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

 // Copyright 2019 Developers of the Rand project.
 //
 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
 // https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
 // <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.

 //! 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] if available, otherwise [`/dev/random`][4] (identical to `/dev/urandom`)
 //! | iOS               | `*‑apple‑ios`      | [`SecRandomCopyBytes`]
 //! | FreeBSD           | `*‑freebsd`        | [`getrandom`][5] if available, otherwise [`kern.arandom`][6]
 //! | OpenBSD           | `*‑openbsd`        | [`getentropy`][7]
 //! | NetBSD            | `*‑netbsd`         | [`kern.arandom`][8]
 //! | Dragonfly BSD     | `*‑dragonfly`      | [`getrandom`][9] if available, otherwise [`/dev/random`][10]
 //! | Solaris, illumos  | `*‑solaris`, `*‑illumos` | [`getrandom`][11] if available, otherwise [`/dev/random`][12]
 //! | Fuchsia OS        | `*‑fuchsia`        | [`cprng_draw`]
 //! | Redox             | `*‑redox`          | `/dev/urandom`
 //! | Haiku             | `*‑haiku`          | `/dev/random` (identical to `/dev/urandom`)
 //! | Hermit            | `x86_64-*-hermit`  | [`RDRAND`]
 //! | SGX               | `x86_64‑*‑sgx`     | [`RDRAND`]
 //! | VxWorks           | `*‑wrs‑vxworks‑*`  | `randABytes` after checking entropy pool initialization with `randSecure`
 //! | ESP-IDF           | `*‑espidf`         | [`esp_fill_random`]
 //! | Emscripten        | `*‑emscripten`     | `/dev/random` (identical to `/dev/urandom`)
 //! | WASI              | `wasm32‑wasi`      | [`random_get`]
 //! | Web Browser       | `wasm32‑*‑unknown` | [`Crypto.getRandomValues`], see [WebAssembly support]
 //! | Node.js           | `wasm32‑*‑unknown` | [`crypto.randomBytes`], see [WebAssembly support]
 //! | SOLID             | `*-kmc-solid_*`    | `SOLID_RNG_SampleRandomBytes`
 //!
 //! 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](https://github.com/rust-lang/rust-bindgen) toolchain.
 //!
 //! This feature has no effect on targets other than `wasm32-unknown-unknown`.
 //!
 //! ### 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.
 //!
 //! ### Indirect Dependencies
 //!
 //! If `getrandom` is not a direct dependency of your crate, you can still
 //! enable any of the above fallback behaviors by enabling the relevant
 //! feature in your root crate's `Cargo.toml`:
 //! ```toml
 //! [dependencies]
 //! getrandom = { version = "0.2", features = ["js"] }
 //! ```
 //!
 //! ## 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.
 //!
 //! ## Error handling
 //!
 //! We always choose failure over returning 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/random/
 //! [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
 //!
 //! [`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
 //! [`SecRandomCopyBytes`]: https://developer.apple.com/documentation/security/1399291-secrandomcopybytes?language=objc
 //! [`cprng_draw`]: https://fuchsia.dev/fuchsia-src/zircon/syscalls/cprng_draw
 //! [`crypto.randomBytes`]: https://nodejs.org/api/crypto.html#crypto_crypto_randombytes_size_callback
 //! [`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

 #![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/0.2.5"
 )]
 #![no_std]
 #![warn(rust_2018_idioms, unused_lifetimes, missing_docs)]
 #![cfg_attr(docsrs, feature(doc_cfg))]

 #[macro_use]
 extern crate cfg_if;

 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 same signature as getrandom.
 cfg_if! {
     if #[cfg(any(target_os = "emscripten", target_os = "haiku",
                  target_os = "redox"))] {
         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;
         #[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(target_os = "ios")] {
         #[path = "ios.rs"] mod imp;
     } else if #[cfg(target_os = "macos")] {
         mod util_libc;
         mod use_file;
         #[path = "macos.rs"] mod imp;
     } else if #[cfg(target_os = "openbsd")] {
         mod util_libc;
         #[path = "openbsd.rs"] mod imp;
     } else if #[cfg(target_os = "wasi")] {
         #[path = "wasi.rs"] mod imp;
     } else if #[cfg(all(target_arch = "x86_64", target_os = "hermit"))] {
         #[path = "rdrand.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"))] {
         #[path = "rdrand.rs"] mod imp;
     } else if #[cfg(all(feature = "rdrand",
                         any(target_arch = "x86_64", target_arch = "x86")))] {
         #[path = "rdrand.rs"] mod imp;
     } else if #[cfg(all(feature = "js",
                         target_arch = "wasm32", target_os = "unknown"))] {
         #[path = "js.rs"] mod imp;
     } else if #[cfg(feature = "custom")] {
         use custom as imp;
     } else if #[cfg(all(target_arch = "wasm32", target_os = "unknown"))] {
         compile_error!("the wasm32-unknown-unknown target is 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).
 pub fn getrandom(dest: &mut [u8]) -> Result<(), Error> {
     if dest.is_empty() {
         return Ok(());
     }
     imp::getrandom_inner(dest)
 }
	// Copyright 2019 Developers of the Rand project.
	//
	// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
	// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
	// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
	// option. This file may not be copied, modified, or distributed
	// except according to those terms.

