Lua

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.

Lua

local chilkat = require("chilkat")

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

local mime = chilkat.Mime.new()

-- Create a multipart/mixed MIME message with two sub-parts.
-- We'll use the Base64 encoding for the 2nd sub-part.
local part1 = chilkat.Mime.new()
local success = part1:set_body_from_plain_text("This is part 1")

local part2 = chilkat.Mime.new()
success = part2:set_body_from_plain_text("This is part 2")
part2.encoding = "base64"

success = mime:new_multipart_mixed()
mime.use_mm_description = false
success = mime:append_part(part1)
success = mime:append_part(part2)

-- Show the MIME message:
print(mime:get_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)
local n = mime.num_parts
print("Num Parts = " .. n)
print("Body = " .. mime:get_body_decoded())

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

-- 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.
local part = chilkat.Mime.new()
mime:part_at(1, part)

print("Decoded Body:")
print(part:get_body_decoded())
print("Encoded Body:")
print(part:get_body_encoded())