Clients should be idempotent

See http://en.wikipedia.org/wiki/Idempotence.

This means that performing the same operation several times will result in the same result. Another of putting this is that is is only the expected outcome of a operation which is relevant, not how to get there.

The consequence is that:

• Put client looks at the ResponseCode, if it is a 'DUPLICATE_FILE_FAILURE' it should look at the returned checksum for the file (if present) and determine if the operation was a success or failure.
• Delete file operations are considered a success, even if the file doesn't exist.
• Replace file from file A to B is considered a success if 'EXISTING_CHECKSUM_FAILURE' is returned and the appended checksum is that of the replacement file (file B)