src/net/sendfile_test.go - go - Git at Google

 // Copyright 2016 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package net

 import (
 	"bytes"
 	"context"
 	"crypto/sha256"
 	"encoding/hex"
 	"errors"
 	"fmt"
 	"internal/poll"
 	"io"
 	"os"
 	"runtime"
 	"strconv"
 	"sync"
 	"testing"
 	"time"
 )

 const (
 	newton       = "../testdata/Isaac.Newton-Opticks.txt"
 	newtonLen    = 567198
 	newtonSHA256 = "d4a9ac22462b35e7821a4f2706c211093da678620a8f9997989ee7cf8d507bbd"
 )

 // expectSendfile runs f, and verifies that internal/poll.SendFile successfully handles
 // a write to wantConn during f's execution.
 //
 // On platforms where supportsSendfile is false, expectSendfile runs f but does not
 // expect a call to SendFile.
 func expectSendfile(t *testing.T, wantConn Conn, f func()) {
 	t.Helper()
 	if !supportsSendfile {
 		f()
 		return
 	}
 	orig := poll.TestHookDidSendFile
 	defer func() {
 		poll.TestHookDidSendFile = orig
 	}()
 	var (
 		called     bool
 		gotHandled bool
 		gotFD      *poll.FD
 	)
 	poll.TestHookDidSendFile = func(dstFD *poll.FD, src int, written int64, err error, handled bool) {
 		if called {
 			t.Error("internal/poll.SendFile called multiple times, want one call")
 		}
 		called = true
 		gotHandled = handled
 		gotFD = dstFD
 	}
 	f()
 	if !called {
 		t.Error("internal/poll.SendFile was not called, want it to be")
 		return
 	}
 	if !gotHandled {
 		t.Error("internal/poll.SendFile did not handle the write, want it to")
 		return
 	}
 	if &wantConn.(*TCPConn).fd.pfd != gotFD {
 		t.Error("internal.poll.SendFile called with unexpected FD")
 	}
 }

 func TestSendfile(t *testing.T) {
 	ln := newLocalListener(t, "tcp")
 	defer ln.Close()

 	errc := make(chan error, 1)
 	go func(ln Listener) {
 		// Wait for a connection.
 		conn, err := ln.Accept()
 		if err != nil {
 			errc <- err
 			close(errc)
 			return
 		}

 		go func() {
 			defer close(errc)
 			defer conn.Close()

 			f, err := os.Open(newton)
 			if err != nil {
 				errc <- err
 				return
 			}
 			defer f.Close()

 			// Return file data using io.Copy, which should use
 			// sendFile if available.
 			var sbytes int64
 			switch runtime.GOOS {
 			case "windows":
 				// Windows is not using sendfile for some reason:
 				// https://go.dev/issue/67042
 				sbytes, err = io.Copy(conn, f)
 			default:
 				expectSendfile(t, conn, func() {
 					sbytes, err = io.Copy(conn, f)
 				})
 			}
 			if err != nil {
 				errc <- err
 				return
 			}

 			if sbytes != newtonLen {
 				errc <- fmt.Errorf("sent %d bytes; expected %d", sbytes, newtonLen)
 				return
 			}
 		}()
 	}(ln)

 	// Connect to listener to retrieve file and verify digest matches
 	// expected.
 	c, err := Dial("tcp", ln.Addr().String())
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer c.Close()

 	h := sha256.New()
 	rbytes, err := io.Copy(h, c)
 	if err != nil {
 		t.Error(err)
 	}

 	if rbytes != newtonLen {
 		t.Errorf("received %d bytes; expected %d", rbytes, newtonLen)
 	}

 	if res := hex.EncodeToString(h.Sum(nil)); res != newtonSHA256 {
 		t.Error("retrieved data hash did not match")
 	}

 	for err := range errc {
 		t.Error(err)
 	}
 }

 func TestSendfileParts(t *testing.T) {
 	ln := newLocalListener(t, "tcp")
 	defer ln.Close()

 	errc := make(chan error, 1)
 	go func(ln Listener) {
 		// Wait for a connection.
 		conn, err := ln.Accept()
 		if err != nil {
 			errc <- err
 			close(errc)
 			return
 		}

 		go func() {
 			defer close(errc)
 			defer conn.Close()

 			f, err := os.Open(newton)
 			if err != nil {
 				errc <- err
 				return
 			}
 			defer f.Close()

