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.

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// Needs #include <CkMime.h>

    CkString strOut;

    CkMime mime;

    bool success;
    success = mime.UnlockComponent("Anything for 30-day trial.");
    if (success == false) {
        strOut.append(mime.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

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

    CkMime part2;
    part2.SetBodyFromPlainText("This is part 2");
    part2.put_Encoding("base64");

    mime.NewMultipartMixed();
    mime.put_UseMmDescription(false);
    mime.AppendPart(part1);
    mime.AppendPart(part2);

    //  Show the MIME message:
    strOut.append(mime.GetMime());
    strOut.append("\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)
    long n;
    n = mime.get_NumParts();
    strOut.append("Num Parts = ");
    strOut.appendInt(n);
    strOut.append("\r\n");
    strOut.append("Body = ");
    strOut.append(mime.GetBodyDecoded());
    strOut.append("\r\n");

    //  The GetEntireBody retrieves the entire content after
    //  the header.  (Perhaps GetEntireBody should've been named
    //  GetEntireContent to make it less confusing...)
    strOut.append("---- EntireBody:");
    strOut.append("\r\n");
    strOut.append(mime.GetEntireBody());
    strOut.append("\r\n");
    strOut.append("********");
    strOut.append("\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:
    CkMime *part = 0;
    //  index 0 is the 1st part, index 1 is the 2nd part.
    part = mime.GetPart(1);
    strOut.append("Decoded Body:");
    strOut.append("\r\n");
    strOut.append(part->GetBodyDecoded());
    strOut.append("\r\n");
    strOut.append("Encoded Body:");
    strOut.append("\r\n");
    strOut.append(part->GetBodyEncoded());
    strOut.append("\r\n");

    delete part;



    SetDlgItemText(IDC_EDIT1,strOut.getUnicode());