From 88a4da2ea21511d4d396aac5ce9117fd92a296b4 Mon Sep 17 00:00:00 2001
From: mbfreder <mbfreder@amazon.com>
Date: Tue, 14 May 2024 11:58:04 -0700
Subject: [PATCH] Add domainName prop to FunctionUrl

---
 packages/aws-cdk-lib/aws-lambda/README.md     |  9 +++++++
 .../aws-lambda/lib/function-url.ts            | 16 +++++++++++-
 .../aws-lambda/test/function-url.test.ts      | 26 +++++++++++++++++++
 3 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/packages/aws-cdk-lib/aws-lambda/README.md b/packages/aws-cdk-lib/aws-lambda/README.md
index 5a876c8ae68eb..6c7010617f569 100644
--- a/packages/aws-cdk-lib/aws-lambda/README.md
+++ b/packages/aws-cdk-lib/aws-lambda/README.md
@@ -480,6 +480,15 @@ new CfnOutput(this, 'TheUrl', {
   value: fnUrl.url,
 });
 ```
+To get the domain name from the function url, simply call `domainName` on the `FunctionUrl` construct:
+```ts
+... 
+
+new CfnOutput(this, 'TheDomainName', {
+  value: fnUrl.domainName,
+});
+```
+The .domainName attribute will return the domain name (the function url, without the scheme and the trailing slash). For example, if fnUrl.url returns `https://*******.lambda-url.ap-southeast-2.on.aws/`, then fnUrl.domainName will return `*******.lambda-url.ap-southeast-2.on.aws`.
 
 Calls to this URL need to be signed with SigV4.
 
diff --git a/packages/aws-cdk-lib/aws-lambda/lib/function-url.ts b/packages/aws-cdk-lib/aws-lambda/lib/function-url.ts
index bed33ec8bae4f..879738646dbb1 100644
--- a/packages/aws-cdk-lib/aws-lambda/lib/function-url.ts
+++ b/packages/aws-cdk-lib/aws-lambda/lib/function-url.ts
@@ -4,7 +4,7 @@ import { IFunction } from './function-base';
 import { IVersion } from './lambda-version';
 import { CfnUrl } from './lambda.generated';
 import * as iam from '../../aws-iam';
-import { Duration, IResource, Resource } from '../../core';
+import { Duration, Fn, IResource, Resource } from '../../core';
 
 /**
  * The auth types for a function url
@@ -133,9 +133,17 @@ export interface IFunctionUrl extends IResource {
    * The url of the Lambda function.
    *
    * @attribute FunctionUrl
+   * For example `https://*******.lambda-url.ap-southeast-2.on.aws/`
    */
   readonly url: string;
 
+  /**
+   * The domain name of the Lambda Function URL
+   *
+   * For example `*******.lambda-url.ap-southeast-2.on.aws`
+   */
+  readonly domainName: string;
+
   /**
    * The ARN of the function this URL refers to
    *
@@ -243,6 +251,12 @@ export class FunctionUrl extends Resource implements IFunctionUrl {
     }
   }
 
+  get domainName(): string {
+    return Fn.select(
+      0, Fn.split('/', Fn.select(1, Fn.split('https://', this.url))),
+    );
+  }
+
   public grantInvokeUrl(grantee: iam.IGrantable): iam.Grant {
     return this.function.grantInvokeUrl(grantee);
   }
diff --git a/packages/aws-cdk-lib/aws-lambda/test/function-url.test.ts b/packages/aws-cdk-lib/aws-lambda/test/function-url.test.ts
index 048fcea4fa1fa..2d936db84393c 100644
--- a/packages/aws-cdk-lib/aws-lambda/test/function-url.test.ts
+++ b/packages/aws-cdk-lib/aws-lambda/test/function-url.test.ts
@@ -118,6 +118,32 @@ describe('FunctionUrl', () => {
     });
   });
 
+  test('function url domain name', () => {
+    // GIVEN
+    const stack = new cdk.Stack();
+    const fn = new lambda.Function(stack, 'MyLambda', {
+      code: new lambda.InlineCode('hello()'),
+      handler: 'index.hello',
+      runtime: lambda.Runtime.NODEJS_14_X,
+    });
+    const aliasName = 'prod';
+    const alias = new lambda.Alias(stack, 'Alias', {
+      aliasName,
+      version: fn.currentVersion,
+    });
+
+    // WHEN
+    const url = new lambda.FunctionUrl(stack, 'FunctionUrl', {
+      function: alias,
+    });
+
+    // THEN
+    const resolved = stack.resolve(stack.toJsonString({ token: url.domainName }));
+    expect(resolved).toEqual({
+      'Fn::Join': ['', ['{"token":"', { 'Fn::Select': [0, { 'Fn::Split': ['/', { 'Fn::Select': [1, { 'Fn::Split': ['https://', { 'Fn::GetAtt': ['FunctionUrl84B92DCA', 'FunctionUrl'] }] }] }] }] }, '"}']],
+    });
+  });
+
   test('throws when configured with Version', () => {
     // GIVEN
     const stack = new cdk.Stack();