Dart

MIME Body vs. Sub-Parts

See more MIME Examples

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.

Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // This example assumes the Chilkat API to have been previously unlocked.
  // See Global Unlock Sample for sample code.

  final mime = CkMime();

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

  final part2 = CkMime();
  part2.setBodyFromPlainText('This is part 2');
  part2.encoding = 'base64';

  mime.newMultipartMixed();
  mime.useMmDescription = false;
  mime.appendPart(part1);
  mime.appendPart(part2);

  // Show the MIME message:
  print(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)
  final n = mime.numParts;
  print('Num Parts = $n');
  print('Body = ${mime.getBodyDecoded()}');

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

  // 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.
  final partVar = CkMime();
  mime.partAt(1, partVar);

  print('Decoded Body:');
  print(partVar.getBodyDecoded());
  print('Encoded Body:');
  print(partVar.getBodyEncoded());
}