Rust program to read a file specified by user input

main.rs

use std::fs::File;
use std::io;
use std::io::Read;

fn main() {
    let mut user_input = String::new();
    io::stdin().read_line(&mut user_input).expect("Failed to read line");

    let result = read_file(String::from(user_input.trim()));
    match result {
        Ok(s) => println!("contents of file {} is:\n{}", user_input, s),
        Err(e) => panic!("{}", e.to_string())
    }   
}

// this could be much shorter as fs::read_to_string exists and could do this whole function in one line
fn read_file(filename: String) -> Result<String, io::Error> {
    let mut file_contents = String::new();
    File::open(filename)?.read_to_string(&mut file_contents)?;
    Ok(file_contents)
}