pub fn replace_host<'a>(bytes: &'a str, host_to_replace: &'a str, target_host: &'a str, target_port: u16) -> Cow<'a, str> {
    let matcher = format!("https?://{}", host_to_replace);
    Regex::new(&matcher)
        .unwrap()
        .replace_all(bytes,
                     |item: &Captures|
                         modify_url(item, target_host, target_port).unwrap_or(String::from("")))
}

fn modify_url(caps: &Captures, host: &str, port: u16) -> Option<String> {
    let first_match = caps.iter().nth(0)?;
    let match_item = first_match?;

    if let Ok(mut url) = Url::parse(match_item.as_str()) {
        url.set_host(Some(host)).ok();
        url.set_port(Some(port)).ok();
        Some(url.to_string())
    } else {
        None
    }
}