MIME Body vs. Sub-Parts

Download Chilkat MIME ActiveX

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.

LOCAL loMime
LOCAL lnSuccess
LOCAL loPart1
LOCAL loPart2
LOCAL n
LOCAL loPart

loMime = CreateObject('Chilkat.Mime')

lnSuccess = loMime.UnlockComponent("Anything for 30-day trial.")
IF (lnSuccess = 0) THEN
    =MESSAGEBOX(loMime.LastErrorText)
    QUIT
ENDIF

*  Create a multipart/mixed MIME message with two sub-parts.
*  We'll use the Base64 encoding for the 2nd sub-part.
loPart1 = CreateObject('Chilkat.Mime')
loPart1.SetBodyFromPlainText("This is part 1")

loPart2 = CreateObject('Chilkat.Mime')
loPart2.SetBodyFromPlainText("This is part 2")
loPart2.Encoding = "base64"

loMime.NewMultipartMixed()
loMime.UseMmDescription = 0
loMime.AppendPart(loPart1)
loMime.AppendPart(loPart2)

*  Show the MIME message:
? loMime.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 = loMime.NumParts
? "Num Parts = " + STR(n)
? "Body = " + loMime.GetBodyDecoded()

*  The GetEntireBody retrieves the entire content after
*  the header.  (Perhaps GetEntireBody should've been named
*  GetEntireContent to make it less confusing...)
? "---- EntireBody:"
? loMime.GetEntireBody()
? "********"

*  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.
loPart = loMime.GetPart(1)
? "Decoded Body:"
? loPart.GetBodyDecoded()
? "Encoded Body:"
? loPart.GetBodyEncoded()

RELEASE loPart