read-restrict

Enforce a strict limit on the number of bytes read from a Read with an error when exceeded.

Synopsis

pub trait ReadExt {
    fn restrict(self, restriction: u64) -> Restrict<Self>
}

impl<R: Read> ReadExt for R {}

impl<T> Restrict<T> {
    pub fn restriction(&self) -> u64;
    pub fn set_restriction(&mut self, restriction: u64);
    pub fn into_inner(self) -> T;
    pub fn get_ref(&self) -> &T;
    pub fn get_mut(&mut self) -> &mut T;
}

impl<T: Read> Read for Restrict<T> {}
impl<T: BufRead> BufRead for Restrict<T> {}

Description

This is a thin wrapper around Read::take which which returns an error when its limit is exceeded. Reads operate as normal, bound strictly to the read limit, following which io::ErrorKind::InvalidData will be returned.

Example

use std::io::{self, ErrorKind, Result};
use std::io::prelude::*;
use std::fs::File;
use read_restrict::ReadExt;

fn main() -> io::Result<()> {
    let f = File::open("foo.txt")?.restrict(5);
    let mut handle = f.restrict(5);
    let mut buf = [0; 8];
    assert_eq!(5, handle.read(&mut buf)?); // reads at most 5 bytes
    assert_eq!(0, handle.restriction()); // is now exhausted
    assert_eq!(ErrorKind::InvalidData, handle.read(&mut buf).unwrap_err().kind());
    Ok(())
}