Migrate PacketBuffer to use pkg/buffer

Benchmark iperf3:
                    Before      After
native->runsc       5.14        5.01    (Gbps)
runsc->native       4.15        4.07    (Gbps)

It did introduce overhead, mainly at the bridge between pkg/buffer and
VectorisedView, the ExtractVV method. Once endpoints start migrating away from
VV, this overhead will be gone.

Updates #2404

PiperOrigin-RevId: 373651666

3 files changed, 177 insertions, 220 deletions

diff --git a/pkg/tcpip/stack/BUILD b/pkg/tcpip/stack/BUILD
index 63ab31083..84aa6a9e4 100644
--- a/pkg/tcpip/stack/BUILD
+++ b/pkg/tcpip/stack/BUILD
@@ -74,6 +74,7 @@ go_library(
     visibility = ["//visibility:public"],
     deps = [
         "//pkg/atomicbitops",
+        "//pkg/buffer",
         "//pkg/ilist",
         "//pkg/log",
         "//pkg/rand",
diff --git a/pkg/tcpip/stack/packet_buffer.go b/pkg/tcpip/stack/packet_buffer.go
index fc3c54e34..e2e073091 100644
--- a/pkg/tcpip/stack/packet_buffer.go
+++ b/pkg/tcpip/stack/packet_buffer.go
@@ -16,9 +16,10 @@ package stack
 import (
 	"fmt"
 
+	"gvisor.dev/gvisor/pkg/buffer"
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/tcpip"
-	"gvisor.dev/gvisor/pkg/tcpip/buffer"
+	tcpipbuffer "gvisor.dev/gvisor/pkg/tcpip/buffer"
 	"gvisor.dev/gvisor/pkg/tcpip/header"
 )
 
@@ -39,7 +40,7 @@ type PacketBufferOptions struct {
 
 	// Data is the initial unparsed data for the new packet. If set, it will be
 	// owned by the new packet.
-	Data buffer.VectorisedView
+	Data tcpipbuffer.VectorisedView
 
 	// IsForwardedPacket identifies that the PacketBuffer being created is for a
 	// forwarded packet.
@@ -56,6 +57,34 @@ type PacketBufferOptions struct {
 // empty. Use of PacketBuffer in any other order is unsupported.
 //
 // PacketBuffer must be created with NewPacketBuffer.
+//
+// Internal structure: A PacketBuffer holds a pointer to buffer.Buffer, which
+// exposes a logically-contiguous byte storage. The underlying storage structure
+// is abstracted out, and should not be a concern here for most of the time.
+//
+// |- reserved ->|
+//               |--->| consumed (incoming)
+// 0             V    V
+// +--------+----+----+--------------------+
+// |        |    |    | current data ...   | (buf)
+// +--------+----+----+--------------------+
+//          ^    |
+//          |<---| pushed (outgoing)
+//
+// When a PacketBuffer is created, a `reserved` header region can be specified,
+// which stack pushes headers in this region for an outgoing packet. There could
+// be no such region for an incoming packet, and `reserved` is 0. The value of
+// `reserved` never changes in the entire lifetime of the packet.
+//
+// Outgoing Packet: When a header is pushed, `pushed` gets incremented by the
+// pushed length, and the current value is stored for each header. PacketBuffer
+// substracts this value from `reserved` to compute the starting offset of each
+// header in `buf`.
+//
+// Incoming Packet: When a header is consumed (a.k.a. parsed), the current
+// `consumed` value is stored for each header, and it gets incremented by the
+// consumed length. PacketBuffer adds this value to `reserved` to compute the
+// starting offset of each header in `buf`.
 type PacketBuffer struct {
 	_ sync.NoCopy
 
@@ -63,28 +92,16 @@ type PacketBuffer struct {
 	// PacketBuffers.
 	PacketBufferEntry
 
-	// data holds the payload of the packet.
-	//
-	// For inbound packets, Data is initially the whole packet. Then gets moved to
-	// headers via PacketHeader.Consume, when the packet is being parsed.
-	//
-	// For outbound packets, Data is the innermost layer, defined by the protocol.
-	// Headers are pushed in front of it via PacketHeader.Push.
-	//
-	// The bytes backing Data are immutable, a.k.a. users shouldn't write to its
-	// backing storage.
-	data buffer.VectorisedView
+	// buf is the underlying buffer for the packet. See struct level docs for
+	// details.
+	buf      *buffer.Buffer
+	reserved int
+	pushed   int
+	consumed int
 
