(PowerShell) 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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[Reflection.Assembly]::LoadFile("C:\myAssemblies\ChilkatDotNet47.dll")

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

$mime = New-Object Chilkat.Mime

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

$part2 = New-Object 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:
$($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)
$n = $mime.NumParts
$("Num Parts = " + $n)
$("Body = " + $mime.GetBodyDecoded())

# The GetEntireBody retrieves the entire content after
# the header.  (Perhaps GetEntireBody should've been named
# GetEntireContent to make it less confusing...)
$("---- EntireBody:")
$($mime.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.
$part = $mime.GetPart(1)
$("Decoded Body:")
$($part.GetBodyDecoded())
$("Encoded Body:")
$($part.GetBodyEncoded())