use NtSetInformationFile if os.Rename fails

atomicwriter/atomicwriter.go

@@ -152,7 +152,7 @@ func (w *atomicFileWriter) Close() (retErr error) {
 		return err
 	}
 	if w.writeErr == nil && w.written {
-		return os.Rename(w.f.Name(), w.fn)
+		return atomicwriterRenameAt(w.f.Name(), w.fn)
 	}
 	return nil
 }

atomicwriter/atomicwriter_unix.go

@@ -0,0 +1,9 @@
+//go:build !windows
+
+package atomicwriter
+
+import "os"
+
+func atomicwriterRenameAt(oldpath, newpath string) error {
+	return os.Rename(oldpath, newpath)
+}

atomicwriter/atomicwriter_windows.go

@@ -0,0 +1,107 @@
+package atomicwriter
+
+import (
+	"os"
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+// fileRenameInformation is the FILE_RENAME_INFORMATION structure used by
+// NtSetInformationFile to rename a file. FileName is a variable-length
+// field; callers must allocate a buffer large enough to hold the full name.
+type fileRenameInformation struct {
+	ReplaceIfExists uint32
+	RootDirectory   windows.Handle
+	FileNameLength  uint32
+	FileName        [1]uint16
+}
+
+// fileRenameInformationEx is the FILE_RENAME_INFORMATION_EX structure used by
+// NtSetInformationFile to rename a file.
+type fileRenameInformationEx struct {
+	Flags          uint32
+	RootDirectory  windows.Handle
+	FileNameLength uint32
+	FileName       [1]uint16
+}
+
+// atomicwriterRenameAt renames oldpath to newpath using os.Rename. If it fails,
+// it attempts to use NtSetInformationFile with FILE_RENAME_POSIX_SEMANTICS,
+// which allows atomic replacement of a file even when the destination
+// is open by another process.
+func atomicwriterRenameAt(oldpath, newpath string) error {
+
+	err := os.Rename(oldpath, newpath)
+	if err == nil {
+		return nil
+	}
+	// Open the source file requesting DELETE access so we can rename it.
+	srcPtr, err := windows.UTF16PtrFromString(oldpath)
+	if err != nil {
+		return &os.PathError{Op: "rename", Path: oldpath, Err: err}
+	}
+	handle, err := windows.CreateFile(
+		srcPtr,
+		windows.DELETE,
+		windows.FILE_SHARE_READ|windows.FILE_SHARE_WRITE|windows.FILE_SHARE_DELETE,
+		nil,
+		windows.OPEN_EXISTING,
+		windows.FILE_ATTRIBUTE_NORMAL,
+		0,
+	)
+	if err != nil {
+		return &os.PathError{Op: "rename", Path: oldpath, Err: err}
+	}
+	defer windows.CloseHandle(handle)
+
+	// NtSetInformationFile requires an absolute NT path (\??\C:\...) when
+	// RootDirectory is NULL.
+	ntNewPath := `\??\` + newpath
+	newPathUTF16, err := windows.UTF16FromString(ntNewPath)
+	if err != nil {
+		return &os.PathError{Op: "rename", Path: newpath, Err: err}
+	}
+
+	fileNameLen := len(newPathUTF16)*2 - 2 // byte length, excluding null terminator
+	renameInfoEx := fileRenameInformationEx{
+		Flags: windows.FILE_RENAME_REPLACE_IF_EXISTS |
+			windows.FILE_RENAME_POSIX_SEMANTICS,
+	}
+	var dummyEx fileRenameInformationEx
+	bufferSizeEx := int(unsafe.Offsetof(dummyEx.FileName)) + fileNameLen
+	bufferEx := make([]byte, bufferSizeEx)
+	infoEx := (*fileRenameInformationEx)(unsafe.Pointer(&bufferEx[0]))
+	infoEx.Flags = renameInfoEx.Flags
+	infoEx.FileNameLength = uint32(fileNameLen)
+	copy((*[windows.MAX_LONG_PATH]uint16)(unsafe.Pointer(&infoEx.FileName[0]))[:fileNameLen/2:fileNameLen/2], newPathUTF16)
+
+	const (
+		FileRenameInformation   = 10
+		FileRenameInformationEx = 65
+	)
+	var iosbEx windows.IO_STATUS_BLOCK
+
+	err = windows.NtSetInformationFile(handle, &iosbEx, &bufferEx[0], uint32(bufferSizeEx), FileRenameInformationEx)
+	if err == nil {
+		return nil
+	}
+
+	// If the extended rename fails, fall back to the original FILE_RENAME_INFORMATION
+	// which is supported on older versions of Windows. This may fail if the destination
+	// file is open by another process, but there's no way to detect that beforehand.
+
+	var dummy fileRenameInformation
+	bufferSize := int(unsafe.Offsetof(dummy.FileName)) + fileNameLen
+	buffer := make([]byte, bufferSize)
+	info := (*fileRenameInformation)(unsafe.Pointer(&buffer[0]))
+	info.ReplaceIfExists = windows.FILE_RENAME_REPLACE_IF_EXISTS | windows.FILE_RENAME_POSIX_SEMANTICS
+	info.FileNameLength = uint32(fileNameLen)
+	copy((*[windows.MAX_LONG_PATH]uint16)(unsafe.Pointer(&info.FileName[0]))[:fileNameLen/2:fileNameLen/2], newPathUTF16)
+
+	var iosb windows.IO_STATUS_BLOCK
+	if err := windows.NtSetInformationFile(handle, &iosb, &buffer[0], uint32(bufferSize), FileRenameInformation); err != nil {
+		return &os.PathError{Op: "rename", Path: newpath, Err: err}
+	}
+	return nil
+}