ThothII/tools/tht/internal/safeio/private_root_windows.go

//go:build windows

package safeio

import (
	"errors"
	"io"
	"os"
	"runtime"
	"sort"
	"time"
	"unsafe"

	"golang.org/x/sys/windows"
)

// windowsPrivateDirectory keeps the root's canonical component handles alive, then uses NT
// RootDirectory-relative opens for every descendant. Unlike a lexical child path, an NT relative
// object name is resolved by the already-open directory handle and cannot be redirected by a
// rename, replacement, or reparse point at the original root path.
type windowsPrivateDirectory struct {
	anchors *windowsParentHandles
	parent  windows.Handle
	handle  windows.Handle
	info    windows.ByHandleFileInformation
}

type windowsPrivateRegularAt struct {
	handle windows.Handle
	info   windows.ByHandleFileInformation
}

func openPrivateDirectory(path string, ensure bool) (PrivateDirectoryHandle, bool, error) {
	anchors, target, err := openCanonicalWindowsParent(path)
	if err != nil || anchors == nil || len(anchors.handles) == 0 {
		if anchors != nil {
			anchors.Close()
		}
		return nil, false, ErrUnsafeFile
	}
	parent := anchors.handles[len(anchors.handles)-1]
	handle, found, err := openWindowsPrivateDirectoryAt(parent, target, false)
	if err != nil {
		anchors.Close()
		return nil, false, ErrUnsafeFile
	}
	if !found {
		// The final root is absent. The retained canonical parent must prove that the same
		// ensure operation could create it; validation itself must remain side-effect free.
		// FILE_APPEND_DATA is the Win32 spelling of directory FILE_ADD_SUBDIRECTORY.
		anchors.Close()
		writableAnchors, writableTarget, probeErr := openCanonicalWindowsParentWithFinalAccess(path, windows.FILE_APPEND_DATA)
		if probeErr != nil || writableAnchors == nil || len(writableAnchors.handles) == 0 {
			if writableAnchors != nil {
				writableAnchors.Close()
			}
			return nil, false, ErrUnsafeFile
		}
		if !ensure {
			writableAnchors.Close()
			return nil, false, nil
		}
		anchors = writableAnchors
		target = writableTarget
		parent = anchors.handles[len(anchors.handles)-1]
		handle, found, err = openWindowsPrivateDirectoryAt(parent, target, true)
		if err != nil || !found {
			anchors.Close()
			return nil, false, ErrUnsafeFile
		}
	}
	value := &windowsPrivateDirectory{anchors: anchors, handle: handle}
	if value.captureAndValidate() != nil {
		_ = value.Close()
		return nil, false, ErrUnsafeFile
	}
	return value, true, nil
}

func openWindowsPrivateDirectoryAt(parent windows.Handle, name string, ensure bool) (windows.Handle, bool, error) {
	if parent == 0 || !validPrivateLeafName(name) {
		return 0, false, ErrUnsafeFile
	}
	for attempt := 0; attempt < 2; attempt++ {
		handle, err := openWindowsRelativeDirectory(parent, name)
		if err == nil {
			return handle, true, nil
		}
		if !isWindowsRelativeNotFound(err) {
			return 0, false, ErrUnsafeFile
		}
		if !ensure {
			return 0, false, nil
		}
		handle, err = createWindowsRelativePrivateDirectory(parent, name)
		if err == nil {
			return handle, true, nil
		}
	}
	return 0, false, ErrUnsafeFile
}

func openWindowsRelativeDirectory(parent windows.Handle, name string) (windows.Handle, error) {
	handle, err := openWindowsRelativeObject(
		parent,
		name,
		// The retained directory handle is also the RootDirectory for create, rename,
		// hard-link, and delete operations below, so it needs the owner's full private
		// directory capability rather than a read-only probe handle.
		windows.FILE_GENERIC_READ|windows.FILE_GENERIC_WRITE|windows.DELETE,
		windows.FILE_OPEN,
		windows.FILE_DIRECTORY_FILE|windows.FILE_SYNCHRONOUS_IO_NONALERT|windows.FILE_OPEN_REPARSE_POINT,
		nil,
	)
	if err != nil {
		return 0, err
	}
	if _, err := privateWindowsDirectoryInfo(handle); err != nil {
		_ = windows.CloseHandle(handle)
		return 0, ErrUnsafeFile
	}
	return handle, nil
}

func createWindowsRelativePrivateDirectory(parent windows.Handle, name string) (windows.Handle, error) {
	security, err := newOwnerOnlySecurityDescriptor()
	if err != nil {
		return 0, ErrUnsafeFile
	}
	defer security.Close()
	handle, err := openWindowsRelativeObject(
		parent,
		name,
		windows.FILE_GENERIC_READ|windows.FILE_GENERIC_WRITE|windows.DELETE,
		windows.FILE_CREATE,
		windows.FILE_DIRECTORY_FILE|windows.FILE_SYNCHRONOUS_IO_NONALERT|windows.FILE_OPEN_REPARSE_POINT,
		security,
	)
	if err != nil {
		return 0, err
	}
	if _, err := privateWindowsDirectoryInfo(handle); err != nil {
		_ = markWindowsHandleForDelete(handle)
		_ = windows.CloseHandle(handle)
		return 0, ErrUnsafeFile
	}
	return handle, nil
}

