backup: allow excluding online-only cloud files

internal/fs/stat_bsd.go

@@ -32,3 +32,8 @@ func extendedStat(fi os.FileInfo) *ExtendedFileInfo {
 		ChangeTime: time.Unix(s.Ctimespec.Unix()),
 	}
 }
+
+// RecallOnDataAccess checks windows-specific attributes to determine if a file is a cloud-only placeholder.
+func (*ExtendedFileInfo) RecallOnDataAccess() (bool, error) {
+	return false, nil
+}

internal/fs/stat_unix.go

@@ -32,3 +32,8 @@ func extendedStat(fi os.FileInfo) *ExtendedFileInfo {
 		ChangeTime: time.Unix(s.Ctim.Unix()),
 	}
 }
+
+// RecallOnDataAccess checks windows-specific attributes to determine if a file is a cloud-only placeholder.
+func (*ExtendedFileInfo) RecallOnDataAccess() (bool, error) {
+	return false, nil
+}

internal/fs/stat_windows.go

@@ -8,6 +8,8 @@ import (
 	"os"
 	"syscall"
 	"time"
+
+	"golang.org/x/sys/windows"
 )
 
 // extendedStat extracts info into an ExtendedFileInfo for Windows.
@@ -36,3 +38,20 @@ func extendedStat(fi os.FileInfo) *ExtendedFileInfo {
 
 	return &extFI
 }
+
+// RecallOnDataAccess checks if a file is available locally on the disk or if the file is
+// just a placeholder which must be downloaded from a remote server. This is typically used
+// in cloud syncing services (e.g. OneDrive) to prevent downloading files from cloud storage
+// until they are accessed.
+func (fi *ExtendedFileInfo) RecallOnDataAccess() (bool, error) {
+	attrs, ok := fi.sys.(*syscall.Win32FileAttributeData)
+	if !ok {
+		return false, fmt.Errorf("could not determine file attributes: %s", fi.Name)
+	}
+
+	if attrs.FileAttributes&windows.FILE_ATTRIBUTE_RECALL_ON_DATA_ACCESS > 0 {
+		return true, nil
+	}
+
+	return false, nil
+}

internal/fs/stat_windows_test.go

@@ -0,0 +1,80 @@
+package fs_test
+
+import (
+	iofs "io/fs"
+	"os"
+	"path/filepath"
+	"syscall"
+	"testing"
+	"time"
+
+	"github.com/restic/restic/internal/fs"
+	rtest "github.com/restic/restic/internal/test"
+	"golang.org/x/sys/windows"
+)
+
+func TestRecallOnDataAccessRealFile(t *testing.T) {
+	// create a temp file for testing
+	tempdir := rtest.TempDir(t)
+	filename := filepath.Join(tempdir, "regular-file")
+	err := os.WriteFile(filename, []byte("foobar"), 0640)
+	rtest.OK(t, err)
+
+	fi, err := os.Stat(filename)
+	rtest.OK(t, err)
+
+	xs := fs.ExtendedStat(fi)
+
+	// ensure we can check attrs without error
+	recall, err := xs.RecallOnDataAccess()
+	rtest.Assert(t, err == nil, "err should be nil", err)
+	rtest.Assert(t, recall == false, "RecallOnDataAccess should be false")
+}
+
+// mockFileInfo implements os.FileInfo for mocking file attributes
+type mockFileInfo struct {
+	FileAttributes uint32
+}
+
+func (m mockFileInfo) IsDir() bool {
+	return false
+}
+func (m mockFileInfo) ModTime() time.Time {
+	return time.Now()
+}
+func (m mockFileInfo) Mode() iofs.FileMode {
+	return 0
+}
+func (m mockFileInfo) Name() string {
+	return "test"
+}
+func (m mockFileInfo) Size() int64 {
+	return 0
+}
+func (m mockFileInfo) Sys() any {
+	return &syscall.Win32FileAttributeData{
+		FileAttributes: m.FileAttributes,
+	}
+}
+
+func TestRecallOnDataAccessMockCloudFile(t *testing.T) {
+	fi := mockFileInfo{
+		FileAttributes: windows.FILE_ATTRIBUTE_RECALL_ON_DATA_ACCESS,
+	}
+	xs := fs.ExtendedStat(fi)
+
+	recall, err := xs.RecallOnDataAccess()
+	rtest.Assert(t, err == nil, "err should be nil", err)
+	rtest.Assert(t, recall, "RecallOnDataAccess should be true")
+}
+
+func TestRecallOnDataAccessMockRegularFile(t *testing.T) {
+	fi := mockFileInfo{
+		FileAttributes: windows.FILE_ATTRIBUTE_ARCHIVE,
+	}
+	xs := fs.ExtendedStat(fi)
+
+	recall, err := xs.RecallOnDataAccess()
+	rtest.Assert(t, err == nil, "err should be nil", err)
+	rtest.Assert(t, recall == false, "RecallOnDataAccess should be false")
+}