http2: avoid copying the options in respond()

respond() copied the user-provided options object on every call just
so it could normalize and locally flip options.endStream, and
prepareResponseHeadersObject() then looked the :status and date
fields up again on the dictionary-mode null-prototype headers copy
it had just built. Use a local variable for endStream and pick up
:status/date while copying the headers instead.

No measurable throughput change on its own; this removes an object
clone and several dictionary-mode property lookups per response.

Signed-off-by: Matteo Collina <hello@matteocollina.com>

Author: mcollina

lib/internal/http2/core.js

@@ -2813,31 +2813,35 @@ function prepareResponseHeaders(stream, headersParam, options) {
 function prepareResponseHeadersObject(oldHeaders, options) {
   assertIsObject(oldHeaders, 'headers', ['Object', 'Array']);
   const headers = { __proto__: null };
+  let statusCode;
+  let hasDate = false;
 
   if (oldHeaders !== null && oldHeaders !== undefined) {
     // This loop is here for performance reason. Do not change.
+    // The :status and date fields are picked up while copying so they do
+    // not have to be looked up again on the null-prototype copy.
     for (const key in oldHeaders) {
       if (ObjectHasOwn(oldHeaders, key)) {
-        headers[key] = oldHeaders[key];
+        const value = oldHeaders[key];
+        headers[key] = value;
+        if (key === HTTP2_HEADER_STATUS)
+          statusCode = value;
+        else if (key === HTTP2_HEADER_DATE)
+          hasDate = value != null;
       }
     }
     headers[kSensitiveHeaders] = oldHeaders[kSensitiveHeaders];
   }
 
-  const statusCode =
-    headers[HTTP2_HEADER_STATUS] =
-      headers[HTTP2_HEADER_STATUS] | 0 || HTTP_STATUS_OK;
+  statusCode = headers[HTTP2_HEADER_STATUS] = statusCode | 0 || HTTP_STATUS_OK;
 
-  if (options.sendDate == null || options.sendDate) {
-    headers[HTTP2_HEADER_DATE] ??= utcDate();
+  if (!hasDate && (options.sendDate == null || options.sendDate)) {
+    headers[HTTP2_HEADER_DATE] = utcDate();
   }
 
   validatePreparedResponseHeaders(headers, statusCode);
 
-  return {
-    headers,
-    statusCode: headers[HTTP2_HEADER_STATUS],
-  };
+  return { headers, statusCode };
 }
 
 function prepareResponseHeadersArray(headers, options) {
@@ -3222,15 +3226,17 @@ class ServerHttp2Stream extends Http2Stream {
     const state = this[kState];
 
     assertIsObject(options, 'options');
-    options = { ...options };
+    // The options are only read, never mutated, so the user-provided object
+    // can be used directly instead of copying it.
+    options ??= kEmptyObject;
 
     debugStreamObj(this, 'initiating response');
     this[kUpdateTimer]();
 
-    options.endStream = !!options.endStream;
+    const endStream = !!options.endStream;
 
     let streamOptions = 0;
-    if (options.endStream)
+    if (endStream)
       streamOptions |= STREAM_OPTION_EMPTY_PAYLOAD;
 
     if (options.waitForTrailers) {
@@ -3253,12 +3259,11 @@ class ServerHttp2Stream extends Http2Stream {
 
     // Close the writable side if the endStream option is set or status
     // is one of known codes with no payload, or it's a head request
-    if (!!options.endStream ||
+    if (endStream ||
         statusCode === HTTP_STATUS_NO_CONTENT ||
         statusCode === HTTP_STATUS_RESET_CONTENT ||
         statusCode === HTTP_STATUS_NOT_MODIFIED ||
         this.headRequest === true) {
-      options.endStream = true;
       this.end();
     }