使用golang实现网络抓包是非常容易的,可以使用谷歌的包github.com/google/gopacket。由于gopacket构建在libpcap之上,我强烈建议您了解该库的工作原理。您可以在C中学习如何使用libpcap进行更深入的了解。

1.libpcap

gopacket是基于libpcap(数据包捕获函数库)的,该库提供的C函数接口用于捕捉经过指定网络接口的数据包,该接口应该是被设为混杂模式。
著名的软件TCPDUMP就是在Libpcap的基础上开发而成的。Libpcap提供的接口函数实现和封装了与数据包截获有关的过程。Libpcap可以在绝大多数Linux平台上运行。
主要有以下功能:
数据包捕获:捕获流经网卡的原始数据包
自定义数据包发送:构造任何格式的原始数据包
流量采集与统计:采集网络中的流量信息
规则过滤:提供自带规则过滤功能,按需要选择过滤规则

2.先决条件
# Get the gopacket package from GitHub
go get github.com/google/gopacket
# Pcap dev headers might be necessary
sudo apt-get install libpcap-dev
3.获取所有的网络设备信息
package main

import (
	"fmt"
	"github.com/google/gopacket/pcap"
	"log"
)

func main() {
	// Find all devices
	devices, err := pcap.FindAllDevs()
	if err != nil {
		log.Fatal(err)
	}

	// Print device information
	fmt.Println("Devices found:")
	for _, device := range devices {
		fmt.Println("\nName: ", device.Name)
		fmt.Println("Description: ", device.Description)
		fmt.Println("Devices addresses: ", device.Description)
		for _, address := range device.Addresses {
			fmt.Println("- IP address: ", address.IP)
			fmt.Println("- Subnet mask: ", address.Netmask)
		}
	}
}
4.打开设备实时捕捉
package main

import (
	"fmt"
	"github.com/google/gopacket"
	"github.com/google/gopacket/pcap"
	"log"
	"time"
)

var (
	device       string = "eth0"
	snapshot_len int32  = 1024
	promiscuous  bool   = false
	err          error
	timeout      time.Duration = 30 * time.Second
	handle       *pcap.Handle
)

func main() {
	// Open device
	handle, err = pcap.OpenLive(device, snapshot_len, promiscuous, timeout)
	if err != nil {
		log.Fatal(err)
	}
	defer handle.Close()

	// Use the handle as a packet source to process all packets
	packetSource := gopacket.NewPacketSource(handle, handle.LinkType())
	for packet := range packetSource.Packets() {
		// Process packet here
		fmt.Println(packet)
	}

}
5.抓取结果保存为pcap格式文件

要写一个pcap格式的文件,我们必须使用gapacket / pcapgo包。这是一个Writer接口和两个有用的函数:WriteFileHeader()和WritePacket()

package main

import (
	"fmt"
	"github.com/google/gopacket"
	"github.com/google/gopacket/layers"
	"github.com/google/gopacket/pcap"
	"github.com/google/gopacket/pcapgo"
	"os"
	"time"
)

var (
	deviceName  string = "eth0"
	snaplen     uint32 = 1024
	snapshotLen int32  = 1024
	promiscuous bool   = false
	err         error
	timeout     time.Duration = -1 * time.Second
	handle      *pcap.Handle
	packetCount int = 0
)

func main() {
	// Open output pcap file and write header
	f, _ := os.Create("test.pcap")
	w := pcapgo.NewWriter(f)
	w.WriteFileHeader(snaplen, layers.LinkTypeEthernet)
	defer f.Close()

	// Open the device for capturing
	handle, err = pcap.OpenLive(deviceName, snapshotLen, promiscuous, timeout)
	if err != nil {
		fmt.Printf("Error opening device %s: %v", deviceName, err)
		os.Exit(1)
	}
	defer handle.Close()

	// Start processing packets
	packetSource := gopacket.NewPacketSource(handle, handle.LinkType())
	for packet := range packetSource.Packets() {
		// Process packet here
		fmt.Println(packet)
		w.WritePacket(packet.Metadata().CaptureInfo, packet.Data())
		packetCount++

		// Only capture 100 and then stop
		if packetCount > 100 {
			break
		}
	}
}
6.读取pcap格式文件来查看分析网络数据包

