// Copyright 2018 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package stack_test

import (
	"testing"

	"gvisor.dev/gvisor/pkg/tcpip"
	"gvisor.dev/gvisor/pkg/tcpip/buffer"
	"gvisor.dev/gvisor/pkg/tcpip/link/channel"
	"gvisor.dev/gvisor/pkg/tcpip/link/loopback"
	"gvisor.dev/gvisor/pkg/tcpip/ports"
	"gvisor.dev/gvisor/pkg/tcpip/stack"
	"gvisor.dev/gvisor/pkg/waiter"
)

const (
	fakeTransNumber    tcpip.TransportProtocolNumber = 1
	fakeTransHeaderLen                               = 3
)

// fakeTransportEndpoint is a transport-layer protocol endpoint. It counts
// received packets; the counts of all endpoints are aggregated in the protocol
// descriptor.
//
// Headers of this protocol are fakeTransHeaderLen bytes, but we currently don't
// use it.
type fakeTransportEndpoint struct {
	stack.TransportEndpointInfo
	stack    *stack.Stack
	proto    *fakeTransportProtocol
	peerAddr tcpip.Address
	route    stack.Route
	uniqueID uint64

	// acceptQueue is non-nil iff bound.
	acceptQueue []fakeTransportEndpoint
}

func (f *fakeTransportEndpoint) Info() tcpip.EndpointInfo {
	return &f.TransportEndpointInfo
}

func (f *fakeTransportEndpoint) Stats() tcpip.EndpointStats {
	return nil
}

func (f *fakeTransportEndpoint) SetOwner(owner tcpip.PacketOwner) {}

func newFakeTransportEndpoint(s *stack.Stack, proto *fakeTransportProtocol, netProto tcpip.NetworkProtocolNumber, uniqueID uint64) tcpip.Endpoint {
	return &fakeTransportEndpoint{stack: s, TransportEndpointInfo: stack.TransportEndpointInfo{NetProto: netProto}, proto: proto, uniqueID: uniqueID}
}

func (f *fakeTransportEndpoint) Abort() {
	f.Close()
}

func (f *fakeTransportEndpoint) Close() {
	f.route.Release()
}

func (*fakeTransportEndpoint) Readiness(mask waiter.EventMask) waiter.EventMask {
	return mask
}

func (*fakeTransportEndpoint) Read(*tcpip.FullAddress) (buffer.View, tcpip.ControlMessages, *tcpip.Error) {
	return buffer.View{}, tcpip.ControlMessages{}, nil
}

func (f *fakeTransportEndpoint) Write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-chan struct{}, *tcpip.Error) {
	if len(f.route.RemoteAddress) == 0 {
		return 0, nil, tcpip.ErrNoRoute
	}

	v, err := p.FullPayload()
	if err != nil {
		return 0, nil, err
	}
	pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
		ReserveHeaderBytes: int(f.route.MaxHeaderLength()) + fakeTransHeaderLen,
		Data:               buffer.View(v).ToVectorisedView(),
	})
	_ = pkt.TransportHeader().Push(fakeTransHeaderLen)
	if err := f.route.WritePacket(nil /* gso */, stack.NetworkHeaderParams{Protocol: fakeTransNumber, TTL: 123, TOS: stack.DefaultTOS}, pkt); err != nil {
		return 0, nil, err
	}

	return int64(len(v)), nil, nil
}

func (f *fakeTransportEndpoint) Peek([][]byte) (int64, tcpip.ControlMessages, *tcpip.Error) {
	return 0, tcpip.ControlMessages{}, nil
}

// SetSockOpt sets a socket option. Currently not supported.
func (*fakeTransportEndpoint) SetSockOpt(interface{}) *tcpip.Error {
	return tcpip.ErrInvalidEndpointState
}

// SetSockOptBool sets a socket option. Currently not supported.
func (*fakeTransportEndpoint) SetSockOptBool(tcpip.SockOptBool, bool) *tcpip.Error {
	return tcpip.ErrInvalidEndpointState
}

// SetSockOptInt sets a socket option. Currently not supported.
func (*fakeTransportEndpoint) SetSockOptInt(tcpip.SockOptInt, int) *tcpip.Error {
	return tcpip.ErrInvalidEndpointState
}

