Provided Methods

fn write<'a>(&'a mut self, src: &'a [u8]) -> Write<'a, Self>
where
    Self: Unpin,

Writes a buffer into this writer, returning how many bytes were written.

Equivalent to:

async fn write(&mut self, buf: &[u8]) -> io::Result<usize>;

This function will attempt to write the entire contents of buf, but the entire write may not succeed, or the write may also generate an error. A call to write represents at most one attempt to write to any wrapped object.

Return

If the return value is Ok(n) then it must be guaranteed that n <= buf.len(). A return value of 0 typically means that the underlying object is no longer able to accept bytes and will likely not be able to in the future as well, or that the buffer provided is empty.

Errors

Each call to write may generate an I/O error indicating that the operation could not be completed. If an error is returned then no bytes in the buffer were written to this writer.

It is not considered an error if the entire buffer could not be written to this writer.

Cancel safety

This method is cancel safe. If it is used as a branch in tokio::select! and another branch completes first, then it is guaranteed that no data was written to this AsyncWrite.

Examples

# #[cfg(not(target_family = "wasm"))]
# {
use tokio::io::{self, AsyncWriteExt};
use tokio::fs::File;

#[tokio::main]
async fn main() -> io::Result<()> {
    let mut file = File::create("foo.txt").await?;

    // Writes some prefix of the byte string, not necessarily all of it.
    file.write(b"some bytes").await?;
    file.flush().await?;
    Ok(())
}
# }

fn write_vectored<'a, 'b>(&'a mut self, bufs: &'a [IoSlice<'b>]) -> WriteVectored<'a, 'b, Self>
where
    Self: Unpin,

Like write, except that it writes from a slice of buffers.

Equivalent to:

async fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize>;

See AsyncWrite::poll_write_vectored for more details.

Cancel safety

This method is cancel safe. If it is used as a branch in tokio::select! and another branch completes first, then it is guaranteed that no data was written to this AsyncWrite.

Examples

# #[cfg(not(target_family = "wasm"))]
# {
use tokio::io::{self, AsyncWriteExt};
use tokio::fs::File;
use std::io::IoSlice;

#[tokio::main]
async fn main() -> io::Result<()> {
    let mut file = File::create("foo.txt").await?;

    let bufs: &[_] = &[
        IoSlice::new(b"hello"),
        IoSlice::new(b" "),
        IoSlice::new(b"world"),
    ];

    file.write_vectored(&bufs).await?;
    file.flush().await?;

    Ok(())
}
# }

fn write_buf<'a, B>(&'a mut self, src: &'a mut B) -> WriteBuf<'a, Self, B>
where
    Self: Sized + Unpin,
    B: Buf,

Writes a buffer into this writer, advancing the buffer's internal cursor.

Equivalent to:

async fn write_buf<B: Buf>(&mut self, buf: &mut B) -> io::Result<usize>;

This function will attempt to write the entire contents of buf, but the entire write may not succeed, or the write may also generate an error. After the operation completes, the buffer's internal cursor is advanced by the number of bytes written. A subsequent call to write_buf using the same buf value will resume from the point that the first call to write_buf completed. A call to write_buf represents at most one attempt to write to any wrapped object.

Return

If the return value is Ok(n) then it must be guaranteed that n <= buf.len(). A return value of 0 typically means that the underlying object is no longer able to accept bytes and will likely not be able to in the future as well, or that the buffer provided is empty.

Errors

Each call to write may generate an I/O error indicating that the operation could not be completed. If an error is returned then no bytes in the buffer were written to this writer.

It is not considered an error if the entire buffer could not be written to this writer.

Cancel safety

This method is cancel safe. If it is used as a branch in tokio::select! and another branch completes first, then it is guaranteed that no data was written to this AsyncWrite.