 			for i := 0; i < 3; i++ {
 				// Return file data using io.CopyN, which should use
 				// sendFile if available.
 				expectSendfile(t, conn, func() {
 					_, err = io.CopyN(conn, f, 3)
 				})
 				if err != nil {
 					errc <- err
 					return
 				}
 			}
 		}()
 	}(ln)

 	c, err := Dial("tcp", ln.Addr().String())
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer c.Close()

 	buf := new(bytes.Buffer)
 	buf.ReadFrom(c)

 	if want, have := "Produced ", buf.String(); have != want {
 		t.Errorf("unexpected server reply %q, want %q", have, want)
 	}

 	for err := range errc {
 		t.Error(err)
 	}
 }

 func TestSendfileSeeked(t *testing.T) {
 	ln := newLocalListener(t, "tcp")
 	defer ln.Close()

 	const seekTo = 65 << 10
 	const sendSize = 10 << 10

 	errc := make(chan error, 1)
 	go func(ln Listener) {
 		// Wait for a connection.
 		conn, err := ln.Accept()
 		if err != nil {
 			errc <- err
 			close(errc)
 			return
 		}

 		go func() {
 			defer close(errc)
 			defer conn.Close()

 			f, err := os.Open(newton)
 			if err != nil {
 				errc <- err
 				return
 			}
 			defer f.Close()
 			if _, err := f.Seek(seekTo, io.SeekStart); err != nil {
 				errc <- err
 				return
 			}

 			expectSendfile(t, conn, func() {
 				_, err = io.CopyN(conn, f, sendSize)
 			})
 			if err != nil {
 				errc <- err
 				return
 			}
 		}()
 	}(ln)

 	c, err := Dial("tcp", ln.Addr().String())
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer c.Close()

 	buf := new(bytes.Buffer)
 	buf.ReadFrom(c)

 	if buf.Len() != sendSize {
 		t.Errorf("Got %d bytes; want %d", buf.Len(), sendSize)
 	}

 	for err := range errc {
 		t.Error(err)
 	}
 }

 // Test that sendfile doesn't put a pipe into blocking mode.
 func TestSendfilePipe(t *testing.T) {
 	switch runtime.GOOS {
 	case "plan9", "windows", "js", "wasip1":
 		// These systems don't support deadlines on pipes.
 		t.Skipf("skipping on %s", runtime.GOOS)
 	}

 	t.Parallel()

 	ln := newLocalListener(t, "tcp")
 	defer ln.Close()

 	r, w, err := os.Pipe()
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer w.Close()
 	defer r.Close()

 	copied := make(chan bool)

 	var wg sync.WaitGroup
 	wg.Add(1)
 	go func() {
 		// Accept a connection and copy 1 byte from the read end of
 		// the pipe to the connection. This will call into sendfile.
 		defer wg.Done()
 		conn, err := ln.Accept()
 		if err != nil {
 			t.Error(err)
 			return
 		}
 		defer conn.Close()
 		// The comment above states that this should call into sendfile,
 		// but empirically it doesn't seem to do so at this time.
 		// If it does, or does on some platforms, this CopyN should be wrapped
 		// in expectSendfile.
 		_, err = io.CopyN(conn, r, 1)
 		if err != nil {
 			t.Error(err)
 			return
 		}
 		// Signal the main goroutine that we've copied the byte.
 		close(copied)
 	}()

 	wg.Add(1)
 	go func() {
 		// Write 1 byte to the write end of the pipe.
 		defer wg.Done()
 		_, err := w.Write([]byte{'a'})
 		if err != nil {
 			t.Error(err)
 		}
 	}()

 	wg.Add(1)
 	go func() {
 		// Connect to the server started two goroutines up and
 		// discard any data that it writes.
 		defer wg.Done()
 		conn, err := Dial("tcp", ln.Addr().String())
 		if err != nil {
 			t.Error(err)
 			return
 		}
 		defer conn.Close()
 		io.Copy(io.Discard, conn)
 	}()

 	// Wait for the byte to be copied, meaning that sendfile has
 	// been called on the pipe.
 	<-copied

 	// Set a very short deadline on the read end of the pipe.
 	if err := r.SetDeadline(time.Now().Add(time.Microsecond)); err != nil {
 		t.Fatal(err)
 	}

 	wg.Add(1)
 	go func() {
 		// Wait for much longer than the deadline and write a byte
 		// to the pipe.
 		defer wg.Done()
 		time.Sleep(50 * time.Millisecond)
 		w.Write([]byte{'b'})
 	}()

