use std::io::prelude::*;
use std::io;
use std::fs::File;
use std::convert::TryInto;
use std::error::Error;

fn main() -> Result<(), Box<dyn Error>> {
    let test_strings = [
        "hello",
        "my name is \n",
        "rust",
        "fearless concurrency!",
    ];

    let file_name = "test.txt";
    {
        let mut file = File::create(file_name)?;
        for &string in &test_strings {
            let string_len: u16 = string.len().try_into()?;
            file.write_all(&string_len.to_le_bytes())?;
            file.write_all(string.as_bytes())?;
        }
    }

    {
        let mut buf = vec![];
        let mut file = File::open(file_name)?;
        loop {
            let mut len_buf = [0u8; 2];
            match file.read_exact(&mut len_buf) {
                Ok(()) => (),
                Err(ref e) if e.kind() == io::ErrorKind::UnexpectedEof => break,
                Err(e) => return Err(e.into()),
            }
            let len = u16::from_le_bytes(len_buf) as usize;
            buf.resize(len, 0);
            file.read_exact(&mut buf)?;
            let string = String::from_utf8_lossy(&buf);
            println!("{}", string);
        }
    }

    Ok(())
}