! outdated platform versions.
//!
//! ### Custom implementations
//!
//! The [`register_custom_getrandom!`] macro allows a user to mark their own
//! function as the backing implementation for [`getrandom`]. See the macro's
//! documentation for more information about writing and registering your own
//! custom implementations.
//!
//! Note that registering a custom implementation only has an effect on targets
//! that would otherwise not compile. Any supported targets (including those
//! using `rdrand` and `js` Cargo features) continue using their normal
//! implementations even if a function is registered.
//!
//! ## Early boot
//!
//! Sometimes, early in the boot process, the OS has not collected enough
//! entropy to securely seed its RNG. This is especially common on virtual
//! machines, where standard "random" events are hard to come by.
//!
//! Some operating system interfaces always block until the RNG is securely
//! seeded. This can take anywhere from a few seconds to more than a minute.
//! A few (Linux, NetBSD and Solaris) offer a choice between blocking and
//! getting an error; in these cases, we always choose to block.
//!
//! On Linux (when the `getrandom` system call is not available), reading from
//! `/dev/urandom` never blocks, even when the OS hasn't collected enough
//! entropy yet. To avoid returning low-entropy bytes, we first poll
//! `/dev/random` and only switch to `/dev/urandom` once this has succeeded.
//!
//! On OpenBSD, this kind of entropy accounting isn't available, and on
//! NetBSD, blocking on it is discouraged. On these platforms, nonblocking
//! interfaces are used, even when reliable entropy may not be available.
//! On the platforms where it is used, the reliability of entropy accounting
//! itself isn't free from controversy. This library provides randomness
//! sourced according to the platform's best practices, but each platform has
//! its own limits on the grade of randomness it can promise in environments
//! with few sources of entropy.
//!
//! ## Error handling
//!
//! We always choose failure over returning known insecure "random" bytes. In
//! general, on supported platforms, failure is highly unlikely, though not
//! impossible. If an error does occur, then it is likely that it will occur
//! on every call to `getrandom`, hence after the first successful call one
//! can be reasonably confident that no errors will occur.
//!
//! [1]: https://manned.org/getrandom.2
//! [2]: https://manned.org/urandom.4
//! [3]: https://www.unix.com/man-page/mojave/2/getentropy/
//! [4]: https://www.unix.com/man-page/mojave/4/urandom/
//! [5]: https://www.freebsd.org/cgi/man.cgi?query=getrandom&manpath=FreeBSD+12.0-stable
//! [7]: https://man.openbsd.org/getentropy.2
//! [8]: https://man.netbsd.org/sysctl.7
//! [9]: https://leaf.dragonflybsd.org/cgi/web-man?command=getrandom
//! [11]: https://docs.oracle.com/cd/E88353_01/html/E37841/getrandom-2.html
//! [12]: https://illumos.org/man/2/getrandom
//! [13]: https://github.com/emscripten-core/emscripten/pull/12240
//! [14]: https://www.qnx.com/developers/docs/7.1/index.html#com.qnx.doc.neutrino.utilities/topic/r/random.html
//! [15]: https://www.ibm.com/docs/en/aix/7.3?topic=files-random-urandom-devices
//! [16]: https://man.netbsd.org/getrandom.2
//! [17]: https://www.gnu.org/software/libc/manual/html_mono/libc.html#index-getrandom
//! [18]: https://github.com/rust3ds/shim-3ds/commit/b01d2568836dea2a65d05d662f8e5f805c64389d
//! [19]: https://github.com/cygwin/cygwin/blob/main/winsup/cygwin/libc/getentropy.cc
//!
