crypt: Implement Optional methods SetTier, GetTier - fixes #2895

This implements optional methods on Object
- ID
- SetTier
- GetTier

And declares that it will not implement MimeType for the FsCheck test.

backend/crypt/crypt.go

@@ -169,6 +169,8 @@ func NewFs(name, rpath string, m configmap.Mapper) (fs.Fs, error) {
 		WriteMimeType:           false,
 		BucketBased:             true,
 		CanHaveEmptyDirectories: true,
+		SetTier:                 true,
+		GetTier:                 true,
 	}).Fill(f).Mask(wrappedFs).WrapsFs(f, wrappedFs)
 
 	return f, err
@@ -839,6 +841,34 @@ func (o *ObjectInfo) Hash(hash hash.Type) (string, error) {
 	return "", nil
 }
 
+// ID returns the ID of the Object if known, or "" if not
+func (o *Object) ID() string {
+	do, ok := o.Object.(fs.IDer)
+	if !ok {
+		return ""
+	}
+	return do.ID()
+}
+
+// SetTier performs changing storage tier of the Object if
+// multiple storage classes supported
+func (o *Object) SetTier(tier string) error {
+	do, ok := o.Object.(fs.SetTierer)
+	if !ok {
+		return errors.New("crypt: underlying remote does not support SetTier")
+	}
+	return do.SetTier(tier)
+}
+
+// GetTier returns storage tier or class of the Object
+func (o *Object) GetTier() string {
+	do, ok := o.Object.(fs.GetTierer)
+	if !ok {
+		return ""
+	}
+	return do.GetTier()
+}
+
 // Check the interfaces are satisfied
 var (
 	_ fs.Fs              = (*Fs)(nil)
@@ -860,4 +890,7 @@ var (
 	_ fs.ObjectInfo      = (*ObjectInfo)(nil)
 	_ fs.Object          = (*Object)(nil)
 	_ fs.ObjectUnWrapper = (*Object)(nil)
+	_ fs.IDer            = (*Object)(nil)
+	_ fs.SetTierer       = (*Object)(nil)
+	_ fs.GetTierer       = (*Object)(nil)
 )