fix(nix-compat/bytes): make BytesReader less hazardous
We now *never* return the final bytes until we've read the padding in full, so read_exact is safe to use. This is implemented by TrailerReader, which splits the phases of reading (and validating) the final 8-byte block, and providing the contained payload bytes to the caller. Change-Id: I0d05946a8af9c260a18d71d2b763ba7a68b3c27f Reviewed-on: https://cl.tvl.fyi/c/depot/+/11518 Tested-by: BuildkiteCI Reviewed-by: flokli <flokli@flokli.de>
This commit is contained in:
edef
parent
70c679eac4
commit
ba46b1818a
2 changed files with 321 additions and 182 deletions
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@ -1,12 +1,13 @@
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use std::{
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io,
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ops::{Bound, RangeBounds, RangeInclusive},
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ops::{Bound, RangeBounds},
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pin::Pin,
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task::{self, ready, Poll},
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};
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use tokio::io::AsyncRead;
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use tokio::io::{AsyncRead, ReadBuf};
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use super::{padding_len, BytesPacketPosition, LEN_SIZE};
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use trailer::TrailerReader;
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mod trailer;
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/// Reads a "bytes wire packet" from the underlying reader.
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/// The format is the same as in [crate::wire::bytes::read_bytes],
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@ -19,21 +20,34 @@ use super::{padding_len, BytesPacketPosition, LEN_SIZE};
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///
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/// Internally, it will first read over the size packet, filling payload_size,
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/// ensuring it fits allowed_size, then return payload data.
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/// It will only signal EOF (returning `Ok(())` without filling the buffer anymore)
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/// when all padding has been successfully consumed too.
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///
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/// This also means, it's important for a user to always read to the end,
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/// and not just call read_exact - otherwise it might not skip over the
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/// padding, and return garbage when reading the next packet.
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/// It will not return the final bytes before all padding has been successfully
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/// consumed as well, but the full length of the reader must be consumed.
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///
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/// In case of an error due to size constraints, or in case of not reading
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/// all the way to the end (and getting a EOF), the underlying reader is no
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/// longer usable and might return garbage.
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pub struct BytesReader<R> {
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inner: R,
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allowed_size: RangeInclusive<u64>,
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payload_size: [u8; 8],
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state: BytesPacketPosition,
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state: State<R>,
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}
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#[derive(Debug)]
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enum State<R> {
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Size {
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reader: Option<R>,
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/// Minimum length (inclusive)
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user_len_min: u64,
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/// Maximum length (inclusive)
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user_len_max: u64,
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filled: u8,
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buf: [u8; 8],
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},
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Body {
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reader: Option<R>,
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consumed: u64,
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user_len: u64,
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},
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Trailer(TrailerReader<R>),
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}
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impl<R> BytesReader<R>
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@ -41,7 +55,7 @@ where
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R: AsyncRead + Unpin,
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{
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/// Constructs a new BytesReader, using the underlying passed reader.
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pub fn new<S: RangeBounds<u64>>(r: R, allowed_size: S) -> Self {
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pub fn new<S: RangeBounds<u64>>(reader: R, allowed_size: S) -> Self {
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let user_len_min = match allowed_size.start_bound() {
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Bound::Included(&n) => n,
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Bound::Excluded(&n) => n.saturating_add(1),
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@ -55,181 +69,148 @@ where
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};
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Self {
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inner: r,
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allowed_size: user_len_min..=user_len_max,
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payload_size: [0; 8],
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state: BytesPacketPosition::Size(0),
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state: State::Size {
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reader: Some(reader),
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user_len_min,
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user_len_max,
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filled: 0,
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buf: [0; 8],
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},
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}
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}
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/// Construct a new BytesReader with a known, and already-read size.
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pub fn with_size(r: R, size: u64) -> Self {
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pub fn with_size(reader: R, size: u64) -> Self {
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Self {
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inner: r,
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allowed_size: size..=size,
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payload_size: u64::to_le_bytes(size),
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state: if size != 0 {
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BytesPacketPosition::Payload(0)
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} else {
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BytesPacketPosition::Padding(0)
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state: State::Body {
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reader: Some(reader),
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consumed: 0,
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user_len: size,
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},
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}
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}
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}
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/// Returns an error if the passed usize is 0.