//! [`BCryptGenRandom`]: https://docs.microsoft.com/en-us/windows/win32/api/bcrypt/nf-bcrypt-bcryptgenrandom
//! [`RtlGenRandom`]: https://learn.microsoft.com/en-us/windows/win32/api/ntsecapi/nf-ntsecapi-rtlgenrandom
//! [`Crypto.getRandomValues`]: https://www.w3.org/TR/WebCryptoAPI/#Crypto-method-getRandomValues
//! [`RDRAND`]: https://software.intel.com/en-us/articles/intel-digital-random-number-generator-drng-software-implementation-guide
//! [`CCRandomGenerateBytes`]: https://opensource.apple.com/source/CommonCrypto/CommonCrypto-60074/include/CommonRandom.h.auto.html
//! [`cprng_draw`]: https://fuchsia.dev/fuchsia-src/zircon/syscalls/cprng_draw
//! [`crypto.randomFillSync`]: https://nodejs.org/api/crypto.html#cryptorandomfillsyncbuffer-offset-size
//! [`esp_fill_random`]: https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/system/random.html#_CPPv415esp_fill_randomPv6size_t
//! [`random_get`]: https://github.com/WebAssembly/WASI/blob/main/phases/snapshot/docs.md#-random_getbuf-pointeru8-buf_len-size---errno
//! [WebAssembly support]: #webassembly-support
//! [`wasm-bindgen`]: https://github.com/rustwasm/wasm-bindgen
//! [`module`]: https://rustwasm.github.io/wasm-bindgen/reference/attributes/on-js-imports/module.html
//! [CommonJS modules]: https://nodejs.org/api/modules.html
//! [ES modules]: https://nodejs.org/api/esm.html
//! [`sys_read_entropy`]: https://github.com/hermit-os/kernel/blob/315f58ff5efc81d9bf0618af85a59963ff55f8b1/src/syscalls/entropy.rs#L47-L55
//! [platform-support]: https://doc.rust-lang.org/stable/rustc/platform-support.html

#![doc(
    html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk.png",
    html_favicon_url = "https://www.rust-lang.org/favicon.ico",
    html_root_url = "https://docs.rs/getrandom/0.2.16"
)]
#![no_std]
#![warn(rust_2018_idioms, unused_lifetimes, missing_docs)]
#![cfg_attr(docsrs, feature(doc_auto_cfg))]

#[macro_use]
extern crate cfg_if;

use crate::util::{slice_as_uninit_mut, slice_assume_init_mut};
use core::mem::MaybeUninit;

mod error;
mod util;
// To prevent a breaking change when targets are added, we always export the
// register_custom_getrandom macro, so old Custom RNG crates continue to build.
#[cfg(feature = "custom")]
mod custom;
#[cfg(feature = "std")]
mod error_impls;

pub use crate::error::Error;

// System-specific implementations.
//
// These should all provide getrandom_inner with the signature
// `fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error>`.
// The function MUST fully initialize `dest` when `Ok(())` is returned.
// The function MUST NOT ever write uninitialized bytes into `dest`,
// regardless of what value it returns.
cfg_if! {
    if #[cfg(any(target_os = "haiku", target_os = "redox", target_os = "nto", target_os = "aix"))] {
        mod util_libc;
        #[path = "use_file.rs"] mod imp;
    } else if #[cfg(any(
        target_os = "macos",
        target_os = "openbsd",
        target_os = "vita",
        target_os = "emscripten",
    ))] {
        mod util_libc;
        #[path = "getentropy.rs"] mod imp;
    } else if #[cfg(any(
        target_os = "dragonfly",
        target_os = "freebsd",
        target_os = "hurd",
        target_os = "illumos",
        // Check for target_arch = "arm" to only include the 3DS. Does not
        // include the Nintendo Switch (which is target_arch = "aarch64").
        all(target_os = "horizon", target_arch = "arm"),
        target_os = "cygwin",
    ))] {
        mod util_libc;
        #[path = "getrandom.rs"] mod imp;
    } else if #[cfg(all(
        not(feature = "linux_disable_fallback"),
        any(
            // Rust supports Android API level 19 (KitKat) [0] and the next upgrade targets
            // level 21 (Lollipop) [1], while `getrandom(2)` was added only in
            // level 23 (Marshmallow). Note that it applies only to the "old" `target_arch`es,
            // RISC-V Android targets sufficiently new API level, same will apply for potential
            // new Android `target_arch`es.
            // [0]: https://blog.rust-lang.org/2023/01/09/android-ndk-update-r25.html
            // [1]: https://github.com/rust-lang/rust/pull/120593
            all(
                target_os = "android",
                any(
                    target_arch = "aarch64",
                    target_arch = "arm",
                    target_arch = "x86",
                    target_arch = "x86_64",
                ),
            ),
            // Only on these `target_arch`es Rust supports Linux kernel versions (3.2+)
            // that precede the version (3.17) in which `getrandom(2)` was added:
            // https://doc.rust-lang.org/stable/rustc/platform-support.html
            all(
                target_os = "linux",
                any(
                    target_arch = "aarch64",
                    target_arch = "arm",
                    target_arch = "powerpc",
                    target_arch = "powerpc64",
                    target_arch = "s390x",
                    target_arch = "x86",
                    target_arch = "x86_64",
                    // Minimum supported Linux kernel version for MUSL targets
                    // is not specified explicitly (as of Rust 1.77) and they
                    // are used in practice to target pre-3.17 kernels.
