Account for Firefox SharedArrayBuffer bug in shared workers

src/backends/wasm_js.rs

@@ -16,7 +16,7 @@ pub use crate::util::{inner_u32, inner_u64};
 #[cfg(not(all(target_arch = "wasm32", any(target_os = "unknown", target_os = "none"))))]
 compile_error!("`wasm_js` backend can be enabled only for OS-less WASM targets!");
 
-use js_sys::{SharedArrayBuffer, Uint8Array, WebAssembly::Memory};
+use js_sys::{JsString, Object, SharedArrayBuffer, Uint8Array, WebAssembly::Memory};
 use wasm_bindgen::{prelude::wasm_bindgen, JsCast, JsValue};
 
 // Size of our temporary Uint8Array buffer used with WebCrypto methods
@@ -38,8 +38,24 @@ pub fn fill_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
                 MEMORY_KIND_NOT_SHARED => false,
                 MEMORY_KIND_SHARED => true,
                 MEMORY_KIND_UNINIT => {
-                    let memory: Memory = wasm_bindgen::memory().unchecked_into();
-                    let val = if memory.buffer().is_instance_of::<SharedArrayBuffer>() {
+                    let buffer = wasm_bindgen::memory().unchecked_into::<Memory>().buffer();
+
+                    // `SharedArrayBuffer` is only available with COOP & COEP. But even without its
+                    // possible to create a shared `WebAssembly.Memory`, so we check for that via
+                    // the constructor name.
+                    //
+                    // Keep in mind that `crossOriginIsolated` is not available on Node.js, in
+                    // which case we can still use `instanceof` because `SharedArrayBuffer` is
+                    // always available.
+                    let shared = match CROSS_ORIGIN_ISOLATED.with(Option::clone) {
+                        Some(true) | None => buffer.is_instance_of::<SharedArrayBuffer>(),
+                        Some(false) => {
+                            let constructor_name = Object::from(buffer).constructor().name();
+                            SHARED_ARRAY_BUFFER_NAME.with(|name| &constructor_name == name)
+                        }
+                    };
+
+                    let val = if shared {
                         MEMORY_KIND_SHARED
                     } else {
                         MEMORY_KIND_NOT_SHARED
@@ -87,6 +103,7 @@ pub fn fill_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
 }
 
 #[wasm_bindgen]
+#[rustfmt::skip]
 extern "C" {
     // Web Crypto API: Crypto interface (https://www.w3.org/TR/WebCryptoAPI/)
     type Crypto;
@@ -98,4 +115,9 @@ extern "C" {
     fn get_random_values(this: &Crypto, buf: &Uint8Array) -> Result<(), JsValue>;
     #[wasm_bindgen(method, js_name = getRandomValues, catch)]
     fn get_random_values_ref(this: &Crypto, buf: &mut [u8]) -> Result<(), JsValue>;
+	// Returns the [`crossOriginIsolated`](https://developer.mozilla.org/en-US/docs/Web/API/crossOriginIsolated) global property.
+	#[wasm_bindgen(thread_local_v2, js_namespace = globalThis, js_name = crossOriginIsolated)]
+	static CROSS_ORIGIN_ISOLATED: Option<bool>;
+    #[wasm_bindgen(thread_local_v2, static_string)]
+    static SHARED_ARRAY_BUFFER_NAME: JsString = "SharedArrayBuffer";
 }