src/net/splice_linux_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 (
 	"internal/poll"
 	"io"
 	"os"
 	"strconv"
 	"sync"
 	"syscall"
 	"testing"
 )

 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("tcp-to-unix", func(t *testing.T) { testSplice(t, "tcp", "unix") })
 	t.Run("tcp-to-file", func(t *testing.T) { testSpliceToFile(t, "tcp", "file") })
 	t.Run("unix-to-file", func(t *testing.T) { testSpliceToFile(t, "unix", "file") })
 	t.Run("no-unixpacket", testSpliceNoUnixpacket)
 	t.Run("no-unixgram", testSpliceNoUnixgram)
 }

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

 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) {
 	hook := hookSplice(t)

 	// We need to use the actual size for startTestSocketPeer when testing with LimitedReader,
 	// otherwise the child process created in startTestSocketPeer will hang infinitely because of
 	// the mismatch of data size to transfer.
 	size := tc.totalSize
 	if tc.limitReadSize > 0 {
 		if tc.limitReadSize < size {
 			size = tc.limitReadSize
 		}
 	}

 	clientUp, serverUp := spawnTestSocketPair(t, tc.upNet)
 	defer serverUp.Close()
 	cleanup, err := startTestSocketPeer(t, clientUp, "w", tc.chunkSize, size)
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer cleanup(t)
 	clientDown, serverDown := spawnTestSocketPair(t, tc.downNet)
 	defer serverDown.Close()
 	cleanup, err = startTestSocketPeer(t, clientDown, "r", tc.chunkSize, size)
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer cleanup(t)

 	var r io.Reader = serverUp
 	if tc.limitReadSize > 0 {
 		r = &io.LimitedReader{
 			N: int64(tc.limitReadSize),
 			R: serverUp,
 		}
 		defer serverUp.Close()
 	}
 	n, err := io.Copy(serverDown, r)
 	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)
 		}
 	}

 	// poll.Splice is expected to be called when the source is not
 	// a wrapper or the destination is TCPConn.
 	if tc.limitReadSize == 0 || tc.downNet == "tcp" {
 		// We should have called poll.Splice with the right file descriptor arguments.
 		if n > 0 && !hook.called {
 			t.Fatal("expected poll.Splice to be called")
 		}

 		verifySpliceFds(t, serverDown, hook, "dst")
 		verifySpliceFds(t, serverUp, hook, "src")

 		// poll.Splice is expected to handle the data transmission successfully.
 		if !hook.handled || hook.written != int64(size) || hook.err != nil {
 			t.Errorf("expected handled = true, written = %d, err = nil, but got handled = %t, written = %d, err = %v",
 				size, hook.handled, hook.written, hook.err)
 		}
 	} else if hook.called {
 		// poll.Splice will certainly not be called when the source
 		// is a wrapper and the destination is not TCPConn.
 		t.Errorf("expected poll.Splice not be called")
 	}
 }

 func verifySpliceFds(t *testing.T, c Conn, hook *spliceHook, fdType string) {
 	t.Helper()

 	sc, ok := c.(syscall.Conn)
 	if !ok {
 		t.Fatalf("expected syscall.Conn")
 	}
 	rc, err := sc.SyscallConn()
 	if err != nil {
 		t.Fatalf("syscall.Conn.SyscallConn error: %v", err)
 	}
 	var hookFd int
 	switch fdType {
 	case "src":
 		hookFd = hook.srcfd
 	case "dst":
 		hookFd = hook.dstfd
 	default:
 		t.Fatalf("unknown fdType %q", fdType)
 	}
 	if err := rc.Control(func(fd uintptr) {
 		if hook.called && hookFd != int(fd) {
 			t.Fatalf("wrong %s file descriptor: got %d, want %d", fdType, hook.dstfd, int(fd))
 		}
 	}); err != nil {
 		t.Fatalf("syscall.RawConn.Control error: %v", err)
 	}
 }

 func (tc spliceTestCase) testFile(t *testing.T) {
 	hook := hookSplice(t)

