重构代码

LICENSE

@@ -0,0 +1,201 @@
+Apache License
+Version 2.0, January 2004
+http://www.apache.org/licenses/
+
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+limitations under the License.

README.md

@@ -0,0 +1,218 @@
+# bcap
+
+`bcap` 是一个轻量的 Go 报文解析库，重点提供两类能力：
+
+- 统一提取报文事实
+- 基于连续报文输出轻量协议提示
+
+它适合作为抓包工具、离线诊断工具、CLI/TUI 浏览器的底层解析层，但并不试图替代完整协议栈、深度重组引擎或最终用户报告系统。
+
+## 1. 核心定位
+
+`bcap` 主包当前围绕 3 个对象展开：
+
+- `Decoder`
+  - 无状态，只负责单包解码，输出 `Packet`
+- `Tracker`
+  - 有状态，只负责基于连续报文做轻量跟踪，输出 `Observation`
+- `Analyzer`
+  - `Decoder + Tracker` 的组合入口，适合大多数直接接入场景
+
+分工可以直接理解为：
+
+- `Decoder` 负责单包事实
+- `Tracker` 负责跨包提示
+- `Analyzer` 负责把两者串起来
+
+## 2. 适用场景
+
+`bcap` 主要适合：
+
+- 在线抓包后的统一元数据提取
+- 离线 pcap 遍历分析
+- TCP/UDP/ICMP/ARP 的统一识别
+- TCP 关键行为提示，例如握手、挥手、重传、keepalive、RST
+
+`bcap` 不直接负责：
+
+- 诊断结论生成
+- CLI/TUI 文案
+- Excel / JSON / 报告拼装
+- 动作编排与干预逻辑
+- 工具侧业务状态缓存
+
+## 3. 快速开始
+
+安装：
+
+```bash
+go get b612.me/bcap
+```
+
+最常见的接入方式是直接使用 `Analyzer`：
+
+```go
+package main
+
+import (
+	"fmt"
+
+	"b612.me/bcap"
+	"github.com/gopacket/gopacket"
+)
+
+func consume(packet gopacket.Packet) error {
+	analyzer := bcap.NewAnalyzer()
+	defer analyzer.Stop()
+
+	obs, err := analyzer.ObservePacket(packet)
+	if err != nil {
+		return err
+	}
+
+	fmt.Println("flow:", obs.Flow.Stable)
+	fmt.Println("protocol:", obs.Packet.Transport.Kind)
+	fmt.Println("summary:", obs.Hints.Summary.Code)
+
+	if obs.Hints.TCP != nil {
+		fmt.Println("tcp event:", obs.Hints.TCP.Event)
+	}
+	return nil
+}
+```
+
+如果你需要自行控制“解码”和“跟踪”两个阶段，也可以拆开使用：
+
+```go
+decoder := bcap.NewDecoder()
+tracker := bcap.NewTracker()
+defer tracker.Stop()
+
+decoded, err := decoder.Decode(packet)
+if err != nil {
+	return err
+}
+
+obs, err := tracker.Observe(decoded)
+if err != nil {
+	return err
+}
+```
+
+## 4. 支持范围
+
+当前主包支持的主要识别范围：
+
+- 链路层
+  - `Ethernet`
+  - `Linux SLL`
+  - `Linux SLL2`
+- 网络层
+  - `IPv4`
+  - `IPv6`
+  - `ARP`
+- 传输层 / 协议层
+  - `TCP`
+  - `UDP`
+  - `ICMPv4`
+  - `ICMPv6`
+  - `Unknown`
+
+当前 TCP 轻量提示重点覆盖：
+
+- 三次握手
+- 四次挥手
+- 普通 ACK
+- 重传
+- keepalive
+- keepalive response
+- RST
+- ECE / CWR
+
+## 5. 如何选接口
+
+优先级建议：
+
+- 大多数工具直接用 `Analyzer`
+- 只要报文事实时用 `Decoder`
+- 你已经有自己的输入管线，只缺轻量状态跟踪时用 `Tracker`
+
+如果没有特殊理由，优先选择 `Analyzer`，接入成本最低。
+
+## 6. 包结构
+
+### 6.1 主包 `b612.me/bcap`
+
+负责：
+
+- 统一事实模型
+- 统一 flow 模型
+- 统一 hint 模型
+- 轻量 TCP 跟踪
+
+### 6.2 子包 `libpcap`
+
+负责：
+
+- 基于 pcap 的抓包输入适配
+
+### 6.3 子包 `nfq`
+
+负责：
+
+- 基于 NFQUEUE 的输入适配
+
+通常的组合方式是：
+
+- `libpcap` / `nfq` 提供输入
+- `bcap.Analyzer` 负责解析与提示
+- 上层工具负责展示、统计、导出和策略
+
+## 7. 文档导航
+
+如果你只是要快速接入，看本 README 基本够用。
+
+如果你要看完整 API、模型字段、配置项和迁移说明，请继续阅读：
+
+- [`doc/api.md`](./doc/api.md)
+
+如果你要看当前架构思路和设计边界，请看：
+
+- [`doc/dev.md`](./doc/dev.md)
+
+## 8. 迁移提示
+
+`bcap` 主包已经移除了旧的胖接口，旧的以下模型不再推荐使用，并且主体已经删除：
+
+- `Packets`
+- `PacketInfo`
+- `ParsePacket`
+- `NewPackets`
+- `NewPacketsWithConfig`
+- `LegacyPacketInfoFromObservation`
+- `GetStateDescription`
+- `PrintStats`
+- `ExportConnectionsToJSON`
+
+新的迁移方向是：
+
+- 单包事实解析改用 `Decoder`
+- 报文观察结果改用 `Observation`
+- TCP 轻量状态识别改用 `Tracker`
+- 大多数场景直接改用 `Analyzer`
+
+## 9. 测试
+
+开发或改动后，至少建议执行：
+
+```bash
+go test ./...
+```
+
+## 10. License
+
+本项目采用 Apache License 2.0。
+
+完整协议文本见：
+
+- [`LICENSE`](./LICENSE)

analyzer.go

@@ -0,0 +1,73 @@
+package bcap
+
+import (
+	"sync"
+	"time"
+
+	"github.com/gopacket/gopacket"
+)
+
+type Analyzer struct {
+	decoder *Decoder
+	tracker *Tracker
+
+	mu            sync.Mutex
+	firstPacketTS time.Time
+}
+
+func NewAnalyzer() *Analyzer {
+	return NewAnalyzerWithConfig(nil)
+}
+
+func NewAnalyzerWithConfig(config *PacketsConfig) *Analyzer {
+	return &Analyzer{
+		decoder: NewDecoder(),
+		tracker: NewTrackerWithConfig(config),
+	}
+}
+
+func (a *Analyzer) Stop() {
+	if a.tracker != nil {
+		a.tracker.Stop()
+	}
+}
+
+func (a *Analyzer) Decoder() *Decoder {
+	return a.decoder
+}
+
+func (a *Analyzer) Tracker() *Tracker {
+	return a.tracker
+}
+
+func (a *Analyzer) ObservePacket(packet gopacket.Packet) (Observation, error) {
+	return a.ObservePacketWithOptions(packet, DecodeOptions{})
+}
+
+func (a *Analyzer) ObservePacketWithOptions(packet gopacket.Packet, opts DecodeOptions) (Observation, error) {
+	if opts.BaseTime.IsZero() {
+		opts.BaseTime = a.ensureBaseTime(packet)
+	}
+	decoded, err := a.decoder.DecodeWithOptions(packet, opts)
+	if err != nil {
+		return Observation{}, err
+	}
+	return a.tracker.Observe(decoded)
+}
+
+func (a *Analyzer) ensureBaseTime(packet gopacket.Packet) time.Time {
+	a.mu.Lock()
+	defer a.mu.Unlock()
+
+	if packet == nil {
+		return time.Time{}
+	}
+	metadata := packet.Metadata()
+	if metadata == nil || metadata.Timestamp.IsZero() {
+		return time.Time{}
+	}
+	if a.firstPacketTS.IsZero() {
+		a.firstPacketTS = metadata.Timestamp
+	}
+	return a.firstPacketTS
+}

api_test.go

@@ -0,0 +1,315 @@
+package bcap
+
+import (
+	"net"
+	"testing"
+	"time"
+)
+
+func TestDecoderDecodeARP(t *testing.T) {
+	decoder := NewDecoder()
+	base := time.Unix(1700005000, 0)
+
+	packet := mustBuildARPPacket(t, base, arpPacketSpec{
+		srcMAC:    "02:00:00:00:00:01",
+		dstMAC:    "ff:ff:ff:ff:ff:ff",
+		senderMAC: "02:00:00:00:00:01",
+		targetMAC: "00:00:00:00:00:00",
+		senderIP:  "10.0.0.1",
+		targetIP:  "10.0.0.2",
+		operation: 1,
+	})
+
+	decoded, err := decoder.Decode(packet)
+	if err != nil {
+		t.Fatalf("decode arp: %v", err)
+	}
+	if decoded.Network.Family != NetworkFamilyARP {
+		t.Fatalf("network family = %q, want %q", decoded.Network.Family, NetworkFamilyARP)
+	}
+	if decoded.Transport.Kind != ProtocolARP {
+		t.Fatalf("protocol = %q, want %q", decoded.Transport.Kind, ProtocolARP)
+	}
+	if decoded.Network.ARP == nil {
+		t.Fatal("expected arp facts")
+	}
+	if decoded.Network.ARP.SenderIP != "10.0.0.1" {
+		t.Fatalf("sender ip = %q, want %q", decoded.Network.ARP.SenderIP, "10.0.0.1")
+	}
+	if decoded.Network.ARP.TargetIP != "10.0.0.2" {
+		t.Fatalf("target ip = %q, want %q", decoded.Network.ARP.TargetIP, "10.0.0.2")
+	}
+}
+
+func TestDecoderDecodeIPv4WithoutTransportReturnsUnknown(t *testing.T) {
+	decoder := NewDecoder()
+	base := time.Unix(1700005001, 0)
+
+	packet := mustBuildIPv4OnlyPacket(t, base, "10.0.0.1", "10.0.0.2")
+	decoded, err := decoder.Decode(packet)
+	if err != nil {
+		t.Fatalf("decode ipv4-only: %v", err)
+	}
+	if decoded.Network.Family != NetworkFamilyIPv4 {
+		t.Fatalf("network family = %q, want %q", decoded.Network.Family, NetworkFamilyIPv4)
+	}
+	if decoded.Transport.Kind != ProtocolUnknown {
+		t.Fatalf("transport kind = %q, want %q", decoded.Transport.Kind, ProtocolUnknown)
+	}
+}
+
+func TestAnalyzerObservePacketTCP(t *testing.T) {
+	analyzer := NewAnalyzer()
+	defer analyzer.Stop()
+	base := time.Unix(1700005002, 0)
+
+	obs, err := analyzer.ObservePacket(mustBuildTCPPacket(t, base, tcpPacketSpec{
+		srcIP:   "10.0.0.1",
+		dstIP:   "10.0.0.2",
+		srcPort: 12345,
+		dstPort: 80,
+		seq:     100,
+		syn:     true,
+		window:  4096,
+	}))
+	if err != nil {
+		t.Fatalf("observe tcp packet: %v", err)
+	}
+	if obs.Flow.Forward.Protocol != ProtocolTCP {
+		t.Fatalf("flow protocol = %q, want %q", obs.Flow.Forward.Protocol, ProtocolTCP)
+	}
+	if obs.Hints.TCP == nil {
+		t.Fatal("expected tcp hint")
+	}
+	if obs.Hints.TCP.Event != TCPEventSYN {
+		t.Fatalf("tcp event = %q, want %q", obs.Hints.TCP.Event, TCPEventSYN)
+	}
+	if obs.Hints.Summary.Code != string(TagTCPHandshakeSYN) {
+		t.Fatalf("summary = %q, want %q", obs.Hints.Summary.Code, TagTCPHandshakeSYN)
+	}
+}
+
+func TestAnalyzerObservePacketARP(t *testing.T) {
+	analyzer := NewAnalyzer()
+	defer analyzer.Stop()
+	base := time.Unix(1700005003, 0)
+
+	obs, err := analyzer.ObservePacket(mustBuildARPPacket(t, base, arpPacketSpec{
+		srcMAC:    "02:00:00:00:00:01",
+		dstMAC:    "ff:ff:ff:ff:ff:ff",
+		senderMAC: "02:00:00:00:00:01",
+		targetMAC: "00:00:00:00:00:00",
+		senderIP:  "10.0.0.1",
+		targetIP:  "10.0.0.2",
+		operation: 1,
+	}))
+	if err != nil {
+		t.Fatalf("observe arp packet: %v", err)
+	}
+	if obs.Flow.Forward.Protocol != ProtocolARP {
+		t.Fatalf("flow protocol = %q, want %q", obs.Flow.Forward.Protocol, ProtocolARP)
+	}
+	if obs.Hints.ARP == nil {
+		t.Fatal("expected arp hint")
+	}
+	if !obs.Hints.ARP.Request {
+		t.Fatal("expected arp request hint")
+	}
+	if obs.Hints.Summary.Code != string(TagARPRequest) {
+		t.Fatalf("summary = %q, want %q", obs.Hints.Summary.Code, TagARPRequest)
+	}
+}
+
+func TestTrackerObserveDecodedTCPWithoutRawPacket(t *testing.T) {
+	decoder := NewDecoder()
+	tracker := NewTracker()
+	defer tracker.Stop()
+	base := time.Unix(1700005004, 0)
+
+	decoded, err := decoder.Decode(mustBuildTCPPacket(t, base, tcpPacketSpec{
+		srcIP:   "10.0.0.1",
+		dstIP:   "10.0.0.2",
+		srcPort: 12345,
+		dstPort: 80,
+		seq:     100,
+		syn:     true,
+		window:  4096,
+	}))
+	if err != nil {
+		t.Fatalf("decode tcp: %v", err)
+	}
+	decoded.Raw.Packet = nil
+
+	obs, err := tracker.Observe(decoded)
+	if err != nil {
+		t.Fatalf("observe decoded tcp: %v", err)
+	}
+	if obs.Hints.TCP == nil {
+		t.Fatal("expected tcp hint")
+	}
+	if obs.Hints.TCP.Event != TCPEventSYN {
+		t.Fatalf("tcp event = %q, want %q", obs.Hints.TCP.Event, TCPEventSYN)
+	}
+}
+
+func TestAnalyzerObservePacketWithOptionsSrcMACOverride(t *testing.T) {
+	analyzer := NewAnalyzer()
+	defer analyzer.Stop()
+
+	override := net.HardwareAddr{0x02, 0xaa, 0xbb, 0xcc, 0xdd, 0xee}
+	base := time.Unix(1700005005, 0)
+
+	obs, err := analyzer.ObservePacketWithOptions(mustBuildTCPPacket(t, base, tcpPacketSpec{
+		srcIP:   "10.0.0.1",
+		dstIP:   "10.0.0.2",
+		srcPort: 12345,
+		dstPort: 80,
+		seq:     100,
+		syn:     true,
+		window:  4096,
+	}), DecodeOptions{
+		SrcMACOverride: override,
+	})
+	if err != nil {
+		t.Fatalf("observe tcp packet with options: %v", err)
+	}
+	if got := obs.Packet.Link.SrcMAC.String(); got != override.String() {
+		t.Fatalf("src mac = %q, want %q", got, override.String())
+	}
+	if obs.Packet.Meta.RelativeTime != 0 {
+		t.Fatalf("relative time = %v, want 0", obs.Packet.Meta.RelativeTime)
+	}
+}
+
+func TestAnalyzerObservePacketTCPKeepaliveResponse(t *testing.T) {
+	analyzer := NewAnalyzer()
+	defer analyzer.Stop()
+	base := time.Unix(1700005006, 0)
+
+	_, err := analyzer.ObservePacket(mustBuildTCPPacket(t, base, tcpPacketSpec{
+		srcIP:   "122.210.105.240",
+		dstIP:   "122.210.110.99",
+		srcPort: 3306,
+		dstPort: 60818,
+		seq:     172126745,
+		ack:     2951532891,
+		ackFlag: true,
+		window:  258,
+	}))
+	if err != nil {
+		t.Fatalf("observe baseline packet: %v", err)
+	}
+
+	probe, err := analyzer.ObservePacket(mustBuildTCPPacket(t, base.Add(75*time.Second), tcpPacketSpec{
+		srcIP:   "122.210.105.240",
+		dstIP:   "122.210.110.99",
+		srcPort: 3306,
+		dstPort: 60818,
+		seq:     172126745,
+		ack:     2951532891,
+		ackFlag: true,
+		window:  258,
+	}))
+	if err != nil {
+		t.Fatalf("observe keepalive probe: %v", err)
+	}
+	if probe.Hints.TCP == nil || probe.Hints.TCP.Event != TCPEventKeepalive {
+		t.Fatalf("probe event = %#v, want %q", probe.Hints.TCP, TCPEventKeepalive)
+	}
+
+	resp, err := analyzer.ObservePacket(mustBuildTCPPacket(t, base.Add(75*time.Second+50*time.Millisecond), tcpPacketSpec{
+		srcIP:   "122.210.110.99",
+		dstIP:   "122.210.105.240",
+		srcPort: 60818,
+		dstPort: 3306,
+		seq:     2951532891,
+		ack:     172126746,
+		ackFlag: true,
+		window:  1024,
+	}))
+	if err != nil {
+		t.Fatalf("observe keepalive response: %v", err)
+	}
+	if resp.Hints.TCP == nil {
+		t.Fatal("expected tcp hint")
+	}
+	if resp.Hints.TCP.LegacyState != StateTcpKeepalive {
+		t.Fatalf("legacy state = %d, want %d", resp.Hints.TCP.LegacyState, StateTcpKeepalive)
+	}
+	if resp.Hints.TCP.Event != TCPEventKeepaliveResp {
+		t.Fatalf("tcp event = %q, want %q", resp.Hints.TCP.Event, TCPEventKeepaliveResp)
+	}
+	if !resp.Hints.TCP.KeepaliveResponse {
+		t.Fatal("expected keepalive response flag")
+	}
+	if resp.Hints.Summary.Code != string(TagTCPKeepaliveResp) {
+		t.Fatalf("summary = %q, want %q", resp.Hints.Summary.Code, TagTCPKeepaliveResp)
+	}
+	if !containsTag(resp.Hints.Tags, TagTCPKeepaliveResp) {
+		t.Fatalf("tags = %v, want %q", resp.Hints.Tags, TagTCPKeepaliveResp)
+	}
+	if !containsTag(resp.Hints.Tags, TagTCPKeepalive) {
+		t.Fatalf("tags = %v, want %q", resp.Hints.Tags, TagTCPKeepalive)
+	}
+}
+
+func TestTrackerCleanupExpiredFlows(t *testing.T) {
+	cfg := DefaultConfig()
+	cfg.ConnectionTimeout = time.Second
+	cfg.CleanupInterval = 0
+
+	decoder := NewDecoder()
+	tracker := NewTrackerWithConfig(cfg)
+	defer tracker.Stop()
+
+	stale, err := decoder.Decode(mustBuildTCPPacket(t, time.Now().Add(-5*time.Second), tcpPacketSpec{
+		srcIP:   "10.0.0.1",
+		dstIP:   "10.0.0.2",
+		srcPort: 12345,
+		dstPort: 80,
+		seq:     100,
+		syn:     true,
+		window:  4096,
+	}))
+	if err != nil {
+		t.Fatalf("decode stale packet: %v", err)
+	}
+	if _, err := tracker.Observe(stale); err != nil {
+		t.Fatalf("observe stale packet: %v", err)
+	}
+
+	fresh, err := decoder.Decode(mustBuildTCPPacket(t, time.Now(), tcpPacketSpec{
+		srcIP:   "10.0.0.3",
+		dstIP:   "10.0.0.4",
+		srcPort: 23456,
+		dstPort: 443,
+		seq:     200,
+		syn:     true,
+		window:  4096,
+	}))
+	if err != nil {
+		t.Fatalf("decode fresh packet: %v", err)
+	}
+	if _, err := tracker.Observe(fresh); err != nil {
+		t.Fatalf("observe fresh packet: %v", err)
+	}
+
+	if got := tracker.ActiveFlowCount(); got != 2 {
+		t.Fatalf("active flow count = %d, want 2", got)
+	}
+	if removed := tracker.CleanupExpiredFlows(); removed != 1 {
+		t.Fatalf("removed stale flows = %d, want 1", removed)
+	}
+	if got := tracker.ActiveFlowCount(); got != 1 {
+		t.Fatalf("active flow count after cleanup = %d, want 1", got)
+	}
+}
+
+func containsTag(tags []Tag, want Tag) bool {
+	for _, tag := range tags {
+		if tag == want {
+			return true
+		}
+	}
+	return false
+}

