Remove count argument from tcpip.Endpoint.Read

The same intent can be specified via the io.Writer.

PiperOrigin-RevId: 352098747

27 files changed, 265 insertions, 165 deletions

diff --git a/pkg/sentry/socket/netstack/netstack.go b/pkg/sentry/socket/netstack/netstack.go
index 03749a8bf..22e128b96 100644
--- a/pkg/sentry/socket/netstack/netstack.go
+++ b/pkg/sentry/socket/netstack/netstack.go
@@ -425,8 +425,13 @@ func (s *SocketOperations) WriteTo(ctx context.Context, _ *fs.File, dst io.Write
 	s.readMu.Lock()
 	defer s.readMu.Unlock()
 
+	w := tcpip.LimitedWriter{
+		W: dst,
+		N: count,
+	}
+
 	// This may return a blocking error.
-	res, err := s.Endpoint.Read(dst, int(count), tcpip.ReadOptions{
+	res, err := s.Endpoint.Read(&w, tcpip.ReadOptions{
 		Peek: dup,
 	})
 	if err != nil {
@@ -2579,7 +2584,10 @@ func (s *socketOpsCommon) nonBlockingRead(ctx context.Context, dst usermem.IOSeq
 	// caller-supplied  buffer.
 	var w io.Writer
 	if !isPacket && trunc {
-		w = ioutil.Discard
+		w = &tcpip.LimitedWriter{
+			W: ioutil.Discard,
+			N: dst.NumBytes(),
+		}
 	} else {
 		w = dst.Writer(ctx)
 	}
@@ -2587,7 +2595,10 @@ func (s *socketOpsCommon) nonBlockingRead(ctx context.Context, dst usermem.IOSeq
 	s.readMu.Lock()
 	defer s.readMu.Unlock()
 
-	res, err := s.Endpoint.Read(w, int(dst.NumBytes()), readOptions)
+	res, err := s.Endpoint.Read(w, readOptions)
+	if err == tcpip.ErrBadBuffer && dst.NumBytes() == 0 {
+		err = nil
+	}
 	if err != nil {
 		return 0, 0, nil, 0, socket.ControlMessages{}, syserr.TranslateNetstackError(err)
 	}
diff --git a/pkg/tcpip/BUILD b/pkg/tcpip/BUILD
index 89b765f1b..e7924e5c2 100644
--- a/pkg/tcpip/BUILD
+++ b/pkg/tcpip/BUILD
@@ -37,6 +37,7 @@ go_test(
     size = "small",
     srcs = ["tcpip_test.go"],
     library = ":tcpip",
+    deps = ["@com_github_google_go_cmp//cmp:go_default_library"],
 )
 
 go_test(
diff --git a/pkg/tcpip/adapters/gonet/gonet.go b/pkg/tcpip/adapters/gonet/gonet.go
index 85a0b8b90..fdeec12d3 100644
--- a/pkg/tcpip/adapters/gonet/gonet.go
+++ b/pkg/tcpip/adapters/gonet/gonet.go
@@ -295,7 +295,7 @@ func commonRead(b []byte, ep tcpip.Endpoint, wq *waiter.Queue, deadline <-chan s
 
 	w := tcpip.SliceWriter(b)
 	opts := tcpip.ReadOptions{NeedRemoteAddr: addr != nil}
-	res, err := ep.Read(&w, len(b), opts)
+	res, err := ep.Read(&w, opts)
 
 	if err == tcpip.ErrWouldBlock {
 		// Create wait queue entry that notifies a channel.
@@ -303,7 +303,7 @@ func commonRead(b []byte, ep tcpip.Endpoint, wq *waiter.Queue, deadline <-chan s
 		wq.EventRegister(&waitEntry, waiter.EventIn)
 		defer wq.EventUnregister(&waitEntry)
 		for {
-			res, err = ep.Read(&w, len(b), opts)
+			res, err = ep.Read(&w, opts)
 			if err != tcpip.ErrWouldBlock {
 				break
 			}
diff --git a/pkg/tcpip/buffer/BUILD b/pkg/tcpip/buffer/BUILD
index c326fab54..c9bcf9326 100644
--- a/pkg/tcpip/buffer/BUILD
+++ b/pkg/tcpip/buffer/BUILD
@@ -12,10 +12,13 @@ go_library(
 )
 
 go_test(
-    name = "buffer_test",
+    name = "buffer_x_test",
     size = "small",
     srcs = [
         "view_test.go",
     ],
-    library = ":buffer",
+    deps = [
+        ":buffer",
+        "//pkg/tcpip",
+    ],
 )
diff --git a/pkg/tcpip/buffer/view.go b/pkg/tcpip/buffer/view.go
index 09d3dac66..91cc62cc8 100644
--- a/pkg/tcpip/buffer/view.go
+++ b/pkg/tcpip/buffer/view.go
@@ -148,23 +148,13 @@ func (vv *VectorisedView) ReadToVV(dstVV *VectorisedView, count int) (copied int
 
 // ReadTo reads up to count bytes from vv to dst. It also removes them from vv
 // unless peek is true.
-func (vv *VectorisedView) ReadTo(dst io.Writer, count int, peek bool) (int, error) {
+func (vv *VectorisedView) ReadTo(dst io.Writer, peek bool) (int, error) {
 	var err error
 	done := 0
 	for _, v := range vv.Views() {
-		remaining := count - done
-		if remaining <= 0 {
-			break
-		}
-		if len(v) > remaining {
-			v = v[:remaining]
-		}
-
 		var n int
 		n, err = dst.Write(v)
-		if n > 0 {
-			done += n
-		}
+		done += n
 		if err != nil {
 			break
 		}
diff --git a/pkg/tcpip/buffer/view_test.go b/pkg/tcpip/buffer/view_test.go
index e0ef8a94d..e7f7cc9f1 100644
--- a/pkg/tcpip/buffer/view_test.go
+++ b/pkg/tcpip/buffer/view_test.go
@@ -12,42 +12,43 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// Package buffer_test contains tests for the VectorisedView type.
-package buffer
+// Package buffer_test contains tests for the buffer.VectorisedView type.
+package buffer_test
 
 import (
 	"bytes"
+	"io"
 	"reflect"
 	"testing"
+
+	"gvisor.dev/gvisor/pkg/tcpip"
+	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 )
 
 // copy returns a deep-copy of the vectorised view.
-func (vv VectorisedView) copy() VectorisedView {
-	uu := VectorisedView{
-		views: make([]View, 0, len(vv.views)),
-		size:  vv.size,
-	}
-	for _, v := range vv.views {
-		uu.views = append(uu.views, append(View(nil), v...))
+func copyVV(vv buffer.VectorisedView) buffer.VectorisedView {
+	views := make([]buffer.View, 0, len(vv.Views()))
+	for _, v := range vv.Views() {
+		views = append(views, append(buffer.View(nil), v...))
 	}
-	return uu
+	return buffer.NewVectorisedView(vv.Size(), views)
 }
 
-// vv is an helper to build VectorisedView from different strings.
-func vv(size int, pieces ...string) VectorisedView {
-	views := make([]View, len(pieces))
+// vv is an helper to build buffer.VectorisedView from different strings.
+func vv(size int, pieces ...string) buffer.VectorisedView {
+	views := make([]buffer.View, len(pieces))
 	for i, p := range pieces {
 		views[i] = []byte(p)
 	}
 
