avoid creating unnecessary headers instance

Author: anonrig

.changeset/red-kiwis-press.md

@@ -0,0 +1,5 @@
+---
+"@opennextjs/aws": patch
+---
+
+Avoid creating unnecessary headers instance on every request

packages/open-next/src/overrides/wrappers/cloudflare-node.ts

@@ -41,15 +41,16 @@ const handler: WrapperHandler<InternalEvent, InternalResult> =
       }): Writable {
         const { statusCode, cookies, headers } = prelude;
 
-        const responseHeaders = new Headers(headers);
-        for (const cookie of cookies) {
-          responseHeaders.append("Set-Cookie", cookie);
-        }
-
         // TODO(vicb): this is a workaround to make PPR work with `wrangler dev`
         // See https://github.com/cloudflare/workers-sdk/issues/8004
         if (url.hostname === "localhost") {
-          responseHeaders.set("Content-Encoding", "identity");
+          headers["content-encoding"] = "identity";
+        }
+
+        // Build headers array - set-cookie must be added separately for each cookie
+        const headerEntries: [string, string][] = Object.entries(headers);
+        for (const cookie of cookies) {
+          headerEntries.push(["set-cookie", cookie]);
         }
 
         const { readable, writable } = new TransformStream({
@@ -60,7 +61,7 @@ const handler: WrapperHandler<InternalEvent, InternalResult> =
         const body = NULL_BODY_STATUSES.has(statusCode) ? null : readable;
         const response = new Response(body, {
           status: statusCode,
-          headers: responseHeaders,
+          headers: headerEntries,
         });
         resolveResponse(response);