 	// headers stores metadata about each header.
 	headers [numHeaderType]headerInfo
 
-	// header is the internal storage for outbound packets. Headers will be pushed
-	// (prepended) on this storage as the packet is being constructed.
-	//
-	// TODO(gvisor.dev/issue/2404): Switch to an implementation that header and
-	// data are held in the same underlying buffer storage.
-	header buffer.Prependable
-
 	// NetworkProtocolNumber is only valid when NetworkHeader().View().IsEmpty()
 	// returns false.
 	// TODO(gvisor.dev/issue/3574): Remove the separately passed protocol
@@ -131,10 +148,14 @@ type PacketBuffer struct {
 // NewPacketBuffer creates a new PacketBuffer with opts.
 func NewPacketBuffer(opts PacketBufferOptions) *PacketBuffer {
 	pk := &PacketBuffer{
-		data: opts.Data,
+		buf: &buffer.Buffer{},
 	}
 	if opts.ReserveHeaderBytes != 0 {
-		pk.header = buffer.NewPrependable(opts.ReserveHeaderBytes)
+		pk.buf.AppendOwned(make([]byte, opts.ReserveHeaderBytes))
+		pk.reserved = opts.ReserveHeaderBytes
+	}
+	for _, v := range opts.Data.Views() {
+		pk.buf.AppendOwned(v)
 	}
 	if opts.IsForwardedPacket {
 		pk.NetworkPacketInfo.IsForwardedPacket = opts.IsForwardedPacket
@@ -145,13 +166,13 @@ func NewPacketBuffer(opts PacketBufferOptions) *PacketBuffer {
 // ReservedHeaderBytes returns the number of bytes initially reserved for
 // headers.
 func (pk *PacketBuffer) ReservedHeaderBytes() int {
-	return pk.header.UsedLength() + pk.header.AvailableLength()
+	return pk.reserved
 }
 
 // AvailableHeaderBytes returns the number of bytes currently available for
 // headers. This is relevant to PacketHeader.Push method only.
 func (pk *PacketBuffer) AvailableHeaderBytes() int {
-	return pk.header.AvailableLength()
+	return pk.reserved - pk.pushed
 }
 
 // LinkHeader returns the handle to link-layer header.
@@ -180,24 +201,18 @@ func (pk *PacketBuffer) TransportHeader() PacketHeader {
 
 // HeaderSize returns the total size of all headers in bytes.
 func (pk *PacketBuffer) HeaderSize() int {
-	// Note for inbound packets (Consume called), headers are not stored in
-	// pk.header. Thus, calculation of size of each header is needed.
-	var size int
-	for i := range pk.headers {
-		size += len(pk.headers[i].buf)
-	}
-	return size
+	return pk.pushed + pk.consumed
 }
 
 // Size returns the size of packet in bytes.
 func (pk *PacketBuffer) Size() int {
-	return pk.HeaderSize() + pk.data.Size()
+	return int(pk.buf.Size()) - pk.headerOffset()
 }
 
 // MemSize returns the estimation size of the pk in memory, including backing
 // buffer data.
 func (pk *PacketBuffer) MemSize() int {
-	return pk.HeaderSize() + pk.data.MemSize() + packetBufferStructSize
+	return int(pk.buf.Size()) + packetBufferStructSize
 }
 
 // Data returns the handle to data portion of pk.
@@ -206,61 +221,65 @@ func (pk *PacketBuffer) Data() PacketData {
 }
 
 // Views returns the underlying storage of the whole packet.
-func (pk *PacketBuffer) Views() []buffer.View {
-	// Optimization for outbound packets that headers are in pk.header.
-	useHeader := true
-	for i := range pk.headers {
-		if !canUseHeader(&pk.headers[i]) {
-			useHeader = false
-			break
-		}
-	}
+func (pk *PacketBuffer) Views() []tcpipbuffer.View {
+	var views []tcpipbuffer.View
+	offset := pk.headerOffset()
+	pk.buf.SubApply(offset, int(pk.buf.Size())-offset, func(v []byte) {
+		views = append(views, v)
+	})
+	return views
+}
 
