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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import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {
    CkMime mime = new CkMime();

    boolean success;
    success = mime.UnlockComponent("Anything for 30-day trial.");
    if (success == false) {
        System.out.println(mime.lastErrorText());
        return;
    }

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

    CkMime part2 = new CkMime();
    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:
    System.out.println(mime.getMime());

    //  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.get_NumParts();
    System.out.println("Num Parts = " + n);
    System.out.println("Body = " + mime.getBodyDecoded());

    //  The GetEntireBody retrieves the entire content after
    //  the header.  (Perhaps GetEntireBody should've been named
    //  GetEntireContent to make it less confusing...)
    System.out.println("---- EntireBody:");
    System.out.println(mime.getEntireBody());
    System.out.println("********");

    //  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;
    //  index 0 is the 1st part, index 1 is the 2nd part.
    part = mime.GetPart(1);
    System.out.println("Decoded Body:");
    System.out.println(part.getBodyDecoded());
    System.out.println("Encoded Body:");
    System.out.println(part.getBodyEncoded());


  }
}