1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208
//! Wrapper type to add buffering to read streams.
use super::SeekFrom;
/// A wrapper to add buffering to a read stream.
///
/// Unlike [`std::io::BufReader`], this wrapper does not invalidate the read
/// buffer every time a [`Seek`](super::Seek) method is called. It also caches
/// the underlying stream position to avoid unnecessary system calls.
///
/// # Limitations
///
/// Reading or seeking the wrapped stream object directly will cause an
/// inconsistency in the internal state of the `BufReader`. Calling
/// [`BufReader::seek_invalidate`] will clear the read buffer and reset the
/// internal state to be consistent with the wrapped stream.
#[cfg_attr(all(doc, nightly), doc(cfg(feature = "std")))]
pub struct BufReader<T> {
inner: std::io::BufReader<T>,
pos: Option<u64>,
}
impl<T: super::Read> BufReader<T> {
/// Creates a new `BufReader<T>` with a default buffer capacity.
pub fn new(inner: T) -> BufReader<T> {
BufReader {
inner: std::io::BufReader::new(inner),
pos: None,
}
}
/// Creates a new `BufReader<T>` with the specified buffer capacity.
pub fn with_capacity(capacity: usize, inner: T) -> BufReader<T> {
BufReader {
inner: std::io::BufReader::with_capacity(capacity, inner),
pos: None,
}
}
}
impl<T> BufReader<T> {
/// Returns a reference to the internally buffered data.
pub fn buffer(&self) -> &[u8] {
self.inner.buffer()
}
/// Returns the number of bytes the internal buffer can hold at once.
pub fn capacity(&self) -> usize {
self.inner.capacity()
}
/// Gets a mutable reference to the underlying reader.
///
/// It is inadvisable to directly read from the underlying reader as it
/// will, at the least, break the cached position information.
pub fn get_mut(&mut self) -> &mut T {
self.inner.get_mut()
}
/// Gets a reference to the underlying reader.
pub fn get_ref(&self) -> &T {
self.inner.get_ref()
}
/// Unwraps this `BufReader<T>`, returning the underlying reader.
///
/// Note that any leftover data in the internal buffer is lost. Therefore,
/// a following read from the underlying reader may lead to data loss.
pub fn into_inner(self) -> T {
self.inner.into_inner()
}
}
impl<T: super::Seek> BufReader<T> {
/// Performs a seek that forces invalidation of the buffer and internal
/// position state.
///
/// # Errors
///
/// Returns an error if seeking fails.
pub fn seek_invalidate(&mut self, pos: SeekFrom) -> super::Result<u64> {
let n = super::Seek::seek(&mut self.inner, pos)?;
self.pos = Some(n);
Ok(n)
}
}
impl<T: super::Read> super::Read for BufReader<T> {
fn read(&mut self, buf: &mut [u8]) -> super::Result<usize> {
let n = self.inner.read(buf)?;
if let Some(pos) = &mut self.pos {
*pos += n as u64;
}
Ok(n)
}
fn read_vectored(&mut self, bufs: &mut [std::io::IoSliceMut<'_>]) -> super::Result<usize> {
let n = self.inner.read_vectored(bufs)?;
if let Some(pos) = &mut self.pos {
*pos += n as u64;
}
Ok(n)
}
fn read_to_end(&mut self, buf: &mut Vec<u8>) -> super::Result<usize> {
let n = self.inner.read_to_end(buf)?;
if let Some(pos) = &mut self.pos {
*pos += n as u64;
}
Ok(n)
}
fn read_to_string(&mut self, buf: &mut String) -> super::Result<usize> {
let n = self.inner.read_to_string(buf)?;
if let Some(pos) = &mut self.pos {
*pos += n as u64;
}
Ok(n)
}
fn read_exact(&mut self, buf: &mut [u8]) -> super::Result<()> {
self.inner.read_exact(buf)?;
if let Some(pos) = &mut self.pos {
*pos += buf.len() as u64;
}
Ok(())
}
}
impl<T: super::Seek> super::Seek for BufReader<T> {
fn seek(&mut self, pos: SeekFrom) -> super::Result<u64> {
let old = self.stream_position()?;
match pos {
SeekFrom::Start(n) => {
if old == n {
Ok(old)
} else {
let rel_n = if n >= old {
i64::try_from(n - old)
} else {
i64::try_from(old - n).map(|n| -n)
};
let n = if let Ok(rel_n) = rel_n {
self.seek(SeekFrom::Current(rel_n))?
} else {
self.inner.seek(pos)?
};
self.pos = Some(n);
Ok(n)
}
}
SeekFrom::End(_) => {
let n = self.inner.seek(pos)?;
self.pos = Some(n);
Ok(n)
}
SeekFrom::Current(rel_n) => {
if rel_n == 0 {
Ok(old)
} else {
// https://github.com/rust-lang/rust/issues/87840
let n = if rel_n >= 0 {
// Lint: The sign is checked in precondition above
#[allow(clippy::cast_sign_loss)]
old.checked_add(rel_n as u64)
} else {
old.checked_sub(rel_n.unsigned_abs())
};
if let Some(n) = n {
self.inner.seek_relative(rel_n)?;
self.pos = Some(n);
Ok(n)
} else {
Err(super::Error::new(
super::ErrorKind::InvalidInput,
"invalid seek to a negative or overflowing position",
))
}
}
}
}
}
fn stream_position(&mut self) -> super::Result<u64> {
Ok(match self.pos {
None => {
let pos = self.inner.stream_position()?;
self.pos = Some(pos);
pos
}
Some(pos) => pos,
})
}
}
impl<T: super::Read> std::io::BufRead for BufReader<T> {
fn fill_buf(&mut self) -> super::Result<&[u8]> {
self.inner.fill_buf()
}
fn consume(&mut self, amt: usize) {
self.inner.consume(amt);
}
}