[][crate]
[][docs]
[][ci]
# read-restrict
Enforce a strict limit on the number of bytes read from a `Read` with an error
when exceeded.
## Synopsis
```rust
pub fn read<P: AsRef<Path>>(path: P, restriction: usize) -> io::Result<Vec<u8>>;
pub fn read_to_string<P: AsRef<Path>>(path: P, restriction: usize) -> io::Result<String>;
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
An adaptor around Rust's standard [`io::Take`] which instead of returning
`Ok(0)` when the read limit is exceeded, instead returns an error of of the kind
[`ErrorKind::InvalidData`].
This is intended for enforcing explicit input limits when simply truncating with
`take` could result in incorrect behaviour.
`read_restrict` also offers restricted variants of [`std::fs::read`] and
[`std::fs::read_to_string`], to conveniently prevent unbounded reads of
overly-large files.
## Example
```rust
use std::io::{Read, Result, ErrorKind};
use read_restrict::ReadExt;
fn main() -> Result<()> {
let f = std::fs::File::open("foo.txt")?;
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(())
}
```
Or more realistically:
```rust
use read_restrict::ReadExt;
fn main() -> std::io::Result<()> {
let input = std::fs::File::open("foo.json")?;
let input = std::io::BufReader::new(input); // buffer for performance
let input = input.restrict(640 * 1024); // 640k should be enough JSON for anyone
let _data = serde_json::from_reader(input)?;
Ok(())
}
```
Or even better:
```rust
fn main() -> std::io::Result<()> {
let input = read_restrict::read_to_string("foo.json", 640 * 1024)?;
let _data = serde_json::from_str(input)?;
Ok(())
}
```
[crate]: https://crates.io/crates/read-restrict
[docs]: https://docs.rs/read-restrict
[ci]: https://github.com/Freaky/read-restrict/actions?query=workflow%3Abuild
[`io::Take`]: https://doc.rust-lang.org/std/io/struct.Take.html
[`ErrorKind::InvalidData`]: https://doc.rust-lang.org/std/io/enum.ErrorKind.html#variant.InvalidData
[`std::fs::read`]: https://doc.rust-lang.org/std/fs/fn.read.html
[`std::fs::read_to_string`]: https://doc.rust-lang.org/std/fs/fn.read_to_string.html