tcpip/link/fdbased/endpoint_test.go - third_party/netstack - Git at Google

 // 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.

 // +build linux

 package fdbased

 import (
 	"bytes"
 	"fmt"
 	"math/rand"
 	"reflect"
 	"syscall"
 	"testing"
 	"time"
 	"unsafe"

 	"github.com/google/netstack/tcpip"
 	"github.com/google/netstack/tcpip/buffer"
 	"github.com/google/netstack/tcpip/header"
 	"github.com/google/netstack/tcpip/link/rawfile"
 	"github.com/google/netstack/tcpip/stack"
 )

 const (
 	mtu        = 1500
 	laddr      = tcpip.LinkAddress("\x11\x22\x33\x44\x55\x66")
 	raddr      = tcpip.LinkAddress("\x77\x88\x99\xaa\xbb\xcc")
 	proto      = 10
 	csumOffset = 48
 	gsoMSS     = 500
 )

 type packetInfo struct {
 	raddr    tcpip.LinkAddress
 	proto    tcpip.NetworkProtocolNumber
 	contents buffer.View
 }

 type context struct {
 	t    *testing.T
 	fds  [2]int
 	ep   stack.LinkEndpoint
 	ch   chan packetInfo
 	done chan struct{}
 }

 func newContext(t *testing.T, opt *Options) *context {
 	fds, err := syscall.Socketpair(syscall.AF_UNIX, syscall.SOCK_SEQPACKET, 0)
 	if err != nil {
 		t.Fatalf("Socketpair failed: %v", err)
 	}

 	done := make(chan struct{}, 1)
 	opt.ClosedFunc = func(*tcpip.Error) {
 		done <- struct{}{}
 	}

 	opt.FDs = []int{fds[1]}
 	ep, err := New(opt)
 	if err != nil {
 		t.Fatalf("Failed to create FD endpoint: %v", err)
 	}

 	c := &context{
 		t:    t,
 		fds:  fds,
 		ep:   ep,
 		ch:   make(chan packetInfo, 100),
 		done: done,
 	}

 	ep.Attach(c)

 	return c
 }

 func (c *context) cleanup() {
 	syscall.Close(c.fds[0])
 	<-c.done
 	syscall.Close(c.fds[1])
 }

 func (c *context) DeliverNetworkPacket(linkEP stack.LinkEndpoint, remote tcpip.LinkAddress, local tcpip.LinkAddress, protocol tcpip.NetworkProtocolNumber, vv buffer.VectorisedView) {
 	c.ch <- packetInfo{remote, protocol, vv.ToView()}
 }

 func TestNoEthernetProperties(t *testing.T) {
 	c := newContext(t, &Options{MTU: mtu})
 	defer c.cleanup()

 	if want, v := uint16(0), c.ep.MaxHeaderLength(); want != v {
 		t.Fatalf("MaxHeaderLength() = %v, want %v", v, want)
 	}

 	if want, v := uint32(mtu), c.ep.MTU(); want != v {
 		t.Fatalf("MTU() = %v, want %v", v, want)
 	}
 }

 func TestEthernetProperties(t *testing.T) {
 	c := newContext(t, &Options{EthernetHeader: true, MTU: mtu})
 	defer c.cleanup()

 	if want, v := uint16(header.EthernetMinimumSize), c.ep.MaxHeaderLength(); want != v {
 		t.Fatalf("MaxHeaderLength() = %v, want %v", v, want)
 	}

 	if want, v := uint32(mtu), c.ep.MTU(); want != v {
 		t.Fatalf("MTU() = %v, want %v", v, want)
 	}
 }

 func TestAddress(t *testing.T) {
 	addrs := []tcpip.LinkAddress{"", "abc", "def"}
 	for _, a := range addrs {
 		t.Run(fmt.Sprintf("Address: %q", a), func(t *testing.T) {
 			c := newContext(t, &Options{Address: a, MTU: mtu})
 			defer c.cleanup()

 			if want, v := a, c.ep.LinkAddress(); want != v {
 				t.Fatalf("LinkAddress() = %v, want %v", v, want)
 			}
 		})
 	}
 }

 func testWritePacket(t *testing.T, plen int, eth bool, gsoMaxSize uint32) {
 	c := newContext(t, &Options{Address: laddr, MTU: mtu, EthernetHeader: eth, GSOMaxSize: gsoMaxSize})
 	defer c.cleanup()

 	r := &stack.Route{
 		RemoteLinkAddress: raddr,
 	}

 	// Build header.
 	hdr := buffer.NewPrependable(int(c.ep.MaxHeaderLength()) + 100)
 	b := hdr.Prepend(100)
 	for i := range b {
 		b[i] = uint8(rand.Intn(256))
 	}

