Rust

Add a Related String Resource to an Email

Demonstrates the Chilkat Email.AddRelatedString method, which adds a text-based related MIME resource, such as a style sheet, from an in-memory string and returns the generated Content-ID. The first argument is the MIME resource name, the second is the text content, and the third is the charset used to encode it. Because the Content-ID is generated by the call, this example adds the style sheet first, then builds an HTML body in a StringBuilder that references the style sheet by that cid:, and passes the result to SetHtmlBody.

Background: Related items are not always images loaded from disk — sometimes the resource is text you already have in memory, like a generated CSS style sheet or an SVG. AddRelatedString lets you embed such content directly without writing a temporary file first. As with other related items, it lives in the multipart/related enclosure and is referenced from the HTML by the Content-ID the method returns.

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Rust

// Demonstrates the AddRelatedString method, which adds a text-based related MIME resource
// (such as a style sheet) from an in-memory string and returns the generated Content-ID.
// The first argument is the resource name, the second is the text content, the third is the charset.

let email = chilkat::Email::new();
email.set_subject("Email with a related style sheet");

// Add the text-based related resource first; capture the generated Content-ID.
let Ok(cid) = email.add_related_string("styles.css", "body { color: navy; }", "utf-8") else {
    println!("{}", email.last_error_text());
    return;
};

// Build the HTML body, referencing the related style sheet by its Content-ID.  A
// placeholder is used and then replaced with the actual Content-ID.
let sb_html = chilkat::StringBuilder::new();
let _ = sb_html.append("<html><head><link rel=\"stylesheet\" href=\"cid:PLACEHOLDER_CID\"/></head><body>Styled content.</body></html>");
let num_replaced = sb_html.replace("PLACEHOLDER_CID", &cid);
email.set_html_body(&sb_html.get_as_string().unwrap_or_default());

println!("Related Content-ID = {}", cid);
println!("NumRelatedItems = {}", email.num_related_items());