Add a crate which wraps `getrandom` but always compiles

[rust-lightning] / possiblyrandom / src / lib.rs

diff --git a/possiblyrandom/src/lib.rs b/possiblyrandom/src/lib.rs
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+++ b/possiblyrandom/src/lib.rs
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+// This file is Copyright its original authors, visible in version control
+// history.
+//
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+//! [`getrandom`] provides access to OS randomness, but will fail to compile on platforms that do
+//! not support fetching OS randomness. This is exactly what you want when you're doing
+//! cryptographic operations, but when you're just opportunistically randomizing, we're fine with
+//! compiling and simply disabling randomization.
+//!
+//! This crate does that, returning only possibly-random data.
+//!
+//! Note that this crate only enables getrandom on a subset of platforms it supports. As getrandom
+//! evolves this crate is unlikely to carefully track all getrandom-supported platforms, however
+//! will use random data on popular platforms.
+
+#![no_std]
+
+#[cfg(feature = "getrandom")]
+extern crate getrandom;
+
+/// Possibly fills `dest` with random data. May fill it with zeros.
+#[inline]
+pub fn getpossiblyrandom(dest: &mut [u8]) {
+       #[cfg(feature = "getrandom")]
+       if getrandom::getrandom(dest).is_err() {
+               dest.fill(0);
+       }
+       #[cfg(not(feature = "getrandom"))]
+       dest.fill(0);
+}