 	// Build payload and write.
 	payload := make(buffer.View, plen)
 	for i := range payload {
 		payload[i] = uint8(rand.Intn(256))
 	}
 	want := append(hdr.View(), payload...)
 	var gso *stack.GSO
 	if gsoMaxSize != 0 {
 		gso = &stack.GSO{
 			Type:       stack.GSOTCPv6,
 			NeedsCsum:  true,
 			CsumOffset: csumOffset,
 			MSS:        gsoMSS,
 			MaxSize:    gsoMaxSize,
 			L3HdrLen:   header.IPv4MaximumHeaderSize,
 		}
 	}
 	if err := c.ep.WritePacket(r, gso, hdr, payload.ToVectorisedView(), proto); err != nil {
 		t.Fatalf("WritePacket failed: %v", err)
 	}

 	// Read from fd, then compare with what we wrote.
 	b = make([]byte, mtu)
 	n, err := syscall.Read(c.fds[0], b)
 	if err != nil {
 		t.Fatalf("Read failed: %v", err)
 	}
 	b = b[:n]
 	if gsoMaxSize != 0 {
 		vnetHdr := *(*virtioNetHdr)(unsafe.Pointer(&b[0]))
 		if vnetHdr.flags&_VIRTIO_NET_HDR_F_NEEDS_CSUM == 0 {
 			t.Fatalf("virtioNetHdr.flags %v  doesn't contain %v", vnetHdr.flags, _VIRTIO_NET_HDR_F_NEEDS_CSUM)
 		}
 		csumStart := header.EthernetMinimumSize + gso.L3HdrLen
 		if vnetHdr.csumStart != csumStart {
 			t.Fatalf("vnetHdr.csumStart = %v, want %v", vnetHdr.csumStart, csumStart)
 		}
 		if vnetHdr.csumOffset != csumOffset {
 			t.Fatalf("vnetHdr.csumOffset = %v, want %v", vnetHdr.csumOffset, csumOffset)
 		}
 		gsoType := uint8(0)
 		if int(gso.MSS) < plen {
 			gsoType = _VIRTIO_NET_HDR_GSO_TCPV6
 		}
 		if vnetHdr.gsoType != gsoType {
 			t.Fatalf("vnetHdr.gsoType = %v, want %v", vnetHdr.gsoType, gsoType)
 		}
 		b = b[virtioNetHdrSize:]
 	}
 	if eth {
 		h := header.Ethernet(b)
 		b = b[header.EthernetMinimumSize:]

 		if a := h.SourceAddress(); a != laddr {
 			t.Fatalf("SourceAddress() = %v, want %v", a, laddr)
 		}

 		if a := h.DestinationAddress(); a != raddr {
 			t.Fatalf("DestinationAddress() = %v, want %v", a, raddr)
 		}

 		if et := h.Type(); et != proto {
 			t.Fatalf("Type() = %v, want %v", et, proto)
 		}
 	}
 	if len(b) != len(want) {
 		t.Fatalf("Read returned %v bytes, want %v", len(b), len(want))
 	}
 	if !bytes.Equal(b, want) {
 		t.Fatalf("Read returned %x, want %x", b, want)
 	}
 }

 func TestWritePacket(t *testing.T) {
 	lengths := []int{0, 100, 1000}
 	eths := []bool{true, false}
 	gsos := []uint32{0, 32768}

 	for _, eth := range eths {
 		for _, plen := range lengths {
 			for _, gso := range gsos {
 				t.Run(
 					fmt.Sprintf("Eth=%v,PayloadLen=%v,GSOMaxSize=%v", eth, plen, gso),
 					func(t *testing.T) {
 						testWritePacket(t, plen, eth, gso)
 					},
 				)
 			}
 		}
 	}
 }

 func TestPreserveSrcAddress(t *testing.T) {
 	baddr := tcpip.LinkAddress("\xcc\xbb\xaa\x77\x88\x99")

 	c := newContext(t, &Options{Address: laddr, MTU: mtu, EthernetHeader: true})
 	defer c.cleanup()

