| use crate::error; |
| use crate::fmt; |
| use crate::io::{ |
| self, ErrorKind, IntoInnerError, IoSlice, Seek, SeekFrom, Write, DEFAULT_BUF_SIZE, |
| }; |
| use crate::mem; |
| use crate::ptr; |
| |
| /// 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 <code>[Vec]\<u8></code>. |
| /// |
| /// It is critical to call [`flush`] before `BufWriter<W>` is dropped. Though |
| /// dropping will attempt to flush 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. |
| /// |
| // HACK(#78696): can't use `crate` for associated items |
| /// [`TcpStream::write`]: super::super::super::net::TcpStream::write |
| /// [`TcpStream`]: crate::net::TcpStream |
| /// [`flush`]: BufWriter::flush |
| #[stable(feature = "rust1", since = "1.0.0")] |
| pub struct BufWriter<W: Write> { |
| inner: W, |
| // The buffer. Avoid using this like a normal `Vec` in common code paths. |
| // That is, don't use `buf.push`, `buf.extend_from_slice`, or any other |
| // methods that require bounds checking or the like. This makes an enormous |
| // difference to performance (we may want to stop using a `Vec` entirely). |
| 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, |
| } |
| |
| 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 at least the specified buffer capacity. |
| /// |
| /// # Examples |
| /// |
| /// Creating a buffer with a buffer of at least 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, buf: Vec::with_capacity(capacity), panicked: false } |
| } |
| |
| /// Send data in our local buffer into the inner writer, looping as |
| /// necessary until either it's all been sent or an error occurs. |
| /// |
| /// Because all the data in the buffer has been reported to our owner as |
| /// "successfully written" (by returning nonzero success values from |
| /// `write`), any 0-length writes from `inner` must be reported as i/o |
| /// errors from this method. |
| pub(in crate::io) fn flush_buf(&mut self) -> io::Result<()> { |
| /// Helper struct to ensure the buffer is updated after all the writes |
| /// are complete. It tracks the number of written bytes and drains them |
| /// all from the front of the buffer when dropped. |
| struct BufGuard<'a> { |
| buffer: &'a mut Vec<u8>, |
| written: usize, |
| } |
| |
| impl<'a> BufGuard<'a> { |
| fn new(buffer: &'a mut Vec<u8>) -> Self { |
| Self { buffer, written: 0 } |
| } |
| |
| /// The unwritten part of the buffer |
| fn remaining(&self) -> &[u8] { |
| &self.buffer[self.written..] |
| } |
| |
| /// Flag some bytes as removed from the front of the buffer |
| fn consume(&mut self, amt: usize) { |
| self.written += amt; |
| } |
| |
| /// true if all of the bytes have been written |
| fn done(&self) -> bool { |
| self.written >= self.buffer.len() |
| } |
| } |
| |
| impl Drop for BufGuard<'_> { |
| fn drop(&mut self) { |
| if self.written > 0 { |
| self.buffer.drain(..self.written); |
| } |
| } |
| } |
| |
| let mut guard = BufGuard::new(&mut self.buf); |
| while !guard.done() { |
| self.panicked = true; |
| let r = self.inner.write(guard.remaining()); |
| self.panicked = false; |
| |
| match r { |
| Ok(0) => { |
| return Err(io::const_io_error!( |
| ErrorKind::WriteZero, |
| "failed to write the buffered data", |
| )); |
| } |
| Ok(n) => guard.consume(n), |
| Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {} |
| Err(e) => return Err(e), |
| } |
| } |
| Ok(()) |
| } |
| |
| /// Buffer some data without flushing it, regardless of the size of the |
| /// data. Writes as much as possible without exceeding capacity. Returns |
| /// the number of bytes written. |
| pub(super) fn write_to_buf(&mut self, buf: &[u8]) -> usize { |
| let available = self.spare_capacity(); |
| let amt_to_buffer = available.min(buf.len()); |
| |
| // SAFETY: `amt_to_buffer` is <= buffer's spare capacity by construction. |
| unsafe { |
| self.write_to_buffer_unchecked(&buf[..amt_to_buffer]); |
| } |
| |
| amt_to_buffer |
| } |
| |
| /// 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 |
| } |
| |
| /// 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 { |
| &mut self.inner |
| } |
| |
| /// 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 |
| } |
| |
| /// Returns a mutable reference to the internal buffer. |
| /// |
| /// This can be used to write data directly into the buffer without triggering writers |
| /// to the underlying writer. |
| /// |
| /// That the buffer is a `Vec` is an implementation detail. |
| /// Callers should not modify the capacity as there currently is no public API to do so |
| /// and thus any capacity changes would be unexpected by the user. |
