wasi: remove dependency on wasi v0.11 (#502)

Having two `wasi` versions in dependencies causes some annoyances in
downstream users, e.g. v0.11 gets show as an "outdated" dependency. The
dependency is removed by directly linking `random_get` by following the
`wasi` code.

Author: newpavlov

Cargo.toml

@@ -21,9 +21,6 @@ core = { version = "1.0", optional = true, package = "rustc-std-workspace-core"
 [target.'cfg(unix)'.dependencies]
 libc = { version = "0.2.154", default-features = false }
 
-[target.'cfg(all(target_arch = "wasm32", target_os = "wasi", target_env = "p1"))'.dependencies]
-wasi = { version = "0.11", default-features = false }
-
 [target.'cfg(all(target_arch = "wasm32", target_os = "wasi", target_env = "p2"))'.dependencies]
 wasi = { version = "0.13", default-features = false }
 

src/wasi.rs

@@ -13,8 +13,22 @@ compile_error!(
 
 #[cfg(target_env = "p1")]
 pub fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
-    unsafe { wasi::random_get(dest.as_mut_ptr().cast::<u8>(), dest.len()) }
-        .map_err(|e| Error::from_os_error(e.raw().into()))
+    // This linking is vendored from the wasi crate:
+    // https://docs.rs/wasi/0.11.0+wasi-snapshot-preview1/src/wasi/lib_generated.rs.html#2344-2350
+    #[link(wasm_import_module = "wasi_snapshot_preview1")]
+    extern "C" {
+        fn random_get(arg0: i32, arg1: i32) -> i32;
+    }
+
+    // Based on the wasi code:
+    // https://docs.rs/wasi/0.11.0+wasi-snapshot-preview1/src/wasi/lib_generated.rs.html#2046-2062
+    // Note that size of an allocated object can not be bigger than isize::MAX bytes.
+    // WASI 0.1 supports only 32-bit WASM, so casting length to `i32` is safe.
+    let ret = unsafe { random_get(dest.as_mut_ptr() as i32, dest.len() as i32) };
+    match ret {
+        0 => Ok(()),
+        _ => Err(Error::from_os_error(ret as u32)),
+    }
 }
 
 #[cfg(target_env = "p2")]