internal/poll: don't skip empty writes on Windows

Empty writes might be important for some protocols. Let Windows decide
what do with them rather than skipping them on our side. This is inline
with the behavior of other platforms.

While here, refactor the Read/Write/Pwrite methods to reduce one
indentation level and make the code easier to read.

Fixes #73084.

Change-Id: Ic5393358e237d53b8be6097cd7359ac0ff205309
Reviewed-on: https://go-review.googlesource.com/c/go/+/661435
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/internal/poll/fd_windows.go

@@ -434,6 +434,10 @@ func (fd *FD) Read(buf []byte) (int, error) {
 		return 0, err
 	}
 	defer fd.readUnlock()
+	if fd.isFile {
+		fd.l.Lock()
+		defer fd.l.Unlock()
+	}
 
 	if len(buf) > maxRW {
 		buf = buf[:maxRW]
@@ -441,13 +445,10 @@ func (fd *FD) Read(buf []byte) (int, error) {
 
 	var n int
 	var err error
-	if fd.isFile {
-		fd.l.Lock()
-		defer fd.l.Unlock()
 	switch fd.kind {
 	case kindConsole:
 		n, err = fd.readConsole(buf)
-		default:
+	case kindFile, kindPipe:
 		o := &fd.rop
 		o.InitBuf(buf)
 		n, err = execIO(o, func(o *operation) error {
@@ -466,11 +467,7 @@ func (fd *FD) Read(buf []byte) (int, error) {
 				err = ErrFileClosing
 			}
 		}
-		}
+	case kindNet:
-		if err != nil {
-			n = 0
-		}
-	} else {
 		o := &fd.rop
 		o.InitBuf(buf)
 		n, err = execIO(o, func(o *operation) error {
@@ -701,19 +698,19 @@ func (fd *FD) Write(buf []byte) (int, error) {
 		defer fd.l.Unlock()
 	}
 
-	ntotal := 0
+	var ntotal int
-	for len(buf) > 0 {
+	for {
-		b := buf
+		max := len(buf)
-		if len(b) > maxRW {
+		if max-ntotal > maxRW {
-			b = b[:maxRW]
+			max = ntotal + maxRW
 		}
+		b := buf[ntotal:max]
 		var n int
 		var err error
-		if fd.isFile {
 		switch fd.kind {
 		case kindConsole:
 			n, err = fd.writeConsole(b)
-			default:
+		case kindPipe, kindFile:
 			o := &fd.wop
 			o.InitBuf(b)
 			n, err = execIO(o, func(o *operation) error {
@@ -726,11 +723,7 @@ func (fd *FD) Write(buf []byte) (int, error) {
 				// we assume it is interrupted by Close.
 				err = ErrFileClosing
 			}
-			}
+		case kindNet:
-			if err != nil {
-				n = 0
-			}
-		} else {
 			if race.Enabled {
 				race.ReleaseMerge(unsafe.Pointer(&ioSync))
 			}
@@ -741,12 +734,13 @@ func (fd *FD) Write(buf []byte) (int, error) {
 			})
 		}
 		ntotal += n
-		if err != nil {
+		if ntotal == len(buf) || err != nil {
 			return ntotal, err
 		}
-		buf = buf[n:]
+		if n == 0 {
+			return ntotal, io.ErrUnexpectedEOF
+		}
 	}
-	return ntotal, nil
 }
 
 // writeConsole writes len(b) bytes to the console File.
@@ -814,26 +808,29 @@ func (fd *FD) Pwrite(buf []byte, off int64) (int, error) {
 	defer syscall.Seek(fd.Sysfd, curoffset, io.SeekStart)
 	defer fd.setOffset(curoffset)
 
-	ntotal := 0
+	var ntotal int
-	for len(buf) > 0 {
+	for {
-		b := buf
+		max := len(buf)
-		if len(b) > maxRW {
+		if max-ntotal > maxRW {
-			b = b[:maxRW]
+			max = ntotal + maxRW
 		}
+		b := buf[ntotal:max]
 		o := &fd.wop
 		o.InitBuf(b)
-		fd.setOffset(off)
+		fd.setOffset(off + int64(ntotal))
 		n, err := execIO(o, func(o *operation) error {
 			return syscall.WriteFile(o.fd.Sysfd, unsafe.Slice(o.buf.Buf, o.buf.Len), &o.qty, &o.o)
 		})
-		ntotal += int(n)
+		if n > 0 {
-		if err != nil {
+			ntotal += n
+		}
+		if ntotal == len(buf) || err != nil {
 			return ntotal, err
 		}
-		buf = buf[n:]
+		if n == 0 {
-		off += int64(n)
+			return ntotal, io.ErrUnexpectedEOF
+		}
 	}
-	return ntotal, nil
 }
 
