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

 // Copyright 2018 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.

 //go:build linux

 package net

 import (
 	"io"
 	"log"
 	"os"
 	"os/exec"
 	"strconv"
 	"sync"
 	"testing"
 	"time"
 )

 func TestSplice(t *testing.T) {
 	t.Run("tcp-to-tcp", func(t *testing.T) { testSplice(t, "tcp", "tcp") })
 	if !testableNetwork("unixgram") {
 		t.Skip("skipping unix-to-tcp tests")
 	}
 	t.Run("unix-to-tcp", func(t *testing.T) { testSplice(t, "unix", "tcp") })
 	t.Run("no-unixpacket", testSpliceNoUnixpacket)
 	t.Run("no-unixgram", testSpliceNoUnixgram)
 }

 func testSplice(t *testing.T, upNet, downNet string) {
 	t.Run("simple", spliceTestCase{upNet, downNet, 128, 128, 0}.test)
 	t.Run("multipleWrite", spliceTestCase{upNet, downNet, 4096, 1 << 20, 0}.test)
 	t.Run("big", spliceTestCase{upNet, downNet, 5 << 20, 1 << 30, 0}.test)
 	t.Run("honorsLimitedReader", spliceTestCase{upNet, downNet, 4096, 1 << 20, 1 << 10}.test)
 	t.Run("updatesLimitedReaderN", spliceTestCase{upNet, downNet, 1024, 4096, 4096 + 100}.test)
 	t.Run("limitedReaderAtLimit", spliceTestCase{upNet, downNet, 32, 128, 128}.test)
 	t.Run("readerAtEOF", func(t *testing.T) { testSpliceReaderAtEOF(t, upNet, downNet) })
 	t.Run("issue25985", func(t *testing.T) { testSpliceIssue25985(t, upNet, downNet) })
 }

 type spliceTestCase struct {
 	upNet, downNet string

 	chunkSize, totalSize int
 	limitReadSize        int
 }

 func (tc spliceTestCase) test(t *testing.T) {
 	clientUp, serverUp, err := spliceTestSocketPair(tc.upNet)
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer serverUp.Close()
 	cleanup, err := startSpliceClient(clientUp, "w", tc.chunkSize, tc.totalSize)
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer cleanup()
 	clientDown, serverDown, err := spliceTestSocketPair(tc.downNet)
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer serverDown.Close()
 	cleanup, err = startSpliceClient(clientDown, "r", tc.chunkSize, tc.totalSize)
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer cleanup()
 	var (
 		r    io.Reader = serverUp
 		size           = tc.totalSize
 	)
 	if tc.limitReadSize > 0 {
 		if tc.limitReadSize < size {
 			size = tc.limitReadSize
 		}

 		r = &io.LimitedReader{
 			N: int64(tc.limitReadSize),
 			R: serverUp,
 		}
 		defer serverUp.Close()
 	}
 	n, err := io.Copy(serverDown, r)
 	serverDown.Close()
 	if err != nil {
 		t.Fatal(err)
 	}
 	if want := int64(size); want != n {
 		t.Errorf("want %d bytes spliced, got %d", want, n)
 	}

 	if tc.limitReadSize > 0 {
 		wantN := 0
 		if tc.limitReadSize > size {
 			wantN = tc.limitReadSize - size
 		}

 		if n := r.(*io.LimitedReader).N; n != int64(wantN) {
 			t.Errorf("r.N = %d, want %d", n, wantN)
 		}
 	}
 }

 func testSpliceReaderAtEOF(t *testing.T, upNet, downNet string) {
 	clientUp, serverUp, err := spliceTestSocketPair(upNet)
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer clientUp.Close()
 	clientDown, serverDown, err := spliceTestSocketPair(downNet)
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer clientDown.Close()

 	serverUp.Close()

 	// We'd like to call net.splice here and check the handled return
 	// value, but we disable splice on old Linux kernels.
 	//
 	// In that case, poll.Splice and net.splice return a non-nil error
 	// and handled == false. We'd ideally like to see handled == true
 	// because the source reader is at EOF, but if we're running on an old
 	// kernel, and splice is disabled, we won't see EOF from net.splice,
 	// because we won't touch the reader at all.
 	//
 	// Trying to untangle the errors from net.splice and match them
 	// against the errors created by the poll package would be brittle,
 	// so this is a higher level test.
 	//
 	// The following ReadFrom should return immediately, regardless of
 	// whether splice is disabled or not. The other side should then
 	// get a goodbye signal. Test for the goodbye signal.
 	msg := "bye"
 	go func() {
 		serverDown.(io.ReaderFrom).ReadFrom(serverUp)
 		io.WriteString(serverDown, msg)
 		serverDown.Close()
 	}()

