Attaching a file to an iCalendar

Question

I have iCalendar meeting requests sending correctly via SMTP (using the code below), but when I attempt to attach a file, the file does not appear as part of the iCalendar. When saving out the .ics after opening it in outlook, the whole file data has been stripped out.

Here's the code I'm using:

System.Net.Mail.MailMessage msg = new System.Net.Mail.MailMessage();
msg.From = new System.Net.Mail.MailAddress("test1@test.com", "test1");
msg.To.Add(new System.Net.Mail.MailAddress("test2@test.com", "test2"));
msg.Subject = "Subject1";
msg.Body = "Body line 1\r\nBody line 2\r\nBody line 3";

System.Net.Mime.ContentType ct = new System.Net.Mime.ContentType("text/calendar");
ct.Parameters.Add("method", "REQUEST");
ct.Parameters.Add("name", "meeting.ics");

System.Text.StringBuilder sb = new System.Text.StringBuilder();
sb.AppendLine("BEGIN:VCALENDAR");

sb.AppendLine("PRODID:-/Microsoft Corporation//Outlook 15.0 MIMEDIR//EN");
sb.AppendLine("VERSION:2.0");
sb.AppendLine("METHOD:REQUEST");
sb.AppendLine("X-MS-OLK-FORCEINSPECTOROPEN:TRUE");

sb.AppendLine("BEGIN:VEVENT");

string file = "D:\\LoadedDate.xlsx";
string filename = Path.GetFileName(file);

sb.Append("ATTACH;ENCODING=BASE64;VALUE=BINARY;X-FILENAME=");
sb.Append(filename).Append(":").AppendLine(Convert.ToBase64String(File.ReadAllBytes(file), Base64FormattingOptions.InsertLineBreaks));

foreach (System.Net.Mail.MailAddress to in msg.To)
{
    sb.AppendLine(String.Format("ATTENDEE;CN=\"{0}\";RSVP=TRUE:mailto:{1}", String.IsNullOrEmpty(to.DisplayName) ? to.Address : to.DisplayName, to.Address));
}
sb.AppendLine("CLASS:PUBLIC");
sb.Append("CREATED:").AppendLine(DateTime.Now.ToUniversalTime().ToString("yyyyMMdd\\THHmmss\\Z"));
sb.Append("DESCRIPTION:").Append(msg.Body.Replace("\r\n", "\\n")).Append("\\n <<").Append(filename).AppendLine(">> \\n");

        string dt = DateTime.Now.AddHours(1).ToUniversalTime().ToString("yyyyMMdd\\THHmmss\\Z");
        sb.AppendLine("DTSTART:" + dt);
        sb.AppendLine("DTSTAMP:" + dt);
        sb.AppendLine("DTEND:" + DateTime.Now.AddHours(5).ToUniversalTime().ToString("yyyyMMdd\\THHmmss\\Z"));
        sb.AppendLine("LAST-MODIFIED:");
        sb.Append("LOCATION:").AppendLine("Location1");
        sb.AppendLine(String.Format("ORGANIZER;CN=\"{0}\":mailto:{0}", msg.From.Address));
        sb.AppendLine("PRIORITY:5");
        sb.AppendLine("SEQUENCE:0");
        sb.Append("SUMMARY;LANGUAGE=en-gb:").AppendLine(msg.Subject);
        sb.AppendLine("TRANSP:OPAQUE");

        // UID should be unique.
        sb.Append("UID:").AppendLine(Guid.NewGuid().ToString());
        sb.Append("X-ALT-DESC;FMTTYPE=text/html:<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 3.2//EN\">\\n");
        sb.Append("<HTML>\\n").Append("<HEAD>\\n").Append("<META HTTP-EQUIV=\"Content-Type\" CONTENT=\"text/html\\; charset=iso-8859-1\">\\n").Append("<META NAME=\"Generator\" CONTENT=\"MS Exchange Server version 14.03.0162.000\">\\n");
        sb.Append("<TITLE>").Append(msg.Subject).Append("</TITLE>\\n");
        sb.Append("</HEAD>\\n").Append("<BODY>\\n").Append("<!--Converted from text/rtf format -->\\n\\n");
        sb.Append("<P DIR=LTR><SPAN LANG=\"en-gb\"><FONT FACE=\"Calibri\">").Append(msg.Body.Replace("\r\n", "</FONT></SPAN></P>\\n\\n<P DIR=LTR><SPAN LANG=\"en-gb\"><FONT FACE=\"Calibri\">")).Append("</FONT></SPAN></P>\\n\\n");
        sb.Append("<P DIR=LTR><SPAN LANG=\"en-gb\"><FONT FACE=\"Arial\" SIZE=2 COLOR=\"#000000\"> &lt\\;&lt\\;").Append(filename).Append("&gt\\;&gt\\; </FONT></SPAN></P>\\n\\n");
        sb.Append("</BODY>\\n").AppendLine("</HTML>");

