fix: Implement random_get for wasm backend (#102)

* fix: Implement random_get for wasm backend

* cspell

barretenberg_wasm/Cargo.toml

@@ -12,6 +12,7 @@ rust-version.workspace = true
 wasmer = { version = "*", default-features = false }
 common = { path = "../common", default-features = false }
 rust-embed = { version = "6.6.0", features = ["debug-embed", "interpolate-folder-path", "include-exclude"] }
+getrandom = "0.2"
 
 [build-dependencies]
 pkg-config = "0.3"

barretenberg_wasm/src/lib.rs

@@ -161,7 +161,13 @@ fn instance_load() -> (Instance, Memory) {
             "fd_close" => Function::new_native(&store, fd_close),
             "proc_exit" =>  Function::new_native(&store, proc_exit),
             "fd_fdstat_get" => Function::new_native(&store, fd_fdstat_get),
-            "random_get" => Function::new_native(&store, random_get),
+            "random_get" => Function::new_native_with_env(
+                &store,
+                Env {
+                    memory: memory.clone(),
+                },
+                random_get
+            ),
             "fd_seek" => Function::new_native(&store, fd_seek),
             "fd_write" => Function::new_native(&store, fd_write),
             "environ_sizes_get" => Function::new_native(&store, environ_sizes_get),
@@ -204,9 +210,22 @@ fn logstr(env: &Env, ptr: i32) {
     println!("{string}");
 }
 
-// TODO: Implement randomization function https://github.com/noir-lang/aztec_backend/issues/101
-fn random_get(_: i32, _: i32) -> i32 {
-    0_i32
+// Based on https://github.com/wasmerio/wasmer/blob/2.3.0/lib/wasi/src/syscalls/mod.rs#L2537
+fn random_get(env: &Env, buf: i32, buf_len: i32) -> i32 {
+    let mut u8_buffer = vec![0; buf_len as usize];
+    let res = getrandom::getrandom(&mut u8_buffer);
+    match res {
+        Ok(()) => {
+            unsafe {
+                env.memory
+                    .uint8view()
+                    .subarray(buf as u32, buf as u32 + buf_len as u32)
+                    .copy_from(&u8_buffer);
+            }
+            0_i32 // __WASI_ESUCCESS
+        }
+        Err(_) => 29_i32, // __WASI_EIO
+    }
 }
 
 fn proc_exit(_: i32) {

cspell.json

@@ -45,6 +45,8 @@
         "TURBOVERIFIER",
         "vals",
         "wasi",
+        "subarray",
+        "ESUCCESS",
         // In Solidity
         //
         "addmod",
@@ -65,6 +67,7 @@
         "indicatif",
         "tempdir",
         "tempfile",
-        "wasmer"
+        "wasmer",
+        "getrandom"
     ]
 }