Add a Related File to an HTML Email

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Demonstrates the Chilkat Email.AddRelatedFile method, which adds the contents of a local file as a related MIME resource and returns the generated Content-ID. The returned value is the bare Content-ID — no angle brackets and no cid: prefix — so if it returns CID-123@example, the HTML reference is cid:CID-123@example. Because the Content-ID is generated by the call, this example adds the image first, then builds the HTML body in a StringBuilder — using a placeholder in the <img> tag that is replaced with the returned Content-ID — and passes the result to SetHtmlBody.

Background: To embed an image so it displays inside an HTML email (rather than being downloaded from a web server), you add it as a "related" part and reference it from the HTML with a cid: URL that matches the part's Content-ID. Since Chilkat assigns that ID when you add the file, the natural order is: add the related file, capture the returned ID, then build the <img src="cid:..."> reference from it. A StringBuilder makes assembling and updating the HTML convenient.

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    //  Demonstrates the AddRelatedFile method, which adds a local file as a related MIME
    //  resource (such as an image displayed by an HTML body) and returns the generated
    //  Content-ID.  The HTML references the item using cid:<Content-ID>.

    email := chilkat.NewEmail()
    email.SetSubject("Email with a related image")

    //  Add the image file as a related item first.  The return value is the bare Content-ID
    //  (no angle brackets and no "cid:" prefix).
    cid := email.AddRelatedFile("qa_data/images/logo.png")
    if email.LastMethodSuccess() == false {
        fmt.Println(email.LastErrorText())
        email.DisposeEmail()
        return
    }

    //  Build the HTML body in a StringBuilder, using a placeholder where the image's
    //  Content-ID will go.
    sbHtml := chilkat.NewStringBuilder()
    sbHtml.Append("<html><body><img src=\"cid:PLACEHOLDER_CID\"/></body></html>")

    //  Replace the placeholder with the actual Content-ID returned by AddRelatedFile.
    numReplaced := sbHtml.Replace("PLACEHOLDER_CID",*cid)

    //  Set the HTML body from the StringBuilder result.
    email.SetHtmlBody(*sbHtml.GetAsString())

    fmt.Println("Related Content-ID = ", *cid)
    fmt.Println("NumRelatedItems = ", email.NumRelatedItems())

    //  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()
    sbHtml.DisposeStringBuilder()