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.

uses
    Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
    Dialogs, StdCtrls,
    CHILKATMIMELib_TLB,
    OleCtrls;

...

procedure TForm1.Button1Click(Sender: TObject);
var
mime: CHILKATMIMELib_TLB.IChilkatMime;
success: Integer;
part1: CHILKATMIMELib_TLB.IChilkatMime;
part2: CHILKATMIMELib_TLB.IChilkatMime;
n: Integer;
part: CHILKATMIMELib_TLB.IChilkatMime;

begin
mime := CoChilkatMime.Create();

success := mime.UnlockComponent('Anything for 30-day trial.');
if (success = 0) then
  begin
    ShowMessage(mime.LastErrorText);
    Exit;
  end;

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

part2 := CoChilkatMime.Create();
part2.SetBodyFromPlainText('This is part 2');
part2.Encoding := 'base64';

mime.NewMultipartMixed();
mime.UseMmDescription := 0;
mime.AppendPart(part1);
mime.AppendPart(part2);

//  Show the MIME message:
Memo1.Lines.Add(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)
n := mime.NumParts;
Memo1.Lines.Add('Num Parts = ' + IntToStr(n));
Memo1.Lines.Add('Body = ' + mime.GetBodyDecoded());

//  The GetEntireBody retrieves the entire content after
//  the header.  (Perhaps GetEntireBody should've been named
//  GetEntireContent to make it less confusing...)
Memo1.Lines.Add('---- EntireBody:');
Memo1.Lines.Add(mime.GetEntireBody());
Memo1.Lines.Add('********');

//  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:

//  index 0 is the 1st part, index 1 is the 2nd part.
part := mime.GetPart(1);
Memo1.Lines.Add('Decoded Body:');
Memo1.Lines.Add(part.GetBodyDecoded());
Memo1.Lines.Add('Encoded Body:');
Memo1.Lines.Add(part.GetBodyEncoded());


end;