fs: add file handle helpers

internal/fs/meta_darwin.go

@@ -0,0 +1,25 @@
+package fs
+
+import (
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+func openMetadataHandle(path string, flag int) (*os.File, error) {
+	flags := O_RDONLY
+	if flag&O_NOFOLLOW != 0 {
+		// open symlink instead of following it
+		flags |= unix.O_SYMLINK
+	}
+	if flag&O_DIRECTORY != 0 {
+		flags |= O_DIRECTORY
+	}
+
+	f, err := os.OpenFile(path, flags, 0)
+	if err != nil {
+		return nil, err
+	}
+	_ = setFlags(f)
+	return f, nil
+}

internal/fs/meta_linux.go

@@ -0,0 +1,25 @@
+package fs
+
+import (
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+func openMetadataHandle(path string, flag int) (*os.File, error) {
+	// O_PATH|O_NOFOLLOW is necessary to also be able to get a handle to symlinks
+	flags := unix.O_PATH
+	if flag&O_NOFOLLOW != 0 {
+		flags |= O_NOFOLLOW
+	}
+	if flag&O_DIRECTORY != 0 {
+		flags |= O_DIRECTORY
+	}
+
+	f, err := os.OpenFile(path, flags, 0)
+	if err != nil {
+		return nil, err
+	}
+	_ = setFlags(f)
+	return f, nil
+}

internal/fs/meta_windows.go

@@ -1,6 +1,9 @@
 package fs
 
 import (
+	"os"
+	"syscall"
+
 	"github.com/restic/restic/internal/debug"
 	"github.com/restic/restic/internal/errors"
 	"github.com/restic/restic/internal/restic"
@@ -58,3 +61,23 @@ func (p *fdMetadataHandle) SecurityDescriptor() (*[]byte, error) {
 	// FIXME
 	return getSecurityDescriptor(p.name)
 }
+
+func openMetadataHandle(path string, flag int) (*os.File, error) {
+	path = fixpath(path)
+	// OpenFile from go does not request FILE_READ_EA so we need our own low-level implementation
+	// according to the windows docs, STANDARD_RIGHTS_READ + FILE_FLAG_BACKUP_SEMANTICS disable security checks on access
+	// if the process holds the SeBackupPrivilege
+	fileAccess := windows.FILE_READ_EA | windows.FILE_READ_ATTRIBUTES | windows.STANDARD_RIGHTS_READ
+	shareMode := windows.FILE_SHARE_READ | windows.FILE_SHARE_WRITE | windows.FILE_SHARE_DELETE
+	attrs := windows.FILE_ATTRIBUTE_NORMAL | windows.FILE_FLAG_BACKUP_SEMANTICS
+	if flag&O_NOFOLLOW != 0 {
+		attrs |= syscall.FILE_FLAG_OPEN_REPARSE_POINT
+	}
+
+	utf16Path := windows.StringToUTF16Ptr(path)
+	handle, err := windows.CreateFile(utf16Path, uint32(fileAccess), uint32(shareMode), nil, windows.OPEN_EXISTING, uint32(attrs), 0)
+	if err != nil {
+		return nil, err
+	}
+	return os.NewFile(uintptr(handle), path), nil
+}