//go:build windows
// +build windows
package winio
import (
"encoding/binary"
"errors"
"fmt"
"io"
"os"
"runtime"
"unicode/utf16"
"github.com/Microsoft/go-winio/internal/fs"
"golang.org/x/sys/windows"
)
//sys backupRead(h windows.Handle, b []byte, bytesRead *uint32, abort bool, processSecurity bool, context *uintptr) (err error) = BackupRead
//sys backupWrite(h windows.Handle, b []byte, bytesWritten *uint32, abort bool, processSecurity bool, context *uintptr) (err error) = BackupWrite
const (
BackupData = uint32(iota + 1)
BackupEaData
BackupSecurity
BackupAlternateData
BackupLink
BackupPropertyData
BackupObjectId //revive:disable-line:var-naming ID, not Id
BackupReparseData
BackupSparseBlock
BackupTxfsData
)
const (
StreamSparseAttributes = uint32(8)
)
//nolint:revive // var-naming: ALL_CAPS
const (
WRITE_DAC = windows.WRITE_DAC
WRITE_OWNER = windows.WRITE_OWNER
ACCESS_SYSTEM_SECURITY = windows.ACCESS_SYSTEM_SECURITY
)
// BackupHeader represents a backup stream of a file.
type BackupHeader struct {
//revive:disable-next-line:var-naming ID, not Id
Id uint32 // The backup stream ID
Attributes uint32 // Stream attributes
Size int64 // The size of the stream in bytes
Name string // The name of the stream (for BackupAlternateData only).
Offset int64 // The offset of the stream in the file (for BackupSparseBlock only).
}
type win32StreamID struct {
StreamID uint32
Attributes uint32
Size uint64
NameSize uint32
}
// BackupStreamReader reads from a stream produced by the BackupRead Win32 API and produces a series
// of BackupHeader values.
type BackupStreamReader struct {
r io.Reader
bytesLeft int64
}
// NewBackupStreamReader produces a BackupStreamReader from any io.Reader.
func NewBackupStreamReader(r io.Reader) *BackupStreamReader {
return &BackupStreamReader{r, 0}
}
// Next returns the next backup stream and prepares for calls to Read(). It skips the remainder of the current stream if
// it was not completely read.
func (r *BackupStreamReader) Next() (*BackupHeader, error) {
if r.bytesLeft > 0 { //nolint:nestif // todo: flatten this
if s, ok := r.r.(io.Seeker); ok {
// Make sure Seek on io.SeekCurrent sometimes succeeds
// before trying the actual seek.
if _, err := s.Seek(0, io.SeekCurrent); err == nil {
if _, err = s.Seek(r.bytesLeft, io.SeekCurrent); err != nil {
return nil, err
}
r.bytesLeft = 0
}
}
if _, err := io.Copy(io.Discard, r); err != nil {
return nil, err
}
}
var wsi win32StreamID
if err := binary.Read(r.r, binary.LittleEndian, &wsi); err != nil {
return nil, err
}
hdr := &BackupHeader{
Id: wsi.StreamID,
Attributes: wsi.Attributes,
Size: int64(wsi.Size),
}
if wsi.NameSize != 0 {
name := make([]uint16, int(wsi.NameSize/2))
if err := binary.Read(r.r, binary.LittleEndian, name); err != nil {
return nil, err
}
hdr.Name = windows.UTF16ToString(name)
}
if wsi.StreamID == BackupSparseBlock {
if err := binary.Read(r.r, binary.LittleEndian, &hdr.Offset); err != nil {
return nil, err
}
hdr.Size -= 8
}
r.bytesLeft = hdr.Size
return hdr, nil
}
// Read reads from the current backup stream.
func (r *BackupStreamReader) Read(b []byte) (int, error) {
if r.bytesLeft == 0 {
return 0, io.EOF
}
if int64(len(b)) > r.bytesLeft {
b = b[:r.bytesLeft]
}
n, err := r.r.Read(b)
r.bytesLeft -= int64(n)
if err == io.EOF {
err = io.ErrUnexpectedEOF
} else if r.bytesLeft == 0 && err == nil {
err = io.EOF
}
return n, err
}
// BackupStreamWriter writes a stream compatible with the BackupWrite Win32 API.
type BackupStreamWriter struct {
w io.Writer
bytesLeft int64
}
// NewBackupStreamWriter produces a BackupStreamWriter on top of an io.Writer.
func NewBackupStreamWriter(w io.Writer) *BackupStreamWriter {
return &BackupStreamWriter{w, 0}
}
// WriteHeader writes the next backup stream header and prepares for calls to Write().