 	// Set LocalLinkAddress in route to the value of the bridged address.
 	r := &stack.Route{
 		RemoteLinkAddress: raddr,
 		LocalLinkAddress:  baddr,
 	}

 	// WritePacket panics given a prependable with anything less than
 	// the minimum size of the ethernet header.
 	hdr := buffer.NewPrependable(header.EthernetMinimumSize)
 	if err := c.ep.WritePacket(r, nil /* gso */, hdr, buffer.VectorisedView{}, proto); err != nil {
 		t.Fatalf("WritePacket failed: %v", err)
 	}

 	// Read from the FD, then compare with what we wrote.
 	b := make([]byte, mtu)
 	n, err := syscall.Read(c.fds[0], b)
 	if err != nil {
 		t.Fatalf("Read failed: %v", err)
 	}
 	b = b[:n]
 	h := header.Ethernet(b)

 	if a := h.SourceAddress(); a != baddr {
 		t.Fatalf("SourceAddress() = %v, want %v", a, baddr)
 	}
 }

 func TestDeliverPacket(t *testing.T) {
 	lengths := []int{100, 1000}
 	eths := []bool{true, false}

 	for _, eth := range eths {
 		for _, plen := range lengths {
 			t.Run(fmt.Sprintf("Eth=%v,PayloadLen=%v", eth, plen), func(t *testing.T) {
 				c := newContext(t, &Options{Address: laddr, MTU: mtu, EthernetHeader: eth})
 				defer c.cleanup()

 				// Build packet.
 				b := make([]byte, plen)
 				all := b
 				for i := range b {
 					b[i] = uint8(rand.Intn(256))
 				}

 				if !eth {
 					// So that it looks like an IPv4 packet.
 					b[0] = 0x40
 				} else {
 					hdr := make(header.Ethernet, header.EthernetMinimumSize)
 					hdr.Encode(&header.EthernetFields{
 						SrcAddr: raddr,
 						DstAddr: laddr,
 						Type:    proto,
 					})
 					all = append(hdr, b...)
 				}

 				// Write packet via the file descriptor.
 				if _, err := syscall.Write(c.fds[0], all); err != nil {
 					t.Fatalf("Write failed: %v", err)
 				}

 				// Receive packet through the endpoint.
 				select {
 				case pi := <-c.ch:
 					want := packetInfo{
 						raddr:    raddr,
 						proto:    proto,
 						contents: b,
 					}
 					if !eth {
 						want.proto = header.IPv4ProtocolNumber
 						want.raddr = ""
 					}
 					if !reflect.DeepEqual(want, pi) {
 						t.Fatalf("Unexpected received packet: %+v, want %+v", pi, want)
 					}
 				case <-time.After(10 * time.Second):
 					t.Fatalf("Timed out waiting for packet")
 				}
 			})
 		}
 	}
 }

 func TestBufConfigMaxLength(t *testing.T) {
 	got := 0
 	for _, i := range BufConfig {
 		got += i
 	}
 	want := header.MaxIPPacketSize // maximum TCP packet size
 	if got < want {
 		t.Errorf("total buffer size is invalid: got %d, want >= %d", got, want)
 	}
 }

 func TestBufConfigFirst(t *testing.T) {
 	// The stack assumes that the TCP/IP header is enterily contained in the first view.
 	// Therefore, the first view needs to be large enough to contain the maximum TCP/IP
 	// header, which is 120 bytes (60 bytes for IP + 60 bytes for TCP).
 	want := 120
 	got := BufConfig[0]
 	if got < want {
 		t.Errorf("first view has an invalid size: got %d, want >= %d", got, want)
 	}
 }

 var capLengthTestCases = []struct {
 	comment     string
 	config      []int
 	n           int
 	wantUsed    int
 	wantLengths []int
 }{
 	{
 		comment:     "Single slice",
 		config:      []int{2},
 		n:           1,
 		wantUsed:    1,
 		wantLengths: []int{1},
 	},
 	{
 		comment:     "Multiple slices",
 		config:      []int{1, 2},
 		n:           2,
 		wantUsed:    2,
 		wantLengths: []int{1, 1},
 	},
 	{
 		comment:     "Entire buffer",
 		config:      []int{1, 2},
 		n:           3,
 		wantUsed:    2,
 		wantLengths: []int{1, 2},
 	},
 	{
 		comment:     "Entire buffer but not on the last slice",
 		config:      []int{1, 2, 3},
 		n:           3,
 		wantUsed:    2,
 		wantLengths: []int{1, 2, 3},
 	},
 }

