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.

CREATE PROCEDURE ChilkatSample
AS
BEGIN
    DECLARE @hr int
    DECLARE @sTmp0 nvarchar(4000)
    DECLARE @mime int
    EXEC @hr = sp_OACreate 'Chilkat.Mime', @mime OUT
    IF @hr <> 0
    BEGIN
        PRINT 'Failed to create ActiveX component'
        RETURN
    END

    DECLARE @success int

    EXEC sp_OAMethod @mime, 'UnlockComponent', @success OUT, 'Anything for 30-day trial.'
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @mime, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        RETURN
      END

    --  Create a multipart/mixed MIME message with two sub-parts.
    --  We'll use the Base64 encoding for the 2nd sub-part.
    DECLARE @part1 int
    EXEC @hr = sp_OACreate 'Chilkat.Mime', @part1 OUT
    IF @hr <> 0
    BEGIN
        PRINT 'Failed to create ActiveX component'
        RETURN
    END

    EXEC sp_OAMethod @part1, 'SetBodyFromPlainText', NULL, 'This is part 1'

    DECLARE @part2 int
    EXEC @hr = sp_OACreate 'Chilkat.Mime', @part2 OUT
    IF @hr <> 0
    BEGIN
        PRINT 'Failed to create ActiveX component'
        RETURN
    END

    EXEC sp_OAMethod @part2, 'SetBodyFromPlainText', NULL, 'This is part 2'
    EXEC sp_OASetProperty @part2, 'Encoding', 'base64'

    EXEC sp_OAMethod @mime, 'NewMultipartMixed', NULL
    EXEC sp_OASetProperty @mime, 'UseMmDescription', 0
    EXEC sp_OAMethod @mime, 'AppendPart', NULL, @part1
    EXEC sp_OAMethod @mime, 'AppendPart', NULL, @part2

    --  Show the MIME message:
    EXEC sp_OAMethod @mime, 'GetMime', @sTmp0 OUT
    PRINT @sTmp0

    --  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)
    DECLARE @n int

    EXEC sp_OAGetProperty @mime, 'NumParts', @n OUT



    PRINT 'Num Parts = ' + STR(@n)

    EXEC sp_OAMethod @mime, 'GetBodyDecoded', @sTmp0 OUT
    PRINT 'Body = ' + @sTmp0

    --  The GetEntireBody retrieves the entire content after
    --  the header.  (Perhaps GetEntireBody should've been named
    --  GetEntireContent to make it less confusing...)

    PRINT '---- EntireBody:'
    EXEC sp_OAMethod @mime, 'GetEntireBody', @sTmp0 OUT
    PRINT @sTmp0

    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:
    DECLARE @part int

    --  index 0 is the 1st part, index 1 is the 2nd part.
    EXEC sp_OAMethod @mime, 'GetPart', @part OUT, 1

    PRINT 'Decoded Body:'
    EXEC sp_OAMethod @part, 'GetBodyDecoded', @sTmp0 OUT
    PRINT @sTmp0

    PRINT 'Encoded Body:'
    EXEC sp_OAMethod @part, 'GetBodyEncoded', @sTmp0 OUT
    PRINT @sTmp0


END
GO