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use crate::codec::decoder::Decoder;
use crate::codec::encoder::Encoder;
use bytes::{Buf, BufMut, BytesMut};
use std::{cmp, fmt, io, str, usize};
/// A simple [`Decoder`] and [`Encoder`] implementation that splits up data into lines.
///
/// [`Decoder`]: crate::codec::Decoder
/// [`Encoder`]: crate::codec::Encoder
#[derive(Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
pub struct LinesCodec {
// Stored index of the next index to examine for a `\n` character.
// This is used to optimize searching.
// For example, if `decode` was called with `abc`, it would hold `3`,
// because that is the next index to examine.
// The next time `decode` is called with `abcde\n`, the method will
// only look at `de\n` before returning.
next_index: usize,
/// The maximum length for a given line. If `usize::MAX`, lines will be
/// read until a `\n` character is reached.
max_length: usize,
/// Are we currently discarding the remainder of a line which was over
/// the length limit?
is_discarding: bool,
}
impl LinesCodec {
/// Returns a `LinesCodec` for splitting up data into lines.
///
/// # Note
///
/// The returned `LinesCodec` will not have an upper bound on the length
/// of a buffered line. See the documentation for [`new_with_max_length`]
/// for information on why this could be a potential security risk.
///
/// [`new_with_max_length`]: crate::codec::LinesCodec::new_with_max_length()
pub fn new() -> LinesCodec {
LinesCodec {
next_index: 0,
max_length: usize::MAX,
is_discarding: false,
}
}
/// Returns a `LinesCodec` with a maximum line length limit.
///
/// If this is set, calls to `LinesCodec::decode` will return a
/// [`LinesCodecError`] when a line exceeds the length limit. Subsequent calls
/// will discard up to `limit` bytes from that line until a newline
/// character is reached, returning `None` until the line over the limit
/// has been fully discarded. After that point, calls to `decode` will
/// function as normal.
///
/// # Note
///
/// Setting a length limit is highly recommended for any `LinesCodec` which
/// will be exposed to untrusted input. Otherwise, the size of the buffer
/// that holds the line currently being read is unbounded. An attacker could
/// exploit this unbounded buffer by sending an unbounded amount of input
/// without any `\n` characters, causing unbounded memory consumption.
///
/// [`LinesCodecError`]: crate::codec::LinesCodecError
pub fn new_with_max_length(max_length: usize) -> Self {
LinesCodec {
max_length,
..LinesCodec::new()
}
}
/// Returns the maximum line length when decoding.
///
/// ```
/// use std::usize;
/// use tokio_util::codec::LinesCodec;
///
/// let codec = LinesCodec::new();
/// assert_eq!(codec.max_length(), usize::MAX);
/// ```
/// ```
/// use tokio_util::codec::LinesCodec;
///
/// let codec = LinesCodec::new_with_max_length(256);
/// assert_eq!(codec.max_length(), 256);
/// ```
pub fn max_length(&self) -> usize {
self.max_length
}
}
fn utf8(buf: &[u8]) -> Result<&str, io::Error> {
str::from_utf8(buf)
.map_err(|_| io::Error::new(io::ErrorKind::InvalidData, "Unable to decode input as UTF8"))
}
fn without_carriage_return(s: &[u8]) -> &[u8] {
if let Some(&b'\r') = s.last() {
&s[..s.len() - 1]
} else {
s
}
}
impl Decoder for LinesCodec {
type Item = String;
type Error = LinesCodecError;
fn decode(&mut self, buf: &mut BytesMut) -> Result<Option<String>, LinesCodecError> {
loop {
// Determine how far into the buffer we'll search for a newline. If
// there's no max_length set, we'll read to the end of the buffer.
let read_to = cmp::min(self.max_length.saturating_add(1), buf.len());
let newline_offset = buf[self.next_index..read_to]
.iter()
.position(|b| *b == b'\n');
match (self.is_discarding, newline_offset) {
(true, Some(offset)) => {
// If we found a newline, discard up to that offset and
// then stop discarding. On the next iteration, we'll try
// to read a line normally.
buf.advance(offset + self.next_index + 1);
self.is_discarding = false;
self.next_index = 0;
}
(true, None) => {
// Otherwise, we didn't find a newline, so we'll discard
// everything we read. On the next iteration, we'll continue
// discarding up to max_len bytes unless we find a newline.
buf.advance(read_to);
self.next_index = 0;
if buf.is_empty() {
return Ok(None);
}
}
(false, Some(offset)) => {
// Found a line!
let newline_index = offset + self.next_index;
self.next_index = 0;
let line = buf.split_to(newline_index + 1);
let line = &line[..line.len() - 1];
let line = without_carriage_return(line);
let line = utf8(line)?;
return Ok(Some(line.to_string()));
}
(false, None) if buf.len() > self.max_length => {
// Reached the maximum length without finding a
// newline, return an error and start discarding on the
// next call.
self.is_discarding = true;
return Err(LinesCodecError::MaxLineLengthExceeded);
}
(false, None) => {
// We didn't find a line or reach the length limit, so the next
// call will resume searching at the current offset.
self.next_index = read_to;
return Ok(None);
}
}
}
}
fn decode_eof(&mut self, buf: &mut BytesMut) -> Result<Option<String>, LinesCodecError> {
Ok(match self.decode(buf)? {
Some(frame) => Some(frame),
None => {
// No terminating newline - return remaining data, if any
if buf.is_empty() || buf == &b"\r"[..] {
None
} else {
let line = buf.split_to(buf.len());
let line = without_carriage_return(&line);
let line = utf8(line)?;
self.next_index = 0;
Some(line.to_string())
}
}
})
}
}
impl<T> Encoder<T> for LinesCodec
where
T: AsRef<str>,
{
type Error = LinesCodecError;
fn encode(&mut self, line: T, buf: &mut BytesMut) -> Result<(), LinesCodecError> {
let line = line.as_ref();
buf.reserve(line.len() + 1);
buf.put(line.as_bytes());
buf.put_u8(b'\n');
Ok(())
}
}
impl Default for LinesCodec {
fn default() -> Self {
Self::new()
}
}
/// An error occurred while encoding or decoding a line.
#[derive(Debug)]
pub enum LinesCodecError {
/// The maximum line length was exceeded.
MaxLineLengthExceeded,
/// An IO error occurred.
Io(io::Error),
}
impl fmt::Display for LinesCodecError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
LinesCodecError::MaxLineLengthExceeded => write!(f, "max line length exceeded"),
LinesCodecError::Io(e) => write!(f, "{}", e),
}
}
}
impl From<io::Error> for LinesCodecError {
fn from(e: io::Error) -> LinesCodecError {
LinesCodecError::Io(e)
}
}
impl std::error::Error for LinesCodecError {}