test(maintenance): Expose ResponseStream object to simplify testing in event handler

packages/event-handler/src/rest/utils.ts

@@ -1,4 +1,4 @@
-import { Duplex, Readable, Writable } from 'node:stream';
+import { Duplex, Readable } from 'node:stream';
 import {
   isRecord,
   isRegExp,
@@ -308,17 +308,12 @@ export const resolvePrefixedPath = (path: Path, prefix?: Path): Path => {
 
 export const HttpResponseStream =
   globalThis.awslambda?.HttpResponseStream ??
-  class LocalHttpResponseStream extends Writable {
-    #contentType: string | undefined;
-
-    setContentType(contentType: string) {
-      this.#contentType = contentType;
-    }
-
+  // biome-ignore lint/complexity/noStaticOnlyClass: This is how the Lambda RIC implements it
+  class LocalHttpResponseStream {
     static from(
       underlyingStream: ResponseStream,
       prelude: Record<string, string>
-    ) {
+    ): ResponseStream {
       underlyingStream.setContentType(
         "'application/vnd.awslambda.http-integration-response'"
       );
@@ -401,22 +396,21 @@ const streamifyResponse =
     return (async (event, responseStream, context) => {
       await handler(event, responseStream, context);
 
-      /* v8 ignore else -- @preserve */
-      if ('chunks' in responseStream && Array.isArray(responseStream.chunks)) {
-        const output = Buffer.concat(responseStream.chunks as Buffer[]);
-        const nullBytes = Buffer.from([0, 0, 0, 0, 0, 0, 0, 0]);
-        const separatorIndex = output.indexOf(nullBytes);
-
-        const preludeBuffer = output.subarray(0, separatorIndex);
-        const bodyBuffer = output.subarray(separatorIndex + 8);
-        const prelude = JSON.parse(preludeBuffer.toString());
-
-        return {
-          body: bodyBuffer.toString(),
-          headers: prelude.headers,
-          statusCode: prelude.statusCode,
-        } as TResult;
-      }
+      /* v8 ignore next -- @preserve */
+      const output: Buffer =
+        (responseStream as ResponseStream).getBuffer?.() ?? Buffer.from([]);
+      const nullBytes = Buffer.from([0, 0, 0, 0, 0, 0, 0, 0]);
+      const separatorIndex = output.indexOf(nullBytes);
+
+      const preludeBuffer = output.subarray(0, separatorIndex);
+      const bodyBuffer = output.subarray(separatorIndex + 8);
+      const prelude = JSON.parse(preludeBuffer.toString());
+
+      return {
+        body: bodyBuffer.toString(),
+        headers: prelude.headers,
+        statusCode: prelude.statusCode,
+      } as TResult;
     }) as StreamifyHandler<TEvent, TResult>;
   });
 

packages/event-handler/src/types/rest.ts

@@ -1,4 +1,4 @@
-import type { Readable } from 'node:stream';
+import type { Readable, Writable } from 'node:stream';
 import type {
   GenericLogger,
   JSONValue,
@@ -12,7 +12,6 @@ import type {
 } from 'aws-lambda';
 import type { HttpStatusCodes, HttpVerbs } from '../rest/constants.js';
 import type { Route } from '../rest/Route.js';
-import type { HttpResponseStream } from '../rest/utils.js';
 import type { ResolveOptions } from './common.js';
 
 type ResponseType = 'ApiGatewayV1' | 'ApiGatewayV2';
@@ -140,9 +139,11 @@ type ValidationResult = {
   issues: string[];
 };
 
-type ResponseStream = InstanceType<typeof HttpResponseStream> & {
-  _onBeforeFirstWrite?: (write: (data: Uint8Array | string) => void) => void;
-};
+interface ResponseStream extends Writable {
+  setContentType(contentType: string): void;
+  _onBeforeFirstWrite?: (writeFn: (chunk: unknown) => void) => void;
+  getBuffer?: () => Buffer;
+}
 
 type V1Headers = {
   headers: Record<string, string>;

packages/event-handler/tests/unit/rest/Router/decorators.test.ts

@@ -17,7 +17,7 @@ import {
   createTestEventV2,
   createTestLambdaClass,
   createTrackingMiddleware,
-  MockResponseStream,
+  ResponseStream,
 } from '../helpers.js';
 
 describe.each([
@@ -498,7 +498,7 @@ describe.each([
       }
 
       const lambda = new Lambda();
-      const responseStream = new MockResponseStream();
+      const responseStream = new ResponseStream();
       const handler = lambda.handler.bind(lambda);
 
       // Act
@@ -540,7 +540,7 @@ describe.each([
       }
 
       const lambda = new Lambda();
-      const responseStream = new MockResponseStream();
+      const responseStream = new ResponseStream();
       const handler = lambda.handler.bind(lambda);
 
       // Act

packages/event-handler/tests/unit/rest/Router/streaming.test.ts

@@ -9,7 +9,7 @@ import {
 import {
   createTestEvent,
   createTestEventV2,
-  MockResponseStream,
+  ResponseStream,
 } from '../helpers.js';
 
 describe.each([
@@ -22,7 +22,7 @@ describe.each([
     app.get('/test', async () => ({ message: 'Hello, World!' }));
 
     const handler = streamify(app);
-    const responseStream = new MockResponseStream();
+    const responseStream = new ResponseStream();
 
