fix(core): drain buffers in flush() when there is no transport

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+### Other Changes
+
+- fix(core): Emit `flush` event in `Client.flush()` when client has no transport
+
 ## 10.48.0
 
 ### Important Changes

packages/core/src/client.ts

@@ -424,12 +424,16 @@ export abstract class Client<O extends ClientOptions = ClientOptions> {
   // @ts-expect-error - PromiseLike is a subset of Promise
   public async flush(timeout?: number): PromiseLike<boolean> {
     const transport = this._transport;
+
+    // Emit `flush` unconditionally so weight-based log/metric flushers drain
+    // their buffers and clear their idle timers, even when no transport is
+    // configured (e.g. no DSN).
+    this.emit('flush');
+
     if (!transport) {
       return true;
     }
 
-    this.emit('flush');
-
     const clientFinished = await this._isClientDoneProcessing(timeout);
     const transportFlushed = await transport.flush(timeout);
 

packages/core/test/lib/client.test.ts

@@ -3115,6 +3115,29 @@ describe('Client', () => {
 
       safeUnrefSpy.mockRestore();
     });
+
+    it('flush() drains the log buffer when client has no transport', async () => {
+      // Client without DSN — _transport is undefined
+      const options = getDefaultTestClientOptions({
+        enableLogs: true,
+      });
+      const client = new TestClient(options);
+      const scope = new Scope();
+      scope.setClient(client);
+
+      const flushLogsHandler = vi.fn();
+      client.on('flushLogs', flushLogsHandler);
+
+      // Capture a log which starts the weight-based flush timer
+      _INTERNAL_captureLog({ message: 'test log', level: 'info' }, scope);
+
+      expect(flushLogsHandler).not.toHaveBeenCalled();
+
+      // flush() should drain the buffer (and clear the timer) even without a transport
+      await client.flush();
+
+      expect(flushLogsHandler).toHaveBeenCalledTimes(1);
+    });
   });
 
   describe('metric weight-based flushing', () => {
@@ -3201,6 +3224,27 @@ describe('Client', () => {
 
       safeUnrefSpy.mockRestore();
     });
+
+    it('flush() drains the metric buffer when client has no transport', async () => {
+      // Client without DSN — _transport is undefined
+      const options = getDefaultTestClientOptions({});
+      const client = new TestClient(options);
+      const scope = new Scope();
+      scope.setClient(client);
+
+      const flushMetricsHandler = vi.fn();
+      client.on('flushMetrics', flushMetricsHandler);
+
+      // Capture a metric which starts the weight-based flush timer
+      _INTERNAL_captureMetric({ name: 'test_metric', value: 42, type: 'counter', attributes: {} }, { scope });
+
+      expect(flushMetricsHandler).not.toHaveBeenCalled();
+
+      // flush() should drain the buffer (and clear the timer) even without a transport
+      await client.flush();
+
+      expect(flushMetricsHandler).toHaveBeenCalledTimes(1);
+    });
   });
 
   describe('promise buffer usage', () => {