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//! Buffering wrappers for I/O traits use crate::io::prelude::*; use crate::cmp; use crate::error; use crate::fmt; use crate::io::{self, Initializer, DEFAULT_BUF_SIZE, Error, ErrorKind, SeekFrom, IoSlice, IoSliceMut}; use crate::memchr; /// The `BufReader<R>` struct adds buffering to any reader. /// /// It can be excessively inefficient to work directly with a [`Read`] instance. /// For example, every call to [`read`][`TcpStream::read`] on [`TcpStream`] /// results in a system call. A `BufReader<R>` performs large, infrequent reads on /// the underlying [`Read`] and maintains an in-memory buffer of the results. /// /// `BufReader<R>` can improve the speed of programs that make *small* and /// *repeated* read calls to the same file or network socket. It does not /// help when reading very large amounts at once, or reading just one or a few /// times. It also provides no advantage when reading from a source that is /// already in memory, like a `Vec<u8>`. /// /// When the `BufReader<R>` is dropped, the contents of its buffer will be /// discarded. Creating multiple instances of a `BufReader<R>` on the same /// stream can cause data loss. /// /// [`Read`]: ../../std/io/trait.Read.html /// [`TcpStream::read`]: ../../std/net/struct.TcpStream.html#method.read /// [`TcpStream`]: ../../std/net/struct.TcpStream.html /// /// # Examples /// /// ```no_run /// use std::io::prelude::*; /// use std::io::BufReader; /// use std::fs::File; /// /// fn main() -> std::io::Result<()> { /// let f = File::open("log.txt")?; /// let mut reader = BufReader::new(f); /// /// let mut line = String::new(); /// let len = reader.read_line(&mut line)?; /// println!("First line is {} bytes long", len); /// Ok(()) /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub struct BufReader<R> { inner: R, buf: Box<[u8]>, pos: usize, cap: usize, } impl<R: Read> BufReader<R> { /// Creates a new `BufReader<R>` with a default buffer capacity. The default is currently 8 KB, /// but may change in the future. /// /// # Examples /// /// ```no_run /// use std::io::BufReader; /// use std::fs::File; /// /// fn main() -> std::io::Result<()> { /// let f = File::open("log.txt")?; /// let reader = BufReader::new(f); /// Ok(()) /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn new(inner: R) -> BufReader<R> { BufReader::with_capacity(DEFAULT_BUF_SIZE, inner) } /// Creates a new `BufReader<R>` with the specified buffer capacity. /// /// # Examples /// /// Creating a buffer with ten bytes of capacity: /// /// ```no_run /// use std::io::BufReader; /// use std::fs::File; /// /// fn main() -> std::io::Result<()> { /// let f = File::open("log.txt")?; /// let reader = BufReader::with_capacity(10, f); /// Ok(()) /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn with_capacity(capacity: usize, inner: R) -> BufReader<R> { unsafe { let mut buffer = Vec::with_capacity(capacity); buffer.set_len(capacity); inner.initializer().initialize(&mut buffer); BufReader { inner, buf: buffer.into_boxed_slice(), pos: 0, cap: 0, } } } } impl<R> BufReader<R> { /// Gets a reference to the underlying reader. /// /// It is inadvisable to directly read from the underlying reader. /// /// # Examples /// /// ```no_run /// use std::io::BufReader; /// use std::fs::File; /// /// fn main() -> std::io::Result<()> { /// let f1 = File::open("log.txt")?; /// let reader = BufReader::new(f1); /// /// let f2 = reader.get_ref(); /// Ok(()) /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn get_ref(&self) -> &R { &self.inner } /// Gets a mutable reference to the underlying reader. /// /// It is inadvisable to directly read from the underlying reader. /// /// # Examples /// /// ```no_run /// use std::io::BufReader; /// use std::fs::File; /// /// fn main() -> std::io::Result<()> { /// let f1 = File::open("log.txt")?; /// let mut reader = BufReader::new(f1); /// /// let f2 = reader.get_mut(); /// Ok(()) /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn get_mut(&mut self) -> &mut R { &mut self.inner } /// Returns a reference to the internally buffered data. /// /// Unlike `fill_buf`, this will not attempt to fill the buffer if it is empty. /// /// # Examples /// /// ```no_run /// use std::io::{BufReader, BufRead}; /// use std::fs::File; /// /// fn main() -> std::io::Result<()> { /// let f = File::open("log.txt")?; /// let mut reader = BufReader::new(f); /// assert!(reader.buffer().is_empty()); /// /// if reader.fill_buf()?.len() > 0 { /// assert!