Use wasi isntead of libc (#64)

Cargo.toml

@@ -28,6 +28,9 @@ core = { version = "1.0", optional = true, package = "rustc-std-workspace-core"
 [target.'cfg(any(unix, target_os = "redox", target_os = "wasi"))'.dependencies]
 libc = { version = "0.2.60", default-features = false }
 
+[target.'cfg(target_os = "wasi")'.dependencies]
+wasi = "0.5"
+
 [target.wasm32-unknown-unknown.dependencies]
 wasm-bindgen = { version = "0.2.29", optional = true }
 stdweb = { version = "0.4.18", optional = true }

src/wasi.rs

@@ -9,12 +9,12 @@
 //! Implementation for WASI
 use crate::Error;
 use core::num::NonZeroU32;
+use wasi::wasi_unstable::random_get;
 
 pub fn getrandom_inner(dest: &mut [u8]) -> Result<(), Error> {
-    let ret =
-        unsafe { libc::__wasi_random_get(dest.as_mut_ptr() as *mut libc::c_void, dest.len()) };
+    let ret = random_get(dest);
     if let Some(code) = NonZeroU32::new(ret as u32) {
-        error!("WASI: __wasi_random_get: failed with {}", ret);
+        error!("WASI: random_get failed with return value {}", code);
         Err(Error::from(code))
     } else {
         Ok(()) // Zero means success for WASI