Return Context Manager for a file-like (stream) object to store a diff.

def receive(self, diff, paths):
        """ Return Context Manager for a file-like (stream) object to store a diff. """
        path = self.selectReceivePath(paths)
        keyName = self._keyName(diff.toUUID, diff.fromUUID, path)

        if self._skipDryRun(logger)("receive %s in %s", keyName, self):
            return None

        progress = _BotoProgress(diff.size) if self.showProgress is True else None
        return _Uploader(self.bucket, keyName, progress)