Tcl

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.

Tcl

load ./chilkat.dll

set success 0

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

set mime [new_CkMime]

# Create a multipart/mixed MIME message with two sub-parts.
# We'll use the Base64 encoding for the 2nd sub-part.
set part1 [new_CkMime]

set success [CkMime_SetBodyFromPlainText $part1 "This is part 1"]

set part2 [new_CkMime]

set success [CkMime_SetBodyFromPlainText $part2 "This is part 2"]
CkMime_put_Encoding $part2 "base64"

set success [CkMime_NewMultipartMixed $mime]
CkMime_put_UseMmDescription $mime 0
set success [CkMime_AppendPart $mime $part1]
set success [CkMime_AppendPart $mime $part2]

# Show the MIME message:
puts [CkMime_getMime $mime]

# 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)
set n [CkMime_get_NumParts $mime]
puts "Num Parts = $n"
puts "Body = [CkMime_getBodyDecoded $mime]"

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

# 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.
set part [new_CkMime]

CkMime_PartAt $mime 1 $part

puts "Decoded Body:"
puts [CkMime_getBodyDecoded $part]
puts "Encoded Body:"
puts [CkMime_getBodyEncoded $part]

delete_CkMime $mime
delete_CkMime $part1
delete_CkMime $part2
delete_CkMime $part