                    target_env = "musl",
                ),
            )
        ),
    ))] {
        mod util_libc;
        mod use_file;
        mod lazy;
        #[path = "linux_android_with_fallback.rs"] mod imp;
    } else if #[cfg(any(target_os = "android", target_os = "linux"))] {
        mod util_libc;
        #[path = "linux_android.rs"] mod imp;
    } else if #[cfg(target_os = "solaris")] {
        mod util_libc;
        #[path = "solaris.rs"] mod imp;
    } else if #[cfg(target_os = "netbsd")] {
        mod util_libc;
        #[path = "netbsd.rs"] mod imp;
    } else if #[cfg(target_os = "fuchsia")] {
        #[path = "fuchsia.rs"] mod imp;
    } else if #[cfg(any(target_os = "ios", target_os = "visionos", target_os = "watchos", target_os = "tvos"))] {
        #[path = "apple-other.rs"] mod imp;
    } else if #[cfg(all(target_arch = "wasm32", target_os = "wasi"))] {
        #[path = "wasi.rs"] mod imp;
    } else if #[cfg(target_os = "hermit")] {
        #[path = "hermit.rs"] mod imp;
    } else if #[cfg(target_os = "vxworks")] {
        mod util_libc;
        #[path = "vxworks.rs"] mod imp;
    } else if #[cfg(target_os = "solid_asp3")] {
        #[path = "solid.rs"] mod imp;
    } else if #[cfg(target_os = "espidf")] {
        #[path = "espidf.rs"] mod imp;
    } else if #[cfg(windows)] {
        #[path = "windows.rs"] mod imp;
    } else if #[cfg(all(target_arch = "x86_64", target_env = "sgx"))] {
        mod lazy;
        #[path = "rdrand.rs"] mod imp;
    } else if #[cfg(all(feature = "rdrand",
                        any(target_arch = "x86_64", target_arch = "x86")))] {
        mod lazy;
        #[path = "rdrand.rs"] mod imp;
    } else if #[cfg(all(feature = "js",
                        any(target_arch = "wasm32", target_arch = "wasm64"),
                        target_os = "unknown"))] {
        #[path = "js.rs"] mod imp;
    } else if #[cfg(feature = "custom")] {
        use custom as imp;
    } else if #[cfg(all(any(target_arch = "wasm32", target_arch = "wasm64"),
                        target_os = "unknown"))] {
        compile_error!("the wasm*-unknown-unknown targets are not supported by \
                        default, you may need to enable the \"js\" feature. \
                        For more information see: \
                        https://docs.rs/getrandom/#webassembly-support");
    } else {
        compile_error!("target is not supported, for more information see: \
                        https://docs.rs/getrandom/#unsupported-targets");
    }
}

/// Fill `dest` with random bytes from the system's preferred random number
/// source.
///
/// This function returns an error on any failure, including partial reads. We
/// make no guarantees regarding the contents of `dest` on error. If `dest` is
/// empty, `getrandom` immediately returns success, making no calls to the
/// underlying operating system.
///
/// Blocking is possible, at least during early boot; see module documentation.
///
/// In general, `getrandom` will be fast enough for interactive usage, though
/// significantly slower than a user-space CSPRNG; for the latter consider
/// [`rand::thread_rng`](https://docs.rs/rand/*/rand/fn.thread_rng.html).
#[inline]
pub fn getrandom(dest: &mut [u8]) -> Result<(), Error> {
    // SAFETY: The `&mut MaybeUninit<_>` reference doesn't escape, and
    // `getrandom_uninit` guarantees it will never de-initialize any part of
    // `dest`.
    getrandom_uninit(unsafe { slice_as_uninit_mut(dest) })?;
    Ok(())
}

/// Version of the `getrandom` function which fills `dest` with random bytes
/// returns a mutable reference to those bytes.
///
/// On successful completion this function is guaranteed to return a slice
/// which points to the same memory as `dest` and has the same length.
/// In other words, it's safe to assume that `dest` is initialized after
/// this function has returned `Ok`.
///
/// No part of `dest` will ever be de-initialized at any point, regardless
/// of what is returned.
///
/// # Examples
///
/// ```ignore
/// # // We ignore this test since `uninit_array` is unstable.
/// #![feature(maybe_uninit_uninit_array)]
/// # fn main() -> Result<(), getrandom::Error> {
/// let mut buf = core::mem::MaybeUninit::uninit_array::<1024>();
/// let buf: &mut [u8] = getrandom::getrandom_uninit(&mut buf)?;
/// # Ok(()) }
/// ```
#[inline]
pub fn getrandom_uninit(dest: &mut [MaybeUninit<u8>]) -> Result<&mut [u8], Error> {
    if !dest.is_empty() {
        imp::getrandom_inner(dest)?;
    }
    // SAFETY: `dest` has been fully initialized by `imp::getrandom_inner`
    // since it returned `Ok`.
