无法从 HttpListenerRequest 读取 InputStream

我一直在创建从chrome扩展名接收文件名和下载链接的下载管理器。
在这种情况下，我决定使用javascript后台页面发送XMLHttpRequest到环回，并创建简单的服务器来接收消息，背景页面如下所示。

背景.js

function showMessageBox(info, tab) {
    var link = decodeURIComponent(info.linkUrl);
    var index = link.search(/[^/'''?]+'.'w{3,4}(?=(['?&].*$|$))/);
    var fileName = link.substring(index);
    alert("will download from " + link + " soon'n File name : " + fileName);
    SendMessage(fileName,link);
}
function SendMessage(fileName, link) {
    var xhr = new XMLHttpRequest();
    xhr.open("POST","http://localhost:6230", false);
    xhr.setRequestHeader("Content-Type", "application/json; charset=UTF-8");
    var JSONstring = JSON.stringify({ FileName: fileName, DownloadLink: link });
    xhr.send(JSONstring);
}

和服务器的一部分。

    private void StartReciever()
    {
        while (true)
        {
            var fileInfo = GetFileInfo();
            Execute.OnUIThread(() => WindowManager.ShowDialog(
                new NewDownloadViewModel(WindowManager, EventAggregator, fileInfo, Engine)));
        }
    }
    private FileInfo GetFileInfo()
    {
        using (var listener = new HttpListener())
        {
            listener.Prefixes.Add("http://localhost:6230/");
            listener.Start();
            var requestContext = listener.GetContext();
            /*var streamReader = new StreamReader(requestContext.Request.InputStream, requestContext.Request.ContentEncoding);
            string jsonString = streamReader.ReadToEnd();*/
            var stream = requestContext.Request.InputStream;
            byte[] buffer = new byte[10240];
            var readbyte = stream.Read(buffer, 0, 102400);
            string ss = Encoding.UTF8.GetString(buffer, 0, readbyte);
            // deserialize string to object
            return new FileInfo();
        }
    }

我想知道为什么流读取在发送消息时总是返回 0。