conn_map.go

@@ -0,0 +1,50 @@
+package bcap
+
+import (
+	"strings"
+	"sync"
+)
+
+func fnvHash(key string) uint32 {
+	hash := uint32(2166136261)
+	for i := 0; i < len(key); i++ {
+		hash ^= uint32(key[i])
+		hash *= 16777619
+	}
+	return hash
+}
+
+var stringBuilderPool = sync.Pool{
+	New: func() interface{} {
+		return &strings.Builder{}
+	},
+}
+
+func getStringBuilder() *strings.Builder {
+	return stringBuilderPool.Get().(*strings.Builder)
+}
+
+func putStringBuilder(sb *strings.Builder) {
+	sb.Reset()
+	stringBuilderPool.Put(sb)
+}
+
+func buildKey(protocol, srcIP, srcPort, dstIP, dstPort string) string {
+	sb := getStringBuilder()
+	defer putStringBuilder(sb)
+
+	sb.WriteString(protocol)
+	sb.WriteString("://")
+	sb.WriteString(srcIP)
+	if srcPort != "" {
+		sb.WriteString(":")
+		sb.WriteString(srcPort)
+	}
+	sb.WriteString("=")
+	sb.WriteString(dstIP)
+	if dstPort != "" {
+		sb.WriteString(":")
+		sb.WriteString(dstPort)
+	}
+	return sb.String()
+}

decoder.go

@@ -0,0 +1,227 @@
+package bcap
+
+import (
+	"net"
+	"strconv"
+	"time"
+
+	"github.com/gopacket/gopacket"
+	"github.com/gopacket/gopacket/layers"
+)
+
+type DecodeOptions struct {
+	BaseTime       time.Time
+	SrcMACOverride net.HardwareAddr
+}
+
+type Decoder struct{}
+
+func NewDecoder() *Decoder {
+	return &Decoder{}
+}
+
+func (d *Decoder) Decode(packet gopacket.Packet) (Packet, error) {
+	return d.DecodeWithOptions(packet, DecodeOptions{})
+}
+
+func (d *Decoder) DecodeWithOptions(packet gopacket.Packet, opts DecodeOptions) (Packet, error) {
+	var decoded Packet
+
+	decoded.Raw.Packet = packet
+	if metadata := packet.Metadata(); metadata != nil {
+		decoded.Meta.Timestamp = metadata.Timestamp
+		decoded.Meta.TimestampMicros = metadata.Timestamp.UnixMicro()
+		decoded.Meta.CaptureLength = metadata.CaptureLength
+		decoded.Meta.Length = metadata.Length
+		if !opts.BaseTime.IsZero() {
+			decoded.Meta.RelativeTime = metadata.Timestamp.Sub(opts.BaseTime)
+		}
+	} else {
+		decoded.Meta.Timestamp = time.Now()
+		decoded.Meta.TimestampMicros = decoded.Meta.Timestamp.UnixMicro()
+	}
+
+	decodeLinkLayer(&decoded, packet)
+	if len(opts.SrcMACOverride) > 0 {
+		decoded.Link.SrcMAC = append(net.HardwareAddr(nil), opts.SrcMACOverride...)
+	}
+
+	if arpLayer := packet.Layer(layers.LayerTypeARP); arpLayer != nil {
+		arp, ok := arpLayer.(*layers.ARP)
+		if !ok {
+			return decoded, NewParseError(ErrTypeNetwork, "ARP", "invalid arp layer", nil)
+		}
+		decodeARP(&decoded, arp)
+		return decoded, nil
+	}
+
+	if err := decodeNetworkLayer(&decoded, packet); err != nil {
+		return decoded, err
+	}
+	decodeTransportLayer(&decoded, packet)
+	return decoded, nil
+}
+
+func decodeLinkLayer(decoded *Packet, packet gopacket.Packet) {
+	decoded.Link.Kind = LinkKindUnknown
+
+	if ethLayer := packet.Layer(layers.LayerTypeEthernet); ethLayer != nil {
+		if eth, ok := ethLayer.(*layers.Ethernet); ok {
+			decoded.Link.Kind = LinkKindEthernet
+			decoded.Link.SrcMAC = append(net.HardwareAddr(nil), eth.SrcMAC...)
+			decoded.Link.DstMAC = append(net.HardwareAddr(nil), eth.DstMAC...)
+			return
+		}
+	}
+	if sllLayer := packet.Layer(layers.LayerTypeLinuxSLL); sllLayer != nil {
+		if sll, ok := sllLayer.(*layers.LinuxSLL); ok {
+			decoded.Link.Kind = LinkKindLinuxSLL
+			if sll.AddrType == 1 && sll.AddrLen == 6 {
+				decoded.Link.SrcMAC = append(net.HardwareAddr(nil), sll.Addr...)
+			}
+			return
+		}
+	}
+	if sll2Layer := packet.Layer(layers.LayerTypeLinuxSLL2); sll2Layer != nil {
+		if sll2, ok := sll2Layer.(*layers.LinuxSLL2); ok {
+			decoded.Link.Kind = LinkKindLinuxSLL2
+			if sll2.ARPHardwareType == 1 && sll2.AddrLength == 6 {
+				decoded.Link.SrcMAC = append(net.HardwareAddr(nil), sll2.Addr...)
+			}
+		}
+	}
+}
+
+func decodeARP(decoded *Packet, arp *layers.ARP) {
+	decoded.Network.Family = NetworkFamilyARP
+	decoded.Network.ProtocolNumber = uint16(arp.Protocol)
+	decoded.Network.ARP = &ARPFacts{
+		Operation: arp.Operation,
+		SenderMAC: append(net.HardwareAddr(nil), arp.SourceHwAddress...),
+		TargetMAC: append(net.HardwareAddr(nil), arp.DstHwAddress...),
+		SenderIP:  arpProtocolAddressString(arp.SourceProtAddress),
+		TargetIP:  arpProtocolAddressString(arp.DstProtAddress),
+	}
+	decoded.Network.SrcIP = decoded.Network.ARP.SenderIP
+	decoded.Network.DstIP = decoded.Network.ARP.TargetIP
+	decoded.Transport.Kind = ProtocolARP
+}
+
+func arpProtocolAddressString(raw []byte) string {
+	switch len(raw) {
+	case net.IPv4len:
+		return net.IP(raw).String()
+	case net.IPv6len:
+		return net.IP(raw).String()
+	default:
+		return ""
+	}
+}
+
+func decodeNetworkLayer(decoded *Packet, packet gopacket.Packet) error {
+	nw := packet.NetworkLayer()
+	if nw == nil {
+		return NewParseError(ErrTypeNetwork, "Network", "no valid network layer found", nil)
+	}
+
+	src, dst := nw.NetworkFlow().Endpoints()
+	decoded.Network.SrcIP = src.String()
+	decoded.Network.DstIP = dst.String()
+
+	switch layer := nw.(type) {
+	case *layers.IPv4:
+		decoded.Network.Family = NetworkFamilyIPv4
+		decoded.Network.TTL = layer.TTL
+		decoded.Network.ProtocolNumber = uint16(layer.Protocol)
+	case *layers.IPv6:
+		decoded.Network.Family = NetworkFamilyIPv6
+		decoded.Network.HopLimit = layer.HopLimit
+		decoded.Network.ProtocolNumber = uint16(layer.NextHeader)
+	default:
+		decoded.Network.Family = NetworkFamilyUnknown
+	}
+	return nil
+}
+
+func decodeTransportLayer(decoded *Packet, packet gopacket.Packet) {
+	if tcpLayer := packet.Layer(layers.LayerTypeTCP); tcpLayer != nil {
+		if tcp, ok := tcpLayer.(*layers.TCP); ok {
+			payloadLen := len(tcpLayer.LayerPayload())
+			decoded.Transport.Kind = ProtocolTCP
+			decoded.Transport.Payload = payloadLen
+			decoded.Transport.TCP = &TCPFacts{
+				SrcPort:  strconv.Itoa(int(tcp.SrcPort)),
+				DstPort:  strconv.Itoa(int(tcp.DstPort)),
+				Seq:      tcp.Seq,
+				Ack:      tcp.Ack,
+				Window:   tcp.Window,
+				SYN:      tcp.SYN,
+				ACK:      tcp.ACK,
+				FIN:      tcp.FIN,
+				RST:      tcp.RST,
+				ECE:      tcp.ECE,
+				CWR:      tcp.CWR,
+				PSH:      tcp.PSH,
+				Checksum: tcp.Checksum,
+				Payload:  payloadLen,
+			}
+			return
+		}
+	}
+	if udpLayer := packet.Layer(layers.LayerTypeUDP); udpLayer != nil {
+		if udp, ok := udpLayer.(*layers.UDP); ok {
+			payloadLen := len(udpLayer.LayerPayload())
+			decoded.Transport.Kind = ProtocolUDP
+			decoded.Transport.Payload = payloadLen
+			decoded.Transport.UDP = &UDPFacts{
+				SrcPort: strconv.Itoa(int(udp.SrcPort)),
+				DstPort: strconv.Itoa(int(udp.DstPort)),
+				Length:  udp.Length,
+				Payload: payloadLen,
+			}
+			return
+		}
+	}
+	if icmpLayer := packet.Layer(layers.LayerTypeICMPv4); icmpLayer != nil {
+		if icmp, ok := icmpLayer.(*layers.ICMPv4); ok {
+			payloadLen := len(icmpLayer.LayerPayload())
+			decoded.Transport.Kind = ProtocolICMPv4
+			decoded.Transport.Payload = payloadLen
+			decoded.Transport.ICMP = &ICMPFacts{
+				Version:  4,
+				Type:     uint8(icmp.TypeCode.Type()),
+				Code:     uint8(icmp.TypeCode.Code()),
+				Checksum: icmp.Checksum,
+				ID:       icmp.Id,
+				Seq:      icmp.Seq,
+				Payload:  payloadLen,
+			}
+			return
+		}
+	}
+	if icmpLayer := packet.Layer(layers.LayerTypeICMPv6); icmpLayer != nil {
+		if icmp, ok := icmpLayer.(*layers.ICMPv6); ok {
+			payloadLen := len(icmpLayer.LayerPayload())
+			decoded.Transport.Kind = ProtocolICMPv6
+			decoded.Transport.Payload = payloadLen
+			decoded.Transport.ICMP = &ICMPFacts{
+				Version:  6,
+				Type:     uint8(icmp.TypeCode.Type()),
+				Code:     uint8(icmp.TypeCode.Code()),
+				Checksum: icmp.Checksum,
+				Payload:  payloadLen,
+			}
+			return
+		}
+	}
+
+	var payloadLen int
+	if app := packet.ApplicationLayer(); app != nil {
+		payloadLen = len(app.Payload())
+	} else if nw := packet.NetworkLayer(); nw != nil {
+		payloadLen = len(nw.LayerPayload())
+	}
+	decoded.Transport.Kind = ProtocolUnknown
+	decoded.Transport.Payload = payloadLen
+	decoded.Transport.Unknown = &UnknownTransportFacts{Payload: payloadLen}
+}