 	buf := make([]byte, 3)
 	_, err = io.ReadFull(clientDown, buf)
 	if err != nil {
 		t.Errorf("clientDown: %v", err)
 	}
 	if string(buf) != msg {
 		t.Errorf("clientDown got %q, want %q", buf, msg)
 	}
 }

 func testSpliceIssue25985(t *testing.T, upNet, downNet string) {
 	front, err := newLocalListener(upNet)
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer front.Close()
 	back, err := newLocalListener(downNet)
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer back.Close()

 	var wg sync.WaitGroup
 	wg.Add(2)

 	proxy := func() {
 		src, err := front.Accept()
 		if err != nil {
 			return
 		}
 		dst, err := Dial(downNet, back.Addr().String())
 		if err != nil {
 			return
 		}
 		defer dst.Close()
 		defer src.Close()
 		go func() {
 			io.Copy(src, dst)
 			wg.Done()
 		}()
 		go func() {
 			io.Copy(dst, src)
 			wg.Done()
 		}()
 	}

 	go proxy()

 	toFront, err := Dial(upNet, front.Addr().String())
 	if err != nil {
 		t.Fatal(err)
 	}

 	io.WriteString(toFront, "foo")
 	toFront.Close()

 	fromProxy, err := back.Accept()
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer fromProxy.Close()

 	_, err = io.ReadAll(fromProxy)
 	if err != nil {
 		t.Fatal(err)
 	}

 	wg.Wait()
 }

 func testSpliceNoUnixpacket(t *testing.T) {
 	clientUp, serverUp, err := spliceTestSocketPair("unixpacket")
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer clientUp.Close()
 	defer serverUp.Close()
 	clientDown, serverDown, err := spliceTestSocketPair("tcp")
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer clientDown.Close()
 	defer serverDown.Close()
 	// If splice called poll.Splice here, we'd get err == syscall.EINVAL
 	// and handled == false.  If poll.Splice gets an EINVAL on the first
 	// try, it assumes the kernel it's running on doesn't support splice
 	// for unix sockets and returns handled == false. This works for our
 	// purposes by somewhat of an accident, but is not entirely correct.
 	//
 	// What we want is err == nil and handled == false, i.e. we never
 	// called poll.Splice, because we know the unix socket's network.
 	_, err, handled := splice(serverDown.(*TCPConn).fd, serverUp)
 	if err != nil || handled != false {
 		t.Fatalf("got err = %v, handled = %t, want nil error, handled == false", err, handled)
 	}
 }

 func testSpliceNoUnixgram(t *testing.T) {
 	addr, err := ResolveUnixAddr("unixgram", testUnixAddr())
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer os.Remove(addr.Name)
 	up, err := ListenUnixgram("unixgram", addr)
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer up.Close()
 	clientDown, serverDown, err := spliceTestSocketPair("tcp")
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer clientDown.Close()
 	defer serverDown.Close()
 	// Analogous to testSpliceNoUnixpacket.
 	_, err, handled := splice(serverDown.(*TCPConn).fd, up)
 	if err != nil || handled != false {
 		t.Fatalf("got err = %v, handled = %t, want nil error, handled == false", err, handled)
 	}
 }

 func BenchmarkSplice(b *testing.B) {
 	testHookUninstaller.Do(uninstallTestHooks)

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

 func benchSplice(b *testing.B, upNet, downNet string) {
 	for i := 0; i <= 10; i++ {
 		chunkSize := 1 << uint(i+10)
 		tc := spliceTestCase{
 			upNet:     upNet,
 			downNet:   downNet,
 			chunkSize: chunkSize,
 		}

 		b.Run(strconv.Itoa(chunkSize), tc.bench)
 	}
 }

 func (tc spliceTestCase) bench(b *testing.B) {
 	// To benchmark the genericReadFrom code path, set this to false.
 	useSplice := true

 	clientUp, serverUp, err := spliceTestSocketPair(tc.upNet)
 	if err != nil {
 		b.Fatal(err)
 	}
 	defer serverUp.Close()

 	cleanup, err := startSpliceClient(clientUp, "w", tc.chunkSize, tc.chunkSize*b.N)
 	if err != nil {
 		b.Fatal(err)
 	}
 	defer cleanup()

