crates/getrandom/src/lib.rs - platform/external/rust/android-crates-io - Git at Google

 //! 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] if available, otherwise [`kern.arandom`][6]
 //! | OpenBSD           | `*‑openbsd`        | [`getentropy`][7]
 //! | NetBSD            | `*‑netbsd`         | [`getrandom`][16] if available, otherwise [`kern.arandom`][8]
 //! | Dragonfly BSD     | `*‑dragonfly`      | [`getrandom`][9] if available, otherwise [`/dev/urandom`][10] (identical to `/dev/random`)
 //! | Solaris, illumos  | `*‑solaris`, `*‑illumos` | [`getrandom`][11] if available, otherwise [`/dev/random`][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      | `armv6k-nintendo-3ds` | [`getrandom`][1]
 //! | PS Vita           | `armv7-sony-vita-newlibeabihf` | [`getentropy`][13]
 //! | QNX Neutrino      | `*‑nto-qnx*`          | [`/dev/urandom`][14] (identical to `/dev/random`)
 //! | AIX               | `*-ibm-aix`        | [`/dev/urandom`][15]
 //!
 //! There is no blanket implementation on `unix` targets that reads from
 //! `/dev/urandom`. This ensures all supported targets are using the recommended
 //! interface and respect maximum buffer sizes.
 //!
 //! 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).
 //!
 //! ### 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]: http://man7.org/linux/man-pages/man2/getrandom.2.html
 //! [2]: http://man7.org/linux/man-pages/man4/urandom.4.html
 //! [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
 //! [6]: https://www.freebsd.org/cgi/man.cgi?query=random&sektion=4
 //! [7]: https://man.openbsd.org/getentropy.2
 //! [8]: https://man.netbsd.org/sysctl.7
 //! [9]: https://leaf.dragonflybsd.org/cgi/web-man?command=getrandom
 //! [10]: https://leaf.dragonflybsd.org/cgi/web-man?command=random&section=4
 //! [11]: https://docs.oracle.com/cd/E88353_01/html/E37841/getrandom-2.html
 //! [12]: https://docs.oracle.com/cd/E86824_01/html/E54777/random-7d.html
 //! [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
 //!
 //! [`BCryptGenRandom`]: https://docs.microsoft.com/en-us/windows/win32/api/bcrypt/nf-bcrypt-bcryptgenrandom
 //! [`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

