(VB.NET UWP/WinRT) 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.

Chilkat Universal Windows Platform (UWP) / WinRT Downloads Chilkat for the Universal Windows Platform (UWP)

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

Dim mime As New Chilkat.Mime

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

Dim part2 As New Chilkat.Mime
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:
Debug.WriteLine(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 Integer = mime.NumParts
Debug.WriteLine("Num Parts = " & n)
Debug.WriteLine("Body = " & mime.GetBodyDecoded())

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

' 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:
Dim part As Chilkat.Mime
' index 0 is the 1st part, index 1 is the 2nd part.
part = mime.GetPart(1)
Debug.WriteLine("Decoded Body:")
Debug.WriteLine(part.GetBodyDecoded())
Debug.WriteLine("Encoded Body:")
Debug.WriteLine(part.GetBodyEncoded())