 	// We need to use the actual size for startTestSocketPeer when testing with LimitedReader,
 	// otherwise the child process created in startTestSocketPeer will hang infinitely because of
 	// the mismatch of data size to transfer.
 	actualSize := tc.totalSize
 	if tc.limitReadSize > 0 {
 		if tc.limitReadSize < actualSize {
 			actualSize = tc.limitReadSize
 		}
 	}

 	f, err := os.OpenFile(os.DevNull, os.O_WRONLY, 0)
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer f.Close()

 	client, server := spawnTestSocketPair(t, tc.upNet)
 	defer server.Close()

 	cleanup, err := startTestSocketPeer(t, client, "w", tc.chunkSize, actualSize)
 	if err != nil {
 		client.Close()
 		t.Fatal("failed to start splice client:", err)
 	}
 	defer cleanup(t)

 	var r io.Reader = server
 	if tc.limitReadSize > 0 {
 		r = &io.LimitedReader{
 			N: int64(tc.limitReadSize),
 			R: r,
 		}
 	}

 	got, err := io.Copy(f, r)
 	if err != nil {
 		t.Fatalf("failed to ReadFrom with error: %v", err)
 	}

 	// We shouldn't have called poll.Splice in TCPConn.WriteTo,
 	// it's supposed to be called from File.ReadFrom.
 	if got > 0 && hook.called {
 		t.Error("expected not poll.Splice to be called")
 	}

 	if want := int64(actualSize); got != want {
 		t.Errorf("got %d bytes, want %d", got, want)
 	}
 	if tc.limitReadSize > 0 {
 		wantN := 0
 		if tc.limitReadSize > actualSize {
 			wantN = tc.limitReadSize - actualSize
 		}

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

 func testSpliceReaderAtEOF(t *testing.T, upNet, downNet string) {
 	// UnixConn doesn't implement io.ReaderFrom, which will fail
 	// the following test in asserting a UnixConn to be an io.ReaderFrom,
 	// so skip this test.
 	if downNet == "unix" {
 		t.Skip("skipping test on unix socket")
 	}

 	hook := hookSplice(t)

 	clientUp, serverUp := spawnTestSocketPair(t, upNet)
 	defer clientUp.Close()
 	clientDown, serverDown := spawnTestSocketPair(t, downNet)
 	defer clientDown.Close()
 	defer serverDown.Close()

 	serverUp.Close()

 	// We'd like to call net.spliceFrom here and check the handled return
 	// value, but we disable splice on old Linux kernels.
 	//
 	// In that case, poll.Splice and net.spliceFrom 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.spliceFrom,
 	// because we won't touch the reader at all.
 	//
 	// Trying to untangle the errors from net.spliceFrom 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)
 	}()

 	buf := make([]byte, 3)
 	n, 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)
 	}

 	// We should have called poll.Splice with the right file descriptor arguments.
 	if n > 0 && !hook.called {
 		t.Fatal("expected poll.Splice to be called")
 	}

 	verifySpliceFds(t, serverDown, hook, "dst")

 	// poll.Splice is expected to handle the data transmission but fail
 	// when working with a closed endpoint, return an error.
 	if !hook.handled || hook.written > 0 || hook.err == nil {
 		t.Errorf("expected handled = true, written = 0, err != nil, but got handled = %t, written = %d, err = %v",
 			hook.handled, hook.written, hook.err)
 	}
 }

 func testSpliceIssue25985(t *testing.T, upNet, downNet string) {
 	front := newLocalListener(t, upNet)
 	defer front.Close()
 	back := newLocalListener(t, downNet)
 	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 := spawnTestSocketPair(t, "unixpacket")
 	defer clientUp.Close()
 	defer serverUp.Close()
 	clientDown, serverDown := spawnTestSocketPair(t, "tcp")
 	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 := spliceFrom(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(t))
 	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 := spawnTestSocketPair(t, "tcp")
 	defer clientDown.Close()
 	defer serverDown.Close()
 	// Analogous to testSpliceNoUnixpacket.
 	_, err, handled := spliceFrom(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") })
 	b.Run("tcp-to-unix", func(b *testing.B) { benchSplice(b, "tcp", "unix") })
 }

