Avoid creating unnecessary ReadableStream on every request

Only create the body ReadableStream if the request actually
has a body.

Author: jasnell

src/workerd/api/global-scope.c++

@@ -146,7 +146,6 @@ kj::Promise<DeferredProxy<void>> ServiceWorkerGlobalScope::request(kj::HttpMetho
     Worker::Lock& lock,
     kj::Maybe<ExportedHandler&> exportedHandler,
     kj::Maybe<jsg::Ref<AbortSignal>> abortSignal) {
-  throwIfInvalidHeaderValue(headers);
   TRACE_EVENT("workerd", "ServiceWorkerGlobalScope::request()");
   // To construct a ReadableStream object, we're supposed to pass in an Own<AsyncInputStream>, so
   // that it can drop the reference whenever it gets GC'ed. But in this case the stream's lifetime
@@ -167,10 +166,9 @@ kj::Promise<DeferredProxy<void>> ServiceWorkerGlobalScope::request(kj::HttpMetho
   CfProperty cf(cfBlobJson);
 
   auto jsHeaders = js.alloc<Headers>(js, headers, Headers::Guard::REQUEST);
-  // We do not automatically decode gzipped request bodies because the fetch() standard doesn't
-  // specify any automatic encoding of requests. https://github.com/whatwg/fetch/issues/589
-  auto b = newSystemStream(kj::addRef(*ownRequestBody), StreamEncoding::IDENTITY);
-  auto jsStream = js.alloc<ReadableStream>(ioContext, kj::mv(b));
+
+  // We only create the body stream if there is a body to read.
+  kj::Maybe<jsg::Ref<ReadableStream>> maybeJsStream = kj::none;
 
   // If the request has "no body", we want `request.body` to be null. But, this is not the same
   // thing as the request having a body that happens to be empty. Unfortunately, KJ HTTP gives us
@@ -196,7 +194,12 @@ kj::Promise<DeferredProxy<void>> ServiceWorkerGlobalScope::request(kj::HttpMetho
   if (headers.get(kj::HttpHeaderId::CONTENT_LENGTH) != kj::none ||
       headers.get(kj::HttpHeaderId::TRANSFER_ENCODING) != kj::none ||
       requestBody.tryGetLength().orDefault(1) > 0) {
+    // We do not automatically decode gzipped request bodies because the fetch() standard doesn't
+    // specify any automatic encoding of requests. https://github.com/whatwg/fetch/issues/589
+    auto b = newSystemStream(kj::addRef(*ownRequestBody), StreamEncoding::IDENTITY);
+    auto jsStream = js.alloc<ReadableStream>(ioContext, kj::mv(b));
     body = Body::ExtractedBody(jsStream.addRef());
+    maybeJsStream = kj::mv(jsStream);
   }
 
   // If the request doesn't specify "Content-Length" or "Transfer-Encoding", set "Content-Length"
@@ -269,21 +272,25 @@ kj::Promise<DeferredProxy<void>> ServiceWorkerGlobalScope::request(kj::HttpMetho
           "the eventual Response) as the argument.");
     }
 
-    if (jsStream->isDisturbed()) {
-      lock.logUncaughtException(
-          "Script consumed request body but didn't call respondWith(). Can't forward request.");
-      return addNoopDeferredProxy(
-          response.sendError(500, "Internal Server Error", ioContext.getHeaderTable()));
-    } else {
-      auto client = ioContext.getHttpClient(IoContext::NEXT_CLIENT_CHANNEL, false,
-          cfBlobJson.map([](kj::StringPtr s) { return kj::str(s); }), "fetch_default"_kjc);
-      auto adapter = kj::newHttpService(*client);
-      auto promise = adapter->request(method, url, headers, requestBody, response);
-      // Default handling doesn't rely on the IoContext at all so we can return it as a
-      // deferred proxy task.
-      return DeferredProxy<void>{promise.attach(kj::mv(adapter), kj::mv(client))};
+    KJ_IF_SOME(jsStream, maybeJsStream) {
+      if (jsStream->isDisturbed()) {
+        lock.logUncaughtException(
+            "Script consumed request body but didn't call respondWith(). Can't forward request.");
+        return addNoopDeferredProxy(
+            response.sendError(500, "Internal Server Error", ioContext.getHeaderTable()));
+      }
+      maybeJsStream = kj::none;  // Release our reference; we don't need it anymore.
     }
+
+    auto client = ioContext.getHttpClient(IoContext::NEXT_CLIENT_CHANNEL, false,
+        cfBlobJson.map([](kj::StringPtr s) { return kj::str(s); }), "fetch_default"_kjc);
+    auto adapter = kj::newHttpService(*client);
+    auto promise = adapter->request(method, url, headers, requestBody, response);
+    // Default handling doesn't rely on the IoContext at all so we can return it as a
+    // deferred proxy task.
+    return DeferredProxy<void>{promise.attach(kj::mv(adapter), kj::mv(client))};
   } else KJ_IF_SOME(promise, event->getResponsePromise(lock)) {
+    maybeJsStream = kj::none;  // Release reference to request body stream. We don't need it.
     auto body2 = kj::addRef(*ownRequestBody);
 
     // HACK: If the client disconnects, the `response` reference is no longer valid. But our