doc/api.md

@@ -0,0 +1,726 @@
+# bcap API 手册
+
+开发者参考文档。快速接入说明见 [`../README.md`](../README.md)。
+
+## 1. 主包职责
+
+主包负责：
+
+- 统一的报文事实层
+- 统一的 flow 表达
+- 统一的轻量 hint 层
+- 以 TCP 为重点的轻状态跟踪
+
+主包不负责：
+
+- 报告生成
+- 业务规则判断
+- 用户侧展示文案
+- 动作编排
+- 深度流重组
+- 应用层协议解析框架
+
+核心对象：
+
+- `Decoder`
+  - 单包事实解码
+- `Tracker`
+  - flow 状态与轻量提示
+- `Analyzer`
+  - `Decoder + Tracker` 组合入口
+
+## 2. 公开入口
+
+### 2.1 `Decoder`
+
+构造：
+
+```go
+decoder := bcap.NewDecoder()
+```
+
+主要方法：
+
+```go
+Decode(packet gopacket.Packet) (Packet, error)
+DecodeWithOptions(packet gopacket.Packet, opts DecodeOptions) (Packet, error)
+```
+
+使用时机：
+
+- 只想获得单包事实
+- 自己维护状态机
+- 想把 `bcap` 当作标准化事实提取层
+
+### 2.2 `Tracker`
+
+构造：
+
+```go
+tracker := bcap.NewTracker()
+tracker := bcap.NewTrackerWithConfig(cfg)
+```
+
+主要方法：
+
+```go
+Observe(packet Packet) (Observation, error)
+CleanupExpiredFlows() int
+ActiveFlowCount() int
+Stop()
+```
+
+使用时机：
+
+- 已经在别处完成解码
+- 只想复用 `bcap` 的 flow / hint 跟踪能力
+
+### 2.3 `Analyzer`
+
+构造：
+
+```go
+analyzer := bcap.NewAnalyzer()
+analyzer := bcap.NewAnalyzerWithConfig(cfg)
+```
+
+主要方法：
+
+```go
+ObservePacket(packet gopacket.Packet) (Observation, error)
+ObservePacketWithOptions(packet gopacket.Packet, opts DecodeOptions) (Observation, error)
+Decoder() *Decoder
+Tracker() *Tracker
+Stop()
+```
+
+使用时机：
+
+- 在线抓包
+- 离线遍历
+- 绝大多数直接接入型工具
+
+## 3. `DecodeOptions`
+
+`DecodeOptions` 目前包含两个字段：
+
+```go
+type DecodeOptions struct {
+    BaseTime       time.Time
+    SrcMACOverride net.HardwareAddr
+}
+```
+
+字段：
+
+- `BaseTime`
+  - 用于计算 `Packet.Meta.RelativeTime`
+  - `Analyzer.ObservePacket(...)` 未显式传入时，会自动以首包时间作为基准
+- `SrcMACOverride`
+  - 用于覆盖源 MAC
+
+## 4. 数据模型
+
+### 4.1 `Packet`
+
+`Packet` 表示单包事实。
+
+```go
+type Packet struct {
+    Meta      Meta
+    Link      LinkFacts
+    Network   NetworkFacts
+    Transport TransportFacts
+    Raw       RawFacts
+}
+```
+
+不包含跨包推断结果。
+
+### 4.2 `Meta`
+
+```go
+type Meta struct {
+    Timestamp       time.Time
+    TimestampMicros int64
+    RelativeTime    time.Duration
+    CaptureLength   int
+    Length          int
+}
+```
+
+字段：
+
+- `Timestamp` / `TimestampMicros`
+  - 捕获时间
+- `RelativeTime`
+  - 相对 `BaseTime` 的时间差
+- `CaptureLength`
+  - 实际捕获长度
+- `Length`
+  - 原始报文长度
+
+### 4.3 `LinkFacts`
+
+```go
+type LinkFacts struct {
+    Kind   LinkKind
+    SrcMAC net.HardwareAddr
+    DstMAC net.HardwareAddr
+}
+```
+
+当前支持的链路类型：
+
+- `LinkKindEthernet`
+- `LinkKindLinuxSLL`
+- `LinkKindLinuxSLL2`
+- `LinkKindUnknown`
+
+### 4.4 `NetworkFacts`
+
+```go
+type NetworkFacts struct {
+    Family         NetworkFamily
+    SrcIP          string
+    DstIP          string
+    TTL            uint8
+    HopLimit       uint8
+    ProtocolNumber uint16
+    ARP            *ARPFacts
+}
+```
+
+当前支持的网络族：
+
+- `NetworkFamilyIPv4`
+- `NetworkFamilyIPv6`
+- `NetworkFamilyARP`
+- `NetworkFamilyUnknown`
+
+备注：
+
+- IPv4 报文主要填 `TTL`
+- IPv6 报文主要填 `HopLimit`
+- ARP 报文会同时填充 `ARP`
+
+### 4.5 `TransportFacts`
+
+```go
+type TransportFacts struct {
+    Kind    ProtocolKind
+    Payload int
+    TCP     *TCPFacts
+    UDP     *UDPFacts
+    ICMP    *ICMPFacts
+    Unknown *UnknownTransportFacts
+}
+```
+
+当前支持协议：
+
+- `ProtocolTCP`
+- `ProtocolUDP`
+- `ProtocolICMPv4`
+- `ProtocolICMPv6`
+- `ProtocolARP`
+- `ProtocolUnknown`
+
+### 4.6 协议事实结构
+
+#### `TCPFacts`
+
+```go
+type TCPFacts struct {
+    SrcPort  string
+    DstPort  string
+    Seq      uint32
+    Ack      uint32
+    Window   uint16
+    SYN      bool
+    ACK      bool
+    FIN      bool
+    RST      bool
+    ECE      bool
+    CWR      bool
+    PSH      bool
+    Checksum uint16
+    Payload  int
+}
+```
+
+#### `UDPFacts`
+
+```go
+type UDPFacts struct {
+    SrcPort string
+    DstPort string
+    Length  uint16
+    Payload int
+}
+```
+
+#### `ICMPFacts`
+
+```go
+type ICMPFacts struct {
+    Version  int
+    Type     uint8
+    Code     uint8
+    Checksum uint16
+    ID       uint16
+    Seq      uint16
+    Payload  int
+}
+```
+
+#### `ARPFacts`
+
+```go
+type ARPFacts struct {
+    Operation uint16
+    SenderMAC net.HardwareAddr
+    TargetMAC net.HardwareAddr
+    SenderIP  string
+    TargetIP  string
+}
+```
+
+### 4.7 `FlowKey` / `FlowRef`
+
+推荐使用结构化 flow，不把字符串 key 当成唯一公共接口。
+
+```go
+type Endpoint struct {
+    IP   string
+    Port string
+}
+
+type FlowKey struct {
+    Family   NetworkFamily
+    Protocol ProtocolKind
+    Src      Endpoint
+    Dst      Endpoint
+}
+
+type FlowRef struct {
+    Forward FlowKey
+    Reverse FlowKey
+    Stable  string
+}
+```
+
+方法：
+
+```go
+func (f FlowKey) StableString() string
+```
+
+字段：
+
+- `Forward`
+  - 当前方向
+- `Reverse`
+  - 反向方向
+- `Stable`
+  - 稳定字符串表达，可用于日志和 map key
+
+### 4.8 `Observation`
+
+```go
+type Observation struct {
+    Packet Packet
+    Flow   FlowRef
+    Hints  HintSet
+}
+```
+
+- `Packet`
+  - 报文事实
+- `Flow`
+  - 流引用
+- `Hints`
+  - 推断结果
+
+## 5. Hint 模型
+
+### 5.1 `HintSet`
+
+```go
+type HintSet struct {
+    Summary SummaryHint
+    Tags    []Tag
+
+    TCP  *TCPHint
+    UDP  *UDPHint
+    ICMP *ICMPHint
+    ARP  *ARPHint
+}
+```
+
+- `Summary`
+  - 摘要代码
+- `Tags`
+  - 标签集合
+- 协议专属 hint
+  - 放在对应子结构中
+
+### 5.2 TCP hints
+
+```go
+type TCPHint struct {
+    Phase             TCPPhase
+    Event             TCPEvent
+    LegacyState       uint8
+    Seq               uint32
+    Ack               uint32
+    Window            uint16
+    Payload           int
+    Retransmission    bool
+    Keepalive         bool
+    KeepaliveResponse bool
+    RST               bool
+    ECE               bool
+    CWR               bool
+}
+```
+
+Phase：
+
+- `TCPPhaseHandshake`
+- `TCPPhaseEstablished`
+- `TCPPhaseTeardown`
+- `TCPPhaseSpecial`
+- `TCPPhaseUnknown`
+
+Event：
+
+- `TCPEventSYN`
+- `TCPEventSYNACK`
+- `TCPEventHandshakeACK`
+- `TCPEventACK`
+- `TCPEventRetransmission`
+- `TCPEventKeepalive`
+- `TCPEventKeepaliveResp`
+- `TCPEventFIN`
+- `TCPEventFINACK`
+- `TCPEventTeardownACK`
+- `TCPEventRST`
+- `TCPEventECE`
+- `TCPEventCWR`
+- `TCPEventUnknown`
+
+常见 Tag：
+
+- `TagTCPHandshakeSYN`
+- `TagTCPHandshakeSYNACK`
+- `TagTCPHandshakeACK`
+- `TagTCPTeardownFIN`
+- `TagTCPTeardownFINACK`
+- `TagTCPTeardownACK`
+- `TagTCPPacket`
+- `TagTCPRetransmit`
+- `TagTCPKeepalive`
+- `TagTCPKeepaliveResp`
+- `TagTCPRst`
+- `TagTCPEce`
+- `TagTCPCwr`
+
+### 5.3 UDP / ICMP / ARP hints
+
+#### `UDPHint`
+
+```go
+type UDPHint struct {
+    Payload int
+}
+```
+
+对应 Tag：
+
+- `TagUDPPacket`
+
+#### `ICMPHint`
+
+```go
+type ICMPHint struct {
+    Version        int
+    Type           uint8
+    Code           uint8
+    IsEcho         bool
+    IsEchoReply    bool
+    IsUnreachable  bool
+    IsTimeExceeded bool
+}
+```
+
+对应 Tag：
+
+- `TagICMPPacket`
+- `TagICMPEchoRequest`
+- `TagICMPEchoReply`
+- `TagICMPUnreachable`
+- `TagICMPTimeExceeded`
+
+#### `ARPHint`
+
+```go
+type ARPHint struct {
+    Operation uint16
+    Request   bool
+    Reply     bool
+}
+```
+
+对应 Tag：
+
+- `TagARPRequest`
+- `TagARPReply`
+
+## 6. TCP 跟踪边界
+
+`Tracker` 对 TCP 只做轻量跟踪，不做完整 TCP 栈模拟。
+
+当前覆盖：
+
+- 握手识别
+- 挥手识别
+- 普通 ACK 识别
+- 重传识别
+- keepalive 识别
+- keepalive response 识别
+- RST / ECE / CWR 识别
+
+实现说明：
+
+- 基于 flow 跟踪
+- 使用有限 segment 记忆辅助判断重传
+- keepalive 使用启发式判断
+- 支持超时清理
+
+不覆盖：
+
+- 严格 TCP 协议验证
+- 深度重组
+- 业务级根因结论
+
+## 7. 配置
+
+### 7.1 `PacketsConfig`
+
+```go
+type PacketsConfig struct {
+    ConnectionTimeout time.Duration
+    CleanupInterval   time.Duration
+}
+```
+
+字段：
+
+- `ConnectionTimeout`
+  - flow 状态保留时长
+- `CleanupInterval`
+  - 自动清理周期
+
+默认值：
+
+```go
+const (
+    DefaultConnectionTimeout = 5 * time.Minute
+    DefaultCleanupInterval   = 1 * time.Minute
+)
+```
+
+默认配置：
+
+```go
+cfg := bcap.DefaultConfig()
+```
+
+### 7.2 生命周期方法
+
+`Tracker`：
+
+- `CleanupExpiredFlows() int`
+- `ActiveFlowCount() int`
+- `Stop()`
+
+`Analyzer`：
+
+- `Decoder() *Decoder`
+- `Tracker() *Tracker`
+- `Stop()`
+
+备注：
+
+- 长生命周期进程退出前调用 `Stop()`
+- 如需自行控制清理节奏，可将 `CleanupInterval` 设为 `0`，再手动调用 `CleanupExpiredFlows()`
+
+## 8. 错误模型
+
+`bcap` 使用 `*ParseError` 表达解析问题：
+
+```go
+type ParseError struct {
+    Type    ParseErrorType
+    Layer   string
+    Message string
+    Err     error
+}
+```
+
+错误类型：
+
+- `ErrTypeLinkLayer`
+- `ErrTypeNetwork`
+- `ErrTypeTransport`
+- `ErrTypeUnsupported`
+
+常见触发条件：
+
+- 没有有效网络层
+- 协议层对象类型不匹配
+- 跟踪阶段缺少必须的协议事实
+
+## 9. 子包
+
+### 9.1 `libpcap`
+
+`libpcap` 子包负责在线抓包输入。
+
+入口：
+
+- `FindAllDevs()`
+- `NewCatch(host, filter)`
+- `NewCatchEth(eth, filter)`
+- `SetRecall(func(gopacket.Packet))`
+- `Run()`
+- `Stop()`
+
+常见组合：
+
+- 子包接收 `gopacket.Packet`
+- 主包 `Analyzer` 做解析和提示
+- 上层工具做展示和统计
+
+### 9.2 `nfq`
+
+`nfq` 子包负责 NFQUEUE 输入适配。
+
+入口：
+
+- `NewNfQueue(ctx, queid, maxqueue)`
+- `SetRecall(func(id uint32, q *nfqueue.Nfqueue, p Packet))`
+- `Run()`
+- `Stop()`
+
+备注：
+
+- `nfq.Packet` 只是 NFQUEUE 输入包装
+- 它不是主包的 `bcap.Packet`
+- 一般仍然从其中取 `gopacket.Packet`，再交给 `Analyzer` 或 `Decoder`
+
+## 10. 示例
+
+### 10.1 直接用 `Analyzer`
+
+```go
+analyzer := bcap.NewAnalyzer()
+defer analyzer.Stop()
+
+obs, err := analyzer.ObservePacket(packet)
+if err != nil {
+	return err
+}
+
+fmt.Println(obs.Flow.Stable)
+fmt.Println(obs.Packet.Transport.Kind)
+fmt.Println(obs.Hints.Summary.Code)
+```
+
+### 10.2 自己管理解码和跟踪
+
+```go
+decoder := bcap.NewDecoder()
+tracker := bcap.NewTracker()
+defer tracker.Stop()
+
+decoded, err := decoder.DecodeWithOptions(packet, bcap.DecodeOptions{
+	BaseTime: firstPacketTS,
+})
+if err != nil {
+	return err
+}
+
+obs, err := tracker.Observe(decoded)
+if err != nil {
+	return err
+}
+```
+
+### 10.3 典型离线遍历
+
+```go
+f, err := os.Open("sample.pcap")
+if err != nil {
+	return err
+}
+defer f.Close()
+
+reader, err := pcapgo.NewReader(f)
+if err != nil {
+	return err
+}
+
+source := gopacket.NewPacketSource(reader, reader.LinkType())
+analyzer := bcap.NewAnalyzer()
+defer analyzer.Stop()
+
+for packet := range source.Packets() {
+	obs, err := analyzer.ObservePacket(packet)
+	if err != nil {
+		continue
+	}
+	fmt.Println(obs.Packet.Network.SrcIP, obs.Hints.Summary.Code)
+}
+```
+
+## 11. 辅助函数
+
+主包还提供两个轻量格式化函数：
+
+- `FormatDuration(time.Duration) string`
+- `FormatBytes(uint64) string`
+
+用于轻量日志与终端展示。
+
+## 12. 迁移说明
+
+主包旧接口已经被清理，删除项包括：
+
+- `Packets`
+- `PacketInfo`
+- `ParsePacket`
+- `NewPackets`
+- `NewPacketsWithConfig`
+- `LegacyPacketInfoFromObservation`
+- `GetStateDescription`
+- `PrintStats`
+- `ExportConnectionsToJSON`
+
+迁移方向：
+
+- 旧的单包解析入口迁到 `Decoder`
+- 旧的“包 + 状态”混合对象迁到 `Observation`
+- 旧的连接跟踪职责迁到 `Tracker`
+- 大部分调用场景直接迁到 `Analyzer`
+
+旧代码如果大量依赖字符串 key：
+
+- 新代码优先改为使用 `FlowRef.Forward` / `FlowRef.Reverse`
+- 如果只是为了日志或 map key，可以继续使用 `FlowRef.Stable`
+
+## 13. 相关文档
+
+- 快速入口见 [`../README.md`](../README.md)
+- 设计备忘见 [`dev.md`](./dev.md)