func (w *BackupStreamWriter) WriteHeader(hdr *BackupHeader) error {
if w.bytesLeft != 0 {
return fmt.Errorf("missing %d bytes", w.bytesLeft)
}
name := utf16.Encode([]rune(hdr.Name))
wsi := win32StreamID{
StreamID: hdr.Id,
Attributes: hdr.Attributes,
Size: uint64(hdr.Size),
NameSize: uint32(len(name) * 2),
}
if hdr.Id == BackupSparseBlock {
// Include space for the int64 block offset
wsi.Size += 8
}
if err := binary.Write(w.w, binary.LittleEndian, &wsi); err != nil {
return err
}
if len(name) != 0 {
if err := binary.Write(w.w, binary.LittleEndian, name); err != nil {
return err
}
}
if hdr.Id == BackupSparseBlock {
if err := binary.Write(w.w, binary.LittleEndian, hdr.Offset); err != nil {
return err
}
}
w.bytesLeft = hdr.Size
return nil
}
// Write writes to the current backup stream.
func (w *BackupStreamWriter) Write(b []byte) (int, error) {
if w.bytesLeft < int64(len(b)) {
return 0, fmt.Errorf("too many bytes by %d", int64(len(b))-w.bytesLeft)
}
n, err := w.w.Write(b)
w.bytesLeft -= int64(n)
return n, err
}
// BackupFileReader provides an io.ReadCloser interface on top of the BackupRead Win32 API.
type BackupFileReader struct {
f *os.File
includeSecurity bool
ctx uintptr
}
// NewBackupFileReader returns a new BackupFileReader from a file handle. If includeSecurity is true,
// Read will attempt to read the security descriptor of the file.
func NewBackupFileReader(f *os.File, includeSecurity bool) *BackupFileReader {
r := &BackupFileReader{f, includeSecurity, 0}
return r
}
// Read reads a backup stream from the file by calling the Win32 API BackupRead().
func (r *BackupFileReader) Read(b []byte) (int, error) {
var bytesRead uint32
err := backupRead(windows.Handle(r.f.Fd()), b, &bytesRead, false, r.includeSecurity, &r.ctx)
if err != nil {
return 0, &os.PathError{Op: "BackupRead", Path: r.f.Name(), Err: err}
}
runtime.KeepAlive(r.f)
if bytesRead == 0 {
return 0, io.EOF
}
return int(bytesRead), nil
}
// Close frees Win32 resources associated with the BackupFileReader. It does not close
// the underlying file.
func (r *BackupFileReader) Close() error {
if r.ctx != 0 {
_ = backupRead(windows.Handle(r.f.Fd()), nil, nil, true, false, &r.ctx)
runtime.KeepAlive(r.f)
r.ctx = 0
}
return nil
}
// BackupFileWriter provides an io.WriteCloser interface on top of the BackupWrite Win32 API.
type BackupFileWriter struct {
f *os.File
includeSecurity bool
ctx uintptr
}
// NewBackupFileWriter returns a new BackupFileWriter from a file handle. If includeSecurity is true,
// Write() will attempt to restore the security descriptor from the stream.
func NewBackupFileWriter(f *os.File, includeSecurity bool) *BackupFileWriter {
w := &BackupFileWriter{f, includeSecurity, 0}
return w
}
// Write restores a portion of the file using the provided backup stream.
func (w *BackupFileWriter) Write(b []byte) (int, error) {
var bytesWritten uint32
err := backupWrite(windows.Handle(w.f.Fd()), b, &bytesWritten, false, w.includeSecurity, &w.ctx)
if err != nil {
return 0, &os.PathError{Op: "BackupWrite", Path: w.f.Name(), Err: err}
}
runtime.KeepAlive(w.f)
if int(bytesWritten) != len(b) {
return int(bytesWritten), errors.New("not all bytes could be written")
}
return len(b), nil
}
// Close frees Win32 resources associated with the BackupFileWriter. It does not
// close the underlying file.
func (w *BackupFileWriter) Close() error {
if w.ctx != 0 {
_ = backupWrite(windows.Handle(w.f.Fd()), nil, nil, true, false, &w.ctx)
runtime.KeepAlive(w.f)
w.ctx = 0
}
return nil
}
// OpenForBackup opens a file or directory, potentially skipping access checks if the backup
// or restore privileges have been acquired.
//
// If the file opened was a directory, it cannot be used with Readdir().
func OpenForBackup(path string, access uint32, share uint32, createmode uint32) (*os.File, error) {
h, err := fs.CreateFile(path,
fs.AccessMask(access),
fs.FileShareMode(share),
nil,
fs.FileCreationDisposition(createmode),
fs.FILE_FLAG_BACKUP_SEMANTICS|fs.FILE_FLAG_OPEN_REPARSE_POINT,
0,
)
if err != nil {
err = &os.PathError{Op: "open", Path: path, Err: err}
return nil, err
}
return os.NewFile(uintptr(h), path), nil
}
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