func openWindowsRelativeObject(
	parent windows.Handle,
	name string,
	access uint32,
	disposition uint32,
	options uint32,
	security *ownerOnlySecurityDescriptor,
) (windows.Handle, error) {
	return openWindowsRelativeObjectWithShareMode(
		parent,
		name,
		access,
		disposition,
		options,
		security,
		windowsRetainedHandleShareMode,
	)
}

func openWindowsRelativeObjectWithShareMode(
	parent windows.Handle,
	name string,
	access uint32,
	disposition uint32,
	options uint32,
	security *ownerOnlySecurityDescriptor,
	shareMode uint32,
) (windows.Handle, error) {
	if parent == 0 || !validPrivateLeafName(name) {
		return 0, ErrUnsafeFile
	}
	access = normalizeWindowsNTDesiredAccess(access)
	objectName, err := windows.NewNTUnicodeString(name)
	if err != nil {
		return 0, ErrUnsafeFile
	}
	attributes := &windows.OBJECT_ATTRIBUTES{
		Length:             uint32(unsafe.Sizeof(windows.OBJECT_ATTRIBUTES{})),
		RootDirectory:      parent,
		ObjectName:         objectName,
		Attributes:         windows.OBJ_CASE_INSENSITIVE,
		SecurityDescriptor: nil,
	}
	if security != nil {
		attributes.SecurityDescriptor = security.descriptor
	}
	var (
		handle         windows.Handle
		status         windows.IO_STATUS_BLOCK
		allocationSize int64
	)
	err = windows.NtCreateFile(
		&handle,
		access,
		attributes,
		&status,
		&allocationSize,
		// NtCreateFile supplies the normal attribute default when this is zero; no
		// explicit creation attribute is needed for these retained open/create calls.
		0,
		shareMode,
		disposition,
		options,
		0,
		0,
	)
	runtime.KeepAlive(objectName)
	runtime.KeepAlive(security)
	if err != nil {
		return 0, err
	}
	return handle, nil
}

func normalizeWindowsNTDesiredAccess(access uint32) uint32 {
	if access&uint32(windows.GENERIC_ALL) != 0 {
		const fileSpecificAll = uint32(0x1ff)
		access = access&^uint32(windows.GENERIC_ALL) |
			uint32(windows.STANDARD_RIGHTS_REQUIRED|windows.SYNCHRONIZE) | fileSpecificAll
	}
	if access&uint32(windows.GENERIC_READ) != 0 {
		access = access&^uint32(windows.GENERIC_READ) | uint32(windows.FILE_GENERIC_READ)
	}
	if access&uint32(windows.GENERIC_WRITE) != 0 {
		access = access&^uint32(windows.GENERIC_WRITE) | uint32(windows.FILE_GENERIC_WRITE)
	}
	if access&uint32(windows.GENERIC_EXECUTE) != 0 {
		access = access&^uint32(windows.GENERIC_EXECUTE) | uint32(windows.FILE_GENERIC_EXECUTE)
	}
	return access
}

func privateWindowsDirectoryInfo(handle windows.Handle) (windows.ByHandleFileInformation, error) {
	var info windows.ByHandleFileInformation
	if handle == 0 || windows.GetFileInformationByHandle(handle, &info) != nil ||
		info.FileAttributes&windows.FILE_ATTRIBUTE_REPARSE_POINT != 0 ||
		info.FileAttributes&windows.FILE_ATTRIBUTE_DIRECTORY == 0 ||
		validateOwnerOnlyDACL(handle) != nil {
		return windows.ByHandleFileInformation{}, ErrUnsafeFile
	}
	return info, nil
}

func privateWindowsRegularInfo(handle windows.Handle, allowedLinks ...uint32) (windows.ByHandleFileInformation, error) {
	var info windows.ByHandleFileInformation
	if handle == 0 || windows.GetFileInformationByHandle(handle, &info) != nil ||
		info.FileAttributes&windows.FILE_ATTRIBUTE_REPARSE_POINT != 0 ||
		info.FileAttributes&windows.FILE_ATTRIBUTE_DIRECTORY != 0 ||
		validateOwnerOnlyDACL(handle) != nil {
		return windows.ByHandleFileInformation{}, ErrUnsafeFile
	}
	for _, links := range allowedLinks {
		if info.NumberOfLinks == links {
			return info, nil
		}
	}
	return windows.ByHandleFileInformation{}, ErrUnsafeFile
}

func isWindowsRelativeNotFound(err error) bool {
	return errors.Is(err, windows.ERROR_FILE_NOT_FOUND) ||
		errors.Is(err, windows.ERROR_PATH_NOT_FOUND) ||
		errors.Is(err, windows.STATUS_NO_SUCH_FILE) ||
		errors.Is(err, windows.STATUS_OBJECT_NAME_NOT_FOUND) ||
		errors.Is(err, windows.STATUS_OBJECT_PATH_NOT_FOUND)
}

