Get a single datastream on a Fedora object; optionally, get the version
        as of a particular date time.

        :param pid: object pid
        :param dsID: datastream id
        :param asOfDateTime: optional datetime; ``must`` be a non-naive datetime
            so it can be converted to a date-time format Fedora can understand
        :param stream: return a streaming response (default: False); use
            is recommended for large datastreams
        :param head: return a HEAD request instead of GET (default: False)
        :param rqst_headers: request headers to be passed through to Fedora,
            such as http range requests

        :rtype: :class:`requests.models.Response`

def getDatastreamDissemination(self, pid, dsID, asOfDateTime=None, stream=False,
                head=False, rqst_headers=None):
        """Get a single datastream on a Fedora object; optionally, get the version
        as of a particular date time.

        :param pid: object pid
        :param dsID: datastream id
        :param asOfDateTime: optional datetime; ``must`` be a non-naive datetime
            so it can be converted to a date-time format Fedora can understand
        :param stream: return a streaming response (default: False); use
            is recommended for large datastreams
        :param head: return a HEAD request instead of GET (default: False)
        :param rqst_headers: request headers to be passed through to Fedora,
            such as http range requests

        :rtype: :class:`requests.models.Response`
        """
        # /objects/{pid}/datastreams/{dsID}/content ? [asOfDateTime] [download]
        http_args = {}
        if rqst_headers is None:
            rqst_headers = {}
        if asOfDateTime:
            http_args['asOfDateTime'] = datetime_to_fedoratime(asOfDateTime)
        url = 'objects/%(pid)s/datastreams/%(dsid)s/content' %  \
            {'pid': pid, 'dsid': dsID}
        if head:
            reqmethod = self.head
        else:
            reqmethod = self.get
        return reqmethod(url, params=http_args, stream=stream, headers=rqst_headers)