internal/poll: don't call SetFilePointerEx in Seek for overlapped handles

Overlapped handles don't have the file pointer updated when performing
I/O operations, so there is no need to call syscall.SetFilePointerEx in
FD.Seek. Updating the in-memory offset is sufficient.

Updates golang#74951 (provides a more complete fix)

Change-Id: Ibede6625cdbd501fc92cfdf8ce2782ec291af2b6
Reviewed-on: https://go-review.googlesource.com/c/go/+/698035
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Damien Neil <[email protected]>

Author: qmuntal

src/internal/poll/fd_windows.go

@@ -1165,11 +1165,29 @@ func (fd *FD) Seek(offset int64, whence int) (int64, error) {
 	}
 	defer fd.readWriteUnlock()
 
-	if !fd.isBlocking && whence == io.SeekCurrent {
-		// Windows doesn't keep the file pointer for overlapped file handles.
-		// We do it ourselves in case to account for any read or write
-		// operations that may have occurred.
-		offset += fd.offset
+	if !fd.isBlocking {
+		// Windows doesn't use the file pointer for overlapped file handles,
+		// there is no point on calling syscall.Seek.
+		var newOffset int64
+		switch whence {
+		case io.SeekStart:
+			newOffset = offset
+		case io.SeekCurrent:
+			newOffset = fd.offset + offset
+		case io.SeekEnd:
+			var size int64
+			if err := windows.GetFileSizeEx(fd.Sysfd, &size); err != nil {
+				return 0, err
+			}
+			newOffset = size + offset
+		default:
+			return 0, windows.ERROR_INVALID_PARAMETER
+		}
+		if newOffset < 0 {
+			return 0, windows.ERROR_NEGATIVE_SEEK
+		}
+		fd.setOffset(newOffset)
+		return newOffset, nil
 	}
 	n, err := syscall.Seek(fd.Sysfd, offset, whence)
 	fd.setOffset(n)

src/internal/syscall/windows/syscall_windows.go

@@ -39,6 +39,7 @@ const (
 	ERROR_NOT_SUPPORTED          syscall.Errno = 50
 	ERROR_CALL_NOT_IMPLEMENTED   syscall.Errno = 120
 	ERROR_INVALID_NAME           syscall.Errno = 123
+	ERROR_NEGATIVE_SEEK          syscall.Errno = 131
 	ERROR_LOCK_FAILED            syscall.Errno = 167
 	ERROR_IO_INCOMPLETE          syscall.Errno = 996
 	ERROR_NO_TOKEN               syscall.Errno = 1008
@@ -195,6 +196,7 @@ const (
 //sys	SetFileInformationByHandle(handle syscall.Handle, fileInformationClass uint32, buf unsafe.Pointer, bufsize uint32) (err error) = kernel32.SetFileInformationByHandle
 //sys	VirtualQuery(address uintptr, buffer *MemoryBasicInformation, length uintptr) (err error) = kernel32.VirtualQuery
 //sys	GetTempPath2(buflen uint32, buf *uint16) (n uint32, err error) = GetTempPath2W
+//sys	GetFileSizeEx(handle syscall.Handle, size *int64) (err error) = kernel32.GetFileSizeEx
 
 const (
 	// flags for CreateToolhelp32Snapshot

src/internal/syscall/windows/zsyscall_windows.go

@@ -1868,10 +1868,26 @@ func TestFileOverlappedSeek(t *testing.T) {
 	if n != int64(len(buf)) {
 		t.Errorf("expected file pointer to be at offset %d, got %d", len(buf), n)
 	}
+	if n, err = f.Seek(1, io.SeekStart); err != nil {
+		t.Fatal(err)
+	} else if n != 1 {
+		t.Errorf("expected file pointer to be at offset %d, got %d", 1, n)
+	}
+	if n, err = f.Seek(-1, io.SeekEnd); err != nil {
+		t.Fatal(err)
+	} else if n != int64(len(content)-1) {
+		t.Errorf("expected file pointer to be at offset %d, got %d", len(content)-1, n)
+	}
+	if _, err := f.Seek(-1, io.SeekStart); !errors.Is(err, windows.ERROR_NEGATIVE_SEEK) {
+		t.Errorf("expected ERROR_NEGATIVE_SEEK, got %v", err)
+	}
+	if _, err := f.Seek(0, -1); !errors.Is(err, windows.ERROR_INVALID_PARAMETER) {
+		t.Errorf("expected ERROR_INVALID_PARAMETER, got %v", err)
+	}
 }
 
-func TestFileOverlappedReadAtVolume(t *testing.T) {
-	// Test that we can use File.ReadAt with an overlapped volume handle.
+func TestFileOverlappedReadAtSeekVolume(t *testing.T) {
+	// Test that we can use File.ReadAt and File.Seek with an overlapped volume handle.
 	// See https://go.dev/issues/74951.
 	t.Parallel()
 	name := `\\.\` + filepath.VolumeName(t.TempDir())
@@ -1888,6 +1904,9 @@ func TestFileOverlappedReadAtVolume(t *testing.T) {
 	if _, err := f.ReadAt(buf[:], 0); err != nil {
 		t.Fatal(err)
 	}
+	if _, err := f.Seek(0, io.SeekCurrent); err != nil {
+		t.Fatal(err)
+	}
 }
 
 func TestPipe(t *testing.T) {