Examples

File implements AsyncWrite and Cursor<&[u8]> implements Buf:

# #[cfg(not(target_family = "wasm"))]
# {
use tokio::io::{self, AsyncWriteExt};
use tokio::fs::File;

use bytes::Buf;
use std::io::Cursor;

#[tokio::main]
async fn main() -> io::Result<()> {
    let mut file = File::create("foo.txt").await?;
    let mut buffer = Cursor::new(b"data to write");

    // Loop until the entire contents of the buffer are written to
    // the file.
    while buffer.has_remaining() {
        // Writes some prefix of the byte string, not necessarily
        // all of it.
        file.write_buf(&mut buffer).await?;
    }
    file.flush().await?;

    Ok(())
}
# }

fn write_all_buf<'a, B>(&'a mut self, src: &'a mut B) -> WriteAllBuf<'a, Self, B>
where
    Self: Sized + Unpin,
    B: Buf,

Attempts to write an entire buffer into this writer.

Equivalent to:

async fn write_all_buf(&mut self, buf: impl Buf) -> Result<(), io::Error> {
    while buf.has_remaining() {
        self.write_buf(&mut buf).await?;
    }
    Ok(())
}

This method will continuously call write until buf.has_remaining() returns false. This method will not return until the entire buffer has been successfully written or an error occurs. The first error generated will be returned.

The buffer is advanced after each chunk is successfully written. After failure, src.chunk() will return the chunk that failed to write.

Cancel safety

If write_all_buf is used as a branch in tokio::select! and another branch completes first, then the data in the provided buffer may have been partially written. However, it is guaranteed that the provided buffer has been advanced by the amount of bytes that have been partially written.

Examples

File implements AsyncWrite and Cursor<&[u8]> implements Buf:

# #[cfg(not(target_family = "wasm"))]
# {
use tokio::io::{self, AsyncWriteExt};
use tokio::fs::File;

use std::io::Cursor;

#[tokio::main]
async fn main() -> io::Result<()> {
    let mut file = File::create("foo.txt").await?;
    let mut buffer = Cursor::new(b"data to write");

    file.write_all_buf(&mut buffer).await?;
    file.flush().await?;
    Ok(())
}
# }

fn write_all<'a>(&'a mut self, src: &'a [u8]) -> WriteAll<'a, Self>
where
    Self: Unpin,

Attempts to write an entire buffer into this writer.

Equivalent to:

async fn write_all(&mut self, buf: &[u8]) -> io::Result<()>;

This method will continuously call write until there is no more data to be written. This method will not return until the entire buffer has been successfully written or such an error occurs. The first error generated from this method will be returned.

Cancel safety

This method is not cancel safe. If it is used as a branch in tokio::select! and another branch completes first, then the provided buffer may have been partially written, but future calls to write_all will start over from the beginning of the buffer.

Errors

This function will return the first error that write returns.

Examples

# #[cfg(not(target_family = "wasm"))]
# {
use tokio::io::{self, AsyncWriteExt};
use tokio::fs::File;

#[tokio::main]
async fn main() -> io::Result<()> {
    let mut file = File::create("foo.txt").await?;

    file.write_all(b"some bytes").await?;
    file.flush().await?;
    Ok(())
}
# }

fn write_u8(&mut self, n: u8) -> WriteU8<&mut Self>
where
    Self: Unpin,

Writes an unsigned 8-bit integer to the underlying writer.

Equivalent to:

async fn write_u8(&mut self, n: u8) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write unsigned 8 bit integers to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_u8(2).await?;
writer.write_u8(5).await?;

assert_eq!(writer, b"\x02\x05");
Ok(())
# }

fn write_i8(&mut self, n: i8) -> WriteI8<&mut Self>
where
    Self: Unpin,

Writes a signed 8-bit integer to the underlying writer.

Equivalent to:

async fn write_i8(&mut self, n: i8) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write signed 8 bit integers to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_i8(-2).await?;
writer.write_i8(126).await?;

assert_eq!(writer, b"\xFE\x7E");
Ok(())
# }

fn write_u16(&mut self, n: u16) -> WriteU16<&mut Self>
where
    Self: Unpin,

Writes an unsigned 16-bit integer in big-endian order to the underlying writer.

