Merge pull request #146 from gabriel-samfira/fix-diskwriter-on-windows

Implement proper renameFile on Windows

diskwriter.go

@@ -205,7 +205,8 @@ func (dw *DiskWriter) HandleChange(kind ChangeKind, p string, fi os.FileInfo, er
 				return errors.Wrapf(err, "failed to remove %s", destPath)
 			}
 		}
-		if err := os.Rename(newPath, destPath); err != nil {
+
+		if err := renameFile(newPath, destPath); err != nil {
 			return errors.Wrapf(err, "failed to rename %s to %s", newPath, destPath)
 		}
 	}

diskwriter_unix.go

@@ -51,3 +51,10 @@ func handleTarTypeBlockCharFifo(path string, stat *types.Stat) error {
 	}
 	return nil
 }
+
+func renameFile(src, dst string) error {
+	if err := os.Rename(src, dst); err != nil {
+		return errors.Wrapf(err, "failed to rename %s to %s", src, dst)
+	}
+	return nil
+}

diskwriter_windows.go

@@ -1,8 +1,15 @@
+//go:build windows
 // +build windows
 
 package fsutil
 
 import (
+	"fmt"
+	iofs "io/fs"
+	"os"
+	"syscall"
+
+	"github.com/Microsoft/go-winio"
 	"github.com/pkg/errors"
 	"github.com/tonistiigi/fsutil/types"
 )
@@ -16,3 +23,75 @@ func rewriteMetadata(p string, stat *types.Stat) error {
 func handleTarTypeBlockCharFifo(path string, stat *types.Stat) error {
 	return errors.New("Not implemented on windows")
 }
+
+func getFileHandle(path string, info iofs.FileInfo) (syscall.Handle, error) {
+	p, err := syscall.UTF16PtrFromString(path)
+	if err != nil {
+		return 0, errors.Wrap(err, "converting string to UTF-16")
+	}
+	attrs := uint32(syscall.FILE_FLAG_BACKUP_SEMANTICS)
+	if info.Mode()&os.ModeSymlink != 0 {
+		// Use FILE_FLAG_OPEN_REPARSE_POINT, otherwise CreateFile will follow symlink.
+		// See https://docs.microsoft.com/en-us/windows/desktop/FileIO/symbolic-link-effects-on-file-systems-functions#createfile-and-createfiletransacted
+		attrs |= syscall.FILE_FLAG_OPEN_REPARSE_POINT
+	}
+	h, err := syscall.CreateFile(p, 0, 0, nil, syscall.OPEN_EXISTING, attrs, 0)
+	if err != nil {
+		return 0, errors.Wrap(err, "getting file handle")
+	}
+	return h, nil
+}
+
+func readlink(path string, info iofs.FileInfo) ([]byte, error) {
+	h, err := getFileHandle(path, info)
+	if err != nil {
+		return nil, errors.Wrap(err, "getting file handle")
+	}
+	defer syscall.CloseHandle(h)
+
+	rdbbuf := make([]byte, syscall.MAXIMUM_REPARSE_DATA_BUFFER_SIZE)
+	var bytesReturned uint32
+	err = syscall.DeviceIoControl(h, syscall.FSCTL_GET_REPARSE_POINT, nil, 0, &rdbbuf[0], uint32(len(rdbbuf)), &bytesReturned, nil)
+	if err != nil {
+		return nil, errors.Wrap(err, "sending I/O control command")
+	}
+	return rdbbuf[:bytesReturned], nil
+}
+
+func getReparsePoint(path string, info iofs.FileInfo) (*winio.ReparsePoint, error) {
+	target, err := readlink(path, info)
+	if err != nil {
+		return nil, errors.Wrap(err, "fetching link")
+	}
+	rp, err := winio.DecodeReparsePoint(target)
+	if err != nil {
+		return nil, errors.Wrap(err, "decoding reparse point")
+	}
+	return rp, nil
+}
+
+func renameFile(src, dst string) error {
+	info, err := os.Lstat(dst)
+	if err != nil {
+		if !os.IsNotExist(err) {
+			return errors.Wrap(err, "getting file info")
+		}
+	}
+
+	if info != nil && info.Mode()&os.ModeSymlink != 0 {
+		dstInfoRp, err := getReparsePoint(dst, info)
+		if err != nil {
+			return errors.Wrap(err, "getting reparse point")
+		}
+		if dstInfoRp.IsMountPoint {
+			return fmt.Errorf("%s is a mount point", dst)
+		}
+		if err := os.Remove(dst); err != nil {
+			return errors.Wrapf(err, "removing %s", dst)
+		}
+	}
+	if err := os.Rename(src, dst); err != nil {
+		return errors.Wrapf(err, "failed to rename %s to %s", src, dst)
+	}
+	return nil
+}