// GetSockOptBool implements tcpip.Endpoint.GetSockOptBool.
func (*fakeTransportEndpoint) GetSockOptBool(opt tcpip.SockOptBool) (bool, *tcpip.Error) {
	return false, tcpip.ErrUnknownProtocolOption
}

// GetSockOptInt implements tcpip.Endpoint.GetSockOptInt.
func (*fakeTransportEndpoint) GetSockOptInt(opt tcpip.SockOptInt) (int, *tcpip.Error) {
	return -1, tcpip.ErrUnknownProtocolOption
}

// GetSockOpt implements tcpip.Endpoint.GetSockOpt.
func (*fakeTransportEndpoint) GetSockOpt(opt interface{}) *tcpip.Error {
	switch opt.(type) {
	case tcpip.ErrorOption:
		return nil
	}
	return tcpip.ErrInvalidEndpointState
}

// Disconnect implements tcpip.Endpoint.Disconnect.
func (*fakeTransportEndpoint) Disconnect() *tcpip.Error {
	return tcpip.ErrNotSupported
}

func (f *fakeTransportEndpoint) Connect(addr tcpip.FullAddress) *tcpip.Error {
	f.peerAddr = addr.Addr

	// Find the route.
	r, err := f.stack.FindRoute(addr.NIC, "", addr.Addr, fakeNetNumber, false /* multicastLoop */)
	if err != nil {
		return tcpip.ErrNoRoute
	}
	defer r.Release()

	// Try to register so that we can start receiving packets.
	f.ID.RemoteAddress = addr.Addr
	err = f.stack.RegisterTransportEndpoint(0, []tcpip.NetworkProtocolNumber{fakeNetNumber}, fakeTransNumber, f.ID, f, ports.Flags{}, 0 /* bindToDevice */)
	if err != nil {
		return err
	}

	f.route = r.Clone()

	return nil
}

func (f *fakeTransportEndpoint) UniqueID() uint64 {
	return f.uniqueID
}

func (f *fakeTransportEndpoint) ConnectEndpoint(e tcpip.Endpoint) *tcpip.Error {
	return nil
}

func (*fakeTransportEndpoint) Shutdown(tcpip.ShutdownFlags) *tcpip.Error {
	return nil
}

func (*fakeTransportEndpoint) Reset() {
}

func (*fakeTransportEndpoint) Listen(int) *tcpip.Error {
	return nil
}

func (f *fakeTransportEndpoint) Accept() (tcpip.Endpoint, *waiter.Queue, *tcpip.Error) {
	if len(f.acceptQueue) == 0 {
		return nil, nil, nil
	}
	a := f.acceptQueue[0]
	f.acceptQueue = f.acceptQueue[1:]
	return &a, nil, nil
}

func (f *fakeTransportEndpoint) Bind(a tcpip.FullAddress) *tcpip.Error {
	if err := f.stack.RegisterTransportEndpoint(
		a.NIC,
		[]tcpip.NetworkProtocolNumber{fakeNetNumber},
		fakeTransNumber,
		stack.TransportEndpointID{LocalAddress: a.Addr},
		f,
		ports.Flags{},
		0, /* bindtoDevice */
	); err != nil {
		return err
	}
	f.acceptQueue = []fakeTransportEndpoint{}
	return nil
}

func (*fakeTransportEndpoint) GetLocalAddress() (tcpip.FullAddress, *tcpip.Error) {
	return tcpip.FullAddress{}, nil
}

func (*fakeTransportEndpoint) GetRemoteAddress() (tcpip.FullAddress, *tcpip.Error) {
	return tcpip.FullAddress{}, nil
}

func (f *fakeTransportEndpoint) HandlePacket(r *stack.Route, id stack.TransportEndpointID, _ *stack.PacketBuffer) {
	// Increment the number of received packets.
	f.proto.packetCount++
	if f.acceptQueue != nil {
		f.acceptQueue = append(f.acceptQueue, fakeTransportEndpoint{
			stack: f.stack,
			TransportEndpointInfo: stack.TransportEndpointInfo{
				ID:       f.ID,
				NetProto: f.NetProto,
			},
			proto:    f.proto,
			peerAddr: r.RemoteAddress,
			route:    r.Clone(),
		})
	}
}