-	dataViews := pk.data.Views()
-
-	var vs []buffer.View
-	if useHeader {
-		vs = make([]buffer.View, 0, 1+len(dataViews))
-		vs = append(vs, pk.header.View())
-	} else {
-		vs = make([]buffer.View, 0, len(pk.headers)+len(dataViews))
-		for i := range pk.headers {
-			if v := pk.headers[i].buf; len(v) > 0 {
-				vs = append(vs, v)
-			}
-		}
-	}
-	return append(vs, dataViews...)
+func (pk *PacketBuffer) headerOffset() int {
+	return pk.reserved - pk.pushed
+}
+
+func (pk *PacketBuffer) headerOffsetOf(typ headerType) int {
+	return pk.reserved + pk.headers[typ].offset
 }
 
-func canUseHeader(h *headerInfo) bool {
-	// h.offset will be negative if the header was pushed in to prependable
-	// portion, or doesn't matter when it's empty.
-	return len(h.buf) == 0 || h.offset < 0
+func (pk *PacketBuffer) dataOffset() int {
+	return pk.reserved + pk.consumed
 }
 
-func (pk *PacketBuffer) push(typ headerType, size int) buffer.View {
+func (pk *PacketBuffer) push(typ headerType, size int) tcpipbuffer.View {
 	h := &pk.headers[typ]
-	if h.buf != nil {
+	if h.length > 0 {
 		panic(fmt.Sprintf("push must not be called twice: type %s", typ))
 	}
-	h.buf = buffer.View(pk.header.Prepend(size))
-	h.offset = -pk.header.UsedLength()
-	return h.buf
+	if pk.pushed+size > pk.reserved {
+		panic("not enough headroom reserved")
+	}
+	pk.pushed += size
+	h.offset = -pk.pushed
+	h.length = size
+	return pk.headerView(typ)
 }
 
-func (pk *PacketBuffer) consume(typ headerType, size int) (v buffer.View, consumed bool) {
+func (pk *PacketBuffer) consume(typ headerType, size int) (v tcpipbuffer.View, consumed bool) {
 	h := &pk.headers[typ]
-	if h.buf != nil {
+	if h.length > 0 {
 		panic(fmt.Sprintf("consume must not be called twice: type %s", typ))
 	}
-	v, ok := pk.data.PullUp(size)
+	if pk.headerOffset()+pk.consumed+size > int(pk.buf.Size()) {
+		return nil, false
+	}
+	h.offset = pk.consumed
+	h.length = size
+	pk.consumed += size
+	return pk.headerView(typ), true
+}
+
+func (pk *PacketBuffer) headerView(typ headerType) tcpipbuffer.View {
+	h := &pk.headers[typ]
+	if h.length == 0 {
+		return nil
+	}
+	v, ok := pk.buf.PullUp(pk.headerOffsetOf(typ), h.length)
 	if !ok {
-		return
+		panic("PullUp failed")
 	}
-	pk.data.TrimFront(size)
-	h.buf = v
-	return h.buf, true
+	return v
 }
 
 // Clone makes a shallow copy of pk.
@@ -270,9 +289,11 @@ func (pk *PacketBuffer) consume(typ headerType, size int) (v buffer.View, consum
 func (pk *PacketBuffer) Clone() *PacketBuffer {
 	return &PacketBuffer{
 		PacketBufferEntry:            pk.PacketBufferEntry,
-		data:                         pk.data.Clone(nil),
+		buf:                          pk.buf,
+		reserved:                     pk.reserved,
+		pushed:                       pk.pushed,
+		consumed:                     pk.consumed,
 		headers:                      pk.headers,
-		header:                       pk.header,
 		Hash:                         pk.Hash,
 		Owner:                        pk.Owner,
 		GSOOptions:                   pk.GSOOptions,
@@ -306,9 +327,11 @@ func (pk *PacketBuffer) Network() header.Network {
 // See PacketBuffer.Data for details about how a packet buffer holds an inbound
 // packet.
 func (pk *PacketBuffer) CloneToInbound() *PacketBuffer {
-	newPk := NewPacketBuffer(PacketBufferOptions{
-		Data: buffer.NewVectorisedView(pk.Size(), pk.Views()),
-	})
+	newPk := &PacketBuffer{
+		buf: pk.buf,
+		// Treat unfilled header portion as reserved.
+		reserved: pk.AvailableHeaderBytes(),
+	}
 	// TODO(gvisor.dev/issue/5696): reimplement conntrack so that no need to
 	// maintain this flag in the packet. Currently conntrack needs this flag to
 	// tell if a noop connection should be inserted at Input hook. Once conntrack
@@ -322,15 +345,12 @@ func (pk *PacketBuffer) CloneToInbound() *PacketBuffer {
 