    Ok(unsafe { slice_assume_init_mut(dest) })
}

Coverage Report

Created: 2025-10-28 06:54

Line	Count	Source
1		//! Interface to the operating system's random number generator.
2		//!
3		//! # Supported targets
4		//!
5		//! \| Target \| Target Triple \| Implementation
6		//! \| ----------------- \| ------------------ \| --------------
7		//! \| Linux, Android \| `‑linux‑` \| [`getrandom`][1] system call if available, otherwise [`/dev/urandom`][2] after successfully polling `/dev/random`
8		//! \| Windows \| `‑windows‑` \| [`BCryptGenRandom`]
9		//! \| macOS \| `*‑apple‑darwin` \| [`getentropy`][3]
10		//! \| iOS, tvOS, watchOS \| `‑apple‑ios`, `-apple-tvos`, `*-apple-watchos` \| [`CCRandomGenerateBytes`]
11		//! \| FreeBSD \| `*‑freebsd` \| [`getrandom`][5]
12		//! \| OpenBSD \| `*‑openbsd` \| [`getentropy`][7]
13		//! \| NetBSD \| `*‑netbsd` \| [`getrandom`][16] if available, otherwise [`kern.arandom`][8]
14		//! \| Dragonfly BSD \| `*‑dragonfly` \| [`getrandom`][9]
15		//! \| Solaris \| `*‑solaris` \| [`getrandom`][11] (with `GRND_RANDOM`)
16		//! \| illumos \| `*‑illumos` \| [`getrandom`][12]
17		//! \| Fuchsia OS \| `*‑fuchsia` \| [`cprng_draw`]
18		//! \| Redox \| `*‑redox` \| `/dev/urandom`
19		//! \| Haiku \| `*‑haiku` \| `/dev/urandom` (identical to `/dev/random`)
20		//! \| Hermit \| `*-hermit` \| [`sys_read_entropy`]
21		//! \| Hurd \| `-hurd-` \| [`getrandom`][17]
22		//! \| SGX \| `x86_64‑*‑sgx` \| [`RDRAND`]
23		//! \| VxWorks \| `‑wrs‑vxworks‑` \| `randABytes` after checking entropy pool initialization with `randSecure`
24		//! \| ESP-IDF \| `*‑espidf` \| [`esp_fill_random`]
25		//! \| Emscripten \| `*‑emscripten` \| [`getentropy`][13]
26		//! \| WASI \| `wasm32‑wasi` \| [`random_get`]
27		//! \| Web Browser and Node.js \| `wasm‑‑unknown` \| [`Crypto.getRandomValues`] if available, then [`crypto.randomFillSync`] if on Node.js, see [WebAssembly support]
28		//! \| SOLID \| `-kmc-solid_` \| `SOLID_RNG_SampleRandomBytes`
29		//! \| Nintendo 3DS \| `*-nintendo-3ds` \| [`getrandom`][18]
30		//! \| PS Vita \| `-vita-` \| [`getentropy`][13]
31		//! \| QNX Neutrino \| `‑nto-qnx` \| [`/dev/urandom`][14] (identical to `/dev/random`)
32		//! \| AIX \| `*-ibm-aix` \| [`/dev/urandom`][15]
33		//! \| Cygwin \| `*-cygwin` \| [`getrandom`][19] (based on [`RtlGenRandom`])
34		//!
35		//! Pull Requests that add support for new targets to `getrandom` are always welcome.
36		//!
37		//! ## Unsupported targets
38		//!
39		//! By default, `getrandom` will not compile on unsupported targets, but certain
40		//! features allow a user to select a "fallback" implementation if no supported
41		//! implementation exists.
42		//!
43		//! All of the below mechanisms only affect unsupported
44		//! targets. Supported targets will _always_ use their supported implementations.
45		//! This prevents a crate from overriding a secure source of randomness
46		//! (either accidentally or intentionally).
47		//!
48		//! ## `/dev/urandom` fallback on Linux and Android
49		//!
50		//! On Linux targets the fallback is present only if either `target_env` is `musl`,
51		//! or `target_arch` is one of the following: `aarch64`, `arm`, `powerpc`, `powerpc64`,
52		//! `s390x`, `x86`, `x86_64`. Other supported targets [require][platform-support]
53		//! kernel versions which support `getrandom` system call, so fallback is not needed.
54		//!
55		//! On Android targets the fallback is present only for the following `target_arch`es:
56		//! `aarch64`, `arm`, `x86`, `x86_64`. Other `target_arch`es (e.g. RISC-V) require
57		//! sufficiently high API levels.
58		//!
