Golang实现IEEE 802.3以太网帧和VLAN标签编解码

在Golang中，可以使用ethernet库来处理IEEE 802.3以太网帧和VLAN标签的编解码。下面我将介绍如何使用这个库进行以太网帧的创建、解析以及VLAN标签的处理。

安装ethernet库

首先需要安装ethernet库：

go get github.com/mdlayher/ethernet

基本用法

1. 创建以太网帧

package main

import (
	"encoding/hex"
	"fmt"
	"log"

	"github.com/mdlayher/ethernet"
)

func main() {
	// 创建以太网帧
	frame := &ethernet.Frame{
		Destination: net.HardwareAddr{0x01, 0x02, 0x03, 0x04, 0x05, 0x06},
		Source:      net.HardwareAddr{0x11, 0x12, 0x13, 0x14, 0x15, 0x16},
		EtherType:   ethernet.EtherTypeIPv4,
		Payload:     []byte("Hello, Ethernet!"),
	}

	// 编码为字节
	b, err := frame.MarshalBinary()
	if err != nil {
		log.Fatal(err)
	}

	fmt.Printf("Encoded frame: %x\n", b)
}

2. 解析以太网帧

func parseEthernetFrame(raw []byte) {
	var frame ethernet.Frame
	if err := frame.UnmarshalBinary(raw); err != nil {
		log.Fatal(err)
	}

	fmt.Printf("Destination: %s\n", frame.Destination)
	fmt.Printf("Source: %s\n", frame.Source)
	fmt.Printf("EtherType: %s (0x%04x)\n", frame.EtherType, frame.EtherType)
	fmt.Printf("Payload: %x\n", frame.Payload)
}

3. 处理VLAN标签

func handleVLAN() {
	// 创建带VLAN标签的帧
	frame := &ethernet.Frame{
		Destination: net.HardwareAddr{0x01, 0x02, 0x03, 0x04, 0x05, 0x06},
		Source:      net.HardwareAddr{0x11, 0x12, 0x13, 0x14, 0x15, 0x16},
		EtherType:   ethernet.EtherTypeVLAN,
		Payload:     []byte("Payload with VLAN tag"),
	}

	// 创建VLAN标签
	vlan := &ethernet.VLAN{
		Priority:    5,       // 优先级 (0-7)
		DropEligible: false,  // DEI标志
		ID:          100,     // VLAN ID (1-4094)
		EtherType:   ethernet.EtherTypeIPv4, // 内层以太网类型
	}

	// 将VLAN标签编码并设置为帧的Payload
	vlanPayload, err := vlan.MarshalBinary()
	if err != nil {
		log.Fatal(err)
	}
	
	// 组合VLAN标签和实际Payload
	frame.Payload = append(vlanPayload, []byte("Actual payload data")...)

	// 编码整个帧
	b, err := frame.MarshalBinary()
	if err != nil {
		log.Fatal(err)
	}

	fmt.Printf("VLAN tagged frame: %x\n", b)
}

4. 解析带VLAN标签的帧

func parseVLANFrame(raw []byte) {
	var frame ethernet.Frame
	if err := frame.UnmarshalBinary(raw); err != nil {
		log.Fatal(err)
	}

	// 检查是否是VLAN帧
	if frame.EtherType == ethernet.EtherTypeVLAN {
		var vlan ethernet.VLAN
		if err := vlan.UnmarshalBinary(frame.Payload[:4]); err != nil {
			log.Fatal(err)
		}

		fmt.Printf("VLAN Priority: %d\n", vlan.Priority)
		fmt.Printf("VLAN Drop Eligible: %t\n", vlan.DropEligible)
		fmt.Printf("VLAN ID: %d\n", vlan.ID)
		fmt.Printf("Inner EtherType: %s (0x%04x)\n", vlan.EtherType, vlan.EtherType)

		// 实际Payload在VLAN标签之后
		actualPayload := frame.Payload[4:]
		fmt.Printf("Actual payload: %x\n", actualPayload)
	}
}

完整示例

下面是一个完整的示例，演示如何创建、编码、解码带VLAN标签的以太网帧：

package main

import (
	"fmt"
	"log"
	"net"

	"github.com/mdlayher/ethernet"
)

func main() {
	// 创建带VLAN标签的以太网帧
	frame := createVLANFrame()
	
	// 编码为字节
	raw, err := frame.MarshalBinary()
	if err != nil {
		log.Fatal(err)
	}
	
	fmt.Printf("Encoded VLAN frame (%d bytes): %x\n", len(raw), raw)
	
	// 解析帧
	parseFrame(raw)
}

func createVLANFrame() *ethernet.Frame {
	// 创建VLAN标签
	vlan := &ethernet.VLAN{
		Priority:     5,
		DropEligible: false,
		ID:          100,
		EtherType:    ethernet.EtherTypeIPv4,
	}
	
	// 编码VLAN标签
	vlanPayload, err := vlan.MarshalBinary()
	if err != nil {
		log.Fatal(err)
	}
	
	// 创建以太网帧
	return &ethernet.Frame{
		Destination: net.HardwareAddr{0x01, 0x02, 0x03, 0x04, 0x05, 0x06},
		Source:      net.HardwareAddr{0x11, 0x12, 0x13, 0x14, 0x15, 0x16},
		EtherType:   ethernet.EtherTypeVLAN,
		Payload:     append(vlanPayload, []byte("Hello, VLAN!")...),
	}
}

func parseFrame(raw []byte) {
	var frame ethernet.Frame
	if err := frame.UnmarshalBinary(raw); err != nil {
		log.Fatal(err)
	}
	
	fmt.Println("\nParsed Ethernet Frame:")
	fmt.Printf("  Destination: %s\n", frame.Destination)
	fmt.Printf("  Source: %s\n", frame.Source)
	fmt.Printf("  EtherType: %s (0x%04x)\n", frame.EtherType, frame.EtherType)
	
	if frame.EtherType == ethernet.EtherTypeVLAN {
		var vlan ethernet.VLAN
		if err := vlan.UnmarshalBinary(frame.Payload[:4]); err != nil {
			log.Fatal(err)
		}
		
		fmt.Println("\nParsed VLAN Tag:")
		fmt.Printf("  Priority: %d\n", vlan.Priority)
		fmt.Printf("  Drop Eligible: %t\n", vlan.DropEligible)
		fmt.Printf("  VLAN ID: %d\n", vlan.ID)
		fmt.Printf("  Inner EtherType: %s (0x%04x)\n", vlan.EtherType, vlan.EtherType)
		
		actualPayload := frame.Payload[4:]
		fmt.Printf("\nActual Payload: %q\n", actualPayload)
	}
}

注意事项

1. ethernet库支持IEEE 802.3以太网帧格式，包括带VLAN标签的帧
2. VLAN标签使用802.1Q标准格式
3. 以太网帧最小长度为64字节（包括CRC），最大长度为1518字节（不包括CRC）
4. 对于Jumbo帧等特殊情况，可能需要特殊处理

通过ethernet库，我们可以方便地在Golang中处理以太网帧和VLAN标签的编解码，这对于网络协议分析、数据包捕获等应用非常有用。