How to use a Result in Rust

main.rs

fn read_username_from_file() -> Result<String, io::Error> {
    let file: Result<File, io::Error> = File::open("user.txt");

    let mut file = match file {
        Ok(file) => file,
        Err(e) => return Err(e),
    };

    let mut buffer = String::new();
    match file.read_to_string(&mut buffer) {
        Ok(_) => Ok(buffer),
        Err(e) => Err(e),
    }
}

fn main() {
    let username = match read_username_from_file() {
        Ok(name) => name,
        Err(_) => {
            println!("Couldn't read username file.");
            read_input("Please enter your username:")
        }
    };

    println!("Your username is {}.", username);
}