func isWindowsRelativeCollision(err error) bool {
	return errors.Is(err, windows.ERROR_FILE_EXISTS) ||
		errors.Is(err, windows.ERROR_ALREADY_EXISTS) ||
		errors.Is(err, windows.STATUS_OBJECT_NAME_COLLISION)
}

func (directory *windowsPrivateDirectory) captureAndValidate() error {
	if directory == nil || directory.handle == 0 {
		return ErrUnsafeFile
	}
	info, err := privateWindowsDirectoryInfo(directory.handle)
	if err != nil {
		return ErrUnsafeFile
	}
	directory.info = info
	return nil
}

func (directory *windowsPrivateDirectory) Close() error {
	if directory == nil {
		return nil
	}
	var result error
	if directory.handle != 0 {
		if err := windows.CloseHandle(directory.handle); err != nil {
			result = ErrUnsafeFile
		}
		directory.handle = 0
	}
	if directory.parent != 0 {
		if err := windows.CloseHandle(directory.parent); err != nil {
			result = ErrUnsafeFile
		}
		directory.parent = 0
	}
	if directory.anchors != nil {
		directory.anchors.Close()
		directory.anchors = nil
	}
	return result
}

func sameWindowsPrivateDirectoryIdentity(left, right windows.ByHandleFileInformation) bool {
	return left.VolumeSerialNumber == right.VolumeSerialNumber && left.FileIndexHigh == right.FileIndexHigh &&
		left.FileIndexLow == right.FileIndexLow && left.FileAttributes == right.FileAttributes
}

func sameWindowsPrivateDirectorySnapshot(left, right windows.ByHandleFileInformation) bool {
	return sameWindowsPrivateDirectoryIdentity(left, right) && left.LastWriteTime == right.LastWriteTime
}

func (directory *windowsPrivateDirectory) Validate() error {
	if directory == nil || directory.handle == 0 || (directory.anchors == nil && directory.parent == 0) {
		return ErrUnsafeFile
	}
	if directory.anchors != nil && len(directory.anchors.handles) == 0 {
		return ErrUnsafeFile
	}
	if directory.parent != 0 {
		if _, err := privateWindowsDirectoryInfo(directory.parent); err != nil {
			return ErrUnsafeFile
		}
	}
	current, err := privateWindowsDirectoryInfo(directory.handle)
	if err != nil || !sameWindowsPrivateDirectoryIdentity(directory.info, current) {
		return ErrUnsafeFile
	}
	return nil
}

func duplicateWindowsRetainedHandle(handle windows.Handle) (windows.Handle, error) {
	if handle == 0 {
		return 0, ErrUnsafeFile
	}
	var duplicate windows.Handle
	process := windows.CurrentProcess()
	if err := windows.DuplicateHandle(process, handle, process, &duplicate, 0, false, windows.DUPLICATE_SAME_ACCESS); err != nil {
		return 0, ErrUnsafeFile
	}
	return duplicate, nil
}

func (directory *windowsPrivateDirectory) OpenChild(name string, ensure bool) (PrivateDirectoryHandle, bool, error) {
	if directory.Validate() != nil || !validPrivateLeafName(name) {
		return nil, false, ErrUnsafeFile
	}
	parent, err := duplicateWindowsRetainedHandle(directory.handle)
	if err != nil {
		return nil, false, ErrUnsafeFile
	}
	handle, found, err := openWindowsPrivateDirectoryAt(parent, name, ensure)
	if err != nil || !found {
		_ = windows.CloseHandle(parent)
		if err != nil {
			return nil, false, ErrUnsafeFile
		}
		return nil, false, nil
	}
	child := &windowsPrivateDirectory{parent: parent, handle: handle}
	if child.captureAndValidate() != nil || directory.Validate() != nil {
		_ = child.Close()
		return nil, false, ErrUnsafeFile
	}
	return child, true, nil
}

func openWindowsPrivateRegularAt(
	parent windows.Handle,
	name string,
	access uint32,
	allowedLinks ...uint32,
) (*windowsPrivateRegularAt, error) {
	return openWindowsPrivateRegularAtWithShareMode(
		parent,
		name,
		access,
		windowsRetainedHandleShareMode,
		allowedLinks...,
	)
}

func openWindowsPrivateRegularAtWithShareMode(
	parent windows.Handle,
	name string,
	access uint32,
	shareMode uint32,
	allowedLinks ...uint32,
) (*windowsPrivateRegularAt, error) {
	handle, err := openWindowsRelativeObjectWithShareMode(
		parent,
		name,
		access,
		windows.FILE_OPEN,
		windows.FILE_NON_DIRECTORY_FILE|windows.FILE_SYNCHRONOUS_IO_NONALERT|windows.FILE_OPEN_REPARSE_POINT,
		nil,
		shareMode,
	)
	if err != nil {
		return nil, err
	}
	info, err := privateWindowsRegularInfo(handle, allowedLinks...)
	if err != nil {
		_ = windows.CloseHandle(handle)
		return nil, ErrUnsafeFile
	}
	return &windowsPrivateRegularAt{handle: handle, info: info}, nil
}

func openWindowsPrivateRegularAtAllowedLinks(
	parent windows.Handle,
	name string,
	access uint32,
	allowedLinks ...uint32,
) (*windowsPrivateRegularAt, error) {
	var (
		lastError   error
		unsafeFound bool
	)
	for _, links := range allowedLinks {
		value, err := openWindowsPrivateRegularAt(parent, name, access, links)
		if err == nil {
			return value, nil
		}
		lastError = err
		if !isWindowsRelativeNotFound(err) {
			unsafeFound = true
		}
	}
	if unsafeFound {
		return nil, ErrUnsafeFile
	}
	return nil, lastError
}

func createWindowsPrivateRegularAt(parent windows.Handle, name string) (*windowsPrivateRegularAt, error) {
	return createWindowsPrivateRegularAtWithAccess(parent, name, windows.FILE_GENERIC_READ|windows.FILE_GENERIC_WRITE|windows.DELETE)
}

