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.

<?php

$mime = new COM("Chilkat.Mime");

$success = $mime->UnlockComponent('Anything for 30-day trial.');
if ($success == false) {
    print $mime->lastErrorText() . "\n";
    exit;
}

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

$part2 = new COM("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:
print $mime->getMime() . "\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)
$n = $mime->NumParts;
print 'Num Parts = ' . $n . "\n";
print 'Body = ' . $mime->getBodyDecoded() . "\n";

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

//  index 0 is the 1st part, index 1 is the 2nd part.
// part is a Chilkat.Mime
$part = $mime->GetPart(1);
print 'Decoded Body:' . "\n";
print $part->getBodyDecoded() . "\n";
print 'Encoded Body:' . "\n";
print $part->getBodyEncoded() . "\n";


?>