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use std::fmt::Debug;
use std::io::Read;
use byteorder::ReadBytesExt;
use crate::Error;
/// A reader that can temporarily buffer bytes read.
pub trait Reader<'de>: ReadBytesExt {
/// Reads exactly `length` bytes.
///
/// If the reader supports borrowing bytes, [`BufferedBytes::Data`] should
/// be returned. Otherwise, the bytes will be read into `scratch`. `scratch`
/// should only be assumed to be valid if [`BufferedBytes::Scratch`] is
/// returned.
fn buffered_read_bytes(
&mut self,
length: usize,
scratch: &mut Vec<u8>,
) -> Result<BufferedBytes<'de>, Error>;
}
/// Bytes that have been read into a buffer.
#[derive(Debug)]
pub enum BufferedBytes<'de> {
/// The bytes that have been read can be borrowed from the source.
Data(&'de [u8]),
/// The bytes that have been read have been stored in the scratch buffer
/// passed to the function reading bytes.
Scratch,
impl BufferedBytes<'_> {
/// Resolves the bytes to a byte slice.
#[inline]
#[must_use]
pub fn as_slice<'a>(&'a self, scratch: &'a [u8]) -> &'a [u8] {
match self {
BufferedBytes::Data(data) => data,
BufferedBytes::Scratch => scratch,
/// Reads data from a slice.
#[allow(clippy::module_name_repetitions)]
pub struct SliceReader<'a> {
pub(crate) data: &'a [u8],
impl<'a> SliceReader<'a> {
/// Returns the remaining bytes to read.
pub const fn len(&self) -> usize {
self.data.len()
/// Returns `true` if there are no bytes remaining to read.
pub const fn is_empty(&self) -> bool {
self.data.is_empty()
impl<'a> Debug for SliceReader<'a> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.debug_struct("SliceReader")
.field(
"preview",
&format!("{:0x?}", &self.data[..8.min(self.data.len())]),
)
.finish()
impl<'a> From<&'a [u8]> for SliceReader<'a> {
fn from(data: &'a [u8]) -> Self {
Self { data }
impl<'a> From<SliceReader<'a>> for &'a [u8] {
fn from(reader: SliceReader<'a>) -> Self {
reader.data
impl<'de> Reader<'de> for SliceReader<'de> {
_scratch: &mut Vec<u8>,
) -> Result<BufferedBytes<'de>, Error> {
if length > self.data.len() {
self.data = &self.data[self.data.len()..];
Err(Error::Eof)
} else {
let (start, remaining) = self.data.split_at(length);
self.data = remaining;
Ok(BufferedBytes::Data(start))
impl<'a> Read for SliceReader<'a> {
fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
let remaining_length = self.data.len();
let (to_copy, remaining) = self.data.split_at(remaining_length.min(buf.len()));
buf[..to_copy.len()].copy_from_slice(to_copy);
Ok(to_copy.len())
fn read_exact(&mut self, buf: &mut [u8]) -> std::io::Result<()> {
self.read(buf).map(|_| ())
/// A reader over [`ReadBytesExt`].
pub struct IoReader<R: ReadBytesExt> {
pub(crate) reader: R,
impl<R: ReadBytesExt> IoReader<R> {
pub(crate) const fn new(reader: R) -> Self {
Self { reader }
impl<'de, R: ReadBytesExt> Reader<'de> for IoReader<R> {
scratch.resize(length, 0);
self.reader.read_exact(scratch)?;
Ok(BufferedBytes::Scratch)
impl<R: ReadBytesExt> Read for IoReader<R> {
self.reader.read(buf)
fn read_vectored(&mut self, bufs: &mut [std::io::IoSliceMut<'_>]) -> std::io::Result<usize> {
self.reader.read_vectored(bufs)
fn read_to_end(&mut self, buf: &mut Vec<u8>) -> std::io::Result<usize> {
self.reader.read_to_end(buf)
fn read_to_string(&mut self, buf: &mut String) -> std::io::Result<usize> {
self.reader.read_to_string(buf)
self.reader.read_exact(buf)
#[test]
fn slice_reader_pub_methods() {
let mut reader = SliceReader::from(&b"a"[..]);
assert_eq!(reader.len(), 1);
assert!(!reader.is_empty());
reader.read_exact(&mut [0]).unwrap();
assert_eq!(reader.len(), 0);
assert!(reader.is_empty());
assert_eq!(<&[u8]>::from(reader), b"");