Rust

Get the Content-ID of a Related Item

Demonstrates the Chilkat Email.GetRelatedContentID method, which returns the Content-ID of a related item (typically an image or style sheet embedded within an HTML email). The index is zero-based. 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 that Content-ID back.

Background: The Content-ID is the anchor that ties an inline resource to the HTML that displays it: the body references cid: plus the ID, and the matching related part carries that same Content-ID. Because an image is binary, it is loaded into a BinData object (here from a file) and added with AddRelatedBd. Reading the Content-ID back lets a program verify or rewrite those links — for example when relocating embedded images or converting a message for display outside a mail client.

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// Demonstrates the GetRelatedContentID method, which returns the Content-ID of a related
// item.  Related items are typically images and style sheets embedded within HTML emails.
// The index is zero-based.

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

// Read the Content-ID of the first related item (index 0).
let cid0 = email.get_related_content_id(0).unwrap_or_default();
println!("Related item 0 Content-ID: {}", cid0);

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