-	return NewVectorisedView(size, views)
+	return buffer.NewVectorisedView(size, views)
 }
 
 var capLengthTestCases = []struct {
 	comment string
-	in      VectorisedView
+	in      buffer.VectorisedView
 	length  int
-	want    VectorisedView
+	want    buffer.VectorisedView
 }{
 	{
 		comment: "Simple case",
@@ -89,7 +90,7 @@ var capLengthTestCases = []struct {
 
 func TestCapLength(t *testing.T) {
 	for _, c := range capLengthTestCases {
-		orig := c.in.copy()
+		orig := copyVV(c.in)
 		c.in.CapLength(c.length)
 		if !reflect.DeepEqual(c.in, c.want) {
 			t.Errorf("Test \"%s\" failed when calling CapLength(%d) on %v. Got %v. Want %v",
@@ -100,9 +101,9 @@ func TestCapLength(t *testing.T) {
 
 var trimFrontTestCases = []struct {
 	comment string
-	in      VectorisedView
+	in      buffer.VectorisedView
 	count   int
-	want    VectorisedView
+	want    buffer.VectorisedView
 }{
 	{
 		comment: "Simple case",
@@ -150,7 +151,7 @@ var trimFrontTestCases = []struct {
 
 func TestTrimFront(t *testing.T) {
 	for _, c := range trimFrontTestCases {
-		orig := c.in.copy()
+		orig := copyVV(c.in)
 		c.in.TrimFront(c.count)
 		if !reflect.DeepEqual(c.in, c.want) {
 			t.Errorf("Test \"%s\" failed when calling TrimFront(%d) on %v. Got %v. Want %v",
@@ -161,8 +162,8 @@ func TestTrimFront(t *testing.T) {
 
 var toViewCases = []struct {
 	comment string
-	in      VectorisedView
-	want    View
+	in      buffer.VectorisedView
+	want    buffer.View
 }{
 	{
 		comment: "Simple case",
@@ -193,28 +194,28 @@ func TestToView(t *testing.T) {
 
 var toCloneCases = []struct {
 	comment  string
-	inView   VectorisedView
-	inBuffer []View
+	inView   buffer.VectorisedView
+	inBuffer []buffer.View
 }{
 	{
 		comment:  "Simple case",
 		inView:   vv(1, "1"),
-		inBuffer: make([]View, 1),
+		inBuffer: make([]buffer.View, 1),
 	},
 	{
 		comment:  "Case with multiple views",
 		inView:   vv(2, "1", "2"),
-		inBuffer: make([]View, 2),
+		inBuffer: make([]buffer.View, 2),
 	},
 	{
 		comment:  "Case with buffer too small",
 		inView:   vv(2, "1", "2"),
-		inBuffer: make([]View, 1),
+		inBuffer: make([]buffer.View, 1),
 	},
 	{
 		comment:  "Case with buffer larger than needed",
 		inView:   vv(1, "1"),
-		inBuffer: make([]View, 2),
+		inBuffer: make([]buffer.View, 2),
 	},
 	{
 		comment:  "Case with nil buffer",
@@ -237,10 +238,10 @@ func TestToClone(t *testing.T) {
 
 type readToTestCases struct {
 	comment     string
-	vv          VectorisedView
+	vv          buffer.VectorisedView
 	bytesToRead int
 	wantBytes   string
-	leftVV      VectorisedView
+	leftVV      buffer.VectorisedView
 }
 
 func createReadToTestCases() []readToTestCases {
@@ -286,7 +287,7 @@ func createReadToTestCases() []readToTestCases {
 func TestVVReadToVV(t *testing.T) {
 	for _, tc := range createReadToTestCases() {
 		t.Run(tc.comment, func(t *testing.T) {
-			var readTo VectorisedView
+			var readTo buffer.VectorisedView
 			inSize := tc.vv.Size()
 			copied := tc.vv.ReadToVV(&readTo, tc.bytesToRead)
 			if got, want := copied, len(tc.wantBytes); got != want {
@@ -308,13 +309,17 @@ func TestVVReadToVV(t *testing.T) {
 func TestVVReadTo(t *testing.T) {
 	for _, tc := range createReadToTestCases() {
 		t.Run(tc.comment, func(t *testing.T) {
-			var dst bytes.Buffer
+			b := make([]byte, tc.bytesToRead)
+			dst := tcpip.SliceWriter(b)
 			origSize := tc.vv.Size()
-			copied, err := tc.vv.ReadTo(&dst, tc.bytesToRead, false /* peek */)
-			if got, want := copied, len(tc.wantBytes); err != nil || got != want {
-				t.Errorf("got ReadTo(&dst, %d, false) = %d, %v; want %d, nil", tc.bytesToRead, got, err, want)
+			copied, err := tc.vv.ReadTo(&dst, false /* peek */)
+			if err != nil && err != io.ErrShortWrite {
+				t.Errorf("got ReadTo(&dst, false) = (_, %s); want nil or io.ErrShortWrite", err)
+			}
+			if got, want := copied, len(tc.wantBytes); got != want {
+				t.Errorf("got ReadTo(&dst, false) = (%d, _); want %d", got, want)
 			}
-			if got, want := string(dst.Bytes()), tc.wantBytes; got != want {
+			if got, want := string(b[:copied]), tc.wantBytes; got != want {
 				t.Errorf("got dst = %q, want %q", got, want)
 			}
 			if got, want := tc.vv.Size(), origSize-copied; got != want {
@@ -330,14 +335,18 @@ func TestVVReadTo(t *testing.T) {
 func TestVVReadToPeek(t *testing.T) {
 	for _, tc := range createReadToTestCases() {
 		t.Run(tc.comment, func(t *testing.T) {
-			var dst bytes.Buffer
+			b := make([]byte, tc.bytesToRead)
+			dst := tcpip.SliceWriter(b)
 			origSize := tc.vv.Size()
 			origData := string(tc.vv.ToView())
-			copied, err := tc.vv.ReadTo(&dst, tc.bytesToRead, true /* peek */)
-			if got, want := copied, len(tc.wantBytes); err != nil || got != want {
-				t.Errorf("got ReadTo(&dst, %d, false) = %d, %v; want %d, nil", tc.bytesToRead, got, err, want)
+			copied, err := tc.vv.ReadTo(&dst, true /* peek */)
+			if err != nil && err != io.ErrShortWrite {
+				t.Errorf("got ReadTo(&dst, true) = (_, %s); want nil or io.ErrShortWrite", err)
+			}
+			if got, want := copied, len(tc.wantBytes); got != want {
+				t.Errorf("got ReadTo(&dst, true) = (%d, _); want %d", got, want)
 			}
-			if got, want := string(dst.Bytes()), tc.wantBytes; got != want {
+			if got, want := string(b[:copied]), tc.wantBytes; got != want {
 				t.Errorf("got dst = %q, want %q", got, want)
 			}
 			// Expect tc.vv is unchanged.
@@ -354,7 +363,7 @@ func TestVVReadToPeek(t *testing.T) {
 func TestVVRead(t *testing.T) {
 	testCases := []struct {
 		comment     string
-		vv          VectorisedView
+		vv          buffer.VectorisedView
 		bytesToRead int
 		readBytes   string
 		leftBytes   string
@@ -399,7 +408,7 @@ func TestVVRead(t *testing.T) {
 
 	for _, tc := range testCases {
 		t.Run(tc.comment, func(t *testing.T) {
-			readTo := NewView(tc.bytesToRead)
+			readTo := buffer.NewView(tc.bytesToRead)
 			inSize := tc.vv.Size()
 			copied, err := tc.vv.Read(readTo)
 			if !tc.wantError && err != nil {
@@ -424,10 +433,10 @@ func TestVVRead(t *testing.T) {
 
