(Go) 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.

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

    mime := chilkat.NewMime()

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

    part2 := chilkat.NewMime()
    success = part2.SetBodyFromPlainText("This is part 2")
    part2.SetEncoding("base64")

    success = mime.NewMultipartMixed()
    mime.SetUseMmDescription(false)
    success = mime.AppendPart(part1)
    success = mime.AppendPart(part2)

    // Show the MIME message:
    fmt.Println(*mime.GetMime())

    // 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.NumParts()
    fmt.Println("Num Parts = ", n)
    fmt.Println("Body = ", *mime.GetBodyDecoded())

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

    // 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 is a Mime
    // index 0 is the 1st part, index 1 is the 2nd part.
    part := mime.GetPart(1)
    fmt.Println("Decoded Body:")
    fmt.Println(*part.GetBodyDecoded())
    fmt.Println("Encoded Body:")
    fmt.Println(*part.GetBodyEncoded())

    part.DisposeMime()

    mime.DisposeMime()
    part1.DisposeMime()
    part2.DisposeMime()