perf(OpenNextResponse): do not store the chunks for streamed responses

.changeset/honest-lamps-smell.md

@@ -0,0 +1,10 @@
+---
+"@opennextjs/aws": minor
+---
+
+perf(OpenNextResponse): do not store the chunks for streamed responses
+
+There is no need to store the chunks for streamed responses.
+Not storing the chunks allows saving memory.
+
+Note that `OpenNextHandler` will now return an empty body for streamed responses.

packages/open-next/src/http/openNextResponse.ts

@@ -20,11 +20,13 @@ export class OpenNextNodeResponse extends Transform implements ServerResponse {
   statusCode!: number;
   statusMessage = "";
   headers: OutgoingHttpHeaders = {};
-  private _cookies: string[] = [];
-  private responseStream?: Writable;
   headersSent = false;
   _chunks: Buffer[] = [];
 
+  private _cookies: string[] = [];
+  private responseStream?: Writable;
+  private bodyLength = 0;
+
   // To comply with the ServerResponse interface :
   strictContentLength = false;
   assignSocket(_socket: Socket): void {
@@ -282,16 +284,13 @@ export class OpenNextNodeResponse extends Transform implements ServerResponse {
     return Buffer.concat(this._chunks);
   }
 
-  getBodyLength(): number {
-    let size = 0;
-    for (const chunk of this._chunks) {
-      size += chunk.length;
-    }
-    return size;
-  }
-
   private _internalWrite(chunk: any, encoding: BufferEncoding) {
-    this._chunks.push(Buffer.from(chunk, encoding));
+    const buffer = Buffer.from(chunk, encoding);
+    this.bodyLength += buffer.length;
+    if (!this.streamCreator) {
+      // Do not keep chunks around for streamed responses
+      this._chunks.push(buffer);
+    }
     this.push(chunk, encoding);
     this.streamCreator?.onWrite?.();
   }
@@ -314,12 +313,11 @@ export class OpenNextNodeResponse extends Transform implements ServerResponse {
       this.flushHeaders();
     }
     // In some cases we might not have a store i.e. for example in the image optimization function
-    // We may want to reconsider this in the future, it might be intersting to have access to this store everywhere
+    // We may want to reconsider this in the future, it might be interesting to have access to this store everywhere
     globalThis.__openNextAls
       ?.getStore()
       ?.pendingPromiseRunner.add(this.onEnd(this.headers));
-    const bodyLength = this.getBodyLength();
-    this.streamCreator?.onFinish?.(bodyLength);
+    this.streamCreator?.onFinish?.(this.bodyLength);
 
     //This is only here because of aws broken streaming implementation.
     //Hopefully one day they will be able to give us a working streaming implementation in lambda for everyone
@@ -328,7 +326,7 @@ export class OpenNextNodeResponse extends Transform implements ServerResponse {
     //BE CAREFUL: Aws keeps rolling out broken streaming implementations even on accounts that had working ones before
     //This is not dependent on the node runtime used
     if (
-      bodyLength === 0 &&
+      this.bodyLength === 0 &&
       // We use an env variable here because not all aws account have the same behavior
       // On some aws accounts the response will hang if the body is empty
       // We are modifying the response body here, this is not a good practice