 func TestReadVDispatcherCapLength(t *testing.T) {
 	for _, c := range capLengthTestCases {
 		// fd does not matter for this test.
 		d := readVDispatcher{fd: -1, e: &endpoint{}}
 		d.views = make([]buffer.View, len(c.config))
 		d.iovecs = make([]syscall.Iovec, len(c.config))
 		d.allocateViews(c.config)

 		used := d.capViews(c.n, c.config)
 		if used != c.wantUsed {
 			t.Errorf("Test %q failed when calling capViews(%d, %v). Got %d. Want %d", c.comment, c.n, c.config, used, c.wantUsed)
 		}
 		lengths := make([]int, len(d.views))
 		for i, v := range d.views {
 			lengths[i] = len(v)
 		}
 		if !reflect.DeepEqual(lengths, c.wantLengths) {
 			t.Errorf("Test %q failed when calling capViews(%d, %v). Got %v. Want %v", c.comment, c.n, c.config, lengths, c.wantLengths)
 		}
 	}
 }

 func TestRecvMMsgDispatcherCapLength(t *testing.T) {
 	for _, c := range capLengthTestCases {
 		d := recvMMsgDispatcher{
 			fd:      -1, // fd does not matter for this test.
 			e:       &endpoint{},
 			views:   make([][]buffer.View, 1),
 			iovecs:  make([][]syscall.Iovec, 1),
 			msgHdrs: make([]rawfile.MMsgHdr, 1),
 		}

 		for i, _ := range d.views {
 			d.views[i] = make([]buffer.View, len(c.config))
 		}
 		for i := range d.iovecs {
 			d.iovecs[i] = make([]syscall.Iovec, len(c.config))
 		}
 		for k, msgHdr := range d.msgHdrs {
 			msgHdr.Msg.Iov = &d.iovecs[k][0]
 			msgHdr.Msg.Iovlen = uint64(len(c.config))
 		}

 		d.allocateViews(c.config)

 		used := d.capViews(0, c.n, c.config)
 		if used != c.wantUsed {
 			t.Errorf("Test %q failed when calling capViews(%d, %v). Got %d. Want %d", c.comment, c.n, c.config, used, c.wantUsed)
 		}
 		lengths := make([]int, len(d.views[0]))
 		for i, v := range d.views[0] {
 			lengths[i] = len(v)
 		}
 		if !reflect.DeepEqual(lengths, c.wantLengths) {
 			t.Errorf("Test %q failed when calling capViews(%d, %v). Got %v. Want %v", c.comment, c.n, c.config, lengths, c.wantLengths)
 		}

 	}
 }
	// 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.

	// +build linux

	package fdbased

	import (
	"bytes"
	"fmt"
	"math/rand"
	"reflect"
	"syscall"
	"testing"
	"time"
	"unsafe"

	"github.com/google/netstack/tcpip"
	"github.com/google/netstack/tcpip/buffer"
	"github.com/google/netstack/tcpip/header"
	"github.com/google/netstack/tcpip/link/rawfile"
	"github.com/google/netstack/tcpip/stack"
	)

	const (
	mtu = 1500
	laddr = tcpip.LinkAddress("\x11\x22\x33\x44\x55\x66")
	raddr = tcpip.LinkAddress("\x77\x88\x99\xaa\xbb\xcc")
	proto = 10
	csumOffset = 48
	gsoMSS = 500
	)

	type packetInfo struct {
	raddr tcpip.LinkAddress
	proto tcpip.NetworkProtocolNumber
	contents buffer.View
	}

	type context struct {
	t *testing.T
	fds [2]int
	ep stack.LinkEndpoint
	ch chan packetInfo
	done chan struct{}
	}

	func newContext(t testing.T, opt Options) *context {
	fds, err := syscall.Socketpair(syscall.AF_UNIX, syscall.SOCK_SEQPACKET, 0)
	if err != nil {
	t.Fatalf("Socketpair failed: %v", err)
	}

	done := make(chan struct{}, 1)
	opt.ClosedFunc = func(*tcpip.Error) {
	done <- struct{}{}
	}

	opt.FDs = []int{fds[1]}
	ep, err := New(opt)
	if err != nil {
	t.Fatalf("Failed to create FD endpoint: %v", err)
	}

