MIME Body vs. Sub-Parts

Explains the difference between sub-parts and body.

MIME documents (i.e. messages) can have a nested structure. The simplest MIME message contains a header followed by content (possibly encoded). The header is delimited from the content by two consecutive CRLF's.

A MIME message may be multipart. If so, then the Content-Type header field indicates "multipart" and the content the follows the header is itself a MIME message, which may also be multipart, etc. You can see how MIME messages effectively have a tree structure. The non-leaf nodes have Content-Types that are "multipart/" and the leaf nodes have non-multipart Content-Types.

The Chilkat MIME component/library uses two terms that need to be understood in order to effectively use the API. These are "body" and "sub-part". A multipart node has 1 or more sub-parts, but its body is empty. A leaf node (i.e. non-multipart node) has no sub-parts, but the body is (usually) non-empty.

This example creates a multipart MIME message and shows the results of getting the sub-parts and body of each node.

Download: Chilkat .NET Assemblies

Chilkat.Mime mime = new Chilkat.Mime();

bool success;
success = mime.UnlockComponent("Anything for 30-day trial.");
if (success == false) {
    MessageBox.Show(mime.LastErrorText);
    return;
}

//  Create a multipart/mixed MIME message with two sub-parts.
//  We'll use the Base64 encoding for the 2nd sub-part.
Chilkat.Mime part1 = new Chilkat.Mime();
part1.SetBodyFromPlainText("This is part 1");

Chilkat.Mime part2 = new Chilkat.Mime();
part2.SetBodyFromPlainText("This is part 2");
part2.Encoding = "base64";

mime.NewMultipartMixed();
mime.UseMmDescription = false;
mime.AppendPart(part1);
mime.AppendPart(part2);

//  Show the MIME message:
textBox1.Text += mime.GetMime() + "\r\n";

//  Here's the MIME:
//  Content-Type: multipart/mixed;
//  	boundary="------------040605030407000302060008"
// 
//  --------------040605030407000302060008
//  Content-Type: text/plain;
//  	 charset="us-ascii"
//  Content-Transfer-Encoding: 7bit
// 
//  This is part 1
//  --------------040605030407000302060008
//  Content-Type: text/plain;
//  	 charset="us-ascii"
//  Content-Transfer-Encoding: base64
// 
//  VGhpcyBpcyBwYXJ0IDI=
// 
//  --------------040605030407000302060008--

//  If we examine the root node of the MIME message,
//  we see that it has 2 sub-parts and the body is empty (as expected)
int n;
n = mime.NumParts;
textBox1.Text += "Num Parts = " + Convert.ToString(n) + "\r\n";
textBox1.Text += "Body = " + mime.GetBodyDecoded() + "\r\n";

//  The GetEntireBody retrieves the entire content after
//  the header.  (Perhaps GetEntireBody should've been named
//  GetEntireContent to make it less confusing...)
textBox1.Text += "---- EntireBody:" + "\r\n";
textBox1.Text += mime.GetEntireBody() + "\r\n";
textBox1.Text += "********" + "\r\n";

//  Now examine the 2nd sub-part.  It has a body encoded
//  using base64.  Get the contents of the body in both
//  decoded and encoded forms:
Chilkat.Mime part = null;
//  index 0 is the 1st part, index 1 is the 2nd part.
part = mime.GetPart(1);
textBox1.Text += "Decoded Body:" + "\r\n";
textBox1.Text += part.GetBodyDecoded() + "\r\n";
textBox1.Text += "Encoded Body:" + "\r\n";
textBox1.Text += part.GetBodyEncoded() + "\r\n";