move wasi-c2 into wasi-common

crates/wasi-common/src/random.rs

@@ -0,0 +1,46 @@
+use cap_rand::RngCore;
+
+/// 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 RngCore for Deterministic {
+    fn next_u32(&mut self) -> u32 {
+        todo!()
+    }
+    fn next_u64(&mut self) -> u64 {
+        todo!()
+    }
+    fn fill_bytes(&mut self, buf: &mut [u8]) {
+        for b in buf.iter_mut() {
+            *b = self.cycle.next().expect("infinite sequence");
+        }
+    }
+    fn try_fill_bytes(&mut self, buf: &mut [u8]) -> Result<(), cap_rand::Error> {
+        self.fill_bytes(buf);
+        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)
+        }
+    }
+}