我们不用打开一个设备进行实时捕获,也可以打开pcap文件进行离线检查。您可以使用tcpdump创建要使用的测试文件。

# Capture packets to test.pcap file
sudo tcpdump -w test.pcap
package main

import (
	"fmt"
	"github.com/google/gopacket"
	"github.com/google/gopacket/pcap"
	"log"
)

var (
	pcapFile string = "test.pcap"
	handle   *pcap.Handle
	err      error
)

func main() {
	// Open file instead of device
	handle, err = pcap.OpenOffline(pcapFile)
	if err != nil {
		log.Fatal(err)
	}
	defer handle.Close()

	// Loop through packets in file
	packetSource := gopacket.NewPacketSource(handle, handle.LinkType())
	for packet := range packetSource.Packets() {
		fmt.Println(packet)
	}
}
7.设置过滤器

只抓取tcp协议80端口的数据

package main

import (
	"fmt"
	"github.com/google/gopacket"
	"github.com/google/gopacket/pcap"
	"log"
	"time"
)

var (
	device       string = "eth0"
	snapshot_len int32  = 1024
	promiscuous  bool   = false
	err          error
	timeout      time.Duration = 30 * time.Second
	handle       *pcap.Handle
)

func main() {
	// Open device
	handle, err = pcap.OpenLive(device, snapshot_len, promiscuous, timeout)
	if err != nil {
		log.Fatal(err)
	}
	defer handle.Close()

	// Set filter
	var filter string = "tcp and port 80"
	err = handle.SetBPFFilter(filter)
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println("Only capturing TCP port 80 packets.")

	packetSource := gopacket.NewPacketSource(handle, handle.LinkType())
	for packet := range packetSource.Packets() {
		// Do something with a packet here.
		fmt.Println(packet)
	}

}
8.解码抓取的数据

我们可以使用原始数据包,并且可将其转换为已知格式。它与不同的层兼容,所以我们可以轻松访问以太网,IP和TCP层。layers包是Go库中新增的,在底层pcap库中不可用。这是一个令人难以置信的有用的包,它是gopacket库的一部分。它允许我们容易地识别包是否包含特定类型的层。该代码示例将显示如何使用layers包来查看数据包是以太网,IP和TCP,并轻松访问这些头文件中的元素。
查找有效载荷取决于所涉及的所有层。每个协议是不同的,必须相应地计算。这就是layer包的魅力所在。 gopacket的作者花了时间为诸如以太网,IP,UDP和TCP等众多已知层创建了相应类型。有效载荷是应用层的一部分。

package main

import (
	"fmt"
	"github.com/google/gopacket"
	"github.com/google/gopacket/layers"
	"github.com/google/gopacket/pcap"
	"log"
	"strings"
	"time"
)

var (
	device      string = "eth0"
	snapshotLen int32  = 1024
	promiscuous bool   = false
	err         error
	timeout     time.Duration = 30 * time.Second
	handle      *pcap.Handle
)

func main() {
	// Open device
	handle, err = pcap.OpenLive(device, snapshotLen, promiscuous, timeout)
	if err != nil {
		log.Fatal(err)
	}
	defer handle.Close()

	packetSource := gopacket.NewPacketSource(handle, handle.LinkType())
	for packet := range packetSource.Packets() {
		printPacketInfo(packet)
	}
}

func printPacketInfo(packet gopacket.Packet) {
	// Let's see if the packet is an ethernet packet
	ethernetLayer := packet.Layer(layers.LayerTypeEthernet)
	if ethernetLayer != nil {
		fmt.Println("Ethernet layer detected.")
		ethernetPacket, _ := ethernetLayer.(*layers.Ethernet)
		fmt.Println("Source MAC: ", ethernetPacket.SrcMAC)
		fmt.Println("Destination MAC: ", ethernetPacket.DstMAC)
		// Ethernet type is typically IPv4 but could be ARP or other
		fmt.Println("Ethernet type: ", ethernetPacket.EthernetType)
		fmt.Println()
	}

	// Let's see if the packet is IP (even though the ether type told us)
	ipLayer := packet.Layer(layers.LayerTypeIPv4)
	if ipLayer != nil {
		fmt.Println("IPv4 layer detected.")
		ip, _ := ipLayer.(*layers.IPv4)

