Storage backend compatibility

Some storage backends do not support all the features of S3:

Atmos

• does not support multi-part upload

Azure

• limits container names to 63 characters and restricts character set to lowercase alphanumeric and dash
• does not support Expires header but does support Cache-Control header
• does not support object-level access control
• does not allow arbitrary list markers, partially emulated by mapping the last key to the opaque marker
• does not return ETag as an MD5 hash, instead returning opaque data

B2

• does not return ETag as an MD5 hash, instead returning SHA1 hash
• multipart upload requires a minimum part size of 100 MB and at least 2 parts

filesystem

• does not support object metadata on Mac OS X, see JDK-8030048

Google Cloud Storage

• does not allow arbitrary list markers, partially emulated by mapping the last key to the opaque marker
• does not return ETag as an MD5 hash, instead returning opaque data

OpenStack Swift

• does not support Content-Language headers
• does not support copying objects with the If-None-Match header
• does not support deleting user metadata keys, only replacing them
• does not support object-level access control
• exposes multipart upload parts as regular keys