Shared via Rust Playground

playground.rs

use std::io::{self, Read, Write};

struct StringRW {
    value: String,
    buffer: Vec<u8>,
}

impl StringRW {
    fn new(value: &str) -> Self {
        StringRW {
            value: value.to_owned(),
            buffer: value.chars().map(|c| c as u8).collect::<Vec<u8>>(),
        }
    }
}

impl Read for StringRW {
    fn read<'a>(&'a mut self, mut buff: &'a mut [u8]) -> Result<usize, io::Error> {
        buff = self.buffer.as_mut_slice();
        Ok(buff.len())
    }
}

fn main() {
    let mut srw = StringRW::new(">>>[]");
    let mut buff: Vec<u8> = Vec::new();
    srw.read(&mut buff);
    println!("{:?}", buff);
}