Function append_list_value 

pub fn append_list_value(headers: &mut Headers, name: &str, value: &str)

Append a field value to a comma-separated list, without repeating it.

This is how Vary collects Accept and Origin (specification section 3).

Examples

use lino_rest_api::headers::{append_list_value, Headers};

let mut headers = Headers::from_pairs([("Vary", "Accept")]);
append_list_value(&mut headers, "Vary", "Origin");
assert_eq!(headers.get("Vary"), Some("Accept, Origin"));