59		//! The fallback can be disabled by enabling the `linux_disable_fallback` crate feature.
60		//! Note that doing so will bump minimum supported Linux kernel version to 3.17 and
61		//! Android API level to 23 (Marshmallow).
62		//!
63		//! ### RDRAND on x86
64		//!
65		//! If the `rdrand` Cargo feature is enabled, `getrandom` will fallback to using
66		//! the [`RDRAND`] instruction to get randomness on `no_std` `x86`/`x86_64`
67		//! targets. This feature has no effect on other CPU architectures.
68		//!
69		//! ### WebAssembly support
70		//!
71		//! This crate fully supports the
72		//! [`wasm32-wasi`](https://github.com/CraneStation/wasi) and
73		//! [`wasm32-unknown-emscripten`](https://www.hellorust.com/setup/emscripten/)
74		//! targets. However, the `wasm32-unknown-unknown` target (i.e. the target used
75		//! by `wasm-pack`) is not automatically
76		//! supported since, from the target name alone, we cannot deduce which
77		//! JavaScript interface is in use (or if JavaScript is available at all).
78		//!
79		//! Instead, if the `js` Cargo feature is enabled, this crate will assume
80		//! that you are building for an environment containing JavaScript, and will
81		//! call the appropriate methods. Both web browser (main window and Web Workers)
82		//! and Node.js environments are supported, invoking the methods
83		//! [described above](#supported-targets) using the [`wasm-bindgen`] toolchain.
84		//!
85		//! To enable the `js` Cargo feature, add the following to the `dependencies`
86		//! section in your `Cargo.toml` file:
87		//! ```toml
88		//! [dependencies]
89		//! getrandom = { version = "0.2", features = ["js"] }
90		//! ```
91		//!
92		//! This can be done even if `getrandom` is not a direct dependency. Cargo
93		//! allows crates to enable features for indirect dependencies.
94		//!
95		//! This feature should only be enabled for binary, test, or benchmark crates.
96		//! Library crates should generally not enable this feature, leaving such a
97		//! decision to users of their library. Also, libraries should not introduce
98		//! their own `js` features just to enable `getrandom`'s `js` feature.
99		//!
100		//! This feature has no effect on targets other than `wasm32-unknown-unknown`.
101		//!
102		//! #### Node.js ES module support
103		//!
104		//! Node.js supports both [CommonJS modules] and [ES modules]. Due to
105		//! limitations in wasm-bindgen's [`module`] support, we cannot directly
106		//! support ES Modules running on Node.js. However, on Node v15 and later, the
107		//! module author can add a simple shim to support the Web Cryptography API:
108		//! ```js
109		//! import { webcrypto } from 'node:crypto'
110		//! globalThis.crypto = webcrypto
111		//! ```
112		//! This crate will then use the provided `webcrypto` implementation.
113		//!
114		//! ### Platform Support
115		//! This crate generally supports the same operating system and platform versions
116		//! that the Rust standard library does. Additional targets may be supported using
117		//! pluggable custom implementations.
118		//!
119		//! This means that as Rust drops support for old versions of operating systems
120		//! (such as old Linux kernel versions, Android API levels, etc) in stable releases,
121		//! `getrandom` may create new patch releases (`0.N.x`) that remove support for
122		//! outdated platform versions.
123		//!
124		//! ### Custom implementations
125		//!
126		//! The [`register_custom_getrandom!`] macro allows a user to mark their own
127		//! function as the backing implementation for [`getrandom`]. See the macro's
128		//! documentation for more information about writing and registering your own
129		//! custom implementations.
130		//!
131		//! Note that registering a custom implementation only has an effect on targets
132		//! that would otherwise not compile. Any supported targets (including those
133		//! using `rdrand` and `js` Cargo features) continue using their normal
134		//! implementations even if a function is registered.
135		//!
136		//! ## Early boot
137		//!
138		//! Sometimes, early in the boot process, the OS has not collected enough
139		//! entropy to securely seed its RNG. This is especially common on virtual
140		//! machines, where standard "random" events are hard to come by.
141		//!
142		//! Some operating system interfaces always block until the RNG is securely
143		//! seeded. This can take anywhere from a few seconds to more than a minute.
144		//! A few (Linux, NetBSD and Solaris) offer a choice between blocking and
145		//! getting an error; in these cases, we always choose to block.
146		//!
147		//! On Linux (when the `getrandom` system call is not available), reading from
148		//! `/dev/urandom` never blocks, even when the OS hasn't collected enough
149		//! entropy yet. To avoid returning low-entropy bytes, we first poll
150		//! `/dev/random` and only switch to `/dev/urandom` once this has succeeded.
