fix(synthetics): asset code validation failed on bundled assets (#26291)

A re-roll of #19342. Thanks @RichiCoder1 for doing most of this work!

This PR moves asset validation from _before_ staging the asset to _after_, and then validates on the staged asset instead. This allows for asset bundling because our prior validation was too eager.

In addition, this construct can help with synthetic canaries + bundled code: https://github.com/mrgrain/cdk-esbuild#amazon-cloudwatch-synthetics-canary-monitoring.

Fixes #11630

Co-authored-by: Richard Simpson richicoder1@outlook.com

----

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

packages/@aws-cdk/aws-synthetics-alpha/lib/code.ts

@@ -4,6 +4,7 @@ import * as s3 from 'aws-cdk-lib/aws-s3';
 import * as s3_assets from 'aws-cdk-lib/aws-s3-assets';
 import { Construct } from 'constructs';
 import { RuntimeFamily } from './runtime';
+import { Stage } from 'aws-cdk-lib/core';
 
 /**
  * The code the canary should execute
@@ -97,8 +98,6 @@ export class AssetCode extends Code {
   }
 
   public bind(scope: Construct, handler: string, family: RuntimeFamily): CodeConfig {
-    this.validateCanaryAsset(handler, family);
-
     // If the same AssetCode is used multiple times, retain only the first instantiation.
     if (!this.asset) {
       this.asset = new s3_assets.Asset(scope, 'Code', {
@@ -107,6 +106,8 @@ export class AssetCode extends Code {
       });
     }
 
+    this.validateCanaryAsset(scope, handler, family);
+
     return {
       s3Location: {
         bucketName: this.asset.s3BucketName,
@@ -124,21 +125,27 @@ export class AssetCode extends Code {
    * Requires canary file to be directly inside node_modules folder.
    * Requires canary file name matches the handler name.
    * @see https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/CloudWatch_Synthetics_Canaries_WritingCanary.html
-   *
-   * @param handler the canary handler
    */
-  private validateCanaryAsset(handler: string, family: RuntimeFamily) {
-    if (path.extname(this.assetPath) !== '.zip') {
-      if (!fs.lstatSync(this.assetPath).isDirectory()) {
+  private validateCanaryAsset(scope: Construct, handler: string, family: RuntimeFamily) {
+    if (!this.asset) {
+      throw new Error("'validateCanaryAsset' must be called after 'this.asset' is instantiated");
+    }
+
+    // Get the staged (or copied) asset path.
+    const assetOutDir = Stage.of(scope)?.assetOutdir;
+    const assetPath = assetOutDir ? path.join(assetOutDir, this.asset.assetPath): this.assetPath;
+
+    if (path.extname(assetPath) !== '.zip') {
+      if (!fs.lstatSync(assetPath).isDirectory()) {
         throw new Error(`Asset must be a .zip file or a directory (${this.assetPath})`);
       }
       const filename = handler.split('.')[0];
       const nodeFilename = `${filename}.js`;
       const pythonFilename = `${filename}.py`;
-      if (family === RuntimeFamily.NODEJS && !fs.existsSync(path.join(this.assetPath, 'nodejs', 'node_modules', nodeFilename))) {
+      if (family === RuntimeFamily.NODEJS && !fs.existsSync(path.join(assetPath, 'nodejs', 'node_modules', nodeFilename))) {
         throw new Error(`The canary resource requires that the handler is present at "nodejs/node_modules/${nodeFilename}" but not found at ${this.assetPath} (https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/CloudWatch_Synthetics_Canaries_WritingCanary_Nodejs.html)`);
       }
-      if (family === RuntimeFamily.PYTHON && !fs.existsSync(path.join(this.assetPath, 'python', pythonFilename))) {
+      if (family === RuntimeFamily.PYTHON && !fs.existsSync(path.join(assetPath, 'python', pythonFilename))) {
         throw new Error(`The canary resource requires that the handler is present at "python/${pythonFilename}" but not found at ${this.assetPath} (https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/CloudWatch_Synthetics_Canaries_WritingCanary_Python.html)`);
       }
     }

packages/@aws-cdk/aws-synthetics-alpha/test/code.test.ts

@@ -1,7 +1,8 @@
+import * as fs from 'fs';
 import * as path from 'path';
 import { Template } from 'aws-cdk-lib/assertions';
 import * as s3 from 'aws-cdk-lib/aws-s3';
-import { App, Stack } from 'aws-cdk-lib';
+import { App, Stack, DockerImage } from 'aws-cdk-lib';
 import * as cxapi from 'aws-cdk-lib/cx-api';
 import * as synthetics from '../lib';
 import { RuntimeFamily } from '../lib';
@@ -167,6 +168,55 @@ describe(synthetics.Code.fromAsset, () => {
     expect(() => synthetics.Code.fromAsset(assetPath).bind(stack, 'incorrect.handler', synthetics.RuntimeFamily.NODEJS))
       .toThrowError(`The canary resource requires that the handler is present at "nodejs/node_modules/incorrect.js" but not found at ${assetPath} (https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/CloudWatch_Synthetics_Canaries_WritingCanary_Nodejs.html)`);
   });
+
+  test('passes if bundling is specified', () => {
+    // GIVEN
+    const stack = new Stack(new App(), 'canaries');
+
+    // WHEN
+    const assetPath = path.join(__dirname, 'canaries', 'nodejs', 'node_modules');
+    const code = synthetics.Code.fromAsset(assetPath, {
+      bundling: {
+        image: DockerImage.fromRegistry('dummy'),
+        local: {
+          tryBundle(outputDir) {
+            const stageDir = path.join(outputDir, 'nodejs', 'node_modules');
+            fs.mkdirSync(path.join(outputDir, 'nodejs'));
+            fs.mkdirSync(stageDir);
+            fs.copyFileSync(path.join(assetPath, 'canary.js'), path.join(stageDir, 'canary.js'));
+            return true;
+          },
+        },
+      },
+    });
+
+    // THEN
+    expect(() => code.bind(stack, 'canary.handler', synthetics.RuntimeFamily.NODEJS))
+      .not.toThrow();
+  });
+
+  test('fails if bundling is specified but folder structure is wrong', () => {
+    // GIVEN
+    const stack = new Stack(new App(), 'canaries');
+
+    // WHEN
+    const assetPath = path.join(__dirname, 'canaries', 'nodejs', 'node_modules');
+    const code = synthetics.Code.fromAsset(assetPath, {
+      bundling: {
+        image: DockerImage.fromRegistry('dummy'),
+        local: {
+          tryBundle(outputDir) {
+            fs.copyFileSync(path.join(assetPath, 'canary.js'), path.join(outputDir, 'canary.js'));
+            return true;
+          },
+        },
+      },
+    });
+
+    // THEN
+    expect(() => code.bind(stack, 'canary.handler', synthetics.RuntimeFamily.NODEJS))
+      .toThrowError(`The canary resource requires that the handler is present at "nodejs/node_modules/canary.js" but not found at ${assetPath} (https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/CloudWatch_Synthetics_Canaries_WritingCanary_Nodejs.html)`);
+  });
 });
 
 describe(synthetics.Code.fromBucket, () => {