获取一个群的聊天记录

如何获取一个群的聊天记录
function chatRecord($ql = '', $cursor = '', $limit = 20) {
    $ql = ! empty ( $ql ) ? "ql=" . $ql : "order+by+timestamp+desc";
    $cursor = ! empty ( $cursor ) ? "&cursor=" . $cursor : '';
    $url="https://a1.easemob.com/dihon/l ... ot%3B . $ql . "&limit=" . $limit . $cursor;
    $access_token = getToken ();
    $header = $access_token;
    $result = postCurl ( $url, '', $header, $type = "GET " );
    return $result;
}
环信给的是好友的聊天记录,怎么获取一个群的聊天记录呢