	c := &context{
	t: t,
	fds: fds,
	ep: ep,
	ch: make(chan packetInfo, 100),
	done: done,
	}

	ep.Attach(c)

	return c
	}

	func (c *context) cleanup() {
	syscall.Close(c.fds[0])
	<-c.done
	syscall.Close(c.fds[1])
	}

	func (c *context) DeliverNetworkPacket(linkEP stack.LinkEndpoint, remote tcpip.LinkAddress, local tcpip.LinkAddress, protocol tcpip.NetworkProtocolNumber, vv buffer.VectorisedView) {
	c.ch <- packetInfo{remote, protocol, vv.ToView()}
	}

	func TestNoEthernetProperties(t *testing.T) {
	c := newContext(t, &Options{MTU: mtu})
	defer c.cleanup()

	if want, v := uint16(0), c.ep.MaxHeaderLength(); want != v {
	t.Fatalf("MaxHeaderLength() = %v, want %v", v, want)
	}

	if want, v := uint32(mtu), c.ep.MTU(); want != v {
	t.Fatalf("MTU() = %v, want %v", v, want)
	}
	}

	func TestEthernetProperties(t *testing.T) {
	c := newContext(t, &Options{EthernetHeader: true, MTU: mtu})
	defer c.cleanup()

	if want, v := uint16(header.EthernetMinimumSize), c.ep.MaxHeaderLength(); want != v {
	t.Fatalf("MaxHeaderLength() = %v, want %v", v, want)
	}

	if want, v := uint32(mtu), c.ep.MTU(); want != v {
	t.Fatalf("MTU() = %v, want %v", v, want)
	}
	}

	func TestAddress(t *testing.T) {
	addrs := []tcpip.LinkAddress{"", "abc", "def"}
	for _, a := range addrs {
	t.Run(fmt.Sprintf("Address: %q", a), func(t *testing.T) {
	c := newContext(t, &Options{Address: a, MTU: mtu})
	defer c.cleanup()

	if want, v := a, c.ep.LinkAddress(); want != v {
	t.Fatalf("LinkAddress() = %v, want %v", v, want)
	}
	})
	}
	}

	func testWritePacket(t *testing.T, plen int, eth bool, gsoMaxSize uint32) {
	c := newContext(t, &Options{Address: laddr, MTU: mtu, EthernetHeader: eth, GSOMaxSize: gsoMaxSize})
	defer c.cleanup()

	r := &stack.Route{
	RemoteLinkAddress: raddr,
	}

	// Build header.
	hdr := buffer.NewPrependable(int(c.ep.MaxHeaderLength()) + 100)
	b := hdr.Prepend(100)
	for i := range b {
	b[i] = uint8(rand.Intn(256))
	}

	// Build payload and write.
	payload := make(buffer.View, plen)
	for i := range payload {
	payload[i] = uint8(rand.Intn(256))
	}
	want := append(hdr.View(), payload...)
	var gso *stack.GSO
	if gsoMaxSize != 0 {
	gso = &stack.GSO{
	Type: stack.GSOTCPv6,
	NeedsCsum: true,
	CsumOffset: csumOffset,
	MSS: gsoMSS,
	MaxSize: gsoMaxSize,
	L3HdrLen: header.IPv4MaximumHeaderSize,
	}
	}
	if err := c.ep.WritePacket(r, gso, hdr, payload.ToVectorisedView(), proto); err != nil {
	t.Fatalf("WritePacket failed: %v", err)
	}

	// Read from fd, then compare with what we wrote.
	b = make([]byte, mtu)
	n, err := syscall.Read(c.fds[0], b)
	if err != nil {
	t.Fatalf("Read failed: %v", err)
	}
	b = b[:n]
	if gsoMaxSize != 0 {
	vnetHdr := (virtioNetHdr)(unsafe.Pointer(&b[0]))
	if vnetHdr.flags&_VIRTIO_NET_HDR_F_NEEDS_CSUM == 0 {
	t.Fatalf("virtioNetHdr.flags %v doesn't contain %v", vnetHdr.flags, _VIRTIO_NET_HDR_F_NEEDS_CSUM)
	}
	csumStart := header.EthernetMinimumSize + gso.L3HdrLen
	if vnetHdr.csumStart != csumStart {
	t.Fatalf("vnetHdr.csumStart = %v, want %v", vnetHdr.csumStart, csumStart)
	}
	if vnetHdr.csumOffset != csumOffset {
	t.Fatalf("vnetHdr.csumOffset = %v, want %v", vnetHdr.csumOffset, csumOffset)
	}
	gsoType := uint8(0)
	if int(gso.MSS) < plen {
	gsoType = _VIRTIO_NET_HDR_GSO_TCPV6
	}
	if vnetHdr.gsoType != gsoType {
	t.Fatalf("vnetHdr.gsoType = %v, want %v", vnetHdr.gsoType, gsoType)
	}
	b = b[virtioNetHdrSize:]
	}
	if eth {
	h := header.Ethernet(b)
	b = b[header.EthernetMinimumSize:]