doc/dev.md

@@ -0,0 +1,518 @@
+# bcap 开发设计备忘
+
+## 1. 这次重构的前提
+
+当前已确认，直接使用 `bcap` 主包的范围很小，主要只有：
+
+- `apps/tcp`
+- `apps/b612` 中的 `tcm`
+- `apps/b612` 中的 `tcpkill`
+
+因此这次讨论 `bcap` 新架构时，可以明确采用以下前提：
+
+1. 可以摒弃旧接口，不必为了兼容历史调用持续背负旧模型。
+2. `bcap` 子包暂时不动，尤其是 `libpcap`、`nfq` 这类输入适配层先保持现状。
+3. 重点只讨论 `bcap` 主包的新职责、新模型和新接口。
+
+## 2. 当前主包存在的问题
+
+当前 `bcap` 主包中，`Packets`、`PacketInfo`、`StateDescript` 这一套模型混合了承担以下几类职责：
+
+- 报文事实解码
+- TCP 状态推断
+- 连接状态缓存
+- 统计汇总
+- 工具侧临时状态寄存
+- 文本格式化辅助
+
+这几个职责混在一起，直接导致了以下问题：
+
+### 2.1 `PacketInfo` 同时承载“事实”和“推断”
+
+例如：
+
+- `SrcIP`、`DstIP`、`SrcMac`、`DstMac` 属于原始事实
+- `TcpSeq`、`TcpAck`、`TcpWindow` 虽然也是事实，但只适用于 TCP
+- `StateDescript` 则是推断结果
+- `Comment` 又是工具业务的临时状态
+
+这会让上层调用方无法区分：哪些字段是包里本来就有的，哪些字段是状态机推出来的，哪些字段甚至只是上层工具临时借位存进去的。
+
+### 2.2 主包过于 TCP 化
+
+当前主模型的核心字段和访问器明显偏向 TCP：
+
+- `TcpSeq()`
+- `TcpAck()`
+- `TcpWindow()`
+- `TcpPayloads()`
+- `StateDescript()`
+
+虽然已经开始支持 UDP、ICMP、ICMPv6，但整体接口风格仍然默认“TCP 才是主角，其他协议只是附带”。如果目标是做“通用 transport/protocol hint”，这个建模方式会持续妨碍扩展。
+
+### 2.3 `Packets` 同时是解析器、状态仓库和工具 scratchpad
+
+当前 `Packets` 既负责：
+
+- 解析 gopacket.Packet
+- 保存连接状态
+- 维护统计
+- 暴露 `Key()` 查询
+- 暴露 `SetComment()` 给上层写入工具状态
+
+这实际上把“协议解析层”和“工具业务状态层”耦死了。
+
+### 2.4 字符串 key 被当成核心接口
+
+当前以 `tcp://a:b-c:d` 这类字符串 key 作为主要流标识，这虽然方便快速实现，但不适合作为长期公共接口。
+
+问题包括：
+
+- 协议语义不够结构化
+- 上层反复自行拼 key
+- 不利于未来支持可逆 flow、单向 packet、无端口协议、ARP 等场景
+
+### 2.5 文本格式化与 JSON 导出混入主包
+
+像 `GetStateDescription`、`PrintStats`、`ExportConnectionsToJSON` 这种能力，不属于主包核心解析模型，应该降级为上层工具职责，或者至少转到辅助层，而不是继续成为主接口的一部分。
+
+## 3. 新架构的总体目标
+
+`bcap` 主包应收敛成：
+
+- 一个统一的报文事实解码层
+- 一个统一的协议 hint 推断层
+- 一个以 TCP 为重点的轻量状态跟踪层
+
+同时明确边界：
+
+### 3.1 `bcap` 应负责的事
+
+- 识别链路层、网络层、传输层协议
+- 提取结构化元数据
+- 输出通用 protocol hint
+- 对 TCP 做轻状态推断
+- 对 UDP/ICMP/ARP 做协议识别和元数据抽取
+- 对未知协议输出“尽量完整的基础事实”
+
+### 3.2 `bcap` 不应负责的事
+
+- 诊断报告拼装
+- 干预动作编排
+- CLI/TUI 展示文案
+- 工具侧临时状态寄存
+- 业务策略倒计时
+- 面向最终用户的统计打印
+
+也就是说，`bcap` 的定位应是“提供事实和提示”，而不是“替工具做决策”。
+
+## 4. 新架构的核心分层
+
+建议主包收敛成 3 个核心对象：
+
+1. `Decoder`
+2. `Tracker`
+3. `Analyzer`
+
+### 4.1 `Decoder`
+
+`Decoder` 是无状态组件，只负责把 `gopacket.Packet` 解码成结构化“事实”。
+
+职责：
+
+- 识别 L2/L3/L4 协议
+- 抽取 MAC、IP、端口、TTL、flags、payload 长度等事实
+- 不做跨包状态推断
+- 不维护连接表
+- 不暴露工具业务状态
+
+### 4.2 `Tracker`
+
+`Tracker` 是有状态组件，只负责基于连续观测结果做轻量 hint 推断。
+
+职责：
+
+- 维护按 flow 组织的轻状态
+- 针对 TCP 输出握手、挥手、重传、keepalive、RST 等 hint
+- 针对 ICMP/ARP 等协议补充轻量语义标签
+- 不负责最终展示
+- 不负责业务动作控制
+
+### 4.3 `Analyzer`
+
+`Analyzer` 是便捷组合层，内部持有 `Decoder + Tracker`，给上层一个简单入口。
+
+典型用途：
+
+- `tcm` / `tcml` 这种一边收包一边展示的工具
+- `diag` 这种离线分析工具
+- `show` 这种需要 packet facts + hints 的浏览工具
+
+这样设计后：
+
+- 只关心事实解码的调用方可直接用 `Decoder`
+- 需要 hint 的调用方可用 `Analyzer`
+- 需要更细粒度控制的调用方可分别持有 `Decoder` 和 `Tracker`
+
+## 5. 新的数据模型
+
+新模型建议明确拆成“事实”和“推断”两层。
+
+### 5.1 第一层：Packet Facts
+
+建议定义统一的结构化事实模型，例如：
+
+```go
+type Packet struct {
+    Meta      Meta
+    Link      LinkFacts
+    Network   NetworkFacts
+    Transport TransportFacts
+    Raw       RawFacts
+}
+```
+
+其中：
+
+- `Meta`：时间戳、捕获长度、原始长度、相对时间等
+- `LinkFacts`：链路层类型、源/目标 MAC、链路层协议等
+- `NetworkFacts`：IPv4/IPv6/ARP 等信息，包含地址、TTL/HopLimit、fragment、protocol number 等
+- `TransportFacts`：TCP/UDP/ICMP/unknown 等结构化内容
+- `RawFacts`：payload 长度、原始 packet 引用等
+
+这层全部表示“包里本来就有”的事实，不包含推断结论。
+
+### 5.2 第二层：Observation
+
+建议把“经过跟踪器分析后的结果”定义为单独对象：
+
+```go
+type Observation struct {
+    Packet Packet
+    Flow   FlowRef
+    Hints  HintSet
+}
+```
+
+这里：
+
+- `Packet` 是原始事实
+- `Flow` 是结构化流引用
+- `Hints` 是推断结果
+
+### 5.3 FlowKey / FlowRef
+
+建议引入结构化 flow 标识，而不是继续把字符串 key 作为主接口。
+
+```go
+type FlowKey struct {
+    Family   NetworkFamily
+    Protocol TransportKind
+    Src      Endpoint
+    Dst      Endpoint
+}
+
+type FlowRef struct {
+    Forward FlowKey
+    Reverse FlowKey
+    Stable  string
+}
+```
+
+其中：
+
+- `Forward` / `Reverse` 提供方向化 key
+- `Stable` 可以保留字符串形式，方便日志、map key、兼容旧调试习惯
+- `Endpoint` 应允许“只有地址没有端口”的协议
+
+### 5.4 HintSet
+
+建议将所有推断信息挂在 `HintSet` 上：
+
+```go
+type HintSet struct {
+    Summary SummaryHint
+    Tags    []Tag
+
+    TCP  *TCPHint
+    UDP  *UDPHint
+    ICMP *ICMPHint
+    ARP  *ARPHint
+}
+```
+
+这样做的好处是：
+
+- `Summary` 提供给 `tcm/tcml` 这类工具快速展示一句话
+- `Tags` 提供统一筛选、着色、统计能力
+- 协议专属 hint 由独立结构体承载，不再污染通用顶层对象
+
+## 6. 协议专属 hint 的建议形态
+
+### 6.1 `TCPHint`
+
+`TCPHint` 是新架构里的重点能力，建议承载：
+
+- seq / ack / window
+- flags
+- payload length
+- options 摘要
+- handshake / teardown 阶段
+- retransmission 判定
+- keepalive 判定
+- keepalive response 判定
+- rst / ece / cwr 等特殊标记
+- 是否疑似 out-of-order
+
+同时建议把原来的 `StateDescript uint8` 弃用，改成更结构化的字段或 tag，例如：
+
+- `Phase: TCPPhase`
+- `Event: TCPEvent`
+- `Tags: []Tag`
+
+### 6.2 `UDPHint`
+
+UDP 先做轻支持即可，建议包括：
+
+- payload length
+- checksum presence / checksum value
+- zero-length payload
+- fragment 上下文关联信息（如果网络层提供）
+
+不建议在主包内直接引入 DNS、QUIC 等应用层推断，除非后续确认收益足够大。
+
+### 6.3 `ICMPHint`
+
+建议至少包括：
+
+- family: v4 / v6
+- type / code
+- id / seq
+- 是否 echo request / echo reply
+- 是否 destination unreachable / time exceeded
+
+这层对 `show` 和 `tcm/tcml` 的“多协议展示”已经足够有价值。
+
+### 6.4 `ARPHint`
+
+如果目标是支持“展示其他协议”，ARP 必须成为一等公民。
+
+建议至少包括：
+
+- operation
+- sender MAC / sender IP
+- target MAC / target IP
+- request / reply tag
+
+同时 `Decoder` 对 ARP 不应再因为没有 `NetworkLayer()` 而直接报错。
+
+## 7. 标签体系建议
+
+建议在主包内定义统一 tag 体系，供所有上层工具复用。
+
+例如：
+
+- `tcp.handshake.syn`
+- `tcp.handshake.synack`
+- `tcp.handshake.ack`
+- `tcp.teardown.fin`
+- `tcp.keepalive`
+- `tcp.keepalive.response`
+- `tcp.retransmit`
+- `tcp.rst`
+- `tcp.ece`
+- `tcp.cwr`
+- `udp.packet`
+- `icmp.echo-request`
+- `icmp.echo-reply`
+- `icmp.unreachable`
+- `arp.request`
+- `arp.reply`
+- `transport.unknown`
+
+这比继续依赖一个不断膨胀的 `StateDescript` 枚举更稳。
+
+## 8. 状态与并发语义
+
+这是新架构里必须提前定死的部分。
+
+### 8.1 `Decoder` 的并发语义
+
+`Decoder` 无状态，应明确支持并发使用。
+
+### 8.2 `Tracker` 的并发语义
+
+`Tracker` 有状态，应明确：
+
+- 同一 flow 的观测结果必须按顺序输入
+- 允许多 flow 并发，但内部状态更新语义以 flow 顺序为准
+- 如果调用方无法保证顺序，则 hint 结果可能退化
+
+这点非常重要。当前的 `shardedMap` 只能提供 map 级线程安全，不能自动提供时序正确性。TCP hint 尤其依赖时序，因此新接口必须把这一点写进设计，而不是默认调用方自己猜。
+
+### 8.3 工具侧临时状态必须外移
+
+例如 `tcml` 的：
+
+- delay countdown
+- block / allow 状态
+- 业务关键字命中后的动作状态
+
+都不应再借用 `Comment/SetComment` 写进 `bcap` 状态仓库。
+
+新架构里，`Tracker` 只维护协议分析所需状态，不维护工具策略状态。
+
+## 9. 错误模型建议
+
+建议错误也按层次整理：
+
+- 解码失败
+- 支持范围外
+- 协议字段损坏
+- 状态推断降级
+
+同时要允许“部分可用”的结果。
+
+例如：
+
+- 能识别到 IPv4，但 transport 未识别
+- 能识别到 ARP，但字段不完整
+- 能拿到 TCP flags，但因为缺少上下文无法判定 retransmit
+
+这种情况下应尽量返回事实层结果，而不是简单整体失败。
+
+## 10. 主包不再保留的旧概念
+
+建议在新架构中明确移除或降级以下旧概念：
+
+- `PacketInfo`
+- `Packets`
+- `StateDescript()`
+- `Comment()` / `SetComment()`
+- `GetStateDescription()`
+- `PrintStats()`
+- `ExportConnectionsToJSON()`
+- 各类以字符串 key 作为核心接口的模型
+
+原因是：
+
+- `PacketInfo` 混杂事实、推断和业务临时状态
+- `Packets` 角色过多，不适合作为长期主对象
+- `StateDescript` 无法优雅承载多协议 hint
+- `Comment/SetComment` 明显越界
+- 格式化和导出不应继续作为主包核心能力
+
+## 11. 建议的新接口形态
+
+建议主包至少提供两层使用方式。
+
+### 11.1 低层接口
+
+```go
+decoder := bcap.NewDecoder(opts)
+pkt, err := decoder.Decode(gpkt)
+
+tracker := bcap.NewTracker(opts)
+obs, err := tracker.Observe(pkt)
+```
+
+适合：
+
+- 想分别控制解码与跟踪的调用方
+- 想单测某一层的调用方
+- 想把事实层和 hint 层分开使用的工具
+
+### 11.2 便捷接口
+
+```go
+analyzer := bcap.NewAnalyzer(opts)
+obs, err := analyzer.ObservePacket(gpkt)
+```
+
+适合：
+
+- `tcm`
+- `tcml`
+- `diag`
+- `show`
+
+这类工具大多要的是“输入 gopacket.Packet，得到事实 + hint”。
+
+## 12. 对现有调用方的迁移影响
+
+### 12.1 `tcpkill`
+
+迁移成本最低。
+
+它主要只需要：
+
+- TCP 四元组
+- seq / ack / window
+- MAC
+
+因此它可以优先迁移到：
+
+- `Decoder`
+- 或 `Analyzer` 中的 `Observation.Packet + Observation.Hints.TCP`
+
+### 12.2 `tcm` / `tcml`
+
+迁移重点在展示层。
+
+它们当前主要依赖：
+
+- `StateDescript`
+- `TcpSeq/TcpAck/TcpWindow/TcpPayloads`
+- `Key/ReverseKey`
+- `Comment/SetComment`
+
+迁移后应改成：
+
+- 用 `Observation.Hints.Summary` 或 `Tags` 做展示语义
+- 用结构化 `FlowRef` 替代字符串 key 拼接
+- 将 `tcml` 的动作状态迁出 `bcap`
+
+### 12.3 `diag`
+
+`diag` 会受益最大。
+
+它本质上就是一个消费“事实 + hint”的离线分析器。等 `bcap` 能稳定输出结构化 TCP/ICMP/ARP/UDP hint 后，`diag` 内部很多启发式逻辑会更容易表达，也更少依赖旧的 TCP 枚举状态。
+
+## 13. 与子包的边界
+
+本次先不动子包，但应明确子包定位：
+
+- `libpcap`：抓包输入适配层
+- `nfq`：NFQUEUE 输入适配层
+
+它们不属于主模型核心，只是 `gopacket.Packet` 的来源适配。
+
+换句话说：
+
+- `bcap` 主包定义“如何理解 packet”
+- 子包定义“packet 从哪里来”
+
+这个边界应该长期保持稳定。
+
+## 14. 当前结论
+
+如果重做 `bcap` 主包，最合理的方向是：
+
+1. 主包已经从 `Packets/PacketInfo` 旧模型切换到 `Decoder/Tracker/Analyzer` 新模型。
+2. 明确分离“报文事实”和“推断 hint”。
+3. 引入结构化 `FlowKey/FlowRef`，不再把字符串 key 作为主接口。
+4. 用 `HintSet + Tags + protocol-specific hints` 取代 `StateDescript`。
+5. 删除 `Comment/SetComment` 这类工具业务越界能力。
+6. 让 `bcap` 成为“轻量协议事实 + hint 提供层”，而不是“工具状态仓库”。
+
+## 15. 推荐的实施顺序
+
+建议真正开始改实现时，按下面顺序推进：
+
+1. 先定义新的公共类型草图：`Packet`、`Observation`、`FlowKey`、`HintSet`、`TCPHint`、`ICMPHint`、`ARPHint`。
+2. 再实现无状态 `Decoder`，保证多协议事实提取完整。
+3. 再实现有状态 `Tracker`，先把 TCP hint 迁进去。
+4. 再提供 `Analyzer` 便捷入口。
+5. 最后再让 `apps/tcp` 和 `apps/b612` 的调用方迁到新接口，并删除旧兼容 facade。
+
+在这个顺序下，主架构会先稳定下来，后续迁移也更可控。

format.go

@@ -0,0 +1,34 @@
+package bcap
+
+import (
+	"fmt"
+	"time"
+)
+
+func FormatDuration(d time.Duration) string {
+	if d < time.Microsecond {
+		return fmt.Sprintf("%dns", d.Nanoseconds())
+	} else if d < time.Millisecond {
+		return fmt.Sprintf("%.2fµs", float64(d.Nanoseconds())/1000.0)
+	} else if d < time.Second {
+		return fmt.Sprintf("%.2fms", float64(d.Microseconds())/1000.0)
+	} else if d < time.Minute {
+		return fmt.Sprintf("%.2fs", d.Seconds())
+	} else if d < time.Hour {
+		return fmt.Sprintf("%.2fm", d.Minutes())
+	}
+	return fmt.Sprintf("%.2fh", d.Hours())
+}
+
+func FormatBytes(bytes uint64) string {
+	const unit = 1024
+	if bytes < unit {
+		return fmt.Sprintf("%d B", bytes)
+	}
+	div, exp := uint64(unit), 0
+	for n := bytes / unit; n >= unit; n /= unit {
+		div *= unit
+		exp++
+	}
+	return fmt.Sprintf("%.2f %cB", float64(bytes)/float64(div), "KMGTPE"[exp])
+}

format_test.go

@@ -0,0 +1,24 @@
+package bcap
+
+import (
+	"testing"
+	"time"
+)
+
+func TestFormatHelpers(t *testing.T) {
+	if got := FormatDuration(500 * time.Nanosecond); got != "500ns" {
+		t.Fatalf("FormatDuration(ns) = %q", got)
+	}
+	if got := FormatDuration(1500 * time.Microsecond); got != "1.50ms" {
+		t.Fatalf("FormatDuration(ms) = %q", got)
+	}
+	if got := FormatDuration(2 * time.Second); got != "2.00s" {
+		t.Fatalf("FormatDuration(s) = %q", got)
+	}
+	if got := FormatBytes(512); got != "512 B" {
+		t.Fatalf("FormatBytes(bytes) = %q", got)
+	}
+	if got := FormatBytes(1536); got != "1.50 KB" {
+		t.Fatalf("FormatBytes(kb) = %q", got)
+	}
+}

