use std::{
io::{Error, ErrorKind},
ops::RangeInclusive,
};
use tokio::io::{AsyncReadExt, AsyncWriteExt};
mod reader;
pub use reader::BytesReader;
mod writer;
pub use writer::BytesWriter;
/// 8 null bytes, used to write out padding.
const EMPTY_BYTES: &[u8; 8] = &[0u8; 8];
/// The length of the size field, in bytes is always 8.
const LEN_SIZE: usize = 8;
#[allow(dead_code)]
/// Read a "bytes wire packet" from the AsyncRead.
/// Rejects reading more than `allowed_size` bytes of payload.
///
/// The packet is made up of three parts:
/// - a length header, u64, LE-encoded
/// - the payload itself
/// - null bytes to the next 8 byte boundary
///
/// Ensures the payload size fits into the `allowed_size` passed,
/// and that the padding is actual null bytes.
///
/// On success, the returned `Vec<u8>` only contains the payload itself.
/// On failure (for example if a too large byte packet was sent), the reader
/// becomes unusable.
///
/// This buffers the entire payload into memory,
/// a streaming version is available at [crate::wire::bytes::BytesReader].
pub async fn read_bytes<R>(
r: &mut R,
allowed_size: RangeInclusive<usize>,
) -> std::io::Result<Vec<u8>>
where
R: AsyncReadExt + Unpin,
{
// read the length field
let len = r.read_u64_le().await?;
let len: usize = len
.try_into()
.ok()
.filter(|len| allowed_size.contains(len))
.ok_or_else(|| {
std::io::Error::new(
std::io::ErrorKind::InvalidData,
"signalled package size not in allowed range",
)
})?;
// calculate the total length, including padding.
// byte packets are padded to 8 byte blocks each.
let padded_len = padding_len(len as u64) as u64 + (len as u64);
let mut limited_reader = r.take(padded_len);
let mut buf = Vec::new();
let s = limited_reader.read_to_end(&mut buf).await?;
// make sure we got exactly the number of bytes, and not less.
if s as u64 != padded_len {
return Err(std::io::ErrorKind::UnexpectedEof.into());
}
let (_content, padding) = buf.split_at(len);
// ensure the padding is all zeroes.
if !padding.iter().all(|e| *e == b'\0') {
return Err(std::io::Error::new(
std::io::ErrorKind::InvalidData,
"padding is not all zeroes",
));
}
// return the data without the padding
buf.truncate(len);
Ok(buf)
}
/// Read a "bytes wire packet" of from the AsyncRead and tries to parse as string.
/// Internally uses [read_bytes].
/// Rejects reading more than `allowed_size` bytes of payload.
pub async fn read_string<R>(
r: &mut R,
allowed_size: RangeInclusive<usize>,
) -> std::io::Result<String>
where
R: AsyncReadExt + Unpin,
{
let bytes = read_bytes(r, allowed_size).await?;
String::from_utf8(bytes).map_err(|e| Error::new(ErrorKind::InvalidData, e))
}
/// Writes a "bytes wire packet" to a (hopefully buffered) [AsyncWriteExt].
///
/// Accepts anything implementing AsRef<[u8]> as payload.
///
/// See [read_bytes] for a description of the format.
///
/// Note: if performance matters to you, make sure your
/// [AsyncWriteExt] handle is buffered. This function is quite
/// write-intesive.
pub async fn write_bytes<W: AsyncWriteExt + Unpin, B: AsRef<[u8]>>(
w: &mut W,
b: B,
) -> std::io::Result<()> {
// write the size packet.
w.write_u64_le(b.as_ref().len() as u64).await?;
// write the payload
w.write_all(b.as_ref()).await?;
// write padding if needed
let padding_len = padding_len(b.as_ref().len() as u64) as usize;
if padding_len != 0 {
w.write_all(&EMPTY_BYTES[..padding_len]).await?;
}
Ok(())
}
/// Computes the number of bytes we should add to len (a length in
/// bytes) to be aligned on 64 bits (8 bytes).
fn padding_len(len: u64) -> u8 {
let aligned = len.wrapping_add(7) & !7;
aligned.wrapping_sub(len) as u8
}
#[cfg(test)]
mod tests {
use tokio_test::{assert_ok, io::Builder};
use super::*;
use hex_literal::hex;
/// The maximum length of bytes packets we're willing to accept in the test
/// cases.
const MAX_LEN: usize = 1024;
#[tokio::test]
async fn test_read_8_bytes() {
let mut mock = Builder::new()
.read(&8u64.to_le_bytes())
.read(&12345678u64.to_le_bytes())
.build();
assert_eq!(
&12345678u64.to_le_bytes(),
read_bytes(&mut mock, 0..=MAX_LEN).await.unwrap().as_slice()
);
}
#[tokio::test]
async fn test_read_9_bytes() {
let mut mock = Builder::new()
.read(&9u64.to_le_bytes())
.read(&hex!("01020304050607080900000000000000"))
.build();
assert_eq!(
hex!("010203040506070809"),
read_bytes(&mut mock, 0..=MAX_LEN).await.unwrap().as_slice()
);
}
#[tokio::test]
async fn test_read_0_bytes() {
// A empty byte packet is essentially just the 0 length field.
// No data is read, and there's zero padding.
let mut mock = Builder::new().read(&0u64.to_le_bytes()).build();
assert_eq!(
hex!(""),
read_bytes(&mut mock, 0..=MAX_LEN).await.unwrap().as_slice()
);
}
#[tokio::test]
/// Ensure we don't read any further than the size field if the length
/// doesn't match the range we want to accept.
async fn test_read_reject_too_large() {
let mut mock = Builder::new().read(&100u64.to_le_bytes()).build();
read_bytes(&mut mock, 10..=10)
.await
.expect_err("expect this to fail");
}
#[tokio::test]
async fn test_write_bytes_no_padding() {
let input = hex!("6478696f34657661");
let len = input.len() as u64;
let mut mock = Builder::new()
.write(&len.to_le_bytes())
.write(&input)
.build();
assert_ok!(write_bytes(&mut mock, &input).await)
}
#[tokio::test]
async fn test_write_bytes_with_padding() {
let input = hex!("322e332e3137");
let len = input.len() as u64;
let mut mock = Builder::new()
.write(&len.to_le_bytes())
.write(&hex!("322e332e31370000"))
.build();
assert_ok!(write_bytes(&mut mock, &input).await)
}
#[tokio::test]
async fn test_write_string() {
let input = "Hello, World!";
let len = input.len() as u64;
let mut mock = Builder::new()
.write(&len.to_le_bytes())
.write(&hex!("48656c6c6f2c20576f726c6421000000"))
.build();
assert_ok!(write_bytes(&mut mock, &input).await)
}
#[test]
fn padding_len_u64_max() {
assert_eq!(padding_len(u64::MAX), 1);
}
}