	if a := h.SourceAddress(); a != laddr {
	t.Fatalf("SourceAddress() = %v, want %v", a, laddr)
	}

	if a := h.DestinationAddress(); a != raddr {
	t.Fatalf("DestinationAddress() = %v, want %v", a, raddr)
	}

	if et := h.Type(); et != proto {
	t.Fatalf("Type() = %v, want %v", et, proto)
	}
	}
	if len(b) != len(want) {
	t.Fatalf("Read returned %v bytes, want %v", len(b), len(want))
	}
	if !bytes.Equal(b, want) {
	t.Fatalf("Read returned %x, want %x", b, want)
	}
	}

	func TestWritePacket(t *testing.T) {
	lengths := []int{0, 100, 1000}
	eths := []bool{true, false}
	gsos := []uint32{0, 32768}

	for _, eth := range eths {
	for _, plen := range lengths {
	for _, gso := range gsos {
	t.Run(
	fmt.Sprintf("Eth=%v,PayloadLen=%v,GSOMaxSize=%v", eth, plen, gso),
	func(t *testing.T) {
	testWritePacket(t, plen, eth, gso)
	},
	)
	}
	}
	}
	}

	func TestPreserveSrcAddress(t *testing.T) {
	baddr := tcpip.LinkAddress("\xcc\xbb\xaa\x77\x88\x99")

	c := newContext(t, &Options{Address: laddr, MTU: mtu, EthernetHeader: true})
	defer c.cleanup()

	// Set LocalLinkAddress in route to the value of the bridged address.
	r := &stack.Route{
	RemoteLinkAddress: raddr,
	LocalLinkAddress: baddr,
	}

	// WritePacket panics given a prependable with anything less than
	// the minimum size of the ethernet header.
	hdr := buffer.NewPrependable(header.EthernetMinimumSize)
	if err := c.ep.WritePacket(r, nil /* gso */, hdr, buffer.VectorisedView{}, proto); err != nil {
	t.Fatalf("WritePacket failed: %v", err)
	}

	// Read from the FD, then compare with what we wrote.
	b := make([]byte, mtu)
	n, err := syscall.Read(c.fds[0], b)
	if err != nil {
	t.Fatalf("Read failed: %v", err)
	}
	b = b[:n]
	h := header.Ethernet(b)

	if a := h.SourceAddress(); a != baddr {
	t.Fatalf("SourceAddress() = %v, want %v", a, baddr)
	}
	}

	func TestDeliverPacket(t *testing.T) {
	lengths := []int{100, 1000}
	eths := []bool{true, false}

	for _, eth := range eths {
	for _, plen := range lengths {
	t.Run(fmt.Sprintf("Eth=%v,PayloadLen=%v", eth, plen), func(t *testing.T) {
	c := newContext(t, &Options{Address: laddr, MTU: mtu, EthernetHeader: eth})
	defer c.cleanup()

	// Build packet.
	b := make([]byte, plen)
	all := b
	for i := range b {
	b[i] = uint8(rand.Intn(256))
	}

	if !eth {
	// So that it looks like an IPv4 packet.
	b[0] = 0x40
	} else {
	hdr := make(header.Ethernet, header.EthernetMinimumSize)
	hdr.Encode(&header.EthernetFields{
	SrcAddr: raddr,
	DstAddr: laddr,
	Type: proto,
	})
	all = append(hdr, b...)
	}

	// Write packet via the file descriptor.
	if _, err := syscall.Write(c.fds[0], all); err != nil {
	t.Fatalf("Write failed: %v", err)
	}