 // headerInfo stores metadata about a header in a packet.
 type headerInfo struct {
-	// buf is the memorized slice for both prepended and consumed header.
-	// When header is prepended, buf serves as memorized value, which is a slice
-	// of pk.header. When header is consumed, buf is the slice pulled out from
-	// pk.Data, which is the only place to hold this header.
-	buf buffer.View
-
-	// offset will be a negative number denoting the offset where this header is
-	// from the end of pk.header, if it is prepended. Otherwise, zero.
+	// offset is the offset of the header in pk.buf relative to
+	// pk.buf[pk.reserved]. See the PacketBuffer struct for details.
 	offset int
+
+	// length is the length of this header.
+	length int
 }
 
 // PacketHeader is a handle object to a header in the underlying packet.
@@ -340,14 +360,14 @@ type PacketHeader struct {
 }
 
 // View returns the underlying storage of h.
-func (h PacketHeader) View() buffer.View {
-	return h.pk.headers[h.typ].buf
+func (h PacketHeader) View() tcpipbuffer.View {
+	return h.pk.headerView(h.typ)
 }
 
 // Push pushes size bytes in the front of its residing packet, and returns the
 // backing storage. Callers may only call one of Push or Consume once on each
 // header in the lifetime of the underlying packet.
-func (h PacketHeader) Push(size int) buffer.View {
+func (h PacketHeader) Push(size int) tcpipbuffer.View {
 	return h.pk.push(h.typ, size)
 }
 
@@ -356,7 +376,7 @@ func (h PacketHeader) Push(size int) buffer.View {
 // size, consumed will be false, and the state of h will not be affected.
 // Callers may only call one of Push or Consume once on each header in the
 // lifetime of the underlying packet.
-func (h PacketHeader) Consume(size int) (v buffer.View, consumed bool) {
+func (h PacketHeader) Consume(size int) (v tcpipbuffer.View, consumed bool) {
 	return h.pk.consume(h.typ, size)
 }
 
@@ -367,55 +387,84 @@ type PacketData struct {
 
 // PullUp returns a contiguous view of size bytes from the beginning of d.
 // Callers should not write to or keep the view for later use.
-func (d PacketData) PullUp(size int) (buffer.View, bool) {
-	return d.pk.data.PullUp(size)
+func (d PacketData) PullUp(size int) (tcpipbuffer.View, bool) {
+	return d.pk.buf.PullUp(d.pk.dataOffset(), size)
 }
 
 // DeleteFront removes count from the beginning of d. It panics if count >
 // d.Size(). All backing storage references after the front of the d are
 // invalidated.
 func (d PacketData) DeleteFront(count int) {
-	d.pk.data.TrimFront(count)
+	if !d.pk.buf.Remove(d.pk.dataOffset(), count) {
+		panic("count > d.Size()")
+	}
 }
 
 // CapLength reduces d to at most length bytes.
 func (d PacketData) CapLength(length int) {
-	d.pk.data.CapLength(length)
+	if length < 0 {
+		panic("length < 0")
+	}
+	if currLength := d.Size(); currLength > length {
+		trim := currLength - length
+		d.pk.buf.Remove(int(d.pk.buf.Size())-trim, trim)
+	}
 }
 
 // Views returns the underlying storage of d in a slice of Views. Caller should
 // not modify the returned slice.
-func (d PacketData) Views() []buffer.View {
-	return d.pk.data.Views()
+func (d PacketData) Views() []tcpipbuffer.View {
+	var views []tcpipbuffer.View
+	offset := d.pk.dataOffset()
+	d.pk.buf.SubApply(offset, int(d.pk.buf.Size())-offset, func(v []byte) {
+		views = append(views, v)
+	})
+	return views
 }
 
 // AppendView appends v into d, taking the ownership of v.
-func (d PacketData) AppendView(v buffer.View) {
-	d.pk.data.AppendView(v)
+func (d PacketData) AppendView(v tcpipbuffer.View) {
+	d.pk.buf.AppendOwned(v)
 }
 
-// ReadFromData moves at most count bytes from the beginning of srcData to the
-// end of d and returns the number of bytes moved.
-func (d PacketData) ReadFromData(srcData PacketData, count int) int {
-	return srcData.pk.data.ReadToVV(&d.pk.data, count)
+// MergeFragment appends the data portion of frag to dst. It takes ownership of
+// frag and frag should not be used again.
+func MergeFragment(dst, frag *PacketBuffer) {
+	frag.buf.TrimFront(int64(frag.dataOffset()))
+	dst.buf.Merge(frag.buf)
 }
 
