feat(etc/fetch): Support `WebAssembly.instantiateStreaming` for file fetches (#12901)

Fetching of local files, added in #12545, returns a response with no
headers, including the `Content-Type` header. This currently makes it
not work with the WebAssembly streaming APIs, which require the response
to have a content type of `application/wasm`.

Since the only way to obtain a `Response` object with a non-empty `url`
field is via `fetch()`, this change changes the content type requirement
to only apply to responses whose url has the `file:` scheme.

1 files changed, 14 insertions, 0 deletions

diff --git a/cli/tests/unit/wasm_test.ts b/cli/tests/unit/wasm_test.ts
index e1659b090..3484b7f81 100644
--- a/cli/tests/unit/wasm_test.ts
+++ b/cli/tests/unit/wasm_test.ts
@@ -77,6 +77,20 @@ Deno.test(async function wasmInstantiateStreaming() {
 });
 
 Deno.test(
+  { permissions: { read: true } },
+  async function wasmFileStreaming() {
+    const url = new URL("../testdata/unreachable.wasm", import.meta.url);
+    assert(url.href.startsWith("file://"));
+
+    const { module } = await WebAssembly.instantiateStreaming(fetch(url));
+    assertEquals(WebAssembly.Module.exports(module), [{
+      name: "unreachable",
+      kind: "function",
+    }]);
+  },
+);
+
+Deno.test(
   { permissions: { net: true } },
   async function wasmStreamingNonTrivial() {
     // deno-dom's WASM file is a real-world non-trivial case that gave us