// createWindowsPrivateRegularAtWithAccess creates the final leaf beneath an already-retained
// parent with an owner-only DACL in the same NtCreateFile operation. The caller never re-resolves
// an absolute pathname after the parent is pinned.
func createWindowsPrivateRegularAtWithAccess(parent windows.Handle, name string, access uint32) (*windowsPrivateRegularAt, error) {
	security, err := newOwnerOnlySecurityDescriptor()
	if err != nil {
		return nil, ErrUnsafeFile
	}
	defer security.Close()
	// The caller's data authority is intentionally preserved (GENERIC_WRITE is used for
	// streaming creates), but privateWindowsRegularInfo must inspect attributes and links
	// before returning the handle. FILE_READ_ATTRIBUTES grants that inspection without
	// adding read-data authority to a write-only create.
	access |= windows.FILE_READ_ATTRIBUTES
	handle, err := openWindowsRelativeObject(
		parent,
		name,
		access|windows.DELETE,
		windows.FILE_CREATE,
		windows.FILE_NON_DIRECTORY_FILE|windows.FILE_SYNCHRONOUS_IO_NONALERT|windows.FILE_OPEN_REPARSE_POINT,
		security,
	)
	if err != nil {
		return nil, err
	}
	info, err := privateWindowsRegularInfo(handle, 1)
	if err != nil {
		_ = markWindowsHandleForDelete(handle)
		_ = windows.CloseHandle(handle)
		return nil, ErrUnsafeFile
	}
	return &windowsPrivateRegularAt{handle: handle, info: info}, nil
}

func (value *windowsPrivateRegularAt) Close() error {
	if value == nil || value.handle == 0 {
		return nil
	}
	handle := value.handle
	value.handle = 0
	if err := windows.CloseHandle(handle); err != nil {
		return ErrUnsafeFile
	}
	return nil
}

func writeWindowsPrivateRegular(value *windowsPrivateRegularAt, contents []byte) error {
	if value == nil || value.handle == 0 || len(contents) == 0 {
		return ErrUnsafeFile
	}
	for remaining := contents; len(remaining) > 0; {
		var written uint32
		if err := windows.WriteFile(value.handle, remaining, &written, nil); err != nil || written == 0 || int(written) > len(remaining) {
			return ErrUnsafeFile
		}
		remaining = remaining[written:]
	}
	if err := windows.FlushFileBuffers(value.handle); err != nil {
		return ErrUnsafeFile
	}
	info, err := privateWindowsRegularInfo(value.handle, 1)
	if err != nil {
		return ErrUnsafeFile
	}
	value.info = info
	return nil
}

func readWindowsPrivateRegular(value *windowsPrivateRegularAt, maximum int64, links uint32) ([]byte, error) {
	if value == nil || value.handle == 0 || maximum < 0 || maximum == int64(^uint64(0)>>1) {
		return nil, ErrUnsafeFile
	}
	contents := make([]byte, 0, 4096)
	buffer := make([]byte, 4096)
	for {
		var read uint32
		err := windows.ReadFile(value.handle, buffer, &read, nil)
		if read > 0 {
			if int64(len(contents))+int64(read) > maximum {
				return nil, ErrUnsafeFile
			}
			contents = append(contents, buffer[:read]...)
		}
		if err != nil {
			if errors.Is(err, windows.ERROR_HANDLE_EOF) {
				break
			}
			return nil, ErrUnsafeFile
		}
		if read == 0 {
			break
		}
	}
	after, err := privateWindowsRegularInfo(value.handle, links)
	if err != nil || !sameWindowsPrivateFile(value.info, after) {
		return nil, ErrUnsafeFile
	}
	value.info = after
	return contents, nil
}

func markWindowsHandleForDelete(handle windows.Handle) error {
	if handle == 0 {
		return ErrUnsafeFile
	}
	buffer := [1]byte{1}
	var status windows.IO_STATUS_BLOCK
	if err := windows.NtSetInformationFile(handle, &status, &buffer[0], uint32(len(buffer)), windows.FileDispositionInformation); err != nil {
		return ErrUnsafeFile
	}
	return nil
}

func finishWindowsPrivateRegularCleanup(mark func() error, close func() error) error {
	failed := false
	if mark == nil || mark() != nil {
		failed = true
	}
	if close == nil || close() != nil {
		failed = true
	}
	if failed {
		return ErrUnsafeFile
	}
	return nil
}

