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: types.rs
    path of file: ./repos/rdms/src/_archive
    
    the code of the file until where you have to start completion: //! Module `types` implement core key-traits and value-traits for
//! built-in types.

use std::{convert::TryInto, ffi, marker};

use crate::{
    core::{Diff, Entry, Footprint, Result, Serialize},
    error::Error,
};

// TODO: instead of using resize()/copy_from_slice() can we use
// extend_from_slice() ?

/// Empty value, can be used for indexing entries that have a
/// key but no value.
#[derive(Copy, Clone, Debug, Default, Eq, PartialEq, PartialOrd, Ord)]
pub str
    
    fn decode(&mut self, buf: &[u8]) -> Result<usize> {
        if buf.len() < 4 {
            let msg = format!("type-Vec<u8>, header {} < 4", buf.len());
            return err_at!(DecodeFail, msg: msg);
        }
        let len: usize = convert_at!(u32::from_be_bytes(array_at!(buf[..4])?))?;
        if buf.len() < (len + 4) {
            let msg = format!("type-Vec<u8>, payload {} < {}", buf.len(), len);
            return err_at!(DecodeFail, msg: msg);
        }
        self.resize(len, 0);
        self.copy_from_slice(&buf[4..len + 4]);
        Ok(len + 4)
    }