model.go

@@ -0,0 +1,258 @@
+package bcap
+
+import (
+	"net"
+	"time"
+
+	"github.com/gopacket/gopacket"
+)
+
+type ProtocolKind string
+
+const (
+	ProtocolUnknown ProtocolKind = "unknown"
+	ProtocolTCP     ProtocolKind = "tcp"
+	ProtocolUDP     ProtocolKind = "udp"
+	ProtocolICMPv4  ProtocolKind = "icmp"
+	ProtocolICMPv6  ProtocolKind = "icmpv6"
+	ProtocolARP     ProtocolKind = "arp"
+)
+
+type NetworkFamily string
+
+const (
+	NetworkFamilyUnknown NetworkFamily = "unknown"
+	NetworkFamilyIPv4    NetworkFamily = "ipv4"
+	NetworkFamilyIPv6    NetworkFamily = "ipv6"
+	NetworkFamilyARP     NetworkFamily = "arp"
+)
+
+type LinkKind string
+
+const (
+	LinkKindUnknown   LinkKind = "unknown"
+	LinkKindEthernet  LinkKind = "ethernet"
+	LinkKindLinuxSLL  LinkKind = "linux_sll"
+	LinkKindLinuxSLL2 LinkKind = "linux_sll2"
+)
+
+type Tag string
+
+const (
+	TagTransportUnknown   Tag = "transport.unknown"
+	TagTCPHandshakeSYN    Tag = "tcp.handshake.syn"
+	TagTCPHandshakeSYNACK Tag = "tcp.handshake.synack"
+	TagTCPHandshakeACK    Tag = "tcp.handshake.ack"
+	TagTCPTeardownFIN     Tag = "tcp.teardown.fin"
+	TagTCPTeardownFINACK  Tag = "tcp.teardown.finack"
+	TagTCPTeardownACK     Tag = "tcp.teardown.ack"
+	TagTCPPacket          Tag = "tcp.packet"
+	TagTCPRetransmit      Tag = "tcp.retransmit"
+	TagTCPKeepalive       Tag = "tcp.keepalive"
+	TagTCPKeepaliveResp   Tag = "tcp.keepalive.response"
+	TagTCPRst             Tag = "tcp.rst"
+	TagTCPEce             Tag = "tcp.ece"
+	TagTCPCwr             Tag = "tcp.cwr"
+	TagUDPPacket          Tag = "udp.packet"
+	TagICMPPacket         Tag = "icmp.packet"
+	TagICMPEchoRequest    Tag = "icmp.echo-request"
+	TagICMPEchoReply      Tag = "icmp.echo-reply"
+	TagICMPUnreachable    Tag = "icmp.unreachable"
+	TagICMPTimeExceeded   Tag = "icmp.time-exceeded"
+	TagARPRequest         Tag = "arp.request"
+	TagARPReply           Tag = "arp.reply"
+)
+
+type Packet struct {
+	Meta      Meta
+	Link      LinkFacts
+	Network   NetworkFacts
+	Transport TransportFacts
+	Raw       RawFacts
+}
+
+type Meta struct {
+	Timestamp       time.Time
+	TimestampMicros int64
+	RelativeTime    time.Duration
+	CaptureLength   int
+	Length          int
+}
+
+type LinkFacts struct {
+	Kind   LinkKind
+	SrcMAC net.HardwareAddr
+	DstMAC net.HardwareAddr
+}
+
+type NetworkFacts struct {
+	Family         NetworkFamily
+	SrcIP          string
+	DstIP          string
+	TTL            uint8
+	HopLimit       uint8
+	ProtocolNumber uint16
+	ARP            *ARPFacts
+}
+
+type ARPFacts struct {
+	Operation uint16
+	SenderMAC net.HardwareAddr
+	TargetMAC net.HardwareAddr
+	SenderIP  string
+	TargetIP  string
+}
+
+type TransportFacts struct {
+	Kind    ProtocolKind
+	Payload int
+	TCP     *TCPFacts
+	UDP     *UDPFacts
+	ICMP    *ICMPFacts
+	Unknown *UnknownTransportFacts
+}
+
+type TCPFacts struct {
+	SrcPort  string
+	DstPort  string
+	Seq      uint32
+	Ack      uint32
+	Window   uint16
+	SYN      bool
+	ACK      bool
+	FIN      bool
+	RST      bool
+	ECE      bool
+	CWR      bool
+	PSH      bool
+	Checksum uint16
+	Payload  int
+}
+
+type UDPFacts struct {
+	SrcPort string
+	DstPort string
+	Length  uint16
+	Payload int
+}
+
+type ICMPFacts struct {
+	Version  int
+	Type     uint8
+	Code     uint8
+	Checksum uint16
+	ID       uint16
+	Seq      uint16
+	Payload  int
+}
+
+type UnknownTransportFacts struct {
+	Payload int
+}
+
+type RawFacts struct {
+	Packet gopacket.Packet
+}
+
+type Endpoint struct {
+	IP   string
+	Port string
+}
+
+type FlowKey struct {
+	Family   NetworkFamily
+	Protocol ProtocolKind
+	Src      Endpoint
+	Dst      Endpoint
+}
+
+type FlowRef struct {
+	Forward FlowKey
+	Reverse FlowKey
+	Stable  string
+}
+
+type Observation struct {
+	Packet Packet
+	Flow   FlowRef
+	Hints  HintSet
+}
+
+type SummaryHint struct {
+	Code string
+}
+
+type HintSet struct {
+	Summary SummaryHint
+	Tags    []Tag
+
+	TCP  *TCPHint
+	UDP  *UDPHint
+	ICMP *ICMPHint
+	ARP  *ARPHint
+}
+
+type TCPPhase string
+
+const (
+	TCPPhaseUnknown     TCPPhase = "unknown"
+	TCPPhaseHandshake   TCPPhase = "handshake"
+	TCPPhaseEstablished TCPPhase = "established"
+	TCPPhaseTeardown    TCPPhase = "teardown"
+	TCPPhaseSpecial     TCPPhase = "special"
+)
+
+type TCPEvent string
+
+const (
+	TCPEventUnknown        TCPEvent = "unknown"
+	TCPEventSYN            TCPEvent = "syn"
+	TCPEventSYNACK         TCPEvent = "synack"
+	TCPEventHandshakeACK   TCPEvent = "handshake_ack"
+	TCPEventACK            TCPEvent = "ack"
+	TCPEventRetransmission TCPEvent = "retransmission"
+	TCPEventKeepalive      TCPEvent = "keepalive"
+	TCPEventKeepaliveResp  TCPEvent = "keepalive_response"
+	TCPEventFIN            TCPEvent = "fin"
+	TCPEventFINACK         TCPEvent = "finack"
+	TCPEventTeardownACK    TCPEvent = "teardown_ack"
+	TCPEventRST            TCPEvent = "rst"
+	TCPEventECE            TCPEvent = "ece"
+	TCPEventCWR            TCPEvent = "cwr"
+)
+
+type TCPHint struct {
+	Phase             TCPPhase
+	Event             TCPEvent
+	LegacyState       uint8
+	Seq               uint32
+	Ack               uint32
+	Window            uint16
+	Payload           int
+	Retransmission    bool
+	Keepalive         bool
+	KeepaliveResponse bool
+	RST               bool
+	ECE               bool
+	CWR               bool
+}
+
+type UDPHint struct {
+	Payload int
+}
+
+type ICMPHint struct {
+	Version        int
+	Type           uint8
+	Code           uint8
+	IsEcho         bool
+	IsEchoReply    bool
+	IsUnreachable  bool
+	IsTimeExceeded bool
+}
+
+type ARPHint struct {
+	Operation uint16
+	Request   bool
+	Reply     bool
+}

nfq/nfqueue.go

@@ -57,7 +57,7 @@ func (n *NfQueue) Run() error {
 	}
 	nfq, err := nfqueue.Open(&cfg)
 	if err != nil {
-		return fmt.Errorf("failed to open nfqueue, err:", err)
+		return fmt.Errorf("failed to open nfqueue: %w", err)
 	}
 
 	if err := nfq.RegisterWithErrorFunc(n.ctx, func(a nfqueue.Attribute) int {
@@ -65,7 +65,7 @@ func (n *NfQueue) Run() error {
 	}, func(e error) int {
 		return 0
 	}); err != nil {
-		return fmt.Errorf("failed to register handlers, err:", err)
+		return fmt.Errorf("failed to register handlers: %w", err)
 	}
 	<-n.ctx.Done()
 	return nil

state.go

@@ -0,0 +1,12 @@
+package bcap
+
+import "time"
+
+const repeatedKeepaliveMinInterval = time.Second
+const trackedTCPSegments = 8
+const keepaliveResponseMaxDelay = 5 * time.Second
+
+type tcpSegmentRange struct {
+	seq uint32
+	end uint32
+}

tcp_seq.go

@@ -0,0 +1,15 @@
+package bcap
+
+func tcpSeqLess(a, b uint32) bool { return int32(a-b) < 0 }
+
+func tcpSeqLEQ(a, b uint32) bool {
+	return a == b || tcpSeqLess(a, b)
+}
+
+func tcpSeqAdd(seq, delta uint32) uint32 {
+	return seq + delta
+}
+
+func tcpSeqPrev(seq uint32) uint32 {
+	return tcpSeqAdd(seq, ^uint32(0))
+}