 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 := spawnTestSocketPair(b, tc.upNet)
 	defer serverUp.Close()

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

 	clientDown, serverDown := spawnTestSocketPair(b, tc.downNet)
 	defer serverDown.Close()

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

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

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

 type spliceFileBench struct {
 	proto     string
 	chunkSize int
 }

 func (bench spliceFileBench) benchSpliceFile(b *testing.B) {
 	f, err := os.OpenFile(os.DevNull, os.O_WRONLY, 0)
 	if err != nil {
 		b.Fatal(err)
 	}
 	defer f.Close()

 	totalSize := b.N * bench.chunkSize

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

 	cleanup, err := startTestSocketPeer(b, client, "w", bench.chunkSize, totalSize)
 	if err != nil {
 		client.Close()
 		b.Fatalf("failed to start splice client: %v", err)
 	}
 	defer cleanup(b)

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

 	got, err := io.Copy(f, server)
 	if err != nil {
 		b.Fatalf("failed to ReadFrom with error: %v", err)
 	}
 	if want := int64(totalSize); got != want {
 		b.Errorf("bytes sent mismatch, got: %d, want: %d", got, want)
 	}
 }

 func hookSplice(t *testing.T) *spliceHook {
 	t.Helper()

 	h := new(spliceHook)
 	h.install()
 	t.Cleanup(h.uninstall)
 	return h
 }

 type spliceHook struct {
 	called bool
 	dstfd  int
 	srcfd  int
 	remain int64

 	written int64
 	handled bool
 	err     error

 	original func(dst, src *poll.FD, remain int64) (int64, bool, error)
 }

 func (h *spliceHook) install() {
 	h.original = pollSplice
 	pollSplice = func(dst, src *poll.FD, remain int64) (int64, bool, error) {
 		h.called = true
 		h.dstfd = dst.Sysfd
 		h.srcfd = src.Sysfd
 		h.remain = remain
 		h.written, h.handled, h.err = h.original(dst, src, remain)
 		return h.written, h.handled, h.err
 	}
 }

 func (h *spliceHook) uninstall() {
 	pollSplice = h.original
 }
	// 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 (
	"internal/poll"
	"io"
	"os"
	"strconv"
	"sync"
	"syscall"
	"testing"
	)

	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("tcp-to-unix", func(t *testing.T) { testSplice(t, "tcp", "unix") })
	t.Run("tcp-to-file", func(t *testing.T) { testSpliceToFile(t, "tcp", "file") })
	t.Run("unix-to-file", func(t *testing.T) { testSpliceToFile(t, "unix", "file") })
	t.Run("no-unixpacket", testSpliceNoUnixpacket)
	t.Run("no-unixgram", testSpliceNoUnixgram)
	}

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

	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) {
	hook := hookSplice(t)

	// We need to use the actual size for startTestSocketPeer when testing with LimitedReader,
	// otherwise the child process created in startTestSocketPeer will hang infinitely because of
	// the mismatch of data size to transfer.
	size := tc.totalSize
	if tc.limitReadSize > 0 {
	if tc.limitReadSize < size {
	size = tc.limitReadSize
	}
	}

	clientUp, serverUp := spawnTestSocketPair(t, tc.upNet)
	defer serverUp.Close()
	cleanup, err := startTestSocketPeer(t, clientUp, "w", tc.chunkSize, size)
	if err != nil {
	t.Fatal(err)
	}
	defer cleanup(t)
	clientDown, serverDown := spawnTestSocketPair(t, tc.downNet)
	defer serverDown.Close()
	cleanup, err = startTestSocketPeer(t, clientDown, "r", tc.chunkSize, size)
	if err != nil {
	t.Fatal(err)
	}
	defer cleanup(t)

	var r io.Reader = serverUp
	if tc.limitReadSize > 0 {
	r = &io.LimitedReader{
	N: int64(tc.limitReadSize),
	R: serverUp,
	}
	defer serverUp.Close()
	}
	n, err := io.Copy(serverDown, r)
	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)
	}
	}

