How to Create and Send Custom TCP Packets using Raw Sockets in Go?

Custom TCP Packet Creation and Raw Socket Transmission with Go

This guide demonstrates how to compose custom TCP packets using gopacket and transmit them via a raw socket in Go. While the original query focused on TCP packet creation, it's crucial to note that the approach also requires customization of the IPv4 header.

Creating a Raw Socket in Go

Contrary to misconceptions, Go provides means to create raw sockets through net.ListenPacket, net.DialIP, or net.ListenIP. The following example illustrates the creation of a raw socket using net.ListenIP:

conn, err := net.ListenIP("ip4:tcp", netaddr)
if err != nil {
    log.Fatalf("ListenIP: %s\n", err)
}

Setting IPv4 Socket Options

To customize the IPv4 header, it's necessary to set the IP_HDRINCL socket option. Unfortunately, Core Go lacks this functionality. However, external packages like ipv4 offer this capability. The NewRawConn function creates a raw connection with IP_HDRINCL set.

Example Code

The following code snippet provides a complete example:

package main

import (
    "code.google.com/p/gopacket"
    "code.google.com/p/gopacket/examples/util"
    "code.google.com/p/gopacket/layers"
    "github.com/dustin/go-ipv4"
    "log"
    "net"
)

const netaddr = "127.0.0.1:666"

func main() {
    defer util.Run()()

    // IPv4-specific operations
    srcIP := net.ParseIP("127.0.0.1")
    dstIP := net.ParseIP("192.168.0.1")

    // Raw socket creation using ipv4 package
    conn, err := ipv4.NewRawConn("ip4:tcp", netaddr, 0)
    if err != nil {
        log.Fatalf("NewRawConn: %s\n", err)
    }

    // TCP/IP packet creation
    tcpLayer := layers.TCP{
        SrcPort: layers.TCPPort(666),
        DstPort: layers.TCPPort(22),
        SYN:     true,
    }
    ipLayer := layers.IPv4{
        SrcIP:    srcIP,
        DstIP:    dstIP,
        Protocol: layers.IPProtocolTCP,
    }
    tcpLayer.SetNetworkLayerForChecksum(&ipLayer)

    // Serialize and transmit the packet
    buf := gopacket.NewSerializeBuffer()
    serializeOpts := gopacket.SerializeOptions{
        FixLengths:       true,
        ComputeChecksums: true,
    }
    err = gopacket.SerializeLayers(buf, serializeOpts, &ipLayer, &tcpLayer)
    if err != nil {
        log.Fatalf("SerializeLayers: %s\n", err)
    }

    _, err = conn.Write(buf.Bytes())
    if err != nil {
        log.Fatalf("Write: %s\n", err)
    }

    log.Print("Custom TCP packet sent!")
}

The above is the detailed content of How to Create and Send Custom TCP Packets using Raw Sockets in Go?. For more information, please follow other related articles on the PHP Chinese website!