do not overwrite unchanged objects or re-delete #30
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When a bucket is restored to an earlier state of itself, only a few objects might actually have changed. Changed objects can be identified by comparing the etag of the desired version with the etag of the most recent version. If the etags agree, the object can be skipped. Because the most recent version of any object is always listed first in the response from list_object_versions, its etag is definitely known when handling the version to be restored. Added a test that checks that no new version is created when the object was not changed. Also running the existing test in a configuration that uses the same source and destination bucket without requiring another call of "s3-pit-restore --test". Because this is a frequent use case, it should be tested without special effort.
When a bucket is restored to an earlier state of itself, do not delete objects that are already deleted in their current state. Added a test that checks that no new delete marker is created when the object was not changed.
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When a bucket is restored to an earlier state of itself, only a few objects might actually have changed. Changed objects can be identified by comparing the etag of the desired version with the etag of the most recent version. If the etags agree, the object can be skipped. Because the most recent version of any object is always listed first in the response from list_object_versions, its etag is definitely known when handling the version to be restored.
Also, do not delete objects that are already deleted in their current state.
Added a test that checks that no new version is created when the object was not changed and that no second delete marker is written.
Also running the existing test in a configuration that uses the same source and destination bucket without requiring another call of "s3-pit-restore --test". Because this is a frequent use case, it should be tested without special effort.
This PR solves a similar, but not the same problem as PR #24. PR #24 can also detect objects that need not be updated when source and target bucket differ, but it needs a separate head_object call for each object. This PR addresses the case of restoring a single bucket to a previous state, only, but without a performance penalty.