func (f *fakeTransportEndpoint) HandleControlPacket(stack.TransportEndpointID, stack.ControlType, uint32, *stack.PacketBuffer) {
	// Increment the number of received control packets.
	f.proto.controlCount++
}

func (f *fakeTransportEndpoint) State() uint32 {
	return 0
}

func (f *fakeTransportEndpoint) ModerateRecvBuf(copied int) {}

func (f *fakeTransportEndpoint) IPTables() (stack.IPTables, error) {
	return stack.IPTables{}, nil
}

func (f *fakeTransportEndpoint) Resume(*stack.Stack) {}

func (f *fakeTransportEndpoint) Wait() {}

type fakeTransportGoodOption bool

type fakeTransportBadOption bool

type fakeTransportInvalidValueOption int

type fakeTransportProtocolOptions struct {
	good bool
}

// fakeTransportProtocol is a transport-layer protocol descriptor. It
// aggregates the number of packets received via endpoints of this protocol.
type fakeTransportProtocol struct {
	packetCount  int
	controlCount int
	opts         fakeTransportProtocolOptions
}

func (*fakeTransportProtocol) Number() tcpip.TransportProtocolNumber {
	return fakeTransNumber
}

func (f *fakeTransportProtocol) NewEndpoint(stack *stack.Stack, netProto tcpip.NetworkProtocolNumber, _ *waiter.Queue) (tcpip.Endpoint, *tcpip.Error) {
	return newFakeTransportEndpoint(stack, f, netProto, stack.UniqueID()), nil
}

func (*fakeTransportProtocol) NewRawEndpoint(stack *stack.Stack, netProto tcpip.NetworkProtocolNumber, _ *waiter.Queue) (tcpip.Endpoint, *tcpip.Error) {
	return nil, tcpip.ErrUnknownProtocol
}

func (*fakeTransportProtocol) MinimumPacketSize() int {
	return fakeTransHeaderLen
}

func (*fakeTransportProtocol) ParsePorts(buffer.View) (src, dst uint16, err *tcpip.Error) {
	return 0, 0, nil
}

func (*fakeTransportProtocol) HandleUnknownDestinationPacket(*stack.Route, stack.TransportEndpointID, *stack.PacketBuffer) bool {
	return true
}

func (f *fakeTransportProtocol) SetOption(option interface{}) *tcpip.Error {
	switch v := option.(type) {
	case fakeTransportGoodOption:
		f.opts.good = bool(v)
		return nil
	case fakeTransportInvalidValueOption:
		return tcpip.ErrInvalidOptionValue
	default:
		return tcpip.ErrUnknownProtocolOption
	}
}

func (f *fakeTransportProtocol) Option(option interface{}) *tcpip.Error {
	switch v := option.(type) {
	case *fakeTransportGoodOption:
		*v = fakeTransportGoodOption(f.opts.good)
		return nil
	default:
		return tcpip.ErrUnknownProtocolOption
	}
}

// Abort implements TransportProtocol.Abort.
func (*fakeTransportProtocol) Abort() {}

// Close implements tcpip.Endpoint.Close.
func (*fakeTransportProtocol) Close() {}

// Wait implements TransportProtocol.Wait.
func (*fakeTransportProtocol) Wait() {}

// Parse implements TransportProtocol.Parse.
func (*fakeTransportProtocol) Parse(pkt *stack.PacketBuffer) bool {
	_, ok := pkt.TransportHeader().Consume(fakeTransHeaderLen)
	return ok
}

func fakeTransFactory() stack.TransportProtocol {
	return &fakeTransportProtocol{}
}

func TestTransportReceive(t *testing.T) {
	linkEP := channel.New(10, defaultMTU, "")
	s := stack.New(stack.Options{
		NetworkProtocols:   []stack.NetworkProtocol{fakeNetFactory()},
		TransportProtocols: []stack.TransportProtocol{fakeTransFactory()},
	})
	if err := s.CreateNIC(1, linkEP); err != nil {
		t.Fatalf("CreateNIC failed: %v", err)
	}

