Asp.Net 通过 MemoryStream 失败下载电子邮件附件

Question

On server side I have a file containing an xml serialization of a standard System.Net.Mail.MailMessage which may contain attachments. I designed a form to allow users to download these attachments.

Attachment download is controlled by the following code:

private byte[] ReadFully(Stream input)
{
    byte[] _buffer = new byte[16 * 1024];
    
    using (MemoryStream _ms = new MemoryStream())
    {
        int _read;
        
        while ((_read = input.Read(_buffer, 0, _buffer.Length)) > 0)
        {
            _ms.Write(_buffer, 0, _read);
        }

        return _ms.ToArray();
    }
}


protected void bntViewAttachment_Click(object sender, EventArgs e)
{
    string _filename = Request.QueryString["file"];

    if (!string.IsNullOrWhiteSpace(_filename))
    {
        MailMessage _message = MailMessageSerializer.Create(Path.Combine(Path.GetFullPath(Path.Combine(Server.MapPath("~"), OUTBOUND_FOLDER)), _filename));

        try
        {

            int _selected = lbAttachments.SelectedIndex;

            if (_selected != -1)
            {
                Attachment _attachment = _message.Attachments[_selected];

                byte[] _data = ReadFully(_attachment.ContentStream);

                if (_data.Length > 0)
                {
                    Response.Clear();
                    Response.ContentType = MimeMapping.GetMimeMapping(_attachment.Name);
                    Response.AddHeader("Content-Disposition", string.Format("attachment;  filename={0}", _attachment.Name));
                    Response.BinaryWrite(_data);
                    Response.End();
                }
                else 
                {
                    lblStatus.Text = "Attachment empty";
                }
            }
        }
        catch (Exception ex)
        {
            lblStatus.Text = "Exception : " + ex.Message;
        }
    }
}

The email message file is provided by Request.QueryString["file"] of course this's not the safest way to operate but right now I have a bigger problem since the download doesn't work at all.. since _data.Length == 0 all the time. lbAttachments is the ListBox showing on the form attachments found inside mail message.

I can attach an example message xml with a single attachment file here .

I'm pretty sure about almost any line of code since I used them in many other cases but for some reason it does not here.

Where's the error?

Answer 1

For some reason the position on the ContentStream must be reset on to its origin.

Adding

input.Seek(0, SeekOrigin.Begin);

on top of

private byte[] ReadFully(Stream input)

Will fix it.

Now the problem is probably the encoding of the stream wrote on the client. At a first glance looks like the exact attachment data that's contained inside the original mail xml file (and thus Base64 or something like that).