 	// If this read does not time out, the pipe was incorrectly
 	// put into blocking mode.
 	_, err = r.Read(make([]byte, 1))
 	if err == nil {
 		t.Error("Read did not time out")
 	} else if !os.IsTimeout(err) {
 		t.Errorf("got error %v, expected a time out", err)
 	}

 	wg.Wait()
 }

 // Issue 43822: tests that returns EOF when conn write timeout.
 func TestSendfileOnWriteTimeoutExceeded(t *testing.T) {
 	ln := newLocalListener(t, "tcp")
 	defer ln.Close()

 	errc := make(chan error, 1)
 	go func(ln Listener) (retErr error) {
 		defer func() {
 			errc <- retErr
 			close(errc)
 		}()

 		conn, err := ln.Accept()
 		if err != nil {
 			return err
 		}
 		defer conn.Close()

 		// Set the write deadline in the past(1h ago). It makes
 		// sure that it is always write timeout.
 		if err := conn.SetWriteDeadline(time.Now().Add(-1 * time.Hour)); err != nil {
 			return err
 		}

 		f, err := os.Open(newton)
 		if err != nil {
 			return err
 		}
 		defer f.Close()

 		// We expect this to use sendfile, but as of the time this comment was written
 		// poll.SendFile on an FD past its timeout can return an error indicating that
 		// it didn't handle the operation, resulting in a non-sendfile retry.
 		// So don't use expectSendfile here.
 		_, err = io.Copy(conn, f)
 		if errors.Is(err, os.ErrDeadlineExceeded) {
 			return nil
 		}

 		if err == nil {
 			err = fmt.Errorf("expected ErrDeadlineExceeded, but got nil")
 		}
 		return err
 	}(ln)

 	conn, err := Dial("tcp", ln.Addr().String())
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer conn.Close()

 	n, err := io.Copy(io.Discard, conn)
 	if err != nil {
 		t.Fatalf("expected nil error, but got %v", err)
 	}
 	if n != 0 {
 		t.Fatalf("expected receive zero, but got %d byte(s)", n)
 	}

 	if err := <-errc; err != nil {
 		t.Fatal(err)
 	}
 }

 func BenchmarkSendfileZeroBytes(b *testing.B) {
 	var (
 		wg          sync.WaitGroup
 		ctx, cancel = context.WithCancel(context.Background())
 	)

 	defer wg.Wait()

 	ln := newLocalListener(b, "tcp")
 	defer ln.Close()

 	tempFile, err := os.CreateTemp(b.TempDir(), "test.txt")
 	if err != nil {
 		b.Fatalf("failed to create temp file: %v", err)
 	}
 	defer tempFile.Close()

 	fileName := tempFile.Name()

 	dataSize := b.N
 	wg.Add(1)
 	go func(f *os.File) {
 		defer wg.Done()

 		for i := 0; i < dataSize; i++ {
 			if _, err := f.Write([]byte{1}); err != nil {
 				b.Errorf("failed to write: %v", err)
 				return
 			}
 			if i%1000 == 0 {
 				f.Sync()
 			}
 		}
 	}(tempFile)

 	b.ResetTimer()
 	b.ReportAllocs()

 	wg.Add(1)
 	go func(ln Listener, fileName string) {
 		defer wg.Done()

 		conn, err := ln.Accept()
 		if err != nil {
 			b.Errorf("failed to accept: %v", err)
 			return
 		}
 		defer conn.Close()

 		f, err := os.OpenFile(fileName, os.O_RDONLY, 0660)
 		if err != nil {
 			b.Errorf("failed to open file: %v", err)
 			return
 		}
 		defer f.Close()

 		for {
 			if ctx.Err() != nil {
 				return
 			}

 			if _, err := io.Copy(conn, f); err != nil {
 				b.Errorf("failed to copy: %v", err)
 				return
 			}
 		}
 	}(ln, fileName)

 	conn, err := Dial("tcp", ln.Addr().String())
 	if err != nil {
 		b.Fatalf("failed to dial: %v", err)
 	}
 	defer conn.Close()

 	n, err := io.CopyN(io.Discard, conn, int64(dataSize))
 	if err != nil {
 		b.Fatalf("failed to copy: %v", err)
 	}
 	if n != int64(dataSize) {
 		b.Fatalf("expected %d copied bytes, but got %d", dataSize, n)
 	}