func closeAndDeleteWindowsPrivateRegular(value *windowsPrivateRegularAt) error {
	if value == nil || value.handle == 0 {
		return ErrUnsafeFile
	}
	return finishWindowsPrivateRegularCleanup(
		func() error { return markWindowsHandleForDelete(value.handle) },
		value.Close,
	)
}

func (directory *windowsPrivateDirectory) CreateRegular(name string, contents []byte) (bool, error) {
	if directory.Validate() != nil || !validPrivateLeafName(name) || len(contents) == 0 {
		return false, ErrUnsafeFile
	}
	value, err := createWindowsPrivateRegularAt(directory.handle, name)
	if err != nil {
		existing, existingErr := openWindowsPrivateRegularAt(directory.handle, name, windows.FILE_GENERIC_READ, 1)
		if existingErr == nil {
			closeErr := existing.Close()
			validateErr := directory.Validate()
			if closeErr != nil || validateErr != nil {
				return false, ErrUnsafeFile
			}
			return false, nil
		}
		return false, ErrUnsafeFile
	}
	published := false
	defer func() {
		if !published {
			_ = closeAndDeleteWindowsPrivateRegular(value)
		}
	}()
	if writeWindowsPrivateRegular(value, contents) != nil || directory.Validate() != nil {
		return false, ErrUnsafeFile
	}
	if value.Close() != nil {
		return false, ErrUnsafeFile
	}
	published = true
	return true, nil
}

func (directory *windowsPrivateDirectory) CreateRegularFile(name string) (*os.File, bool, error) {
	if directory.Validate() != nil || !validPrivateLeafName(name) {
		return nil, false, ErrUnsafeFile
	}
	value, err := createWindowsPrivateRegularAt(directory.handle, name)
	if err != nil {
		existing, existingErr := openWindowsPrivateRegularAt(directory.handle, name, windows.FILE_GENERIC_READ, 1)
		if existingErr == nil {
			if existing.Close() != nil || directory.Validate() != nil {
				return nil, false, ErrUnsafeFile
			}
			return nil, false, nil
		}
		return nil, false, ErrUnsafeFile
	}
	failed := true
	defer func() {
		if failed {
			_ = closeAndDeleteWindowsPrivateRegular(value)
		}
	}()
	info, err := privateWindowsRegularInfo(value.handle, 1)
	if err != nil || directory.Validate() != nil {
		return nil, false, ErrUnsafeFile
	}
	value.info = info
	file := os.NewFile(uintptr(value.handle), "tht-safeio-private-root-stream")
	if file == nil {
		return nil, false, ErrUnsafeFile
	}
	value.handle = 0
	failed = false
	return file, true, nil
}

func (directory *windowsPrivateDirectory) ReadRegular(name string, maximum int64) ([]byte, bool, error) {
	if directory.Validate() != nil || !validPrivateLeafName(name) || maximum < 0 || maximum == int64(^uint64(0)>>1) {
		return nil, false, ErrUnsafeFile
	}
	value, err := openWindowsPrivateRegularAt(directory.handle, name, windows.FILE_GENERIC_READ, 1)
	if isWindowsRelativeNotFound(err) {
		return nil, false, nil
	}
	if err != nil {
		return nil, false, ErrUnsafeFile
	}
	defer value.Close()
	contents, err := readWindowsPrivateRegular(value, maximum, 1)
	if err != nil || directory.Validate() != nil {
		return nil, false, ErrUnsafeFile
	}
	return contents, true, nil
}

type windowsRelativeNameInformation struct {
	Flags          uint32
	RootDirectory  windows.Handle
	FileNameLength uint32
	FileName       [1]uint16
}

func setWindowsRelativeNameInformation(
	handle windows.Handle,
	parent windows.Handle,
	name string,
	class uint32,
	flags uint32,
) error {
	if handle == 0 || parent == 0 || !validPrivateLeafName(name) {
		return ErrUnsafeFile
	}
	encoded, err := windows.UTF16FromString(name)
	if err != nil || len(encoded) < 2 {
		return ErrUnsafeFile
	}
	nameBytes := (len(encoded) - 1) * 2
	var header windowsRelativeNameInformation
	size := int(unsafe.Offsetof(header.FileName)) + nameBytes
	buffer := make([]byte, size)
	value := (*windowsRelativeNameInformation)(unsafe.Pointer(&buffer[0]))
	value.Flags = flags
	value.RootDirectory = parent
	value.FileNameLength = uint32(nameBytes)
	copy(unsafe.Slice(&value.FileName[0], len(encoded)-1), encoded[:len(encoded)-1])
	var status windows.IO_STATUS_BLOCK
	if err := windows.NtSetInformationFile(handle, &status, &buffer[0], uint32(len(buffer)), class); err != nil {
		return ErrUnsafeFile
	}
	runtime.KeepAlive(encoded)
	runtime.KeepAlive(buffer)
	return nil
}

func renameWindowsPrivateRegularAt(handle windows.Handle, parent windows.Handle, name string) error {
	return setWindowsRelativeNameInformation(handle, parent, name, windows.FileRenameInformation, windows.FILE_RENAME_REPLACE_IF_EXISTS)
}

