Allow telemetry exporters to GCP to utilize user's login credentials, if requested (#13778)

packages/core/src/utils/debugLogger.ts

@@ -4,6 +4,9 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import * as fs from 'node:fs';
+import * as util from 'node:util';
+
 /**
  * A simple, centralized logger for developer-facing debug messages.
  *
@@ -17,19 +20,47 @@
  * will intercept these calls and route them to the debug drawer UI.
  */
 class DebugLogger {
+  private logStream: fs.WriteStream | undefined;
+
+  constructor() {
+    this.logStream = process.env['GEMINI_DEBUG_LOG_FILE']
+      ? fs.createWriteStream(process.env['GEMINI_DEBUG_LOG_FILE'], {
+          flags: 'a',
+        })
+      : undefined;
+    // Handle potential errors with the stream
+    this.logStream?.on('error', (err) => {
+      // Log to console as a fallback, but don't crash the app
+      console.error('Error writing to debug log stream:', err);
+    });
+  }
+
+  private writeToFile(level: string, args: unknown[]) {
+    if (this.logStream) {
+      const message = util.format(...args);
+      const timestamp = new Date().toISOString();
+      const logEntry = `[${timestamp}] [${level}] ${message}\n`;
+      this.logStream.write(logEntry);
+    }
+  }
+
   log(...args: unknown[]): void {
+    this.writeToFile('LOG', args);
     console.log(...args);
   }
 
   warn(...args: unknown[]): void {
+    this.writeToFile('WARN', args);
     console.warn(...args);
   }
 
   error(...args: unknown[]): void {
+    this.writeToFile('ERROR', args);
     console.error(...args);
   }
 
   debug(...args: unknown[]): void {
+    this.writeToFile('DEBUG', args);
     console.debug(...args);
   }
 }