wasmtime_wasi/
random.rs

1use cap_rand::RngCore;
2
3/// Implement `insecure-random` using a deterministic cycle of bytes.
4pub struct Deterministic {
5    cycle: std::iter::Cycle<std::vec::IntoIter<u8>>,
6}
7
8impl Deterministic {
9    pub fn new(bytes: Vec<u8>) -> Self {
10        Deterministic {
11            cycle: bytes.into_iter().cycle(),
12        }
13    }
14}
15
16impl RngCore for Deterministic {
17    fn next_u32(&mut self) -> u32 {
18        let b0 = self.cycle.next().expect("infinite sequence");
19        let b1 = self.cycle.next().expect("infinite sequence");
20        let b2 = self.cycle.next().expect("infinite sequence");
21        let b3 = self.cycle.next().expect("infinite sequence");
22        ((b0 as u32) << 24) + ((b1 as u32) << 16) + ((b2 as u32) << 8) + (b3 as u32)
23    }
24    fn next_u64(&mut self) -> u64 {
25        let w0 = self.next_u32();
26        let w1 = self.next_u32();
27        ((w0 as u64) << 32) + (w1 as u64)
28    }
29    fn fill_bytes(&mut self, buf: &mut [u8]) {
30        for b in buf.iter_mut() {
31            *b = self.cycle.next().expect("infinite sequence");
32        }
33    }
34    fn try_fill_bytes(&mut self, buf: &mut [u8]) -> Result<(), cap_rand::Error> {
35        self.fill_bytes(buf);
36        Ok(())
37    }
38}
39
40#[cfg(test)]
41mod test {
42    use super::*;
43    #[test]
44    fn deterministic() {
45        let mut det = Deterministic::new(vec![1, 2, 3, 4]);
46        let mut buf = vec![0; 1024];
47        det.try_fill_bytes(&mut buf).expect("get randomness");
48        for (ix, b) in buf.iter().enumerate() {
49            assert_eq!(*b, (ix % 4) as u8 + 1)
50        }
51    }
52}
53
54pub fn thread_rng() -> Box<dyn RngCore + Send> {
55    use cap_rand::{Rng, SeedableRng};
56    let mut rng = cap_rand::thread_rng(cap_rand::ambient_authority());
57    Box::new(cap_rand::rngs::StdRng::from_seed(rng.r#gen()))
58}
wasmtime_wasi/random.rs

wasmtime_wasi/
random.rs
