Support webassembly instantiate streaming (#431)

* Allow loadPolicy to accept a PromiseLike<Response> or Response to be able to use WebAssembly.instantiateStreaming over WebAssembly.instantiate internally

Signed-off-by: Eric Tucker <[email protected]>

* Only accept promise instead of Promise for streaming

Signed-off-by: Eric Tucker <[email protected]>

Author: Tucker-Eric

src/opa.js

@@ -262,18 +262,23 @@ function _preparePolicy(env, wasm, memory) {
  * It will return a Promise, depending on the input type the promise
  * resolves to both a compiled WebAssembly.Module and its first WebAssembly.Instance
  * or to the WebAssemblyInstance.
- * @param {BufferSource | WebAssembly.Module} policyWasm
+ * @param {BufferSource | WebAssembly.Module | Response | Promise<Response>} policyWasm
  * @param {WebAssembly.Memory} memory
  * @param {{ [builtinName: string]: Function }} customBuiltins
  * @returns {Promise<{ policy: WebAssembly.WebAssemblyInstantiatedSource | WebAssembly.Instance, minorVersion: number }>}
  */
 async function _loadPolicy(policyWasm, memory, customBuiltins) {
   const env = {};
 
-  const wasm = await WebAssembly.instantiate(
-    policyWasm,
-    _importObject(env, memory, customBuiltins),
-  );
+  const isStreaming = policyWasm instanceof Response ||
+    policyWasm instanceof Promise;
+
+  const importObject = _importObject(env, memory, customBuiltins);
+
+  const wasm =
+    await (isStreaming
+      ? WebAssembly.instantiateStreaming(policyWasm, importObject)
+      : WebAssembly.instantiate(policyWasm, importObject));
 
   return _preparePolicy(env, wasm, memory);
 }
@@ -460,7 +465,7 @@ module.exports = {
    * To set custom memory size specify number of memory pages
    * as second param.
    * Defaults to 5 pages (320KB).
-   * @param {BufferSource | WebAssembly.Module} regoWasm
+   * @param {BufferSource | WebAssembly.Module | Response | Promise<Response>} regoWasm
    * @param {number | WebAssembly.MemoryDescriptor} memoryDescriptor For backwards-compatibility, a 'number' argument is taken to be the initial memory size.
    * @param {{ [builtinName: string]: Function }} customBuiltins A map from string names to builtin functions
    * @returns {Promise<LoadedPolicy>}

test/browser-integration.test.js

@@ -41,6 +41,22 @@ test("esm script should expose working opa module", async () => {
   ]);
 });
 
+test("loadPolicy should allow for a response object that resolves to a fetched wasm module", async () => {
+  const result = await page.evaluate(async function () {
+    // NOTE: Paths are evaluated relative to the project root.
+    const { default: opa } = await import("/dist/opa-wasm-browser.esm.js");
+    const policy = await opa.loadPolicy(
+      fetch("/test/fixtures/multiple-entrypoints/policy.wasm"),
+    );
+    return policy.evaluate({}, "example/one");
+  });
+  expect(result).toEqual([
+    {
+      result: { myOtherRule: false, myRule: false },
+    },
+  ]);
+});
+
 test("default script should expose working opa global", async () => {
   // Load module into global scope.
   const script = fs.readFileSync(