You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: ipsec.go
    path of file: ./repos/nff-go/test/performance
    
    the code of the file until where you have to start completion: // Only IPv4, Only tunnel, Only ESP, Only AES-128-CBC
package main

import (
	"bytes"
	"crypto/aes"
	"crypto/cipher"
	"crypto/hmac"
	"crypto/sha1"
	"flag"
	"hash"
	"unsafe"

	"github.com/intel-go/nff-go/flow"
	"github.com/intel-go/nff-go/packet"
	"github.com/int
    
func encapsulation(currentPacket *packet.Packet, context flow.UserContext) bool {
	// Limitation: All packets will be encapsulated as 1230
	currentPacket.EncapsulateHead(etherLen, outerIPLen+espHeadLen)

	currentPacket.ParseL3()
	ipv4 := currentPacket.GetIPv4()
	if ipv4 != nil {
		*(*([4]byte))(unsafe.Pointer(&ipv4.SrcAddr)) = [4]byte{111, 22, 3, 0}
		*(*([4]byte))(unsafe.Pointer(&ipv4.DstAddr)) = [4]byte{3, 22, 111, 0}
		ipv4.VersionIhl = 0x45
		ipv4.NextProtoID = esp

		encapsulationSPI123(currentPacket, context)
	}
	return true
}