add immutable guard for fetch response headers.

MayyaSunil · moz-wptsync-bot · commit 4c41b4ec55b2 · 2022-11-28T10:48:52.000Z
Differential Revision: https://phabricator.services.mozilla.com/D162209 bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1574174 gecko-commit: fcb447986ee1be3457e44c8b43167a193788f48e gecko-reviewers: edenchuang, necko-reviewers
diff --git a/fetch/api/response/response-static-error.any.js b/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;
 
