read_buffer

This crate provides ReadBuffer and DynReadBuffer, two wrappers to safely read into a buffer from a Read.

Motivation

With the default way of reading into a buffer using Read::read like this:

use std::io::Read;

let mut reader = [1, 2, 3, 4].as_slice(); // Read is implemented for &[u8]
let mut buffer = [0; 16];

let length = reader.read(&mut buffer)?;
assert_eq!(buffer[..length], [1, 2, 3, 4]);

there's nothing stopping you from accessing more data of the buffer than what was read or even outright ignoring the Result of Read::read:

use std::io::Read;

let mut reader = [8, 8, 8, 8].as_slice();
let mut buffer = [0; 8];

// Ignoring the result of Read::read which might fail
reader.read(&mut buffer);

// Reading too much data
assert_eq!(buffer, [8, 8, 8, 8, 0, 0, 0, 0]);

let mut reader = [1, 2, 3].as_slice();

reader.read(&mut buffer);

// Reading garbage data from previous call to Read::read
assert_eq!(buffer[..4], [1, 2, 3, 8]);

ReadBuffer and DynReadBuffer provide wrappers that only let you access the data that was actually read, and force you to check the Result before accessing the data.

Examples

use read_buffer::ReadBuffer;

let mut reader = [8, 8, 8, 8].as_slice();
let mut buffer: ReadBuffer<8> = ReadBuffer::new();

// We are forced to check the Result of read_from to access the data we read
let read_data = buffer.read_from(&mut reader)?;

// read_data is a slice over only the data we actually read,
// trying to access the buffer past that point would panic
let eight = read_data[3];
// let zero = read_data[4]; would panic

assert_eq!(eight, 8);
assert_eq!(read_data, [8, 8, 8, 8]);

// We can reuse the same buffer for the next read, just as with Read::read

let mut reader = [1, 2, 3].as_slice();

let read_data = buffer.read_from(&mut reader)?;

// Again, we get a slice over only the data that was just read,
// trying to read garbage data from the previous call to read_from
// here would panic
let three = read_data[2];
// let eight = read_data[3]; would panic

assert_eq!(three, 3);
assert_eq!(read_data, [1, 2, 3]);