fix(ext/fetch): better error if no content-type

The streaming WASM support code inspects the Response object's
Content-Type header but if that was missing, it failed with a fairly
inscrutable "String.prototype.toLowerCase called on null or undefined"
exception. Now it raises a more legible "Invalid WebAssembly content
type" exception.

1 files changed, 13 insertions, 0 deletions

diff --git a/cli/tests/unit/wasm_test.ts b/cli/tests/unit/wasm_test.ts
index c2180db3c..938eeab7a 100644
--- a/cli/tests/unit/wasm_test.ts
+++ b/cli/tests/unit/wasm_test.ts
@@ -48,6 +48,19 @@ unitTest(
   },
 );
 
+unitTest(
+  async function wasmInstantiateStreamingNoContentType() {
+    await assertThrowsAsync(
+      async () => {
+        const response = Promise.resolve(new Response(simpleWasm));
+        await WebAssembly.instantiateStreaming(response);
+      },
+      TypeError,
+      "Invalid WebAssembly content type.",
+    );
+  },
+);
+
 unitTest(async function wasmInstantiateStreaming() {
   let isomorphic = "";
   for (const byte of simpleWasm) {