From 6ced7b0383769807bdd864ebbf6a16a418d3f821 Mon Sep 17 00:00:00 2001
From: Ben Noordhuis <info@bnoordhuis.nl>
Date: Mon, 16 Aug 2021 12:53:30 +0200
Subject: [PATCH] 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.
---
 cli/tests/unit/wasm_test.ts | 13 +++++++++++++
 ext/fetch/26_fetch.js       |  5 +++--
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/cli/tests/unit/wasm_test.ts b/cli/tests/unit/wasm_test.ts
index c2180db3c9..938eeab7a9 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) {
diff --git a/ext/fetch/26_fetch.js b/ext/fetch/26_fetch.js
index 2d7180691f..edd14abf18 100644
--- a/ext/fetch/26_fetch.js
+++ b/ext/fetch/26_fetch.js
@@ -503,9 +503,10 @@
         // The spec is ambiguous here, see
         // https://github.com/WebAssembly/spec/issues/1138. The WPT tests
         // expect the raw value of the Content-Type attribute lowercased.
+        const contentType = res.headers.get("Content-Type");
         if (
-          StringPrototypeToLowerCase(res.headers.get("Content-Type")) !==
-            "application/wasm"
+          typeof contentType !== "string" ||
+          StringPrototypeToLowerCase(contentType) !== "application/wasm"
         ) {
           throw new TypeError("Invalid WebAssembly content type.");
         }