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#[inline]
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fn ensure_nonzero_bytes_read(bytes_read: usize) -> Result<usize, io::Error> {
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if bytes_read == 0 {
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Err(io::Error::new(
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io::ErrorKind::UnexpectedEof,
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"underlying reader returned EOF",
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))
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} else {
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Ok(bytes_read)
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}
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}
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impl<R> AsyncRead for BytesReader<R>
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where
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R: AsyncRead + Unpin,
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{
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impl<R: AsyncRead + Unpin> AsyncRead for BytesReader<R> {
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fn poll_read(
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self: Pin<&mut Self>,
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cx: &mut task::Context,
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buf: &mut tokio::io::ReadBuf,
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buf: &mut ReadBuf,
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) -> Poll<io::Result<()>> {
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let this = self.get_mut();
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let this = &mut self.get_mut().state;
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// Use a loop, so we can deal with (multiple) state transitions.
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loop {
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match this.state {
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BytesPacketPosition::Size(LEN_SIZE) => {
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// used in case an invalid size was signalled.
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Err(io::Error::new(
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io::ErrorKind::InvalidData,
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"signalled package size not in allowed range",
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))?
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}
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BytesPacketPosition::Size(pos) => {
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// try to read more of the size field.
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// We wrap a ReadBuf around this.payload_size here, and set_filled.
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let mut read_buf = tokio::io::ReadBuf::new(&mut this.payload_size);
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read_buf.advance(pos);
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ready!(Pin::new(&mut this.inner).poll_read(cx, &mut read_buf))?;
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match this {
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State::Size {
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reader,
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user_len_min,
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user_len_max,
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filled: 8,
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buf,
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} => {
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let reader = reader.take().unwrap();
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ensure_nonzero_bytes_read(read_buf.filled().len() - pos)?;
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let total_size_read = read_buf.filled().len();
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if total_size_read == LEN_SIZE {
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// If the entire payload size was read, parse it
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let payload_size = u64::from_le_bytes(this.payload_size);
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if !this.allowed_size.contains(&payload_size) {
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// If it's not in the allowed
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// range, transition to failure mode
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// `BytesPacketPosition::Size(LEN_SIZE)`, where only
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// an error is returned.
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this.state = BytesPacketPosition::Size(LEN_SIZE)
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} else if payload_size == 0 {
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// If the payload size is 0, move on to reading padding directly.
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this.state = BytesPacketPosition::Padding(0)
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} else {
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// Else, transition to reading the payload.
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this.state = BytesPacketPosition::Payload(0)
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}
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} else {
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// If we still need to read more of payload size, update
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// our position in the state.
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this.state = BytesPacketPosition::Size(total_size_read)
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}
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}
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BytesPacketPosition::Payload(pos) => {
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let signalled_size = u64::from_le_bytes(this.payload_size);
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// We don't enter this match arm at all if we're expecting empty payload
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debug_assert!(signalled_size > 0, "signalled size must be larger than 0");
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// Read from the underlying reader into buf
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// We cap the ReadBuf to the size of the payload, as we
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// don't want to leak padding to the caller.
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let bytes_read = ensure_nonzero_bytes_read({
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// Reducing these two u64 to usize on 32bits is fine - we
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// only care about not reading too much, not too less.
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let mut limited_buf = buf.take((signalled_size - pos) as usize);
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ready!(Pin::new(&mut this.inner).poll_read(cx, &mut limited_buf))?;
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limited_buf.filled().len()
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})?;
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// SAFETY: we just did populate this, but through limited_buf.
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unsafe { buf.assume_init(bytes_read) }
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buf.advance(bytes_read);
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if pos + bytes_read as u64 == signalled_size {
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// If we now read all payload, transition to padding
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// state.
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this.state = BytesPacketPosition::Padding(0);
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} else {
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// if we didn't read everything yet, update our position
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// in the state.
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this.state = BytesPacketPosition::Payload(pos + bytes_read as u64);
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}
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// We return from poll_read here.
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// This is important, as any error (or even Pending) from
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// the underlying reader on the next read (be it padding or
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// payload) would require us to roll back buf, as generally
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// a AsyncRead::poll_read may not advance the buffer in case
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// of a nonsuccessful read.
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// It can't be misinterpreted as EOF, as we definitely *did*
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// write something into buf if we come to here (we pass
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// `ensure_nonzero_bytes_read`).
