Emailing attachments with long names and accents

Question

We've had an issue with sending emails that contain attachments with long names and accents in them.

The size or type don't seem to affect the outcome (I tried with txt & pdf, 300kb and 3833kb in size)

After some searching around, I found this post http://social.msdn.microsoft.com/Forums/en-US/dotnetframeworkde/thread/b6c764f7-4697-4394-b45f-128a24306d55 that show how to get around the problem.

If my name is really long (see attachement2 variable name), it will work. But in the case of a slight shorter name (see attachment1 variable name), the name comes out as -=_iso-8859-1_Q_Example,_Example_and_other_

I think it has to do with the following line somehow in SplitEncodedAttachmentName encodedAttachmentName = encodedAttachmentName.Remove(encodedAttachmentName.Length - encodingtoken.Length, encodingtoken.Length);

Here's a watch of the vars attach1 - "=?ISO-8859-1?Q?Example=2c_Example_and_other_Repr=e9senta.txt?="

attach2 - "=?ISO-8859-1?Q?Example=2c_Example_and_other_Repr=e9sentant_Example_Examp?==?ISO-8859-1?Q?le_Example_Example_Example_Example2.txt?="

I can't seem to get the attachment1 to be sent properly..

(I did answer this question in the past - MailMessage Attachment filename with accents but I had a bug, refactored and came across this issue..)

Here is the smallest code example I could come up that causes the error.

class Program
{
    static void Main(string[] args)
    {
        Attachment attachment = new Attachment(@"c:\client\temp\Example,_Example_and_other_Représenta.pdf"); //3488kb
        Attachment attachment2 = new Attachment(@"c:\client\temp\Example,_Example_and_other_Représentant_Example_Example_Example_Example_Example_Example.pdf"); //3488kb

        Console.WriteLine(attachment.Name);

        MailMessage mm = new MailMessage();
         mm.From = new MailAddress("toemail");
         mm.To.Add("toemail");
        mm.Subject = "Yo";
        mm.Body = "hello";
        mm.Attachments.Add(CreateAttachment(attachment, attachment.Name)); // =_iso-8859-1_Q_Example,_Example_and_other_
        mm.Attachments.Add(CreateAttachment(attachment2, attachment2.Name));

        SmtpClient smtp = new SmtpClient("SmptServer");
        smtp.Send(mm);
    }

    /// <summary>
    /// This method fixes the name of the attachment to allow accents
    /// </summary>
    /// <remarks>Taken from http://social.msdn.microsoft.com/Forums/en-US/dotnetframeworkde/thread/b6c764f7-4697-4394-b45f-128a24306d55</remarks>
    public static Attachment CreateAttachment(Attachment attachmentFile, string displayName)
    {
        Attachment attachment = attachmentFile;
        attachment.TransferEncoding = TransferEncoding.Base64;

        string tranferEncodingMarker = "Q";
        string encodingMarker = "ISO-8859-1";
        int maxChunkLength = 76;

        attachment.NameEncoding = Encoding.GetEncoding(encodingMarker);

        string encodingtoken = String.Format("=?{0}?{1}?", encodingMarker, tranferEncodingMarker);
        string softbreak = "?=";
        string encodedAttachmentName = encodingtoken;
        encodedAttachmentName = HttpUtility.UrlEncode(displayName, Encoding.Default).Replace("+", " ").Replace("%", "=");

        encodedAttachmentName = SplitEncodedAttachmentName(encodingtoken, softbreak, maxChunkLength, encodedAttachmentName);
        attachment.Name = encodedAttachmentName;

        return attachment;
    }


    private static IEnumerable<string> SplitByLength(string stringToSplit, int length)
    {
        while (stringToSplit.Length > length)
        {
            yield return stringToSplit.Substring(0, length);
            stringToSplit = stringToSplit.Substring(length);
        }

        if (stringToSplit.Length > 0)
        {
            yield return stringToSplit;
        }
    }

    private static string SplitEncodedAttachmentName(string encodingtoken, string softbreak, int maxChunkLength, string encoded)
    {
        int splitLength = maxChunkLength - encodingtoken.Length - (softbreak.Length * 2);
        var parts = SplitByLength(encoded, splitLength);

        string encodedAttachmentName = encodingtoken;

        foreach (var part in parts)
        {
            encodedAttachmentName += part + softbreak + encodingtoken;
        }

        encodedAttachmentName = encodedAttachmentName.Remove(encodedAttachmentName.Length - encodingtoken.Length, encodingtoken.Length);

        return encodedAttachmentName;
    }
}

score 4 · Accepted Answer · answered May 18 '12 at 18:04

It turns out there's a bug report - https://connect.microsoft.com/VisualStudio/feedback/details/696372/filename-encoding-error-when-encoding-utf-8-and-encoded-name-exceeds-the-length-of-a-single-mime-header-line#details

and a kb article to fix the initial issue of long names with special characters. http://support.microsoft.com/kb/2402064

After installing the kb,

I changed

mm.Attachments.Add(CreateAttachment(attachment, attachment.Name)); mm.Attachments.Add(CreateAttachment(attachment2, attachment2.Name));

back to what is should be mm.Attachments.Add(attachment); mm.Attachments.Add(attachment2);

and everything worked..

Emailing attachments with long names and accents

1 Answers1