chore(cli): file sink telemetry client writes valid json (#710)

Pulled out of #631. Now writes valid json to the telemetry file

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

Author: kaizencc

packages/aws-cdk/lib/cli/telemetry/file-sink.ts

@@ -1,6 +1,5 @@
-import * as fs from 'fs';
-import * as path from 'path';
 import { ToolkitError, type IIoHost } from '@aws-cdk/toolkit-lib';
+import * as fs from 'fs-extra';
 import type { TelemetrySchema } from './schema';
 import type { ITelemetrySink } from './sink-interface';
 import { IoHelper } from '../../api-private';
@@ -38,23 +37,19 @@ export class FileTelemetrySink implements ITelemetrySink {
       throw new ToolkitError(`Telemetry file already exists at ${this.logFilePath}`);
     }
 
-    // Create the file if necessary
-    const directory = path.dirname(this.logFilePath);
-    if (!fs.existsSync(directory)) {
-      fs.mkdirSync(directory, { recursive: true });
-    }
+    // Create the file
+    fs.ensureFileSync(this.logFilePath);
+    fs.writeJsonSync(this.logFilePath, []);
   }
 
   /**
    * Emit an event.
    */
   public async emit(event: TelemetrySchema): Promise<void> {
     try {
-      // Format the events as a JSON string with pretty printing
-      const output = JSON.stringify(event, null, 2) + '\n';
-
-      // Write to file
-      fs.appendFileSync(this.logFilePath, output);
+      const json = fs.readJsonSync(this.logFilePath);
+      json.push(event);
+      fs.writeJSONSync(this.logFilePath, json, { spaces: 2 });
     } catch (e: any) {
       // Never throw errors, just log them via ioHost
       await this.ioHelper.defaults.trace(`Failed to add telemetry event: ${e.message}`);

packages/aws-cdk/test/cli/telemetry/file-sink.test.ts

@@ -1,6 +1,6 @@
-import * as fs from 'fs';
 import * as os from 'os';
 import * as path from 'path';
+import * as fs from 'fs-extra';
 import { IoHelper } from '../../../lib/api-private';
 import { CliIoHost } from '../../../lib/cli/io-host';
 import { FileTelemetrySink } from '../../../lib/cli/telemetry/file-sink';
@@ -69,10 +69,8 @@ describe('FileTelemetrySink', () => {
     await client.emit(testEvent);
 
     // THEN
-    expect(fs.existsSync(logFilePath)).toBe(true);
-    const fileContent = fs.readFileSync(logFilePath, 'utf8');
-    const parsedContent = JSON.parse(fileContent);
-    expect(parsedContent).toEqual(testEvent);
+    const fileJson = fs.readJSONSync(logFilePath, 'utf8');
+    expect(fileJson).toEqual([testEvent]);
   });
 
   test('appends data to a file', async () => {
@@ -116,11 +114,9 @@ describe('FileTelemetrySink', () => {
 
     // THEN
     expect(fs.existsSync(logFilePath)).toBe(true);
-    const fileContent = fs.readFileSync(logFilePath, 'utf8');
-
-    // The file should contain two JSON objects, each pretty-printed with a newline
-    const expectedSingleEvent = JSON.stringify(testEvent, null, 2) + '\n';
-    expect(fileContent).toBe(expectedSingleEvent + expectedSingleEvent);
+    const fileJson = fs.readJSONSync(logFilePath, 'utf8');
+    const expectedJson = [testEvent, testEvent];
+    expect(fileJson).toEqual(expectedJson);
   });
 
   test('constructor throws if file already exists', async () => {
@@ -178,8 +174,8 @@ describe('FileTelemetrySink', () => {
 
     const client = new FileTelemetrySink({ logFilePath, ioHost });
 
-    // Mock fs.appendFileSync to throw an error
-    jest.spyOn(fs, 'appendFileSync').mockImplementation(() => {
+    // Mock fs.writeJSONSync to throw an error
+    jest.spyOn(fs, 'writeJSONSync').mockImplementation(() => {
       throw new Error('File write error');
     });