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return Ok(()).into();
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}
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BytesPacketPosition::Padding(pos) => {
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// Consume whatever padding is left, ensuring it's all null
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// bytes. Only return `Ready(Ok(()))` once we're past the
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// padding (or in cases where polling the inner reader
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// returns `Poll::Pending`).
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let signalled_size = u64::from_le_bytes(this.payload_size);
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let total_padding_len = padding_len(signalled_size) as usize;
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let padding_len_remaining = total_padding_len - pos;
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if padding_len_remaining != 0 {
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// create a buffer only accepting the number of remaining padding bytes.
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let mut buf = [0; 8];
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let mut padding_buf = tokio::io::ReadBuf::new(&mut buf);
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let mut padding_buf = padding_buf.take(padding_len_remaining);
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// read into padding_buf.
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ready!(Pin::new(&mut this.inner).poll_read(cx, &mut padding_buf))?;
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let bytes_read = ensure_nonzero_bytes_read(padding_buf.filled().len())?;
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this.state = BytesPacketPosition::Padding(pos + bytes_read);
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// ensure the bytes are not null bytes
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if !padding_buf.filled().iter().all(|e| *e == b'\0') {
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return Err(io::Error::new(
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io::ErrorKind::InvalidData,
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"padding is not all zeroes",
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))
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let data_len = u64::from_le_bytes(*buf);
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if data_len < *user_len_min || data_len > *user_len_max {
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return Err(io::Error::new(io::ErrorKind::InvalidData, "invalid size"))
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.into();
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}
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// if we still have padding to read, run the loop again.
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*this = State::Body {
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reader: Some(reader),
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consumed: 0,
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user_len: data_len,
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};
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}
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State::Size {
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reader,
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filled,
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buf,
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..
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} => {
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let reader = reader.as_mut().unwrap();
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let mut read_buf = ReadBuf::new(&mut buf[..]);
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read_buf.advance(*filled as usize);
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ready!(Pin::new(reader).poll_read(cx, &mut read_buf))?;
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let new_filled = read_buf.filled().len() as u8;
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if *filled == new_filled {
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return Err(io::ErrorKind::UnexpectedEof.into()).into();
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}
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*filled = new_filled;
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}
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State::Body {
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reader,
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consumed,
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user_len,
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} => {
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let body_len = *user_len & !7;
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let remaining = body_len - *consumed;
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let reader = if remaining == 0 {
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let reader = reader.take().unwrap();
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let user_len = (*user_len & 7) as u8;
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*this = State::Trailer(TrailerReader::new(reader, user_len));
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continue;
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} else {
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reader.as_mut().unwrap()
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};
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let mut bytes_read = 0;
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ready!(with_limited(buf, remaining, |buf| {
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let ret = Pin::new(reader).poll_read(cx, buf);
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bytes_read = buf.initialized().len();
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ret
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}))?;
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*consumed += bytes_read as u64;
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return if bytes_read != 0 {
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Ok(())
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} else {
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Err(io::ErrorKind::UnexpectedEof.into())
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}
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// return EOF
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return Ok(()).into();
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.into();
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}
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State::Trailer(reader) => {
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return Pin::new(reader).poll_read(cx, buf);
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}
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}
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}
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}
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}
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/// Make a limited version of `buf`, consisting only of up to `n` bytes of the unfilled section, and call `f` with it.
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/// After `f` returns, we propagate the filled cursor advancement back to `buf`.
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fn with_limited<R>(buf: &mut ReadBuf, n: u64, f: impl FnOnce(&mut ReadBuf) -> R) -> R {
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let mut nbuf = buf.take(n.try_into().unwrap_or(usize::MAX));
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let ptr = nbuf.initialized().as_ptr();
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let ret = f(&mut nbuf);
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// SAFETY: `ReadBuf::take` only returns the *unfilled* section of `buf`,
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// so anything filled is new, initialized data.
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//
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// We verify that `nbuf` still points to the same buffer,
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// so we're sure it hasn't been swapped out.
