From 7e243eddbeb998f5665969ea2f0badd01772565f Mon Sep 17 00:00:00 2001
From: sbs44 <83440025+sbs44@users.noreply.github.com>
Date: Fri, 10 Apr 2026 08:39:44 -0400
Subject: [PATCH] fix(core): Emit `flush` event in `Client.flush()` when client
 has no transport

`Client.flush()` short-circuited before emitting the `flush` event when
the client had no transport (e.g. no DSN was configured), leaving the
weight-based flushers for logs and metrics with idle `setTimeout`
handles that never resolved. Emit `flush` unconditionally so the
weight-based flusher listeners drain their buffers and clear the timers
on every `flush()` call.
---
 CHANGELOG.md                          |  4 +++
 packages/core/src/client.ts           |  8 +++--
 packages/core/test/lib/client.test.ts | 44 +++++++++++++++++++++++++++
 3 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8141da2e6276..004ff1bc1134 100644
--- a/CHANGELOG.md
+++ b/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
diff --git a/packages/core/src/client.ts b/packages/core/src/client.ts
index 6c3ca949f38e..9d7091794826 100644
--- a/packages/core/src/client.ts
+++ b/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);
 
diff --git a/packages/core/test/lib/client.test.ts b/packages/core/test/lib/client.test.ts
index 1548a4aecce4..a8971498cef8 100644
--- a/packages/core/test/lib/client.test.ts
+++ b/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', () => {