Create a packet from raw bytes and write to pcap file using gopacket

Question

I want to create a packet from raw bytes using gopacket and write the packets to a pcap file.

I created a UDP packet from raw bytes as below.

package main

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

var (
        device       string = "eth0"
        snapshot_len int32  = 65535
        promiscuous  bool   = false
        err          error
        timeout      time.Duration = 30 * time.Second
        handle       *pcap.Handle
        buffer       gopacket.SerializeBuffer
        options      gopacket.SerializeOptions
)

func main() {
        ethernetLayer := &layers.Ethernet{
            SrcMAC: net.HardwareAddr{0xFF, 0xAA, 0xFA, 0xAA, 0xFF, 0xAA},
            DstMAC: net.HardwareAddr{0xBD, 0xBD, 0xBD, 0xBD, 0xBD, 0xBD},
        }
        ipLayer := &layers.IPv4{
            SrcIP: net.IP{127,0,0,1},
            DstIP: net.IP{8,8,8,8},
        }
        udpLayer := &layers.UDP{
            SrcPort: 51190,
            DstPort: 4789,
        }
        rawBytes := []byte{10, 20, 30}
        buffer = gopacket.NewSerializeBuffer()
        gopacket.SerializeLayers(buffer, options,
                ethernetLayer,
                ipLayer,
                udpLayer,
                gopacket.Payload(rawBytes),
        )
        outgoingPacket := buffer.Bytes()
        fmt.Println(outgoingPacket)
        ethpacket := gopacket.NewPacket(outgoingPacket,
                                    layers.LayerTypeEthernet,
                                    gopacket.Default )

I am struck how to write these packets to a pcap file. This is that part of the code.

        f, err := os.Create("temp.pcap")
        if err != nil {
                log.Fatal(err)
                os.Exit(1)
        }
        defer f.Close()

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

        //handle.WritePacketData(outgoingPacket)
        w := pcapgo.NewWriter(f)
        w.WriteFileHeader(uint32(snapshot_len), layers.LinkTypeEthernet)
        w.WritePacket(ethpacket.Metadata().CaptureInfo, ethpacket.Data())
       

This is the error I am getting. Please help how to proceed further

[root@centos-sqa-blr01 gopacket]# go run create_pcap.go
#command-line-arguments
./create_pcap.go:75:26: packet.MetaData undefined (type gopacket.Packet has no field or method MetaData, but does have Metadata)

Answer 1

Notice the error info: "MetaData" is not "Metadata".

Guess you need to modify:

-            w.WritePacket(packet.MetaData().CaptureInfo, ethpacket.Data())
+            w.WritePacket(packet.Metadata().CaptureInfo, ethpacket.Data())

UPDATE:

If u just want to create and write a packet, comment the following codes. It works for me.

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