分片机制开始实现 大致是使用了一个map管理+小根堆自动排序实现的

tcpip/header/ipv4.go

@@ -48,7 +48,7 @@ type IPv4Fields struct {
 	TotalLength uint16
 
 	// ID is the "identification" field of an IPv4 packet.
-	// 标识符
+	// 标识符 注意这个ID对于每个IP报文来说是唯一的 它的每个分片共享这个ID来标识它们同属一个报文
 	ID uint16
 
 	// Flags is the "flags" field of an IPv4 packet.
@@ -294,6 +294,8 @@ func atoi[T int | int8 | int16 | int32 | int64 | uint | uint8 |uint16 | uint32](
 }
 
 func (b IPv4) String() string {
+	for i := range b.Payload() {
+		if i != int(b.PayloadLength()-1) && b.Payload()[i]^b.Payload()[i+1] != 0 {
 			return fmt.Sprintf(ipv4Fmt, atoi(IPVersion(b)), atoi(b.HeaderLength()), atoi(0), atoi(b.TotalLength()),
 				atoi(b.ID()), atoi(b.Flags()>>2), atoi((b.Flags()&2)>>1), atoi(b.Flags()&1), atoi(b.FragmentOffset()),
 				atoi(b.TTL()), atoi(b.Protocol()), atoi(b.Checksum()),
@@ -301,3 +303,11 @@ func (b IPv4) String() string {
 				b.DestinationAddress().String(),
 				b.Payload())
 		}
+	}
+	return fmt.Sprintf(ipv4Fmt, atoi(IPVersion(b)), atoi(b.HeaderLength()), atoi(0), atoi(b.TotalLength()),
+		atoi(b.ID()), atoi(b.Flags()>>2), atoi((b.Flags()&2)>>1), atoi(b.Flags()&1), atoi(b.FragmentOffset()),
+		atoi(b.TTL()), atoi(b.Protocol()), atoi(b.Checksum()),
+		b.SourceAddress().String(),
+		b.DestinationAddress().String(),
+		fmt.Sprintf("%v x %d", b.Payload()[0], b.PayloadLength()))
+}

tcpip/network/fragmentation/fragmentation.go

@@ -22,16 +22,18 @@ const HighFragThreshold = 4 << 20 // 4MB
 // net.ipv4.ipfrag_low_thresh for more information.
 const LowFragThreshold = 3 << 20 // 3MB
 
+// Fragmentation 分片处理器对象
 type Fragmentation struct {
 	mu           sync.Mutex
 	highLimit    int
 	lowLimit     int
-	reassemblers map[uint32]*reassembler
+	reassemblers map[uint32]*reassembler // IP报文hash:重组器
 	rList        reassemblerList
 	size         int
 	timeout      time.Duration
 }
 
+// NewFragmentation 新建一个分片处理器
 func NewFragmentation(highMemoryLimit, lowMemoryLimit int, reassemblingTimeout time.Duration) *Fragmentation {
 	if lowMemoryLimit >= highMemoryLimit {
 		lowMemoryLimit = highMemoryLimit
@@ -49,20 +51,41 @@ func NewFragmentation(highMemoryLimit, lowMemoryLimit int, reassemblingTimeout t
 	}
 }
 
+// Process 处理ip报文分片
 func (f *Fragmentation) Process(id uint32, first, last uint16, more bool, vv buffer.VectorisedView) (buffer.VectorisedView, bool) {
-	log.Println("分片机制工作中", id, first, last, vv.First())
 	f.mu.Lock()
 	r, ok := f.reassemblers[id]
-	if ok && r.tooOld(f.timeout) {
+	if ok && r.tooOld(f.timeout) { // 检测一个分片是否存在超过了30s
 		// This is very likely to be an id-collision or someone performing a slow-rate attack.
-		//f.release(r)
+		f.release(r)
 		ok = false
 	}
-	if !ok {
+	if !ok { // 首次注册该报文的分片
 		r = newReassembler(id)
 		f.reassemblers[id] = r
 		f.rList.PushFront(r)
 	}
 	f.mu.Unlock()
+
+	//res, done, consumed := r.process(first, last, more, vv)
+	log.Printf("[%d]的分片 [%d,%d) 合并中\n", id, first, last)
+	r.process(first, last, more, vv)
+
 	return buffer.VectorisedView{}, false
 }
+
+func (f *Fragmentation) release(r *reassembler) {
+	// Before releasing a fragment we need to check if r is already marked as done.
+	// Otherwise, we would delete it twice.
+	if r.checkDoneOrMark() {
+		return
+	}
+
+	delete(f.reassemblers, r.id)
+	f.rList.Remove(r)
+	f.size -= r.size
+	if f.size < 0 {
+		log.Printf("memory counter < 0 (%d), this is an accounting bug that requires investigation", f.size)
+		f.size = 0
+	}
+}

tcpip/network/fragmentation/fragmentation_test.go

@@ -1,6 +1,8 @@
 package fragmentation_test
 
 import (
+	"log"
+	"math"
 	"netstack/tcpip"
 	"netstack/tcpip/buffer"
 	"netstack/tcpip/header"
@@ -23,6 +25,7 @@ type testContext struct {
 	t      *testing.T
 	linkEP *channel.Endpoint
 	s      *stack.Stack
+	id     uint16
 }
 
 func newTestContext(t *testing.T) *testContext {
@@ -55,6 +58,7 @@ func newTestContext(t *testing.T) *testContext {
 		t:      t,
 		s:      s,
 		linkEP: linkEP,
+		id:     uint16(time.Now().Unix() % math.MaxUint16),
 	}
 }
 
