Bug 1574174 - add immutable guard for fetch response headers. r=edenchuang,necko-reviewers

Differential Revision: https://phabricator.services.mozilla.com/D162209

dom/fetch/Fetch.cpp

@@ -649,6 +649,13 @@ void MainThreadFetchResolver::OnResponseAvailableInternal(
     }
 
     mResponse = new Response(go, std::move(aResponse), mSignalImpl);
+    // response headers received from the network should be immutable
+    // all response header settings must be done before this point
+    // see Bug 1574174
+    ErrorResult result;
+    mResponse->Headers_()->SetGuard(HeadersGuardEnum::Immutable, result);
+    MOZ_ASSERT(!result.Failed());
+
     BrowsingContext* bc = inner ? inner->GetBrowsingContext() : nullptr;
     bc = bc ? bc->Top() : nullptr;
     if (bc && bc->IsLoading()) {
@@ -725,6 +732,14 @@ class WorkerFetchResponseRunnable final : public MainThreadWorkerRunnable {
       RefPtr<Response> response =
           new Response(global, mInternalResponse.clonePtr(),
                        mResolver->GetAbortSignalForTargetThread());
+
+      // response headers received from the network should be immutable,
+      // all response header settings must be done before this point
+      // see Bug 1574174
+      ErrorResult result;
+      response->Headers_()->SetGuard(HeadersGuardEnum::Immutable, result);
+      MOZ_ASSERT(!result.Failed());
+
       promise->MaybeResolve(response);
     } else {
       if (fetchObserver) {

testing/web-platform/tests/fetch/api/response/response-static-error.any.js

@@ -11,6 +11,18 @@ test(function() {
   assert_true(responseError.headers.entries().next().done, "Headers should be empty");
 }, "Check response returned by static method error()");
 
+promise_test (async function() {
+  let response = await fetch("../resources/data.json");
+
+  try {
+    response.headers.append('name', 'value');
+  } catch (e) {
+    assert_equals(e.constructor.name, "TypeError");
+  }
+
+  assert_not_equals(response.headers.get("name"), "value", "response headers should be immutable");
+}, "Ensure response headers are immutable");
+
 test(function() {
   const headers = Response.error().headers;