	{
		subnet, err := tcpip.NewSubnet("\x00", "\x00")
		if err != nil {
			t.Fatal(err)
		}
		s.SetRouteTable([]tcpip.Route{{Destination: subnet, Gateway: "\x00", NIC: 1}})
	}

	if err := s.AddAddress(1, fakeNetNumber, "\x01"); err != nil {
		t.Fatalf("AddAddress failed: %v", err)
	}

	// Create endpoint and connect to remote address.
	wq := waiter.Queue{}
	ep, err := s.NewEndpoint(fakeTransNumber, fakeNetNumber, &wq)
	if err != nil {
		t.Fatalf("NewEndpoint failed: %v", err)
	}

	if err := ep.Connect(tcpip.FullAddress{0, "\x02", 0}); err != nil {
		t.Fatalf("Connect failed: %v", err)
	}

	fakeTrans := s.TransportProtocolInstance(fakeTransNumber).(*fakeTransportProtocol)

	// Create buffer that will hold the packet.
	buf := buffer.NewView(30)

	// Make sure packet with wrong protocol is not delivered.
	buf[0] = 1
	buf[2] = 0
	linkEP.InjectInbound(fakeNetNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
		Data: buf.ToVectorisedView(),
	}))
	if fakeTrans.packetCount != 0 {
		t.Errorf("packetCount = %d, want %d", fakeTrans.packetCount, 0)
	}

	// Make sure packet from the wrong source is not delivered.
	buf[0] = 1
	buf[1] = 3
	buf[2] = byte(fakeTransNumber)
	linkEP.InjectInbound(fakeNetNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
		Data: buf.ToVectorisedView(),
	}))
	if fakeTrans.packetCount != 0 {
		t.Errorf("packetCount = %d, want %d", fakeTrans.packetCount, 0)
	}

	// Make sure packet is delivered.
	buf[0] = 1
	buf[1] = 2
	buf[2] = byte(fakeTransNumber)
	linkEP.InjectInbound(fakeNetNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
		Data: buf.ToVectorisedView(),
	}))
	if fakeTrans.packetCount != 1 {
		t.Errorf("packetCount = %d, want %d", fakeTrans.packetCount, 1)
	}
}

func TestTransportControlReceive(t *testing.T) {
	linkEP := channel.New(10, defaultMTU, "")
	s := stack.New(stack.Options{
		NetworkProtocols:   []stack.NetworkProtocol{fakeNetFactory()},
		TransportProtocols: []stack.TransportProtocol{fakeTransFactory()},
	})
	if err := s.CreateNIC(1, linkEP); err != nil {
		t.Fatalf("CreateNIC failed: %v", err)
	}

	{
		subnet, err := tcpip.NewSubnet("\x00", "\x00")
		if err != nil {
			t.Fatal(err)
		}
		s.SetRouteTable([]tcpip.Route{{Destination: subnet, Gateway: "\x00", NIC: 1}})
	}

	if err := s.AddAddress(1, fakeNetNumber, "\x01"); err != nil {
		t.Fatalf("AddAddress failed: %v", err)
	}

	// Create endpoint and connect to remote address.
	wq := waiter.Queue{}
	ep, err := s.NewEndpoint(fakeTransNumber, fakeNetNumber, &wq)
	if err != nil {
		t.Fatalf("NewEndpoint failed: %v", err)
	}

	if err := ep.Connect(tcpip.FullAddress{0, "\x02", 0}); err != nil {
		t.Fatalf("Connect failed: %v", err)
	}

	fakeTrans := s.TransportProtocolInstance(fakeTransNumber).(*fakeTransportProtocol)

	// Create buffer that will hold the control packet.
	buf := buffer.NewView(2*fakeNetHeaderLen + 30)

	// Outer packet contains the control protocol number.
	buf[0] = 1
	buf[1] = 0xfe
	buf[2] = uint8(fakeControlProtocol)

	// Make sure packet with wrong protocol is not delivered.
	buf[fakeNetHeaderLen+0] = 0
	buf[fakeNetHeaderLen+1] = 1
	buf[fakeNetHeaderLen+2] = 0
	linkEP.InjectInbound(fakeNetNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
		Data: buf.ToVectorisedView(),
	}))
	if fakeTrans.controlCount != 0 {
		t.Errorf("controlCount = %d, want %d", fakeTrans.controlCount, 0)
	}

