C# http下载文件

public static string HttpWebDown(string url, string saveName, string cookiesStr = "", string tokenStr = "")
{
    try
    {
        System.Net.HttpWebRequest request = (System.Net.HttpWebRequest)System.Net.WebRequest.Create(url);
        request.Method = "GET";
        if (cookiesStr != null && cookiesStr.Length > 0)
        {
            request.Headers.Add("Cookie", cookiesStr);
        }
        //X-Access-Token: eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJleHAiOjE2NjYwOTc3NzMsInVzZXJuYW1lIjoiSklOU0dMWSJ9.DoAC6d6VTvylNBLYKKsxITxmOX-9pQ_trssOZU0S7Js
        if (tokenStr != null && tokenStr.Length > 0)
        {
            request.Headers.Add("X-Access-Token", tokenStr);
        }

        var webResponse = request.GetResponse();

        var response2 = (System.Net.HttpWebResponse)request.GetResponse();

        string fileExt = Path.GetExtension(webResponse.ResponseUri.LocalPath);  //.txt

        System.IO.Stream receiveStream = webResponse.GetResponseStream();

        using (FileStream writer = new FileStream($@"D:\downloads\{saveName}{fileExt}", FileMode.OpenOrCreate, FileAccess.Write))
        {
            byte[] buffer = new byte[1024];
            int c = 0;
            while ((c = receiveStream.Read(buffer, 0, buffer.Length)) > 0)
            {
                writer.Write(buffer, 0, c);
            }
        }

        receiveStream.Close();
        webResponse.Close();

        return "";

    }
    catch (Exception ex){ return ex.Message; }
}