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>

3 files changed, 99 insertions, 75 deletions

diff --git a/src/internal/poll/fd_windows.go b/src/internal/poll/fd_windows.go
index 14b1febbf4..81c8293911 100644
--- a/src/internal/poll/fd_windows.go
+++ b/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]
@@ -441,36 +445,29 @@ 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:
-			o := &fd.rop
-			o.InitBuf(buf)
-			n, err = execIO(o, func(o *operation) error {
-				return syscall.ReadFile(o.fd.Sysfd, unsafe.Slice(o.buf.Buf, o.buf.Len), &o.qty, o.overlapped())
-			})
-			fd.addOffset(n)
-			if fd.kind == kindPipe && err != nil {
-				switch err {
-				case syscall.ERROR_BROKEN_PIPE:
-					// Returned by pipes when the other end is closed.
-					err = nil
-				case syscall.ERROR_OPERATION_ABORTED:
-					// Close uses CancelIoEx to interrupt concurrent I/O for pipes.
-					// If the fd is a pipe and the Read was interrupted by CancelIoEx,
-					// we assume it is interrupted by Close.
-					err = ErrFileClosing
-				}
+	switch fd.kind {
+	case kindConsole:
+		n, err = fd.readConsole(buf)
+	case kindFile, kindPipe:
+		o := &fd.rop
+		o.InitBuf(buf)
+		n, err = execIO(o, func(o *operation) error {
+			return syscall.ReadFile(o.fd.Sysfd, unsafe.Slice(o.buf.Buf, o.buf.Len), &o.qty, o.overlapped())
+		})
+		fd.addOffset(n)
+		if fd.kind == kindPipe && err != nil {
+			switch err {
+			case syscall.ERROR_BROKEN_PIPE:
+				// Returned by pipes when the other end is closed.
+				err = nil
+			case syscall.ERROR_OPERATION_ABORTED:
+				// Close uses CancelIoEx to interrupt concurrent I/O for pipes.
+				// If the fd is a pipe and the Read was interrupted by CancelIoEx,
+				// we assume it is interrupted by Close.
+				err = ErrFileClosing
 			}
 		}
-		if err != nil {
-			n = 0
-		}
-	} else {
+	case kindNet:
 		o := &fd.rop
 		o.InitBuf(buf)
 		n, err = execIO(o, func(o *operation) error {
@@ -701,36 +698,32 @@ func (fd *FD) Write(buf []byte) (int, error) {
 		defer fd.l.Unlock()
 	}
 
-	ntotal := 0
-	for len(buf) > 0 {
-		b := buf
-		if len(b) > maxRW {
-			b = b[:maxRW]
+	var ntotal int
+	for {
+		max := len(buf)
+		if max-ntotal > 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:
-				o := &fd.wop
-				o.InitBuf(b)
-				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.overlapped())
-				})
-				fd.addOffset(n)
-				if fd.kind == kindPipe && err == syscall.ERROR_OPERATION_ABORTED {
-					// Close uses CancelIoEx to interrupt concurrent I/O for pipes.
-					// If the fd is a pipe and the Write was interrupted by CancelIoEx,
-					// we assume it is interrupted by Close.
-					err = ErrFileClosing
-				}
-			}
-			if err != nil {
-				n = 0
+		switch fd.kind {
+		case kindConsole:
+			n, err = fd.writeConsole(b)
+		case kindPipe, kindFile:
+			o := &fd.wop
+			o.InitBuf(b)
+			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.overlapped())
+			})
+			fd.addOffset(n)
+			if fd.kind == kindPipe && err == syscall.ERROR_OPERATION_ABORTED {
+				// Close uses CancelIoEx to interrupt concurrent I/O for pipes.
+				// If the fd is a pipe and the Write was interrupted by CancelIoEx,
+				// we assume it is interrupted by Close.
+				err = ErrFileClosing
 			}
-		} else {
+		case kindNet:
 			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
-	for len(buf) > 0 {
-		b := buf
-		if len(b) > maxRW {
-			b = b[:maxRW]
+	var ntotal int
+	for {
+		max := len(buf)
+		if max-ntotal > 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 err != nil {
+		if n > 0 {
+			ntotal += n
+		}
+		if ntotal == len(buf) || err != nil {
 			return ntotal, err
 		}
-		buf = buf[n:]
-		off += int64(n)
+		if n == 0 {
+			return ntotal, io.ErrUnexpectedEOF
+		}
 	}
-	return ntotal, nil
 }
 
 // Writev emulates the Unix writev system call.
diff --git a/src/internal/poll/fd_windows_test.go b/src/internal/poll/fd_windows_test.go
index f2bc9b2a21..f5fa4a26e3 100644
--- a/src/internal/poll/fd_windows_test.go
+++ b/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)
 }
diff --git a/src/internal/syscall/windows/syscall_windows.go b/src/internal/syscall/windows/syscall_windows.go
index af542c8003..3a197f1c26 100644
--- a/src/internal/syscall/windows/syscall_windows.go
+++ b/src/internal/syscall/windows/syscall_windows.go
@@ -509,7 +509,8 @@ const (
 	PIPE_ACCESS_OUTBOUND = 0x00000002
 	PIPE_ACCESS_DUPLEX   = 0x00000003
 
-	PIPE_TYPE_BYTE = 0x00000000
+	PIPE_TYPE_BYTE    = 0x00000000
+	PIPE_TYPE_MESSAGE = 0x00000004
 )
 
 //sys	GetOverlappedResult(handle syscall.Handle, overlapped *syscall.Overlapped, done *uint32, wait bool) (err error)