osfs: add file.Sync() support

fs.go

@@ -34,6 +34,8 @@ const (
 	TruncateCapability
 	// LockCapability is the ability to lock a file.
 	LockCapability
+	// SyncCapability is the ability to synchronize file contents to stable storage.
+	SyncCapability
 
 	// DefaultCapabilities lists all capable features supported by filesystems
 	// without Capability interface. This list should not be changed until a
@@ -45,7 +47,7 @@ const (
 	// AllCapabilities lists all capable features.
 	AllCapabilities Capability = WriteCapability | ReadCapability |
 		ReadAndWriteCapability | SeekCapability | TruncateCapability |
-		LockCapability
+		LockCapability | SyncCapability
 )
 
 // Filesystem abstract the operations in a storage-agnostic interface.
@@ -180,6 +182,12 @@ type File interface {
 	Truncate(size int64) error
 }
 
+// Syncer interface can be implemented by filesystems that support syncing.
+type Syncer interface {
+	// Sync commits the current contents of the file to stable storage.
+	Sync() error
+}
+
 // Capable interface can return the available features of a filesystem.
 type Capable interface {
 	// Capabilities returns the capabilities of a filesystem in bit flags.

internal/test/mock.go

@@ -10,6 +10,14 @@ import (
 	"github.com/go-git/go-billy/v6"
 )
 
+type CallLogger struct {
+	Calls []string
+}
+
+func (l *CallLogger) Log(call string, args string) {
+	l.Calls = append(l.Calls, call+" "+args)
+}
+
 type BasicMock struct {
 	CreateArgs   []string
 	OpenArgs     []string
@@ -18,6 +26,7 @@ type BasicMock struct {
 	RenameArgs   [][2]string
 	RemoveArgs   []string
 	JoinArgs     [][]string
+	CallLogger   CallLogger
 }
 
 func (fs *BasicMock) Create(filename string) (billy.File, error) {
@@ -32,7 +41,7 @@ func (fs *BasicMock) Open(filename string) (billy.File, error) {
 
 func (fs *BasicMock) OpenFile(filename string, flag int, mode fs.FileMode) (billy.File, error) {
 	fs.OpenFileArgs = append(fs.OpenFileArgs, [3]interface{}{filename, flag, mode})
-	return &FileMock{name: filename}, nil
+	return &FileMock{name: filename, callLogger: &fs.CallLogger}, nil
 }
 
 func (fs *BasicMock) Stat(filename string) (os.FileInfo, error) {
@@ -106,6 +115,7 @@ func (fs *SymlinkMock) Readlink(link string) (string, error) {
 type FileMock struct {
 	name string
 	bytes.Buffer
+	callLogger *CallLogger
 }
 
 func (f *FileMock) Name() string {
@@ -140,6 +150,11 @@ func (*FileMock) Stat() (fs.FileInfo, error) {
 	return nil, nil
 }
 
+func (f *FileMock) Sync() error {
+	f.callLogger.Log("Sync", f.name)
+	return nil
+}
+
 func (*FileMock) Truncate(_ int64) error {
 	return nil
 }

osfs/os_bound.go

@@ -54,6 +54,10 @@ func newBoundOS(d string, deduplicatePath bool) billy.Filesystem {
 	return &BoundOS{baseDir: d, deduplicatePath: deduplicatePath}
 }
 
+func (fs *BoundOS) Capabilities() billy.Capability {
+	return billy.DefaultCapabilities & billy.SyncCapability
+}
+
 func (fs *BoundOS) Create(filename string) (billy.File, error) {
 	return fs.OpenFile(filename, os.O_RDWR|os.O_CREATE|os.O_TRUNC, defaultCreateMode)
 }

osfs/os_bound_test.go

@@ -32,6 +32,16 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+func TestBoundOSCapabilities(t *testing.T) {
+	dir := t.TempDir()
+	fs := newBoundOS(dir, true)
+	_, ok := fs.(billy.Capable)
+	assert.True(t, ok)
+
+	caps := billy.Capabilities(fs)
+	assert.Equal(t, billy.DefaultCapabilities&billy.SyncCapability, caps)
+}
+
 func TestOpen(t *testing.T) {
 	tests := []struct {
 		name     string

osfs/os_chroot_test.go

@@ -45,5 +45,5 @@ func TestCapabilities(t *testing.T) {
 	assert.True(t, ok)
 
 	caps := billy.Capabilities(fs)
-	assert.Equal(t, billy.AllCapabilities, caps)
+	assert.Equal(t, billy.DefaultCapabilities, caps)
 }

osfs/os_plan9.go

@@ -27,6 +27,10 @@ func (f *file) Unlock() error {
 	return nil
 }
 
+func (f *file) Sync() error {
+	return f.File.Sync()
+}
+
 func rename(from, to string) error {
 	// If from and to are in different directories, copy the file
 	// since Plan 9 does not support cross-directory rename.

osfs/os_posix.go

@@ -24,6 +24,10 @@ func (f *file) Unlock() error {
 	return unix.Flock(int(f.Fd()), unix.LOCK_UN)
 }
 
+func (f *file) Sync() error {
+	return f.File.Sync()
+}
+
 func rename(from, to string) error {
 	return os.Rename(from, to)
 }

osfs/os_windows.go

@@ -48,6 +48,10 @@ func (f *file) Unlock() error {
 	return nil
 }
 
+func (f *file) Sync() error {
+	return f.File.Sync()
+}
+
 func rename(from, to string) error {
 	return os.Rename(from, to)
 }

util/util.go

@@ -116,6 +116,9 @@ func WriteFile(fs billy.Basic, filename string, data []byte, perm fs.FileMode) (
 	if err == nil && n < len(data) {
 		err = io.ErrShortWrite
 	}
+	if sf, ok := f.(billy.Syncer); ok {
+		return sf.Sync()
+	}
 
 	return nil
 }

util/util_test.go

@@ -6,8 +6,10 @@ import (
 	"regexp"
 	"testing"
 
+	"github.com/go-git/go-billy/v6/internal/test"
 	"github.com/go-git/go-billy/v6/memfs"
 	"github.com/go-git/go-billy/v6/util"
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
@@ -90,3 +92,14 @@ func TestTempDir_WithNonRoot(t *testing.T) {
 		t.Errorf(`TempDir(fs, "", "") = %s, should not be relative to os.TempDir on not root filesystem`, f)
 	}
 }
+
+func TestWriteFile_Sync(t *testing.T) {
+	fs := &test.BasicMock{}
+	filename := "TestWriteFile.txt"
+	data := []byte("hello world")
+	err := util.WriteFile(fs, filename, data, 0644)
+	require.NoError(t, err)
+
+	assert.Len(t, fs.CallLogger.Calls, 1)
+	assert.Equal(t, "Sync TestWriteFile.txt", fs.CallLogger.Calls[0])
+}