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unsafe {
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// ensure our buffer hasn't been swapped out
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assert_eq!(nbuf.initialized().as_ptr(), ptr);
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let n = nbuf.filled().len();
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buf.assume_init(n);
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buf.advance(n);
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}
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ret
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}
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#[cfg(test)]
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mod tests {
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use std::time::Duration;
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use crate::wire::bytes::write_bytes;
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use crate::wire::bytes::{padding_len, write_bytes};
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use hex_literal::hex;
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use lazy_static::lazy_static;
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use rstest::rstest;
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@ -390,13 +371,12 @@ mod tests {
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);
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}
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/// Start a 9 bytes payload packet, but return an error at various stages *after* the actual payload.
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/// read_exact with a 9 bytes buffer is expected to succeed, but any further
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/// read, as well as read_to_end are expected to fail.
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/// Start a 9 bytes payload packet, but don't supply the necessary padding.
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/// This is expected to always fail before returning the final data.
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#[rstest]
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#[case::before_padding(8 + 9)]
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#[case::during_padding(8 + 9 + 2)]
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#[case::after_padding(8 + 9 + padding_len(9) as usize)]
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#[case::after_padding(8 + 9 + padding_len(9) as usize - 1)]
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#[tokio::test]
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async fn read_9b_eof_after_payload(#[case] offset: usize) {
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let payload = &hex!("FF0102030405060708");
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@ -405,28 +385,12 @@ mod tests {
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.build();
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let mut r = BytesReader::new(&mut mock, ..MAX_LEN);
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let mut buf = [0; 9];
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// read_exact of the payload will succeed, but a subsequent read will
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// read_exact of the payload *body* will succeed, but a subsequent read will
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// return UnexpectedEof error.
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r.read_exact(&mut buf).await.expect("should succeed");
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assert_eq!(r.read_exact(&mut [0; 8]).await.unwrap(), 8);
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assert_eq!(
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r.read_exact(&mut buf[4..=4])
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.await
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.expect_err("must fail")
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.kind(),
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std::io::ErrorKind::UnexpectedEof
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);
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// read_to_end will fail.
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let mut mock = Builder::new()
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.read(&produce_packet_bytes(payload).await[..8 + payload.len()])
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.build();
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let mut r = BytesReader::new(&mut mock, ..MAX_LEN);
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let mut buf = Vec::new();
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assert_eq!(
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r.read_to_end(&mut buf).await.expect_err("must fail").kind(),
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r.read_exact(&mut [0]).await.unwrap_err().kind(),
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std::io::ErrorKind::UnexpectedEof
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);
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}
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175
tvix/nix-compat/src/wire/bytes/reader/trailer.rs
Normal file
175
tvix/nix-compat/src/wire/bytes/reader/trailer.rs
Normal file
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@ -0,0 +1,175 @@
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use std::{
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pin::Pin,
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task::{self, ready, Poll},
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};
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use tokio::io::{self, AsyncRead, ReadBuf};
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|
