From 7c1e1156fd3b9de599fe0fba4437bd0970f2127a Mon Sep 17 00:00:00 2001
From: haramjeong <04harams77@gmail.com>
Date: Mon, 7 Sep 2026 10:07:44 +0900
Subject: [PATCH] doc: clarify sub-1000ms behavior in socket.setKeepAlive

The current documentation states that `initialDelay` and `interval`
are divided by 1000 and rounded down, but does not explicitly mention
that values less than 1000ms will result in 0 seconds. This can lead
to confusion when users pass values like 400ms expecting sub-second
keepalive delays.

Add a concrete example showing that 400ms rounds down to 0 seconds.

Refs: https://github.com/nodejs/node/issues/57712

Signed-off-by: haramjeong <04harams77@gmail.com>
---
 doc/api/net.md | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/doc/api/net.md b/doc/api/net.md
index d0b0e34c6504..91fd837cd49b 100644
--- a/doc/api/net.md
+++ b/doc/api/net.md
@@ -1669,7 +1669,9 @@ corresponding system default unchanged.
 
 `initialDelay` and `interval` are specified in milliseconds but the
 underlying socket options are configured in whole seconds; the values are
-divided by `1000` and rounded down before being applied.
+divided by `1000` and rounded down before being applied. For example,
+setting `initialDelay` to `400` will result in a `TCP_KEEPIDLE` of `0`
+seconds (since `400 / 1000` rounds down to `0`).
 
 Enabling the keep-alive functionality will set the following socket options: