Struct borsh::maybestd::io::BufWriter1.0.0[][src]

pub struct BufWriter<W> where
    W: Write
{ /* fields omitted */ }

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 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 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:

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>:

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.

Implementations

impl<W> BufWriter<W> where
    W: Write
[src]

pub fn new(inner: W) -> BufWriter<W>

Notable traits for BufWriter<W>

impl<W> Write for BufWriter<W> where
    W: Write
[src]

Creates a new BufWriter<W> with a default buffer capacity. The default is currently 8 KB, but may change in the future.

Examples

use std::io::BufWriter;
use std::net::TcpStream;

let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());

pub fn with_capacity(capacity: usize, inner: W) -> BufWriter<W>

Notable traits for BufWriter<W>

impl<W> Write for BufWriter<W> where
    W: Write
[src]

Creates a new BufWriter<W> with the specified buffer capacity.

Examples

Creating a buffer with a buffer of a hundred bytes.

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);

pub fn get_ref(&self) -> &W

Notable traits for &'_ mut R

impl<'_, R> Read for &'_ mut R where
    R: Read + ?Sized
impl<'_, W> Write for &'_ mut W where
    W: Write + ?Sized
[src]

Gets a reference to the underlying writer.

Examples

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();

pub fn get_mut(&mut self) -> &mut W

Notable traits for &'_ mut R

impl<'_, R> Read for &'_ mut R where
    R: Read + ?Sized
impl<'_, W> Write for &'_ mut W where
    W: Write + ?Sized
[src]

Gets a mutable reference to the underlying writer.

It is inadvisable to directly write to the underlying writer.

Examples

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();

pub fn buffer(&self) -> &[u8]

Notable traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]
1.37.0[src]

Returns a reference to the internally buffered data.

Examples

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();

pub fn capacity(&self) -> usize1.46.0[src]

Returns the number of bytes the internal buffer can hold without flushing.

Examples

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();

pub fn into_inner(self) -> Result<W, IntoInnerError<BufWriter<W>>>[src]

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

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();

pub fn into_raw_parts(self) -> (W, Result<Vec<u8, Global>, WriterPanicked>)[src]

🔬 This is a nightly-only experimental API. (bufwriter_into_raw_parts)

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_raw_parts makes no attempt to flush data and cannot fail.

Examples

#![feature(bufwriter_into_raw_parts)]
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_raw_parts();
assert_eq!(recovered_writer.len(), 0);
assert_eq!(&buffered_data.unwrap(), b"ata");

Trait Implementations

impl<W> Debug for BufWriter<W> where
    W: Write + Debug
[src]

impl<W> Drop for BufWriter<W> where
    W: Write
[src]

impl<W> Seek for BufWriter<W> where
    W: Write + Seek
[src]

pub fn seek(&mut self, pos: SeekFrom) -> Result<u64, Error>[src]

Seek to the offset, in bytes, in the underlying writer.

Seeking always writes out the internal buffer before seeking.

impl<W> Write for BufWriter<W> where
    W: Write
[src]

Auto Trait Implementations

impl<W> RefUnwindSafe for BufWriter<W> where
    W: RefUnwindSafe

impl<W> Send for BufWriter<W> where
    W: Send

impl<W> Sync for BufWriter<W> where
    W: Sync

impl<W> Unpin for BufWriter<W> where
    W: Unpin

impl<W> UnwindSafe for BufWriter<W> where
    W: UnwindSafe

Blanket Implementations

impl<T> Any for T where
    T: 'static + ?Sized
[src]

impl<T> Borrow<T> for T where
    T: ?Sized
[src]

impl<T> BorrowMut<T> for T where
    T: ?Sized
[src]

impl<T> From<T> for T[src]

impl<T, U> Into<U> for T where
    U: From<T>, 
[src]

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 
[src]

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 
[src]

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.