c# Base64 in email attachment

Question

I know that i'm stuck in a silly problem...and now i am here with hope, that you can help me. Simple situation: I need to send email with attachment from database. I have done it by myself, but...i don't know why, but attachment in email what was send is incorrect. Preciously attachment contents code, what i get from my database.

My code:

static void IncomeMessage()
{
    SqlConnection conn = new SqlConnection("Data Source=xxx;Initial Catalog=xxx;User ID=xxx;Password=xxx");
    SqlCommand cmd = new SqlCommand("Here is my SQL SELECT", conn);
    SqlDataAdapter da = new SqlDataAdapter(cmd);
    DataTable dt = new DataTable();
    da.Fill(dt);

    foreach (DataRow dr in dt.Rows)
    {
        try
        {
            var AID = dr["ID"].ToString();
            var Ids = dr["MessageID"].ToString();
            var SuperOrganizationTitle = dr["SuperOrganizationTitle"].ToString();
            var Date = dr["Date"].ToString();
            var Title = dr["Title"].ToString();
            var Description = dr["Description"].ToString();
            var DBFile = dr["File"].ToString();
            var Filename = dr["FileName"].ToString();

            MailMessage oMail = new MailMessage("test@test.com", "guntisvindels@gmail.com", "New message with theme: " + Title, "Message Income: " + Date + " From " + SuperOrganizationTitle + ". Message Content: " + Description);

            DBFile = GetBase64(DBFile);

            var bytes = Encoding.ASCII.GetBytes(DBFile);
            MemoryStream strm = new MemoryStream(bytes);
            Attachment data = new Attachment(strm, Filename);
            ContentDisposition disposition = data.ContentDisposition;
            data.ContentId = Filename;
            data.ContentDisposition.Inline = true;
            oMail.Attachments.Add(data);

            SmtpClient oSmtp = new SmtpClient();
            SmtpClient oServer = new SmtpClient("test.test.com");

            oServer.Send(oMail);
        }
        catch (Exception ex)
        {
            //TraceAdd("Error=" + ex.Message.ToString());
        }
    }
}

For removing unnessessary data ( tags) from database File field i use this code

public static string GetBase64(string str)
{
    var index1 = str.IndexOf("<content>");
    index1 = index1 + "<content>".Length;
    var index2 = str.IndexOf("</content>");
    var kek = Slice(str, index1, index2);
    return kek;
}

public static string Slice(string source, int start, int end)
{
    if (end < 0)
    {
        end = source.Length + end;
    }
    int len = end - start;
    return source.Substring(start, len);
}

When launching my code I can send email to me, and I'll recieve it. But message content attachment with my Base64 code from database File field. Here is a question - Where I got wrong, and how can I recieve email with correct attachment that has been written into database. Thank you for your attention

P.S Attachment in database is written correctly, because K2 integration platform can correctly display it

Here is example what database contain in File column (DBFile)

<file><name>zinojums.html</name><content>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</content></file>

Answer 1

Right now the method you're using to create binary data from your string takes no account of the fact the string is base64-encoded specifically.

You need to replace

var bytes = Encoding.ASCII.GetBytes(DBFile);

with

var bytes = Convert.FromBase64String(DBFile);