	// Make sure packet from the wrong source is not delivered.
	buf[fakeNetHeaderLen+0] = 3
	buf[fakeNetHeaderLen+1] = 1
	buf[fakeNetHeaderLen+2] = byte(fakeTransNumber)
	linkEP.InjectInbound(fakeNetNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
		Data: buf.ToVectorisedView(),
	}))
	if fakeTrans.controlCount != 0 {
		t.Errorf("controlCount = %d, want %d", fakeTrans.controlCount, 0)
	}

	// Make sure packet is delivered.
	buf[fakeNetHeaderLen+0] = 2
	buf[fakeNetHeaderLen+1] = 1
	buf[fakeNetHeaderLen+2] = byte(fakeTransNumber)
	linkEP.InjectInbound(fakeNetNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
		Data: buf.ToVectorisedView(),
	}))
	if fakeTrans.controlCount != 1 {
		t.Errorf("controlCount = %d, want %d", fakeTrans.controlCount, 1)
	}
}

func TestTransportSend(t *testing.T) {
	linkEP := channel.New(10, defaultMTU, "")
	s := stack.New(stack.Options{
		NetworkProtocols:   []stack.NetworkProtocol{fakeNetFactory()},
		TransportProtocols: []stack.TransportProtocol{fakeTransFactory()},
	})
	if err := s.CreateNIC(1, linkEP); err != nil {
		t.Fatalf("CreateNIC failed: %v", err)
	}

	if err := s.AddAddress(1, fakeNetNumber, "\x01"); err != nil {
		t.Fatalf("AddAddress failed: %v", err)
	}

	{
		subnet, err := tcpip.NewSubnet("\x00", "\x00")
		if err != nil {
			t.Fatal(err)
		}
		s.SetRouteTable([]tcpip.Route{{Destination: subnet, Gateway: "\x00", NIC: 1}})
	}

	// Create endpoint and bind it.
	wq := waiter.Queue{}
	ep, err := s.NewEndpoint(fakeTransNumber, fakeNetNumber, &wq)
	if err != nil {
		t.Fatalf("NewEndpoint failed: %v", err)
	}

	if err := ep.Connect(tcpip.FullAddress{0, "\x02", 0}); err != nil {
		t.Fatalf("Connect failed: %v", err)
	}

	// Create buffer that will hold the payload.
	view := buffer.NewView(30)
	_, _, err = ep.Write(tcpip.SlicePayload(view), tcpip.WriteOptions{})
	if err != nil {
		t.Fatalf("write failed: %v", err)
	}

	fakeNet := s.NetworkProtocolInstance(fakeNetNumber).(*fakeNetworkProtocol)

	if fakeNet.sendPacketCount[2] != 1 {
		t.Errorf("sendPacketCount = %d, want %d", fakeNet.sendPacketCount[2], 1)
	}
}

func TestTransportOptions(t *testing.T) {
	s := stack.New(stack.Options{
		NetworkProtocols:   []stack.NetworkProtocol{fakeNetFactory()},
		TransportProtocols: []stack.TransportProtocol{fakeTransFactory()},
	})

	// Try an unsupported transport protocol.
	if err := s.SetTransportProtocolOption(tcpip.TransportProtocolNumber(99999), fakeTransportGoodOption(false)); err != tcpip.ErrUnknownProtocol {
		t.Fatalf("SetTransportProtocolOption(fakeTrans2, blah, false) = %v, want = tcpip.ErrUnknownProtocol", err)
	}

	testCases := []struct {
		option   interface{}
		wantErr  *tcpip.Error
		verifier func(t *testing.T, p stack.TransportProtocol)
	}{
		{fakeTransportGoodOption(true), nil, func(t *testing.T, p stack.TransportProtocol) {
			t.Helper()
			fakeTrans := p.(*fakeTransportProtocol)
			if fakeTrans.opts.good != true {
				t.Fatalf("fakeTrans.opts.good = false, want = true")
			}
			var v fakeTransportGoodOption
			if err := s.TransportProtocolOption(fakeTransNumber, &v); err != nil {
				t.Fatalf("s.TransportProtocolOption(fakeTransNumber, &v) = %v, want = nil, where v is option %T", v, err)
			}
			if v != true {
				t.Fatalf("s.TransportProtocolOption(fakeTransNumber, &v) returned v = %v, want = true", v)
			}

