From a3ae280a7fd7d32da120dcf3b0f1ddd52f2e27d7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E6=BA=90=E6=96=87=E9=9B=A8?=
 <41315874+fumiama@users.noreply.github.com>
Date: Sat, 5 Aug 2023 10:55:40 +0800
Subject: [PATCH] fix: mtu calculation

---
 gold/link/me.go   |  4 ----
 gold/link/peer.go |  2 +-
 gold/link/send.go | 40 +++++++++++++++++++++-------------------
 3 files changed, 22 insertions(+), 24 deletions(-)

diff --git a/gold/link/me.go b/gold/link/me.go
index 6aee9a2..82e8d2f 100644
--- a/gold/link/me.go
+++ b/gold/link/me.go
@@ -170,10 +170,6 @@ func (m *Me) sendAllSameDst(packet []byte) (n int) {
 			break
 		}
 		i += int(totl)
-		if i > int(m.mtu) {
-			logrus.Debugln("[me] wrap exceed mtu, break")
-			break
-		}
 		ptr = rem[i:]
 		logrus.Debugln("[me] wrap", totl, "bytes packet to send together")
 	}
diff --git a/gold/link/peer.go b/gold/link/peer.go
index 19ff734..991e912 100644
--- a/gold/link/peer.go
+++ b/gold/link/peer.go
@@ -32,7 +32,7 @@ func (m *Me) AddPeer(cfg *PeerConfig) (l *Link) {
 	if ok {
 		return
 	}
-	if cfg.MTU == 0 || cfg.MTU == 65535 || cfg.MTU%8 != 0 || (m.mtu != 0 && cfg.MTU > m.mtu) {
+	if cfg.MTU == 0 || (m.mtu != 0 && cfg.MTU > m.mtu) {
 		panic("invalid mtu for peer " + cfg.PeerIP)
 	}
 	l = &Link{
diff --git a/gold/link/send.go b/gold/link/send.go
index b3d5aea..fbebaf3 100644
--- a/gold/link/send.go
+++ b/gold/link/send.go
@@ -21,39 +21,44 @@ func (l *Link) WriteAndPut(p *head.Packet, istransfer bool) (n int, err error) {
 	sndcnt := atomic.AddUintptr(&l.sendcount, 1)
 	mtu := l.mtu
 	if l.mturandomrange > 0 {
-		mtu -= uint16(rand.Intn(int(l.mturandomrange))) & 0xfff8
-	}
-	logrus.Debugln("[send] mtu:", mtu, ", count:", sndcnt, ", additional data:", uint16(sndcnt))
-	if len(p.Data) <= int(mtu) {
-		if !istransfer {
-			l.encrypt(p, uint16(sndcnt), teatype)
-		}
-		defer p.Put()
-		return l.write(p, teatype, uint16(sndcnt), mtu, uint32(len(p.Data)), 0, istransfer, false)
+		mtu -= uint16(rand.Intn(int(l.mturandomrange)))
 	}
+	logrus.Debugln("[send] mtu:", mtu, ", count:", sndcnt, ", additional data:", uint16(sndcnt)&0x0fff)
 	if !istransfer {
 		l.encrypt(p, uint16(sndcnt), teatype)
 	}
+	delta := (int(mtu) - 60) & 0x0000fff8
+	if delta <= 0 {
+		logrus.Warnln("[send] reset invalid data frag len", delta, "to 8")
+		delta = 8
+	}
+	if len(p.Data) <= delta {
+		defer p.Put()
+		return l.write(p, teatype, uint16(sndcnt), uint32(len(p.Data)), 0, istransfer, false)
+	}
+	if istransfer && p.Flags&0x4000 == 0x4000 && len(p.Data) > delta {
+		return 0, errors.New("drop dont fragmnet big trans packet")
+	}
 	data := p.Data
 	ttl := p.TTL
 	totl := uint32(len(data))
 	i := 0
 	packet := head.SelectPacket()
 	*packet = *p
-	for ; int(totl)-i > int(mtu); i += int(mtu) {
-		logrus.Debugln("[send] split frag [", i, "~", i+int(mtu), "], remain:", int(totl)-i-int(mtu))
-		packet.Data = data[:int(mtu)]
-		cnt, err := l.write(packet, teatype, uint16(sndcnt), mtu, totl, uint16(i>>3), istransfer, true)
+	for ; int(totl)-i > delta; i += delta {
+		logrus.Debugln("[send] split frag [", i, "~", i+delta, "], remain:", int(totl)-i-delta)
+		packet.Data = data[:delta]
+		cnt, err := l.write(packet, teatype, uint16(sndcnt), totl, uint16(i>>3), istransfer, true)
 		n += cnt
 		if err != nil {
 			return n, err
 		}
-		data = data[int(mtu):]
+		data = data[delta:]
 		packet.TTL = ttl
 	}
 	packet.Put()
 	p.Data = data
-	cnt, err := l.write(p, teatype, uint16(sndcnt), mtu, totl, uint16(i>>3), istransfer, false)
+	cnt, err := l.write(p, teatype, uint16(sndcnt), totl, uint16(i>>3), istransfer, false)
 	p.Put()
 	n += cnt
 	return n, err
@@ -80,13 +85,10 @@ func (l *Link) encrypt(p *head.Packet, sndcnt uint16, teatype uint8) {
 }
 
 // write 向 peer 发一个包
-func (l *Link) write(p *head.Packet, teatype uint8, additional, mtu uint16, datasz uint32, offset uint16, istransfer, hasmore bool) (n int, err error) {
+func (l *Link) write(p *head.Packet, teatype uint8, additional uint16, datasz uint32, offset uint16, istransfer, hasmore bool) (n int, err error) {
 	var d []byte
 	var cl func()
 	if istransfer {
-		if p.Flags&0x4000 == 0x4000 && len(p.Data) > int(mtu) {
-			return len(p.Data), errors.New("drop dont fragmnet big trans packet")
-		}
 		d, cl = p.Marshal(nil, teatype, additional, 0, 0, false, false)
 	} else {
 		d, cl = p.Marshal(l.me.me, teatype, additional, datasz, offset, false, hasmore)