fix: wrong response when repeated requests for external source

.editorconfig

@@ -0,0 +1,13 @@
+# EditorConfig is awesome: https://EditorConfig.org
+
+# top-most EditorConfig file
+root = true
+
+# Unix-style newlines with a newline ending every file
+[*]
+indent_style = space
+indent_size = 2
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true

.gitignore

@@ -6,3 +6,6 @@ node_modules
 **/.terraform/*
 *.tfstate
 *.tfstate.*
+
+# IntelliJ IDEA
+/.idea/

lib/handler.ts

@@ -12,6 +12,7 @@ import S3 from 'aws-sdk/clients/s3';
 
 import { imageOptimizer, S3Config } from './image-optimizer';
 import { normalizeHeaders } from './normalized-headers';
+import { createDeferred } from './utils';
 
 function generateS3Config(bucketName?: string): S3Config | undefined {
   let s3: S3;
@@ -81,6 +82,8 @@ export async function handler(
 
   const resBuffers: Buffer[] = [];
   const resMock: any = new Writable();
+  const defer = createDeferred();
+  let didCallEnd = false;
 
   resMock.write = (chunk: Buffer | string) => {
     resBuffers.push(Buffer.isBuffer(chunk) ? chunk : Buffer.from(chunk));
@@ -98,6 +101,13 @@ export async function handler(
     (mockHeaders[name.toLowerCase()] = value);
   resMock._implicitHeader = () => {};
 
+  resMock.originalEnd = resMock.end;
+  resMock.on('close', () => defer.resolve());
+  resMock.end = (message: any) => {
+    didCallEnd = true;
+    resMock.originalEnd(message);
+  };
+
   const parsedUrl = parseUrl(reqMock.url, true);
   const result = await imageOptimizer(
     imageConfig,
@@ -123,6 +133,9 @@ export async function handler(
     normalizedHeaders['cache-control'] = 'public, max-age=60';
   }
 
+  if (didCallEnd) defer.resolve();
+  await defer.promise;
+
   return {
     statusCode: resMock.statusCode || 200,
     body: Buffer.concat(resBuffers).toString('base64'),

lib/utils.ts

@@ -0,0 +1,19 @@
+export interface Deferred<T = never> {
+  promise: Promise<T>;
+  resolve: (value?: T | PromiseLike<T>) => void;
+  reject: (reason?: any) => void;
+}
+
+export function createDeferred<T>() {
+  let r;
+  let j;
+
+  const promise = new Promise<T>(
+    (resolve: (value: any) => void, reject: (reason?: any) => void): void => {
+      r = resolve;
+      j = reject;
+    }
+  );
+
+  return ({ promise, resolve: r, reject: j } as unknown) as Deferred<T>;
+}

test/image-optimizer.test.ts

@@ -11,7 +11,7 @@ import S3 from 'aws-sdk/clients/s3';
 import * as path from 'path';
 
 import { imageOptimizer, S3Config } from '../lib/image-optimizer';
-import { createDeferred } from './utils';
+import { createDeferred } from '../lib/utils';
 import { s3PublicDir } from './utils/s3-public-dir';
 import { acceptAllFixtures, acceptWebpFixtures } from './constants';