	//! 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] if available, otherwise [`/dev/random`][4] (identical to `/dev/urandom`)
	//! \| iOS \| `*‑apple‑ios` \| [`SecRandomCopyBytes`]
	//! \| FreeBSD \| `*‑freebsd` \| [`getrandom`][5] if available, otherwise [`kern.arandom`][6]
	//! \| OpenBSD \| `*‑openbsd` \| [`getentropy`][7]
	//! \| NetBSD \| `*‑netbsd` \| [`kern.arandom`][8]
	//! \| Dragonfly BSD \| `*‑dragonfly` \| [`getrandom`][9] if available, otherwise [`/dev/random`][10]
	//! \| Solaris, illumos \| `‑solaris`, `‑illumos` \| [`getrandom`][11] if available, otherwise [`/dev/random`][12]
	//! \| Fuchsia OS \| `*‑fuchsia` \| [`cprng_draw`]
	//! \| Redox \| `*‑redox` \| `/dev/urandom`
	//! \| Haiku \| `*‑haiku` \| `/dev/random` (identical to `/dev/urandom`)
	//! \| Hermit \| `x86_64-*-hermit` \| [`RDRAND`]
	//! \| SGX \| `x86_64‑*‑sgx` \| [`RDRAND`]
	//! \| VxWorks \| `‑wrs‑vxworks‑` \| `randABytes` after checking entropy pool initialization with `randSecure`
	//! \| ESP-IDF \| `*‑espidf` \| [`esp_fill_random`]
	//! \| Emscripten \| `*‑emscripten` \| `/dev/random` (identical to `/dev/urandom`)
	//! \| WASI \| `wasm32‑wasi` \| [`random_get`]
	//! \| Web Browser \| `wasm32‑*‑unknown` \| [`Crypto.getRandomValues`], see [WebAssembly support]
	//! \| Node.js \| `wasm32‑*‑unknown` \| [`crypto.randomBytes`], see [WebAssembly support]
	//! \| SOLID \| `-kmc-solid_` \| `SOLID_RNG_SampleRandomBytes`
	//!
	//! 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](https://github.com/rust-lang/rust-bindgen) toolchain.
	//!
	//! This feature has no effect on targets other than `wasm32-unknown-unknown`.
	//!
	//! ### 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.
	//!
	//! ### Indirect Dependencies
	//!
	//! If `getrandom` is not a direct dependency of your crate, you can still
	//! enable any of the above fallback behaviors by enabling the relevant
	//! feature in your root crate's `Cargo.toml`:
	//! ```toml
	//! [dependencies]
	//! getrandom = { version = "0.2", features = ["js"] }
	//! ```
	//!
	//! ## 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.
	//!
	//! ## Error handling
	//!
	//! We always choose failure over returning 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/random/
	//! [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
	//!
	//! [`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
	//! [`SecRandomCopyBytes`]: https://developer.apple.com/documentation/security/1399291-secrandomcopybytes?language=objc
	//! [`cprng_draw`]: https://fuchsia.dev/fuchsia-src/zircon/syscalls/cprng_draw
	//! [`crypto.randomBytes`]: https://nodejs.org/api/crypto.html#crypto_crypto_randombytes_size_callback
	//! [`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

	#![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/0.2.5"
	)]
	#![no_std]
	#![warn(rust_2018_idioms, unused_lifetimes, missing_docs)]
	#![cfg_attr(docsrs, feature(doc_cfg))]

	#[macro_use]
	extern crate cfg_if;

	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 same signature as getrandom.
	cfg_if! {
	if #[cfg(any(target_os = "emscripten", target_os = "haiku",
	target_os = "redox"))] {
	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;
	#[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(target_os = "ios")] {
	#[path = "ios.rs"] mod imp;
	} else if #[cfg(target_os = "macos")] {
	mod util_libc;
	mod use_file;
	#[path = "macos.rs"] mod imp;
	} else if #[cfg(target_os = "openbsd")] {
	mod util_libc;
	#[path = "openbsd.rs"] mod imp;
	} else if #[cfg(target_os = "wasi")] {
	#[path = "wasi.rs"] mod imp;
	} else if #[cfg(all(target_arch = "x86_64", target_os = "hermit"))] {
	#[path = "rdrand.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"))] {
	#[path = "rdrand.rs"] mod imp;
	} else if #[cfg(all(feature = "rdrand",
	any(target_arch = "x86_64", target_arch = "x86")))] {
	#[path = "rdrand.rs"] mod imp;
	} else if #[cfg(all(feature = "js",
	target_arch = "wasm32", target_os = "unknown"))] {
	#[path = "js.rs"] mod imp;
	} else if #[cfg(feature = "custom")] {
	use custom as imp;
	} else if #[cfg(all(target_arch = "wasm32", target_os = "unknown"))] {
	compile_error!("the wasm32-unknown-unknown target is 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).
	pub fn getrandom(dest: &mut [u8]) -> Result<(), Error> {
	if dest.is_empty() {
	return Ok(());
	}
	imp::getrandom_inner(dest)
	}