1 files changed, 229 insertions, 0 deletions
diff --git a/rand/src/reseeding.rs b/rand/src/reseeding.rs
new file mode 100644
index 0000000..1f24e20
--- /dev/null
+++ b/rand/src/reseeding.rs
@@ -0,0 +1,229 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// 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. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! A wrapper around another RNG that reseeds it after it
+//! generates a certain number of random bytes.
+
+use core::default::Default;
+
+use {Rng, SeedableRng};
+
+/// How many bytes of entropy the underling RNG is allowed to generate
+/// before it is reseeded
+const DEFAULT_GENERATION_THRESHOLD: u64 = 32 * 1024;
+
+/// A wrapper around any RNG which reseeds the underlying RNG after it
+/// has generated a certain number of random bytes.
+#[derive(Debug)]
+pub struct ReseedingRng<R, Rsdr> {
+    rng: R,
+    generation_threshold: u64,
+    bytes_generated: u64,
+    /// Controls the behaviour when reseeding the RNG.
+    pub reseeder: Rsdr,
+}
+
+impl<R: Rng, Rsdr: Reseeder<R>> ReseedingRng<R, Rsdr> {
+    /// Create a new `ReseedingRng` with the given parameters.
+    ///
+    /// # Arguments
+    ///
+    /// * `rng`: the random number generator to use.
+    /// * `generation_threshold`: the number of bytes of entropy at which to reseed the RNG.
+    /// * `reseeder`: the reseeding object to use.
+    pub fn new(rng: R, generation_threshold: u64, reseeder: Rsdr) -> ReseedingRng<R,Rsdr> {
+        ReseedingRng {
+            rng: rng,
+            generation_threshold: generation_threshold,
+            bytes_generated: 0,
+            reseeder: reseeder
+        }
+    }
+
+    /// Reseed the internal RNG if the number of bytes that have been
+    /// generated exceed the threshold.
+    pub fn reseed_if_necessary(&mut self) {
+        if self.bytes_generated >= self.generation_threshold {
+            self.reseeder.reseed(&mut self.rng);
+            self.bytes_generated = 0;
+        }
+    }
+}
+
+
+impl<R: Rng, Rsdr: Reseeder<R>> Rng for ReseedingRng<R, Rsdr> {
+    fn next_u32(&mut self) -> u32 {
+        self.reseed_if_necessary();
+        self.bytes_generated += 4;
+        self.rng.next_u32()
+    }
+
+    fn next_u64(&mut self) -> u64 {
+        self.reseed_if_necessary();
+        self.bytes_generated += 8;
+        self.rng.next_u64()
+    }
+
+    fn fill_bytes(&mut self, dest: &mut [u8]) {
+        self.reseed_if_necessary();
+        self.bytes_generated += dest.len() as u64;
+        self.rng.fill_bytes(dest)
+    }
+}
+
+impl<S, R: SeedableRng<S>, Rsdr: Reseeder<R> + Default>
+     SeedableRng<(Rsdr, S)> for ReseedingRng<R, Rsdr> {
+    fn reseed(&mut self, (rsdr, seed): (Rsdr, S)) {
+        self.rng.reseed(seed);
+        self.reseeder = rsdr;
+        self.bytes_generated = 0;
+    }
+
+    /// Create a new `ReseedingRng` from the given reseeder and
+    /// seed. This uses a default value for `generation_threshold`.
+    fn from_seed((rsdr, seed): (Rsdr, S)) -> ReseedingRng<R, Rsdr> {
+        ReseedingRng {
+            rng: SeedableRng::from_seed(seed),
+            generation_threshold: DEFAULT_GENERATION_THRESHOLD,
+            bytes_generated: 0,
+            reseeder: rsdr
+        }
+    }
+}
+
+/// Something that can be used to reseed an RNG via `ReseedingRng`.