func linkWindowsPrivateRegularAt(handle windows.Handle, parent windows.Handle, name string) error {
	return setWindowsRelativeNameInformation(handle, parent, name, windows.FileLinkInformation, 0)
}

func createWindowsPrivateTemporaryAt(parent windows.Handle, contents []byte) (*windowsPrivateRegularAt, error) {
	for attempt := 0; attempt < 16; attempt++ {
		name, err := randomTemporaryName()
		if err != nil {
			return nil, ErrUnsafeFile
		}
		value, err := createWindowsPrivateRegularAt(parent, name)
		if err != nil {
			if isWindowsRelativeCollision(err) {
				continue
			}
			return nil, ErrUnsafeFile
		}
		if writeWindowsPrivateRegular(value, contents) == nil {
			return value, nil
		}
		_ = closeAndDeleteWindowsPrivateRegular(value)
		return nil, ErrUnsafeFile
	}
	return nil, ErrUnsafeFile
}

func (directory *windowsPrivateDirectory) ReplaceRegular(name string, contents []byte) error {
	if directory.Validate() != nil || !validPrivateLeafName(name) || len(contents) == 0 {
		return ErrUnsafeFile
	}
	existing, err := openWindowsPrivateRegularAt(directory.handle, name, windows.FILE_GENERIC_READ, 1)
	if err != nil {
		return ErrUnsafeFile
	}
	if existing.Close() != nil {
		return ErrUnsafeFile
	}
	temporary, err := createWindowsPrivateTemporaryAt(directory.handle, contents)
	if err != nil {
		return ErrUnsafeFile
	}
	renamed := false
	defer func() {
		if !renamed {
			_ = closeAndDeleteWindowsPrivateRegular(temporary)
		}
	}()
	current, err := openWindowsPrivateRegularAt(directory.handle, name, windows.FILE_GENERIC_READ, 1)
	if err != nil {
		return ErrUnsafeFile
	}
	currentCloseErr := current.Close()
	currentValidateErr := directory.Validate()
	if currentCloseErr != nil || currentValidateErr != nil {
		return ErrUnsafeFile
	}
	renameErr := renameWindowsPrivateRegularAt(temporary.handle, directory.handle, name)
	temporaryCloseErr := temporary.Close()
	if renameErr != nil || temporaryCloseErr != nil {
		return ErrUnsafeFile
	}
	renamed = true
	replaced, err := openWindowsPrivateRegularAt(directory.handle, name, windows.FILE_GENERIC_READ, 1)
	if err != nil {
		return ErrUnsafeFile
	}
	replacedCloseErr := replaced.Close()
	replacedValidateErr := directory.Validate()
	if replacedCloseErr != nil || replacedValidateErr != nil {
		return ErrUnsafeFile
	}
	return nil
}

func (directory *windowsPrivateDirectory) RemoveRegular(name string) (bool, error) {
	if directory.Validate() != nil || !validPrivateLeafName(name) {
		return false, ErrUnsafeFile
	}
	value, err := openWindowsPrivateRegularAt(directory.handle, name, windows.FILE_GENERIC_READ|windows.DELETE, 1)
	if isWindowsRelativeNotFound(err) {
		return false, nil
	}
	if err != nil {
		return false, ErrUnsafeFile
	}
	cleanupErr := closeAndDeleteWindowsPrivateRegular(value)
	validateErr := directory.Validate()
	if cleanupErr != nil || validateErr != nil {
		return false, ErrUnsafeFile
	}
	return true, nil
}