 	clientDown, serverDown, err := spliceTestSocketPair(tc.downNet)
 	if err != nil {
 		b.Fatal(err)
 	}
 	defer serverDown.Close()

 	cleanup, err = startSpliceClient(clientDown, "r", tc.chunkSize, tc.chunkSize*b.N)
 	if err != nil {
 		b.Fatal(err)
 	}
 	defer cleanup()

 	b.SetBytes(int64(tc.chunkSize))
 	b.ResetTimer()

 	if useSplice {
 		_, err := io.Copy(serverDown, serverUp)
 		if err != nil {
 			b.Fatal(err)
 		}
 	} else {
 		type onlyReader struct {
 			io.Reader
 		}
 		_, err := io.Copy(serverDown, onlyReader{serverUp})
 		if err != nil {
 			b.Fatal(err)
 		}
 	}
 }

 func spliceTestSocketPair(net string) (client, server Conn, err error) {
 	ln, err := newLocalListener(net)
 	if err != nil {
 		return nil, nil, err
 	}
 	defer ln.Close()
 	var cerr, serr error
 	acceptDone := make(chan struct{})
 	go func() {
 		server, serr = ln.Accept()
 		acceptDone <- struct{}{}
 	}()
 	client, cerr = Dial(ln.Addr().Network(), ln.Addr().String())
 	<-acceptDone
 	if cerr != nil {
 		if server != nil {
 			server.Close()
 		}
 		return nil, nil, cerr
 	}
 	if serr != nil {
 		if client != nil {
 			client.Close()
 		}
 		return nil, nil, serr
 	}
 	return client, server, nil
 }

 func startSpliceClient(conn Conn, op string, chunkSize, totalSize int) (func(), error) {
 	f, err := conn.(interface{ File() (*os.File, error) }).File()
 	if err != nil {
 		return nil, err
 	}

 	cmd := exec.Command(os.Args[0], os.Args[1:]...)
 	cmd.Env = []string{
 		"GO_NET_TEST_SPLICE=1",
 		"GO_NET_TEST_SPLICE_OP=" + op,
 		"GO_NET_TEST_SPLICE_CHUNK_SIZE=" + strconv.Itoa(chunkSize),
 		"GO_NET_TEST_SPLICE_TOTAL_SIZE=" + strconv.Itoa(totalSize),
 		"TMPDIR=" + os.Getenv("TMPDIR"),
 	}
 	cmd.ExtraFiles = append(cmd.ExtraFiles, f)
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = os.Stderr

 	if err := cmd.Start(); err != nil {
 		return nil, err
 	}

 	donec := make(chan struct{})
 	go func() {
 		cmd.Wait()
 		conn.Close()
 		f.Close()
 		close(donec)
 	}()

 	return func() {
 		select {
 		case <-donec:
 		case <-time.After(5 * time.Second):
 			log.Printf("killing splice client after 5 second shutdown timeout")
 			cmd.Process.Kill()
 			select {
 			case <-donec:
 			case <-time.After(5 * time.Second):
 				log.Printf("splice client didn't die after 10 seconds")
 			}
 		}
 	}, nil
 }

 func init() {
 	if os.Getenv("GO_NET_TEST_SPLICE") == "" {
 		return
 	}
 	defer os.Exit(0)

 	f := os.NewFile(uintptr(3), "splice-test-conn")
 	defer f.Close()

 	conn, err := FileConn(f)
 	if err != nil {
 		log.Fatal(err)
 	}

 	var chunkSize int
 	if chunkSize, err = strconv.Atoi(os.Getenv("GO_NET_TEST_SPLICE_CHUNK_SIZE")); err != nil {
 		log.Fatal(err)
 	}
 	buf := make([]byte, chunkSize)

 	var totalSize int
 	if totalSize, err = strconv.Atoi(os.Getenv("GO_NET_TEST_SPLICE_TOTAL_SIZE")); err != nil {
 		log.Fatal(err)
 	}

 	var fn func([]byte) (int, error)
 	switch op := os.Getenv("GO_NET_TEST_SPLICE_OP"); op {
 	case "r":
 		fn = conn.Read
 	case "w":
 		defer conn.Close()

 		fn = conn.Write
 	default:
 		log.Fatalf("unknown op %q", op)
 	}

 	var n int
 	for count := 0; count < totalSize; count += n {
 		if count+chunkSize > totalSize {
 			buf = buf[:totalSize-count]
 		}

 		var err error
 		if n, err = fn(buf); err != nil {
 			return
 		}
 	}
 }
	// Copyright 2018 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.