(!reader.buffer().is_empty()); /// } /// Ok(()) /// } /// ``` #[stable(feature = "bufreader_buffer", since = "1.37.0")] pub fn buffer(&self) -> &[u8] { &self.buf[self.pos..self.cap] } /// Unwraps this `BufReader<R>`, returning the underlying reader. /// /// Note that any leftover data in the internal buffer is lost. /// /// # Examples /// /// ```no_run /// use std::io::BufReader; /// use std::fs::File; /// /// fn main() -> std::io::Result<()> { /// let f1 = File::open("log.txt")?; /// let reader = BufReader::new(f1); /// /// let f2 = reader.into_inner(); /// Ok(()) /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn into_inner(self) -> R { self.inner } /// Invalidates all data in the internal buffer. #[inline] fn discard_buffer(&mut self) { self.pos = 0; self.cap = 0; } } impl<R: Seek> BufReader<R> { /// Seeks relative to the current position. If the new position lies within the buffer, /// the buffer will not be flushed, allowing for more efficient seeks. /// This method does not return the location of the underlying reader, so the caller /// must track this information themselves if it is required. #[unstable(feature = "bufreader_seek_relative", issue = "31100")] pub fn seek_relative(&mut self, offset: i64) -> io::Result<()> { let pos = self.pos as u64; if offset < 0 { if let Some(new_pos) = pos.checked_sub((-offset) as u64) { self.pos = new_pos as usize; return Ok(()) } } else { if let Some(new_pos) = pos.checked_add(offset as u64) { if new_pos <= self.cap as u64 { self.pos = new_pos as usize; return Ok(()) } } } self.seek(SeekFrom::Current(offset)).map(|_|()) } } #[stable(feature = "rust1", since = "1.0.0")] impl<R: Read> Read for BufReader<R> { fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> { // If we don't have any buffered data and we're doing a massive read // (larger than our internal buffer), bypass our internal buffer // entirely. if self.pos == self.cap && buf.len() >= self.buf.len() { self.discard_buffer(); return self.inner.read(buf); } let nread = { let mut rem = self.fill_buf()?; rem.read(buf)? }; self.consume(nread); Ok(nread) } fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> { let total_len = bufs.iter().map(|b| b.len()).sum::<usize>(); if self.pos == self.cap && total_len >= self.buf.len() { self.discard_buffer(); return self.inner.read_vectored(bufs); } let nread = { let mut rem = self.fill_buf()?; rem.read_vectored(bufs)? }; self.consume(nread); Ok(nread) } // we can't skip unconditionally because of the large buffer case in read. unsafe fn initializer(&self) -> Initializer { self.inner.initializer() } } #[stable(feature = "rust1", since = "1.0.0")] impl<R: Read> BufRead for BufReader<R> { fn fill_buf(&mut self) -> io::Result<&[u8]> { // If we've reached the end of our internal buffer then we need to fetch // some more data from the underlying reader. // Branch using `>=` instead of the more correct `==` // to tell the compiler that the pos..cap slice is always valid. if self.pos >= self.cap { debug_assert!(self.pos == self.cap); self.cap = self.inner.read(&mut self.buf)?; self.pos = 0; } Ok(&self.buf[self.pos..self.cap]) } fn consume(&mut self, amt: usize) { self.pos = cmp::min(self.pos + amt, self.cap); } } #[stable(feature = "rust1", since = "1.0.0")] impl<R> fmt::Debug for BufReader<R> where R: fmt::Debug { fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result { fmt.debug_struct("BufReader") .field("reader", &self.inner) .field("buffer", &format_args!("{}/{}", self.cap - self.pos, self.buf.len())) .finish() } } #[stable(feature = "rust1", since = "1.0.0")] impl<R: Seek> Seek for BufReader<R> { /// Seek to an offset, in bytes, in the underlying reader. /// /// The position used for seeking with `SeekFrom::Current(_)` is the /// position the underlying reader would be at if the `BufReader<R>` had no /// internal buffer. /// /// Seeking always discards the internal buffer, even if the seek position /// would otherwise fall within it. This guarantees that calling /// `.into_inner()` immediately after a seek yields the underlying reader /// at the same position. /// /// To seek without discarding the internal buffer, use [`BufReader::seek_relative`]. /// /// See [`std::io::Seek`] for more details. /// /// Note: In the edge case where you're seeking with `SeekFrom::Current(n)` /// where `n` minus the internal buffer length overflows an `i64`, two /// seeks will be performed instead of one. If the second seek returns /// `Err`, the underlying reader will be left at the same position it would /// have if you called `seek` with `SeekFrom::Current(0)`. /// /// [`BufReader::seek_relative`]: struct.BufReader.html#method.seek_relative /// [`std::io::Seek`]: trait.Seek.html fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> { let result: u64; if let SeekFrom::Current(n) = pos { let remainder = (self.cap - self.pos) as i64; // it should be safe to assume that remainder fits within an i64 as the alternative // means we managed to allocate 8 exbibytes and that's absurd. // But it's not out of the realm of possibility for some weird underlying reader to // support seeking by i64::min_value() so we need to handle underflow when subtracting // remainder. if let Some(offset) = n.checked_sub(remainder) { result = self.inner.seek(SeekFrom::Current(offset))?; } else { // seek backwards by our remainder, and then by the offset self.inner.seek(SeekFrom::Current(-remainder))?; self.discard_buffer(); result = self.inner.seek(SeekFrom::Current(n))?; } } else { // Seeking with Start/End doesn't care about our buffer length. result = self.inner.seek(pos)?; } self.discard_buffer(); Ok(result) } } /// Wraps a writer and buffers its