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

loMime = createobject("CkMime")

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

loPart2 = createobject("CkMime")
llSuccess = loPart2.SetBodyFromPlainText("This is part 2")
loPart2.Encoding = "base64"

llSuccess = loMime.NewMultipartMixed()
loMime.UseMmDescription = .F.
llSuccess = loMime.AppendPart(loPart1)
llSuccess = 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


release loMime
release loPart1
release loPart2