	//go:build linux

	package net

	import (
	"io"
	"log"
	"os"
	"os/exec"
	"strconv"
	"sync"
	"testing"
	"time"
	)

	func TestSplice(t *testing.T) {
	t.Run("tcp-to-tcp", func(t *testing.T) { testSplice(t, "tcp", "tcp") })
	if !testableNetwork("unixgram") {
	t.Skip("skipping unix-to-tcp tests")
	}
	t.Run("unix-to-tcp", func(t *testing.T) { testSplice(t, "unix", "tcp") })
	t.Run("no-unixpacket", testSpliceNoUnixpacket)
	t.Run("no-unixgram", testSpliceNoUnixgram)
	}

	func testSplice(t *testing.T, upNet, downNet string) {
	t.Run("simple", spliceTestCase{upNet, downNet, 128, 128, 0}.test)
	t.Run("multipleWrite", spliceTestCase{upNet, downNet, 4096, 1 << 20, 0}.test)
	t.Run("big", spliceTestCase{upNet, downNet, 5 << 20, 1 << 30, 0}.test)
	t.Run("honorsLimitedReader", spliceTestCase{upNet, downNet, 4096, 1 << 20, 1 << 10}.test)
	t.Run("updatesLimitedReaderN", spliceTestCase{upNet, downNet, 1024, 4096, 4096 + 100}.test)
	t.Run("limitedReaderAtLimit", spliceTestCase{upNet, downNet, 32, 128, 128}.test)
	t.Run("readerAtEOF", func(t *testing.T) { testSpliceReaderAtEOF(t, upNet, downNet) })
	t.Run("issue25985", func(t *testing.T) { testSpliceIssue25985(t, upNet, downNet) })
	}

	type spliceTestCase struct {
	upNet, downNet string

	chunkSize, totalSize int
	limitReadSize int
	}

	func (tc spliceTestCase) test(t *testing.T) {
	clientUp, serverUp, err := spliceTestSocketPair(tc.upNet)
	if err != nil {
	t.Fatal(err)
	}
	defer serverUp.Close()
	cleanup, err := startSpliceClient(clientUp, "w", tc.chunkSize, tc.totalSize)
	if err != nil {
	t.Fatal(err)
	}
	defer cleanup()
	clientDown, serverDown, err := spliceTestSocketPair(tc.downNet)
	if err != nil {
	t.Fatal(err)
	}
	defer serverDown.Close()
	cleanup, err = startSpliceClient(clientDown, "r", tc.chunkSize, tc.totalSize)
	if err != nil {
	t.Fatal(err)
	}
	defer cleanup()
	var (
	r io.Reader = serverUp
	size = tc.totalSize
	)
	if tc.limitReadSize > 0 {
	if tc.limitReadSize < size {
	size = tc.limitReadSize
	}

	r = &io.LimitedReader{
	N: int64(tc.limitReadSize),
	R: serverUp,
	}
	defer serverUp.Close()
	}
	n, err := io.Copy(serverDown, r)
	serverDown.Close()
	if err != nil {
	t.Fatal(err)
	}
	if want := int64(size); want != n {
	t.Errorf("want %d bytes spliced, got %d", want, n)
	}

	if tc.limitReadSize > 0 {
	wantN := 0
	if tc.limitReadSize > size {
	wantN = tc.limitReadSize - size
	}

	if n := r.(*io.LimitedReader).N; n != int64(wantN) {
	t.Errorf("r.N = %d, want %d", n, wantN)
	}
	}
	}

	func testSpliceReaderAtEOF(t *testing.T, upNet, downNet string) {
	clientUp, serverUp, err := spliceTestSocketPair(upNet)
	if err != nil {
	t.Fatal(err)
	}
	defer clientUp.Close()
	clientDown, serverDown, err := spliceTestSocketPair(downNet)
	if err != nil {
	t.Fatal(err)
	}
	defer clientDown.Close()

	serverUp.Close()