func (directory *windowsPrivateDirectory) ListPage(
	maximumEntries int,
	afterName string,
	validName func(string) bool,
	validLinks func(string, uint64) bool,
) (PrivateDirectoryPage, error) {
	if directory.Validate() != nil || maximumEntries < 1 || maximumEntries > 4096 || validName == nil || validLinks == nil ||
		(afterName != "" && !validName(afterName)) {
		return PrivateDirectoryPage{}, ErrUnsafeFile
	}
	var before windows.ByHandleFileInformation
	if err := windows.GetFileInformationByHandle(directory.handle, &before); err != nil ||
		!sameWindowsPrivateDirectoryIdentity(directory.info, before) {
		return PrivateDirectoryPage{}, ErrUnsafeFile
	}
	duplicate, err := duplicateWindowsRetainedHandle(directory.handle)
	if err != nil {
		return PrivateDirectoryPage{}, ErrUnsafeFile
	}
	file := os.NewFile(uintptr(duplicate), "tht-safeio-private-root-list")
	if file == nil {
		_ = windows.CloseHandle(duplicate)
		return PrivateDirectoryPage{}, ErrUnsafeFile
	}
	defer file.Close()
	seen := make(map[string]struct{}, maximumEntries+1)
	selected := make([]PrivateDirectoryEntry, 0, maximumEntries+1)
	scanned := 0
	for {
		entries, readErr := file.ReadDir(1)
		if readErr != nil && !errors.Is(readErr, io.EOF) {
			return PrivateDirectoryPage{}, ErrUnsafeFile
		}
		if len(entries) == 0 {
			break
		}
		if len(entries) != 1 {
			return PrivateDirectoryPage{}, ErrUnsafeFile
		}
		scanned++
		if scanned > maximumPrivateDirectoryPageScanEntries {
			return PrivateDirectoryPage{}, ErrUnsafeFile
		}
		name := entries[0].Name()
		if !validPrivateLeafName(name) || !validName(name) {
			return PrivateDirectoryPage{}, ErrUnsafeFile
		}
		if _, duplicate := seen[name]; duplicate {
			return PrivateDirectoryPage{}, ErrUnsafeFile
		}
		seen[name] = struct{}{}
		value, valueErr := openWindowsPrivateRegularAtAllowedLinks(directory.handle, name, windows.FILE_GENERIC_READ, 1, 2)
		if valueErr != nil {
			return PrivateDirectoryPage{}, ErrUnsafeFile
		}
		info := value.info
		if value.Close() != nil {
			return PrivateDirectoryPage{}, ErrUnsafeFile
		}
		if !validLinks(name, uint64(info.NumberOfLinks)) {
			return PrivateDirectoryPage{}, ErrUnsafeFile
		}
		if name > afterName {
			selected = appendBoundedPrivateDirectoryEntry(selected, PrivateDirectoryEntry{
				Name: name, ModifiedUnixMs: time.Unix(0, info.LastWriteTime.Nanoseconds()).UnixMilli(),
			}, maximumEntries+1)
		}
		if errors.Is(readErr, io.EOF) {
			break
		}
	}
	var after windows.ByHandleFileInformation
	if windows.GetFileInformationByHandle(directory.handle, &after) != nil || directory.Validate() != nil ||
		!sameWindowsPrivateDirectorySnapshot(before, after) {
		return PrivateDirectoryPage{}, ErrUnsafeFile
	}
	sort.Slice(selected, func(left, right int) bool { return selected[left].Name < selected[right].Name })
	more := len(selected) > maximumEntries
	if more {
		selected = selected[:maximumEntries]
	}
	return PrivateDirectoryPage{Entries: selected, More: more}, nil
}

func sameWindowsRelativeClaim(source, claim *windowsPrivateRegularAt) bool {
	return source != nil && claim != nil && sameWindowsPrivateFile(source.info, claim.info)
}

func finishWindowsClaimCleanup(closeClaim, deleteSource, deleteClaim, validate func() error) error {
	failed := false
	for _, operation := range []func() error{closeClaim, deleteSource, deleteClaim, validate} {
		if operation == nil || operation() != nil {
			failed = true
		}
	}
	if failed {
		return ErrUnsafeFile
	}
	return nil
}

func windowsRelativeClaimPairExists(directory *windowsPrivateDirectory, source, claim string) (bool, error) {
	left, err := openWindowsPrivateRegularAt(directory.handle, source, windows.FILE_GENERIC_READ, 2)
	if isWindowsRelativeNotFound(err) {
		return false, nil
	}
	if err != nil {
		return false, ErrUnsafeFile
	}
	defer left.Close()
	right, err := openWindowsPrivateRegularAt(directory.handle, claim, windows.FILE_GENERIC_READ, 2)
	if isWindowsRelativeNotFound(err) {
		return false, nil
	}
	if err != nil {
		return false, ErrUnsafeFile
	}
	defer right.Close()
	return sameWindowsRelativeClaim(left, right), nil
}

func windowsRelativeClaimAbsentOrOrphan(directory *windowsPrivateDirectory, source, claim string) (bool, error) {
	current, err := openWindowsPrivateRegularAtAllowedLinks(directory.handle, source, windows.FILE_GENERIC_READ, 1, 2)
	if err == nil {
		_ = current.Close()
		return false, nil
	}
	if !isWindowsRelativeNotFound(err) {
		return false, ErrUnsafeFile
	}
	orphan, err := openWindowsPrivateRegularAt(directory.handle, claim, windows.FILE_GENERIC_READ, 1)
	if err == nil {
		_ = orphan.Close()
		return true, nil
	}
	if isWindowsRelativeNotFound(err) {
		return true, nil
	}
	return false, ErrUnsafeFile
}

const windowsClaimSharingRetries = 100

func openWindowsPrivateClaimSource(directory windows.Handle, source string) (*windowsPrivateRegularAt, error) {
	for attempt := 0; ; attempt++ {
		value, err := openWindowsPrivateRegularAt(
			directory,
			source,
			windows.FILE_GENERIC_READ|windows.FILE_GENERIC_WRITE|windows.DELETE,
			1,
		)
		if !errors.Is(err, windows.ERROR_SHARING_VIOLATION) &&
			!errors.Is(err, windows.STATUS_SHARING_VIOLATION) {
			return value, err
		}
		if attempt == windowsClaimSharingRetries {
			return nil, err
		}
		time.Sleep(time.Millisecond)
	}
}