 	cancel()
 }

 func BenchmarkSendFile(b *testing.B) {
 	if runtime.GOOS == "windows" {
 		// TODO(panjf2000): Windows has not yet implemented FileConn,
 		//		remove this when it's implemented in https://go.dev/issues/9503.
 		b.Skipf("skipping on %s", runtime.GOOS)
 	}

 	b.Run("file-to-tcp", func(b *testing.B) { benchmarkSendFile(b, "tcp") })
 	b.Run("file-to-unix", func(b *testing.B) { benchmarkSendFile(b, "unix") })
 }

 func benchmarkSendFile(b *testing.B, proto string) {
 	for i := 0; i <= 10; i++ {
 		size := 1 << (i + 10)
 		bench := sendFileBench{
 			proto:     proto,
 			chunkSize: size,
 		}
 		b.Run(strconv.Itoa(size), bench.benchSendFile)
 	}
 }

 type sendFileBench struct {
 	proto     string
 	chunkSize int
 }

 func (bench sendFileBench) benchSendFile(b *testing.B) {
 	fileSize := b.N * bench.chunkSize
 	f := createTempFile(b, fileSize)

 	client, server := spawnTestSocketPair(b, bench.proto)
 	defer server.Close()

 	cleanUp, err := startTestSocketPeer(b, client, "r", bench.chunkSize, fileSize)
 	if err != nil {
 		client.Close()
 		b.Fatal(err)
 	}
 	defer cleanUp(b)

 	b.ReportAllocs()
 	b.SetBytes(int64(bench.chunkSize))
 	b.ResetTimer()

 	// Data go from file to socket via sendfile(2).
 	sent, err := io.Copy(server, f)
 	if err != nil {
 		b.Fatalf("failed to copy data with sendfile, error: %v", err)
 	}
 	if sent != int64(fileSize) {
 		b.Fatalf("bytes sent mismatch, got: %d, want: %d", sent, fileSize)
 	}
 }

 func createTempFile(b *testing.B, size int) *os.File {
 	f, err := os.CreateTemp(b.TempDir(), "sendfile-bench")
 	if err != nil {
 		b.Fatalf("failed to create temporary file: %v", err)
 	}
 	b.Cleanup(func() {
 		f.Close()
 	})

 	data := make([]byte, size)
 	if _, err := f.Write(data); err != nil {
 		b.Fatalf("failed to create and feed the file: %v", err)
 	}
 	if err := f.Sync(); err != nil {
 		b.Fatalf("failed to save the file: %v", err)
 	}
 	if _, err := f.Seek(0, io.SeekStart); err != nil {
 		b.Fatalf("failed to rewind the file: %v", err)
 	}

 	return f
 }
	// Copyright 2016 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package net

	import (
	"bytes"
	"context"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"fmt"
	"internal/poll"
	"io"
	"os"
	"runtime"
	"strconv"
	"sync"
	"testing"
	"time"
	)

	const (
	newton = "../testdata/Isaac.Newton-Opticks.txt"
	newtonLen = 567198
	newtonSHA256 = "d4a9ac22462b35e7821a4f2706c211093da678620a8f9997989ee7cf8d507bbd"
	)

	// expectSendfile runs f, and verifies that internal/poll.SendFile successfully handles
	// a write to wantConn during f's execution.
	//
	// On platforms where supportsSendfile is false, expectSendfile runs f but does not
	// expect a call to SendFile.
	func expectSendfile(t *testing.T, wantConn Conn, f func()) {
	t.Helper()
	if !supportsSendfile {
	f()
	return
	}
	orig := poll.TestHookDidSendFile
	defer func() {
	poll.TestHookDidSendFile = orig
	}()
	var (
	called bool
	gotHandled bool
	gotFD *poll.FD
	)
	poll.TestHookDidSendFile = func(dstFD *poll.FD, src int, written int64, err error, handled bool) {
	if called {
	t.Error("internal/poll.SendFile called multiple times, want one call")
	}
	called = true
	gotHandled = handled
	gotFD = dstFD
	}
	f()
	if !called {
	t.Error("internal/poll.SendFile was not called, want it to be")
	return
	}
	if !gotHandled {
	t.Error("internal/poll.SendFile did not handle the write, want it to")
	return
	}
	if &wantConn.(*TCPConn).fd.pfd != gotFD {
	t.Error("internal.poll.SendFile called with unexpected FD")
	}
	}

	func TestSendfile(t *testing.T) {
	ln := newLocalListener(t, "tcp")
	defer ln.Close()

	errc := make(chan error, 1)
	go func(ln Listener) {
	// Wait for a connection.
	conn, err := ln.Accept()
	if err != nil {
	errc <- err
	close(errc)
	return
	}

	go func() {
	defer close(errc)
	defer conn.Close()

	f, err := os.Open(newton)
	if err != nil {
	errc <- err
	return
	}
	defer f.Close()