 var pullUpTestCases = []struct {
 	comment string
-	in      VectorisedView
+	in      buffer.VectorisedView
 	count   int
 	want    []byte
-	result  VectorisedView
+	result  buffer.VectorisedView
 	ok      bool
 }{
 	{
@@ -521,7 +530,7 @@ func TestPullUp(t *testing.T) {
 			t.Errorf("Test %q failed when calling PullUp(%d) on %v. Got an ok of %t. Want %t",
 				c.comment, c.count, c.in, ok, c.ok)
 		}
-		if bytes.Compare(got, View(c.want)) != 0 {
+		if bytes.Compare(got, buffer.View(c.want)) != 0 {
 			t.Errorf("Test %q failed when calling PullUp(%d) on %v. Got %v. Want %v",
 				c.comment, c.count, c.in, got, c.want)
 		}
@@ -536,12 +545,12 @@ func TestPullUp(t *testing.T) {
 
 func TestToVectorisedView(t *testing.T) {
 	testCases := []struct {
-		in   View
-		want VectorisedView
+		in   buffer.View
+		want buffer.VectorisedView
 	}{
-		{nil, VectorisedView{}},
-		{View{}, VectorisedView{}},
-		{View{'a'}, VectorisedView{size: 1, views: []View{{'a'}}}},
+		{nil, buffer.VectorisedView{}},
+		{buffer.View{}, buffer.VectorisedView{}},
+		{buffer.View{'a'}, buffer.NewVectorisedView(1, []buffer.View{{'a'}})},
 	}
 	for _, tc := range testCases {
 		if got, want := tc.in.ToVectorisedView(), tc.want; !reflect.DeepEqual(got, want) {
@@ -552,15 +561,15 @@ func TestToVectorisedView(t *testing.T) {
 
 func TestAppendView(t *testing.T) {
 	testCases := []struct {
-		vv   VectorisedView
-		in   View
-		want VectorisedView
+		vv   buffer.VectorisedView
+		in   buffer.View
+		want buffer.VectorisedView
 	}{
-		{VectorisedView{}, nil, VectorisedView{}},
-		{VectorisedView{}, View{}, VectorisedView{}},
-		{VectorisedView{[]View{{'a', 'b', 'c', 'd'}}, 4}, nil, VectorisedView{[]View{{'a', 'b', 'c', 'd'}}, 4}},
-		{VectorisedView{[]View{{'a', 'b', 'c', 'd'}}, 4}, View{}, VectorisedView{[]View{{'a', 'b', 'c', 'd'}}, 4}},
-		{VectorisedView{[]View{{'a', 'b', 'c', 'd'}}, 4}, View{'e'}, VectorisedView{[]View{{'a', 'b', 'c', 'd'}, {'e'}}, 5}},
+		{buffer.VectorisedView{}, nil, buffer.VectorisedView{}},
+		{buffer.VectorisedView{}, buffer.View{}, buffer.VectorisedView{}},
+		{buffer.NewVectorisedView(4, []buffer.View{{'a', 'b', 'c', 'd'}}), nil, buffer.NewVectorisedView(4, []buffer.View{{'a', 'b', 'c', 'd'}})},
+		{buffer.NewVectorisedView(4, []buffer.View{{'a', 'b', 'c', 'd'}}), buffer.View{}, buffer.NewVectorisedView(4, []buffer.View{{'a', 'b', 'c', 'd'}})},
+		{buffer.NewVectorisedView(4, []buffer.View{{'a', 'b', 'c', 'd'}}), buffer.View{'e'}, buffer.NewVectorisedView(5, []buffer.View{{'a', 'b', 'c', 'd'}, {'e'}})},
 	}
 	for _, tc := range testCases {
 		tc.vv.AppendView(tc.in)
diff --git a/pkg/tcpip/network/ipv4/ipv4_test.go b/pkg/tcpip/network/ipv4/ipv4_test.go
index 1c4919b1e..a9e137c24 100644
--- a/pkg/tcpip/network/ipv4/ipv4_test.go
+++ b/pkg/tcpip/network/ipv4/ipv4_test.go
@@ -2410,10 +2410,9 @@ func TestReceiveFragments(t *testing.T) {
 				t.Errorf("got UDP Rx Packets = %d, want = %d", got, want)
 			}
 
-			const rcvSize = 65536 // Account for reassembled packets.
 			for i, expectedPayload := range test.expectedPayloads {
 				var buf bytes.Buffer
-				result, err := ep.Read(&buf, rcvSize, tcpip.ReadOptions{})
+				result, err := ep.Read(&buf, tcpip.ReadOptions{})
 				if err != nil {
 					t.Fatalf("(i=%d) Read: %s", i, err)
 				}
@@ -2428,7 +2427,7 @@ func TestReceiveFragments(t *testing.T) {
 				}
 			}
 
-			if res, err := ep.Read(ioutil.Discard, rcvSize, tcpip.ReadOptions{}); err != tcpip.ErrWouldBlock {
+			if res, err := ep.Read(ioutil.Discard, tcpip.ReadOptions{}); err != tcpip.ErrWouldBlock {
 				t.Fatalf("(last) got Read = (%v, %v), want = (_, %s)", res, err, tcpip.ErrWouldBlock)
 			}
 		})
diff --git a/pkg/tcpip/network/ipv6/ipv6_test.go b/pkg/tcpip/network/ipv6/ipv6_test.go
index 360025b20..b65c9d060 100644
--- a/pkg/tcpip/network/ipv6/ipv6_test.go
+++ b/pkg/tcpip/network/ipv6/ipv6_test.go
@@ -846,14 +846,13 @@ func TestReceiveIPv6ExtHdrs(t *testing.T) {
 		},
 	}
 
-	const mtu = header.IPv6MinimumMTU
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
 			s := stack.New(stack.Options{
 				NetworkProtocols:   []stack.NetworkProtocolFactory{NewProtocol},
 				TransportProtocols: []stack.TransportProtocolFactory{udp.NewProtocol},
 			})
-			e := channel.New(1, mtu, linkAddr1)
+			e := channel.New(1, header.IPv6MinimumMTU, linkAddr1)
 			if err := s.CreateNIC(nicID, e); err != nil {
 				t.Fatalf("CreateNIC(%d, _) = %s", nicID, err)
 			}
@@ -983,7 +982,7 @@ func TestReceiveIPv6ExtHdrs(t *testing.T) {
 				t.Errorf("got UDP Rx Packets = %d, want = 1", got)
 			}
 			var buf bytes.Buffer
-			result, err := ep.Read(&buf, mtu, tcpip.ReadOptions{})
+			result, err := ep.Read(&buf, tcpip.ReadOptions{})
 			if err != nil {
 				t.Fatalf("Read: %s", err)
 			}
@@ -998,7 +997,7 @@ func TestReceiveIPv6ExtHdrs(t *testing.T) {
 			}
 
 			// Should not have any more UDP packets.
-			if res, err := ep.Read(ioutil.Discard, mtu, tcpip.ReadOptions{}); err != tcpip.ErrWouldBlock {
+			if res, err := ep.Read(ioutil.Discard, tcpip.ReadOptions{}); err != tcpip.ErrWouldBlock {
 				t.Fatalf("got Read = (%v, %v), want = (_, %s)", res, err, tcpip.ErrWouldBlock)
 			}
 		})
@@ -1979,10 +1978,9 @@ func TestReceiveIPv6Fragments(t *testing.T) {
 				t.Errorf("got UDP Rx Packets = %d, want = %d", got, want)
 			}
 
