copySourceIfUnmodifiedSince
Copies the object if it hasn't been modified since the specified time.
If both the x-amz-copy-source-if-match and x-amz-copy-source-if-unmodified-since headers are present in the request and evaluate as follows, Amazon S3 returns 200 OK and copies the data:
x-amz-copy-source-if-matchcondition evaluates to truex-amz-copy-source-if-unmodified-sincecondition evaluates to false