Equivalent to:

async fn write_u16(&mut self, n: u16) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write unsigned 16-bit integers to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_u16(517).await?;
writer.write_u16(768).await?;

assert_eq!(writer, b"\x02\x05\x03\x00");
Ok(())
# }

fn write_i16(&mut self, n: i16) -> WriteI16<&mut Self>
where
    Self: Unpin,

Writes a signed 16-bit integer in big-endian order to the underlying writer.

Equivalent to:

async fn write_i16(&mut self, n: i16) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write signed 16-bit integers to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_i16(193).await?;
writer.write_i16(-132).await?;

assert_eq!(writer, b"\x00\xc1\xff\x7c");
Ok(())
# }

fn write_u32(&mut self, n: u32) -> WriteU32<&mut Self>
where
    Self: Unpin,

Writes an unsigned 32-bit integer in big-endian order to the underlying writer.

Equivalent to:

async fn write_u32(&mut self, n: u32) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write unsigned 32-bit integers to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_u32(267).await?;
writer.write_u32(1205419366).await?;

assert_eq!(writer, b"\x00\x00\x01\x0b\x47\xd9\x3d\x66");
Ok(())
# }

fn write_i32(&mut self, n: i32) -> WriteI32<&mut Self>
where
    Self: Unpin,

Writes a signed 32-bit integer in big-endian order to the underlying writer.

Equivalent to:

async fn write_i32(&mut self, n: i32) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write signed 32-bit integers to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_i32(267).await?;
writer.write_i32(1205419366).await?;

assert_eq!(writer, b"\x00\x00\x01\x0b\x47\xd9\x3d\x66");
Ok(())
# }

fn write_u64(&mut self, n: u64) -> WriteU64<&mut Self>
where
    Self: Unpin,

Writes an unsigned 64-bit integer in big-endian order to the underlying writer.

Equivalent to:

async fn write_u64(&mut self, n: u64) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write unsigned 64-bit integers to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_u64(918733457491587).await?;
writer.write_u64(143).await?;

assert_eq!(writer, b"\x00\x03\x43\x95\x4d\x60\x86\x83\x00\x00\x00\x00\x00\x00\x00\x8f");
Ok(())
# }

fn write_i64(&mut self, n: i64) -> WriteI64<&mut Self>
where
    Self: Unpin,

Writes an signed 64-bit integer in big-endian order to the underlying writer.

Equivalent to:

async fn write_i64(&mut self, n: i64) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write signed 64-bit integers to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_i64(i64::MIN).await?;
writer.write_i64(i64::MAX).await?;

assert_eq!(writer, b"\x80\x00\x00\x00\x00\x00\x00\x00\x7f\xff\xff\xff\xff\xff\xff\xff");
Ok(())
# }

fn write_u128(&mut self, n: u128) -> WriteU128<&mut Self>
where
    Self: Unpin,

Writes an unsigned 128-bit integer in big-endian order to the underlying writer.

Equivalent to:

async fn write_u128(&mut self, n: u128) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write unsigned 128-bit integers to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_u128(16947640962301618749969007319746179).await?;

assert_eq!(writer, vec![
    0x00, 0x03, 0x43, 0x95, 0x4d, 0x60, 0x86, 0x83,
    0x00, 0x03, 0x43, 0x95, 0x4d, 0x60, 0x86, 0x83
]);
Ok(())
# }

fn write_i128(&mut self, n: i128) -> WriteI128<&mut Self>
where
    Self: Unpin,

Writes an signed 128-bit integer in big-endian order to the underlying writer.

Equivalent to:

async fn write_i128(&mut self, n: i128) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write signed 128-bit integers to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_i128(i128::MIN).await?;

assert_eq!(writer, vec![
    0x80, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0
]);
Ok(())
# }

fn write_f32(&mut self, n: f32) -> WriteF32<&mut Self>
where
    Self: Unpin,

Writes an 32-bit floating point type in big-endian order to the underlying writer.

