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.

Download Chilkat Ruby Library

require 'chilkat'

mime = Chilkat::CkMime.new()

success = mime.UnlockComponent("Anything for 30-day trial.")
if (success == false)
    print mime.lastErrorText() + "\n"
    exit
end

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

part2 = Chilkat::CkMime.new()
part2.SetBodyFromPlainText("This is part 2")
part2.put_Encoding("base64")

mime.NewMultipartMixed()
mime.put_UseMmDescription(false)
mime.AppendPart(part1)
mime.AppendPart(part2)

#  Show the MIME message:
print mime.getMime() + "\n";

#  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.get_NumParts()
print "Num Parts = " + n.to_s() + "\n";
print "Body = " + mime.getBodyDecoded() + "\n";

#  The GetEntireBody retrieves the entire content after
#  the header.  (Perhaps GetEntireBody should've been named
#  GetEntireContent to make it less confusing...)
print "---- EntireBody:" + "\n";
print mime.getEntireBody() + "\n";
print "********" + "\n";

#  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 is a CkMime
part = mime.GetPart(1)
print "Decoded Body:" + "\n";
print part.getBodyDecoded() + "\n";
print "Encoded Body:" + "\n";
print part.getBodyEncoded() + "\n";