     // Act
     const result = await handler(
@@ -47,7 +47,7 @@ describe.each([
     });
 
     const handler = streamify(app);
-    const responseStream = new MockResponseStream();
+    const responseStream = new ResponseStream();
 
     // Act
     const result = await handler(
@@ -65,7 +65,7 @@ describe.each([
     // Prepare
     const app = new Router();
     const handler = streamify(app);
-    const responseStream = new MockResponseStream();
+    const responseStream = new ResponseStream();
 
     // Act
     const result = await handler(
@@ -93,7 +93,7 @@ describe.each([
     app.get('/test', () => ({ message: 'middleware test' }));
 
     const handler = streamify(app);
-    const responseStream = new MockResponseStream();
+    const responseStream = new ResponseStream();
 
     // Act
     const result = await handler(
@@ -116,7 +116,7 @@ describe.each([
     });
 
     const handler = streamify(app);
-    const responseStream = new MockResponseStream();
+    const responseStream = new ResponseStream();
 
     // Act
     const result = await handler(
@@ -145,7 +145,7 @@ describe.each([
     });
 
     const handler = streamify(app);
-    const responseStream = new MockResponseStream();
+    const responseStream = new ResponseStream();
 
     // Act
     const result = await handler(
@@ -193,7 +193,7 @@ describe.each([
     const app = new Router();
     app.get('/test', handlerFn);
     const handler = streamify(app);
-    const responseStream = new MockResponseStream();
+    const responseStream = new ResponseStream();
 
     // Act
     const result = await handler(
@@ -212,7 +212,7 @@ describe.each([
     const app = new Router();
     app.get('/test', () => new Response(null, { status: 204 }));
     const handler = streamify(app);
-    const responseStream = new MockResponseStream();
+    const responseStream = new ResponseStream();
 
     // Act
     const result = await handler(
@@ -231,7 +231,7 @@ describe.each([
     const app = new Router();
     app.get('/test', () => new Response(undefined, { status: 200 }));
     const handler = streamify(app);
-    const responseStream = new MockResponseStream();
+    const responseStream = new ResponseStream();
 
     // Act
     const result = await handler(
@@ -256,7 +256,7 @@ describe.each([
 
     app.get('/test', () => new Response(errorStream, { status: 200 }));
     const handler = streamify(app);
-    const responseStream = new MockResponseStream();
+    const responseStream = new ResponseStream();
 
     // Act & Assess
     await expect(
@@ -275,7 +275,7 @@ describe.each([
     });
 
     const handler = streamify(app);
-    const responseStream = new MockResponseStream();
+    const responseStream = new ResponseStream();
 
     // Act
     const result = await handler(
@@ -299,7 +299,7 @@ describe.each([
     });
 
     const handler = streamify(app);
-    const responseStream = new MockResponseStream();
+    const responseStream = new ResponseStream();
 
     // Act
     const result = await handler(
@@ -323,7 +323,7 @@ describe.each([
     const app = new Router();
     const handler = streamify(app);
     const invalidEvent = { invalid: 'event' };
-    const responseStream = new MockResponseStream();
+    const responseStream = new ResponseStream();
 
     // Act & Assess
     await expect(
@@ -344,7 +344,7 @@ describe.each([
     }));
 
     const handler = streamify(app);
-    const responseStream = new MockResponseStream();
+    const responseStream = new ResponseStream();
 
     // Act
     const result = await handler(

packages/event-handler/tests/unit/rest/helpers.ts

@@ -1,3 +1,4 @@
+import { Writable } from 'node:stream';
 import type {
   APIGatewayProxyEvent,
   APIGatewayProxyEventV2,
@@ -6,8 +7,11 @@ import type {
   Context,
 } from 'aws-lambda';
 import type { Router } from '../../../src/rest/Router.js';
-import { HttpResponseStream } from '../../../src/rest/utils.js';
-import type { HandlerResponse, Middleware } from '../../../src/types/rest.js';
+import type {
+  HandlerResponse,
+  ResponseStream as IResponseStream,
+  Middleware,
+} from '../../../src/types/rest.js';
 
 export const createTestEvent = (
   path: string,
@@ -129,24 +133,34 @@ export const createHeaderCheckMiddleware = (headers: {
   };
 };
 
-// Mock ResponseStream that extends the actual ResponseStream class
-export class MockResponseStream extends HttpResponseStream {
-  public chunks: Buffer[] = [];
+export class ResponseStream extends Writable implements IResponseStream {
+  // biome-ignore lint/correctness/noUnusedPrivateClassMembers: This is how the Lambda RIC implements it
+  #contentType: string | undefined;
+  readonly #chunks: Buffer[] = [];
   public _onBeforeFirstWrite?: (
     write: (data: Uint8Array | string) => void
   ) => void;
   #firstWrite = true;
 
+  setContentType(contentType: string) {
+    this.#contentType = contentType;
+  }
+
   _write(chunk: Buffer, _encoding: string, callback: () => void): void {
+    /* v8 ignore else -- @preserve */
     if (this.#firstWrite && this._onBeforeFirstWrite) {
       this._onBeforeFirstWrite((data: Uint8Array | string) => {
-        this.chunks.push(Buffer.from(data));
+        this.#chunks.push(Buffer.from(data));
       });
       this.#firstWrite = false;
     }
-    this.chunks.push(chunk);
+    this.#chunks.push(chunk);
     callback();
   }
+
+  public getBuffer(): Buffer {
+    return Buffer.concat(this.#chunks);
+  }
 }
 
 // Create a handler function from the Router instance