tcp_test.go

@@ -0,0 +1,747 @@
+package bcap
+
+import (
+	"testing"
+	"time"
+
+	"github.com/gopacket/gopacket"
+)
+
+func TestObserveTCPStateTransitions(t *testing.T) {
+	analyzer := newTestAnalyzer()
+	defer analyzer.Stop()
+	base := time.Unix(1700000000, 0)
+
+	cases := []struct {
+		name    string
+		packet  func(time.Time) observedPacket
+		want    uint8
+		wantLen int
+	}{
+		{
+			name: "syn",
+			packet: func(ts time.Time) observedPacket {
+				return mustObservePacket(t, analyzer, mustBuildTCPPacket(t, ts, tcpPacketSpec{
+					srcIP:   "10.0.0.1",
+					dstIP:   "10.0.0.2",
+					srcPort: 40000,
+					dstPort: 3306,
+					seq:     100,
+					syn:     true,
+					window:  4096,
+				}))
+			},
+			want:    StateTcpConnect1,
+			wantLen: 0,
+		},
+		{
+			name: "synack",
+			packet: func(ts time.Time) observedPacket {
+				return mustObservePacket(t, analyzer, mustBuildTCPPacket(t, ts, tcpPacketSpec{
+					srcIP:   "10.0.0.2",
+					dstIP:   "10.0.0.1",
+					srcPort: 3306,
+					dstPort: 40000,
+					seq:     500,
+					ack:     101,
+					syn:     true,
+					ackFlag: true,
+					window:  4096,
+				}))
+			},
+			want:    StateTcpConnect2,
+			wantLen: 0,
+		},
+		{
+			name: "ack",
+			packet: func(ts time.Time) observedPacket {
+				return mustObservePacket(t, analyzer, mustBuildTCPPacket(t, ts, tcpPacketSpec{
+					srcIP:   "10.0.0.1",
+					dstIP:   "10.0.0.2",
+					srcPort: 40000,
+					dstPort: 3306,
+					seq:     101,
+					ack:     501,
+					ackFlag: true,
+					window:  4096,
+				}))
+			},
+			want:    StateTcpConnect3,
+			wantLen: 0,
+		},
+		{
+			name: "server-ack",
+			packet: func(ts time.Time) observedPacket {
+				return mustObservePacket(t, analyzer, mustBuildTCPPacket(t, ts, tcpPacketSpec{
+					srcIP:   "10.0.0.2",
+					dstIP:   "10.0.0.1",
+					srcPort: 3306,
+					dstPort: 40000,
+					seq:     501,
+					ack:     101,
+					ackFlag: true,
+					window:  4096,
+				}))
+			},
+			want:    StateTcpAckOk,
+			wantLen: 0,
+		},
+		{
+			name: "client-data",
+			packet: func(ts time.Time) observedPacket {
+				return mustObservePacket(t, analyzer, mustBuildTCPPacket(t, ts, tcpPacketSpec{
+					srcIP:   "10.0.0.1",
+					dstIP:   "10.0.0.2",
+					srcPort: 40000,
+					dstPort: 3306,
+					seq:     101,
+					ack:     501,
+					ackFlag: true,
+					window:  4096,
+					payload: []byte("hello"),
+				}))
+			},
+			want:    StateTcpAckOk,
+			wantLen: 5,
+		},
+		{
+			name: "retransmission",
+			packet: func(ts time.Time) observedPacket {
+				return mustObservePacket(t, analyzer, mustBuildTCPPacket(t, ts, tcpPacketSpec{
+					srcIP:   "10.0.0.1",
+					dstIP:   "10.0.0.2",
+					srcPort: 40000,
+					dstPort: 3306,
+					seq:     101,
+					ack:     501,
+					ackFlag: true,
+					window:  4096,
+					payload: []byte("hello"),
+				}))
+			},
+			want:    StateTcpRetransmit,
+			wantLen: 5,
+		},
+		{
+			name: "server-ack-after-data",
+			packet: func(ts time.Time) observedPacket {
+				return mustObservePacket(t, analyzer, mustBuildTCPPacket(t, ts, tcpPacketSpec{
+					srcIP:   "10.0.0.2",
+					dstIP:   "10.0.0.1",
+					srcPort: 3306,
+					dstPort: 40000,
+					seq:     501,
+					ack:     106,
+					ackFlag: true,
+					window:  4096,
+				}))
+			},
+			want:    StateTcpAckOk,
+			wantLen: 0,
+		},
+		{
+			name: "keepalive",
+			packet: func(ts time.Time) observedPacket {
+				return mustObservePacket(t, analyzer, mustBuildTCPPacket(t, ts, tcpPacketSpec{
+					srcIP:   "10.0.0.1",
+					dstIP:   "10.0.0.2",
+					srcPort: 40000,
+					dstPort: 3306,
+					seq:     105,
+					ack:     501,
+					ackFlag: true,
+					window:  4096,
+				}))
+			},
+			want:    StateTcpKeepalive,
+			wantLen: 0,
+		},
+	}
+
+	for i, tc := range cases {
+		info := tc.packet(base.Add(time.Duration(i) * time.Millisecond))
+		if info.StateDescript() != tc.want {
+			t.Fatalf("%s: state = %d, want %d", tc.name, info.StateDescript(), tc.want)
+		}
+		if info.TcpPayloads() != tc.wantLen {
+			t.Fatalf("%s: payload len = %d, want %d", tc.name, info.TcpPayloads(), tc.wantLen)
+		}
+	}
+}
+
+func TestObserveTCPRepeatedKeepaliveWithoutReverseResponse(t *testing.T) {
+	analyzer := newTestAnalyzer()
+	defer analyzer.Stop()
+	base := time.Unix(1700000500, 0)
+
+	first := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base, tcpPacketSpec{
+		srcIP:   "122.210.105.240",
+		dstIP:   "122.210.110.99",
+		srcPort: 3306,
+		dstPort: 60818,
+		seq:     172126745,
+		ack:     2951532891,
+		ackFlag: true,
+		window:  258,
+	}))
+	if first.StateDescript() != StateTcpAckOk {
+		t.Fatalf("first probe state = %d, want %d", first.StateDescript(), StateTcpAckOk)
+	}
+
+	second := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(75*time.Second), tcpPacketSpec{
+		srcIP:   "122.210.105.240",
+		dstIP:   "122.210.110.99",
+		srcPort: 3306,
+		dstPort: 60818,
+		seq:     172126745,
+		ack:     2951532891,
+		ackFlag: true,
+		window:  258,
+	}))
+	if second.StateDescript() != StateTcpKeepalive {
+		t.Fatalf("second probe state = %d, want %d", second.StateDescript(), StateTcpKeepalive)
+	}
+
+	third := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(150*time.Second), tcpPacketSpec{
+		srcIP:   "122.210.105.240",
+		dstIP:   "122.210.110.99",
+		srcPort: 3306,
+		dstPort: 60818,
+		seq:     172126745,
+		ack:     2951532891,
+		ackFlag: true,
+		window:  258,
+	}))
+	if third.StateDescript() != StateTcpKeepalive {
+		t.Fatalf("third probe state = %d, want %d", third.StateDescript(), StateTcpKeepalive)
+	}
+}
+
+func TestObserveTCPKeepaliveResponseAck(t *testing.T) {
+	analyzer := newTestAnalyzer()
+	defer analyzer.Stop()
+	base := time.Unix(1700000530, 0)
+
+	_ = mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base, tcpPacketSpec{
+		srcIP:   "122.210.105.240",
+		dstIP:   "122.210.110.99",
+		srcPort: 3306,
+		dstPort: 60818,
+		seq:     172126745,
+		ack:     2951532891,
+		ackFlag: true,
+		window:  258,
+	}))
+
+	probe := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(75*time.Second), tcpPacketSpec{
+		srcIP:   "122.210.105.240",
+		dstIP:   "122.210.110.99",
+		srcPort: 3306,
+		dstPort: 60818,
+		seq:     172126745,
+		ack:     2951532891,
+		ackFlag: true,
+		window:  258,
+	}))
+	if probe.StateDescript() != StateTcpKeepalive {
+		t.Fatalf("probe state = %d, want %d", probe.StateDescript(), StateTcpKeepalive)
+	}
+
+	resp := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(75*time.Second+50*time.Millisecond), tcpPacketSpec{
+		srcIP:   "122.210.110.99",
+		dstIP:   "122.210.105.240",
+		srcPort: 60818,
+		dstPort: 3306,
+		seq:     2951532891,
+		ack:     172126746,
+		ackFlag: true,
+		window:  1024,
+	}))
+	if resp.StateDescript() != StateTcpKeepalive {
+		t.Fatalf("keepalive response state = %d, want %d", resp.StateDescript(), StateTcpKeepalive)
+	}
+	if resp.Hints.TCP == nil || resp.Hints.TCP.Event != TCPEventKeepaliveResp {
+		t.Fatalf("response event = %#v, want %q", resp.Hints.TCP, TCPEventKeepaliveResp)
+	}
+}
+
+func TestObserveTCPKeepaliveResponseAfterWindowFallsBackToAck(t *testing.T) {
+	analyzer := newTestAnalyzer()
+	defer analyzer.Stop()
+	base := time.Unix(1700000540, 0)
+
+	_ = mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base, tcpPacketSpec{
+		srcIP:   "122.210.105.240",
+		dstIP:   "122.210.110.99",
+		srcPort: 3306,
+		dstPort: 60818,
+		seq:     172126745,
+		ack:     2951532891,
+		ackFlag: true,
+		window:  258,
+	}))
+
+	probe := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(75*time.Second), tcpPacketSpec{
+		srcIP:   "122.210.105.240",
+		dstIP:   "122.210.110.99",
+		srcPort: 3306,
+		dstPort: 60818,
+		seq:     172126745,
+		ack:     2951532891,
+		ackFlag: true,
+		window:  258,
+	}))
+	if probe.StateDescript() != StateTcpKeepalive {
+		t.Fatalf("probe state = %d, want %d", probe.StateDescript(), StateTcpKeepalive)
+	}
+
+	resp := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(75*time.Second+keepaliveResponseMaxDelay+time.Second), tcpPacketSpec{
+		srcIP:   "122.210.110.99",
+		dstIP:   "122.210.105.240",
+		srcPort: 60818,
+		dstPort: 3306,
+		seq:     2951532891,
+		ack:     172126746,
+		ackFlag: true,
+		window:  1024,
+	}))
+	if resp.StateDescript() != StateTcpAckOk {
+		t.Fatalf("late keepalive response state = %d, want %d", resp.StateDescript(), StateTcpAckOk)
+	}
+}
+
+func TestObserveTCPRepeatedAckWithoutGapStaysAck(t *testing.T) {
+	analyzer := newTestAnalyzer()
+	defer analyzer.Stop()
+	base := time.Unix(1700000550, 0)
+
+	_ = mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base, tcpPacketSpec{
+		srcIP:   "10.10.0.1",
+		dstIP:   "10.10.0.2",
+		srcPort: 3306,
+		dstPort: 60818,
+		seq:     5000,
+		ack:     9000,
+		ackFlag: true,
+		window:  512,
+	}))
+
+	next := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(100*time.Millisecond), tcpPacketSpec{
+		srcIP:   "10.10.0.1",
+		dstIP:   "10.10.0.2",
+		srcPort: 3306,
+		dstPort: 60818,
+		seq:     5000,
+		ack:     9000,
+		ackFlag: true,
+		window:  512,
+	}))
+	if next.StateDescript() != StateTcpAckOk {
+		t.Fatalf("short-gap ack state = %d, want %d", next.StateDescript(), StateTcpAckOk)
+	}
+}
+
+func TestObserveTCPPostHandshakeDataIsNotConnect3Again(t *testing.T) {
+	analyzer := newTestAnalyzer()
+	defer analyzer.Stop()
+	base := time.Unix(1700000565, 0)
+
+	syn := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base, tcpPacketSpec{
+		srcIP:   "10.11.0.1",
+		dstIP:   "10.11.0.2",
+		srcPort: 40000,
+		dstPort: 3306,
+		seq:     100,
+		syn:     true,
+		window:  4096,
+	}))
+	if syn.StateDescript() != StateTcpConnect1 {
+		t.Fatalf("syn state = %d, want %d", syn.StateDescript(), StateTcpConnect1)
+	}
+
+	synack := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(time.Millisecond), tcpPacketSpec{
+		srcIP:   "10.11.0.2",
+		dstIP:   "10.11.0.1",
+		srcPort: 3306,
+		dstPort: 40000,
+		seq:     500,
+		ack:     101,
+		syn:     true,
+		ackFlag: true,
+		window:  4096,
+	}))
+	if synack.StateDescript() != StateTcpConnect2 {
+		t.Fatalf("synack state = %d, want %d", synack.StateDescript(), StateTcpConnect2)
+	}
+
+	ack := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(2*time.Millisecond), tcpPacketSpec{
+		srcIP:   "10.11.0.1",
+		dstIP:   "10.11.0.2",
+		srcPort: 40000,
+		dstPort: 3306,
+		seq:     101,
+		ack:     501,
+		ackFlag: true,
+		window:  4096,
+	}))
+	if ack.StateDescript() != StateTcpConnect3 {
+		t.Fatalf("handshake ack state = %d, want %d", ack.StateDescript(), StateTcpConnect3)
+	}
+
+	data := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(3*time.Millisecond), tcpPacketSpec{
+		srcIP:   "10.11.0.1",
+		dstIP:   "10.11.0.2",
+		srcPort: 40000,
+		dstPort: 3306,
+		seq:     101,
+		ack:     501,
+		ackFlag: true,
+		window:  4096,
+		payload: []byte("hello"),
+	}))
+	if data.StateDescript() != StateTcpAckOk {
+		t.Fatalf("post-handshake data state = %d, want %d", data.StateDescript(), StateTcpAckOk)
+	}
+}
+
+func TestObserveTCPHandshakeAcrossSequenceWraparound(t *testing.T) {
+	analyzer := newTestAnalyzer()
+	defer analyzer.Stop()
+	base := time.Unix(1700000575, 0)
+
+	syn := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base, tcpPacketSpec{
+		srcIP:   "10.12.0.1",
+		dstIP:   "10.12.0.2",
+		srcPort: 40001,
+		dstPort: 3306,
+		seq:     ^uint32(0),
+		syn:     true,
+		window:  4096,
+	}))
+	if syn.StateDescript() != StateTcpConnect1 {
+		t.Fatalf("wrap syn state = %d, want %d", syn.StateDescript(), StateTcpConnect1)
+	}
+
+	synack := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(time.Millisecond), tcpPacketSpec{
+		srcIP:   "10.12.0.2",
+		dstIP:   "10.12.0.1",
+		srcPort: 3306,
+		dstPort: 40001,
+		seq:     500,
+		ack:     0,
+		syn:     true,
+		ackFlag: true,
+		window:  4096,
+	}))
+	if synack.StateDescript() != StateTcpConnect2 {
+		t.Fatalf("wrap synack state = %d, want %d", synack.StateDescript(), StateTcpConnect2)
+	}
+
+	ack := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(2*time.Millisecond), tcpPacketSpec{
+		srcIP:   "10.12.0.1",
+		dstIP:   "10.12.0.2",
+		srcPort: 40001,
+		dstPort: 3306,
+		seq:     0,
+		ack:     501,
+		ackFlag: true,
+		window:  4096,
+	}))
+	if ack.StateDescript() != StateTcpConnect3 {
+		t.Fatalf("wrap handshake ack state = %d, want %d", ack.StateDescript(), StateTcpConnect3)
+	}
+
+	data := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(3*time.Millisecond), tcpPacketSpec{
+		srcIP:   "10.12.0.1",
+		dstIP:   "10.12.0.2",
+		srcPort: 40001,
+		dstPort: 3306,
+		seq:     0,
+		ack:     501,
+		ackFlag: true,
+		window:  4096,
+		payload: []byte("hi"),
+	}))
+	if data.StateDescript() != StateTcpAckOk {
+		t.Fatalf("wrap post-handshake data state = %d, want %d", data.StateDescript(), StateTcpAckOk)
+	}
+}
+
+func TestObserveTCPGapFillDoesNotLookLikeRetransmission(t *testing.T) {
+	analyzer := newTestAnalyzer()
+	defer analyzer.Stop()
+	base := time.Unix(1700000580, 0)
+
+	_, _ = mustEstablishTCPConnection(
+		t,
+		analyzer,
+		base,
+		"10.20.0.1",
+		44000,
+		"10.20.0.2",
+		3306,
+		100,
+		500,
+	)
+
+	_ = mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(3*time.Millisecond), tcpPacketSpec{
+		srcIP:   "10.20.0.2",
+		dstIP:   "10.20.0.1",
+		srcPort: 3306,
+		dstPort: 44000,
+		seq:     501,
+		ack:     101,
+		ackFlag: true,
+		window:  4096,
+	}))
+
+	first := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(4*time.Millisecond), tcpPacketSpec{
+		srcIP:   "10.20.0.1",
+		dstIP:   "10.20.0.2",
+		srcPort: 44000,
+		dstPort: 3306,
+		seq:     101,
+		ack:     501,
+		ackFlag: true,
+		window:  4096,
+		payload: []byte("AAAAA"),
+	}))
+	if first.StateDescript() != StateTcpAckOk {
+		t.Fatalf("first payload state = %d, want %d", first.StateDescript(), StateTcpAckOk)
+	}
+
+	later := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(5*time.Millisecond), tcpPacketSpec{
+		srcIP:   "10.20.0.1",
+		dstIP:   "10.20.0.2",
+		srcPort: 44000,
+		dstPort: 3306,
+		seq:     111,
+		ack:     501,
+		ackFlag: true,
+		window:  4096,
+		payload: []byte("CCCCC"),
+	}))
+	if later.StateDescript() != StateTcpAckOk {
+		t.Fatalf("later payload state = %d, want %d", later.StateDescript(), StateTcpAckOk)
+	}
+
+	gapFill := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(6*time.Millisecond), tcpPacketSpec{
+		srcIP:   "10.20.0.1",
+		dstIP:   "10.20.0.2",
+		srcPort: 44000,
+		dstPort: 3306,
+		seq:     106,
+		ack:     501,
+		ackFlag: true,
+		window:  4096,
+		payload: []byte("BBBBB"),
+	}))
+	if gapFill.StateDescript() != StateTcpAckOk {
+		t.Fatalf("gap-fill state = %d, want %d", gapFill.StateDescript(), StateTcpAckOk)
+	}
+}
+
+func TestObserveTCPRSTClearsTrackedFlows(t *testing.T) {
+	analyzer := newTestAnalyzer()
+	defer analyzer.Stop()
+	base := time.Unix(1700001000, 0)
+
+	inputs := []gopacket.Packet{
+		mustBuildTCPPacket(t, base, tcpPacketSpec{
+			srcIP:   "10.0.0.1",
+			dstIP:   "10.0.0.2",
+			srcPort: 40001,
+			dstPort: 3306,
+			seq:     100,
+			syn:     true,
+			window:  4096,
+		}),
+		mustBuildTCPPacket(t, base.Add(time.Millisecond), tcpPacketSpec{
+			srcIP:   "10.0.0.2",
+			dstIP:   "10.0.0.1",
+			srcPort: 3306,
+			dstPort: 40001,
+			seq:     500,
+			ack:     101,
+			syn:     true,
+			ackFlag: true,
+			window:  4096,
+		}),
+		mustBuildTCPPacket(t, base.Add(2*time.Millisecond), tcpPacketSpec{
+			srcIP:   "10.0.0.1",
+			dstIP:   "10.0.0.2",
+			srcPort: 40001,
+			dstPort: 3306,
+			seq:     101,
+			ack:     501,
+			ackFlag: true,
+			window:  4096,
+		}),
+	}
+
+	for _, packet := range inputs {
+		_ = mustObservePacket(t, analyzer, packet)
+	}
+
+	info := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(3*time.Millisecond), tcpPacketSpec{
+		srcIP:   "10.0.0.2",
+		dstIP:   "10.0.0.1",
+		srcPort: 3306,
+		dstPort: 40001,
+		seq:     501,
+		ack:     101,
+		ackFlag: true,
+		rst:     true,
+		window:  4096,
+	}))
+	if info.StateDescript() != StateTcpRst {
+		t.Fatalf("rst state = %d, want %d", info.StateDescript(), StateTcpRst)
+	}
+	if got := analyzer.Tracker().ActiveFlowCount(); got != 0 {
+		t.Fatalf("active flow count = %d, want 0", got)
+	}
+}
+
+func TestObserveTCPFourWayCloseSequence(t *testing.T) {
+	analyzer := newTestAnalyzer()
+	defer analyzer.Stop()
+	base := time.Unix(1700004000, 0)
+
+	_, _ = mustEstablishTCPConnection(
+		t,
+		analyzer,
+		base,
+		"10.0.1.1",
+		41000,
+		"10.0.1.2",
+		3306,
+		100,
+		500,
+	)
+
+	info := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(3*time.Millisecond), tcpPacketSpec{
+		srcIP:   "10.0.1.1",
+		dstIP:   "10.0.1.2",
+		srcPort: 41000,
+		dstPort: 3306,
+		seq:     101,
+		ack:     501,
+		ackFlag: true,
+		fin:     true,
+		window:  4096,
+	}))
+	if info.StateDescript() != StateTcpDisconnect1 {
+		t.Fatalf("client fin state = %d, want %d", info.StateDescript(), StateTcpDisconnect1)
+	}
+
+	info = mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(4*time.Millisecond), tcpPacketSpec{
+		srcIP:   "10.0.1.2",
+		dstIP:   "10.0.1.1",
+		srcPort: 3306,
+		dstPort: 41000,
+		seq:     501,
+		ack:     102,
+		ackFlag: true,
+		window:  4096,
+	}))
+	if info.StateDescript() != StateTcpDisconnect2 {
+		t.Fatalf("server ack state = %d, want %d", info.StateDescript(), StateTcpDisconnect2)
+	}
+
+	info = mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(5*time.Millisecond), tcpPacketSpec{
+		srcIP:   "10.0.1.2",
+		dstIP:   "10.0.1.1",
+		srcPort: 3306,
+		dstPort: 41000,
+		seq:     501,
+		ack:     102,
+		ackFlag: true,
+		fin:     true,
+		window:  4096,
+	}))
+	if info.StateDescript() != StateTcpDisconnect3 {
+		t.Fatalf("server fin state = %d, want %d", info.StateDescript(), StateTcpDisconnect3)
+	}
+
+	info = mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(6*time.Millisecond), tcpPacketSpec{
+		srcIP:   "10.0.1.1",
+		dstIP:   "10.0.1.2",
+		srcPort: 41000,
+		dstPort: 3306,
+		seq:     102,
+		ack:     502,
+		ackFlag: true,
+		window:  4096,
+	}))
+	if info.StateDescript() != StateTcpDisconnect4 {
+		t.Fatalf("final ack state = %d, want %d", info.StateDescript(), StateTcpDisconnect4)
+	}
+	if got := analyzer.Tracker().ActiveFlowCount(); got != 0 {
+		t.Fatalf("active flow count after close = %d, want 0", got)
+	}
+}
+
+func TestObserveTCPDisconnect23CombinedFinAck(t *testing.T) {
+	analyzer := newTestAnalyzer()
+	defer analyzer.Stop()
+	base := time.Unix(1700005000, 0)
+
+	_, _ = mustEstablishTCPConnection(
+		t,
+		analyzer,
+		base,
+		"10.0.2.1",
+		42000,
+		"10.0.2.2",
+		3306,
+		100,
+		500,
+	)
+
+	info := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(3*time.Millisecond), tcpPacketSpec{
+		srcIP:   "10.0.2.1",
+		dstIP:   "10.0.2.2",
+		srcPort: 42000,
+		dstPort: 3306,
+		seq:     101,
+		ack:     501,
+		ackFlag: true,
+		fin:     true,
+		window:  4096,
+	}))
+	if info.StateDescript() != StateTcpDisconnect1 {
+		t.Fatalf("client fin state = %d, want %d", info.StateDescript(), StateTcpDisconnect1)
+	}
+
+	info = mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(4*time.Millisecond), tcpPacketSpec{
+		srcIP:   "10.0.2.2",
+		dstIP:   "10.0.2.1",
+		srcPort: 3306,
+		dstPort: 42000,
+		seq:     600,
+		ack:     102,
+		ackFlag: true,
+		fin:     true,
+		window:  4096,
+	}))
+	if info.StateDescript() != StateTcpDisconnect23 {
+		t.Fatalf("combined fin-ack state = %d, want %d", info.StateDescript(), StateTcpDisconnect23)
+	}
+
+	info = mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(5*time.Millisecond), tcpPacketSpec{
+		srcIP:   "10.0.2.1",
+		dstIP:   "10.0.2.2",
+		srcPort: 42000,
+		dstPort: 3306,
+		seq:     102,
+		ack:     601,
+		ackFlag: true,
+		window:  4096,
+	}))
+	if info.StateDescript() != StateTcpDisconnect4 {
+		t.Fatalf("final ack state = %d, want %d", info.StateDescript(), StateTcpDisconnect4)
+	}
+	if got := analyzer.Tracker().ActiveFlowCount(); got != 0 {
+		t.Fatalf("active flow count after combined close = %d, want 0", got)
+	}
+}