 #![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/0.2.12"
 )]
 #![no_std]
 #![warn(rust_2018_idioms, unused_lifetimes, missing_docs)]
 #![cfg_attr(docsrs, feature(doc_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 = "android", target_os = "linux"))] {
         mod util_libc;
         mod use_file;
         mod lazy;
         #[path = "linux_android.rs"] mod imp;
     } else if #[cfg(any(target_os = "illumos", target_os = "solaris"))] {
         mod util_libc;
         mod use_file;
         #[path = "solaris_illumos.rs"] mod imp;
     } else if #[cfg(any(target_os = "freebsd", target_os = "netbsd"))] {
         mod util_libc;
         #[path = "bsd_arandom.rs"] mod imp;
     } else if #[cfg(target_os = "dragonfly")] {
         mod util_libc;
         mod use_file;
         #[path = "dragonfly.rs"] mod imp;
     } else if #[cfg(target_os = "fuchsia")] {
         #[path = "fuchsia.rs"] mod imp;
     } else if #[cfg(any(target_os = "ios", target_os = "watchos", target_os = "tvos"))] {
         #[path = "apple-other.rs"] mod imp;
     } else if #[cfg(target_os = "macos")] {
         mod util_libc;
         #[path = "macos.rs"] mod imp;
     } else if #[cfg(target_os = "openbsd")] {
         mod util_libc;
         #[path = "openbsd.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_os = "horizon", target_arch = "arm"))] {
         // We check for target_arch = "arm" because the Nintendo Switch also
         // uses Horizon OS (it is aarch64).
         mod util_libc;
         #[path = "3ds.rs"] mod imp;
     } else if #[cfg(target_os = "vita")] {
         mod util_libc;
         #[path = "vita.rs"] mod imp;
     } else if #[cfg(target_os = "emscripten")] {
         mod util_libc;
         #[path = "emscripten.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(target_os = "hurd")] {
         mod util_libc;
         #[path = "hurd.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) })
 }
	//! 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] if available, otherwise [`kern.arandom`][6]
	//! \| OpenBSD \| `*‑openbsd` \| [`getentropy`][7]
	//! \| NetBSD \| `*‑netbsd` \| [`getrandom`][16] if available, otherwise [`kern.arandom`][8]
	//! \| Dragonfly BSD \| `*‑dragonfly` \| [`getrandom`][9] if available, otherwise [`/dev/urandom`][10] (identical to `/dev/random`)
	//! \| Solaris, illumos \| `‑solaris`, `‑illumos` \| [`getrandom`][11] if available, otherwise [`/dev/random`][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 \| `armv6k-nintendo-3ds` \| [`getrandom`][1]
	//! \| PS Vita \| `armv7-sony-vita-newlibeabihf` \| [`getentropy`][13]
	//! \| QNX Neutrino \| `‑nto-qnx` \| [`/dev/urandom`][14] (identical to `/dev/random`)
	//! \| AIX \| `*-ibm-aix` \| [`/dev/urandom`][15]
	//!
	//! There is no blanket implementation on `unix` targets that reads from
	//! `/dev/urandom`. This ensures all supported targets are using the recommended
	//! interface and respect maximum buffer sizes.
	//!
	//! 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).
	//!
	//! ### 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]: http://man7.org/linux/man-pages/man2/getrandom.2.html
	//! [2]: http://man7.org/linux/man-pages/man4/urandom.4.html
	//! [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
	//! [6]: https://www.freebsd.org/cgi/man.cgi?query=random&sektion=4
	//! [7]: https://man.openbsd.org/getentropy.2
	//! [8]: https://man.netbsd.org/sysctl.7
	//! [9]: https://leaf.dragonflybsd.org/cgi/web-man?command=getrandom
	//! [10]: https://leaf.dragonflybsd.org/cgi/web-man?command=random&section=4
	//! [11]: https://docs.oracle.com/cd/E88353_01/html/E37841/getrandom-2.html
	//! [12]: https://docs.oracle.com/cd/E86824_01/html/E54777/random-7d.html
	//! [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
	//!
	//! [`BCryptGenRandom`]: https://docs.microsoft.com/en-us/windows/win32/api/bcrypt/nf-bcrypt-bcryptgenrandom
	//! [`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

	#![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/0.2.12"
	)]
	#![no_std]
	#![warn(rust_2018_idioms, unused_lifetimes, missing_docs)]
	#![cfg_attr(docsrs, feature(doc_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 = "android", target_os = "linux"))] {
	mod util_libc;
	mod use_file;
	mod lazy;
	#[path = "linux_android.rs"] mod imp;
	} else if #[cfg(any(target_os = "illumos", target_os = "solaris"))] {
	mod util_libc;
	mod use_file;
	#[path = "solaris_illumos.rs"] mod imp;
	} else if #[cfg(any(target_os = "freebsd", target_os = "netbsd"))] {
	mod util_libc;
	#[path = "bsd_arandom.rs"] mod imp;
	} else if #[cfg(target_os = "dragonfly")] {
	mod util_libc;
	mod use_file;
	#[path = "dragonfly.rs"] mod imp;
	} else if #[cfg(target_os = "fuchsia")] {
	#[path = "fuchsia.rs"] mod imp;
	} else if #[cfg(any(target_os = "ios", target_os = "watchos", target_os = "tvos"))] {
	#[path = "apple-other.rs"] mod imp;
	} else if #[cfg(target_os = "macos")] {
	mod util_libc;
	#[path = "macos.rs"] mod imp;
	} else if #[cfg(target_os = "openbsd")] {
	mod util_libc;
	#[path = "openbsd.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_os = "horizon", target_arch = "arm"))] {
	// We check for target_arch = "arm" because the Nintendo Switch also
	// uses Horizon OS (it is aarch64).
	mod util_libc;
	#[path = "3ds.rs"] mod imp;
	} else if #[cfg(target_os = "vita")] {
	mod util_libc;
	#[path = "vita.rs"] mod imp;
	} else if #[cfg(target_os = "emscripten")] {
	mod util_libc;
	#[path = "emscripten.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(target_os = "hurd")] {
	mod util_libc;
	#[path = "hurd.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) })
	}