		}},
		{fakeTransportBadOption(true), tcpip.ErrUnknownProtocolOption, nil},
		{fakeTransportInvalidValueOption(1), tcpip.ErrInvalidOptionValue, nil},
	}
	for _, tc := range testCases {
		if got := s.SetTransportProtocolOption(fakeTransNumber, tc.option); got != tc.wantErr {
			t.Errorf("s.SetTransportProtocolOption(fakeTrans, %v) = %v, want = %v", tc.option, got, tc.wantErr)
		}
		if tc.verifier != nil {
			tc.verifier(t, s.TransportProtocolInstance(fakeTransNumber))
		}
	}
}

func TestTransportForwarding(t *testing.T) {
	s := stack.New(stack.Options{
		NetworkProtocols:   []stack.NetworkProtocol{fakeNetFactory()},
		TransportProtocols: []stack.TransportProtocol{fakeTransFactory()},
	})
	s.SetForwarding(true)

	// TODO(b/123449044): Change this to a channel NIC.
	ep1 := loopback.New()
	if err := s.CreateNIC(1, ep1); err != nil {
		t.Fatalf("CreateNIC #1 failed: %v", err)
	}
	if err := s.AddAddress(1, fakeNetNumber, "\x01"); err != nil {
		t.Fatalf("AddAddress #1 failed: %v", err)
	}

	ep2 := channel.New(10, defaultMTU, "")
	if err := s.CreateNIC(2, ep2); err != nil {
		t.Fatalf("CreateNIC #2 failed: %v", err)
	}
	if err := s.AddAddress(2, fakeNetNumber, "\x02"); err != nil {
		t.Fatalf("AddAddress #2 failed: %v", err)
	}

	// Route all packets to address 3 to NIC 2 and all packets to address
	// 1 to NIC 1.
	{
		subnet0, err := tcpip.NewSubnet("\x03", "\xff")
		if err != nil {
			t.Fatal(err)
		}
		subnet1, err := tcpip.NewSubnet("\x01", "\xff")
		if err != nil {
			t.Fatal(err)
		}
		s.SetRouteTable([]tcpip.Route{
			{Destination: subnet0, Gateway: "\x00", NIC: 2},
			{Destination: subnet1, Gateway: "\x00", NIC: 1},
		})
	}

	wq := waiter.Queue{}
	ep, err := s.NewEndpoint(fakeTransNumber, fakeNetNumber, &wq)
	if err != nil {
		t.Fatalf("NewEndpoint failed: %v", err)
	}

	if err := ep.Bind(tcpip.FullAddress{Addr: "\x01", NIC: 1}); err != nil {
		t.Fatalf("Bind failed: %v", err)
	}

	// Send a packet to address 1 from address 3.
	req := buffer.NewView(30)
	req[0] = 1
	req[1] = 3
	req[2] = byte(fakeTransNumber)
	ep2.InjectInbound(fakeNetNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
		Data: req.ToVectorisedView(),
	}))

	aep, _, err := ep.Accept()
	if err != nil || aep == nil {
		t.Fatalf("Accept failed: %v, %v", aep, err)
	}

	resp := buffer.NewView(30)
	if _, _, err := aep.Write(tcpip.SlicePayload(resp), tcpip.WriteOptions{}); err != nil {
		t.Fatalf("Write failed: %v", err)
	}

	p, ok := ep2.Read()
	if !ok {
		t.Fatal("Response packet not forwarded")
	}

	nh := stack.PayloadSince(p.Pkt.NetworkHeader())
	if dst := nh[0]; dst != 3 {
		t.Errorf("Response packet has incorrect destination addresss: got = %d, want = 3", dst)
	}
	if src := nh[1]; src != 1 {
		t.Errorf("Response packet has incorrect source addresss: got = %d, want = 3", src)
	}
}