Equivalent to:

async fn write_f32(&mut self, n: f32) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write 32-bit floating point type to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_f32(f32::MIN).await?;

assert_eq!(writer, vec![0xff, 0x7f, 0xff, 0xff]);
Ok(())
# }

fn write_f64(&mut self, n: f64) -> WriteF64<&mut Self>
where
    Self: Unpin,

Writes an 64-bit floating point type in big-endian order to the underlying writer.

Equivalent to:

async fn write_f64(&mut self, n: f64) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write 64-bit floating point type to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_f64(f64::MIN).await?;

assert_eq!(writer, vec![
    0xff, 0xef, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff
]);
Ok(())
# }

fn write_u16_le(&mut self, n: u16) -> WriteU16Le<&mut Self>
where
    Self: Unpin,

Writes an unsigned 16-bit integer in little-endian order to the underlying writer.

Equivalent to:

async fn write_u16_le(&mut self, n: u16) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write unsigned 16-bit integers to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_u16_le(517).await?;
writer.write_u16_le(768).await?;

assert_eq!(writer, b"\x05\x02\x00\x03");
Ok(())
# }

fn write_i16_le(&mut self, n: i16) -> WriteI16Le<&mut Self>
where
    Self: Unpin,

Writes a signed 16-bit integer in little-endian order to the underlying writer.

Equivalent to:

async fn write_i16_le(&mut self, n: i16) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write signed 16-bit integers to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_i16_le(193).await?;
writer.write_i16_le(-132).await?;

assert_eq!(writer, b"\xc1\x00\x7c\xff");
Ok(())
# }

fn write_u32_le(&mut self, n: u32) -> WriteU32Le<&mut Self>
where
    Self: Unpin,

Writes an unsigned 32-bit integer in little-endian order to the underlying writer.

Equivalent to:

async fn write_u32_le(&mut self, n: u32) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write unsigned 32-bit integers to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_u32_le(267).await?;
writer.write_u32_le(1205419366).await?;

assert_eq!(writer, b"\x0b\x01\x00\x00\x66\x3d\xd9\x47");
Ok(())
# }

fn write_i32_le(&mut self, n: i32) -> WriteI32Le<&mut Self>
where
    Self: Unpin,

Writes a signed 32-bit integer in little-endian order to the underlying writer.

Equivalent to:

async fn write_i32_le(&mut self, n: i32) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write signed 32-bit integers to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_i32_le(267).await?;
writer.write_i32_le(1205419366).await?;

assert_eq!(writer, b"\x0b\x01\x00\x00\x66\x3d\xd9\x47");
Ok(())
# }

fn write_u64_le(&mut self, n: u64) -> WriteU64Le<&mut Self>
where
    Self: Unpin,

Writes an unsigned 64-bit integer in little-endian order to the underlying writer.

Equivalent to:

async fn write_u64_le(&mut self, n: u64) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write unsigned 64-bit integers to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_u64_le(918733457491587).await?;
writer.write_u64_le(143).await?;

assert_eq!(writer, b"\x83\x86\x60\x4d\x95\x43\x03\x00\x8f\x00\x00\x00\x00\x00\x00\x00");
Ok(())
# }

fn write_i64_le(&mut self, n: i64) -> WriteI64Le<&mut Self>
where
    Self: Unpin,

Writes an signed 64-bit integer in little-endian order to the underlying writer.

Equivalent to:

async fn write_i64_le(&mut self, n: i64) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write signed 64-bit integers to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_i64_le(i64::MIN).await?;
writer.write_i64_le(i64::MAX).await?;

assert_eq!(writer, b"\x00\x00\x00\x00\x00\x00\x00\x80\xff\xff\xff\xff\xff\xff\xff\x7f");
Ok(())
# }

fn write_u128_le(&mut self, n: u128) -> WriteU128Le<&mut Self>
where
    Self: Unpin,

Writes an unsigned 128-bit integer in little-endian order to the underlying writer.

