From 43d2c47d8ac1faf652f7f8dbc012c39339b2db13 Mon Sep 17 00:00:00 2001
From: xtaci <daniel820313@gmail.com>
Date: Wed, 1 Jul 2020 18:04:55 +0800
Subject: [PATCH] flush when input has make a window slide

---
 kcp.go | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/kcp.go b/kcp.go
index 57eabc5..e11e424 100644
--- a/kcp.go
+++ b/kcp.go
@@ -441,7 +441,7 @@ func (kcp *KCP) parse_fastack(sn, ts uint32) {
 	}
 }
 
-func (kcp *KCP) parse_una(una uint32) {
+func (kcp *KCP) parse_una(una uint32) int {
 	count := 0
 	for k := range kcp.snd_buf {
 		seg := &kcp.snd_buf[k]
@@ -455,6 +455,7 @@ func (kcp *KCP) parse_una(una uint32) {
 	if count > 0 {
 		kcp.snd_buf = kcp.remove_front(kcp.snd_buf, count)
 	}
+	return count
 }
 
 // ack append
@@ -534,6 +535,7 @@ func (kcp *KCP) Input(data []byte, regular, ackNoDelay bool) int {
 	var latest uint32 // the latest ack packet
 	var flag int
 	var inSegs uint64
+	var windowSlides bool
 
 	for {
 		var ts, sn, length, una, conv uint32
@@ -569,7 +571,9 @@ func (kcp *KCP) Input(data []byte, regular, ackNoDelay bool) int {
 		if regular {
 			kcp.rmt_wnd = uint32(wnd)
 		}
-		kcp.parse_una(una)
+		if kcp.parse_una(una) > 0 {
+			windowSlides = true
+		}
 		kcp.shrink_buf()
 
 		if cmd == IKCP_CMD_ACK {
@@ -650,6 +654,10 @@ func (kcp *KCP) Input(data []byte, regular, ackNoDelay bool) int {
 		}
 	}
 
+	if windowSlides { // if window has slided, flush
+		kcp.flush(false)
+	}
+
 	if ackNoDelay && len(kcp.acklist) > 0 { // ack immediately
 		kcp.flush(true)
 	}