Get a Header Attribute of a Related Item

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Demonstrates the Chilkat Email.GetRelatedAttr method, which returns a header-field attribute value from a header field of the Nth related item. The first argument is the zero-based related-item index, the second names a header field, and the third names an attribute within it. This example loads an image from a file into a BinData object, adds it as a related item with AddRelatedBd (capturing the generated Content-ID and referencing it from the HTML), then reads the name attribute of the related item's Content-Type header.

Background: Related items (inline images, style sheets) are MIME parts whose headers may carry named parameters — for instance Content-Type: image/png; name="logo.png". Because an image is binary, it is loaded into a BinData object (here from a file) and added with AddRelatedBd, rather than being treated as text. GetRelatedAttr then extracts one named attribute from a chosen header of a specific related part, the related-item analogue of GetAttachmentAttr, so you don't have to parse the raw header yourself.

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    success := false

    //  Demonstrates the GetRelatedAttr method, which returns a header-field attribute value
    //  from a header field of the Nth related item.  The first argument is the zero-based related-item
    //  index, the second is the header field name, and the third is the attribute name.

    email := chilkat.NewEmail()
    email.SetSubject("GetRelatedAttr example")

    //  Load the image data from a file into a BinData object.
    bdImage := chilkat.NewBinData()
    success = bdImage.LoadFile("qa_data/images/logo.png")
    if success == false {
        fmt.Println(bdImage.LastErrorText())
        email.DisposeEmail()
        bdImage.DisposeBinData()
        return
    }

    //  Add the image as a related item from the BinData; capture its generated Content-ID.
    cid := email.AddRelatedBd("logo.png",bdImage)
    if email.LastMethodSuccess() == false {
        fmt.Println(email.LastErrorText())
        email.DisposeEmail()
        bdImage.DisposeBinData()
        return
    }

    //  Reference the related item in the HTML body by its Content-ID.
    sbHtml := chilkat.NewStringBuilder()
    sbHtml.Append("<html><body><img src=\"cid:PLACEHOLDER_CID\"/></body></html>")
    numReplaced := sbHtml.Replace("PLACEHOLDER_CID",*cid)
    email.SetHtmlBody(*sbHtml.GetAsString())

    //  Get the "name" attribute of the related item's Content-Type header (index 0).
    val := email.GetRelatedAttr(0,"Content-Type","name")
    fmt.Println("Related item Content-Type name attribute: ", *val)

    //  Note: The path "qa_data/images/logo.png" is a relative local filesystem path,
    //  relative to the current working directory of the running application.

    email.DisposeEmail()
    bdImage.DisposeBinData()
    sbHtml.DisposeStringBuilder()