fix bug: udp write 提供了对外封装的Write()

表现为一个阻塞操作，如果本地arp缓存失效，就会重新发起一次arp广播，更新目标ip地址的MAC 更新后将再次尝试写数据

cmd/netstack/main.go

@@ -184,10 +184,17 @@ func (conn *UdpConn) Read(rcv []byte) (int, error) {
 	}
 }
 
-func (conn *UdpConn) Write(snd []byte) {
-	_, _, err := conn.ep.Write(tcpip.SlicePayload(snd), tcpip.WriteOptions{To: &conn.raddr})
+func (conn *UdpConn) Write(snd []byte) error {
+	for {
+		_, notifyCh, err := conn.ep.Write(tcpip.SlicePayload(snd), tcpip.WriteOptions{To: &conn.raddr})
 		if err != nil {
-		log.Fatal(err)
+			if err == tcpip.ErrNoLinkAddress {
+				<-notifyCh
+				continue
+			}
+			return fmt.Errorf("%s", err.String())
+		}
+		return nil
 	}
 }
 

tcpip/network/arp/arp.go

@@ -151,7 +151,7 @@ func (*protocol) LinkAddressRequest(addr, localAddr tcpip.Address, linkEP stack.
 	copy(h.HardwareAddressSender(), linkEP.LinkAddress())
 	copy(h.ProtocolAddressSender(), localAddr)
 	copy(h.ProtocolAddressTarget(), addr)
-
+	log.Println("arp发起广播 寻找:", addr)
 	return linkEP.WritePacket(r, hdr, buffer.VectorisedView{}, ProtocolNumber)
 }
 

tcpip/stack/linkaddrcache.go

@@ -201,7 +201,8 @@ func (c *linkAddrCache) makeAndAddEntry(k tcpip.FullAddress, v tcpip.LinkAddress
 }
 
 // get reports any known link address for k.
-func (c *linkAddrCache) get(k tcpip.FullAddress, linkRes LinkAddressResolver, localAddr tcpip.Address, linkEP LinkEndpoint, waker *sleep.Waker) (tcpip.LinkAddress, <-chan struct{}, *tcpip.Error) {
+func (c *linkAddrCache) get(k tcpip.FullAddress, linkRes LinkAddressResolver,
+	localAddr tcpip.Address, linkEP LinkEndpoint, waker *sleep.Waker) (tcpip.LinkAddress, <-chan struct{}, *tcpip.Error) {
 	log.Println("在arp本地缓存中寻找", k)
 	if linkRes != nil {
 		if addr, ok := linkRes.ResolveStaticAddress(k.Addr); ok {
@@ -214,7 +215,7 @@ func (c *linkAddrCache) get(k tcpip.FullAddress, linkRes LinkAddressResolver, lo
 	// 尝试从缓存中得到MAC地址
 	if entry, ok := c.cache[k]; ok {
 		switch s := entry.state(); s {
-		case expired:
+		case expired: // 过期了
 		case ready:
 			return entry.linkAddr, nil, nil
 		case failed:
@@ -251,7 +252,8 @@ func (c *linkAddrCache) removeWaker(k tcpip.FullAddress, waker *sleep.Waker) {
 	}
 }
 
-func (c *linkAddrCache) startAddressResolution(k tcpip.FullAddress, linkRes LinkAddressResolver, localAddr tcpip.Address, linkEP LinkEndpoint, done <-chan struct{}) {
+func (c *linkAddrCache) startAddressResolution(k tcpip.FullAddress, linkRes LinkAddressResolver,
+	localAddr tcpip.Address, linkEP LinkEndpoint, done <-chan struct{}) {
 	for i := 0; ; i++ {
 		// Send link request, then wait for the timeout limit and check
 		// whether the request succeeded.

tcpip/stack/stack.go

@@ -13,7 +13,8 @@ import (
 
 const (
 	// ageLimit is set to the same cache stale time used in Linux.
-	ageLimit = 1 * time.Minute
+	//ageLimit = 1 * time.Minute
+	ageLimit = 5 * time.Second
 	// resolutionTimeout is set to the same ARP timeout used in Linux.
 	resolutionTimeout = 1 * time.Second
 	// resolutionAttempts is set to the same ARP retries used in Linux.