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#[derive(Debug)]
|
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pub enum TrailerReader<R> {
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Reading {
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reader: R,
|
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user_len: u8,
|
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filled: u8,
|
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buf: [u8; 8],
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},
|
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Releasing {
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off: u8,
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len: u8,
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buf: [u8; 8],
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},
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Done,
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}
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|
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impl<R: AsyncRead + Unpin> TrailerReader<R> {
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pub fn new(reader: R, user_len: u8) -> Self {
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if user_len == 0 {
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return Self::Done;
|
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}
|
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|
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assert!(user_len < 8, "payload in trailer must be less than 8 bytes");
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Self::Reading {
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reader,
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user_len,
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filled: 0,
|
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buf: [0; 8],
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}
|
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}
|
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}
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|
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impl<R: AsyncRead + Unpin> AsyncRead for TrailerReader<R> {
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fn poll_read(
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self: Pin<&mut Self>,
|
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cx: &mut task::Context,
|
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user_buf: &mut ReadBuf,
|
||||
) -> Poll<io::Result<()>> {
|
||||
let this = self.get_mut();
|
||||
|
||||
loop {
|
||||
match this {
|
||||
&mut Self::Reading {
|
||||
reader: _,
|
||||
user_len,
|
||||
filled: 8,
|
||||
buf,
|
||||
} => {
|
||||
*this = Self::Releasing {
|
||||
off: 0,
|
||||
len: user_len,
|
||||
buf,
|
||||
};
|
||||
}
|
||||
Self::Reading {
|
||||
reader,
|
||||
user_len,
|
||||
filled,
|
||||
buf,
|
||||
} => {
|
||||
let mut read_buf = ReadBuf::new(&mut buf[..]);
|
||||
read_buf.advance(*filled as usize);
|
||||
ready!(Pin::new(reader).poll_read(cx, &mut read_buf))?;
|
||||
|
||||
let new_filled = read_buf.filled().len() as u8;
|
||||
if *filled == new_filled {
|
||||
return Err(io::ErrorKind::UnexpectedEof.into()).into();
|
||||
}
|
||||
|
||||
*filled = new_filled;
|
||||
|
||||
// ensure the padding is all zeroes
|
||||
if (u64::from_le_bytes(*buf) >> (*user_len * 8)) != 0 {
|
||||
return Err(io::ErrorKind::InvalidData.into()).into();
|
||||
}
|
||||
}
|
||||
Self::Releasing { off: 8, .. } => {
|
||||
*this = Self::Done;
|
||||
}
|
||||
Self::Releasing { off, len, buf } => {
|
||||
assert_ne!(user_buf.remaining(), 0);
|
||||
|
||||
let buf = &buf[*off as usize..*len as usize];
|
||||
let buf = &buf[..usize::min(buf.len(), user_buf.remaining())];
|
||||
|
||||
user_buf.put_slice(buf);
|
||||
*off += buf.len() as u8;
|
||||
|
||||
break;
|
||||
}
|
||||
Self::Done => break,
|
||||
}
|
||||
}
|
||||
|
||||
Ok(()).into()
|
||||
}
|
||||
}
|
||||
|
||||
#[cfg(test)]
|
||||
mod tests {
|
||||
use std::time::Duration;
|
||||
use tokio::io::AsyncReadExt;
|
||||
|
||||
use super::*;
|
||||
|
||||
#[tokio::test]
|
||||
async fn unexpected_eof() {
|
||||
let reader = tokio_test::io::Builder::new()
|
||||
.read(&[0xed])
|
||||
.wait(Duration::ZERO)
|
||||
.read(&[0xef, 0x00])
|
||||
.build();
|
||||
|
||||
let mut reader = TrailerReader::new(reader, 2);
|
||||
|
||||
let mut buf = vec![];
|
||||
assert_eq!(
|
||||
reader.read_to_end(&mut buf).await.unwrap_err().kind(),
|
||||
io::ErrorKind::UnexpectedEof
|
||||
);
|
||||
}
|
||||
|
||||
#[tokio::test]
|
||||
async fn invalid_padding() {
|
||||
let reader = tokio_test::io::Builder::new()
|
||||
.read(&[0xed])
|
||||
.wait(Duration::ZERO)
|
||||
.read(&[0xef, 0x01, 0x00])
|
||||
.wait(Duration::ZERO)
|
||||
.build();
|
||||
|
||||
let mut reader = TrailerReader::new(reader, 2);
|
||||
|
||||
let mut buf = vec![];
|
||||
assert_eq!(
|
||||
reader.read_to_end(&mut buf).await.unwrap_err().kind(),
|
||||
io::ErrorKind::InvalidData
|
||||
);
|
||||
}
|
||||
|
||||
#[tokio::test]
|
||||
async fn success() {
|
||||
let reader = tokio_test::io::Builder::new()
|
||||
.read(&[0xed])
|
||||
.wait(Duration::ZERO)
|
||||
.read(&[0xef, 0x00])
|
||||
.wait(Duration::ZERO)
|
||||
.read(&[0x00, 0x00, 0x00, 0x00, 0x00])
|
||||
.build();
|
||||
|
||||
let mut reader = TrailerReader::new(reader, 2);
|
||||
|
||||
let mut buf = vec![];
|
||||
reader.read_to_end(&mut buf).await.unwrap();
|
||||
|
||||
assert_eq!(buf, &[0xed, 0xef]);
|
||||
}
|
||||
|
||||
#[tokio::test]
|
||||
async fn no_padding() {
|
||||
let reader = tokio_test::io::Builder::new().build();
|
||||
let mut reader = TrailerReader::new(reader, 0);
|
||||
|
||||
let mut buf = vec![];
|
||||
reader.read_to_end(&mut buf).await.unwrap();
|
||||
assert!(buf.is_empty());
|
||||
}
|
||||
}
|
||||
Loading…
Reference in a new issue