		// IP layer variables:
		// Version (Either 4 or 6)
		// IHL (IP Header Length in 32-bit words)
		// TOS, Length, Id, Flags, FragOffset, TTL, Protocol (TCP?),
		// Checksum, SrcIP, DstIP
		fmt.Printf("From %s to %s\n", ip.SrcIP, ip.DstIP)
		fmt.Println("Protocol: ", ip.Protocol)
		fmt.Println()
	}

	// Let's see if the packet is TCP
	tcpLayer := packet.Layer(layers.LayerTypeTCP)
	if tcpLayer != nil {
		fmt.Println("TCP layer detected.")
		tcp, _ := tcpLayer.(*layers.TCP)

		// TCP layer variables:
		// SrcPort, DstPort, Seq, Ack, DataOffset, Window, Checksum, Urgent
		// Bool flags: FIN, SYN, RST, PSH, ACK, URG, ECE, CWR, NS
		fmt.Printf("From port %d to %d\n", tcp.SrcPort, tcp.DstPort)
		fmt.Println("Sequence number: ", tcp.Seq)
		fmt.Println()
	}

	// Iterate over all layers, printing out each layer type
	fmt.Println("All packet layers:")
	for _, layer := range packet.Layers() {
		fmt.Println("- ", layer.LayerType())
	}

	// When iterating through packet.Layers() above,
	// if it lists Payload layer then that is the same as
	// this applicationLayer. applicationLayer contains the payload
	applicationLayer := packet.ApplicationLayer()
	if applicationLayer != nil {
		fmt.Println("Application layer/Payload found.")
		fmt.Printf("%s\n", applicationLayer.Payload())

		// Search for a string inside the payload
		if strings.Contains(string(applicationLayer.Payload()), "HTTP") {
			fmt.Println("HTTP found!")
		}
	}

	// Check for errors
	if err := packet.ErrorLayer(); err != nil {
		fmt.Println("Error decoding some part of the packet:", err)
	}
}
9.构造发送数据包

这个例子做了几件事情。首先将显示如何使用网络设备发送原始字节。这样就可以像串行连接一样使用它来发送数据。这对于真正的低层数据传输非常有用,但如果您想与应用程序进行交互,您应该构建可以识别该数据包的其他硬件和软件。接下来,它将显示如何使用以太网,IP和TCP层创建一个数据包。一切都是默认空的。要完成它,我们创建另一个数据包,但实际上填写了以太网层的一些MAC地址,IPv4的一些IP地址和TCP层的端口号。你应该看到如何伪装数据包和仿冒网络设备。TCP层结构体具有可读取和可设置的SYN,FIN,ACK标志。这有助于操纵和模糊TCP三次握手,会话和端口扫描。pcap库提供了一种发送字节的简单方法,但gopacket中的图层可帮助我们为多层创建字节结构。

package main

import (
	"github.com/google/gopacket"
	"github.com/google/gopacket/layers"
	"github.com/google/gopacket/pcap"
	"log"
	"net"
	"time"
)

var (
	device       string = "eth0"
	snapshot_len int32  = 1024
	promiscuous  bool   = false
	err          error
	timeout      time.Duration = 30 * time.Second
	handle       *pcap.Handle
	buffer       gopacket.SerializeBuffer
	options      gopacket.SerializeOptions
)

func main() {
	// Open device
	handle, err = pcap.OpenLive(device, snapshot_len, promiscuous, timeout)
	if err != nil {
		log.Fatal(err)
	}
	defer handle.Close()

	// Send raw bytes over wire
	rawBytes := []byte{10, 20, 30}
	err = handle.WritePacketData(rawBytes)
	if err != nil {
		log.Fatal(err)
	}

	// Create a properly formed packet, just with
	// empty details. Should fill out MAC addresses,
	// IP addresses, etc.
	buffer = gopacket.NewSerializeBuffer()
	gopacket.SerializeLayers(buffer, options,
		&layers.Ethernet{},
		&layers.IPv4{},
		&layers.TCP{},
		gopacket.Payload(rawBytes),
	)
	outgoingPacket := buffer.Bytes()
	// Send our packet
	err = handle.WritePacketData(outgoingPacket)
	if err != nil {
		log.Fatal(err)
	}