151		//!
152		//! On OpenBSD, this kind of entropy accounting isn't available, and on
153		//! NetBSD, blocking on it is discouraged. On these platforms, nonblocking
154		//! interfaces are used, even when reliable entropy may not be available.
155		//! On the platforms where it is used, the reliability of entropy accounting
156		//! itself isn't free from controversy. This library provides randomness
157		//! sourced according to the platform's best practices, but each platform has
158		//! its own limits on the grade of randomness it can promise in environments
159		//! with few sources of entropy.
160		//!
161		//! ## Error handling
162		//!
163		//! We always choose failure over returning known insecure "random" bytes. In
164		//! general, on supported platforms, failure is highly unlikely, though not
165		//! impossible. If an error does occur, then it is likely that it will occur
166		//! on every call to `getrandom`, hence after the first successful call one
167		//! can be reasonably confident that no errors will occur.
168		//!
169		//! [1]: https://manned.org/getrandom.2
170		//! [2]: https://manned.org/urandom.4
171		//! [3]: https://www.unix.com/man-page/mojave/2/getentropy/
172		//! [4]: https://www.unix.com/man-page/mojave/4/urandom/
173		//! [5]: https://www.freebsd.org/cgi/man.cgi?query=getrandom&manpath=FreeBSD+12.0-stable
174		//! [7]: https://man.openbsd.org/getentropy.2
175		//! [8]: https://man.netbsd.org/sysctl.7
176		//! [9]: https://leaf.dragonflybsd.org/cgi/web-man?command=getrandom
177		//! [11]: https://docs.oracle.com/cd/E88353_01/html/E37841/getrandom-2.html
178		//! [12]: https://illumos.org/man/2/getrandom
179		//! [13]: https://github.com/emscripten-core/emscripten/pull/12240
180		//! [14]: https://www.qnx.com/developers/docs/7.1/index.html#com.qnx.doc.neutrino.utilities/topic/r/random.html
181		//! [15]: https://www.ibm.com/docs/en/aix/7.3?topic=files-random-urandom-devices
182		//! [16]: https://man.netbsd.org/getrandom.2
183		//! [17]: https://www.gnu.org/software/libc/manual/html_mono/libc.html#index-getrandom
184		//! [18]: https://github.com/rust3ds/shim-3ds/commit/b01d2568836dea2a65d05d662f8e5f805c64389d
185		//! [19]: https://github.com/cygwin/cygwin/blob/main/winsup/cygwin/libc/getentropy.cc
186		//!
187		//! [`BCryptGenRandom`]: https://docs.microsoft.com/en-us/windows/win32/api/bcrypt/nf-bcrypt-bcryptgenrandom
188		//! [`RtlGenRandom`]: https://learn.microsoft.com/en-us/windows/win32/api/ntsecapi/nf-ntsecapi-rtlgenrandom
189		//! [`Crypto.getRandomValues`]: https://www.w3.org/TR/WebCryptoAPI/#Crypto-method-getRandomValues
190		//! [`RDRAND`]: https://software.intel.com/en-us/articles/intel-digital-random-number-generator-drng-software-implementation-guide
191		//! [`CCRandomGenerateBytes`]: https://opensource.apple.com/source/CommonCrypto/CommonCrypto-60074/include/CommonRandom.h.auto.html
192		//! [`cprng_draw`]: https://fuchsia.dev/fuchsia-src/zircon/syscalls/cprng_draw
193		//! [`crypto.randomFillSync`]: https://nodejs.org/api/crypto.html#cryptorandomfillsyncbuffer-offset-size
194		//! [`esp_fill_random`]: https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/system/random.html#_CPPv415esp_fill_randomPv6size_t
195		//! [`random_get`]: https://github.com/WebAssembly/WASI/blob/main/phases/snapshot/docs.md#-random_getbuf-pointeru8-buf_len-size---errno
196		//! [WebAssembly support]: #webassembly-support
197		//! [`wasm-bindgen`]: https://github.com/rustwasm/wasm-bindgen
198		//! [`module`]: https://rustwasm.github.io/wasm-bindgen/reference/attributes/on-js-imports/module.html
199		//! [CommonJS modules]: https://nodejs.org/api/modules.html
200		//! [ES modules]: https://nodejs.org/api/esm.html
201		//! [`sys_read_entropy`]: https://github.com/hermit-os/kernel/blob/315f58ff5efc81d9bf0618af85a59963ff55f8b1/src/syscalls/entropy.rs#L47-L55
202		//! [platform-support]: https://doc.rust-lang.org/stable/rustc/platform-support.html
203
204		#![doc(
205		html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk.png",
206		html_favicon_url = "https://www.rust-lang.org/favicon.ico",
207		html_root_url = "https://docs.rs/getrandom/0.2.16"
208		)]
209		#![no_std]
210		#![warn(rust_2018_idioms, unused_lifetimes, missing_docs)]
211		#![cfg_attr(docsrs, feature(doc_auto_cfg))]
212
213		#[macro_use]
214		extern crate cfg_if;
215
216		use crate::util::{slice_as_uninit_mut, slice_assume_init_mut};
217		use core::mem::MaybeUninit;
218
219		mod error;
220		mod util;
221		// To prevent a breaking change when targets are added, we always export the
222		// register_custom_getrandom macro, so old Custom RNG crates continue to build.