	// poll.Splice is expected to be called when the source is not
	// a wrapper or the destination is TCPConn.
	if tc.limitReadSize == 0 \|\| tc.downNet == "tcp" {
	// We should have called poll.Splice with the right file descriptor arguments.
	if n > 0 && !hook.called {
	t.Fatal("expected poll.Splice to be called")
	}

	verifySpliceFds(t, serverDown, hook, "dst")
	verifySpliceFds(t, serverUp, hook, "src")

	// poll.Splice is expected to handle the data transmission successfully.
	if !hook.handled \|\| hook.written != int64(size) \|\| hook.err != nil {
	t.Errorf("expected handled = true, written = %d, err = nil, but got handled = %t, written = %d, err = %v",
	size, hook.handled, hook.written, hook.err)
	}
	} else if hook.called {
	// poll.Splice will certainly not be called when the source
	// is a wrapper and the destination is not TCPConn.
	t.Errorf("expected poll.Splice not be called")
	}
	}

	func verifySpliceFds(t testing.T, c Conn, hook spliceHook, fdType string) {
	t.Helper()

	sc, ok := c.(syscall.Conn)
	if !ok {
	t.Fatalf("expected syscall.Conn")
	}
	rc, err := sc.SyscallConn()
	if err != nil {
	t.Fatalf("syscall.Conn.SyscallConn error: %v", err)
	}
	var hookFd int
	switch fdType {
	case "src":
	hookFd = hook.srcfd
	case "dst":
	hookFd = hook.dstfd
	default:
	t.Fatalf("unknown fdType %q", fdType)
	}
	if err := rc.Control(func(fd uintptr) {
	if hook.called && hookFd != int(fd) {
	t.Fatalf("wrong %s file descriptor: got %d, want %d", fdType, hook.dstfd, int(fd))
	}
	}); err != nil {
	t.Fatalf("syscall.RawConn.Control error: %v", err)
	}
	}

	func (tc spliceTestCase) testFile(t *testing.T) {
	hook := hookSplice(t)

	// We need to use the actual size for startTestSocketPeer when testing with LimitedReader,
	// otherwise the child process created in startTestSocketPeer will hang infinitely because of
	// the mismatch of data size to transfer.
	actualSize := tc.totalSize
	if tc.limitReadSize > 0 {
	if tc.limitReadSize < actualSize {
	actualSize = tc.limitReadSize
	}
	}

	f, err := os.OpenFile(os.DevNull, os.O_WRONLY, 0)
	if err != nil {
	t.Fatal(err)
	}
	defer f.Close()

	client, server := spawnTestSocketPair(t, tc.upNet)
	defer server.Close()

	cleanup, err := startTestSocketPeer(t, client, "w", tc.chunkSize, actualSize)
	if err != nil {
	client.Close()
	t.Fatal("failed to start splice client:", err)
	}
	defer cleanup(t)

	var r io.Reader = server
	if tc.limitReadSize > 0 {
	r = &io.LimitedReader{
	N: int64(tc.limitReadSize),
	R: r,
	}
	}

	got, err := io.Copy(f, r)
	if err != nil {
	t.Fatalf("failed to ReadFrom with error: %v", err)
	}

	// We shouldn't have called poll.Splice in TCPConn.WriteTo,
	// it's supposed to be called from File.ReadFrom.
	if got > 0 && hook.called {
	t.Error("expected not poll.Splice to be called")
	}

	if want := int64(actualSize); got != want {
	t.Errorf("got %d bytes, want %d", got, want)
	}
	if tc.limitReadSize > 0 {
	wantN := 0
	if tc.limitReadSize > actualSize {
	wantN = tc.limitReadSize - actualSize
	}