	// This time lets fill out some information
	ipLayer := &layers.IPv4{
		SrcIP: net.IP{127, 0, 0, 1},
		DstIP: net.IP{8, 8, 8, 8},
	}
	ethernetLayer := &layers.Ethernet{
		SrcMAC: net.HardwareAddr{0xFF, 0xAA, 0xFA, 0xAA, 0xFF, 0xAA},
		DstMAC: net.HardwareAddr{0xBD, 0xBD, 0xBD, 0xBD, 0xBD, 0xBD},
	}
	tcpLayer := &layers.TCP{
		SrcPort: layers.TCPPort(4321),
		DstPort: layers.TCPPort(80),
	}
	// And create the packet with the layers
	buffer = gopacket.NewSerializeBuffer()
	gopacket.SerializeLayers(buffer, options,
		ethernetLayer,
		ipLayer,
		tcpLayer,
		gopacket.Payload(rawBytes),
	)
	outgoingPacket = buffer.Bytes()
}
10.更多的解码/构造数据包的例子
package main

import (
	"fmt"
	"github.com/google/gopacket"
	"github.com/google/gopacket/layers"
)

func main() {
	// If we don't have a handle to a device or a file, but we have a bunch
	// of raw bytes, we can try to decode them in to packet information

	// NewPacket() takes the raw bytes that make up the packet as the first parameter
	// The second parameter is the lowest level layer you want to decode. It will
	// decode that layer and all layers on top of it. The third layer
	// is the type of decoding: default(all at once), lazy(on demand), and NoCopy
	// which will not create a copy of the buffer

	// Create an packet with ethernet, IP, TCP, and payload layers
	// We are creating one we know will be decoded properly but
	// your byte source could be anything. If any of the packets
	// come back as nil, that means it could not decode it in to
	// the proper layer (malformed or incorrect packet type)
	payload := []byte{2, 4, 6}
	options := gopacket.SerializeOptions{}
	buffer := gopacket.NewSerializeBuffer()
	gopacket.SerializeLayers(buffer, options,
		&layers.Ethernet{},
		&layers.IPv4{},
		&layers.TCP{},
		gopacket.Payload(payload),
	)
	rawBytes := buffer.Bytes()

	// Decode an ethernet packet
	ethPacket :=
		gopacket.NewPacket(
			rawBytes,
			layers.LayerTypeEthernet,
			gopacket.Default,
		)

	// with Lazy decoding it will only decode what it needs when it needs it
	// This is not concurrency safe. If using concurrency, use default
	ipPacket :=
		gopacket.NewPacket(
			rawBytes,
			layers.LayerTypeIPv4,
			gopacket.Lazy,
		)

	// With the NoCopy option, the underlying slices are referenced
	// directly and not copied. If the underlying bytes change so will
	// the packet
	tcpPacket :=
		gopacket.NewPacket(
			rawBytes,
			layers.LayerTypeTCP,
			gopacket.NoCopy,
		)

	fmt.Println(ethPacket)
	fmt.Println(ipPacket)
	fmt.Println(tcpPacket)
}
11.自定义layer


下一个程序将显示如何创建自己的layer。构建gopacket layer包不包含的协议。如果您要创建自己的l33t协议,甚至不使用TCP / IP或以太网,这是很有用的。

package main

import (
	"fmt"
	"github.com/google/gopacket"
)

// Create custom layer structure
type CustomLayer struct {
	// This layer just has two bytes at the front
	SomeByte    byte
	AnotherByte byte
	restOfData  []byte
}

// Register the layer type so we can use it
// The first argument is an ID. Use negative
// or 2000+ for custom layers. It must be unique
var CustomLayerType = gopacket.RegisterLayerType(
	2001,
	gopacket.LayerTypeMetadata{
		"CustomLayerType",
		gopacket.DecodeFunc(decodeCustomLayer),
	},
)

// When we inquire about the type, what type of layer should
// we say it is? We want it to return our custom layer type
func (l CustomLayer) LayerType() gopacket.LayerType {
	return CustomLayerType
}

// LayerContents returns the information that our layer
// provides. In this case it is a header layer so
// we return the header information
func (l CustomLayer) LayerContents() []byte {
	return []byte{l.SomeByte, l.AnotherByte}
}

// LayerPayload returns the subsequent layer built
// on top of our layer or raw payload
func (l CustomLayer) LayerPayload() []byte {
	return l.restOfData
}

// Custom decode function. We can name it whatever we want
// but it should have the same arguments and return value
// When the layer is registered we tell it to use this decode function
func decodeCustomLayer(data []byte, p gopacket.PacketBuilder) error {
	// AddLayer appends to the list of layers that the packet has
	p.AddLayer(&CustomLayer{data[0], data[1], data[2:]})

	// The return value tells the packet what layer to expect
	// with the rest of the data. It could be another header layer,
	// nothing, or a payload layer.

