VPN Client

To create a VPN client program in Go, follow these steps:

Step 1: Initialize the Go Module

First, create a new directory for your project and initialize the Go module.

mkdir vpnclient
cd vpnclient
go mod init github.com/username/vpnclient

Step 2: Install Dependencies

You will need the gopacket library for packet handling and tun2socks for tunneling.

go get github.com/google/gopacket
go get github.com/eycorsican/go-tun2socks

Step 3: Create the `vpnclient.go` File

Create a vpnclient.go file to handle the VPN client functionality.

// vpnclient.go
package main

import (
    "fmt"
    "github.com/eycorsican/go-tun2socks/core"
    "github.com/google/gopacket"
    "github.com/google/gopacket/layers"
    "github.com/google/gopacket/pcap"
    "log"
    "os"
    "os/signal"
    "syscall"
)

// StartVPNClient starts the VPN client.
func StartVPNClient(iface string) {
    handle, err := pcap.OpenLive(iface, 1600, true, pcap.BlockForever)
    if err != nil {
        log.Fatalf("Failed to open device: %v", err)
    }
    defer handle.Close()

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

// processPacket processes a single packet.
func processPacket(packet gopacket.Packet) {
    ipLayer := packet.Layer(layers.LayerTypeIPv4)
    if ipLayer != nil {
        ip, _ := ipLayer.(*layers.IPv4)
        fmt.Printf("From %s to %s\n", ip.SrcIP, ip.DstIP)
    }
}

Step 4: Create the `main.go` File

Create a main.go file to use the VPN client functionality.

// main.go
package main

import (
    "fmt"
    "os"
    "os/signal"
    "syscall"
)

func main() {
    if len(os.Args) != 2 {
        fmt.Println("Usage: vpnclient <network_interface>")
        os.Exit(1)
    }

    iface := os.Args[1]

    go StartVPNClient(iface)

    // Handle termination signals
    sigs := make(chan os.Signal, 1)
    signal.Notify(sigs, syscall.SIGINT, syscall.SIGTERM)
    <-sigs

    fmt.Println("Shutting down VPN client...")
}

Step 5: Run the Program

Run the program using the go run command.

go run main.go <network_interface>

Replace <network_interface> with the name of the network interface you want to use (e.g., eth0 on Linux or en0 on macOS). This will start the VPN client on the specified network interface.

Last modified: 19 December 2024