| pub(in crate::io) fn buffer_mut(&mut self) -> &mut Vec<u8> { |
| &mut self.buf |
| } |
| |
| /// Returns the number of bytes the internal buffer can hold without flushing. |
| /// |
| /// # Examples |
| /// |
| /// ```no_run |
| /// use std::io::BufWriter; |
| /// use std::net::TcpStream; |
| /// |
| /// let buf_writer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap()); |
| /// |
| /// // Check the capacity of the inner buffer |
| /// let capacity = buf_writer.capacity(); |
| /// // Calculate how many bytes can be written without flushing |
| /// let without_flush = capacity - buf_writer.buffer().len(); |
| /// ``` |
| #[stable(feature = "buffered_io_capacity", since = "1.46.0")] |
| pub fn capacity(&self) -> usize { |
| self.buf.capacity() |
| } |
| |
| /// 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::new(self, e)), |
| Ok(()) => Ok(self.into_parts().0), |
| } |
| } |
| |
| /// Disassembles this `BufWriter<W>`, returning the underlying writer, and any buffered but |
| /// unwritten data. |
| /// |
| /// If the underlying writer panicked, it is not known what portion of the data was written. |
| /// In this case, we return `WriterPanicked` for the buffered data (from which the buffer |
| /// contents can still be recovered). |
| /// |
| /// `into_parts` makes no attempt to flush data and cannot fail. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use std::io::{BufWriter, Write}; |
| /// |
| /// let mut buffer = [0u8; 10]; |
| /// let mut stream = BufWriter::new(buffer.as_mut()); |
| /// write!(stream, "too much data").unwrap(); |
| /// stream.flush().expect_err("it doesn't fit"); |
| /// let (recovered_writer, buffered_data) = stream.into_parts(); |
| /// assert_eq!(recovered_writer.len(), 0); |
| /// assert_eq!(&buffered_data.unwrap(), b"ata"); |
| /// ``` |
| #[stable(feature = "bufwriter_into_parts", since = "1.56.0")] |
| pub fn into_parts(mut self) -> (W, Result<Vec<u8>, WriterPanicked>) { |
| let buf = mem::take(&mut self.buf); |
| let buf = if !self.panicked { Ok(buf) } else { Err(WriterPanicked { buf }) }; |
| |
| // SAFETY: forget(self) prevents double dropping inner |
| let inner = unsafe { ptr::read(&mut self.inner) }; |
| mem::forget(self); |
| |
| (inner, buf) |
| } |
| |
| // Ensure this function does not get inlined into `write`, so that it |
| // remains inlineable and its common path remains as short as possible. |
| // If this function ends up being called frequently relative to `write`, |
| // it's likely a sign that the client is using an improperly sized buffer |
| // or their write patterns are somewhat pathological. |
| #[cold] |
| #[inline(never)] |
| fn write_cold(&mut self, buf: &[u8]) -> io::Result<usize> { |
| if buf.len() > self.spare_capacity() { |
| self.flush_buf()?; |
| } |
| |
| // Why not len > capacity? To avoid a needless trip through the buffer when the input |
| // exactly fills it. We'd just need to flush it to the underlying writer anyway. |
| if buf.len() >= self.buf.capacity() { |
| self.panicked = true; |
| let r = self.get_mut().write(buf); |
| self.panicked = false; |
| r |
| } else { |
| // Write to the buffer. In this case, we write to the buffer even if it fills it |
| // exactly. Doing otherwise would mean flushing the buffer, then writing this |
| // input to the inner writer, which in many cases would be a worse strategy. |
| |
| // SAFETY: There was either enough spare capacity already, or there wasn't and we |
| // flushed the buffer to ensure that there is. In the latter case, we know that there |
| // is because flushing ensured that our entire buffer is spare capacity, and we entered |
| // this block because the input buffer length is less than that capacity. In either |
| // case, it's safe to write the input buffer to our buffer. |
| unsafe { |
| self.write_to_buffer_unchecked(buf); |
| } |
| |
| Ok(buf.len()) |
| } |
| } |
| |
| // Ensure this function does not get inlined into `write_all`, so that it |
| // remains inlineable and its common path remains as short as possible. |
| // If this function ends up being called frequently relative to `write_all`, |
| // it's likely a sign that the client is using an improperly sized buffer |
| // or their write patterns are somewhat pathological. |
| #[cold] |
| #[inline(never)] |
| fn write_all_cold(&mut self, buf: &[u8]) -> io::Result<()> { |
| // Normally, `write_all` just calls `write` in a loop. We can do better |
| // by calling `self.get_mut().write_all()` directly, which avoids |
| // round trips through the buffer in the event of a series of partial |