	// nil means this is the last layer. No more decoding
	// return nil

	// Returning another layer type tells it to decode
	// the next layer with that layer's decoder function
	// return p.NextDecoder(layers.LayerTypeEthernet)

	// Returning payload type means the rest of the data
	// is raw payload. It will set the application layer
	// contents with the payload
	return p.NextDecoder(gopacket.LayerTypePayload)
}

func main() {
	// If you create your own encoding and decoding you can essentially
	// create your own protocol or implement a protocol that is not
	// already defined in the layers package. In our example we are just
	// wrapping a normal ethernet packet with our own layer.
	// Creating your own protocol is good if you want to create
	// some obfuscated binary data type that was difficult for others
	// to decode

	// Finally, decode your packets:
	rawBytes := []byte{0xF0, 0x0F, 65, 65, 66, 67, 68}
	packet := gopacket.NewPacket(
		rawBytes,
		CustomLayerType,
		gopacket.Default,
	)
	fmt.Println("Created packet out of raw bytes.")
	fmt.Println(packet)

	// Decode the packet as our custom layer
	customLayer := packet.Layer(CustomLayerType)
	if customLayer != nil {
		fmt.Println("Packet was successfully decoded with custom layer decoder.")
		customLayerContent, _ := customLayer.(*CustomLayer)
		// Now we can access the elements of the custom struct
		fmt.Println("Payload: ", customLayerContent.LayerPayload())
		fmt.Println("SomeByte element:", customLayerContent.SomeByte)
		fmt.Println("AnotherByte element:", customLayerContent.AnotherByte)
	}
}
12.更快地解码数据包

如果我们知道我们要预期的得到的层,我们可以使用现有的结构来存储分组信息,而不是为每个需要时间和内存的分组创建新的结构。使用DecodingLayerParser更快。就像编组和解组数据一样。

package main

import (
	"fmt"
	"github.com/google/gopacket"
	"github.com/google/gopacket/layers"
	"github.com/google/gopacket/pcap"
	"log"
	"time"
)

var (
	device       string = "eth0"
	snapshot_len int32  = 1024
	promiscuous  bool   = false
	err          error
	timeout      time.Duration = 30 * time.Second
	handle       *pcap.Handle
	// Will reuse these for each packet
	ethLayer layers.Ethernet
	ipLayer  layers.IPv4
	tcpLayer layers.TCP
)

func main() {
	// Open device
	handle, err = pcap.OpenLive(device, snapshot_len, promiscuous, timeout)
	if err != nil {
		log.Fatal(err)
	}
	defer handle.Close()

	packetSource := gopacket.NewPacketSource(handle, handle.LinkType())
	for packet := range packetSource.Packets() {
		parser := gopacket.NewDecodingLayerParser(
			layers.LayerTypeEthernet,
			&ethLayer,
			&ipLayer,
			&tcpLayer,
		)
		foundLayerTypes := []gopacket.LayerType{}

		err := parser.DecodeLayers(packet.Data(), &foundLayerTypes)
		if err != nil {
			fmt.Println("Trouble decoding layers: ", err)
		}

		for _, layerType := range foundLayerTypes {
			if layerType == layers.LayerTypeIPv4 {
				fmt.Println("IPv4: ", ipLayer.SrcIP, "->", ipLayer.DstIP)
			}
			if layerType == layers.LayerTypeTCP {
				fmt.Println("TCP Port: ", tcpLayer.SrcPort, "->", tcpLayer.DstPort)
				fmt.Println("TCP SYN:", tcpLayer.SYN, " | ACK:", tcpLayer.ACK)
			}
		}
	}
}
13.tcp流重组

gopacket包提供了一些名为Flow和Endpoint的类型。我没有机会深入探索这些文档,但文档中有一个使用它来将特定TCP流发送到数据包通道的示例。https://godoc.org/github.com/google/gopacket