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.

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.

Gets a reference to the underlying writer.

Examples

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

# #[expect(unused_mut)]
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();

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();

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();

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.

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();

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

Examples

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

# #[expect(unused_mut)]
let mut buffer = BufWriter::new(TcpStream::connect("127.0.0.1:34254").unwrap());

Attempts to allocate an internal buffer, then calls the provided function to retrieve the inner writer W.

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.

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

let stream = TcpStream::connect("127.0.0.1:34254").unwrap();
# #[expect(unused_mut)]
let mut buffer = BufWriter::with_capacity(100, stream);

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;

# #[expect(unused_mut)]
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();

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");