Object versioning in swift is implemented by setting a flag on the container
to tell swift to version all objects in the container. The flag is the
``X-Versions-Location`` header on the container, and its value is the
container where the versions are stored.
When data is ``PUT`` into a versioned container (a container with the
versioning flag turned on), the existing data in the file is redirected to a
new object and the data in the ``PUT`` request is saved as the data for the
versioned object. The new object name (for the previous version) is
``<versions_container>/<object_name>/<timestamp>``, where the timestamp is
generated by converting the ``Last-Modified`` header value of the current
version to a unix timestamp.
A ``GET`` to a versioned object will return the current version of the object
without having to do any request redirects or metadata lookups.
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