	// Return file data using io.Copy, which should use
	// sendFile if available.
	var sbytes int64
	switch runtime.GOOS {
	case "windows":
	// Windows is not using sendfile for some reason:
	// https://go.dev/issue/67042
	sbytes, err = io.Copy(conn, f)
	default:
	expectSendfile(t, conn, func() {
	sbytes, err = io.Copy(conn, f)
	})
	}
	if err != nil {
	errc <- err
	return
	}

	if sbytes != newtonLen {
	errc <- fmt.Errorf("sent %d bytes; expected %d", sbytes, newtonLen)
	return
	}
	}()
	}(ln)

	// Connect to listener to retrieve file and verify digest matches
	// expected.
	c, err := Dial("tcp", ln.Addr().String())
	if err != nil {
	t.Fatal(err)
	}
	defer c.Close()

	h := sha256.New()
	rbytes, err := io.Copy(h, c)
	if err != nil {
	t.Error(err)
	}

	if rbytes != newtonLen {
	t.Errorf("received %d bytes; expected %d", rbytes, newtonLen)
	}

	if res := hex.EncodeToString(h.Sum(nil)); res != newtonSHA256 {
	t.Error("retrieved data hash did not match")
	}

	for err := range errc {
	t.Error(err)
	}
	}

	func TestSendfileParts(t *testing.T) {
	ln := newLocalListener(t, "tcp")
	defer ln.Close()

	errc := make(chan error, 1)
	go func(ln Listener) {
	// Wait for a connection.
	conn, err := ln.Accept()
	if err != nil {
	errc <- err
	close(errc)
	return
	}

	go func() {
	defer close(errc)
	defer conn.Close()

	f, err := os.Open(newton)
	if err != nil {
	errc <- err
	return
	}
	defer f.Close()

	for i := 0; i < 3; i++ {
	// Return file data using io.CopyN, which should use
	// sendFile if available.
	expectSendfile(t, conn, func() {
	_, err = io.CopyN(conn, f, 3)
	})
	if err != nil {
	errc <- err
	return
	}
	}
	}()
	}(ln)

	c, err := Dial("tcp", ln.Addr().String())
	if err != nil {
	t.Fatal(err)
	}
	defer c.Close()

	buf := new(bytes.Buffer)
	buf.ReadFrom(c)

	if want, have := "Produced ", buf.String(); have != want {
	t.Errorf("unexpected server reply %q, want %q", have, want)
	}

	for err := range errc {
	t.Error(err)
	}
	}

	func TestSendfileSeeked(t *testing.T) {
	ln := newLocalListener(t, "tcp")
	defer ln.Close()

	const seekTo = 65 << 10
	const sendSize = 10 << 10

	errc := make(chan error, 1)
	go func(ln Listener) {
	// Wait for a connection.
	conn, err := ln.Accept()
	if err != nil {
	errc <- err
	close(errc)
	return
	}

	go func() {
	defer close(errc)
	defer conn.Close()

	f, err := os.Open(newton)
	if err != nil {
	errc <- err
	return
	}
	defer f.Close()
	if _, err := f.Seek(seekTo, io.SeekStart); err != nil {
	errc <- err
	return
	}

	expectSendfile(t, conn, func() {
	_, err = io.CopyN(conn, f, sendSize)
	})
	if err != nil {
	errc <- err
	return
	}
	}()
	}(ln)

	c, err := Dial("tcp", ln.Addr().String())
	if err != nil {
	t.Fatal(err)
	}
	defer c.Close()

	buf := new(bytes.Buffer)
	buf.ReadFrom(c)

	if buf.Len() != sendSize {
	t.Errorf("Got %d bytes; want %d", buf.Len(), sendSize)
	}

	for err := range errc {
	t.Error(err)
	}
	}

	// Test that sendfile doesn't put a pipe into blocking mode.
	func TestSendfilePipe(t *testing.T) {
	switch runtime.GOOS {
	case "plan9", "windows", "js", "wasip1":
	// These systems don't support deadlines on pipes.
	t.Skipf("skipping on %s", runtime.GOOS)
	}

