Add OsRng

Author: dhardy

src/lib.rs

@@ -39,6 +39,13 @@ mod util;
 #[cfg(feature = "std")]
 mod error_std_impls;
 
+#[cfg(feature = "rng")]
+mod rng;
+#[cfg(feature = "rng")]
+pub extern crate rand_core;
+#[cfg(feature = "rng")]
+pub use rng::OsRng;
+
 pub use crate::error::{Error, RawOsError};
 
 /// Fill `dest` with random bytes from the system's preferred random number source.

src/rng.rs

@@ -0,0 +1,60 @@
+//! rand_core adapter
+
+use crate::Error;
+use rand_core::{TryCryptoRng, TryRngCore};
+
+/// An RNG over the operating-system's random data source
+///
+/// This is a zero-sized struct. It can be freely constructed with just `OsRng`.
+///
+/// This struct is also available as [`rand::rngs::OsRng`] when using [rand].
+///
+/// # Usage example
+/// ```
+/// use getrandom::{rand_core::{TryRngCore, RngCore}, OsRng};
+///
+/// let mut key = [0u8; 32];
+/// OsRng.try_fill_bytes(&mut key).unwrap();
+///
+/// let mut rng = OsRng.unwrap_err();
+/// let random_u64 = rng.next_u64();
+/// ```
+///
+/// [rand]: https://crates.io/crates/rand
+/// [`rand::rngs::OsRng`]: https://docs.rs/rand/latest/rand/rngs/struct.OsRng.html
+#[derive(Clone, Copy, Debug, Default)]
+pub struct OsRng;
+
+impl TryRngCore for OsRng {
+    type Error = Error;
+
+    #[inline]
+    fn try_next_u32(&mut self) -> Result<u32, Error> {
+        crate::u32()
+    }
+
+    #[inline]
+    fn try_next_u64(&mut self) -> Result<u64, Error> {
+        crate::u64()
+    }
+
+    #[inline]
+    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
+        crate::fill(dest)
+    }
+}
+
+impl TryCryptoRng for OsRng {}
+
+#[test]
+fn test_os_rng() {
+    let x = OsRng.try_next_u64().unwrap();
+    let y = OsRng.try_next_u64().unwrap();
+    assert!(x != 0);
+    assert!(x != y);
+}
+
+#[test]
+fn test_construction() {
+    assert!(OsRng.try_next_u64().unwrap() != 0);
+}