test_helpers_test.go

@@ -0,0 +1,354 @@
+package bcap
+
+import (
+	"net"
+	"testing"
+	"time"
+
+	"github.com/gopacket/gopacket"
+	"github.com/gopacket/gopacket/layers"
+)
+
+type observedPacket struct {
+	Observation
+	Key        string
+	ReverseKey string
+}
+
+func wrapObservedPacket(obs Observation) observedPacket {
+	return observedPacket{
+		Observation: obs,
+		Key:         obs.Flow.Forward.StableString(),
+		ReverseKey:  obs.Flow.Reverse.StableString(),
+	}
+}
+
+func (p observedPacket) StateDescript() uint8 {
+	return legacyStateFromObservation(p.Observation)
+}
+
+func (p observedPacket) TcpPayloads() int {
+	if tcp := p.Packet.Transport.TCP; tcp != nil {
+		return tcp.Payload
+	}
+	return p.Packet.Transport.Payload
+}
+
+func (p observedPacket) TcpSeq() uint32 {
+	if tcp := p.Packet.Transport.TCP; tcp != nil {
+		return tcp.Seq
+	}
+	return 0
+}
+
+func (p observedPacket) TcpAck() uint32 {
+	if tcp := p.Packet.Transport.TCP; tcp != nil {
+		return tcp.Ack
+	}
+	return 0
+}
+
+func (p observedPacket) TcpWindow() uint16 {
+	if tcp := p.Packet.Transport.TCP; tcp != nil {
+		return tcp.Window
+	}
+	return 0
+}
+
+func legacyStateFromObservation(obs Observation) uint8 {
+	switch obs.Packet.Transport.Kind {
+	case ProtocolTCP:
+		if obs.Hints.TCP != nil {
+			return obs.Hints.TCP.LegacyState
+		}
+	case ProtocolUDP:
+		return StateUdp
+	case ProtocolICMPv4:
+		return StateIcmp
+	case ProtocolICMPv6:
+		return StateIcmpv6
+	}
+	return StateUnknown
+}
+
+type tcpPacketSpec struct {
+	srcIP   string
+	dstIP   string
+	srcPort uint16
+	dstPort uint16
+	seq     uint32
+	ack     uint32
+	syn     bool
+	ackFlag bool
+	fin     bool
+	rst     bool
+	ece     bool
+	cwr     bool
+	window  uint16
+	payload []byte
+}
+
+type udpPacketSpec struct {
+	srcIP   string
+	dstIP   string
+	srcPort uint16
+	dstPort uint16
+	payload []byte
+}
+
+type icmpPacketSpec struct {
+	srcIP   string
+	dstIP   string
+	typ     uint8
+	code    uint8
+	id      uint16
+	seq     uint16
+	payload []byte
+}
+
+type arpPacketSpec struct {
+	srcMAC    string
+	dstMAC    string
+	senderMAC string
+	targetMAC string
+	senderIP  string
+	targetIP  string
+	operation uint16
+}
+
+func newTestAnalyzer() *Analyzer {
+	cfg := DefaultConfig()
+	cfg.CleanupInterval = 0
+	return NewAnalyzerWithConfig(cfg)
+}
+
+func mustObservePacket(t *testing.T, analyzer *Analyzer, packet gopacket.Packet) observedPacket {
+	t.Helper()
+
+	obs, err := analyzer.ObservePacket(packet)
+	if err != nil {
+		t.Fatalf("observe packet: %v", err)
+	}
+	return wrapObservedPacket(obs)
+}
+
+func mustEstablishTCPConnection(
+	t *testing.T,
+	analyzer *Analyzer,
+	base time.Time,
+	clientIP string,
+	clientPort uint16,
+	serverIP string,
+	serverPort uint16,
+	clientSeq uint32,
+	serverSeq uint32,
+) (string, string) {
+	t.Helper()
+
+	mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base, tcpPacketSpec{
+		srcIP:   clientIP,
+		dstIP:   serverIP,
+		srcPort: clientPort,
+		dstPort: serverPort,
+		seq:     clientSeq,
+		syn:     true,
+		window:  4096,
+	}))
+
+	serverInfo := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(time.Millisecond), tcpPacketSpec{
+		srcIP:   serverIP,
+		dstIP:   clientIP,
+		srcPort: serverPort,
+		dstPort: clientPort,
+		seq:     serverSeq,
+		ack:     clientSeq + 1,
+		syn:     true,
+		ackFlag: true,
+		window:  4096,
+	}))
+
+	clientInfo := mustObservePacket(t, analyzer, mustBuildTCPPacket(t, base.Add(2*time.Millisecond), tcpPacketSpec{
+		srcIP:   clientIP,
+		dstIP:   serverIP,
+		srcPort: clientPort,
+		dstPort: serverPort,
+		seq:     clientSeq + 1,
+		ack:     serverSeq + 1,
+		ackFlag: true,
+		window:  4096,
+	}))
+
+	return clientInfo.Key, serverInfo.Key
+}
+
+func mustBuildTCPPacket(t *testing.T, ts time.Time, spec tcpPacketSpec) gopacket.Packet {
+	t.Helper()
+
+	ip := &layers.IPv4{
+		Version:  4,
+		IHL:      5,
+		TTL:      64,
+		SrcIP:    net.ParseIP(spec.srcIP).To4(),
+		DstIP:    net.ParseIP(spec.dstIP).To4(),
+		Protocol: layers.IPProtocolTCP,
+	}
+	tcp := &layers.TCP{
+		SrcPort: layers.TCPPort(spec.srcPort),
+		DstPort: layers.TCPPort(spec.dstPort),
+		Seq:     spec.seq,
+		Ack:     spec.ack,
+		SYN:     spec.syn,
+		ACK:     spec.ackFlag,
+		FIN:     spec.fin,
+		RST:     spec.rst,
+		ECE:     spec.ece,
+		CWR:     spec.cwr,
+		Window:  spec.window,
+	}
+	tcp.SetNetworkLayerForChecksum(ip)
+
+	buf := gopacket.NewSerializeBuffer()
+	opts := gopacket.SerializeOptions{
+		FixLengths:       true,
+		ComputeChecksums: true,
+	}
+	if err := gopacket.SerializeLayers(buf, opts, ip, tcp, gopacket.Payload(spec.payload)); err != nil {
+		t.Fatalf("serialize tcp packet: %v", err)
+	}
+
+	packet := gopacket.NewPacket(buf.Bytes(), layers.LayerTypeIPv4, gopacket.Default)
+	packet.Metadata().Timestamp = ts
+	return packet
+}
+
+func mustBuildUDPPacket(t *testing.T, ts time.Time, spec udpPacketSpec) gopacket.Packet {
+	t.Helper()
+
+	ip := &layers.IPv4{
+		Version:  4,
+		IHL:      5,
+		TTL:      64,
+		SrcIP:    net.ParseIP(spec.srcIP).To4(),
+		DstIP:    net.ParseIP(spec.dstIP).To4(),
+		Protocol: layers.IPProtocolUDP,
+	}
+	udp := &layers.UDP{
+		SrcPort: layers.UDPPort(spec.srcPort),
+		DstPort: layers.UDPPort(spec.dstPort),
+	}
+	udp.SetNetworkLayerForChecksum(ip)
+
+	buf := gopacket.NewSerializeBuffer()
+	opts := gopacket.SerializeOptions{
+		FixLengths:       true,
+		ComputeChecksums: true,
+	}
+	if err := gopacket.SerializeLayers(buf, opts, ip, udp, gopacket.Payload(spec.payload)); err != nil {
+		t.Fatalf("serialize udp packet: %v", err)
+	}
+
+	packet := gopacket.NewPacket(buf.Bytes(), layers.LayerTypeIPv4, gopacket.Default)
+	packet.Metadata().Timestamp = ts
+	return packet
+}
+
+func mustBuildICMPPacket(t *testing.T, ts time.Time, spec icmpPacketSpec) gopacket.Packet {
+	t.Helper()
+
+	ip := &layers.IPv4{
+		Version:  4,
+		IHL:      5,
+		TTL:      64,
+		SrcIP:    net.ParseIP(spec.srcIP).To4(),
+		DstIP:    net.ParseIP(spec.dstIP).To4(),
+		Protocol: layers.IPProtocolICMPv4,
+	}
+	icmp := &layers.ICMPv4{
+		TypeCode: layers.CreateICMPv4TypeCode(spec.typ, spec.code),
+		Id:       spec.id,
+		Seq:      spec.seq,
+	}
+
+	buf := gopacket.NewSerializeBuffer()
+	opts := gopacket.SerializeOptions{
+		FixLengths:       true,
+		ComputeChecksums: true,
+	}
+	if err := gopacket.SerializeLayers(buf, opts, ip, icmp, gopacket.Payload(spec.payload)); err != nil {
+		t.Fatalf("serialize icmp packet: %v", err)
+	}
+
+	packet := gopacket.NewPacket(buf.Bytes(), layers.LayerTypeIPv4, gopacket.Default)
+	packet.Metadata().Timestamp = ts
+	return packet
+}
+
+func mustBuildIPv4OnlyPacket(t *testing.T, ts time.Time, srcIP, dstIP string) gopacket.Packet {
+	t.Helper()
+
+	ip := &layers.IPv4{
+		Version:  4,
+		IHL:      5,
+		TTL:      64,
+		SrcIP:    net.ParseIP(srcIP).To4(),
+		DstIP:    net.ParseIP(dstIP).To4(),
+		Protocol: layers.IPProtocolNoNextHeader,
+	}
+
+	buf := gopacket.NewSerializeBuffer()
+	opts := gopacket.SerializeOptions{
+		FixLengths:       true,
+		ComputeChecksums: true,
+	}
+	if err := gopacket.SerializeLayers(buf, opts, ip); err != nil {
+		t.Fatalf("serialize ipv4-only packet: %v", err)
+	}
+
+	packet := gopacket.NewPacket(buf.Bytes(), layers.LayerTypeIPv4, gopacket.Default)
+	packet.Metadata().Timestamp = ts
+	return packet
+}
+
+func mustBuildARPPacket(t *testing.T, ts time.Time, spec arpPacketSpec) gopacket.Packet {
+	t.Helper()
+
+	eth := &layers.Ethernet{
+		SrcMAC:       mustMAC(t, spec.srcMAC),
+		DstMAC:       mustMAC(t, spec.dstMAC),
+		EthernetType: layers.EthernetTypeARP,
+	}
+	arp := &layers.ARP{
+		AddrType:          layers.LinkTypeEthernet,
+		Protocol:          layers.EthernetTypeIPv4,
+		HwAddressSize:     6,
+		ProtAddressSize:   4,
+		Operation:         spec.operation,
+		SourceHwAddress:   []byte(mustMAC(t, spec.senderMAC)),
+		SourceProtAddress: []byte(net.ParseIP(spec.senderIP).To4()),
+		DstHwAddress:      []byte(mustMAC(t, spec.targetMAC)),
+		DstProtAddress:    []byte(net.ParseIP(spec.targetIP).To4()),
+	}
+
+	buf := gopacket.NewSerializeBuffer()
+	opts := gopacket.SerializeOptions{
+		FixLengths:       true,
+		ComputeChecksums: true,
+	}
+	if err := gopacket.SerializeLayers(buf, opts, eth, arp); err != nil {
+		t.Fatalf("serialize arp packet: %v", err)
+	}
+
+	packet := gopacket.NewPacket(buf.Bytes(), layers.LayerTypeEthernet, gopacket.Default)
+	packet.Metadata().Timestamp = ts
+	return packet
+}
+
+func mustMAC(t *testing.T, raw string) net.HardwareAddr {
+	t.Helper()
+
+	hw, err := net.ParseMAC(raw)
+	if err != nil {
+		t.Fatalf("parse mac %q: %v", raw, err)
+	}
+	return hw
+}

tracker.go

@@ -0,0 +1,348 @@
+package bcap
+
+import (
+	"sync"
+	"time"
+)
+
+type Tracker struct {
+	config *PacketsConfig
+
+	mu            sync.Mutex
+	tcpStates     map[string]trackerTCPState
+	cleanupTicker *time.Ticker
+	stopCleanup   chan struct{}
+	cleanupOnce   sync.Once
+	stopOnce      sync.Once
+}
+
+func NewTracker() *Tracker {
+	return NewTrackerWithConfig(nil)
+}
+
+func NewTrackerWithConfig(config *PacketsConfig) *Tracker {
+	if config == nil {
+		config = DefaultConfig()
+	}
+	tracker := &Tracker{
+		config:      config,
+		tcpStates:   make(map[string]trackerTCPState),
+		stopCleanup: make(chan struct{}),
+	}
+	if config.CleanupInterval > 0 {
+		tracker.startAutoCleanup()
+	}
+	return tracker
+}
+
+func (t *Tracker) Stop() {
+	t.stopOnce.Do(func() {
+		close(t.stopCleanup)
+	})
+}
+
+func (t *Tracker) startAutoCleanup() {
+	t.cleanupOnce.Do(func() {
+		t.cleanupTicker = time.NewTicker(t.config.CleanupInterval)
+		go func() {
+			for {
+				select {
+				case <-t.cleanupTicker.C:
+					t.CleanupExpiredFlows()
+				case <-t.stopCleanup:
+					t.cleanupTicker.Stop()
+					return
+				}
+			}
+		}()
+	})
+}
+
+func (t *Tracker) CleanupExpiredFlows() int {
+	timeout := t.config.ConnectionTimeout
+	if timeout <= 0 {
+		return 0
+	}
+	now := time.Now()
+	removed := 0
+
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	for key, state := range t.tcpStates {
+		if state.lastSeen.IsZero() {
+			continue
+		}
+		if now.Sub(state.lastSeen) <= timeout {
+			continue
+		}
+		delete(t.tcpStates, key)
+		removed++
+	}
+	return removed
+}
+
+func (t *Tracker) ActiveFlowCount() int {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	return len(t.tcpStates)
+}
+
+func (t *Tracker) Observe(packet Packet) (Observation, error) {
+	obs := newObservation(packet)
+
+	switch packet.Transport.Kind {
+	case ProtocolTCP:
+		hints, err := t.observeTCP(packet, obs.Flow)
+		if err != nil {
+			return Observation{}, err
+		}
+		obs.Hints = hints
+		return obs, nil
+	case ProtocolUDP:
+		obs.Hints = newUDPHints(packet)
+		return obs, nil
+	case ProtocolICMPv4, ProtocolICMPv6:
+		obs.Hints = newICMPHints(packet)
+		return obs, nil
+	case ProtocolARP:
+		obs.Hints = newARPHints(packet)
+		return obs, nil
+	default:
+		obs.Hints = HintSet{
+			Summary: SummaryHint{Code: string(TagTransportUnknown)},
+			Tags:    []Tag{TagTransportUnknown},
+		}
+		return obs, nil
+	}
+}
+
+func newObservation(packet Packet) Observation {
+	return Observation{
+		Packet: packet,
+		Flow:   newFlowRef(packet),
+	}
+}
+
+func newFlowRef(packet Packet) FlowRef {
+	forward := FlowKey{
+		Family:   packet.Network.Family,
+		Protocol: packet.Transport.Kind,
+		Src: Endpoint{
+			IP:   packet.Network.SrcIP,
+			Port: packetSourcePort(packet),
+		},
+		Dst: Endpoint{
+			IP:   packet.Network.DstIP,
+			Port: packetDestinationPort(packet),
+		},
+	}
+	reverse := FlowKey{
+		Family:   packet.Network.Family,
+		Protocol: packet.Transport.Kind,
+		Src:      forward.Dst,
+		Dst:      forward.Src,
+	}
+	return FlowRef{
+		Forward: forward,
+		Reverse: reverse,
+		Stable:  stableFlowKey(forward),
+	}
+}
+
+func stableFlowKey(key FlowKey) string {
+	return buildKey(string(key.Protocol), key.Src.IP, key.Src.Port, key.Dst.IP, key.Dst.Port)
+}
+
+func packetSourcePort(packet Packet) string {
+	switch packet.Transport.Kind {
+	case ProtocolTCP:
+		if packet.Transport.TCP != nil {
+			return packet.Transport.TCP.SrcPort
+		}
+	case ProtocolUDP:
+		if packet.Transport.UDP != nil {
+			return packet.Transport.UDP.SrcPort
+		}
+	}
+	return ""
+}
+
+func packetDestinationPort(packet Packet) string {
+	switch packet.Transport.Kind {
+	case ProtocolTCP:
+		if packet.Transport.TCP != nil {
+			return packet.Transport.TCP.DstPort
+		}
+	case ProtocolUDP:
+		if packet.Transport.UDP != nil {
+			return packet.Transport.UDP.DstPort
+		}
+	}
+	return ""
+}
+
+func primaryTag(tags []Tag, fallback Tag) Tag {
+	if len(tags) == 0 {
+		return fallback
+	}
+	return tags[0]
+}
+
+type tcpHintOptions struct {
+	keepaliveResponse bool
+}
+
+func newTCPHints(packet Packet, legacyState uint8, opts tcpHintOptions) HintSet {
+	tags, phase, event := legacyTCPTags(legacyState, opts)
+	hints := HintSet{
+		Summary: SummaryHint{Code: string(primaryTag(tags, TagTCPPacket))},
+		Tags:    tags,
+	}
+
+	if packet.Transport.TCP != nil {
+		hints.TCP = &TCPHint{
+			Phase:             phase,
+			Event:             event,
+			LegacyState:       legacyState,
+			Seq:               packet.Transport.TCP.Seq,
+			Ack:               packet.Transport.TCP.Ack,
+			Window:            packet.Transport.TCP.Window,
+			Payload:           packet.Transport.TCP.Payload,
+			Retransmission:    legacyState == StateTcpRetransmit,
+			Keepalive:         legacyState == StateTcpKeepalive,
+			KeepaliveResponse: opts.keepaliveResponse,
+			RST:               legacyState == StateTcpRst,
+			ECE:               legacyState == StateTcpEce,
+			CWR:               legacyState == StateTcpCwr,
+		}
+	}
+	return hints
+}
+
+func legacyTCPTags(state uint8, opts tcpHintOptions) ([]Tag, TCPPhase, TCPEvent) {
+	switch state {
+	case StateTcpConnect1:
+		return []Tag{TagTCPHandshakeSYN}, TCPPhaseHandshake, TCPEventSYN
+	case StateTcpConnect2:
+		return []Tag{TagTCPHandshakeSYNACK}, TCPPhaseHandshake, TCPEventSYNACK
+	case StateTcpConnect3:
+		return []Tag{TagTCPHandshakeACK}, TCPPhaseHandshake, TCPEventHandshakeACK
+	case StateTcpDisconnect1:
+		return []Tag{TagTCPTeardownFIN}, TCPPhaseTeardown, TCPEventFIN
+	case StateTcpDisconnect2, StateTcpDisconnect4:
+		return []Tag{TagTCPTeardownACK}, TCPPhaseTeardown, TCPEventTeardownACK
+	case StateTcpDisconnect23:
+		return []Tag{TagTCPTeardownFINACK}, TCPPhaseTeardown, TCPEventFINACK
+	case StateTcpDisconnect3:
+		return []Tag{TagTCPTeardownFIN}, TCPPhaseTeardown, TCPEventFIN
+	case StateTcpAckOk:
+		return []Tag{TagTCPPacket}, TCPPhaseEstablished, TCPEventACK
+	case StateTcpRetransmit:
+		return []Tag{TagTCPRetransmit, TagTCPPacket}, TCPPhaseEstablished, TCPEventRetransmission
+	case StateTcpKeepalive:
+		if opts.keepaliveResponse {
+			return []Tag{TagTCPKeepaliveResp, TagTCPKeepalive, TagTCPPacket}, TCPPhaseEstablished, TCPEventKeepaliveResp
+		}
+		return []Tag{TagTCPKeepalive, TagTCPPacket}, TCPPhaseEstablished, TCPEventKeepalive
+	case StateTcpRst:
+		return []Tag{TagTCPRst, TagTCPPacket}, TCPPhaseSpecial, TCPEventRST
+	case StateTcpEce:
+		return []Tag{TagTCPEce, TagTCPPacket}, TCPPhaseSpecial, TCPEventECE
+	case StateTcpCwr:
+		return []Tag{TagTCPCwr, TagTCPPacket}, TCPPhaseSpecial, TCPEventCWR
+	default:
+		return []Tag{TagTCPPacket}, TCPPhaseUnknown, TCPEventUnknown
+	}
+}
+
+func newUDPHints(packet Packet) HintSet {
+	return HintSet{
+		Summary: SummaryHint{Code: string(TagUDPPacket)},
+		Tags:    []Tag{TagUDPPacket},
+		UDP: &UDPHint{
+			Payload: packet.Transport.Payload,
+		},
+	}
+}
+
+func newICMPHints(packet Packet) HintSet {
+	hints := HintSet{
+		Summary: SummaryHint{Code: string(TagICMPPacket)},
+		Tags:    []Tag{TagICMPPacket},
+	}
+	if packet.Transport.ICMP == nil {
+		return hints
+	}
+
+	item := &ICMPHint{
+		Version: packet.Transport.ICMP.Version,
+		Type:    packet.Transport.ICMP.Type,
+		Code:    packet.Transport.ICMP.Code,
+	}
+	switch packet.Transport.Kind {
+	case ProtocolICMPv4:
+		switch packet.Transport.ICMP.Type {
+		case 8:
+			item.IsEcho = true
+			hints.Summary.Code = string(TagICMPEchoRequest)
+			hints.Tags = append(hints.Tags, TagICMPEchoRequest)
+		case 0:
+			item.IsEchoReply = true
+			hints.Summary.Code = string(TagICMPEchoReply)
+			hints.Tags = append(hints.Tags, TagICMPEchoReply)
+		case 3:
+			item.IsUnreachable = true
+			hints.Summary.Code = string(TagICMPUnreachable)
+			hints.Tags = append(hints.Tags, TagICMPUnreachable)
+		case 11:
+			item.IsTimeExceeded = true
+			hints.Summary.Code = string(TagICMPTimeExceeded)
+			hints.Tags = append(hints.Tags, TagICMPTimeExceeded)
+		}
+	case ProtocolICMPv6:
+		switch packet.Transport.ICMP.Type {
+		case 128:
+			item.IsEcho = true
+			hints.Summary.Code = string(TagICMPEchoRequest)
+			hints.Tags = append(hints.Tags, TagICMPEchoRequest)
+		case 129:
+			item.IsEchoReply = true
+			hints.Summary.Code = string(TagICMPEchoReply)
+			hints.Tags = append(hints.Tags, TagICMPEchoReply)
+		case 1:
+			item.IsUnreachable = true
+			hints.Summary.Code = string(TagICMPUnreachable)
+			hints.Tags = append(hints.Tags, TagICMPUnreachable)
+		case 3:
+			item.IsTimeExceeded = true
+			hints.Summary.Code = string(TagICMPTimeExceeded)
+			hints.Tags = append(hints.Tags, TagICMPTimeExceeded)
+		}
+	}
+	hints.ICMP = item
+	return hints
+}
+
+func newARPHints(packet Packet) HintSet {
+	hints := HintSet{
+		Summary: SummaryHint{Code: string(TagTransportUnknown)},
+		Tags:    []Tag{TagTransportUnknown},
+	}
+	if packet.Network.ARP == nil {
+		return hints
+	}
+	item := &ARPHint{Operation: packet.Network.ARP.Operation}
+	switch packet.Network.ARP.Operation {
+	case 1:
+		item.Request = true
+		hints.Summary.Code = string(TagARPRequest)
+		hints.Tags = []Tag{TagARPRequest}
+	case 2:
+		item.Reply = true
+		hints.Summary.Code = string(TagARPReply)
+		hints.Tags = []Tag{TagARPReply}
+	}
+	hints.ARP = item
+	return hints
+}