	t.Parallel()

	ln := newLocalListener(t, "tcp")
	defer ln.Close()

	r, w, err := os.Pipe()
	if err != nil {
	t.Fatal(err)
	}
	defer w.Close()
	defer r.Close()

	copied := make(chan bool)

	var wg sync.WaitGroup
	wg.Add(1)
	go func() {
	// Accept a connection and copy 1 byte from the read end of
	// the pipe to the connection. This will call into sendfile.
	defer wg.Done()
	conn, err := ln.Accept()
	if err != nil {
	t.Error(err)
	return
	}
	defer conn.Close()
	// The comment above states that this should call into sendfile,
	// but empirically it doesn't seem to do so at this time.
	// If it does, or does on some platforms, this CopyN should be wrapped
	// in expectSendfile.
	_, err = io.CopyN(conn, r, 1)
	if err != nil {
	t.Error(err)
	return
	}
	// Signal the main goroutine that we've copied the byte.
	close(copied)
	}()

	wg.Add(1)
	go func() {
	// Write 1 byte to the write end of the pipe.
	defer wg.Done()
	_, err := w.Write([]byte{'a'})
	if err != nil {
	t.Error(err)
	}
	}()

	wg.Add(1)
	go func() {
	// Connect to the server started two goroutines up and
	// discard any data that it writes.
	defer wg.Done()
	conn, err := Dial("tcp", ln.Addr().String())
	if err != nil {
	t.Error(err)
	return
	}
	defer conn.Close()
	io.Copy(io.Discard, conn)
	}()

	// Wait for the byte to be copied, meaning that sendfile has
	// been called on the pipe.
	<-copied

	// Set a very short deadline on the read end of the pipe.
	if err := r.SetDeadline(time.Now().Add(time.Microsecond)); err != nil {
	t.Fatal(err)
	}

	wg.Add(1)
	go func() {
	// Wait for much longer than the deadline and write a byte
	// to the pipe.
	defer wg.Done()
	time.Sleep(50 * time.Millisecond)
	w.Write([]byte{'b'})
	}()

	// If this read does not time out, the pipe was incorrectly
	// put into blocking mode.
	_, err = r.Read(make([]byte, 1))
	if err == nil {
	t.Error("Read did not time out")
	} else if !os.IsTimeout(err) {
	t.Errorf("got error %v, expected a time out", err)
	}

	wg.Wait()
	}

	// Issue 43822: tests that returns EOF when conn write timeout.
	func TestSendfileOnWriteTimeoutExceeded(t *testing.T) {
	ln := newLocalListener(t, "tcp")
	defer ln.Close()

	errc := make(chan error, 1)
	go func(ln Listener) (retErr error) {
	defer func() {
	errc <- retErr
	close(errc)
	}()

	conn, err := ln.Accept()
	if err != nil {
	return err
	}
	defer conn.Close()

	// Set the write deadline in the past(1h ago). It makes
	// sure that it is always write timeout.
	if err := conn.SetWriteDeadline(time.Now().Add(-1 * time.Hour)); err != nil {
	return err
	}

	f, err := os.Open(newton)
	if err != nil {
	return err
	}
	defer f.Close()

	// We expect this to use sendfile, but as of the time this comment was written
	// poll.SendFile on an FD past its timeout can return an error indicating that
	// it didn't handle the operation, resulting in a non-sendfile retry.
	// So don't use expectSendfile here.
	_, err = io.Copy(conn, f)
	if errors.Is(err, os.ErrDeadlineExceeded) {
	return nil
	}

	if err == nil {
	err = fmt.Errorf("expected ErrDeadlineExceeded, but got nil")
	}
	return err
	}(ln)

	conn, err := Dial("tcp", ln.Addr().String())
	if err != nil {
	t.Fatal(err)
	}
	defer conn.Close()

	n, err := io.Copy(io.Discard, conn)
	if err != nil {
	t.Fatalf("expected nil error, but got %v", err)
	}
	if n != 0 {
	t.Fatalf("expected receive zero, but got %d byte(s)", n)
	}

	if err := <-errc; err != nil {
	t.Fatal(err)
	}
	}

	func BenchmarkSendfileZeroBytes(b *testing.B) {
	var (
	wg sync.WaitGroup
	ctx, cancel = context.WithCancel(context.Background())
	)