	// Receive packet through the endpoint.
	select {
	case pi := <-c.ch:
	want := packetInfo{
	raddr: raddr,
	proto: proto,
	contents: b,
	}
	if !eth {
	want.proto = header.IPv4ProtocolNumber
	want.raddr = ""
	}
	if !reflect.DeepEqual(want, pi) {
	t.Fatalf("Unexpected received packet: %+v, want %+v", pi, want)
	}
	case <-time.After(10 * time.Second):
	t.Fatalf("Timed out waiting for packet")
	}
	})
	}
	}
	}

	func TestBufConfigMaxLength(t *testing.T) {
	got := 0
	for _, i := range BufConfig {
	got += i
	}
	want := header.MaxIPPacketSize // maximum TCP packet size
	if got < want {
	t.Errorf("total buffer size is invalid: got %d, want >= %d", got, want)
	}
	}

	func TestBufConfigFirst(t *testing.T) {
	// The stack assumes that the TCP/IP header is enterily contained in the first view.
	// Therefore, the first view needs to be large enough to contain the maximum TCP/IP
	// header, which is 120 bytes (60 bytes for IP + 60 bytes for TCP).
	want := 120
	got := BufConfig[0]
	if got < want {
	t.Errorf("first view has an invalid size: got %d, want >= %d", got, want)
	}
	}

	var capLengthTestCases = []struct {
	comment string
	config []int
	n int
	wantUsed int
	wantLengths []int
	}{
	{
	comment: "Single slice",
	config: []int{2},
	n: 1,
	wantUsed: 1,
	wantLengths: []int{1},
	},
	{
	comment: "Multiple slices",
	config: []int{1, 2},
	n: 2,
	wantUsed: 2,
	wantLengths: []int{1, 1},
	},
	{
	comment: "Entire buffer",
	config: []int{1, 2},
	n: 3,
	wantUsed: 2,
	wantLengths: []int{1, 2},
	},
	{
	comment: "Entire buffer but not on the last slice",
	config: []int{1, 2, 3},
	n: 3,
	wantUsed: 2,
	wantLengths: []int{1, 2, 3},
	},
	}

	func TestReadVDispatcherCapLength(t *testing.T) {
	for _, c := range capLengthTestCases {
	// fd does not matter for this test.
	d := readVDispatcher{fd: -1, e: &endpoint{}}
	d.views = make([]buffer.View, len(c.config))
	d.iovecs = make([]syscall.Iovec, len(c.config))
	d.allocateViews(c.config)

	used := d.capViews(c.n, c.config)
	if used != c.wantUsed {
	t.Errorf("Test %q failed when calling capViews(%d, %v). Got %d. Want %d", c.comment, c.n, c.config, used, c.wantUsed)
	}
	lengths := make([]int, len(d.views))
	for i, v := range d.views {
	lengths[i] = len(v)
	}
	if !reflect.DeepEqual(lengths, c.wantLengths) {
	t.Errorf("Test %q failed when calling capViews(%d, %v). Got %v. Want %v", c.comment, c.n, c.config, lengths, c.wantLengths)
	}
	}
	}

	func TestRecvMMsgDispatcherCapLength(t *testing.T) {
	for _, c := range capLengthTestCases {
	d := recvMMsgDispatcher{
	fd: -1, // fd does not matter for this test.
	e: &endpoint{},
	views: make([][]buffer.View, 1),
	iovecs: make([][]syscall.Iovec, 1),
	msgHdrs: make([]rawfile.MMsgHdr, 1),
	}

	for i, _ := range d.views {
	d.views[i] = make([]buffer.View, len(c.config))
	}
	for i := range d.iovecs {
	d.iovecs[i] = make([]syscall.Iovec, len(c.config))
	}
	for k, msgHdr := range d.msgHdrs {
	msgHdr.Msg.Iov = &d.iovecs[k][0]
	msgHdr.Msg.Iovlen = uint64(len(c.config))
	}

	d.allocateViews(c.config)

	used := d.capViews(0, c.n, c.config)
	if used != c.wantUsed {
	t.Errorf("Test %q failed when calling capViews(%d, %v). Got %d. Want %d", c.comment, c.n, c.config, used, c.wantUsed)
	}
	lengths := make([]int, len(d.views[0]))
	for i, v := range d.views[0] {
	lengths[i] = len(v)
	}
	if !reflect.DeepEqual(lengths, c.wantLengths) {
	t.Errorf("Test %q failed when calling capViews(%d, %v). Got %v. Want %v", c.comment, c.n, c.config, lengths, c.wantLengths)
	}

	}
	}