C# attaching a zip file inside a MIME Soap File

Not particularly familiar with MIME or SOAP, so I probably shouldn't be chiming in here, but it's been nearly a day and no one else has responded yet so I'll give it a shot. ;)

You're probably going to want to change your transfer encoding to base64, and then use Convert.ToBase64String() to convert the bytes of your zip file to a base64-encoded string.

Then your message should look like:

MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="MIMEBoundary"

This section is ignored by mail clients, dunno about your SOAP stuff
--MIMEBoundary
Content-Type: text/plain

Hello there.
--MIMEBoundary
Content-Type: application/octet-stream
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="file.zip"

PGh0bWw+CiAgPGhlYWQ+CiAgPC9oZWFkPgogIDxib2R5PgogICAgPHA+VGhpcyBpcyB0aGUg
Ym9keSBvZiB0aGUgbWVzc2FnZS48L3A+CiAgPC9ib2R5Pgo8L2h0bWw+Cg==
--MIMEBoundary--

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Thanks so much for the reply.  It makes perfect sense.  Only issue is that my documentation states.  

The Content-Transfer-Encoding header for the MIME part that contains the ZIP file must be:
Content-Transfer-Encoding: Binary

Well, like I said - not really an expert on the subject...my experience with MIME is as it pertains to SMTP & Internet mail, and generally mail servers will only accept text data (though there is a BINARY MIME extension that introduces a BDAT verb to replace the DATA verb) - hence the need to Base64-encode binary data into a string of ASCII text.

I was under the impression SOAP stuff was also strictly a text-based service - don't think you can have raw bytes in the middle of an XML document without some kind of encoding.  Maybe it means to base64 encode the binary data and use the Binary header?

Though, to implement binary encoding is easy - it just means attach the bytes as they are, un-changed.  So, in C#:

byte[] mimeMessage = CreateZipMimeMessage("C:\\test.zip");
static byte[] CreateZipMimeMessage(string zipFile)
{
	// It's your responsability to make sure the boundary string
	// is unique, and doesn't appear anywhere in the data itself
	string boundary = "MIMEBoundary";

	StringBuilder startText = new StringBuilder();
	StringBuilder endText = new StringBuilder();

	startText.AppendLine("MIME-Version: 1.0");
	startText.AppendFormat("Content-Type: multipart/mixed; boundary=\"{0}\"\r\n\r\n", boundary);
	startText.AppendLine("This is a BINARY MIME compliant message.");
	startText.AppendFormat("--{0}", boundary);

	startText.AppendLine("Content-Type: application/octet-stream");
	startText.AppendLine("Content-Location: SubmissionZip");
	startText.AppendLine("Content-Transfer-Encoding: binary");
	startText.AppendFormat("Content-Disposition: attachment; filename=\"{0}\"\r\n\r\n", Path.GetFileName(zipFile));

	byte[] zipBytes = File.ReadAllBytes(zipFile);

	endText.AppendFormat("--{0}--\r\n", boundary);

	List<byte> returnValue = new List<byte>();

	returnValue.AddRange(Encoding.ASCII.GetBytes(startText.ToString()));
	returnValue.AddRange(zipBytes);
	returnValue.AddRange(Encoding.ASCII.GetBytes(endText.ToString()));

	return returnValue.ToArray();
}

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Would give you:

MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="MIMEBoundary"

This is a BINARY MIME compliant message.
--MIMEBoundary
Content-Type: application/octet-stream
Content-Location: SubmissionZip
Content-Transfer-Encoding: binary
Content-Disposition: attachment; filename="test.zip"

<non-text binary data>
--MIMEBoundary--

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You have been so very helpful.  One last question how do I print out the mimeMessage or save it to a file?  This whole area is new and there doesn't seem to much I've found searching.

Thanks again for your help.

Thanks so much for all your help.  You helped me through this.