-			const rcvSize = 65536 // Account for reassembled packets.
 			for i, p := range test.expectedPayloads {
 				var buf bytes.Buffer
-				_, err := ep.Read(&buf, rcvSize, tcpip.ReadOptions{})
+				_, err := ep.Read(&buf, tcpip.ReadOptions{})
 				if err != nil {
 					t.Fatalf("(i=%d) Read: %s", i, err)
 				}
@@ -1991,7 +1989,7 @@ func TestReceiveIPv6Fragments(t *testing.T) {
 				}
 			}
 
-			if res, err := ep.Read(ioutil.Discard, rcvSize, tcpip.ReadOptions{}); err != tcpip.ErrWouldBlock {
+			if res, err := ep.Read(ioutil.Discard, tcpip.ReadOptions{}); err != tcpip.ErrWouldBlock {
 				t.Fatalf("(last) got Read = (%v, %v), want = (_, %s)", res, err, tcpip.ErrWouldBlock)
 			}
 		})
diff --git a/pkg/tcpip/sample/tun_tcp_connect/main.go b/pkg/tcpip/sample/tun_tcp_connect/main.go
index a7da9dcd9..3b4f900e3 100644
--- a/pkg/tcpip/sample/tun_tcp_connect/main.go
+++ b/pkg/tcpip/sample/tun_tcp_connect/main.go
@@ -44,7 +44,6 @@ import (
 	"bufio"
 	"fmt"
 	"log"
-	"math"
 	"math/rand"
 	"net"
 	"os"
@@ -201,7 +200,7 @@ func main() {
 	// connection from its side.
 	wq.EventRegister(&waitEntry, waiter.EventIn)
 	for {
-		_, err := ep.Read(os.Stdout, math.MaxUint16, tcpip.ReadOptions{})
+		_, err := ep.Read(os.Stdout, tcpip.ReadOptions{})
 		if err != nil {
 			if err == tcpip.ErrClosedForReceive {
 				break
diff --git a/pkg/tcpip/sample/tun_tcp_echo/main.go b/pkg/tcpip/sample/tun_tcp_echo/main.go
index a80fa0474..3ac562756 100644
--- a/pkg/tcpip/sample/tun_tcp_echo/main.go
+++ b/pkg/tcpip/sample/tun_tcp_echo/main.go
@@ -20,10 +20,9 @@
 package main
 
 import (
-	"bytes"
 	"flag"
+	"io"
 	"log"
-	"math"
 	"math/rand"
 	"net"
 	"os"
@@ -46,6 +45,31 @@ import (
 var tap = flag.Bool("tap", false, "use tap istead of tun")
 var mac = flag.String("mac", "aa:00:01:01:01:01", "mac address to use in tap device")
 
+type endpointWriter struct {
+	ep tcpip.Endpoint
+}
+
+type tcpipError struct {
+	inner *tcpip.Error
+}
+
+func (e *tcpipError) Error() string {
+	return e.inner.String()
+}
+
+func (e *endpointWriter) Write(p []byte) (int, error) {
+	n, err := e.ep.Write(tcpip.SlicePayload(p), tcpip.WriteOptions{})
+	if err != nil {
+		return int(n), &tcpipError{
+			inner: err,
+		}
+	}
+	if n != int64(len(p)) {
+		return int(n), io.ErrShortWrite
+	}
+	return int(n), nil
+}
+
 func echo(wq *waiter.Queue, ep tcpip.Endpoint) {
 	defer ep.Close()
 
@@ -55,9 +79,12 @@ func echo(wq *waiter.Queue, ep tcpip.Endpoint) {
 	wq.EventRegister(&waitEntry, waiter.EventIn)
 	defer wq.EventUnregister(&waitEntry)
 
+	w := endpointWriter{
+		ep: ep,
+	}
+
 	for {
-		var buf bytes.Buffer
-		_, err := ep.Read(&buf, math.MaxUint16, tcpip.ReadOptions{})
+		_, err := ep.Read(&w, tcpip.ReadOptions{})
 		if err != nil {
 			if err == tcpip.ErrWouldBlock {
 				<-notifyCh
@@ -66,8 +93,6 @@ func echo(wq *waiter.Queue, ep tcpip.Endpoint) {
 
 			return
 		}
-
-		ep.Write(tcpip.SlicePayload(buf.Bytes()), tcpip.WriteOptions{})
 	}
 }
 
diff --git a/pkg/tcpip/stack/transport_demuxer_test.go b/pkg/tcpip/stack/transport_demuxer_test.go
index 859278f0b..57e1f8354 100644
--- a/pkg/tcpip/stack/transport_demuxer_test.go
+++ b/pkg/tcpip/stack/transport_demuxer_test.go
@@ -352,7 +352,7 @@ func TestBindToDeviceDistribution(t *testing.T) {
 						}
 
 						ep := <-pollChannel
-						if _, err := ep.Read(ioutil.Discard, math.MaxUint16, tcpip.ReadOptions{}); err != nil {
+						if _, err := ep.Read(ioutil.Discard, tcpip.ReadOptions{}); err != nil {
 							t.Fatalf("Read on endpoint %d failed: %s", eps[ep], err)
 						}
 						stats[ep]++
diff --git a/pkg/tcpip/stack/transport_test.go b/pkg/tcpip/stack/transport_test.go
index a2ab7537c..9d39533a1 100644
--- a/pkg/tcpip/stack/transport_test.go
+++ b/pkg/tcpip/stack/transport_test.go
@@ -86,7 +86,7 @@ func (*fakeTransportEndpoint) Readiness(mask waiter.EventMask) waiter.EventMask
 	return mask
 }
 
-func (*fakeTransportEndpoint) Read(io.Writer, int, tcpip.ReadOptions) (tcpip.ReadResult, *tcpip.Error) {
+func (*fakeTransportEndpoint) Read(io.Writer, tcpip.ReadOptions) (tcpip.ReadResult, *tcpip.Error) {
 	return tcpip.ReadResult{}, nil
 }
 
diff --git a/pkg/tcpip/tcpip.go b/pkg/tcpip/tcpip.go
index 49d4912ad..56aac093c 100644
--- a/pkg/tcpip/tcpip.go
+++ b/pkg/tcpip/tcpip.go
@@ -505,10 +505,34 @@ type SliceWriter []byte
 func (s *SliceWriter) Write(b []byte) (int, error) {
 	n := copy(*s, b)
 	*s = (*s)[n:]
-	if n < len(b) {
-		return n, io.ErrShortWrite
+	var err error
+	if n != len(b) {
+		err = io.ErrShortWrite
 	}
-	return n, nil
+	return n, err
+}
+
+var _ io.Writer = (*LimitedWriter)(nil)
+
+// A LimitedWriter writes to W but limits the amount of data copied to just N
+// bytes. Each call to Write updates N to reflect the new amount remaining.
+type LimitedWriter struct {
+	W io.Writer
+	N int64
+}
+
+func (l *LimitedWriter) Write(p []byte) (int, error) {
+	pLen := int64(len(p))
+	if pLen > l.N {
+		p = p[:l.N]
+	}
+	n, err := l.W.Write(p)
+	n64 := int64(n)
+	if err == nil && n64 != pLen {
+		err = io.ErrShortWrite
+	}
+	l.N -= n64
+	return n, err
 }
 
