Rust

Set a MIME Header Field

Demonstrates the Chilkat Mime.SetHeaderField method, which sets a single header field. The first argument is the field name and the second is the value. All existing occurrences are removed and one replacement is inserted, or a new field is added if none exists.

Background: For headers that should appear exactly once — Subject, From, Content-Type — this is the method to use, because it guarantees a single occurrence no matter how many times you call it. That idempotence is the key difference from AddHeaderField, which would leave duplicates behind. Setting an empty value removes the field.

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Rust


// Demonstrates the Mime.SetHeaderField method, which sets a single header field.  The 1st argument
// is the field name and the 2nd is the value.  All existing occurrences are removed and one
// replacement is inserted (or a new field is added if none exists).

let mime = chilkat::Mime::new();

if mime.set_body_from_plain_text("Hello.").is_err() {
    println!("{}", mime.last_error_text());
    return;
}

// Unlike AddHeaderField, SetHeaderField ensures exactly one field with this name.
if mime.set_header_field("Subject", "Weekly Report").is_err() {
    println!("{}", mime.last_error_text());
    return;
}

// Setting it again replaces the previous value rather than adding a duplicate.
if mime.set_header_field("Subject", "Weekly Report (revised)").is_err() {
    println!("{}", mime.last_error_text());
    return;
}

let Ok(subject) = mime.get_header_field("Subject") else {
    println!("{}", mime.last_error_text());
    return;
};

println!("Subject: {}", subject);