        sb.AppendLine("X-MICROSOFT-CDO-BUSYSTATUS:BUSY");
        sb.AppendLine("X-MICROSOFT-CDO-IMPORTANCE:1");
        sb.AppendLine("X-MICROSOFT-DISALLOW-COUNTER:FALSE");
        sb.AppendLine("X-MS-OLK-AUTOFILLLOCATION:FALSE");
        sb.AppendLine("X-MS-OLK-AUTOSTARTCHECK:FALSE");
        sb.AppendLine("X-MS-OLK-CONFTYPE:0");
        sb.AppendFormat("X-MS-OLK-SENDER;CN=\"{0}\":mailto:{0}", msg.From.Address).AppendLine();

        sb.AppendLine("STATUS:TENTATIVE");
        sb.AppendLine("BEGIN:VALARM");
        sb.AppendLine("TRIGGER:-PT15M");
        sb.AppendLine("ACTION:DISPLAY");
        sb.AppendLine("DESCRIPTION:Reminder");
        sb.AppendLine("END:VALARM");
        sb.AppendLine("END:VEVENT");

        sb.AppendLine("END:VCALENDAR");

        System.Net.Mail.AlternateView av = System.Net.Mail.AlternateView.CreateAlternateViewFromString(sb.ToString(), ct);

        msg.AlternateViews.Add(av);

        System.Net.Mail.SmtpClient client = new System.Net.Mail.SmtpClient("mailserver");
        client.Send(msg);

I've had a look at the RFC for iCalendars (https://www.rfc-editor.org/rfc/rfc5545), and I think I've done everything according to what the spec says. I'm guessing that there is either a problem with the way the file is read in (the Convert.ToBase64String bit), or I'm missing something with the alternate view (I've seen other people adding multiple views).

Things I have tried:

Replacing the Convert.ToBase64String(File.ReadAllBytes(file), Base64FormattingOptions.InsertLineBreaks) with Convert.ToBase64String(File.ReadAllBytes(file), Base64FormattingOptions.None).
Using System.Text.Encoding to convert the file to BASE64 (without success).
Attaching files to the email directly (using the MailMessage.Attachments), but that just makes the email appear as a normal email.

I've also had a look at the DDay.iCal project on sourceforge (http://sourceforge.net/projects/dday-ical/), but I couldn't figure out how that worked when it came to attaching a file.

One requirement I have for this is that the file has to be embedded / attached to the email, I cannot add it as a URI unfortunately.

Can anyone help?

Update: Following arnaudq's advice, I have implemented wrapping the lines at 75 characters as mentioned in the RFC. The resulting MIME message looks like the following:

BEGIN:VCALENDAR
PRODID:-//Microsoft Corporation//Outlook 15.0 MIMEDIR//EN
VERSION:2.0
METHOD:REQUEST
X-MS-OLK-FORCEINSPECTOROPEN:TRUE
BEGIN:VEVENT
ATTACH;ENCODING=BASE64;VALUE=BINARY;X-FILENAME=test.txt:U0ZMb2dObwlTRkxvYWR
 lZERhdGUNCjkxNzY3NC8xCTI3LzExLzIwMTIgMTg6MzANCjkxMjIwNS8xCTI3LzExLzIwMTIgM
 Tg6MzANCjkxMjI0Ni8xCTI3LzExLzIwMTIgMTg6MzANCjkxMjI1Mi8xCTI3LzExLzIwMTIgMTg
 6MzANCjkxMjQyMS8xCTI3LzExLzIwMTIgMTg6MzANCjkxMjQyMi8xCTI3LzExLzIwMTIgMTg6M
 zANCjkxNTMyMS8xCTI3LzExLzIwMTIgMTg6MzANCjkxNTQzNS8xCTI3LzExLzIwMTIgMTg6MzA
 NCjkxNTU5OS8xCTI3LzExLzIwMTIgMTg6MzANCjkxNjc3NC8xCTI3LzExLzIwMTIgMTg6MzANC
 jkxNjk1OS8xCTI3LzExLzIwMTIgMTg6MzANCjkxNjk2MC8xCTI3LzExLzIwMTIgMTg6MzANCjk
 xNzM2Ny8xCTI3LzExLzIwMTIgMTg6MzANCjkxNzQzNC8xCTI3LzExLzIwMTIgMTg6MzANCjkxN
 DczMS8xCTI3LzExLzIwMTIgMTg6MzANCjkxNDczMi8xCTI3LzExLzIwMTIgMTg6MzANCjkxNDc
 0My8xCTI3LzExLzIwMTIgMTg6MzANCjkxNDc0NC8xCTI3LzExLzIwMTIgMTg6MzANCjkxNDc0N
 S8xCTI3LzExLzIwMTIgMTg6MzANCjkxNDc0Ni8xCTI3LzExLzIwMTIgMTg6MzANCjkxNDc2MS8
 xCTI3LzExLzIwMTIgMTg6MzANCjkxNDc2Mi8xCTI3LzExLzIwMTIgMTg6MzANCjkxNDc2My8xC
 TI3LzExLzIwMTIgMTg6MzANCjkxNTYzNS8xCTI3LzExLzIwMTIgMTg6MzANCjkxNTYzOC8xCTI
 3LzExLzIwMTIgMTg6MzANCjkxNTY0MC8xCTI3LzExLzIwMTIgMTg6MzANCjkxNTY0MS8xCTI3L
 zExLzIwMTIgMTg6MzANCjkxNTY1OS8xCTI3LzExLzIwMTIgMTg6MzANCjkxNTc3Ni8xCTI3LzE
 xLzIwMTIgMTg6MzANCjkxNTc3Ny8xCTI3LzExLzIwMTIgMTg6MzANCjkxNTc3OC8xCTI3LzExL
 zIwMTIgMTg6MzANCg==
ATTENDEE;CN="Test 1";RSVP=TRUE:mailto:test1@test.com
CLASS:PUBLIC
CREATED:20150318T095735Z
DESCRIPTION:Body line 1
 Body line 2
 Body line 3
 <<test.txt>> 
DTSTART:20150318T105735Z
DTSTAMP:20150318T105735Z
DTEND:20150318T145735Z
LAST-MODIFIED:
LOCATION:Location1
ORGANIZER;CN="test2@test.com":mailto:test2@test.com
PRIORITY:5
SEQUENCE:0
SUMMARY;LANGUAGE=en-gb:Subject1
TRANSP:OPAQUE
UID:40306717-c29a-42d1-b03e-0240a93c2ea2
X-ALT-DESC;FMTTYPE=text/html:<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//E
 N"><HTML><HEAD><META HTTP-EQUIV="Content-Type" CONTENT="text/html\; charse
 t=iso-8859-1"><META NAME="Generator" CONTENT="MS Exchange Server version 1
 4.03.0162.000"><TITLE>Subject1</TITLE></HEAD><BODY><!--Converted from text
 /rtf format --><P DIR=LTR><SPAN LANG="en-gb"><FONT FACE="Calibri">Body lin
 e 1</FONT></SPAN></P><P DIR=LTR><SPAN LANG="en-gb"><FONT FACE="Calibri"></
 FONT></SPAN></P>Body line 2</FONT></SPAN></P><P DIR=LTR><SPAN LANG="en-gb"
 ><FONT FACE="Calibri"></FONT></SPAN></P>Body line 3<P DIR=LTR><SPAN LANG="
 en-gb"><FONT FACE="Arial" SIZE=2 COLOR="#000000"> &lt\;&lt\;test.txt&gt\;&
 gt\; </FONT></SPAN></P></BODY></HTML>
X-MICROSOFT-CDO-BUSYSTATUS:BUSY
X-MICROSOFT-CDO-IMPORTANCE:1
X-MICROSOFT-DISALLOW-COUNTER:FALSE
X-MS-OLK-AUTOFILLLOCATION:FALSE
X-MS-OLK-AUTOSTARTCHECK:FALSE
X-MS-OLK-CONFTYPE:0
STATUS:TENTATIVE
BEGIN:VALARM
TRIGGER:-PT15M
ACTION:DISPLAY
DESCRIPTION:Reminder
END:VALARM
END:VEVENT
END:VCALENDAR

Unfortunately, this still doesn't work and the file (in this case a simple plain text file) does not come through with the calendar entry in Outlook.

What's really interesting is that saving the above MIME message to a file manually and renaming to a .ics then opening it does display the attached file correctly. This makes me think that there is something wrong with the way I'm sending the message, instead of the iCalendar markup.