| // writes in some circumstances. |
| |
| if buf.len() > self.spare_capacity() { |
| self.flush_buf()?; |
| } |
| |
| // Why not len > capacity? To avoid a needless trip through the buffer when the input |
| // exactly fills it. We'd just need to flush it to the underlying writer anyway. |
| if buf.len() >= self.buf.capacity() { |
| self.panicked = true; |
| let r = self.get_mut().write_all(buf); |
| self.panicked = false; |
| r |
| } else { |
| // Write to the buffer. In this case, we write to the buffer even if it fills it |
| // exactly. Doing otherwise would mean flushing the buffer, then writing this |
| // input to the inner writer, which in many cases would be a worse strategy. |
| |
| // SAFETY: There was either enough spare capacity already, or there wasn't and we |
| // flushed the buffer to ensure that there is. In the latter case, we know that there |
| // is because flushing ensured that our entire buffer is spare capacity, and we entered |
| // this block because the input buffer length is less than that capacity. In either |
| // case, it's safe to write the input buffer to our buffer. |
| unsafe { |
| self.write_to_buffer_unchecked(buf); |
| } |
| |
| Ok(()) |
| } |
| } |
| |
| // SAFETY: Requires `buf.len() <= self.buf.capacity() - self.buf.len()`, |
| // i.e., that input buffer length is less than or equal to spare capacity. |
| #[inline] |
| unsafe fn write_to_buffer_unchecked(&mut self, buf: &[u8]) { |
| debug_assert!(buf.len() <= self.spare_capacity()); |
| let old_len = self.buf.len(); |
| let buf_len = buf.len(); |
| let src = buf.as_ptr(); |
| let dst = self.buf.as_mut_ptr().add(old_len); |
| ptr::copy_nonoverlapping(src, dst, buf_len); |
| self.buf.set_len(old_len + buf_len); |
| } |
| |
| #[inline] |
| fn spare_capacity(&self) -> usize { |
| self.buf.capacity() - self.buf.len() |
| } |
| } |
| |
| #[stable(feature = "bufwriter_into_parts", since = "1.56.0")] |
| /// Error returned for the buffered data from `BufWriter::into_parts`, when the underlying |
| /// writer has previously panicked. Contains the (possibly partly written) buffered data. |
| /// |
| /// # Example |
| /// |
| /// ``` |
| /// use std::io::{self, BufWriter, Write}; |
| /// use std::panic::{catch_unwind, AssertUnwindSafe}; |
| /// |
| /// struct PanickingWriter; |
| /// impl Write for PanickingWriter { |
| /// fn write(&mut self, buf: &[u8]) -> io::Result<usize> { panic!() } |
| /// fn flush(&mut self) -> io::Result<()> { panic!() } |
| /// } |
| /// |
| /// let mut stream = BufWriter::new(PanickingWriter); |
| /// write!(stream, "some data").unwrap(); |
| /// let result = catch_unwind(AssertUnwindSafe(|| { |
| /// stream.flush().unwrap() |
| /// })); |
| /// assert!(result.is_err()); |
| /// let (recovered_writer, buffered_data) = stream.into_parts(); |
| /// assert!(matches!(recovered_writer, PanickingWriter)); |
| /// assert_eq!(buffered_data.unwrap_err().into_inner(), b"some data"); |
| /// ``` |
| pub struct WriterPanicked { |
| buf: Vec<u8>, |
| } |
| |
| impl WriterPanicked { |
| /// Returns the perhaps-unwritten data. Some of this data may have been written by the |
| /// panicking call(s) to the underlying writer, so simply writing it again is not a good idea. |
| #[must_use = "`self` will be dropped if the result is not used"] |
| #[stable(feature = "bufwriter_into_parts", since = "1.56.0")] |
| pub fn into_inner(self) -> Vec<u8> { |
| self.buf |
| } |
| |
| const DESCRIPTION: &'static str = |
| "BufWriter inner writer panicked, what data remains unwritten is not known"; |
| } |
| |
| #[stable(feature = "bufwriter_into_parts", since = "1.56.0")] |
| impl error::Error for WriterPanicked { |
| #[allow(deprecated, deprecated_in_future)] |
| fn description(&self) -> &str { |
| Self::DESCRIPTION |
| } |
| } |
| |
| #[stable(feature = "bufwriter_into_parts", since = "1.56.0")] |
| impl fmt::Display for WriterPanicked { |
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| write!(f, "{}", Self::DESCRIPTION) |
| } |
| } |
| |
| #[stable(feature = "bufwriter_into_parts", since = "1.56.0")] |
| impl fmt::Debug for WriterPanicked { |
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| f.debug_struct("WriterPanicked") |
| .field("buffer", &format_args!("{}/{}", self.buf.len(), self.buf.capacity())) |
| .finish() |
| } |
| } |
| |
| #[stable(feature = "rust1", since = "1.0.0")] |
| impl<W: Write> Write for BufWriter<W> { |
| #[inline] |
| fn write(&mut self, buf: &[u8]) -> io::Result<usize> { |
| // Use < instead of <= to avoid a needless trip through the buffer in some cases. |
