Rust

Add a Related File to an HTML Email

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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Rust

// 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>.

let email = chilkat::Email::new();
email.set_subject("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).
let Ok(cid) = email.add_related_file("qa_data/images/logo.png") else {
    println!("{}", email.last_error_text());
    return;
};

// Build the HTML body in a StringBuilder, using a placeholder where the image's
// Content-ID will go.
let sb_html = chilkat::StringBuilder::new();
let _ = sb_html.append("<html><body><img src=\"cid:PLACEHOLDER_CID\"/></body></html>");

// Replace the placeholder with the actual Content-ID returned by AddRelatedFile.
let num_replaced = sb_html.replace("PLACEHOLDER_CID", &cid);

// Set the HTML body from the StringBuilder result.
email.set_html_body(&sb_html.get_as_string().unwrap_or_default());

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

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