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

	func testSpliceReaderAtEOF(t *testing.T, upNet, downNet string) {
	// UnixConn doesn't implement io.ReaderFrom, which will fail
	// the following test in asserting a UnixConn to be an io.ReaderFrom,
	// so skip this test.
	if downNet == "unix" {
	t.Skip("skipping test on unix socket")
	}

	hook := hookSplice(t)

	clientUp, serverUp := spawnTestSocketPair(t, upNet)
	defer clientUp.Close()
	clientDown, serverDown := spawnTestSocketPair(t, downNet)
	defer clientDown.Close()
	defer serverDown.Close()

	serverUp.Close()

	// We'd like to call net.spliceFrom here and check the handled return
	// value, but we disable splice on old Linux kernels.
	//
	// In that case, poll.Splice and net.spliceFrom 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.spliceFrom,
	// because we won't touch the reader at all.
	//
	// Trying to untangle the errors from net.spliceFrom 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)
	}()

	buf := make([]byte, 3)
	n, 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)
	}

	// We should have called poll.Splice with the right file descriptor arguments.
	if n > 0 && !hook.called {
	t.Fatal("expected poll.Splice to be called")
	}

	verifySpliceFds(t, serverDown, hook, "dst")

	// poll.Splice is expected to handle the data transmission but fail
	// when working with a closed endpoint, return an error.
	if !hook.handled \|\| hook.written > 0 \|\| hook.err == nil {
	t.Errorf("expected handled = true, written = 0, err != nil, but got handled = %t, written = %d, err = %v",
	hook.handled, hook.written, hook.err)
	}
	}

	func testSpliceIssue25985(t *testing.T, upNet, downNet string) {
	front := newLocalListener(t, upNet)
	defer front.Close()
	back := newLocalListener(t, downNet)
	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 := spawnTestSocketPair(t, "unixpacket")
	defer clientUp.Close()
	defer serverUp.Close()
	clientDown, serverDown := spawnTestSocketPair(t, "tcp")
	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 := spliceFrom(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(t))
	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 := spawnTestSocketPair(t, "tcp")
	defer clientDown.Close()
	defer serverDown.Close()
	// Analogous to testSpliceNoUnixpacket.
	_, err, handled := spliceFrom(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") })
	b.Run("tcp-to-unix", func(b *testing.B) { benchSplice(b, "tcp", "unix") })
	}

	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 := spawnTestSocketPair(b, tc.upNet)
	defer serverUp.Close()

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

	clientDown, serverDown := spawnTestSocketPair(b, tc.downNet)
	defer serverDown.Close()

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

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

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

	type spliceFileBench struct {
	proto string
	chunkSize int
	}

	func (bench spliceFileBench) benchSpliceFile(b *testing.B) {
	f, err := os.OpenFile(os.DevNull, os.O_WRONLY, 0)
	if err != nil {
	b.Fatal(err)
	}
	defer f.Close()

	totalSize := b.N * bench.chunkSize

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

	cleanup, err := startTestSocketPeer(b, client, "w", bench.chunkSize, totalSize)
	if err != nil {
	client.Close()
	b.Fatalf("failed to start splice client: %v", err)
	}
	defer cleanup(b)

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

	got, err := io.Copy(f, server)
	if err != nil {
	b.Fatalf("failed to ReadFrom with error: %v", err)
	}
	if want := int64(totalSize); got != want {
	b.Errorf("bytes sent mismatch, got: %d, want: %d", got, want)
	}
	}

	func hookSplice(t testing.T) spliceHook {
	t.Helper()

	h := new(spliceHook)
	h.install()
	t.Cleanup(h.uninstall)
	return h
	}

	type spliceHook struct {
	called bool
	dstfd int
	srcfd int
	remain int64

	written int64
	handled bool
	err error

	original func(dst, src *poll.FD, remain int64) (int64, bool, error)
	}

	func (h *spliceHook) install() {
	h.original = pollSplice
	pollSplice = func(dst, src *poll.FD, remain int64) (int64, bool, error) {
	h.called = true
	h.dstfd = dst.Sysfd
	h.srcfd = src.Sysfd
	h.remain = remain
	h.written, h.handled, h.err = h.original(dst, src, remain)
	return h.written, h.handled, h.err
	}
	}

	func (h *spliceHook) uninstall() {
	pollSplice = h.original
	}