12 bytes is best performance for GCM, but for CTR.

32 bytes to select AES-256.

completeMultipartUpload - represents input fields for completing multipart upload.

completePart - completed part container.

ListObjectsInfo - container for list objects.

PartTooSmall - error if part size is less than 5MB.

completedParts - is a collection satisfying sort.Interface.