output. /// /// It can be excessively inefficient to work directly with something that /// implements [`Write`]. For example, every call to /// [`write`][`TcpStream::write`] on [`TcpStream`] results in a system call. A /// `BufWriter<W>` keeps an in-memory buffer of data and writes it to an underlying /// writer in large, infrequent batches. /// /// `BufWriter<W>` can improve the speed of programs that make *small* and /// *repeated* write calls to the same file or network socket. It does not /// help when writing very large amounts at once, or writing just one or a few /// times. It also provides no advantage when writing to a destination that is /// in memory, like a `Vec<u8>`. /// /// It is critical to call [`flush`] before `BufWriter<W>` is dropped. Though /// dropping will attempt to flush the the contents of the buffer, any errors /// that happen in the process of dropping will be ignored. Calling ['flush'] /// ensures that the buffer is empty and thus dropping will not even attempt /// file operations. /// /// # Examples /// /// Let's write the numbers one through ten to a [`TcpStream`]: /// /// ```no_run /// use std::io::prelude::*; /// use std::net::TcpStream; /// /// let mut stream = TcpStream::connect("127.0.0.1:34254").unwrap(); /// /// for i in 0..10 { /// stream.write(&[i+1]).unwrap(); /// } /// ``` /// /// Because we're not buffering, we write each one in turn, incurring the /// overhead of a system call per byte written. We can fix this with a /// `BufWriter<W>`: /// /// ```no_run /// use std::io::prelude::*; /// use std::io::BufWriter; /// use std::net::TcpStream; /// /// let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap()); /// /// for i in 0..10 { /// stream.write(&[i+1]).unwrap(); /// } /// stream.flush().unwrap(); /// ``` /// /// By wrapping the stream with a `BufWriter<W>`, these ten writes are all grouped /// together by the buffer and will all be written out in one system call when /// the `stream` is flushed. /// /// [`Write`]: ../../std/io/trait.Write.html /// [`TcpStream::write`]: ../../std/net/struct.TcpStream.html#method.write /// [`TcpStream`]: ../../std/net/struct.TcpStream.html /// [`flush`]: #method.flush #[stable(feature = "rust1", since = "1.0.0")] pub struct BufWriter<W: Write> { inner: Option<W>, buf: Vec<u8>, // #30888: If the inner writer panics in a call to write, we don't want to // write the buffered data a second time in BufWriter's destructor. This // flag tells the Drop impl if it should skip the flush. panicked: bool, } /// An error returned by `into_inner` which combines an error that /// happened while writing out the buffer, and the buffered writer object /// which may be used to recover from the condition. /// /// # Examples /// /// ```no_run /// use std::io::BufWriter; /// use std::net::TcpStream; /// /// let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap()); /// /// // do stuff with the stream /// /// // we want to get our `TcpStream` back, so let's try: /// /// let stream = match stream.into_inner() { /// Ok(s) => s, /// Err(e) => { /// // Here, e is an IntoInnerError /// panic!("An error occurred"); /// } /// }; /// ``` #[derive(Debug)] #[stable(feature = "rust1", since = "1.0.0")] pub struct IntoInnerError<W>(W, Error); impl<W: Write> BufWriter<W> { /// Creates a new `BufWriter<W>` with a default buffer capacity. The default is currently 8 KB, /// but may change in the future. /// /// # Examples /// /// ```no_run /// use std::io::BufWriter; /// use std::net::TcpStream; /// /// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap()); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn new(inner: W) -> BufWriter<W> { BufWriter::with_capacity(DEFAULT_BUF_SIZE, inner) } /// Creates a new `BufWriter<W>` with the specified buffer capacity. /// /// # Examples /// /// Creating a buffer with a buffer of a hundred bytes. /// /// ```no_run /// use std::io::BufWriter; /// use std::net::TcpStream; /// /// let stream = TcpStream::connect("127.0.0.1:34254").unwrap(); /// let mut buffer = BufWriter::with_capacity(100, stream); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn with_capacity(capacity: usize, inner: W) -> BufWriter<W> { BufWriter { inner: Some(inner), buf: Vec::with_capacity(capacity), panicked: false, } } fn flush_buf(&mut self) -> io::Result<()> { let mut written = 0; let len = self.buf.len(); let mut ret = Ok(()); while written < len { self.panicked = true; let r = self.inner.as_mut().unwrap().write(&self.buf[written..]); self.panicked = false; match r { Ok(0) => { ret = Err(Error::new(ErrorKind::WriteZero, "failed to write the buffered data")); break; } Ok(n) => written += n, Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {} Err(e) => { ret = Err(e); break } } } if written > 0 { self.buf.drain(..written); } ret } /// Gets a reference to the underlying writer. /// /// # Examples /// /// ```no_run /// use std::io::BufWriter; /// use std::net::TcpStream; /// /// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap()); /// /// // we can use reference just like buffer /// let reference = buffer.get_ref(); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn get_ref(&self) -> &W { self.inner.as_ref().unwrap() } /// Gets a mutable reference to the underlying writer. /// /// It is inadvisable to directly write to the underlying writer. /// /// # Examples /// /// ```no_run /// use std::io::BufWriter; /// use std::net::TcpStream; /// /// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap()); /// /// // we can use reference just like buffer /// let reference = buffer.get_mut(); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn get_mut(&mut self) -> &mut W { self.inner.as_mut().unwrap() } /// Returns a reference to the internally buffered data. /// /// # Examples /// /// ```no_run /// use std::io::BufWriter; /// use std::net::TcpStream; /// /// let buf_writer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap()); /// /// // See how many bytes are currently buffered /// let bytes_buffered = buf_writer.buffer().len(); /// ``` #[stable(feature = "bufreader_buffer", since = "1.37.0")] pub fn buffer(&self) -> &[u8] { &self.buf } /// Unwraps this `BufWriter<W>`, returning the underlying writer. /// /// The buffer is written out before returning the writer. /// /// # Errors /// /// An `Err` will be returned if an error occurs while flushing the buffer. /// /// # Examples /// /// ```no_run /// use std::io::BufWriter; /// use std::net::TcpStream; /// /// let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap()); /// /// // unwrap the TcpStream and flush the buffer /// let stream = buffer.into_inner().unwrap(); /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn into_inner(mut self) -> Result<W, IntoInnerError<BufWriter<W>>> { match self.flush_buf() { Err(e) => Err(IntoInnerError(self, e)), Ok(()) => Ok(self.inner.take().unwrap()) } } } #[stable(feature = "rust1", since = "1.0.0")] impl<W: Write> Write for BufWriter<W> { fn write(&mut self, buf: &[u8]) -> io::Result<usize> { if self.buf.len() + buf.len() > self.buf.capacity() { self.flush_buf()?; } if buf.len() >= self.buf.capacity() { self.panicked = true; let r = self.get_mut().write(buf); self.panicked = false; r } else { self.buf.write(buf) } } fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> { let total_len = bufs.iter().map(|b| b.len()).sum::<usize>(); if self.buf.len() + total_len > self.buf.capacity() { self.flush_buf()?; } if total_len >= self.buf.capacity() { self.panicked = true; let r = self.get_mut().write_vectored(bufs); self.panicked = false; r } else { self.buf.write_vectored(bufs) } } fn flush(&mut self) -> io::Result<()> { self.flush_buf().and_then(|()| self.get_mut().flush()) } } #[stable(feature = "rust1", since = "1.0.0")] impl<W: Write> fmt::Debug for BufWriter<W> where W: fmt::Debug { fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result { fmt.debug_struct("BufWriter") .field("writer", &self.inner.as_ref().unwrap()) .field("buffer", &format_args!("{}/{}", self.buf.len(), self.buf.capacity())) .finish() } } #[stable(feature = "rust1", since = "1.0.0")] impl<W: Write + Seek> Seek for BufWriter<W> { /// Seek to the offset, in bytes, in the underlying writer. /// /// Seeking always writes out the internal buffer before seeking. fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> { self.flush_buf().and_then(|_| self.get_mut().seek(pos)) } } #[stable(feature = "rust1", since = "1.0.0")] impl<W: Write> Drop for BufWriter<W> { fn drop(&mut self) { if self.inner.is_some() && !self.panicked { // dtors should not panic, so we ignore a failed flush let _r = self.flush_buf(); } } } impl<W> IntoInnerError<W> { /// Returns the error which caused the call to `into_inner()` to fail. /// /// This error was returned when attempting to write the internal buffer. /// /// # Examples /// /// ```no_run /// use std::io::BufWriter; /// use std::net::TcpStream; /// /// let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap()); /// /// // do stuff with the stream /// /// // we want to get our `TcpStream` back, so let's try: /// /// let stream = match stream.into_inner() { /// Ok(s) => s, /// Err(e) => { /// // Here, e is an IntoInnerError, let's log the inner error. /// // /// // We'll just 'log' to stdout for this example. /// println!("{}", e.error()); /// /// panic!("An unexpected error occurred."); /// } /// }; /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn error(&self) -> &Error { &self.1 } /// Returns the buffered writer instance which generated the error. /// /// The returned object can be used for error recovery, such as /// re-inspecting the buffer. /// /// # Examples /// /// ```no_run /// use std::io::BufWriter; /// use std::net::TcpStream; /// /// let mut stream = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap()); /// /// // do stuff with the stream /// /// // we want to get our `TcpStream` back, so let's try: /// /// let stream = match stream.into_inner() { /// Ok(s) => s, /// Err(e) => { /// // Here, e is an IntoInnerError, let's re-examine the buffer: /// let buffer = e.into_inner(); /// /// // do stuff to try to recover /// /// // afterwards, let's just return the stream /// buffer.into_inner().unwrap() /// } /// }; /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn into_inner(self) -> W { self.0 } } #[stable(feature = "rust1", since = "1.0.0")] impl<W> From<IntoInnerError<W>> for Error { fn from(iie: IntoInnerError<W>) -> Error { iie.1 } } #[stable(feature = "rust1", since = "1.0.0")] impl<W: Send + fmt::Debug> error::Error for IntoInnerError<W> { fn description(&self) -> &str { error::Error::description(self.error()) } } #[stable(feature = "rust1", since = "1.0.0")] impl<W> fmt::Display for IntoInnerError<W> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { self.error().fmt(f) } } /// Wraps a writer and buffers output to it, flushing whenever a newline /// (`0x0a`, `'\n'`) is detected. /// /// The [`BufWriter`][bufwriter] struct wraps a writer and buffers its output. /// But it only does this batched write when it goes out of scope, or when the /// internal buffer is full. Sometimes, you'd prefer to write each line as it's /// completed, rather than the entire buffer at once. Enter `LineWriter`. It /// does exactly that. /// /// Like [`BufWriter`][bufwriter], a `LineWriter`’s buffer will also be flushed when the /// `LineWriter` goes out of scope or when its internal buffer is full. /// /// [bufwriter]: struct.BufWriter.html /// /// If there's still a partial line in the buffer when the `LineWriter` is /// dropped, it will flush those contents. /// /// # Examples /// /// We can use `LineWriter` to write one line at a time, significantly /// reducing the number of actual writes to the file. /// /// ```no_run /// use std::fs::{self, File}; /// use std::io::prelude::*; /// use std::io::LineWriter; /// /// fn main() -> std::io::Result<()> { /// let road_not_taken = b"I shall be telling this with a sigh /// Somewhere ages and ages hence: /// Two roads diverged in a wood, and I - /// I took the one less traveled by, /// And that has made all the difference."; /// /// let file = File::create("poem.txt")?; /// let mut file = LineWriter::new(file); /// /// file.write_all(b"I shall be telling this with a sigh")?; /// /// // No bytes are written until a newline is encountered (or /// // the internal buffer is filled). /// assert_eq!(fs::read_to_string("poem.txt")?, ""); /// file.write_all(b"\n")?; /// assert_eq!( /// fs::read_to_string("poem.txt")?, /// "I shall be telling this with a sigh\n", /// ); /// /// // Write the rest of the poem. /// file.write_all(b"Somewhere ages and ages hence: /// Two roads diverged in a wood, and I - /// I took the one less traveled by, /// And that has made all the difference.")?; /// /// // The last line of the poem doesn't end in a newline, so /// // we have to flush or drop the `LineWriter` to finish /// // writing. /// file.flush()?; /// /// // Confirm the whole poem was written. /// assert_eq!(fs::read("poem.txt")?, &road_not_taken[..]); /// Ok(()) /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub struct LineWriter<W: Write> { inner: BufWriter<W>, need_flush: bool, } impl<W: Write> LineWriter<W> { /// Creates a new `LineWriter`. /// /// # Examples /// /// ```no_run /// use std::fs::File; /// use std::io::LineWriter; /// /// fn main() -> std::io::Result<()> { /// let file = File::create("poem.txt")?; /// let file = LineWriter::new(file); /// Ok(()) /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn new(inner: W) -> LineWriter<W> { // Lines typically aren't that long, don't use a giant buffer LineWriter::with_capacity(1024, inner) } /// Creates a new `LineWriter` with a specified capacity for the internal /// buffer. /// /// # Examples /// /// ```no_run /// use std::fs::File; /// use std::io::LineWriter; /// /// fn main() -> std::io::Result<()> { /// let file = File::create("poem.txt")?; /// let file = LineWriter::with_capacity(100, file); /// Ok(()) /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn with_capacity(capacity: usize, inner: W) -> LineWriter<W> { LineWriter { inner: BufWriter::with_capacity(capacity, inner), need_flush: false, } } /// Gets a reference to the underlying writer. /// /// # Examples /// /// ```no_run /// use std::fs::File; /// use std::io::LineWriter; /// /// fn main() -> std::io::Result<()> { /// let file = File::create("poem.txt")?; /// let file = LineWriter::new(file); /// /// let reference = file.get_ref(); /// Ok(()) /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn get_ref(&self) -> &W { self.inner.get_ref() } /// Gets a mutable reference to the underlying writer. /// /// Caution must be taken when calling methods on the mutable reference /// returned as extra writes could corrupt the output stream. /// /// # Examples /// /// ```no_run /// use std::fs::File; /// use std::io::LineWriter; /// /// fn main() -> std::io::Result<()> { /// let file = File::create("poem.txt")?; /// let mut file = LineWriter::new(file); /// /// // we can use reference just like file /// let reference = file.get_mut(); /// Ok(()) /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn get_mut(&mut self) -> &mut W { self.inner.get_mut() } /// Unwraps this `LineWriter`, returning the underlying writer. /// /// The internal