Add reader option to local content reader at

Allows optimized copying from a local content file into another file.

Signed-off-by: Derek McGowan <derek@mcg.dev>

content/helpers.go

@@ -37,10 +37,16 @@ var bufPool = sync.Pool{
 	},
 }
 
+type reader interface {
+	Reader() io.Reader
+}
+
 // NewReader returns a io.Reader from a ReaderAt
 func NewReader(ra ReaderAt) io.Reader {
-	rd := io.NewSectionReader(ra, 0, ra.Size())
-	return rd
+	if rd, ok := ra.(reader); ok {
+		return rd.Reader()
+	}
+	return io.NewSectionReader(ra, 0, ra.Size())
 }
 
 // ReadBlob retrieves the entire contents of the blob from the provider.