fs: add Wrap feature for FS to identify their parent FS (#1884)

cache/cache.go

@@ -206,6 +206,7 @@ type Storage interface {
 // Fs represents a wrapped fs.Fs
 type Fs struct {
 	fs.Fs
+	wrapper fs.Fs
 
 	name     string
 	root     string
@@ -379,7 +380,9 @@ func NewFs(name, rpath string) (fs.Fs, error) {
 		PutStream:               f.PutStream,
 		CleanUp:                 f.CleanUp,
 		UnWrap:                  f.UnWrap,
-	}).Fill(f).Mask(wrappedFs)
+		WrapFs:                  f.WrapFs,
+		SetWrapper:              f.SetWrapper,
+	}).Fill(f).Mask(wrappedFs).WrapsFs(f, wrappedFs)
 
 	return f, wrapErr
 }
@@ -938,6 +941,16 @@ func (f *Fs) UnWrap() fs.Fs {
 	return f.Fs
 }
 
+// WrapFs returns the Fs that is wrapping this Fs
+func (f *Fs) WrapFs() fs.Fs {
+	return f.wrapper
+}
+
+// SetWrapper sets the Fs that is wrapping this Fs
+func (f *Fs) SetWrapper(wrapper fs.Fs) {
+	f.wrapper = wrapper
+}
+
 // DirCacheFlush flushes the dir cache
 func (f *Fs) DirCacheFlush() {
 	_ = f.cache.RemoveDir("")
@@ -963,5 +976,6 @@ var (
 	_ fs.PutStreamer    = (*Fs)(nil)
 	_ fs.CleanUpper     = (*Fs)(nil)
 	_ fs.UnWrapper      = (*Fs)(nil)
+	_ fs.Wrapper        = (*Fs)(nil)
 	_ fs.ListRer        = (*Fs)(nil)
 )

crypt/crypt.go

@@ -129,7 +129,7 @@ func NewFs(name, rpath string) (fs.Fs, error) {
 		WriteMimeType:           false,
 		BucketBased:             true,
 		CanHaveEmptyDirectories: true,
-	}).Fill(f).Mask(wrappedFs)
+	}).Fill(f).Mask(wrappedFs).WrapsFs(f, wrappedFs)
 
 	doDirChangeNotify := wrappedFs.Features().DirChangeNotify
 	if doDirChangeNotify != nil {

fs/fs.go

@@ -301,6 +301,12 @@ type Features struct {
 	// UnWrap returns the Fs that this Fs is wrapping
 	UnWrap func() Fs
 
+	// WrapFs returns the Fs that is wrapping this Fs
+	WrapFs func() Fs
+
+	// SetWrapper sets the Fs that is wrapping this Fs
+	SetWrapper func(f Fs)
+
 	// DirCacheFlush resets the directory cache - used in testing
 	// as an optional interface
 	DirCacheFlush func()
@@ -413,6 +419,10 @@ func (ft *Features) Fill(f Fs) *Features {
 	if do, ok := f.(UnWrapper); ok {
 		ft.UnWrap = do.UnWrap
 	}
+	if do, ok := f.(Wrapper); ok {
+		ft.WrapFs = do.WrapFs
+		ft.SetWrapper = do.SetWrapper
+	}
 	if do, ok := f.(DirCacheFlusher); ok {
 		ft.DirCacheFlush = do.DirCacheFlush
 	}
@@ -438,7 +448,7 @@ func (ft *Features) Fill(f Fs) *Features {
 //
 // Only optional features which are implemented in both the original
 // Fs AND the one passed in will be advertised.  Any features which
-// aren't in both will be set to false/nil, except for UnWrap which
+// aren't in both will be set to false/nil, except for UnWrap/Wrap which
 // will be left untouched.
 func (ft *Features) Mask(f Fs) *Features {
 	mask := f.Features()
@@ -487,7 +497,7 @@ func (ft *Features) Mask(f Fs) *Features {
 	return ft.DisableList(Config.DisableFeatures)
 }
 
-// Wrap makes a Copy of the features passed in, overriding the UnWrap
+// Wrap makes a Copy of the features passed in, overriding the UnWrap/Wrap
 // method only if available in f.
 func (ft *Features) Wrap(f Fs) *Features {
 	copy := new(Features)
@@ -495,9 +505,22 @@ func (ft *Features) Wrap(f Fs) *Features {
 	if do, ok := f.(UnWrapper); ok {
 		copy.UnWrap = do.UnWrap
 	}
+	if do, ok := f.(Wrapper); ok {
+		copy.WrapFs = do.WrapFs
+		copy.SetWrapper = do.SetWrapper
+	}
 	return copy
 }
 
+// WrapsFs adds extra information between `f` which wraps `w`
+func (ft *Features) WrapsFs(f Fs, w Fs) *Features {
+	wFeatures := w.Features()
+	if wFeatures.WrapFs != nil && wFeatures.SetWrapper != nil {
+		wFeatures.SetWrapper(f)
+	}
+	return ft
+}
+
 // Purger is an optional interfaces for Fs
 type Purger interface {
 	// Purge all files in the root and the root directory
@@ -564,6 +587,14 @@ type UnWrapper interface {
 	UnWrap() Fs
 }
 
+// Wrapper is an optional interfaces for Fs
+type Wrapper interface {
+	// Wrap returns the Fs that is wrapping this Fs
+	WrapFs() Fs
+	// SetWrapper sets the Fs that is wrapping this Fs
+	SetWrapper(f Fs)
+}
+
 // DirCacheFlusher is an optional interface for Fs
 type DirCacheFlusher interface {
 	// DirCacheFlush resets the directory cache - used in testing