buffer is written out before returning the writer. /// /// # Errors /// /// An `Err` will be returned if an error occurs while flushing the buffer. /// /// # Examples /// /// ```no_run /// use std::fs::File; /// use std::io::LineWriter; /// /// fn main() -> std::io::Result<()> { /// let file = File::create("poem.txt")?; /// /// let writer: LineWriter<File> = LineWriter::new(file); /// /// let file: File = writer.into_inner()?; /// Ok(()) /// } /// ``` #[stable(feature = "rust1", since = "1.0.0")] pub fn into_inner(self) -> Result<W, IntoInnerError<LineWriter<W>>> { self.inner.into_inner().map_err(|IntoInnerError(buf, e)| { IntoInnerError(LineWriter { inner: buf, need_flush: false, }, e) }) } } #[stable(feature = "rust1", since = "1.0.0")] impl<W: Write> Write for LineWriter<W> { fn write(&mut self, buf: &[u8]) -> io::Result<usize> { if self.need_flush { self.flush()?; } // Find the last newline character in the buffer provided. If found then // we're going to write all the data up to that point and then flush, // otherwise we just write the whole block to the underlying writer. let i = match memchr::memrchr(b'\n', buf) { Some(i) => i, None => return self.inner.write(buf), }; // Ok, we're going to write a partial amount of the data given first // followed by flushing the newline. After we've successfully written // some data then we *must* report that we wrote that data, so future // errors are ignored. We set our internal `need_flush` flag, though, in // case flushing fails and we need to try it first next time. let n = self.inner.write(&buf[..=i])?; self.need_flush = true; if self.flush().is_err() || n != i + 1 { return Ok(n) } // At this point we successfully wrote `i + 1` bytes and flushed it out, // meaning that the entire line is now flushed out on the screen. While // we can attempt to finish writing the rest of the data provided. // Remember though that we ignore errors here as we've successfully // written data, so we need to report that. match self.inner.write(&buf[i + 1..]) { Ok(i) => Ok(n + i), Err(_) => Ok(n), } } fn flush(&mut self) -> io::Result<()> { self.inner.flush()?; self.need_flush = false; Ok(()) } } #[stable(feature = "rust1", since = "1.0.0")] impl<W: Write> fmt::Debug for LineWriter<W> where W: fmt::Debug { fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result { fmt.debug_struct("LineWriter") .field("writer", &self.inner.inner) .field("buffer", &format_args!("{}/{}", self.inner.buf.len(), self.inner.buf.capacity())) .finish() } } #[cfg(test)] mod tests { use crate::io::prelude::*; use crate::io::{self, BufReader, BufWriter, LineWriter, SeekFrom}; use crate::sync::atomic::{AtomicUsize, Ordering}; use crate::thread; /// A dummy reader intended at testing short-reads propagation. pub struct ShortReader { lengths: Vec<usize>, } impl Read for ShortReader { fn read(&mut self, _: &mut [u8]) -> io::Result<usize> { if self.lengths.is_empty() { Ok(0) } else { Ok(self.lengths.remove(0)) } } } #[test] fn test_buffered_reader() { let inner: &[u8] = &[5, 6, 7, 0, 1, 2, 3, 4]; let mut reader = BufReader::with_capacity(2, inner); let mut buf = [0, 0, 0]; let nread = reader.read(&mut buf); assert_eq!(nread.unwrap(), 3); assert_eq!(buf, [5, 6, 7]); assert_eq!(reader.buffer(), []); let mut buf = [0, 0]; let nread = reader.read(&mut buf); assert_eq!(nread.unwrap(), 2); assert_eq!(buf, [0, 1]); assert_eq!(reader.buffer(), []); let mut buf = [0]; let nread = reader.read(&mut buf); assert_eq!(nread.unwrap(), 1); assert_eq!(buf, [2]); assert_eq!(reader.buffer(), [3]); let mut buf = [0, 0, 0]; let nread = reader.read(&mut buf); assert_eq!(nread.unwrap(), 1); assert_eq!(buf, [3, 0, 0]); assert_eq!(reader.buffer(), []); let nread = reader.read(&mut buf); assert_eq!(nread.unwrap(), 1); assert_eq!(buf, [4, 0, 0]); assert_eq!(reader.buffer(), []); assert_eq!(reader.read(&mut buf).unwrap(), 0); } #[test] fn test_buffered_reader_seek() { let inner: &[u8] = &[5, 6, 7, 0, 1, 2, 3, 4]; let mut reader = BufReader::with_capacity(2, io::Cursor::new(inner)); assert_eq!(reader.seek(SeekFrom::Start(3)).ok(), Some(3)); assert_eq!(reader.fill_buf().ok(), Some(&[0, 1][..])); assert_eq!(reader.seek(SeekFrom::Current(0)).ok(), Some(3)); assert_eq!(reader.fill_buf().ok(), Some(&[0, 1][..])); assert_eq!(reader.seek(SeekFrom::Current(1)).ok(), Some(4)); assert_eq!(reader.fill_buf().ok(), Some(&[1, 2][..])); reader.consume(1); assert_eq!(reader.seek(SeekFrom::Current(-2)).ok(), Some(3)); } #[test] fn test_buffered_reader_seek_relative() { let inner: &[u8] = &[5, 6, 7, 0, 1, 2, 3, 4]; let mut reader = BufReader::with_capacity(2, io::Cursor::new(inner)); assert!(reader.seek_relative(3).is_ok()); assert_eq!(reader.fill_buf().ok(), Some(&[0, 1][..])); assert!(reader.seek_relative(0).is_ok()); assert_eq!(reader.fill_buf().ok(), Some(&[0, 1][..])); assert!(reader.seek_relative(1).is_ok()); assert_eq!(reader.fill_buf().ok(), Some(&[1][..])); assert!(reader.seek_relative(-1).is_ok()); assert_eq!(reader.fill_buf().ok(), Some(&[0, 1][..])); assert!(reader.seek_relative(2).is_ok()); assert_eq!