223		#[cfg(feature = "custom")]
224		mod custom;
225		#[cfg(feature = "std")]
226		mod error_impls;
227
228		pub use crate::error::Error;
229
230		// System-specific implementations.
231		//
232		// These should all provide getrandom_inner with the signature
233		// `fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error>`.
234		// The function MUST fully initialize `dest` when `Ok(())` is returned.
235		// The function MUST NOT ever write uninitialized bytes into `dest`,
236		// regardless of what value it returns.
237		cfg_if! {
238		if #[cfg(any(target_os = "haiku", target_os = "redox", target_os = "nto", target_os = "aix"))] {
239		mod util_libc;
240		#[path = "use_file.rs"] mod imp;
241		} else if #[cfg(any(
242		target_os = "macos",
243		target_os = "openbsd",
244		target_os = "vita",
245		target_os = "emscripten",
246		))] {
247		mod util_libc;
248		#[path = "getentropy.rs"] mod imp;
249		} else if #[cfg(any(
250		target_os = "dragonfly",
251		target_os = "freebsd",
252		target_os = "hurd",
253		target_os = "illumos",
254		// Check for target_arch = "arm" to only include the 3DS. Does not
255		// include the Nintendo Switch (which is target_arch = "aarch64").
256		all(target_os = "horizon", target_arch = "arm"),
257		target_os = "cygwin",
258		))] {
259		mod util_libc;
260		#[path = "getrandom.rs"] mod imp;
261		} else if #[cfg(all(
262		not(feature = "linux_disable_fallback"),
263		any(
264		// Rust supports Android API level 19 (KitKat) [0] and the next upgrade targets
265		// level 21 (Lollipop) [1], while `getrandom(2)` was added only in
266		// level 23 (Marshmallow). Note that it applies only to the "old" `target_arch`es,
267		// RISC-V Android targets sufficiently new API level, same will apply for potential
268		// new Android `target_arch`es.
269		// [0]: https://blog.rust-lang.org/2023/01/09/android-ndk-update-r25.html
270		// [1]: https://github.com/rust-lang/rust/pull/120593
271		all(
272		target_os = "android",
273		any(
274		target_arch = "aarch64",
275		target_arch = "arm",
276		target_arch = "x86",
277		target_arch = "x86_64",
278		),
279		),
280		// Only on these `target_arch`es Rust supports Linux kernel versions (3.2+)
281		// that precede the version (3.17) in which `getrandom(2)` was added:
282		// https://doc.rust-lang.org/stable/rustc/platform-support.html
283		all(
284		target_os = "linux",
285		any(
286		target_arch = "aarch64",
287		target_arch = "arm",
288		target_arch = "powerpc",
289		target_arch = "powerpc64",
290		target_arch = "s390x",
291		target_arch = "x86",
292		target_arch = "x86_64",
293		// Minimum supported Linux kernel version for MUSL targets
294		// is not specified explicitly (as of Rust 1.77) and they
295		// are used in practice to target pre-3.17 kernels.
