wasmtime_wasi/
random.rs

1use cap_rand::{Rng as _, RngCore, SeedableRng as _};
2use wasmtime::component::HasData;
3
4/// A helper struct which implements [`HasData`] for the `wasi:random` APIs.
5///
6/// This can be useful when directly calling `add_to_linker` functions directly,
7/// such as [`wasmtime_wasi::p2::bindings::random::random::add_to_linker`] as
8/// the `D` type parameter. See [`HasData`] for more information about the type
9/// parameter's purpose.
10///
11/// When using this type you can skip the [`WasiRandomView`] trait, for
12/// example.
13///
14/// # Examples
15///
16/// ```
17/// use wasmtime::component::Linker;
18/// use wasmtime::{Engine, Result, Config};
19/// use wasmtime_wasi::random::*;
20///
21/// struct MyStoreState {
22///     random: WasiRandomCtx,
23/// }
24///
25/// fn main() -> Result<()> {
26///     let mut config = Config::new();
27///     config.async_support(true);
28///     let engine = Engine::new(&config)?;
29///     let mut linker = Linker::new(&engine);
30///
31///     wasmtime_wasi::p2::bindings::random::random::add_to_linker::<MyStoreState, WasiRandom>(
32///         &mut linker,
33///         |state| &mut state.random,
34///     )?;
35///     Ok(())
36/// }
37/// ```
38pub struct WasiRandom;
39
40impl HasData for WasiRandom {
41    type Data<'a> = &'a mut WasiRandomCtx;
42}
43
44pub struct WasiRandomCtx {
45    pub(crate) random: Box<dyn RngCore + Send>,
46    pub(crate) insecure_random: Box<dyn RngCore + Send>,
47    pub(crate) insecure_random_seed: u128,
48}
49
50impl Default for WasiRandomCtx {
51    fn default() -> Self {
52        // For the insecure random API, use `SmallRng`, which is fast. It's
53        // also insecure, but that's the deal here.
54        let insecure_random = Box::new(
55            cap_rand::rngs::SmallRng::from_rng(cap_rand::thread_rng(cap_rand::ambient_authority()))
56                .unwrap(),
57        );
58        // For the insecure random seed, use a `u128` generated from
59        // `thread_rng()`, so that it's not guessable from the insecure_random
60        // API.
61        let insecure_random_seed =
62            cap_rand::thread_rng(cap_rand::ambient_authority()).r#gen::<u128>();
63        Self {
64            random: thread_rng(),
65            insecure_random,
66            insecure_random_seed,
67        }
68    }
69}
70
71pub trait WasiRandomView: Send {
72    fn random(&mut self) -> &mut WasiRandomCtx;
73}
74
75impl WasiRandomView for WasiRandomCtx {
76    fn random(&mut self) -> &mut WasiRandomCtx {
77        self
78    }
79}
80
81/// Implement `insecure-random` using a deterministic cycle of bytes.
82pub struct Deterministic {
83    cycle: std::iter::Cycle<std::vec::IntoIter<u8>>,
84}
85
86impl Deterministic {
87    pub fn new(bytes: Vec<u8>) -> Self {
88        Deterministic {
89            cycle: bytes.into_iter().cycle(),
90        }
91    }
92}
93
94impl RngCore for Deterministic {
95    fn next_u32(&mut self) -> u32 {
96        let b0 = self.cycle.next().expect("infinite sequence");
97        let b1 = self.cycle.next().expect("infinite sequence");
98        let b2 = self.cycle.next().expect("infinite sequence");
99        let b3 = self.cycle.next().expect("infinite sequence");
100        ((b0 as u32) << 24) + ((b1 as u32) << 16) + ((b2 as u32) << 8) + (b3 as u32)
101    }
102    fn next_u64(&mut self) -> u64 {
103        let w0 = self.next_u32();
104        let w1 = self.next_u32();
105        ((w0 as u64) << 32) + (w1 as u64)
106    }
107    fn fill_bytes(&mut self, buf: &mut [u8]) {
108        for b in buf.iter_mut() {
109            *b = self.cycle.next().expect("infinite sequence");
110        }
111    }
112    fn try_fill_bytes(&mut self, buf: &mut [u8]) -> Result<(), cap_rand::Error> {
113        self.fill_bytes(buf);
114        Ok(())
115    }
116}
117
118#[cfg(test)]
119mod test {
120    use super::*;
121    #[test]
122    fn deterministic() {
123        let mut det = Deterministic::new(vec![1, 2, 3, 4]);
124        let mut buf = vec![0; 1024];
125        det.try_fill_bytes(&mut buf).expect("get randomness");
126        for (ix, b) in buf.iter().enumerate() {
127            assert_eq!(*b, (ix % 4) as u8 + 1)
128        }
129    }
130}
131
132pub fn thread_rng() -> Box<dyn RngCore + Send> {
133    use cap_rand::{Rng, SeedableRng};
134    let mut rng = cap_rand::thread_rng(cap_rand::ambient_authority());
135    Box::new(cap_rand::rngs::StdRng::from_seed(rng.r#gen()))
136}
wasmtime_wasi/random.rs

wasmtime_wasi/
random.rs