	// We'd like to call net.splice here and check the handled return
	// value, but we disable splice on old Linux kernels.
	//
	// In that case, poll.Splice and net.splice return a non-nil error
	// and handled == false. We'd ideally like to see handled == true
	// because the source reader is at EOF, but if we're running on an old
	// kernel, and splice is disabled, we won't see EOF from net.splice,
	// because we won't touch the reader at all.
	//
	// Trying to untangle the errors from net.splice and match them
	// against the errors created by the poll package would be brittle,
	// so this is a higher level test.
	//
	// The following ReadFrom should return immediately, regardless of
	// whether splice is disabled or not. The other side should then
	// get a goodbye signal. Test for the goodbye signal.
	msg := "bye"
	go func() {
	serverDown.(io.ReaderFrom).ReadFrom(serverUp)
	io.WriteString(serverDown, msg)
	serverDown.Close()
	}()

	buf := make([]byte, 3)
	_, err = io.ReadFull(clientDown, buf)
	if err != nil {
	t.Errorf("clientDown: %v", err)
	}
	if string(buf) != msg {
	t.Errorf("clientDown got %q, want %q", buf, msg)
	}
	}

	func testSpliceIssue25985(t *testing.T, upNet, downNet string) {
	front, err := newLocalListener(upNet)
	if err != nil {
	t.Fatal(err)
	}
	defer front.Close()
	back, err := newLocalListener(downNet)
	if err != nil {
	t.Fatal(err)
	}
	defer back.Close()

	var wg sync.WaitGroup
	wg.Add(2)

	proxy := func() {
	src, err := front.Accept()
	if err != nil {
	return
	}
	dst, err := Dial(downNet, back.Addr().String())
	if err != nil {
	return
	}
	defer dst.Close()
	defer src.Close()
	go func() {
	io.Copy(src, dst)
	wg.Done()
	}()
	go func() {
	io.Copy(dst, src)
	wg.Done()
	}()
	}

	go proxy()

	toFront, err := Dial(upNet, front.Addr().String())
	if err != nil {
	t.Fatal(err)
	}

	io.WriteString(toFront, "foo")
	toFront.Close()

	fromProxy, err := back.Accept()
	if err != nil {
	t.Fatal(err)
	}
	defer fromProxy.Close()

	_, err = io.ReadAll(fromProxy)
	if err != nil {
	t.Fatal(err)
	}

	wg.Wait()
	}

	func testSpliceNoUnixpacket(t *testing.T) {
	clientUp, serverUp, err := spliceTestSocketPair("unixpacket")
	if err != nil {
	t.Fatal(err)
	}
	defer clientUp.Close()
	defer serverUp.Close()
	clientDown, serverDown, err := spliceTestSocketPair("tcp")
	if err != nil {
	t.Fatal(err)
	}
	defer clientDown.Close()
	defer serverDown.Close()
	// If splice called poll.Splice here, we'd get err == syscall.EINVAL
	// and handled == false. If poll.Splice gets an EINVAL on the first
	// try, it assumes the kernel it's running on doesn't support splice
	// for unix sockets and returns handled == false. This works for our
	// purposes by somewhat of an accident, but is not entirely correct.
	//
	// What we want is err == nil and handled == false, i.e. we never
	// called poll.Splice, because we know the unix socket's network.
	_, err, handled := splice(serverDown.(*TCPConn).fd, serverUp)
	if err != nil \|\| handled != false {
	t.Fatalf("got err = %v, handled = %t, want nil error, handled == false", err, handled)
	}
	}

	func testSpliceNoUnixgram(t *testing.T) {
	addr, err := ResolveUnixAddr("unixgram", testUnixAddr())
	if err != nil {
	t.Fatal(err)
	}
	defer os.Remove(addr.Name)
	up, err := ListenUnixgram("unixgram", addr)
	if err != nil {
	t.Fatal(err)
	}
	defer up.Close()
	clientDown, serverDown, err := spliceTestSocketPair("tcp")
	if err != nil {
	t.Fatal(err)
	}
	defer clientDown.Close()
	defer serverDown.Close()
	// Analogous to testSpliceNoUnixpacket.
	_, err, handled := splice(serverDown.(*TCPConn).fd, up)
	if err != nil \|\| handled != false {
	t.Fatalf("got err = %v, handled = %t, want nil error, handled == false", err, handled)
	}
	}

	func BenchmarkSplice(b *testing.B) {
	testHookUninstaller.Do(uninstallTestHooks)