+///
+/// # Example
+///
+/// ```rust
+/// use rand::{Rng, SeedableRng, StdRng};
+/// use rand::reseeding::{Reseeder, ReseedingRng};
+///
+/// struct TickTockReseeder { tick: bool }
+/// impl Reseeder<StdRng> for TickTockReseeder {
+///     fn reseed(&mut self, rng: &mut StdRng) {
+///         let val = if self.tick {0} else {1};
+///         rng.reseed(&[val]);
+///         self.tick = !self.tick;
+///     }
+/// }
+/// fn main() {
+///     let rsdr = TickTockReseeder { tick: true };
+///
+///     let inner = StdRng::new().unwrap();
+///     let mut rng = ReseedingRng::new(inner, 10, rsdr);
+///
+///     // this will repeat, because it gets reseeded very regularly.
+///     let s: String = rng.gen_ascii_chars().take(100).collect();
+///     println!("{}", s);
+/// }
+///
+/// ```
+pub trait Reseeder<R> {
+    /// Reseed the given RNG.
+    fn reseed(&mut self, rng: &mut R);
+}
+
+/// Reseed an RNG using a `Default` instance. This reseeds by
+/// replacing the RNG with the result of a `Default::default` call.
+#[derive(Clone, Copy, Debug)]
+pub struct ReseedWithDefault;
+
+impl<R: Rng + Default> Reseeder<R> for ReseedWithDefault {
+    fn reseed(&mut self, rng: &mut R) {
+        *rng = Default::default();
+    }
+}
+impl Default for ReseedWithDefault {
+    fn default() -> ReseedWithDefault { ReseedWithDefault }
+}
+
+#[cfg(test)]
+mod test {
+    use std::default::Default;
+    use std::iter::repeat;
+    use super::{ReseedingRng, ReseedWithDefault};
+    use {SeedableRng, Rng};
+
+    struct Counter {
+        i: u32
+    }
+
+    impl Rng for Counter {
+        fn next_u32(&mut self) -> u32 {
+            self.i += 1;
+            // very random
+            self.i - 1
+        }
+    }
+    impl Default for Counter {
+        fn default() -> Counter {
+            Counter { i: 0 }
+        }
+    }
+    impl SeedableRng<u32> for Counter {
+        fn reseed(&mut self, seed: u32) {
+            self.i = seed;
+        }
+        fn from_seed(seed: u32) -> Counter {
+            Counter { i: seed }
+        }
+    }
+    type MyRng = ReseedingRng<Counter, ReseedWithDefault>;
+
+    #[test]
+    fn test_reseeding() {
+        let mut rs = ReseedingRng::new(Counter {i:0}, 400, ReseedWithDefault);
+
+        let mut i = 0;
+        for _ in 0..1000 {
+            assert_eq!(rs.next_u32(), i % 100);
+            i += 1;
+        }
+    }
+
+    #[test]
+    fn test_rng_seeded() {
+        let mut ra: MyRng = SeedableRng::from_seed((ReseedWithDefault, 2));
+        let mut rb: MyRng = SeedableRng::from_seed((ReseedWithDefault, 2));
+        assert!(::test::iter_eq(ra.gen_ascii_chars().take(100),
+                                rb.gen_ascii_chars().take(100)));
+    }
+
+    #[test]
+    fn test_rng_reseed() {
+        let mut r: MyRng = SeedableRng::from_seed((ReseedWithDefault, 3));
+        let string1: String = r.gen_ascii_chars().take(100).collect();
+
+        r.reseed((ReseedWithDefault, 3));
+
+        let string2: String = r.gen_ascii_chars().take(100).collect();
+        assert_eq!(string1, string2);
+    }
+
+    const FILL_BYTES_V_LEN: usize = 13579;
+    #[test]
+    fn test_rng_fill_bytes() {
+        let mut v = repeat(0u8).take(FILL_BYTES_V_LEN).collect::<Vec<_>>();
+        ::test::rng().fill_bytes(&mut v);
+
+        // Sanity test: if we've gotten here, `fill_bytes` has not infinitely
+        // recursed.
+        assert_eq!(v.len(), FILL_BYTES_V_LEN);
+
+        // To test that `fill_bytes` actually did something, check that the
+        // average of `v` is not 0.
+        let mut sum = 0.0;
+        for &x in v.iter() {
+            sum += x as f64;
+        }
+        assert!(sum / v.len() as f64 != 0.0);
+    }
+}