 // A ControlMessages contains socket control messages for IP sockets.
@@ -623,7 +647,7 @@ type Endpoint interface {
 	// If non-zero number of bytes are successfully read and written to dst, err
 	// must be nil. Otherwise, if dst failed to write anything, ErrBadBuffer
 	// should be returned.
-	Read(dst io.Writer, count int, opts ReadOptions) (res ReadResult, err *Error)
+	Read(dst io.Writer, opts ReadOptions) (res ReadResult, err *Error)
 
 	// Write writes data to the endpoint's peer. This method does not block if
 	// the data cannot be written.
diff --git a/pkg/tcpip/tcpip_test.go b/pkg/tcpip/tcpip_test.go
index 9bd563c46..269081ff8 100644
--- a/pkg/tcpip/tcpip_test.go
+++ b/pkg/tcpip/tcpip_test.go
@@ -15,12 +15,46 @@
 package tcpip
 
 import (
+	"bytes"
 	"fmt"
+	"io"
 	"net"
 	"strings"
 	"testing"
+
+	"github.com/google/go-cmp/cmp"
 )
 
+func TestLimitedWriter_Write(t *testing.T) {
+	var b bytes.Buffer
+	l := LimitedWriter{
+		W: &b,
+		N: 5,
+	}
+	if n, err := l.Write([]byte{0, 1, 2}); err != nil {
+		t.Errorf("got l.Write(3/5) = (_, %s), want nil", err)
+	} else if n != 3 {
+		t.Errorf("got l.Write(3/5) = (%d, _), want 3", n)
+	}
+	if n, err := l.Write([]byte{3, 4, 5}); err != io.ErrShortWrite {
+		t.Errorf("got l.Write(3/2) = (_, %s), want io.ErrShortWrite", err)
+	} else if n != 2 {
+		t.Errorf("got l.Write(3/2) = (%d, _), want 2", n)
+	}
+	if l.N != 0 {
+		t.Errorf("got l.N = %d, want 0", l.N)
+	}
+	l.N = 1
+	if n, err := l.Write([]byte{5}); err != nil {
+		t.Errorf("got l.Write(1/1) = (_, %s), want nil", err)
+	} else if n != 1 {
+		t.Errorf("got l.Write(1/1) = (%d, _), want 1", n)
+	}
+	if diff := cmp.Diff(b.Bytes(), []byte{0, 1, 2, 3, 4, 5}); diff != "" {
+		t.Errorf("%T wrote incorrect data: (-want +got):\n%s", l, diff)
+	}
+}
+
 func TestSubnetContains(t *testing.T) {
 	tests := []struct {
 		s    Address
diff --git a/pkg/tcpip/tests/integration/forward_test.go b/pkg/tcpip/tests/integration/forward_test.go
index 49acd504e..ac9670f9a 100644
--- a/pkg/tcpip/tests/integration/forward_test.go
+++ b/pkg/tcpip/tests/integration/forward_test.go
@@ -457,7 +457,7 @@ func TestForwarding(t *testing.T) {
 						<-ch
 						var buf bytes.Buffer
 						opts := tcpip.ReadOptions{NeedRemoteAddr: subTest.needRemoteAddr}
-						res, err := ep.Read(&buf, len(data), opts)
+						res, err := ep.Read(&buf, opts)
 						if err != nil {
 							t.Fatalf("ep.Read(_, %d, %#v): %s", len(data), opts, err)
 						}
diff --git a/pkg/tcpip/tests/integration/link_resolution_test.go b/pkg/tcpip/tests/integration/link_resolution_test.go
index ed00c90d4..3f06c2145 100644
--- a/pkg/tcpip/tests/integration/link_resolution_test.go
+++ b/pkg/tcpip/tests/integration/link_resolution_test.go
@@ -218,7 +218,7 @@ func TestPing(t *testing.T) {
 
 			var buf bytes.Buffer
 			opts := tcpip.ReadOptions{NeedRemoteAddr: true}
-			res, err := ep.Read(&buf, len(icmpBuf), opts)
+			res, err := ep.Read(&buf, opts)
 			if err != nil {
 				t.Fatalf("ep.Read(_, %d, %#v): %s", len(icmpBuf), opts, err)
 			}
diff --git a/pkg/tcpip/tests/integration/loopback_test.go b/pkg/tcpip/tests/integration/loopback_test.go
index a59f25cc3..3b13ba04d 100644
--- a/pkg/tcpip/tests/integration/loopback_test.go
+++ b/pkg/tcpip/tests/integration/loopback_test.go
@@ -242,9 +242,9 @@ func TestLoopbackAcceptAllInSubnetUDP(t *testing.T) {
 
 			var buf bytes.Buffer
 			opts := tcpip.ReadOptions{NeedRemoteAddr: true}
-			if res, err := rep.Read(&buf, len(data), opts); test.expectRx {
+			if res, err := rep.Read(&buf, opts); test.expectRx {
 				if err != nil {
-					t.Fatalf("rep.Read(_, %d, %#v): %s", len(data), opts, err)
+					t.Fatalf("rep.Read(_, %#v): %s", opts, err)
 				}
 				if diff := cmp.Diff(tcpip.ReadResult{
 					Count: buf.Len(),
diff --git a/pkg/tcpip/tests/integration/multicast_broadcast_test.go b/pkg/tcpip/tests/integration/multicast_broadcast_test.go
index eabc87938..ce7c16bd1 100644
--- a/pkg/tcpip/tests/integration/multicast_broadcast_test.go
+++ b/pkg/tcpip/tests/integration/multicast_broadcast_test.go
@@ -466,9 +466,9 @@ func TestIncomingMulticastAndBroadcast(t *testing.T) {
 			test.rxUDP(e, test.remoteAddr, test.dstAddr, data)
 			var buf bytes.Buffer
 			var opts tcpip.ReadOptions
-			if res, err := ep.Read(&buf, len(data), opts); test.expectRx {
+			if res, err := ep.Read(&buf, opts); test.expectRx {
 				if err != nil {
-					t.Fatalf("ep.Read(_, %d, %#v): %s", len(data), opts, err)
+					t.Fatalf("ep.Read(_, %#v): %s", opts, err)
 				}
 				if diff := cmp.Diff(tcpip.ReadResult{
 					Count: buf.Len(),
@@ -598,7 +598,7 @@ func TestReuseAddrAndBroadcast(t *testing.T) {
 					<-rep.ch
 
 					var buf bytes.Buffer
-					result, err := rep.ep.Read(&buf, len(data), tcpip.ReadOptions{})
+					result, err := rep.ep.Read(&buf, tcpip.ReadOptions{})
 					if err != nil {
 						t.Errorf("(eps[%d] write) eps[%d].Read: %s", i, j, err)
 						continue
@@ -738,7 +738,7 @@ func TestUDPAddRemoveMembershipSocketOption(t *testing.T) {
 					}
 					test.rxUDP(e, test.remoteAddr, test.multicastAddr, data)
 					var buf bytes.Buffer
-					result, err := ep.Read(&buf, len(data), tcpip.ReadOptions{})
+					result, err := ep.Read(&buf, tcpip.ReadOptions{})
 					if err != nil {
 						t.Fatalf("ep.Read: %s", err)
 					} else {
@@ -759,7 +759,7 @@ func TestUDPAddRemoveMembershipSocketOption(t *testing.T) {
 					if err := ep.SetSockOpt(&removeOpt); err != nil {
 						t.Fatalf("ep.SetSockOpt(&%#v): %s", removeOpt, err)
 					}
-					if _, err := ep.Read(&buf, 1, tcpip.ReadOptions{}); err != tcpip.ErrWouldBlock {
+					if _, err := ep.Read(&buf, tcpip.ReadOptions{}); err != tcpip.ErrWouldBlock {
 						t.Fatalf("got ep.Read = (_, %s), want = (_, %s)", err, tcpip.ErrWouldBlock)
 					}
 				})
diff --git a/pkg/tcpip/tests/integration/route_test.go b/pkg/tcpip/tests/integration/route_test.go
index 76f7f54c6..b222d2b05 100644
--- a/pkg/tcpip/tests/integration/route_test.go
+++ b/pkg/tcpip/tests/integration/route_test.go
@@ -16,7 +16,6 @@ package integration_test
 
