tor-hscrypto: implement Rng.gen() for RendCookie

Cargo.lock

@@ -4197,6 +4197,7 @@ dependencies = [
  "humantime 2.1.0",
  "itertools",
  "paste",
+ "rand 0.8.5",
  "rand_core 0.6.4",
  "safelog",
  "serde",

crates/tor-hscrypto/Cargo.toml

@@ -21,6 +21,7 @@ derive_more = "0.99.3"
 digest = "0.10.0"
 itertools = "0.10.1"
 paste = "1"
+rand = "0.8"
 rand_core = "0.6.2"
 safelog = { path = "../safelog", version = "0.3.1" }
 serde = { version = "1.0.103", features = ["derive"] }

crates/tor-hscrypto/src/lib.rs

@@ -91,3 +91,9 @@ define_bytes! {
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 pub struct RendCookie([u8; REND_COOKIE_LEN]);
 }
+
+impl rand::distributions::Distribution<RendCookie> for rand::distributions::Standard {
+    fn sample<R: rand::Rng + ?Sized>(&self, rng: &mut R) -> RendCookie {
+        RendCookie(rng.gen::<[u8; REND_COOKIE_LEN]>().into())
+    }
+}