From 9e82747d62e57ee7498c8f3f54c313917891273a Mon Sep 17 00:00:00 2001
From: Bhasker Hariharan <bhaskerh@google.com>
Date: Fri, 6 Nov 2020 13:53:21 -0800
Subject: Return early in walkSACK if segment has no SACK blocks.

This avoids a needless allocation.

Updates #231

PiperOrigin-RevId: 341113160
---
 pkg/tcpip/transport/tcp/snd.go | 4 ++++
 1 file changed, 4 insertions(+)

(limited to 'pkg/tcpip')

diff --git a/pkg/tcpip/transport/tcp/snd.go b/pkg/tcpip/transport/tcp/snd.go
index 6fa8d63cd..ab5fa4fb7 100644
--- a/pkg/tcpip/transport/tcp/snd.go
+++ b/pkg/tcpip/transport/tcp/snd.go
@@ -1285,6 +1285,10 @@ func (s *sender) checkDuplicateAck(seg *segment) (rtx bool) {
 // See: https://tools.ietf.org/html/draft-ietf-tcpm-rack-08#section-7.2
 // steps 2 and 3.
 func (s *sender) walkSACK(rcvdSeg *segment) {
+	if len(rcvdSeg.parsedOptions.SACKBlocks) == 0 {
+		return
+	}
+
 	// Sort the SACK blocks. The first block is the most recent unacked
 	// block. The following blocks can be in arbitrary order.
 	sackBlocks := make([]header.SACKBlock, len(rcvdSeg.parsedOptions.SACKBlocks))
-- 
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