Any ideas what is wrong?

Unfortunately not. I gave up in the end and just send a second email with the files attached. — Paul F, Jan 04 '16 at 09:23

score 2 · Answer 1 · answered Apr 16 '15 at 10:29

@paul, I made the following changes and its working fine for me. I need to verify this fix on all email clients. I tested on MS Outlook 2013, ios, MS Outlook 2010 and its working fine.

MailMessage msg = new MailMessage();
AlternateView alternate = AlternateView.CreateAlternateViewFromString(body, null, "text/html");
Stream stream = new MemoryStream(attachment.Bytes);// Bytes of file
LinkedResource resource = new LinkedResource(stream);                                                               
resource.ContentId = attachment.Name.Replace(".", "") + DateTime.Now.Ticks.ToString();
resource.ContentType.Name = attachment.Name;//Name of file              
resource.TransferEncoding = System.Net.Mime.TransferEncoding.Base64;                               
alternate.LinkedResources.Add(resource);
msg.AlternateViews.Add(alternate);

I am not modifying .ics file to add ATTACH property(ATTACH;ENCODING=BASE64;VALUE=BINARY;X-FILENAME=)

attachment.Bytes ？ Could you tell me the detailed method? thanks — TTCM, Jan 07 '21 at 07:17

score 2 · Answer 2 · edited May 08 '15 at 12:31

String iCall = CreateICal();


            System.Net.Mime.ContentType ct = new System.Net.Mime.ContentType("text/calendar");
            ct.Parameters.Add("charset", @"utf-8");
            ct.Parameters.Add("method", "REQUEST");
            AlternateView avCal = AlternateView.CreateAlternateViewFromString(iCall, ct);



            System.Net.Mime.ContentType cthtml = new System.Net.Mime.ContentType("text/html");
            cthtml.Parameters.Add("charset", @"utf-8");
            AlternateView avHtml = AlternateView.CreateAlternateViewFromString(this.mHTML, cthtml);

            mail.AlternateViews.Add(avHtml);
            mail.AlternateViews.Add(avCal);


            foreach (LinkedResource resource in arrattach)
            {
                avHtml.LinkedResources.Add(resource);
            }

            client.Send(mail);

score 1 · Answer 3 · edited Oct 07 '21 at 10:58

1

First, while you do make use of line breaks, it looks like you are not using the kind of line breaks that iCalendar expects. In short, each line after the first one should be prefixed with a space character and the lines should be less than 75 octets in length. See https://www.rfc-editor.org/rfc/rfc5545#section-3.1

(In general, for this type of interop issue, showing us the end result MIME message is more useful than the code that was used to generate it)

Then, as far as I remember, Outlook prefers attachments to be transmitted in a multipart/related containing the iCalendar stream and the attachment in different mime parts. See https://www.rfc-editor.org/rfc/rfc6047#section-4.6 for an example.

Finally, you might want to try sending an invitation with attachment from Outlook and see how the MIME message that it does send is structured.

edited Oct 07 '21 at 10:58

Community

1
1

answered Mar 18 '15 at 07:57

Arnaud Quillaud

4,420
1
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8

I've updated the question now - it seems that wrapping has fixed the MIME message (creating and opening the .ics manually works - the attached file is displayed), but it is still lost when sending the mail message through Smtp. Am I missing something with the AlternateView(s) needed? – Paul F Mar 18 '15 at 10:11
Well, this probably means that the client does not like inline icalendar ATTACHMENT property. Did you have a look at RFC6047 or tried to look at what Outlook sends when sending an invitation with attachment ? – Arnaud Quillaud Mar 18 '15 at 18:11
I looked through RFC6047, my inline attachment seems to match it correctly, but I couldn't figure out how to send a multipart email using the cid property through .NET using SMTP. I've tried saving a .ics form Outlook, and mine is in the same format (near enough). If I save my .ics to the file system instead of emailing it, then open it, the file opens in Outlook with the embedded attachment. I think either the way I am sending the email, or the Exchange server, or Outlook on the client-side must be removing the attached file, but I don't know how to find out which, or why it is happening. – Paul F Mar 20 '15 at 09:00
@PaulF did you figure this out? – Todd Horst Apr 10 '15 at 20:01
Unfortunately not. I gave up in the end and I instead send the attached files in a separate email to the iCalendar email. – Paul F Apr 13 '15 at 10:03

Attaching a file to an iCalendar

3 Answers3

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