 // Writev emulates the Unix writev system call.

src/internal/poll/fd_windows_test.go

@@ -239,7 +239,7 @@ var currentProces = sync.OnceValue(func() string {
 
 var pipeCounter atomic.Uint64
 
-func newPipe(t testing.TB, overlapped bool) (string, *poll.FD) {
+func newPipe(t testing.TB, overlapped, message bool) (string, *poll.FD) {
 	name := `\\.\pipe\go-internal-poll-test-` + currentProces() + `-` + strconv.FormatUint(pipeCounter.Add(1), 10)
 	wname, err := syscall.UTF16PtrFromString(name)
 	if err != nil {
@@ -250,7 +250,11 @@ func newPipe(t testing.TB, overlapped bool) (string, *poll.FD) {
 	if overlapped {
 		flags |= syscall.FILE_FLAG_OVERLAPPED
 	}
-	h, err := windows.CreateNamedPipe(wname, uint32(flags), windows.PIPE_TYPE_BYTE, 1, 4096, 4096, 0, nil)
+	typ := windows.PIPE_TYPE_BYTE
+	if message {
+		typ = windows.PIPE_TYPE_MESSAGE
+	}
+	h, err := windows.CreateNamedPipe(wname, uint32(flags), uint32(typ), 1, 4096, 4096, 0, nil)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -358,22 +362,22 @@ func TestFile(t *testing.T) {
 
 func TestPipe(t *testing.T) {
 	t.Run("overlapped", func(t *testing.T) {
-		name, pipe := newPipe(t, true)
+		name, pipe := newPipe(t, true, false)
 		file := newFile(t, name, true)
 		testReadWrite(t, pipe, file)
 	})
 	t.Run("overlapped-write", func(t *testing.T) {
-		name, pipe := newPipe(t, true)
+		name, pipe := newPipe(t, true, false)
 		file := newFile(t, name, false)
 		testReadWrite(t, file, pipe)
 	})
 	t.Run("overlapped-read", func(t *testing.T) {
-		name, pipe := newPipe(t, false)
+		name, pipe := newPipe(t, false, false)
 		file := newFile(t, name, true)
 		testReadWrite(t, file, pipe)
 	})
 	t.Run("sync", func(t *testing.T) {
-		name, pipe := newPipe(t, false)
+		name, pipe := newPipe(t, false, false)
 		file := newFile(t, name, false)
 		testReadWrite(t, file, pipe)
 	})
@@ -397,6 +401,28 @@ func TestPipe(t *testing.T) {
 	})
 }
 
+func TestPipeWriteEOF(t *testing.T) {
+	name, pipe := newPipe(t, false, true)
+	file := newFile(t, name, false)
+	read := make(chan struct{}, 1)
+	go func() {
+		_, err := pipe.Write(nil)
+		read <- struct{}{}
+		if err != nil {
+			t.Error(err)
+		}
+	}()
+	<-read
+	var buf [10]byte
+	n, err := file.Read(buf[:])
+	if err != io.EOF {
+		t.Errorf("expected EOF, got %v", err)
+	}
+	if n != 0 {
+		t.Errorf("expected 0 bytes, got %d", n)
+	}
+}
+
 func BenchmarkReadOverlapped(b *testing.B) {
 	benchmarkRead(b, true)
 }

src/internal/syscall/windows/syscall_windows.go

@@ -510,6 +510,7 @@ const (
 	PIPE_ACCESS_DUPLEX   = 0x00000003
 
 	PIPE_TYPE_BYTE    = 0x00000000
+	PIPE_TYPE_MESSAGE = 0x00000004
 )
 
 //sys	GetOverlappedResult(handle syscall.Handle, overlapped *syscall.Overlapped, done *uint32, wait bool) (err error)