Implement std::io::Read for RngCore

rand_core/src/error.rs

@@ -14,6 +14,8 @@ use core::fmt;
 
 #[cfg(feature="std")]
 use std::error::Error as stdError;
+#[cfg(feature="std")]
+use std::io;
 
 /// Error kind which can be matched over.
 #[derive(PartialEq, Eq, Debug, Copy, Clone)]
@@ -161,3 +163,17 @@ impl stdError for Error {
         self.cause.as_ref().map(|e| e.as_ref() as &stdError)
     }
 }
+
+#[cfg(feature="std")]
+impl From<Error> for io::Error {
+    fn from(error: Error) -> Self {
+        use std::io::ErrorKind::*;
+        match error.kind {
+            ErrorKind::Unavailable => io::Error::new(NotFound, error),
+            ErrorKind::Unexpected |
+            ErrorKind::Transient => io::Error::new(Other, error),
+            ErrorKind::NotReady => io::Error::new(WouldBlock, error),
+            ErrorKind::__Nonexhaustive => unreachable!(),
+        }
+    }
+}

rand_core/src/lib.rs

@@ -439,3 +439,11 @@ impl<R: RngCore + ?Sized> RngCore for Box<R> {
         (**self).try_fill_bytes(dest)
     }
 }
+
+#[cfg(feature="std")]
+impl std::io::Read for RngCore {
+    fn read(&mut self, buf: &mut [u8]) -> Result<usize, std::io::Error> {
+        self.try_fill_bytes(buf)?;
+        Ok(buf.len())
+    }
+}