 import (
 	"bytes"
-	"math"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
@@ -208,9 +207,9 @@ func TestLocalPing(t *testing.T) {
 
 			var buf bytes.Buffer
 			opts := tcpip.ReadOptions{NeedRemoteAddr: true}
-			res, err := ep.Read(&buf, math.MaxUint16, opts)
+			res, err := ep.Read(&buf, opts)
 			if err != nil {
-				t.Fatalf("ep.Read(_, %d, %#v): %s", math.MaxUint16, opts, err)
+				t.Fatalf("ep.Read(_, %#v): %s", opts, err)
 			}
 			if diff := cmp.Diff(tcpip.ReadResult{
 				Count:      buf.Len(),
@@ -351,7 +350,7 @@ func TestLocalUDP(t *testing.T) {
 
 					var clientAddr tcpip.FullAddress
 					var readBuf bytes.Buffer
-					if read, err := server.Read(&readBuf, math.MaxUint16, tcpip.ReadOptions{NeedRemoteAddr: true}); err != nil {
+					if read, err := server.Read(&readBuf, tcpip.ReadOptions{NeedRemoteAddr: true}); err != nil {
 						t.Fatalf("server.Read(_): %s", err)
 					} else {
 						clientAddr = read.RemoteAddr
@@ -393,7 +392,7 @@ func TestLocalUDP(t *testing.T) {
 					<-clientCH
 
 					readBuf.Reset()
-					if read, err := client.Read(&readBuf, math.MaxUint16, tcpip.ReadOptions{NeedRemoteAddr: true}); err != nil {
+					if read, err := client.Read(&readBuf, tcpip.ReadOptions{NeedRemoteAddr: true}); err != nil {
 						t.Fatalf("client.Read(_): %s", err)
 					} else {
 						if diff := cmp.Diff(tcpip.ReadResult{
diff --git a/pkg/tcpip/transport/icmp/endpoint.go b/pkg/tcpip/transport/icmp/endpoint.go
index 87277fbd3..256e19296 100644
--- a/pkg/tcpip/transport/icmp/endpoint.go
+++ b/pkg/tcpip/transport/icmp/endpoint.go
@@ -154,7 +154,7 @@ func (e *endpoint) SetOwner(owner tcpip.PacketOwner) {
 }
 
 // Read implements tcpip.Endpoint.Read.
-func (e *endpoint) Read(dst io.Writer, count int, opts tcpip.ReadOptions) (tcpip.ReadResult, *tcpip.Error) {
+func (e *endpoint) Read(dst io.Writer, opts tcpip.ReadOptions) (tcpip.ReadResult, *tcpip.Error) {
 	e.rcvMu.Lock()
 
 	if e.rcvList.Empty() {
@@ -186,7 +186,7 @@ func (e *endpoint) Read(dst io.Writer, count int, opts tcpip.ReadOptions) (tcpip
 		res.RemoteAddr = p.senderAddress
 	}
 
-	n, err := p.data.ReadTo(dst, count, opts.Peek)
+	n, err := p.data.ReadTo(dst, opts.Peek)
 	if n == 0 && err != nil {
 		return res, tcpip.ErrBadBuffer
 	}
diff --git a/pkg/tcpip/transport/packet/endpoint.go b/pkg/tcpip/transport/packet/endpoint.go
index c3b3b8d34..c0d6fb442 100644
--- a/pkg/tcpip/transport/packet/endpoint.go
+++ b/pkg/tcpip/transport/packet/endpoint.go
@@ -162,7 +162,7 @@ func (ep *endpoint) Close() {
 func (ep *endpoint) ModerateRecvBuf(copied int) {}
 
 // Read implements tcpip.Endpoint.Read.
-func (ep *endpoint) Read(dst io.Writer, count int, opts tcpip.ReadOptions) (tcpip.ReadResult, *tcpip.Error) {
+func (ep *endpoint) Read(dst io.Writer, opts tcpip.ReadOptions) (tcpip.ReadResult, *tcpip.Error) {
 	ep.rcvMu.Lock()
 
 	// If there's no data to read, return that read would block or that the
@@ -199,7 +199,7 @@ func (ep *endpoint) Read(dst io.Writer, count int, opts tcpip.ReadOptions) (tcpi
 		res.LinkPacketInfo = packet.packetInfo
 	}
 
-	n, err := packet.data.ReadTo(dst, count, opts.Peek)
+	n, err := packet.data.ReadTo(dst, opts.Peek)
 	if n == 0 && err != nil {
 		return res, tcpip.ErrBadBuffer
 	}
diff --git a/pkg/tcpip/transport/raw/endpoint.go b/pkg/tcpip/transport/raw/endpoint.go
index 425bcf3ee..ae743f75e 100644
--- a/pkg/tcpip/transport/raw/endpoint.go
+++ b/pkg/tcpip/transport/raw/endpoint.go
@@ -191,7 +191,7 @@ func (e *endpoint) SetOwner(owner tcpip.PacketOwner) {
 }
 
 // Read implements tcpip.Endpoint.Read.
-func (e *endpoint) Read(dst io.Writer, count int, opts tcpip.ReadOptions) (tcpip.ReadResult, *tcpip.Error) {
+func (e *endpoint) Read(dst io.Writer, opts tcpip.ReadOptions) (tcpip.ReadResult, *tcpip.Error) {
 	e.rcvMu.Lock()
 
 	// If there's no data to read, return that read would block or that the
@@ -225,7 +225,7 @@ func (e *endpoint) Read(dst io.Writer, count int, opts tcpip.ReadOptions) (tcpip
 		res.RemoteAddr = pkt.senderAddr
 	}
 
-	n, err := pkt.data.ReadTo(dst, count, opts.Peek)
+	n, err := pkt.data.ReadTo(dst, opts.Peek)
 	if n == 0 && err != nil {
 		return res, tcpip.ErrBadBuffer
 	}
diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index a4508e871..ea509ac73 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -1328,7 +1328,7 @@ func (e *endpoint) UpdateLastError(err *tcpip.Error) {
 }
 
 // Read implements tcpip.Endpoint.Read.
-func (e *endpoint) Read(dst io.Writer, count int, opts tcpip.ReadOptions) (tcpip.ReadResult, *tcpip.Error) {
+func (e *endpoint) Read(dst io.Writer, opts tcpip.ReadOptions) (tcpip.ReadResult, *tcpip.Error) {
 	e.rcvReadMu.Lock()
 	defer e.rcvReadMu.Unlock()
 
@@ -1346,9 +1346,9 @@ func (e *endpoint) Read(dst io.Writer, count int, opts tcpip.ReadOptions) (tcpip
 	var err error
 	done := 0
 	s := first
-	for s != nil && done < count {
+	for s != nil {
 		var n int
-		n, err = s.data.ReadTo(dst, count-done, opts.Peek)
+		n, err = s.data.ReadTo(dst, opts.Peek)
 		// Book keeping first then error handling.
 