(reader.fill_buf().ok(), Some(&[2, 3][..])); } #[test] fn test_buffered_reader_invalidated_after_read() { let inner: &[u8] = &[5, 6, 7, 0, 1, 2, 3, 4]; let mut reader = BufReader::with_capacity(3, io::Cursor::new(inner)); assert_eq!(reader.fill_buf().ok(), Some(&[5, 6, 7][..])); reader.consume(3); let mut buffer = [0, 0, 0, 0, 0]; assert_eq!(reader.read(&mut buffer).ok(), Some(5)); assert_eq!(buffer, [0, 1, 2, 3, 4]); assert!(reader.seek_relative(-2).is_ok()); let mut buffer = [0, 0]; assert_eq!(reader.read(&mut buffer).ok(), Some(2)); assert_eq!(buffer, [3, 4]); } #[test] fn test_buffered_reader_invalidated_after_seek() { let inner: &[u8] = &[5, 6, 7, 0, 1, 2, 3, 4]; let mut reader = BufReader::with_capacity(3, io::Cursor::new(inner)); assert_eq!(reader.fill_buf().ok(), Some(&[5, 6, 7][..])); reader.consume(3); assert!(reader.seek(SeekFrom::Current(5)).is_ok()); assert!(reader.seek_relative(-2).is_ok()); let mut buffer = [0, 0]; assert_eq!(reader.read(&mut buffer).ok(), Some(2)); assert_eq!(buffer, [3, 4]); } #[test] fn test_buffered_reader_seek_underflow() { // gimmick reader that yields its position modulo 256 for each byte struct PositionReader { pos: u64 } impl Read for PositionReader { fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> { let len = buf.len(); for x in buf { *x = self.pos as u8; self.pos = self.pos.wrapping_add(1); } Ok(len) } } impl Seek for PositionReader { fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> { match pos { SeekFrom::Start(n) => { self.pos = n; } SeekFrom::Current(n) => { self.pos = self.pos.wrapping_add(n as u64); } SeekFrom::End(n) => { self.pos = u64::max_value().wrapping_add(n as u64); } } Ok(self.pos) } } let mut reader = BufReader::with_capacity(5, PositionReader { pos: 0 }); assert_eq!(reader.fill_buf().ok(), Some(&[0, 1, 2, 3, 4][..])); assert_eq!(reader.seek(SeekFrom::End(-5)).ok(), Some(u64::max_value()-5)); assert_eq!(reader.fill_buf().ok().map(|s| s.len()), Some(5)); // the following seek will require two underlying seeks let expected = 9223372036854775802; assert_eq!(reader.seek(SeekFrom::Current(i64::min_value())).ok(), Some(expected)); assert_eq!(reader.fill_buf().ok().map(|s| s.len()), Some(5)); // seeking to 0 should empty the buffer. assert_eq!(reader.seek(SeekFrom::Current(0)).ok(), Some(expected)); assert_eq!(reader.get_ref().pos, expected); } #[test] fn test_buffered_reader_seek_underflow_discard_buffer_between_seeks() { // gimmick reader that returns Err after first seek struct ErrAfterFirstSeekReader { first_seek: bool, } impl Read for ErrAfterFirstSeekReader { fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> { for x in &mut *buf { *x = 0; } Ok(buf.len()) } } impl Seek for ErrAfterFirstSeekReader { fn seek(&mut self, _: SeekFrom) -> io::Result<u64> { if self.first_seek { self.first_seek = false; Ok(0) } else { Err(io::Error::new(io::ErrorKind::Other, "oh no!")) } } } let mut reader = BufReader::with_capacity(5, ErrAfterFirstSeekReader { first_seek: true }); assert_eq!(reader.fill_buf().ok(), Some(&[0, 0, 0, 0, 0][..])); // The following seek will require two underlying seeks. The first will // succeed but the second will fail. This should still invalidate the // buffer. assert!(reader.seek(SeekFrom::Current(i64::min_value())).is_err()); assert_eq!(reader.buffer().len(), 0); } #[test] fn test_buffered_writer() { let inner = Vec::new(); let mut writer = BufWriter::with_capacity(2, inner); writer.write(&[0, 1]).unwrap(); assert_eq!(writer.buffer(), []); assert_eq!(*writer.get_ref(), [0, 1]); writer.write(&[2]).unwrap(); assert_eq!(writer.buffer(), [2]); assert_eq!(*writer.get_ref(), [0, 1]); writer.write(&[3]).unwrap(); assert_eq!(writer.buffer(), [2, 3]); assert_eq!(*writer.get_ref(), [0, 1]); writer.flush().unwrap(); assert_eq!(writer.buffer(), []); assert_eq!(*writer.get_ref(), [0, 1, 2, 3]); writer.write(&[4]).unwrap(); writer.write(&[5]).unwrap(); assert_eq!(writer.buffer(), [4, 5]); assert_eq!(*writer.get_ref(), [0, 1, 2, 3]); writer.write(&[6]).unwrap(); assert_eq!(writer.buffer(), [6]); assert_eq!(*writer.get_ref(), [0, 1, 2, 3, 4, 5]); writer.write(&[7, 8]).unwrap(); assert_eq!(writer.buffer(), []); assert_eq!(*writer.get_ref(), [0, 1, 2, 3, 4, 5, 6, 7, 8]); writer.write(&[9, 10, 11]).unwrap(); assert_eq!(writer.buffer(), []); assert_eq!(*writer.get_ref(), [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]); writer.flush().unwrap(); assert_eq!(writer.buffer(), []); assert_eq!(*writer.get_ref(), [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]); } #[test] fn test_buffered_writer_inner_flushes() { let mut w = BufWriter::with_capacity(3, Vec::new()); w.write(&[0, 1]).unwrap(); assert_eq!(*w.get_ref(), []); let w = w.into_inner().unwrap(); assert_eq!(w, [0, 1]); } #[test] fn test_buffered_writer_seek() { let mut w = BufWriter::with_capacity(3, io::Cursor::new(Vec::new())); w.write_all(&[0, 1, 2, 3, 4, 5]).unwrap(); w.write_all(&[6, 7]).unwrap(); assert_eq!(w.seek(SeekFrom::Current(0)).ok(), Some(8)); assert_eq!(&w.get_ref().get_ref()[..], &[0, 1, 2, 3, 4, 5, 6, 7][..]); assert_eq!(w.seek(SeekFrom::Start(2)).ok(), Some(2)); w.write_all(&[8, 9]).unwrap(); assert_eq!