feat(apigatewayv2): Import existing WebSocketApi from attributes (#18958)

Closes: #18755

----

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

Author: vincent-turato

packages/@aws-cdk/aws-apigatewayv2/README.md

@@ -404,6 +404,12 @@ webSocketApi.addRoute('sendmessage', {
 });
 ```
 
+To import an existing WebSocketApi:
+
+```ts
+const webSocketApi = apigwv2.WebSocketApi.fromWebSocketApiAttributes(this, 'mywsapi', { webSocketId: 'api-1234' });
+```
+
 ### Manage Connections Permission
 
 Grant permission to use API Gateway Management API of a WebSocket API by calling the `grantManageConnections` API.

packages/@aws-cdk/aws-apigatewayv2/lib/websocket/api.ts

@@ -85,11 +85,47 @@ export interface WebSocketApiProps {
   readonly defaultRouteOptions?: WebSocketRouteOptions;
 }
 
+/**
+ * Attributes for importing a WebSocketApi into the CDK
+ */
+export interface WebSocketApiAttributes {
+  /**
+   * The identifier of the WebSocketApi
+   */
+  readonly webSocketId: string;
+
+  /**
+   * The endpoint URL of the WebSocketApi
+   * @default - throw san error if apiEndpoint is accessed.
+   */
+  readonly apiEndpoint?: string;
+}
+
+
 /**
  * Create a new API Gateway WebSocket API endpoint.
  * @resource AWS::ApiGatewayV2::Api
  */
 export class WebSocketApi extends ApiBase implements IWebSocketApi {
+  /**
+   * Import an existing WebSocket API into this CDK app.
+   */
+  public static fromWebSocketApiAttributes(scope: Construct, id: string, attrs: WebSocketApiAttributes): IWebSocketApi {
+    class Import extends ApiBase {
+      public readonly apiId = attrs.webSocketId;
+      public readonly websocketApiId = attrs.webSocketId;
+      private readonly _apiEndpoint = attrs.apiEndpoint;
+
+      public get apiEndpoint(): string {
+        if (!this._apiEndpoint) {
+          throw new Error('apiEndpoint is not configured on the imported WebSocketApi.');
+        }
+        return this._apiEndpoint;
+      }
+    }
+    return new Import(scope, id);
+  }
+
   public readonly apiId: string;
   public readonly apiEndpoint: string;
 

packages/@aws-cdk/aws-apigatewayv2/test/websocket/api.test.ts

@@ -107,6 +107,25 @@ describe('WebSocketApi', () => {
     });
   });
 
+  test('import', () => {
+    // GIVEN
+    const stack = new Stack();
+    const imported = WebSocketApi.fromWebSocketApiAttributes(stack, 'imported', { webSocketId: 'ws-1234', apiEndpoint: 'api-endpoint' });
+
+    // THEN
+    expect(imported.apiId).toEqual('ws-1234');
+    expect(imported.apiEndpoint).toEqual('api-endpoint');
+  });
+
+  test('apiEndpoint for imported', () => {
+    // GIVEN
+    const stack = new Stack();
+    const api = WebSocketApi.fromWebSocketApiAttributes(stack, 'imported', { webSocketId: 'api-1234' });
+
+    // THEN
+    expect(() => api.apiEndpoint).toThrow(/apiEndpoint is not configured/);
+  });
+
   describe('grantManageConnections', () => {
     test('adds an IAM policy to the principal', () => {
       // GIVEN