@@ -101,23 +105,24 @@ func TestFragmentationBase(t *testing.T) {
 		t.Fatalf("Case #1 Time Out\n")
 	}
 
-	// 一个纯粹的IP报文
-	v = make(buffer.View, header.IPv4MinimumSize+256)
+	// 一个纯粹的IP报文 Part1
+	pLen := ((1500 - header.EthernetMinimumSize - header.IPv4MinimumSize) >> 3) << 3
+	v = make(buffer.View, header.IPv4MinimumSize+pLen)
 	hdr := buffer.NewPrependable(header.IPv4MinimumSize)
 	ip := header.IPv4(hdr.Prepend(header.IPv4MinimumSize))
-	buf := make(buffer.View, 256)
+	buf := make(buffer.View, pLen)
 	for i := range buf {
 		buf[i] = 1
 	}
-	payload := buffer.NewVectorisedView(256, buf.ToVectorisedView().Views())
+	payload := buffer.NewVectorisedView(pLen, buf.ToVectorisedView().Views())
 	length := uint16(hdr.UsedLength() + payload.Size())
 	// ip首部编码
 	ip.Encode(&header.IPv4Fields{
 		IHL:            header.IPv4MinimumSize,
 		TotalLength:    length,
-		ID:             uint16(2),
+		ID:             c.id,
 		Flags:          0x1,
-		FragmentOffset: 1024,
+		FragmentOffset: 0,
 		TTL:            255,
 		Protocol:       uint8(0x6), // tcp 伪装报文
 		SrcAddr:        senderIPv4,
@@ -136,4 +141,29 @@ func TestFragmentationBase(t *testing.T) {
 
 	inject(stackAddr1)
 
+	// 一个纯粹的IP报文 Part2
+	pLen = 256
+	v = make(buffer.View, header.IPv4MinimumSize+pLen)
+	payload = buffer.NewVectorisedView(pLen, buf.ToVectorisedView().Views())
+	length = uint16(hdr.UsedLength() + payload.Size())
+	// ip首部编码
+	ip.Encode(&header.IPv4Fields{
+		IHL:            header.IPv4MinimumSize,
+		TotalLength:    length,
+		ID:             c.id,
+		FragmentOffset: 1464,
+		TTL:            255,
+		Protocol:       uint8(0x6), // tcp 伪装报文
+		SrcAddr:        senderIPv4,
+		DstAddr:        stackAddr1,
+	})
+	//ip.SetFlagsFragmentOffset()
+	// 计算校验和和设置校验和
+	ip.SetChecksum(^ip.CalculateChecksum())
+	copy(v, ip)
+	copy(v[header.IPv4MinimumSize:], payload.First())
+	log.Println(ip.FragmentOffset())
+
+	inject(stackAddr1)
+
 }

tcpip/network/fragmentation/reassembler.go

@@ -30,6 +30,7 @@ type hole struct {
 	deleted bool
 }
 
+// 重组器对象
 type reassembler struct {
 	reassemblerEntry
 	id           uint32
@@ -37,7 +38,7 @@ type reassembler struct {
 	mu           sync.Mutex
 	holes        []hole
 	deleted      int
-	heap         fragHeap
+	heap         fragHeap // 小根堆用来自动排序
 	done         bool
 	creationTime time.Time
 }

tcpip/network/ipv4/ipv4.go

@@ -121,7 +121,6 @@ func (e *endpoint) WritePacket(r *stack.Route, hdr buffer.Prependable, payload b
 func (e *endpoint) HandlePacket(r *stack.Route, vv buffer.VectorisedView) {
 	// 得到ip报文
 	h := header.IPv4(vv.First())
-	log.Println(h)
 	// 检查报文是否有效
 	if !h.IsValid(vv.Size()) {
 		return
@@ -133,7 +132,7 @@ func (e *endpoint) HandlePacket(r *stack.Route, vv buffer.VectorisedView) {
 	vv.TrimFront(hlen)
 	vv.CapLength(tlen - hlen)
 
-	// 报文重组 TODO
+	// 报文重组
 	more := (h.Flags() & header.IPv4FlagMoreFragments) != 0
 	// 是否需要ip重组
 	if more || h.FragmentOffset() != 0 {

tcpip/stack/nic.go

@@ -365,7 +365,12 @@ func (n *NIC) DeliverNetworkPacket(linkEP LinkEndpoint, remoteLinkAddr, localLin
 		return
 	}
 	src, dst := netProto.ParseAddresses(vv.First())
-	log.Printf("设备[%v]准备从 [%s] 向 [%s] 分发数据: %v\n", linkEP.LinkAddress(), src, dst, vv.ToView())
+	log.Printf("设备[%v]准备从 [%s] 向 [%s] 分发数据: %v\n", linkEP.LinkAddress(), src, dst, func() []byte {
+		if len(vv.ToView()) > 64 {
+			return vv.ToView()[:64]
+		}
+		return vv.ToView()
+	}())
 	// 根据网络协议和数据包的目的地址，找到网络端
 	// 然后将数据包分发给网络层
 	if ref := n.getRef(protocol, dst); ref != nil {