+ // Use CopyN to avoid allocating the 32KB buffer in io.Copy for bodies
+ // smaller than 32KB. Fall back to io.Copy if we fail to determine the size.
+ size, err := aws.SeekerLen(reader)
+ if err != nil {
+ io.Copy(hash, reader)
+ } else {
+ io.CopyN(hash, reader, size)
+ }
+
+ return hash.Sum(nil), nil