From 4064566ecaf999e6d097f16f47c16453fbc67d8e Mon Sep 17 00:00:00 2001
From: Jordan Whited <jordan@tailscale.com>
Date: Thu, 10 Jul 2025 21:36:38 -0700
Subject: [PATCH] device: fix keepalive detection in TX path

Updates tailscale/corp#30364

Signed-off-by: Jordan Whited <jordan@tailscale.com>
---
 device/send.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/device/send.go b/device/send.go
index bf854b7..c8bb079 100644
--- a/device/send.go
+++ b/device/send.go
@@ -517,7 +517,7 @@ func (peer *Peer) RoutineSequentialSender(maxBatchSize int) {
 		dataSent := false
 		elemsContainer.Lock()
 		for _, elem := range elemsContainer.elems {
-			if len(elem.packet) != MessageKeepaliveSize {
+			if len(elem.packet[MessageEncapsulatingTransportSize:]) != MessageKeepaliveSize {
 				dataSent = true
 			}
 			bufs = append(bufs, elem.packet)