always send new segments before retransmission checks

kcp.go

@@ -687,51 +687,61 @@ func (kcp *KCP) flush() {
 	}
 
 	// sliding window, controlled by snd_nxt && sna_una+cwnd
-	count := 0
+	newSegsCount := 0
 	for k := range kcp.snd_queue {
 		if _itimediff(kcp.snd_nxt, kcp.snd_una+cwnd) >= 0 {
 			break
 		}
 		newseg := kcp.snd_queue[k]
 		newseg.conv = kcp.conv
 		newseg.cmd = IKCP_CMD_PUSH
-		newseg.wnd = seg.wnd
-		newseg.ts = current
 		newseg.sn = kcp.snd_nxt
-		newseg.una = kcp.rcv_nxt
-		newseg.resendts = newseg.ts
-		newseg.rto = kcp.rx_rto
 		kcp.snd_buf = append(kcp.snd_buf, newseg)
 		kcp.snd_nxt++
-		count++
+		newSegsCount++
 		kcp.snd_queue[k].data = nil
 	}
-	kcp.snd_queue = kcp.snd_queue[count:]
-
-	// flag pending data
-	hasPending := false
-	if count > 0 {
-		hasPending = true
-	}
+	kcp.snd_queue = kcp.snd_queue[newSegsCount:]
 
 	// calculate resent
 	resent := uint32(kcp.fastresend)
 	if kcp.fastresend <= 0 {
 		resent = 0xffffffff
 	}
 
-	// flush data segments
+	// counters
 	var lostSegs, fastRetransSegs, earlyRetransSegs uint64
-	for k := range kcp.snd_buf {
+
+	// send new segments
+	for k := len(kcp.snd_buf) - newSegsCount; k < len(kcp.snd_buf); k++ {
+		current := currentMs()
+		segment := &kcp.snd_buf[k]
+		segment.xmit++
+		segment.rto = kcp.rx_rto
+		segment.resendts = current + segment.rto
+		segment.ts = current
+		segment.wnd = seg.wnd
+		segment.una = kcp.rcv_nxt
+
+		size := len(buffer) - len(ptr)
+		need := IKCP_OVERHEAD + len(segment.data)
+
+		if size+need > int(kcp.mtu) {
+			kcp.output(buffer, size)
+			ptr = buffer
+		}
+
+		ptr = segment.encode(ptr)
+		copy(ptr, segment.data)
+		ptr = ptr[len(segment.data):]
+	}
+
+	// check for retransmissions
+	for k := 0; k < len(kcp.snd_buf)-newSegsCount; k++ {
 		current := currentMs()
 		segment := &kcp.snd_buf[k]
 		needsend := false
-		if segment.xmit == 0 {
-			needsend = true
-			segment.xmit++
-			segment.rto = kcp.rx_rto
-			segment.resendts = current + segment.rto
-		} else if _itimediff(current, segment.resendts) >= 0 {
+		if _itimediff(current, segment.resendts) >= 0 { // RTO
 			needsend = true
 			segment.xmit++
 			kcp.xmit++
@@ -753,7 +763,7 @@ func (kcp *KCP) flush() {
 				change++
 				fastRetransSegs++
 			}
-		} else if segment.fastack > 0 && !hasPending { // early retransmit
+		} else if segment.fastack > 0 && newSegsCount == 0 { // early retransmit
 			lastsend := segment.resendts - segment.rto
 			if _itimediff(current, lastsend) >= kcp.rx_srtt>>2 {
 				needsend = true
@@ -788,17 +798,18 @@ func (kcp *KCP) flush() {
 		}
 	}
 
-	atomic.AddUint64(&DefaultSnmp.RetransSegs, lostSegs+fastRetransSegs+earlyRetransSegs)
-	atomic.AddUint64(&DefaultSnmp.LostSegs, lostSegs)
-	atomic.AddUint64(&DefaultSnmp.EarlyRetransSegs, earlyRetransSegs)
-	atomic.AddUint64(&DefaultSnmp.FastRetransSegs, fastRetransSegs)
-
 	// flash remain segments
 	size := len(buffer) - len(ptr)
 	if size > 0 {
 		kcp.output(buffer, size)
 	}
 
+	// counter updates
+	atomic.AddUint64(&DefaultSnmp.RetransSegs, lostSegs+fastRetransSegs+earlyRetransSegs)
+	atomic.AddUint64(&DefaultSnmp.LostSegs, lostSegs)
+	atomic.AddUint64(&DefaultSnmp.EarlyRetransSegs, earlyRetransSegs)
+	atomic.AddUint64(&DefaultSnmp.FastRetransSegs, fastRetransSegs)
+
 	// update ssthresh
 	// rate halving, https://tools.ietf.org/html/rfc6937
 	if change != 0 {