(PureBasic) 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.

Chilkat PureBasic Module Download Chilkat PureBasic Module

IncludeFile "CkMime.pb"

Procedure ChilkatExample()

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

    mime.i = CkMime::ckCreate()
    If mime.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; Create a multipart/mixed MIME message with two sub-parts.
    ; We'll use the Base64 encoding for the 2nd sub-part.
    part1.i = CkMime::ckCreate()
    If part1.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success.i = CkMime::ckSetBodyFromPlainText(part1,"This is part 1")

    part2.i = CkMime::ckCreate()
    If part2.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkMime::ckSetBodyFromPlainText(part2,"This is part 2")
    CkMime::setCkEncoding(part2, "base64")

    success = CkMime::ckNewMultipartMixed(mime)
    CkMime::setCkUseMmDescription(mime, 0)
    success = CkMime::ckAppendPart(mime,part1)
    success = CkMime::ckAppendPart(mime,part2)

    ; Show the MIME message:
    Debug CkMime::ckGetMime(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)
    n.i = CkMime::ckNumParts(mime)
    Debug "Num Parts = " + Str(n)
    Debug "Body = " + CkMime::ckGetBodyDecoded(mime)

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

    ; 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:
    part.i
    ; index 0 is the 1st part, index 1 is the 2nd part.
    part = CkMime::ckGetPart(mime,1)
    Debug "Decoded Body:"
    Debug CkMime::ckGetBodyDecoded(part)
    Debug "Encoded Body:"
    Debug CkMime::ckGetBodyEncoded(part)

    CkMime::ckDispose(part)



    CkMime::ckDispose(mime)
    CkMime::ckDispose(part1)
    CkMime::ckDispose(part2)


    ProcedureReturn
EndProcedure