Let the caller's parameters take precedence in append mode #1373

Part of #1342 (item 2).

Decision

In append mode, the caller's parameters take precedence over the appended object's. Object-lock fields of the existing object are not forwarded.

Current state (29cc1d3, offline)

S3FileTarget.resolve updates the request with appended.to_api_repr() (s3.py:3017). When appending to an object with KMS encryption and object lock, the caller's ContentType, StorageClass, Metadata and ServerSideEncryption are replaced by the old object's. ObjectLockMode and ObjectLockRetainUntilDate are forwarded to the new object. docs/filesystem.md describes the append as keeping the old object's metadata.

Compatibility

Behavior change for callers who passed parameters to an append, and for object-lock settings (release note). The appended object's attributes stay the default when the caller gives none.