(&w.into_inner().unwrap().into_inner()[..], &[0, 1, 8, 9, 4, 5, 6, 7]); } #[test] fn test_read_until() { let inner: &[u8] = &[0, 1, 2, 1, 0]; let mut reader = BufReader::with_capacity(2, inner); let mut v = Vec::new(); reader.read_until(0, &mut v).unwrap(); assert_eq!(v, [0]); v.truncate(0); reader.read_until(2, &mut v).unwrap(); assert_eq!(v, [1, 2]); v.truncate(0); reader.read_until(1, &mut v).unwrap(); assert_eq!(v, [1]); v.truncate(0); reader.read_until(8, &mut v).unwrap(); assert_eq!(v, [0]); v.truncate(0); reader.read_until(9, &mut v).unwrap(); assert_eq!(v, []); } #[test] fn test_line_buffer_fail_flush() { // Issue #32085 struct FailFlushWriter<'a>(&'a mut Vec<u8>); impl Write for FailFlushWriter<'_> { fn write(&mut self, buf: &[u8]) -> io::Result<usize> { self.0.extend_from_slice(buf); Ok(buf.len()) } fn flush(&mut self) -> io::Result<()> { Err(io::Error::new(io::ErrorKind::Other, "flush failed")) } } let mut buf = Vec::new(); { let mut writer = LineWriter::new(FailFlushWriter(&mut buf)); let to_write = b"abc\ndef"; if let Ok(written) = writer.write(to_write) { assert!(written < to_write.len(), "didn't flush on new line"); // PASS return; } } assert!(buf.is_empty(), "write returned an error but wrote data"); } #[test] fn test_line_buffer() { let mut writer = LineWriter::new(Vec::new()); writer.write(&[0]).unwrap(); assert_eq!(*writer.get_ref(), []); writer.write(&[1]).unwrap(); assert_eq!(*writer.get_ref(), []); writer.flush().unwrap(); assert_eq!(*writer.get_ref(), [0, 1]); writer.write(&[0, b'\n', 1, b'\n', 2]).unwrap(); assert_eq!(*writer.get_ref(), [0, 1, 0, b'\n', 1, b'\n']); writer.flush().unwrap(); assert_eq!(*writer.get_ref(), [0, 1, 0, b'\n', 1, b'\n', 2]); writer.write(&[3, b'\n']).unwrap(); assert_eq!(*writer.get_ref(), [0, 1, 0, b'\n', 1, b'\n', 2, 3, b'\n']); } #[test] fn test_read_line() { let in_buf: &[u8] = b"a\nb\nc"; let mut reader = BufReader::with_capacity(2, in_buf); let mut s = String::new(); reader.read_line(&mut s).unwrap(); assert_eq!(s, "a\n"); s.truncate(0); reader.read_line(&mut s).unwrap(); assert_eq!(s, "b\n"); s.truncate(0); reader.read_line(&mut s).unwrap(); assert_eq!(s, "c"); s.truncate(0); reader.read_line(&mut s).unwrap(); assert_eq!(s, ""); } #[test] fn test_lines() { let in_buf: &[u8] = b"a\nb\nc"; let reader = BufReader::with_capacity(2, in_buf); let mut it = reader.lines(); assert_eq!(it.next().unwrap().unwrap(), "a".to_string()); assert_eq!(it.next().unwrap().unwrap(), "b".to_string()); assert_eq!(it.next().unwrap().unwrap(), "c".to_string()); assert!(it.next().is_none()); } #[test] fn test_short_reads() { let inner = ShortReader{lengths: vec![0, 1, 2, 0, 1, 0]}; let mut reader = BufReader::new(inner); let mut buf = [0, 0]; assert_eq!(reader.read(&mut buf).unwrap(), 0); assert_eq!(reader.read(&mut buf).unwrap(), 1); assert_eq!(reader.read(&mut buf).unwrap(), 2); assert_eq!(reader.read(&mut buf).unwrap(), 0); assert_eq!(reader.read(&mut buf).unwrap(), 1); assert_eq!(reader.read(&mut buf).unwrap(), 0); assert_eq!(reader.read(&mut buf).unwrap(), 0); } #[test] #[should_panic] fn dont_panic_in_drop_on_panicked_flush() { struct FailFlushWriter; impl Write for FailFlushWriter { fn write(&mut self, buf: &[u8]) -> io::Result<usize> { Ok(buf.len()) } fn flush(&mut self) -> io::Result<()> { Err(io::Error::last_os_error()) } } let writer = FailFlushWriter; let _writer = BufWriter::new(writer); // If writer panics *again* due to the flush error then the process will // abort. panic!(); } #[test] #[cfg_attr(target_os = "emscripten", ignore)] fn panic_in_write_doesnt_flush_in_drop() { static WRITES: AtomicUsize = AtomicUsize::new(0); struct PanicWriter; impl Write for PanicWriter { fn write(&mut self, _: &[u8]) -> io::Result<usize> { WRITES.fetch_add(1, Ordering::SeqCst); panic!(); } fn flush(&mut self) -> io::Result<()> { Ok(()) } } thread::spawn(|| { let mut writer = BufWriter::new(PanicWriter); let _ = writer.write(b"hello world"); let _ = writer.flush(); }).join().unwrap_err(); assert_eq!(WRITES.load(Ordering::SeqCst), 1); } #[bench] fn bench_buffered_reader(b: &mut test::Bencher) { b.iter(|| { BufReader::new(io::empty()) }); } #[bench] fn bench_buffered_writer(b: &mut test::Bencher) { b.iter(|| { BufWriter::new(io::sink()) }); } struct AcceptOneThenFail { written: bool, flushed: bool, } impl Write for AcceptOneThenFail { fn write(&mut self, data: &[u8]) -> io::Result<usize> { if !self.written { assert_eq!(data, b"a\nb\n"); self.written = true; Ok(data.len()) } else { Err(io::Error::new(io::ErrorKind::NotFound, "test")) } } fn flush(&mut self) -> io::Result<()> { assert!(self.written); assert!(!self.flushed); self.flushed = true; Err(io::Error::new(io::ErrorKind::Other, "test")) } } #[test] fn erroneous_flush_retried() { let a = AcceptOneThenFail { written: false, flushed: false, }; let mut l = LineWriter::new(a); assert_eq!(l.write(b"a\nb\na").unwrap(), 4); assert!(l.get_ref().written); assert!(l.get_ref().flushed); l.get_mut().flushed = false; assert_eq!(l.write(b"a").unwrap_err().kind(), io::ErrorKind::Other) } }