rewrites.rs

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()) {
        // The following 2 method calls will mutate
        // the url, but return *different* Errors if they fail
        // 
        // Because I don't care about the actual error, only
        // if it succeeded or failed, you can convert a Result
        // to Option via .ok()
        //
        // So if setting the host or port fails here, just do
        // nothing and the `?` will short-circuit and return a None
        // for this function
        url.set_host(Some(host)).ok()?;
        url.set_port(Some(port)).ok()?;
        Some(url.to_string())
    } else {
        None
    }
}