B4X

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.

B4X

Dim success As Boolean = False

'  This example assumes the Chilkat API to have been previously unlocked.
'  See Global Unlock Sample for sample code.

Dim mime As ChilkatMime
mime.Initialize

'  Create a multipart/mixed MIME message with two sub-parts.
'  We'll use the Base64 encoding for the 2nd sub-part.
Dim part1 As ChilkatMime
part1.Initialize
success = part1.SetBodyFromPlainText("This is part 1")

Dim part2 As ChilkatMime
part2.Initialize
success = part2.SetBodyFromPlainText("This is part 2")
part2.Encoding = "base64"

success = mime.NewMultipartMixed
mime.UseMmDescription = False
success = mime.AppendPart(part1)
success = mime.AppendPart(part2)

'  Show the MIME message:
Log(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)
Dim n As Int = mime.NumParts
Log("Num Parts = " & n)
Log("Body = " & mime.GetBodyDecoded)

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

'  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.
Dim part As ChilkatMime
part.Initialize
mime.PartAt(1, part)

Log("Decoded Body:")
Log(part.GetBodyDecoded)
Log("Encoded Body:")
Log(part.GetBodyEncoded)