added custom buffer size error handling

pkg/fs/metadata.go

@@ -273,6 +273,31 @@ func (mh *MetadataHandler) close() {
 	close(mh.fs.done)
 }
 
+type Error string
+
+func (e Error) Error() string {
+	return string(e)
+}
+
+const (
+	IOErr Error = "input/output error"
+)
+
+func MapError(err error) error {
+	if err == nil {
+		return nil
+	}
+	s := err.Error()
+	if strings.HasSuffix(s, IOErr.Error()) {
+		return IOErr
+	}
+	return nil
+}
+
+func IsIOErr(err error) bool {
+	return MapError(err) == IOErr
+}
+
 type Metadata struct {
 	mu     sync.RWMutex `json:"-"`
 	fs     *FS          `json:"-"`
@@ -293,6 +318,15 @@ func (md *Metadata) Delete() error {
 	return md.fs.RemoveDst(md.name)
 }
 
+func (md *Metadata) FullyCached() bool {
+	md.mu.RLock()
+	defer md.mu.RUnlock()
+	if len(md.Chunks) == 0 {
+		return false
+	}
+	return md.Size == md.Chunks[0][1]
+}
+
 func (md *Metadata) HasChunk(off int64, n int) bool {
 	md.mu.RLock()
 	defer md.mu.RUnlock()