tracker_tcp.go

@@ -0,0 +1,278 @@
+package bcap
+
+import "time"
+
+type trackerTCPState struct {
+	firstSeen   time.Time
+	lastSeen    time.Time
+	packetCount uint64
+	byteCount   uint64
+
+	seq          uint32
+	ack          uint32
+	window       uint16
+	payload      int
+	finState     bool
+	synState     bool
+	isFirst      bool
+	state        uint8
+	segments     [trackedTCPSegments]tcpSegmentRange
+	segmentCount int
+	segmentNext  int
+}
+
+func (t *Tracker) observeTCP(packet Packet, flow FlowRef) (HintSet, error) {
+	tcp := packet.Transport.TCP
+	if tcp == nil {
+		return HintSet{}, NewParseError(ErrTypeTransport, "TCP", "missing tcp facts", nil)
+	}
+
+	forwardKey := flow.Forward.StableString()
+	reverseKey := flow.Reverse.StableString()
+	if forwardKey == "" {
+		forwardKey = flow.Stable
+	}
+	if reverseKey == "" {
+		reverseKey = stableFlowKey(flow.Reverse)
+	}
+
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	lastState, exists := t.tcpStates[forwardKey]
+	if !exists {
+		lastState = trackerTCPState{
+			firstSeen: packet.Meta.Timestamp,
+			lastSeen:  packet.Meta.Timestamp,
+			isFirst:   true,
+		}
+	}
+	lastReverse := t.tcpStates[reverseKey]
+
+	payloadLen := tcp.Payload
+	seqEnd := tcpSeqAdvanceFacts(tcp.Seq, tcp.SYN, tcp.FIN, payloadLen)
+	state := StateUnknown
+	hintOpts := tcpHintOptions{}
+	connectionClosed := false
+
+	if tcp.RST {
+		state = StateTcpRst
+		connectionClosed = true
+		delete(t.tcpStates, forwardKey)
+		delete(t.tcpStates, reverseKey)
+	} else if tcp.SYN && !tcp.ACK {
+		state = StateTcpConnect1
+	} else if tcp.SYN && tcp.ACK {
+		state = StateTcpConnect2
+	} else if tcp.ACK && !tcp.FIN {
+		state, hintOpts, connectionClosed = classifyTrackerAckNoFIN(packet, tcp, seqEnd, lastState, lastReverse)
+		if connectionClosed {
+			delete(t.tcpStates, forwardKey)
+			delete(t.tcpStates, reverseKey)
+		}
+	} else if tcp.ACK && tcp.FIN {
+		state = classifyTrackerAckFIN(tcp, lastState, lastReverse)
+	}
+
+	if !connectionClosed {
+		next := trackerTCPState{
+			firstSeen:    firstSeenOrNow(lastState.firstSeen, packet.Meta.Timestamp),
+			lastSeen:     packet.Meta.Timestamp,
+			packetCount:  lastState.packetCount + 1,
+			byteCount:    lastState.byteCount + packetWireLength(packet),
+			seq:          tcp.Seq,
+			ack:          tcp.Ack,
+			window:       tcp.Window,
+			payload:      payloadLen,
+			finState:     tcp.FIN,
+			synState:     tcp.SYN,
+			isFirst:      false,
+			state:        state,
+			segments:     lastState.segments,
+			segmentCount: lastState.segmentCount,
+			segmentNext:  lastState.segmentNext,
+		}
+		next.rememberSegment(tcp.Seq, seqEnd)
+		t.tcpStates[forwardKey] = next
+	}
+
+	return newTCPHints(packet, state, hintOpts), nil
+}
+
+func (f FlowKey) StableString() string {
+	return stableFlowKey(f)
+}
+
+func firstSeenOrNow(firstSeen, fallback time.Time) time.Time {
+	if firstSeen.IsZero() {
+		return fallback
+	}
+	return firstSeen
+}
+
+func packetWireLength(packet Packet) uint64 {
+	switch {
+	case packet.Meta.Length > 0:
+		return uint64(packet.Meta.Length)
+	case packet.Meta.CaptureLength > 0:
+		return uint64(packet.Meta.CaptureLength)
+	case packet.Raw.Packet != nil:
+		return uint64(len(packet.Raw.Packet.Data()))
+	default:
+		return 0
+	}
+}
+
+func tcpSeqAdvanceFacts(seq uint32, syn, fin bool, payloadLen int) uint32 {
+	span := payloadLen
+	if syn {
+		span++
+	}
+	if fin {
+		span++
+	}
+	return tcpSeqAdd(seq, uint32(span))
+}
+
+func classifyTrackerAckNoFIN(
+	packet Packet,
+	tcp *TCPFacts,
+	seqEnd uint32,
+	lastState, lastReverse trackerTCPState,
+) (uint8, tcpHintOptions, bool) {
+	if isTrackerHandshakeAck(lastState, lastReverse, tcp.Ack) {
+		return StateTcpConnect3, tcpHintOptions{}, false
+	}
+	if tcp.CWR {
+		return StateTcpCwr, tcpHintOptions{}, false
+	}
+	if tcp.ECE {
+		return StateTcpEce, tcpHintOptions{}, false
+	}
+	if state, opts, ok := classifyTrackerTCPKeepalive(packet, tcp, lastState, lastReverse); ok {
+		return state, opts, false
+	}
+	if lastState.hasSeenSegment(tcp.Seq, seqEnd) {
+		return StateTcpRetransmit, tcpHintOptions{}, false
+	}
+	if lastReverse.finState && lastState.finState {
+		return StateTcpDisconnect4, tcpHintOptions{}, true
+	}
+	if lastReverse.finState && tcpSeqAdd(lastReverse.seq, 1) == tcp.Ack {
+		return StateTcpDisconnect2, tcpHintOptions{}, false
+	}
+	return StateTcpAckOk, tcpHintOptions{}, false
+}
+
+func classifyTrackerAckFIN(tcp *TCPFacts, lastState, lastReverse trackerTCPState) uint8 {
+	if !lastReverse.finState {
+		return StateTcpDisconnect1
+	}
+	if lastReverse.finState && tcpSeqAdd(lastReverse.seq, 1) == tcp.Ack &&
+		lastState.ack == tcp.Ack && lastState.seq == tcp.Seq {
+		return StateTcpDisconnect3
+	}
+	return StateTcpDisconnect23
+}
+
+func isTrackerHandshakeAck(lastState, lastReverse trackerTCPState, ack uint32) bool {
+	if lastReverse.state != StateTcpConnect2 {
+		return false
+	}
+	if tcpSeqAdd(lastReverse.seq, 1) != ack {
+		return false
+	}
+	return lastState.state == StateTcpConnect1 && lastState.synState
+}
+
+func classifyTrackerTCPKeepalive(packet Packet, tcp *TCPFacts, lastState, lastReverse trackerTCPState) (uint8, tcpHintOptions, bool) {
+	if isTrackerRepeatedKeepaliveProbe(packet, tcp, lastState, lastReverse) {
+		return StateTcpKeepalive, tcpHintOptions{}, true
+	}
+	if lastReverse.matchesKeepaliveResponse(packet, tcp) {
+		return StateTcpKeepalive, tcpHintOptions{keepaliveResponse: true}, true
+	}
+	if tcp.Seq == tcpSeqPrev(lastReverse.ack) &&
+		tcp.Seq == tcpSeqPrev(tcpSeqAdd(lastState.seq, uint32(lastState.payload))) {
+		return StateTcpKeepalive, tcpHintOptions{}, true
+	}
+	return StateUnknown, tcpHintOptions{}, false
+}
+
+func isTrackerRepeatedKeepaliveProbe(packet Packet, tcp *TCPFacts, lastState, lastReverse trackerTCPState) bool {
+	if lastState.isFirst {
+		return false
+	}
+	if tcp == nil || !tcp.ACK || tcp.SYN || tcp.FIN || tcp.RST || tcp.ECE || tcp.CWR {
+		return false
+	}
+	if tcp.Payload != 0 {
+		return false
+	}
+	if lastState.synState || lastState.finState || lastState.payload != 0 {
+		return false
+	}
+	switch lastState.state {
+	case StateTcpAckOk, StateTcpKeepalive, StateTcpConnect3, StateTcpDisconnect2:
+	default:
+		return false
+	}
+	if tcp.Seq != lastState.seq || tcp.Ack != lastState.ack || tcp.Window != lastState.window {
+		return false
+	}
+	if packet.Meta.Timestamp.Sub(lastState.lastSeen) < repeatedKeepaliveMinInterval {
+		return false
+	}
+	if !lastReverse.lastSeen.IsZero() && lastReverse.lastSeen.After(lastState.lastSeen) {
+		return false
+	}
+	return true
+}
+
+func (s trackerTCPState) matchesKeepaliveResponse(packet Packet, tcp *TCPFacts) bool {
+	if tcp == nil || s.state != StateTcpKeepalive {
+		return false
+	}
+	if !tcp.ACK || tcp.SYN || tcp.FIN || tcp.RST || tcp.ECE || tcp.CWR {
+		return false
+	}
+	if tcp.Payload != 0 {
+		return false
+	}
+	if packet.Meta.Timestamp.Sub(s.lastSeen) > keepaliveResponseMaxDelay {
+		return false
+	}
+	return tcp.Seq == s.ack && tcp.Ack == tcpSeqAdd(s.seq, 1)
+}
+
+func (s trackerTCPState) hasSeenSegment(seq, end uint32) bool {
+	if !tcpSeqLess(seq, end) {
+		return false
+	}
+	for i := 0; i < s.segmentCount; i++ {
+		seg := s.segments[i]
+		if !tcpSeqLess(seg.seq, seg.end) {
+			continue
+		}
+		if !tcpSeqLess(seq, seg.seq) && tcpSeqLEQ(end, seg.end) {
+			return true
+		}
+	}
+	return false
+}
+
+func (s *trackerTCPState) rememberSegment(seq, end uint32) {
+	if !tcpSeqLess(seq, end) {
+		return
+	}
+	if s.hasSeenSegment(seq, end) {
+		return
+	}
+	if s.segmentCount < trackedTCPSegments {
+		s.segments[s.segmentCount] = tcpSegmentRange{seq: seq, end: end}
+		s.segmentCount++
+		return
+	}
+	s.segments[s.segmentNext] = tcpSegmentRange{seq: seq, end: end}
+	s.segmentNext = (s.segmentNext + 1) % trackedTCPSegments
+}

types.go

@@ -0,0 +1,102 @@
+package bcap
+
+import (
+	"fmt"
+	"time"
+)
+
+type ParseErrorType int
+
+const (
+	ErrTypeNone ParseErrorType = iota
+	ErrTypeLinkLayer
+	ErrTypeNetwork
+	ErrTypeTransport
+	ErrTypeUnsupported
+)
+
+type ParseError struct {
+	Type    ParseErrorType
+	Layer   string
+	Message string
+	Err     error
+}
+
+func (e *ParseError) Error() string {
+	if e.Err != nil {
+		return fmt.Sprintf("[%s] %s: %v", e.Layer, e.Message, e.Err)
+	}
+	return fmt.Sprintf("[%s] %s", e.Layer, e.Message)
+}
+
+func NewParseError(errType ParseErrorType, layer, message string, err error) *ParseError {
+	return &ParseError{
+		Type:    errType,
+		Layer:   layer,
+		Message: message,
+		Err:     err,
+	}
+}
+
+const (
+	StateUnknown         uint8 = 0
+	StateTcpConnect1     uint8 = 1
+	StateTcpConnect2     uint8 = 2
+	StateTcpConnect3     uint8 = 3
+	StateTcpDisconnect1  uint8 = 4
+	StateTcpDisconnect2  uint8 = 5
+	StateTcpDisconnect23 uint8 = 6
+	StateTcpDisconnect3  uint8 = 7
+	StateTcpDisconnect4  uint8 = 8
+	StateTcpAckOk        uint8 = 9
+	StateTcpRetransmit   uint8 = 10
+	StateTcpEce          uint8 = 11
+	StateTcpCwr          uint8 = 12
+	StateTcpRst          uint8 = 13
+	StateTcpKeepalive    uint8 = 14
+	StateUdp             uint8 = 20
+	StateIcmp            uint8 = 30
+	StateIcmpv6          uint8 = 31
+)
+
+const (
+	DefaultConnectionTimeout = 5 * time.Minute
+	DefaultCleanupInterval   = 1 * time.Minute
+)
+
+type PacketsConfig struct {
+	ConnectionTimeout time.Duration
+	CleanupInterval   time.Duration
+}
+
+func DefaultConfig() *PacketsConfig {
+	return &PacketsConfig{
+		ConnectionTimeout: DefaultConnectionTimeout,
+		CleanupInterval:   DefaultCleanupInterval,
+	}
+}
+
+type ErrorStats struct {
+	LinkLayerErrors   uint64
+	NetworkErrors     uint64
+	TransportErrors   uint64
+	UnsupportedErrors uint64
+	TotalErrors       uint64
+}
+
+type ConnectionStats struct {
+	ActiveConnections  int64
+	TotalConnections   uint64
+	ClosedConnections  uint64
+	TimeoutConnections uint64
+	TcpConnections     int64
+	UdpConnections     int64
+	IcmpConnections    int64
+}
+
+type Stats struct {
+	Errors      ErrorStats
+	Connections ConnectionStats
+	StartTime   time.Time
+	LastCleanup time.Time
+}