 		done += n
diff --git a/pkg/tcpip/transport/tcp/tcp_test.go b/pkg/tcpip/transport/tcp/tcp_test.go
index 729bf7ef5..93683b921 100644
--- a/pkg/tcpip/transport/tcp/tcp_test.go
+++ b/pkg/tcpip/transport/tcp/tcp_test.go
@@ -50,7 +50,7 @@ type endpointTester struct {
 // CheckReadError issues a read to the endpoint and checking for an error.
 func (e *endpointTester) CheckReadError(t *testing.T, want *tcpip.Error) {
 	t.Helper()
-	res, got := e.ep.Read(ioutil.Discard, 1, tcpip.ReadOptions{})
+	res, got := e.ep.Read(ioutil.Discard, tcpip.ReadOptions{})
 	if got != want {
 		t.Fatalf("ep.Read = %s, want %s", got, want)
 	}
@@ -61,10 +61,10 @@ func (e *endpointTester) CheckReadError(t *testing.T, want *tcpip.Error) {
 
 // CheckRead issues a read to the endpoint and checking for a success, returning
 // the data read.
-func (e *endpointTester) CheckRead(t *testing.T, count int) []byte {
+func (e *endpointTester) CheckRead(t *testing.T) []byte {
 	t.Helper()
 	var buf bytes.Buffer
-	res, err := e.ep.Read(&buf, count, tcpip.ReadOptions{})
+	res, err := e.ep.Read(&buf, tcpip.ReadOptions{})
 	if err != nil {
 		t.Fatalf("ep.Read = _, %s; want _, nil", err)
 	}
@@ -81,9 +81,12 @@ func (e *endpointTester) CheckRead(t *testing.T, count int) []byte {
 func (e *endpointTester) CheckReadFull(t *testing.T, count int, notifyRead <-chan struct{}, timeout time.Duration) []byte {
 	t.Helper()
 	var buf bytes.Buffer
-	var done int
-	for done < count {
-		res, err := e.ep.Read(&buf, count-done, tcpip.ReadOptions{})
+	w := tcpip.LimitedWriter{
+		W: &buf,
+		N: int64(count),
+	}
+	for w.N != 0 {
+		_, err := e.ep.Read(&w, tcpip.ReadOptions{})
 		if err == tcpip.ErrWouldBlock {
 			// Wait for receive to be notified.
 			select {
@@ -95,7 +98,6 @@ func (e *endpointTester) CheckReadFull(t *testing.T, count int, notifyRead <-cha
 		} else if err != nil {
 			t.Fatalf("ep.Read = _, %s; want _, nil", err)
 		}
-		done += res.Count
 	}
 	return buf.Bytes()
 }
@@ -820,7 +822,7 @@ func TestSimpleReceive(t *testing.T) {
 	}
 
 	// Receive data.
-	v := ept.CheckRead(t, defaultMTU)
+	v := ept.CheckRead(t)
 	if !bytes.Equal(data, v) {
 		t.Fatalf("got data = %v, want = %v", v, data)
 	}
@@ -1928,7 +1930,7 @@ func TestFullWindowReceive(t *testing.T) {
 	)
 
 	// Receive data and check it.
-	v := ept.CheckRead(t, defaultMTU)
+	v := ept.CheckRead(t)
 	if !bytes.Equal(data, v) {
 		t.Fatalf("got data = %v, want = %v", v, data)
 	}
@@ -2015,7 +2017,7 @@ func TestSmallSegReceiveWindowAdvertisement(t *testing.T) {
 	// Read the data so that the subsequent ACK from the endpoint
 	// grows the right edge of the window.
 	var buf bytes.Buffer
-	if _, err := c.EP.Read(&buf, math.MaxUint16, tcpip.ReadOptions{}); err != nil {
+	if _, err := c.EP.Read(&buf, tcpip.ReadOptions{}); err != nil {
 		t.Fatalf("c.EP.Read: %s", err)
 	}
 
@@ -2075,7 +2077,7 @@ func TestNoWindowShrinking(t *testing.T) {
 	}
 
 	// Read the 1 byte payload we just sent.
-	if got, want := payload, ept.CheckRead(t, 1); !bytes.Equal(got, want) {
+	if got, want := payload, ept.CheckRead(t); !bytes.Equal(got, want) {
 		t.Fatalf("got data: %v, want: %v", got, want)
 	}
 
@@ -2570,13 +2572,16 @@ func TestZeroScaledWindowReceive(t *testing.T) {
 	// update to be sent. For 1MSS worth of window to be available we need to
 	// read at least 128KB. Since our segments above were 50KB each it means
 	// we need to read at 3 packets.
-	sz := 0
-	for sz < defaultMTU*2 {
-		res, err := c.EP.Read(ioutil.Discard, defaultMTU, tcpip.ReadOptions{})
+	w := tcpip.LimitedWriter{
+		W: ioutil.Discard,
+		N: defaultMTU * 2,
+	}
+	for w.N != 0 {
+		res, err := c.EP.Read(&w, tcpip.ReadOptions{})
+		t.Logf("err=%v res=%#v", err, res)
 		if err != nil {
 			t.Fatalf("Read failed: %s", err)
 		}
-		sz += res.Count
 	}
 
 	checker.IPv4(t, c.GetPacket(),
@@ -3271,12 +3276,12 @@ func TestReceiveOnResetConnection(t *testing.T) {
 
 loop:
 	for {
-		switch _, err := c.EP.Read(ioutil.Discard, defaultMTU, tcpip.ReadOptions{}); err {
+		switch _, err := c.EP.Read(ioutil.Discard, tcpip.ReadOptions{}); err {
 		case tcpip.ErrWouldBlock:
 			select {
 			case <-ch:
 				// Expect the state to be StateError and subsequent Reads to fail with HardError.
-				if _, err := c.EP.Read(ioutil.Discard, math.MaxUint16, tcpip.ReadOptions{}); err != tcpip.ErrConnectionReset {
+				if _, err := c.EP.Read(ioutil.Discard, tcpip.ReadOptions{}); err != tcpip.ErrConnectionReset {
 					t.Fatalf("got c.EP.Read() = %s, want = %s", err, tcpip.ErrConnectionReset)
 				}
 				break loop
@@ -4224,7 +4229,7 @@ func TestReadAfterClosedState(t *testing.T) {
 
 	// Check that peek works.
 	var peekBuf bytes.Buffer
-	res, err := c.EP.Read(&peekBuf, 10, tcpip.ReadOptions{Peek: true})
+	res, err := c.EP.Read(&peekBuf, tcpip.ReadOptions{Peek: true})
 	if err != nil {
 		t.Fatalf("Peek failed: %s", err)
 	}
@@ -4237,7 +4242,7 @@ func TestReadAfterClosedState(t *testing.T) {
 	}
 
 	// Receive data.
-	v := ept.CheckRead(t, defaultMTU)
+	v := ept.CheckRead(t)
 	if !bytes.Equal(data, v) {
 		t.Fatalf("got data = %v, want = %v", v, data)
 	}
@@ -4246,8 +4251,8 @@ func TestReadAfterClosedState(t *testing.T) {
 	// right error code.
 	ept.CheckReadError(t, tcpip.ErrClosedForReceive)
 	var buf bytes.Buffer
-	if _, err := c.EP.Read(&buf, 1, tcpip.ReadOptions{Peek: true}); err != tcpip.ErrClosedForReceive {
-		t.Fatalf("c.EP.Read(_, _, {Peek: true}) = %v, %s; want _, %s", res, err, tcpip.ErrClosedForReceive)
+	if _, err := c.EP.Read(&buf, tcpip.ReadOptions{Peek: true}); err != tcpip.ErrClosedForReceive {
+		t.Fatalf("c.EP.Read(_, {Peek: true}) = %v, %s; want _, %s", res, err, tcpip.ErrClosedForReceive)
 	}
 }
 
