wasi-common 45.0.0

WASI implementation in Rust
Documentation 
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use core::convert::Infallible;
use rand::{Rng, TryRng};

/// Implement `WasiRandom` using a deterministic cycle of bytes.
pub struct Deterministic {
    cycle: std::iter::Cycle<std::vec::IntoIter<u8>>,
}

impl Deterministic {
    pub fn new(bytes: Vec<u8>) -> Self {
        Deterministic {
            cycle: bytes.into_iter().cycle(),
        }
    }
}

impl TryRng for Deterministic {
    type Error = Infallible;
    fn try_next_u32(&mut self) -> Result<u32, Infallible> {
        let b0 = self.cycle.next().expect("infinite sequence");
        let b1 = self.cycle.next().expect("infinite sequence");
        let b2 = self.cycle.next().expect("infinite sequence");
        let b3 = self.cycle.next().expect("infinite sequence");
        Ok(((b0 as u32) << 24) + ((b1 as u32) << 16) + ((b2 as u32) << 8) + (b3 as u32))
    }
    fn try_next_u64(&mut self) -> Result<u64, Infallible> {
        let w0 = self.next_u32();
        let w1 = self.next_u32();
        Ok(((w0 as u64) << 32) + (w1 as u64))
    }
    fn try_fill_bytes(&mut self, buf: &mut [u8]) -> Result<(), Infallible> {
        for b in buf.iter_mut() {
            *b = self.cycle.next().expect("infinite sequence");
        }
        Ok(())
    }
}

#[cfg(test)]
mod test {
    use super::*;
    #[test]
    fn deterministic() {
        let mut det = Deterministic::new(vec![1, 2, 3, 4]);
        let mut buf = vec![0; 1024];
        det.try_fill_bytes(&mut buf).expect("get randomness");
        for (ix, b) in buf.iter().enumerate() {
            assert_eq!(*b, (ix % 4) as u8 + 1)
        }
    }
}