296		target_env = "musl",
297		),
298		)
299		),
300		))] {
301		mod util_libc;
302		mod use_file;
303		mod lazy;
304		#[path = "linux_android_with_fallback.rs"] mod imp;
305		} else if #[cfg(any(target_os = "android", target_os = "linux"))] {
306		mod util_libc;
307		#[path = "linux_android.rs"] mod imp;
308		} else if #[cfg(target_os = "solaris")] {
309		mod util_libc;
310		#[path = "solaris.rs"] mod imp;
311		} else if #[cfg(target_os = "netbsd")] {
312		mod util_libc;
313		#[path = "netbsd.rs"] mod imp;
314		} else if #[cfg(target_os = "fuchsia")] {
315		#[path = "fuchsia.rs"] mod imp;
316		} else if #[cfg(any(target_os = "ios", target_os = "visionos", target_os = "watchos", target_os = "tvos"))] {
317		#[path = "apple-other.rs"] mod imp;
318		} else if #[cfg(all(target_arch = "wasm32", target_os = "wasi"))] {
319		#[path = "wasi.rs"] mod imp;
320		} else if #[cfg(target_os = "hermit")] {
321		#[path = "hermit.rs"] mod imp;
322		} else if #[cfg(target_os = "vxworks")] {
323		mod util_libc;
324		#[path = "vxworks.rs"] mod imp;
325		} else if #[cfg(target_os = "solid_asp3")] {
326		#[path = "solid.rs"] mod imp;
327		} else if #[cfg(target_os = "espidf")] {
328		#[path = "espidf.rs"] mod imp;
329		} else if #[cfg(windows)] {
330		#[path = "windows.rs"] mod imp;
331		} else if #[cfg(all(target_arch = "x86_64", target_env = "sgx"))] {
332		mod lazy;
333		#[path = "rdrand.rs"] mod imp;
334		} else if #[cfg(all(feature = "rdrand",
335		any(target_arch = "x86_64", target_arch = "x86")))] {
336		mod lazy;
337		#[path = "rdrand.rs"] mod imp;
338		} else if #[cfg(all(feature = "js",
339		any(target_arch = "wasm32", target_arch = "wasm64"),
340		target_os = "unknown"))] {
341		#[path = "js.rs"] mod imp;
342		} else if #[cfg(feature = "custom")] {
343		use custom as imp;
344		} else if #[cfg(all(any(target_arch = "wasm32", target_arch = "wasm64"),
345		target_os = "unknown"))] {
346		compile_error!("the wasm*-unknown-unknown targets are not supported by \
347		default, you may need to enable the \"js\" feature. \
348		For more information see: \
349		https://docs.rs/getrandom/#webassembly-support");
350		} else {
351		compile_error!("target is not supported, for more information see: \
352		https://docs.rs/getrandom/#unsupported-targets");
353		}
354		}
355
356		/// Fill `dest` with random bytes from the system's preferred random number
357		/// source.
358		///
359		/// This function returns an error on any failure, including partial reads. We
360		/// make no guarantees regarding the contents of `dest` on error. If `dest` is
361		/// empty, `getrandom` immediately returns success, making no calls to the
362		/// underlying operating system.
363		///
364		/// Blocking is possible, at least during early boot; see module documentation.
365		///
366		/// In general, `getrandom` will be fast enough for interactive usage, though
367		/// significantly slower than a user-space CSPRNG; for the latter consider
368		/// [`rand::thread_rng`](https://docs.rs/rand/*/rand/fn.thread_rng.html).
369		#[inline]
370	0	pub fn getrandom(dest: &mut [u8]) -> Result<(), Error> {
371		// SAFETY: The `&mut MaybeUninit<_>` reference doesn't escape, and
372		// `getrandom_uninit` guarantees it will never de-initialize any part of
373		// `dest`.
374	0	getrandom_uninit(unsafe { slice_as_uninit_mut(dest) })?;
375	0	Ok(())
376	0	} Unexecuted instantiation: getrandom::getrandom Unexecuted instantiation: getrandom::getrandom
377
378		/// Version of the `getrandom` function which fills `dest` with random bytes
379		/// returns a mutable reference to those bytes.
380		///
381		/// On successful completion this function is guaranteed to return a slice
382		/// which points to the same memory as `dest` and has the same length.
383		/// In other words, it's safe to assume that `dest` is initialized after
384		/// this function has returned `Ok`.
385		///
386		/// No part of `dest` will ever be de-initialized at any point, regardless
387		/// of what is returned.
388		///
389		/// # Examples
390		///
391		/// ```ignore
392		/// # // We ignore this test since `uninit_array` is unstable.
393		/// #![feature(maybe_uninit_uninit_array)]
394		/// # fn main() -> Result<(), getrandom::Error> {
395		/// let mut buf = core::mem::MaybeUninit::uninit_array::<1024>();
396		/// let buf: &mut [u8] = getrandom::getrandom_uninit(&mut buf)?;
397		/// # Ok(()) }
398		/// ```
399		#[inline]
400	0	pub fn getrandom_uninit(dest: &mut [MaybeUninit<u8>]) -> Result<&mut [u8], Error> {
401	0	if !dest.is_empty() {
402	0	imp::getrandom_inner(dest)?;
403	0	}
404		// SAFETY: `dest` has been fully initialized by `imp::getrandom_inner`
405		// since it returned `Ok`.
406	0	Ok(unsafe { slice_assume_init_mut(dest) })
407	0	} Unexecuted instantiation: getrandom::getrandom_uninit Unexecuted instantiation: getrandom::getrandom_uninit