@@ -6205,7 +6210,7 @@ func TestReceiveBufferAutoTuningApplicationLimited(t *testing.T) {
 	// Now read all the data from the endpoint and verify that advertised
 	// window increases to the full available buffer size.
 	for {
-		_, err := c.EP.Read(ioutil.Discard, defaultMTU, tcpip.ReadOptions{})
+		_, err := c.EP.Read(ioutil.Discard, tcpip.ReadOptions{})
 		if err == tcpip.ErrWouldBlock {
 			break
 		}
@@ -6329,7 +6334,7 @@ func TestReceiveBufferAutoTuning(t *testing.T) {
 		// to happen before we measure the new window.
 		totalCopied := 0
 		for {
-			res, err := c.EP.Read(ioutil.Discard, defaultMTU, tcpip.ReadOptions{})
+			res, err := c.EP.Read(ioutil.Discard, tcpip.ReadOptions{})
 			if err == tcpip.ErrWouldBlock {
 				break
 			}
@@ -7387,15 +7392,17 @@ func TestIncreaseWindowOnRead(t *testing.T) {
 
 	// We now have < 1 MSS in the buffer space. Read at least > 2 MSS
 	// worth of data as receive buffer space
-	read := 0
-	// defaultMTU is a good enough estimate for the MSS used for this
-	// connection.
-	for read < defaultMTU*2 {
-		res, err := c.EP.Read(ioutil.Discard, defaultMTU, tcpip.ReadOptions{})
+	w := tcpip.LimitedWriter{
+		W: ioutil.Discard,
+		// defaultMTU is a good enough estimate for the MSS used for this
+		// connection.
+		N: defaultMTU * 2,
+	}
+	for w.N != 0 {
+		_, err := c.EP.Read(&w, tcpip.ReadOptions{})
 		if err != nil {
 			t.Fatalf("Read failed: %s", err)
 		}
-		read += res.Count
 	}
 
 	// After reading > MSS worth of data, we surely crossed MSS. See the ack:
diff --git a/pkg/tcpip/transport/tcp/tcp_timestamp_test.go b/pkg/tcpip/transport/tcp/tcp_timestamp_test.go
index 88fb054bb..b65091c3c 100644
--- a/pkg/tcpip/transport/tcp/tcp_timestamp_test.go
+++ b/pkg/tcpip/transport/tcp/tcp_timestamp_test.go
@@ -106,18 +106,19 @@ func TestTimeStampEnabledConnect(t *testing.T) {
 	// There should be 5 views to read and each of them should
 	// contain the same data.
 	for i := 0; i < 5; i++ {
-		var buf bytes.Buffer
-		result, err := c.EP.Read(&buf, len(data), tcpip.ReadOptions{})
+		buf := make([]byte, len(data))
+		w := tcpip.SliceWriter(buf)
+		result, err := c.EP.Read(&w, tcpip.ReadOptions{})
 		if err != nil {
 			t.Fatalf("Unexpected error from Read: %v", err)
 		}
 		if diff := cmp.Diff(tcpip.ReadResult{
-			Count: buf.Len(),
-			Total: buf.Len(),
+			Count: len(buf),
+			Total: len(buf),
 		}, result, checker.IgnoreCmpPath("ControlMessages")); diff != "" {
 			t.Errorf("Read: unexpected result (-want +got):\n%s", diff)
 		}
-		if got, want := buf.Bytes(), data; bytes.Compare(got, want) != 0 {
+		if got, want := buf, data; bytes.Compare(got, want) != 0 {
 			t.Fatalf("Data is different: got: %v, want: %v", got, want)
 		}
 	}
@@ -295,7 +296,7 @@ func TestSegmentNotDroppedWhenTimestampMissing(t *testing.T) {
 
 	// Issue a read and we should data.
 	var buf bytes.Buffer
-	result, err := c.EP.Read(&buf, defaultMTU, tcpip.ReadOptions{})
+	result, err := c.EP.Read(&buf, tcpip.ReadOptions{})
 	if err != nil {
 		t.Fatalf("Unexpected error from Read: %v", err)
 	}
diff --git a/pkg/tcpip/transport/udp/endpoint.go b/pkg/tcpip/transport/udp/endpoint.go
index 520a0ac9d..9f9b3d510 100644
--- a/pkg/tcpip/transport/udp/endpoint.go
+++ b/pkg/tcpip/transport/udp/endpoint.go
@@ -284,7 +284,7 @@ func (e *endpoint) Close() {
 func (e *endpoint) ModerateRecvBuf(copied int) {}
 
 // Read implements tcpip.Endpoint.Read.
-func (e *endpoint) Read(dst io.Writer, count int, opts tcpip.ReadOptions) (tcpip.ReadResult, *tcpip.Error) {
+func (e *endpoint) Read(dst io.Writer, opts tcpip.ReadOptions) (tcpip.ReadResult, *tcpip.Error) {
 	if err := e.LastError(); err != nil {
 		return tcpip.ReadResult{}, err
 	}
@@ -340,7 +340,7 @@ func (e *endpoint) Read(dst io.Writer, count int, opts tcpip.ReadOptions) (tcpip
 		res.RemoteAddr = p.senderAddress
 	}
 
-	n, err := p.data.ReadTo(dst, count, opts.Peek)
+	n, err := p.data.ReadTo(dst, opts.Peek)
 	if n == 0 && err != nil {
 		return res, tcpip.ErrBadBuffer
 	}
diff --git a/pkg/tcpip/transport/udp/udp_test.go b/pkg/tcpip/transport/udp/udp_test.go
index 52403ed78..4e2123fe9 100644
--- a/pkg/tcpip/transport/udp/udp_test.go
+++ b/pkg/tcpip/transport/udp/udp_test.go
@@ -598,12 +598,12 @@ func testReadInternal(c *testContext, flow testFlow, packetShouldBeDropped, expe
 	epstats := c.ep.Stats().(*tcpip.TransportEndpointStats).Clone()
 
 	var buf bytes.Buffer
-	res, err := c.ep.Read(&buf, defaultMTU, tcpip.ReadOptions{NeedRemoteAddr: true})
+	res, err := c.ep.Read(&buf, tcpip.ReadOptions{NeedRemoteAddr: true})
 	if err == tcpip.ErrWouldBlock {
 		// Wait for data to become available.
 		select {
 		case <-ch:
-			res, err = c.ep.Read(&buf, defaultMTU, tcpip.ReadOptions{NeedRemoteAddr: true})
+			res, err = c.ep.Read(&buf, tcpip.ReadOptions{NeedRemoteAddr: true})
 
 		case <-time.After(300 * time.Millisecond):
 			if packetShouldBeDropped {
@@ -839,7 +839,7 @@ func TestV4ReadSelfSource(t *testing.T) {
 				t.Errorf("c.s.Stats().IP.InvalidSourceAddressesReceived got %d, want %d", got, tt.wantInvalidSource)
 			}
 
-			if _, err := c.ep.Read(ioutil.Discard, defaultMTU, tcpip.ReadOptions{}); err != tt.wantErr {
+			if _, err := c.ep.Read(ioutil.Discard, tcpip.ReadOptions{}); err != tt.wantErr {
 				t.Errorf("got c.ep.Read = %s, want = %s", err, tt.wantErr)
 			}
 		})