GoDivert

Go bindings for WinDivert.

WinDivert is a user-mode packet capture-and-divert package for Windows.

Installation

go get github.com/williamfhe/godivert

Introduction

The binding's documentation can be found Here.

If you don't have the WinDivert dll installed on your System or you want to load a specific WinDivert dll you should do :

godivert.LoadDLL("PathToThe64bitDLL", "PathToThe32bitDLL")

The path can be a relative path to the .exe current directory or an absolute path.

Note that the driver must be in the same directory as the dll. LoadDLL will then load the dll depending on your OS architecture.

To start create a new instance of WinDivertHandle by calling NewWinDivertHandle and passing the filter as a parameter.

Documentation of the filter can be found Here.

winDivert, err := godivert.NewWinDivertHandle("Your filter here")

WinDivertHandle is struct that you can use to call WinDivert's function like Recv or Send.

You can divert a packet from the network stack by using winDivert.Recv() where winDivert is an instance of WinDivertHandle.

packet, err := winDivert.Recv()

You can then choose to send the packet or modify it.

packet.SetDstPort(1234) // Sets the destination port
packet.Send(winDivert) // Sends the packet back on the network stack

You can get and set values from the packet's header by using the header package. Documentation on this package can be found Here .

As the packet has been modified the checksums have to be recalculated before sending it back on the network stack.

It is done automatically if the packet has been modified when calling packet.Send but you can do it manually by calling packet.CalcNewChecksum.

To receive packets you can also use winDivert.Packets.

packetChan, err := winDivert.Packets()

Here packetChan is a channel of *godivert.Packet coming directly from the network stack.

Note that all packets diverted are guaranteed to match the filter given in godivert.NewWinDivertHandle("You filter here")

Examples

Capturing and Printing a Packet

package main

import (
    "fmt"
    "github.com/williamfhe/godivert"
)

func main() {
    winDivert, err := godivert.NewWinDivertHandle("true")
    if err != nil {
        panic(err)
    }

    packet, err := winDivert.Recv()
    if err != nil {
        panic(err)
    }
    defer winDivert.Close()

    fmt.Println(packet)

    packet.Send(winDivert)

}

Wait for a packet and print it.

Blocking Protocol by IP

package main

import (
    "net"
    "time"
    "github.com/williamfhe/godivert"
)

var cloudflareDNS = net.ParseIP("1.1.1.1")

func checkPacket(wd *godivert.WinDivertHandle, packetChan <-chan *godivert.Packet) {
    for packet := range packetChan {
        if !packet.DstIP().Equal(cloudflareDNS) {
            packet.Send(wd)
        }
    }
}

func main() {
    winDivert, err := godivert.NewWinDivertHandle("icmp")
    if err != nil {
        panic(err)
    }
    defer winDivert.Close()

    packetChan, err := winDivert.Packets()
    if err != nil {
        panic(err)
    }

    go checkPacket(winDivert, packetChan)

    time.Sleep(1 * time.Minute)
}

Forbid all ICMP packets to reach 1.1.1.1 for 1 minute.

Try it :

ping 1.1.1.1

Packet Count

package main

import (
    "fmt"
    "time"
    "github.com/williamfhe/godivert"
    "github.com/williamfhe/godivert/header"
)

var icmpv4, icmpv6, udp, tcp, unknown, served uint

func checkPacket(wd *godivert.WinDivertHandle, packetChan  <- chan *godivert.Packet) {
    for packet := range packetChan {
        countPacket(packet)
        wd.Send(packet)
    }
}

func countPacket(packet *godivert.Packet) {
    served++
    switch packet.NextHeaderType() {
    case header.ICMPv4:
        icmpv4++
    case header.ICMPv6:
        icmpv6++
    case header.TCP:
        tcp++
    case header.UDP:
        udp++
    default:
        unknown++
    }
}


func main() {
    winDivert, err := godivert.NewWinDivertHandle("true")
    if err != nil {
        panic(err)
    }

    fmt.Println("Starting")
    defer winDivert.Close()

    packetChan, err := winDivert.Packets()
    if err != nil {
        panic(err)
    }

    n := 50
    for i := 0; i < n; i++ {
        go checkPacket(winDivert, packetChan)
    }

    time.Sleep(15 * time.Second)

    fmt.Println("Stopping...")

    fmt.Printf("Served: %d packets\n", served)

    fmt.Printf("ICMPv4=%d ICMPv6=%d UDP=%d TCP=%d Unknown=%d", icmpv4, icmpv6, udp, tcp, unknown)
}

Count all protocols passing by for 15 seconds.