 // ReadFromVV moves at most count bytes from the beginning of srcVV to the end
 // of d and returns the number of bytes moved.
-func (d PacketData) ReadFromVV(srcVV *buffer.VectorisedView, count int) int {
-	return srcVV.ReadToVV(&d.pk.data, count)
+func (d PacketData) ReadFromVV(srcVV *tcpipbuffer.VectorisedView, count int) int {
+	done := 0
+	for _, v := range srcVV.Views() {
+		if len(v) < count {
+			count -= len(v)
+			done += len(v)
+			d.pk.buf.AppendOwned(v)
+		} else {
+			v = v[:count]
+			count -= len(v)
+			done += len(v)
+			d.pk.buf.Append(v)
+			break
+		}
+	}
+	srcVV.TrimFront(done)
+	return done
 }
 
 // Size returns the number of bytes in the data payload of the packet.
 func (d PacketData) Size() int {
-	return d.pk.data.Size()
+	return int(d.pk.buf.Size()) - d.pk.dataOffset()
 }
 
 // AsRange returns a Range representing the current data payload of the packet.
 func (d PacketData) AsRange() Range {
 	return Range{
 		pk:     d.pk,
-		offset: d.pk.HeaderSize(),
+		offset: d.pk.dataOffset(),
 		length: d.Size(),
 	}
 }
@@ -425,17 +474,12 @@ func (d PacketData) AsRange() Range {
 //
 // This method exists for compatibility between PacketBuffer and VectorisedView.
 // It may be removed later and should be used with care.
-func (d PacketData) ExtractVV() buffer.VectorisedView {
-	return d.pk.data
-}
-
-// Replace replaces the data portion of the packet with vv, taking the ownership
-// of vv.
-//
-// This method exists for compatibility between PacketBuffer and VectorisedView.
-// It may be removed later and should be used with care.
-func (d PacketData) Replace(vv buffer.VectorisedView) {
-	d.pk.data = vv
+func (d PacketData) ExtractVV() tcpipbuffer.VectorisedView {
+	var vv tcpipbuffer.VectorisedView
+	d.pk.buf.SubApply(d.pk.dataOffset(), d.pk.Size(), func(v []byte) {
+		vv.AppendView(v)
+	})
+	return vv
 }
 
 // Range represents a contiguous subportion of a PacketBuffer.
@@ -479,9 +523,9 @@ func (r Range) Capped(max int) Range {
 // AsView returns the backing storage of r if possible. It will allocate a new
 // View if r spans multiple pieces internally. Caller should not write to the
 // returned View in any way.
-func (r Range) AsView() buffer.View {
+func (r Range) AsView() tcpipbuffer.View {
 	var allocated bool
-	var v buffer.View
+	var v tcpipbuffer.View
 	r.iterate(func(b []byte) {
 		if v == nil {
 			// v has not been assigned, allowing first view to be returned.
@@ -502,7 +546,7 @@ func (r Range) AsView() buffer.View {
 }
 
 // ToOwnedView returns a owned copy of data in r.
-func (r Range) ToOwnedView() buffer.View {
+func (r Range) ToOwnedView() tcpipbuffer.View {
 	if r.length == 0 {
 		return nil
 	}
@@ -523,63 +567,7 @@ func (r Range) Checksum() uint16 {
 // iterate calls fn for each piece in r. fn is always called with a non-empty
 // slice.
 func (r Range) iterate(fn func([]byte)) {
-	w := window{
-		offset: r.offset,
-		length: r.length,
-	}
-	// Header portion.
-	for i := range r.pk.headers {
-		if b := w.process(r.pk.headers[i].buf); len(b) > 0 {
-			fn(b)
-		}
-		if w.isDone() {
-			break
-		}
-	}
-	// Data portion.
-	if !w.isDone() {
-		for _, v := range r.pk.data.Views() {
-			if b := w.process(v); len(b) > 0 {
-				fn(b)
-			}
-			if w.isDone() {
-				break
-			}
-		}
-	}
-}
-
-// window represents contiguous region of byte stream. User would call process()
-// to input bytes, and obtain a subslice that is inside the window.
-type window struct {
-	offset int
-	length int
-}
-
-// isDone returns true if the window has passed and further process() calls will
-// always return an empty slice. This can be used to end processing early.
-func (w *window) isDone() bool {
-	return w.length == 0
-}
-
-// process feeds b in and returns a subslice that is inside the window. The
-// returned slice will be a subslice of b, and it does not keep b after method
-// returns. This method may return an empty slice if nothing in b is inside the
-// window.
-func (w *window) process(b []byte) (inWindow []byte) {
-	if w.offset >= len(b) {
-		w.offset -= len(b)
-		return nil
-	}
-	if w.offset > 0 {
-		b = b[w.offset:]
-		w.offset = 0
-	}
-	if w.length < len(b) {
-		b = b[:w.length]
-	}
-	w.length -= len(b)
-	return b
+	r.pk.buf.SubApply(r.offset, r.length, fn)
 }
 