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

	func benchSplice(b *testing.B, upNet, downNet string) {
	for i := 0; i <= 10; i++ {
	chunkSize := 1 << uint(i+10)
	tc := spliceTestCase{
	upNet: upNet,
	downNet: downNet,
	chunkSize: chunkSize,
	}

	b.Run(strconv.Itoa(chunkSize), tc.bench)
	}
	}

	func (tc spliceTestCase) bench(b *testing.B) {
	// To benchmark the genericReadFrom code path, set this to false.
	useSplice := true

	clientUp, serverUp, err := spliceTestSocketPair(tc.upNet)
	if err != nil {
	b.Fatal(err)
	}
	defer serverUp.Close()

	cleanup, err := startSpliceClient(clientUp, "w", tc.chunkSize, tc.chunkSize*b.N)
	if err != nil {
	b.Fatal(err)
	}
	defer cleanup()

	clientDown, serverDown, err := spliceTestSocketPair(tc.downNet)
	if err != nil {
	b.Fatal(err)
	}
	defer serverDown.Close()

	cleanup, err = startSpliceClient(clientDown, "r", tc.chunkSize, tc.chunkSize*b.N)
	if err != nil {
	b.Fatal(err)
	}
	defer cleanup()

	b.SetBytes(int64(tc.chunkSize))
	b.ResetTimer()

	if useSplice {
	_, err := io.Copy(serverDown, serverUp)
	if err != nil {
	b.Fatal(err)
	}
	} else {
	type onlyReader struct {
	io.Reader
	}
	_, err := io.Copy(serverDown, onlyReader{serverUp})
	if err != nil {
	b.Fatal(err)
	}
	}
	}

	func spliceTestSocketPair(net string) (client, server Conn, err error) {
	ln, err := newLocalListener(net)
	if err != nil {
	return nil, nil, err
	}
	defer ln.Close()
	var cerr, serr error
	acceptDone := make(chan struct{})
	go func() {
	server, serr = ln.Accept()
	acceptDone <- struct{}{}
	}()
	client, cerr = Dial(ln.Addr().Network(), ln.Addr().String())
	<-acceptDone
	if cerr != nil {
	if server != nil {
	server.Close()
	}
	return nil, nil, cerr
	}
	if serr != nil {
	if client != nil {
	client.Close()
	}
	return nil, nil, serr
	}
	return client, server, nil
	}

	func startSpliceClient(conn Conn, op string, chunkSize, totalSize int) (func(), error) {
	f, err := conn.(interface{ File() (*os.File, error) }).File()
	if err != nil {
	return nil, err
	}

	cmd := exec.Command(os.Args[0], os.Args[1:]...)
	cmd.Env = []string{
	"GO_NET_TEST_SPLICE=1",
	"GO_NET_TEST_SPLICE_OP=" + op,
	"GO_NET_TEST_SPLICE_CHUNK_SIZE=" + strconv.Itoa(chunkSize),
	"GO_NET_TEST_SPLICE_TOTAL_SIZE=" + strconv.Itoa(totalSize),
	"TMPDIR=" + os.Getenv("TMPDIR"),
	}
	cmd.ExtraFiles = append(cmd.ExtraFiles, f)
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr

	if err := cmd.Start(); err != nil {
	return nil, err
	}

	donec := make(chan struct{})
	go func() {
	cmd.Wait()
	conn.Close()
	f.Close()
	close(donec)
	}()

	return func() {
	select {
	case <-donec:
	case <-time.After(5 * time.Second):
	log.Printf("killing splice client after 5 second shutdown timeout")
	cmd.Process.Kill()
	select {
	case <-donec:
	case <-time.After(5 * time.Second):
	log.Printf("splice client didn't die after 10 seconds")
	}
	}
	}, nil
	}

	func init() {
	if os.Getenv("GO_NET_TEST_SPLICE") == "" {
	return
	}
	defer os.Exit(0)

	f := os.NewFile(uintptr(3), "splice-test-conn")
	defer f.Close()

	conn, err := FileConn(f)
	if err != nil {
	log.Fatal(err)
	}

	var chunkSize int
	if chunkSize, err = strconv.Atoi(os.Getenv("GO_NET_TEST_SPLICE_CHUNK_SIZE")); err != nil {
	log.Fatal(err)
	}
	buf := make([]byte, chunkSize)

	var totalSize int
	if totalSize, err = strconv.Atoi(os.Getenv("GO_NET_TEST_SPLICE_TOTAL_SIZE")); err != nil {
	log.Fatal(err)
	}

	var fn func([]byte) (int, error)
	switch op := os.Getenv("GO_NET_TEST_SPLICE_OP"); op {
	case "r":
	fn = conn.Read
	case "w":
	defer conn.Close()

	fn = conn.Write
	default:
	log.Fatalf("unknown op %q", op)
	}

	var n int
	for count := 0; count < totalSize; count += n {
	if count+chunkSize > totalSize {
	buf = buf[:totalSize-count]
	}

	var err error
	if n, err = fn(buf); err != nil {
	return
	}
	}
	}