Initial commit

src/tests/mock_rng.rs

@@ -0,0 +1,63 @@
+// Copyright (c) Facebook, Inc. and its affiliates.
+//
+// This source code is licensed under the MIT license found in the
+// LICENSE file in the root directory of this source tree.
+
+use rand_core::{CryptoRng, Error, RngCore};
+use std::cmp::min;
+
+/// A simple implementation of `RngCore` for testing purposes.
+///
+/// This generates a cyclic sequence (i.e. cycles over an initial buffer)
+///
+///
+#[derive(Debug, Clone)]
+pub struct CycleRng {
+    v: Vec<u8>,
+}
+
+impl CycleRng {
+    /// Create a `CycleRng`, yielding a sequence starting with
+    /// `initial` and looping thereafter
+    pub fn new(initial: Vec<u8>) -> Self {
+        CycleRng { v: initial }
+    }
+}
+
+fn rotate_left<T>(data: &mut [T], steps: usize) {
+    if data.is_empty() {
+        return;
+    }
+    let steps = steps % data.len();
+
+    data[..steps].reverse();
+    data[steps..].reverse();
+    data.reverse();
+}
+
+impl RngCore for CycleRng {
+    fn next_u32(&mut self) -> u32 {
+        unimplemented!()
+    }
+
+    #[inline]
+    fn next_u64(&mut self) -> u64 {
+        unimplemented!()
+    }
+
+    #[inline]
+    fn fill_bytes(&mut self, dest: &mut [u8]) {
+        let len = min(self.v.len(), dest.len());
+        (&mut dest[..len]).copy_from_slice(&self.v[..len]);
+        rotate_left(&mut self.v, len);
+    }
+
+    #[inline]
+    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
+        self.fill_bytes(dest);
+        Ok(())
+    }
+}
+
+// This is meant for testing only
+impl CryptoRng for CycleRng {}