 // PayloadSince returns packet payload starting from and including a particular
@@ -587,21 +575,14 @@ func (w *window) process(b []byte) (inWindow []byte) {
 //
 // The returned View is owned by the caller - its backing buffer is separate
 // from the packet header's underlying packet buffer.
-func PayloadSince(h PacketHeader) buffer.View {
-	size := h.pk.data.Size()
-	for _, hinfo := range h.pk.headers[h.typ:] {
-		size += len(hinfo.buf)
+func PayloadSince(h PacketHeader) tcpipbuffer.View {
+	offset := h.pk.headerOffset()
+	for i := headerType(0); i < h.typ; i++ {
+		offset += h.pk.headers[i].length
 	}
-
-	v := make(buffer.View, 0, size)
-
-	for _, hinfo := range h.pk.headers[h.typ:] {
-		v = append(v, hinfo.buf...)
-	}
-
-	for _, view := range h.pk.data.Views() {
-		v = append(v, view...)
-	}
-
-	return v
+	return Range{
+		pk:     h.pk,
+		offset: offset,
+		length: int(h.pk.buf.Size()) - offset,
+	}.ToOwnedView()
 }
diff --git a/pkg/tcpip/stack/packet_buffer_test.go b/pkg/tcpip/stack/packet_buffer_test.go
index bd4eb4fed..1c1aeb950 100644
--- a/pkg/tcpip/stack/packet_buffer_test.go
+++ b/pkg/tcpip/stack/packet_buffer_test.go
@@ -444,23 +444,8 @@ func TestPacketBufferData(t *testing.T) {
 				checkData(t, pkt, []byte(tc.data+s))
 			})
 
-			// ReadFromData/VV
+			// ReadFromVV
 			for _, n := range []int{0, 1, 2, 7, 10, 14, 20} {
-				t.Run(fmt.Sprintf("ReadFromData%d", n), func(t *testing.T) {
-					s := "TO READ"
-					otherPkt := NewPacketBuffer(PacketBufferOptions{
-						Data: vv(s, s),
-					})
-					s += s
-
-					pkt := tc.makePkt(t)
-					pkt.Data().ReadFromData(otherPkt.Data(), n)
-
-					if n < len(s) {
-						s = s[:n]
-					}
-					checkData(t, pkt, []byte(tc.data+s))
-				})
 				t.Run(fmt.Sprintf("ReadFromVV%d", n), func(t *testing.T) {
 					s := "TO READ"
 					srcVV := vv(s, s)
@@ -487,16 +472,6 @@ func TestPacketBufferData(t *testing.T) {
 					t.Errorf("pkt.Data().ExtractVV().ToOwnedView() = %q, want %q", got, want)
 				}
 			})
-
-			// Replace
-			t.Run("Replace", func(t *testing.T) {
-				s := "REPLACED"
-
-				pkt := tc.makePkt(t)
-				pkt.Data().Replace(vv(s))
-
-				checkData(t, pkt, []byte(s))
-			})
 		})
 	}
 }
@@ -568,7 +543,7 @@ func checkViewEqual(t *testing.T, what string, got, want buffer.View) {
 func checkData(t *testing.T, pkt *PacketBuffer, want []byte) {
 	t.Helper()
 	if got := concatViews(pkt.Data().Views()...); !bytes.Equal(got, want) {
-		t.Errorf("pkt.Data().Views() = %x, want %x", got, want)
+		t.Errorf("pkt.Data().Views() = 0x%x, want 0x%x", got, want)
 	}
 	if got := pkt.Data().Size(); got != len(want) {
 		t.Errorf("pkt.Data().Size() = %d, want %d", got, len(want))