| // See `write_cold` for details. |
| if buf.len() < self.spare_capacity() { |
| // SAFETY: safe by above conditional. |
| unsafe { |
| self.write_to_buffer_unchecked(buf); |
| } |
| |
| Ok(buf.len()) |
| } else { |
| self.write_cold(buf) |
| } |
| } |
| |
| #[inline] |
| fn write_all(&mut self, buf: &[u8]) -> io::Result<()> { |
| // Use < instead of <= to avoid a needless trip through the buffer in some cases. |
| // See `write_all_cold` for details. |
| if buf.len() < self.spare_capacity() { |
| // SAFETY: safe by above conditional. |
| unsafe { |
| self.write_to_buffer_unchecked(buf); |
| } |
| |
| Ok(()) |
| } else { |
| self.write_all_cold(buf) |
| } |
| } |
| |
| fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> { |
| // FIXME: Consider applying `#[inline]` / `#[inline(never)]` optimizations already applied |
| // to `write` and `write_all`. The performance benefits can be significant. See #79930. |
| if self.get_ref().is_write_vectored() { |
| // We have to handle the possibility that the total length of the buffers overflows |
| // `usize` (even though this can only happen if multiple `IoSlice`s reference the |
| // same underlying buffer, as otherwise the buffers wouldn't fit in memory). If the |
| // computation overflows, then surely the input cannot fit in our buffer, so we forward |
| // to the inner writer's `write_vectored` method to let it handle it appropriately. |
| let saturated_total_len = |
| bufs.iter().fold(0usize, |acc, b| acc.saturating_add(b.len())); |
| |
| if saturated_total_len > self.spare_capacity() { |
| // Flush if the total length of the input exceeds our buffer's spare capacity. |
| // If we would have overflowed, this condition also holds, and we need to flush. |
| self.flush_buf()?; |
| } |
| |
| if saturated_total_len >= self.buf.capacity() { |
| // Forward to our inner writer if the total length of the input is greater than or |
| // equal to our buffer capacity. If we would have overflowed, this condition also |
| // holds, and we punt to the inner writer. |
| self.panicked = true; |
| let r = self.get_mut().write_vectored(bufs); |
| self.panicked = false; |
| r |
| } else { |
| // `saturated_total_len < self.buf.capacity()` implies that we did not saturate. |
| |
| // SAFETY: We checked whether or not the spare capacity was large enough above. If |
| // it was, then we're safe already. If it wasn't, we flushed, making sufficient |
| // room for any input <= the buffer size, which includes this input. |
| unsafe { |
| bufs.iter().for_each(|b| self.write_to_buffer_unchecked(b)); |
| }; |
| |
| Ok(saturated_total_len) |
| } |
| } else { |
| let mut iter = bufs.iter(); |
| let mut total_written = if let Some(buf) = iter.by_ref().find(|&buf| !buf.is_empty()) { |
| // This is the first non-empty slice to write, so if it does |
| // not fit in the buffer, we still get to flush and proceed. |
| if buf.len() > self.spare_capacity() { |
| self.flush_buf()?; |
| } |
| if buf.len() >= self.buf.capacity() { |
| // The slice is at least as large as the buffering capacity, |
| // so it's better to write it directly, bypassing the buffer. |
| self.panicked = true; |
| let r = self.get_mut().write(buf); |
| self.panicked = false; |
| return r; |
| } else { |
| // SAFETY: We checked whether or not the spare capacity was large enough above. |
| // If it was, then we're safe already. If it wasn't, we flushed, making |
| // sufficient room for any input <= the buffer size, which includes this input. |
| unsafe { |
| self.write_to_buffer_unchecked(buf); |
| } |
| |
| buf.len() |
| } |
| } else { |
| return Ok(0); |
| }; |
| debug_assert!(total_written != 0); |
| for buf in iter { |
| if buf.len() <= self.spare_capacity() { |
| // SAFETY: safe by above conditional. |
| unsafe { |
| self.write_to_buffer_unchecked(buf); |
| } |
| |
| // This cannot overflow `usize`. If we are here, we've written all of the bytes |
| // so far to our buffer, and we've ensured that we never exceed the buffer's |
| // capacity. Therefore, `total_written` <= `self.buf.capacity()` <= `usize::MAX`. |
| total_written += buf.len(); |
| } else { |
| break; |
| } |
| } |
| Ok(total_written) |
| } |
| } |
| |
| fn is_write_vectored(&self) -> bool { |
| true |
| } |
| |
| 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) |
| .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()?; |
| 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.panicked { |
| // dtors should not panic, so we ignore a failed flush |
| let _r = self.flush_buf(); |
| } |
| } |
| } |
