You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: file_server.rs
    path of file: ./repos/nixpacks/src/nixpacks/builder/docker
    
    the code of the file until where you have to start completion: // use actix_multipart::Multipart;
use actix_web::http::header::HeaderValue;
use actix_web::{
    middleware, rt, web, App as ActixApp, Error as ActixError, HttpRequest, 
    
    fn get_free_port(&self) -> u16 {
        for _ in 1..3 {
            // try 2 times
            if let Some(port) = pick_unused_port() {
                return port;
            }
        }

        // last try to get free port then fail if no ports available
        pick_unused_port().expect("No ports available")
    }