From d4ae55609c4026cef5936aaf9d93c35566f740a7 Mon Sep 17 00:00:00 2001
From: Dan Gohman <dev@sunfishcode.online>
Date: Wed, 21 Dec 2022 13:38:18 -0800
Subject: [PATCH] Add a way to get a random `u64`.

This anticipates https://github.com/WebAssembly/wasi-random/pull/18.
---
 host/src/random.rs |  6 +++++-
 src/lib.rs         |  2 +-
 wit/wasi.wit       | 11 ++++++++++-
 3 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/host/src/random.rs b/host/src/random.rs
index 35a5f816..36c76aa8 100644
--- a/host/src/random.rs
+++ b/host/src/random.rs
@@ -4,10 +4,14 @@ use crate::{wasi_random, WasiCtx};
 
 #[async_trait::async_trait]
 impl wasi_random::WasiRandom for WasiCtx {
-    async fn getrandom(&mut self, len: u32) -> anyhow::Result<Vec<u8>> {
+    async fn get_random_bytes(&mut self, len: u32) -> anyhow::Result<Vec<u8>> {
         Ok((&mut self.random)
             .sample_iter(Standard)
             .take(len as usize)
             .collect())
     }
+
+    async fn get_random_u64(&mut self) -> anyhow::Result<u64> {
+        Ok((&mut self.random).sample(Standard))
+    }
 }
diff --git a/src/lib.rs b/src/lib.rs
index 16bf4d48..f105f667 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1474,7 +1474,7 @@ pub unsafe extern "C" fn random_get(buf: *mut u8, buf_len: Size) -> Errno {
         state.register_buffer(buf, buf_len);
 
         assert_eq!(buf_len as u32 as Size, buf_len);
-        let result = wasi_random::getrandom(buf_len as u32);
+        let result = wasi_random::get_random_bytes(buf_len as u32);
         assert_eq!(result.as_ptr(), buf);
 
         // The returned buffer's memory was allocated in `buf`, so don't separately
diff --git a/wit/wasi.wit b/wit/wasi.wit
index 3f2faa6e..da050637 100644
--- a/wit/wasi.wit
+++ b/wit/wasi.wit
@@ -151,7 +151,16 @@ interface wasi-random {
   ///
   /// Deterministic environments must omit this function, rather than
   /// implementing it with deterministic data.
-  getrandom: func(len: u32) -> list<u8>
+  get-random-bytes: func(len: u32) -> list<u8>
+
+  /// Return a random `u64` value.
+  ///
+  /// This function must produce data from an adaquately seeded CSPRNG, so it
+  /// must not block, and the returned data is always unpredictable.
+  ///
+  /// Deterministic environments must omit this function, rather than
+  /// implementing it with deterministic data.
+  get-random-u64: func() -> u64
 
   /// A value containing 128 random bits.
   ///