	defer wg.Wait()

	ln := newLocalListener(b, "tcp")
	defer ln.Close()

	tempFile, err := os.CreateTemp(b.TempDir(), "test.txt")
	if err != nil {
	b.Fatalf("failed to create temp file: %v", err)
	}
	defer tempFile.Close()

	fileName := tempFile.Name()

	dataSize := b.N
	wg.Add(1)
	go func(f *os.File) {
	defer wg.Done()

	for i := 0; i < dataSize; i++ {
	if _, err := f.Write([]byte{1}); err != nil {
	b.Errorf("failed to write: %v", err)
	return
	}
	if i%1000 == 0 {
	f.Sync()
	}
	}
	}(tempFile)

	b.ResetTimer()
	b.ReportAllocs()

	wg.Add(1)
	go func(ln Listener, fileName string) {
	defer wg.Done()

	conn, err := ln.Accept()
	if err != nil {
	b.Errorf("failed to accept: %v", err)
	return
	}
	defer conn.Close()

	f, err := os.OpenFile(fileName, os.O_RDONLY, 0660)
	if err != nil {
	b.Errorf("failed to open file: %v", err)
	return
	}
	defer f.Close()

	for {
	if ctx.Err() != nil {
	return
	}

	if _, err := io.Copy(conn, f); err != nil {
	b.Errorf("failed to copy: %v", err)
	return
	}
	}
	}(ln, fileName)

	conn, err := Dial("tcp", ln.Addr().String())
	if err != nil {
	b.Fatalf("failed to dial: %v", err)
	}
	defer conn.Close()

	n, err := io.CopyN(io.Discard, conn, int64(dataSize))
	if err != nil {
	b.Fatalf("failed to copy: %v", err)
	}
	if n != int64(dataSize) {
	b.Fatalf("expected %d copied bytes, but got %d", dataSize, n)
	}

	cancel()
	}

	func BenchmarkSendFile(b *testing.B) {
	if runtime.GOOS == "windows" {
	// TODO(panjf2000): Windows has not yet implemented FileConn,
	// remove this when it's implemented in https://go.dev/issues/9503.
	b.Skipf("skipping on %s", runtime.GOOS)
	}

	b.Run("file-to-tcp", func(b *testing.B) { benchmarkSendFile(b, "tcp") })
	b.Run("file-to-unix", func(b *testing.B) { benchmarkSendFile(b, "unix") })
	}

	func benchmarkSendFile(b *testing.B, proto string) {
	for i := 0; i <= 10; i++ {
	size := 1 << (i + 10)
	bench := sendFileBench{
	proto: proto,
	chunkSize: size,
	}
	b.Run(strconv.Itoa(size), bench.benchSendFile)
	}
	}

	type sendFileBench struct {
	proto string
	chunkSize int
	}

	func (bench sendFileBench) benchSendFile(b *testing.B) {
	fileSize := b.N * bench.chunkSize
	f := createTempFile(b, fileSize)

	client, server := spawnTestSocketPair(b, bench.proto)
	defer server.Close()

	cleanUp, err := startTestSocketPeer(b, client, "r", bench.chunkSize, fileSize)
	if err != nil {
	client.Close()
	b.Fatal(err)
	}
	defer cleanUp(b)

	b.ReportAllocs()
	b.SetBytes(int64(bench.chunkSize))
	b.ResetTimer()

	// Data go from file to socket via sendfile(2).
	sent, err := io.Copy(server, f)
	if err != nil {
	b.Fatalf("failed to copy data with sendfile, error: %v", err)
	}
	if sent != int64(fileSize) {
	b.Fatalf("bytes sent mismatch, got: %d, want: %d", sent, fileSize)
	}
	}

	func createTempFile(b testing.B, size int) os.File {
	f, err := os.CreateTemp(b.TempDir(), "sendfile-bench")
	if err != nil {
	b.Fatalf("failed to create temporary file: %v", err)
	}
	b.Cleanup(func() {
	f.Close()
	})

	data := make([]byte, size)
	if _, err := f.Write(data); err != nil {
	b.Fatalf("failed to create and feed the file: %v", err)
	}
	if err := f.Sync(); err != nil {
	b.Fatalf("failed to save the file: %v", err)
	}
	if _, err := f.Seek(0, io.SeekStart); err != nil {
	b.Fatalf("failed to rewind the file: %v", err)
	}

	return f
	}