fix(custom-resources): buffers returned by AwsCustomResource are unus…

…able (#9977)

Convert buffers to strings when flattening the API response.

Closes #9969, closes #10017


----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/custom-resources/lib/aws-custom-resource/runtime/index.ts

@@ -13,11 +13,12 @@ export function flatten(object: object): { [key: string]: string } {
     {},
     ...function _flatten(child: any, path: string[] = []): any {
       return [].concat(...Object.keys(child)
-        .map(key =>
-          typeof child[key] === 'object' && child[key] !== null
-            ? _flatten(child[key], path.concat([key]))
-            : ({ [path.concat([key]).join('.')]: child[key] }),
-        ));
+        .map(key => {
+          const childKey = Buffer.isBuffer(child[key]) ? child[key].toString('utf8') : child[key];
+          return typeof childKey === 'object' && childKey !== null
+            ? _flatten(childKey, path.concat([key]))
+            : ({ [path.concat([key]).join('.')]: childKey });
+        }));
     }(object),
   );
 }

packages/@aws-cdk/custom-resources/test/aws-custom-resource/aws-custom-resource-provider.test.ts

@@ -411,6 +411,24 @@ test('flatten correctly flattens a nested object', () => {
   });
 });
 
+test('flatten correctly flattens an object with buffers', () => {
+  expect(flatten({
+    body: Buffer.from('body'),
+    nested: {
+      buffer: Buffer.from('buffer'),
+      array: [
+        Buffer.from('array.0'),
+        Buffer.from('array.1'),
+      ],
+    },
+  })).toEqual({
+    'body': 'body',
+    'nested.buffer': 'buffer',
+    'nested.array.0': 'array.0',
+    'nested.array.1': 'array.1',
+  });
+});
+
 test('installs the latest SDK', async () => {
   const tmpPath = '/tmp/node_modules/aws-sdk';
 
@@ -455,4 +473,7 @@ test('installs the latest SDK', async () => {
   expect(request.isDone()).toBeTruthy();
 
   expect(() => require.resolve(tmpPath)).not.toThrow();
+
+  // clean up aws-sdk install
+  await fs.remove(tmpPath);
 });