Rust

Get a Header Attribute of a Related Item

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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// 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.

let email = chilkat::Email::new();
email.set_subject("GetRelatedAttr example");

// Load the image data from a file into a BinData object.
let bd_image = chilkat::BinData::new();
if bd_image.load_file("qa_data/images/logo.png").is_err() {
    println!("{}", bd_image.last_error_text());
    return;
}

// Add the image as a related item from the BinData; capture its generated Content-ID.
let Ok(cid) = email.add_related_bd("logo.png", &bd_image) else {
    println!("{}", email.last_error_text());
    return;
};

// Reference the related item in the HTML body by its Content-ID.
let sb_html = chilkat::StringBuilder::new();
let _ = sb_html.append("<html><body><img src=\"cid:PLACEHOLDER_CID\"/></body></html>");
let num_replaced = sb_html.replace("PLACEHOLDER_CID", &cid);
email.set_html_body(&sb_html.get_as_string().unwrap_or_default());

// Get the "name" attribute of the related item's Content-Type header (index 0).
let val = email.get_related_attr(0, "Content-Type", "name").unwrap_or_default();
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.