Some of the benchmark updates from the headers change

src/workerd/tests/bench-api-headers.c++

@@ -14,6 +14,12 @@ namespace {
 struct ApiHeaders: public benchmark::Fixture {
   virtual ~ApiHeaders() noexcept(true) {}
 
+  struct Header {
+    bool append;
+    kj::StringPtr name;
+    kj::StringPtr value;
+  };
+
   void SetUp(benchmark::State& state) noexcept(true) override {
     fixture = kj::heap<TestFixture>();
 
@@ -45,6 +51,22 @@ struct ApiHeaders: public benchmark::Fixture {
   kj::Own<TestFixture> fixture;
   kj::Own<kj::HttpHeaderTable> table;
   kj::Own<kj::HttpHeaders> kjHeaders;
+  Header kHeaders[13] = {Header{false, "Host"_kj, "example.com"_kj},
+    Header{false, "User-Agent"_kj,
+      "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36"_kj},
+    Header{false, "Accept"_kj,
+      "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8"_kj},
+    Header{false, "Accept-Language"_kj, "en-US,en;q=0.9"_kj},
+    Header{false, "Accept-Encoding"_kj, "gzip, deflate, br"_kj},
+    Header{false, "Content-Type"_kj, "application/json; charset=utf-8"_kj},
+    Header{false, "Authorization"_kj,
+      "Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIn0"_kj},
+    Header{false, "Cache-Control"_kj, "no-cache, no-store, must-revalidate"_kj},
+    Header{false, "Content-Length"_kj, "1234"_kj},
+    Header{false, "Referer"_kj, "https://www.example.com/page?query=value&other=param"_kj},
+    Header{false, "X-Forwarded-For"_kj, "203.0.113.1, 198.51.100.17"_kj},
+    Header{true, "Set-Cookie"_kj, "new_session=token123; Path=/; Secure; HttpOnly"_kj},
+    Header{true, "Set-Cookie"_kj, "new_session=token124; Path=/abc; Secure; HttpOnly"_kj}};
 };
 
 // initialization performs a lot of copying, benchmark it
@@ -61,5 +83,27 @@ BENCHMARK_F(ApiHeaders, constructor)(benchmark::State& state) {
   });
 }
 
+BENCHMARK_F(ApiHeaders, set_append)(benchmark::State& state) {
+  fixture->runInIoContext([&](const TestFixture::Environment& env) {
+    auto& js = env.js;
+    for (auto _: state) {
+      for (size_t i = 0; i < 1000; ++i) {
+        auto headers = js.alloc<api::Headers>();
+        // Set common headers with various representative lengths
+        for (int n = 0; n < 13; n++) {
+          auto& h = kHeaders[n];
+          if (h.append) {
+            headers->append(
+                env.js, jsg::ByteString(kj::str(h.name)), jsg::ByteString(kj::str(h.value)));
+          } else {
+            headers->set(
+                env.js, jsg::ByteString(kj::str(h.name)), jsg::ByteString(kj::str(h.value)));
+          }
+        }
+        benchmark::DoNotOptimize(i);
+      }
+    }
+  });
+}
 }  // namespace
 }  // namespace workerd

src/workerd/tests/bench-response.c++

@@ -88,9 +88,11 @@ BENCHMARK_F(Response, arrayBufferBody)(benchmark::State& state) {
 BENCHMARK_F(Response, jsonResponse)(benchmark::State& state) {
   fixture->runInIoContext([&](const TestFixture::Environment& env) {
     auto& js = env.js;
+    // Prepare object to serialize. Do this outside the loop to avoid measuring its repeated
+    // construction cost. What we want to measure is just the cost of the api::Response::json_ call.
+    auto obj = js.obj();
+    obj.set(js, "key"_kj, js.str("value"_kj));
     for (auto _: state) {
-      auto obj = js.obj();
-      obj.set(js, js.str("key"_kj), js.str("value"_kj));
       benchmark::DoNotOptimize(api::Response::json_(js, obj, kj::none));
     }
   });