func (directory *windowsPrivateDirectory) ClaimRegular(source, claim string) (bool, error) {
	if directory.Validate() != nil || !validPrivateLeafName(source) || !validPrivateLeafName(claim) {
		return false, ErrUnsafeFile
	}
	// A concurrent winner temporarily holds the source with DELETE access and deliberately
	// without FILE_SHARE_DELETE. Wait only for that specific, bounded contention before
	// observing the resulting pair or absence below. Persistent sharing remains unsafe.
	value, err := openWindowsPrivateClaimSource(directory.handle, source)
	if err != nil {
		pair, pairErr := windowsRelativeClaimPairExists(directory, source, claim)
		if pairErr == nil && pair {
			return false, nil
		}
		orphan, orphanErr := windowsRelativeClaimAbsentOrOrphan(directory, source, claim)
		if orphanErr == nil && orphan {
			return false, nil
		}
		return false, ErrUnsafeFile
	}
	defer value.Close()
	if linkWindowsPrivateRegularAt(value.handle, directory.handle, claim) != nil {
		existing, existingErr := openWindowsPrivateRegularAtAllowedLinks(directory.handle, claim, windows.FILE_GENERIC_READ, 1, 2)
		if existingErr == nil {
			_ = existing.Close()
			return false, nil
		}
		return false, ErrUnsafeFile
	}
	after, err := privateWindowsRegularInfo(value.handle, 2)
	if err != nil {
		return false, ErrUnsafeFile
	}
	value.info = after
	claimed, err := openWindowsPrivateRegularAt(directory.handle, claim, windows.FILE_GENERIC_READ, 2)
	if err != nil {
		return false, ErrUnsafeFile
	}
	defer claimed.Close()
	if !sameWindowsRelativeClaim(value, claimed) || directory.Validate() != nil {
		return false, ErrUnsafeFile
	}
	return true, nil
}

func (directory *windowsPrivateDirectory) ReadClaim(source, claim string, maximum int64) ([]byte, bool, error) {
	if directory.Validate() != nil || !validPrivateLeafName(source) || !validPrivateLeafName(claim) ||
		maximum < 0 || maximum == int64(^uint64(0)>>1) {
		return nil, false, ErrUnsafeFile
	}
	value, err := openWindowsPrivateRegularAt(directory.handle, source, windows.FILE_GENERIC_READ, 2)
	if err != nil {
		orphan, orphanErr := windowsRelativeClaimAbsentOrOrphan(directory, source, claim)
		if orphanErr == nil && orphan {
			return nil, false, nil
		}
		return nil, false, ErrUnsafeFile
	}
	defer value.Close()
	claimed, err := openWindowsPrivateRegularAt(directory.handle, claim, windows.FILE_GENERIC_READ, 2)
	if isWindowsRelativeNotFound(err) {
		return nil, false, nil
	}
	if err != nil {
		return nil, false, ErrUnsafeFile
	}
	defer claimed.Close()
	if !sameWindowsRelativeClaim(value, claimed) {
		return nil, false, ErrUnsafeFile
	}
	contents, err := readWindowsPrivateRegular(value, maximum, 2)
	if err != nil {
		return nil, false, ErrUnsafeFile
	}
	afterClaim, err := privateWindowsRegularInfo(claimed.handle, 2)
	if err != nil || !sameWindowsPrivateFile(value.info, afterClaim) || directory.Validate() != nil {
		return nil, false, ErrUnsafeFile
	}
	return contents, true, nil
}

func (directory *windowsPrivateDirectory) RemoveClaim(source, claim string) (bool, error) {
	if directory.Validate() != nil || !validPrivateLeafName(source) || !validPrivateLeafName(claim) {
		return false, ErrUnsafeFile
	}
	value, err := openWindowsPrivateRegularAt(directory.handle, source, windows.FILE_GENERIC_READ|windows.DELETE, 2)
	if err != nil {
		orphan, orphanErr := windowsRelativeClaimAbsentOrOrphan(directory, source, claim)
		if orphanErr == nil && orphan {
			return false, nil
		}
		return false, ErrUnsafeFile
	}
	claimed, err := openWindowsPrivateRegularAtWithShareMode(
		directory.handle,
		claim,
		windows.FILE_GENERIC_READ,
		windowsRetainedHandleShareMode|windows.FILE_SHARE_DELETE,
		2,
	)
	if isWindowsRelativeNotFound(err) {
		closeErr := value.Close()
		validateErr := directory.Validate()
		if closeErr != nil || validateErr != nil {
			return false, ErrUnsafeFile
		}
		return false, nil
	}
	if err != nil || !sameWindowsRelativeClaim(value, claimed) {
		valueCloseErr := value.Close()
		claimedCloseErr := error(nil)
		if claimed != nil {
			claimedCloseErr = claimed.Close()
		}
		if valueCloseErr != nil || claimedCloseErr != nil || directory.Validate() != nil {
			return false, ErrUnsafeFile
		}
		return false, ErrUnsafeFile
	}
	cleanupErr := finishWindowsClaimCleanup(
		claimed.Close,
		func() error { return closeAndDeleteWindowsPrivateRegular(value) },
		func() error {
			remaining, remainingErr := openWindowsPrivateRegularAt(directory.handle, claim, windows.FILE_GENERIC_READ|windows.DELETE, 1)
			if remainingErr != nil {
				return ErrUnsafeFile
			}
			return closeAndDeleteWindowsPrivateRegular(remaining)
		},
		directory.Validate,
	)
	if cleanupErr != nil {
		return false, ErrUnsafeFile
	}
	return true, nil
}