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C# attaching a zip file inside a MIME Soap File

Posted on 2011-03-17
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Last Modified: 2013-11-18
I have an issue that is just puzzling me.  I need to attach a zip file in a MIME Soap file.  It will be uploaded using a standard browser upload tool.  I'm just not figuring this one out.

I've attached what I need to accomplish.  I know how to create the soap xml it's not bad but how do i add the MIME parts and the zip file.

Thanks so much.
--MIMEBoundary
Content-Type: application/octet-steam
Content-Transfer-Encoding: Binary
Content-Location: SubmissionZip
... (attachment ZIP file containing submissions goes here)
--MIMEBoundary--

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Question by:coreb
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Expert Comment

by:Todd Gerbert
ID: 35165532
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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Author Comment

by:coreb
ID: 35166217
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
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LVL 33

Expert Comment

by:Todd Gerbert
ID: 35166486
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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Author Comment

by:coreb
ID: 35166628
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.
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Accepted Solution

by:
Todd Gerbert earned 500 total points
ID: 35166768
The method in my example above uses binary encoding, so the bytes of the zip file are just stuck as they are into the middle of the MIME stuff; without encoding of some sort (i.e. Base64) there's no way to represent this data, except as a series of bytes.  Therefore that method just returns a byte[] array.  You can do whatever you want with it from there - e.g. File.WriteAllBytes(CreateZipMimeMessage("C:\\test.zip"")); to write it to a file.

You won't be able to print it, show it or put it in an XML document though, because it contains binary data that can't be represented as text.


This version below is basically the same thing, except uses base64 encoding.  This method returns a string, so you can save it to a text file, send it to a printer, show it in a MessageBox, etc.
static string 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 mimeMessage = new StringBuilder();

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

	mimeMessage.AppendLine("Content-Type: application/octet-stream");
	mimeMessage.AppendLine("Content-Location: SubmissionZip");
	mimeMessage.AppendLine("Content-Transfer-Encoding: base64");
	mimeMessage.AppendFormat("Content-Disposition: attachment; filename=\"{0}\"\r\n\r\n", Path.GetFileName(zipFile));

	byte[] zipFileBytes = File.ReadAllBytes(zipFile);
	string zipFileAsBase64 = Convert.ToBase64String(zipFileBytes);
	mimeMessage.AppendFormat("{0}\r\n--{1}--\r\n", zipFileAsBase64, boundary);

	return mimeMessage.ToString();
}

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Author Closing Comment

by:coreb
ID: 35167793
Thanks so much for all your help.  You helped me through this.
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