From 7dd808f7f34dde3e6da0bb431e040ff1572a622e Mon Sep 17 00:00:00 2001
From: apalchys <andrei@palchys.com>
Date: Wed, 26 Feb 2025 17:24:03 +0100
Subject: [PATCH] fix: support Web API ReadableStream when
 streamifyResponse:true

---
 packages/core/__tests__/index.js | 28 ++++++++++++++++++++++++++--
 packages/core/index.js           |  3 ++-
 2 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/packages/core/__tests__/index.js b/packages/core/__tests__/index.js
index 2ecb88ec3..ee0edce84 100644
--- a/packages/core/__tests__/index.js
+++ b/packages/core/__tests__/index.js
@@ -932,11 +932,35 @@ test('Should return with streamifyResponse:true using empty body string and prel
   equal(content(), input)
 })
 
-test('Should return with streamifyResponse:true using ReadableStream', async (t) => {
+// https://nodejs.org/api/stream.html#readable-streams
+test('Should return with streamifyResponse:true using Node Readable stream', async (t) => {
   const input = 'x'.repeat(1024 * 1024)
   const handler = middy(
     async (event, context, { signal }) => {
-      return createReadableStream(input)
+      return createReadableStream(input) // returns Readable stream
+    },
+    {
+      streamifyResponse: true
+    }
+  )
+
+  const { responseStream, chunkResponse } = createResponseStreamMockAndCapture()
+  const response = await handler(event, responseStream, context)
+  equal(response, undefined)
+  equal(chunkResponse(), input)
+})
+
+// https://developer.mozilla.org/en-US/docs/Web/API/ReadableStream
+test('Should return with streamifyResponse:true using Web API ReadableStream', async (t) => {
+  const input = 'x'.repeat(1024 * 1024)
+  const handler = middy(
+    async (event, context, { signal }) => {
+      return new ReadableStream({
+        async start (controller) {
+          controller.enqueue(input)
+          controller.close()
+        }
+      })
     },
     {
       streamifyResponse: true
diff --git a/packages/core/index.js b/packages/core/index.js
index 0fdf81521..b42405e9d 100644
--- a/packages/core/index.js
+++ b/packages/core/index.js
@@ -1,5 +1,6 @@
 /* global awslambda */
 import { Readable } from 'node:stream'
+import { ReadableStream } from 'node:stream/web'
 import { pipeline } from 'node:stream/promises'
 import { setTimeout } from 'node:timers'
 
@@ -64,7 +65,7 @@ const middy = (lambdaHandler = defaultLambdaHandler, plugin = {}) => {
       }
 
       let handlerStream
-      if (handlerBody._readableState) {
+      if (handlerBody._readableState || handlerBody instanceof ReadableStream) {
         handlerStream = handlerBody
       } else if (typeof handlerBody === 'string') {
         // #1189