Equivalent to:

async fn write_u128_le(&mut self, n: u128) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write unsigned 128-bit integers to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_u128_le(16947640962301618749969007319746179).await?;

assert_eq!(writer, vec![
    0x83, 0x86, 0x60, 0x4d, 0x95, 0x43, 0x03, 0x00,
    0x83, 0x86, 0x60, 0x4d, 0x95, 0x43, 0x03, 0x00,
]);
Ok(())
# }

fn write_i128_le(&mut self, n: i128) -> WriteI128Le<&mut Self>
where
    Self: Unpin,

Writes an signed 128-bit integer in little-endian order to the underlying writer.

Equivalent to:

async fn write_i128_le(&mut self, n: i128) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write signed 128-bit integers to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_i128_le(i128::MIN).await?;

assert_eq!(writer, vec![
    0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0x80
]);
Ok(())
# }

fn write_f32_le(&mut self, n: f32) -> WriteF32Le<&mut Self>
where
    Self: Unpin,

Writes an 32-bit floating point type in little-endian order to the underlying writer.

Equivalent to:

async fn write_f32_le(&mut self, n: f32) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write 32-bit floating point type to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_f32_le(f32::MIN).await?;

assert_eq!(writer, vec![0xff, 0xff, 0x7f, 0xff]);
Ok(())
# }

fn write_f64_le(&mut self, n: f64) -> WriteF64Le<&mut Self>
where
    Self: Unpin,

Writes an 64-bit floating point type in little-endian order to the underlying writer.

Equivalent to:

async fn write_f64_le(&mut self, n: f64) -> io::Result<()>;

It is recommended to use a buffered writer to avoid excessive syscalls.

Errors

This method returns the same errors as AsyncWriteExt::write_all.

Examples

Write 64-bit floating point type to a AsyncWrite:

use tokio::io::{self, AsyncWriteExt};

# #[tokio::main(flavor = "current_thread")]
# async fn main() -> io::Result<()> {
let mut writer = Vec::new();

writer.write_f64_le(f64::MIN).await?;

assert_eq!(writer, vec![
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xef, 0xff
]);
Ok(())
# }

fn flush(&mut self) -> Flush<'_, Self>
where
    Self: Unpin,

Flushes this output stream, ensuring that all intermediately buffered contents reach their destination.

Equivalent to:

async fn flush(&mut self) -> io::Result<()>;

Errors

It is considered an error if not all bytes could be written due to I/O errors or EOF being reached.

Cancel safety

This method is cancel safe.

If flush is used as a branch in tokio::select! and another branch completes first, then the buffered data in this AsyncWrite may have been partially flushed. However, it is guaranteed that the buffer is advanced by the amount of bytes that have been partially flushed.

Examples

# #[cfg(not(target_family = "wasm"))]
# {
use tokio::io::{self, BufWriter, AsyncWriteExt};
use tokio::fs::File;

#[tokio::main]
async fn main() -> io::Result<()> {
    let f = File::create("foo.txt").await?;
    let mut buffer = BufWriter::new(f);

    buffer.write_all(b"some bytes").await?;
    buffer.flush().await?;
    Ok(())
}
# }

fn shutdown(&mut self) -> Shutdown<'_, Self>
where
    Self: Unpin,

Shuts down the output stream, ensuring that the value can be dropped cleanly.

Equivalent to:

async fn shutdown(&mut self) -> io::Result<()>;

Similar to flush, all intermediately buffered content is written to the underlying stream. Once the operation completes, the caller should no longer attempt to write to the stream. For example, the TcpStream implementation will issue a shutdown(Write) sys call.

Examples

# #[cfg(not(target_family = "wasm"))]
# {
use tokio::io::{self, BufWriter, AsyncWriteExt};
use tokio::fs::File;

#[tokio::main]
async fn main() -> io::Result<()> {
    let f = File::create("foo.txt").await?;
    let mut buffer = BufWriter::new(f);

    buffer.write_all(b"some bytes").await?;
    buffer.shutdown().await?;
    Ok(())
}
# }