refactor(StreamCreator): allow opting-out of retaining the chunks (#994)

Author: vicb

.changeset/honest-lamps-smell.md

@@ -1,11 +1,8 @@
 ---
-"@opennextjs/aws": minor
+"@opennextjs/aws": patch
 ---
 
 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.
-
-BREAKING CHANGE: Note that `OpenNextHandler` will now return an empty body if your wrapper provides a `StreamCreator`
-This could break custom converters.
+Not storing the chunks allows saving memory.

.changeset/warm-rats-crash.md

@@ -0,0 +1,5 @@
+---
+"@opennextjs/aws": patch
+---
+
+refactor(StreamCreator): allow opting-out of retaining the chunks

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

@@ -287,8 +287,8 @@ export class OpenNextNodeResponse extends Transform implements ServerResponse {
   private _internalWrite(chunk: any, encoding: BufferEncoding) {
     const buffer = Buffer.from(chunk, encoding);
     this.bodyLength += buffer.length;
-    if (!this.streamCreator) {
-      // Do not keep chunks around for streamed responses
+    if (this.streamCreator?.retainChunks !== false) {
+      // Avoid keeping chunks around when the `StreamCreator` supports it to save memory
       this._chunks.push(buffer);
     }
     this.push(chunk, encoding);

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

@@ -70,6 +70,8 @@ const handler: WrapperHandler<InternalEvent, InternalResult> =
       // Ensures that the response we pass to NextServer is aborted if the request is aborted
       // By doing this `request.signal.onabort` will work in route handlers
       abortSignal: abortSignal,
+      // There is no need to retain the chunks that were pushed to the response stream.
+      retainChunks: false,
     };
 
     ctx.waitUntil(

packages/open-next/src/types/open-next.ts

@@ -56,6 +56,18 @@ export interface StreamCreator {
   onWrite?: () => void;
   onFinish?: (length: number) => void;
   abortSignal?: AbortSignal;
+  /**
+   * Normally there is no need to retain the chunks that have been pushed to the response stream.
+   *
+   * However some implementations use a fake `StreamCreator` and expect the chunks to be retained.
+   * When your stream controller implementation doesn't need to retain the chunk, you can set this
+   * to `false` to reduce memory usage.
+   *
+   * @see https://github.com/opennextjs/opennextjs-aws/blob/main/packages/open-next/src/overrides/wrappers/aws-lambda.ts
+   *
+   * @default true for backward compatibility.
+   */
+  retainChunks?: boolean;
 }
 
 export type WaitUntil = (promise: Promise<void>) => void;