From bf2dc9e5d16600e19194ebc78a30b8f4dd4cadb1 Mon Sep 17 00:00:00 2001
From: "Kamat, Trivikram" <16024985+trivikr@users.noreply.github.com>
Date: Sat, 15 Aug 2026 14:14:25 -0700
Subject: [PATCH] diagnostics_channel: validate before channel activation

Validate the first subscription before calling markActive().
This prevents invalid callbacks from leaving channels active and
notifying native consumers without an installed subscriber.

Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com>
Assisted-by: codex:gpt-5.6-sol
---
 lib/diagnostics_channel.js                                      | 1 +
 .../parallel/test-diagnostics-channel-object-channel-pub-sub.js | 2 ++
 test/parallel/test-diagnostics-channel-pub-sub.js               | 2 ++
 3 files changed, 5 insertions(+)

diff --git a/lib/diagnostics_channel.js b/lib/diagnostics_channel.js
index 998f17aa61d6..7c1f4fa845ed 100644
--- a/lib/diagnostics_channel.js
+++ b/lib/diagnostics_channel.js
@@ -229,6 +229,7 @@ class Channel {
   }
 
   subscribe(subscription) {
+    validateFunction(subscription, 'subscription');
     markActive(this);
     this.subscribe(subscription);
   }
diff --git a/test/parallel/test-diagnostics-channel-object-channel-pub-sub.js b/test/parallel/test-diagnostics-channel-object-channel-pub-sub.js
index 9498419b806c..f02544936559 100644
--- a/test/parallel/test-diagnostics-channel-object-channel-pub-sub.js
+++ b/test/parallel/test-diagnostics-channel-object-channel-pub-sub.js
@@ -44,3 +44,5 @@ assert.ok(!channel.unsubscribe(subscriber));
 assert.throws(() => {
   channel.subscribe(null);
 }, { code: 'ERR_INVALID_ARG_TYPE' });
+assert.ok(!channel.hasSubscribers);
+assert.ok(!dc.hasSubscribers('test'));
diff --git a/test/parallel/test-diagnostics-channel-pub-sub.js b/test/parallel/test-diagnostics-channel-pub-sub.js
index a7232ab58ce8..e3a868b7ce0c 100644
--- a/test/parallel/test-diagnostics-channel-pub-sub.js
+++ b/test/parallel/test-diagnostics-channel-pub-sub.js
@@ -42,6 +42,8 @@ assert.ok(!dc.unsubscribe(name, subscriber));
 assert.throws(() => {
   dc.subscribe(name, null);
 }, { code: 'ERR_INVALID_ARG_TYPE' });
+assert.ok(!channel.hasSubscribers);
+assert.ok(!dc.hasSubscribers(name));
 
 // Reaching zero subscribers should not delete from the channels map as there
 // will be no more weakref to incRef if another subscribe happens while the