Trait tokio::io::AsyncWriteExt

pub trait AsyncWriteExt: AsyncWrite {
    fn write<'a>(&'a mut self, src: &'a [u8]) -> Write<'a, Self>
    where
        Self: Unpin,
    { ... }
    fn write_buf<'a, B>(&'a mut self, src: &'a mut B) -> WriteBuf<'a, Self, B>
    where
        Self: Sized + Unpin,
        B: Buf,
    { ... }
    fn write_all<'a>(&'a mut self, src: &'a [u8]) -> WriteAll<'a, Self>
    where
        Self: Unpin,
    { ... }
    fn write_u8<'a>(&'a mut self, n: u8) -> WriteU8<&'a mut Self>
    where
        Self: Unpin,
    { ... }
    fn write_i8<'a>(&'a mut self, n: i8) -> WriteI8<&'a mut Self>
    where
        Self: Unpin,
    { ... }
    fn write_u16<'a>(&'a mut self, n: u16) -> WriteU16<&'a mut Self>
    where
        Self: Unpin,
    { ... }
    fn write_i16<'a>(&'a mut self, n: i16) -> WriteI16<&'a mut Self>
    where
        Self: Unpin,
    { ... }
    fn write_u32<'a>(&'a mut self, n: u32) -> WriteU32<&'a mut Self>
    where
        Self: Unpin,
    { ... }
    fn write_i32<'a>(&'a mut self, n: i32) -> WriteI32<&'a mut Self>
    where
        Self: Unpin,
    { ... }
    fn write_u64<'a>(&'a mut self, n: u64) -> WriteU64<&'a mut Self>
    where
        Self: Unpin,
    { ... }
    fn write_i64<'a>(&'a mut self, n: i64) -> WriteI64<&'a mut Self>
    where
        Self: Unpin,
    { ... }
    fn write_u128<'a>(&'a mut self, n: u128) -> WriteU128<&'a mut Self>
    where
        Self: Unpin,
    { ... }
    fn write_i128<'a>(&'a mut self, n: i128) -> WriteI128<&'a mut Self>
    where
        Self: Unpin,
    { ... }
    fn write_u16_le<'a>(&'a mut self, n: u16) -> WriteU16Le<&'a mut Self>
    where
        Self: Unpin,
    { ... }
    fn write_i16_le<'a>(&'a mut self, n: i16) -> WriteI16Le<&'a mut Self>
    where
        Self: Unpin,
    { ... }
    fn write_u32_le<'a>(&'a mut self, n: u32) -> WriteU32Le<&'a mut Self>
    where
        Self: Unpin,
    { ... }
    fn write_i32_le<'a>(&'a mut self, n: i32) -> WriteI32Le<&'a mut Self>
    where
        Self: Unpin,
    { ... }
    fn write_u64_le<'a>(&'a mut self, n: u64) -> WriteU64Le<&'a mut Self>
    where
        Self: Unpin,
    { ... }
    fn write_i64_le<'a>(&'a mut self, n: i64) -> WriteI64Le<&'a mut Self>
    where
        Self: Unpin,
    { ... }
    fn write_u128_le<'a>(&'a mut self, n: u128) -> WriteU128Le<&'a mut Self>
    where
        Self: Unpin,
    { ... }
    fn write_i128_le<'a>(&'a mut self, n: i128) -> WriteI128Le<&'a mut Self>
    where
        Self: Unpin,
    { ... }
    fn flush(&mut self) -> Flush<'_, Self>
    where
        Self: Unpin,
    { ... }
    fn shutdown(&mut self) -> Shutdown<'_, Self>
    where
        Self: Unpin,
    { ... }
}

Writes bytes to a sink.

Implemented as an extention trait, adding utility methods to all AsyncWrite types. Callers will tend to import this trait instead of AsyncWrite.

As a convenience, this trait may be imported using the prelude:

use tokio::prelude::*;
use tokio::fs::File;

#[tokio::main]
async fn main() -> io::Result<()> {
    let data = b"some bytes";

    let mut pos = 0;
    let mut buffer = File::create("foo.txt").await?;

    while pos < data.len() {
        let bytes_written = buffer.write(&data[pos..]).await?;
        pos += bytes_written;
    }

    Ok(())
}

See module documentation for more details.

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.

Examples

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?;
    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.

Examples

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

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?;
    }

    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.

Errors

This function will return the first error that write returns.

Examples

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

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

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

fn write_u8<'a>(&'a mut self, n: u8) -> WriteU8<&'a 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]
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<'a>(&'a mut self, n: i8) -> WriteI8<&'a mut Self> where
    Self: Unpin, 

Writes an unsigned 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 unsigned 8 bit integers to a AsyncWrite:

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

#[tokio::main]
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_u16<'a>(&'a mut self, n: u16) -> WriteU16<&'a 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]
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<'a>(&'a mut self, n: i16) -> WriteI16<&'a 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]
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<'a>(&'a mut self, n: u32) -> WriteU32<&'a 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]
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<'a>(&'a mut self, n: i32) -> WriteI32<&'a 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]
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<'a>(&'a mut self, n: u64) -> WriteU64<&'a 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]
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<'a>(&'a mut self, n: i64) -> WriteI64<&'a 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]
async fn main() -> io::Result<()> {
    let mut writer = Vec::new();

    writer.write_i64(i64::min_value()).await?;
    writer.write_i64(i64::max_value()).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<'a>(&'a mut self, n: u128) -> WriteU128<&'a 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]
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<'a>(&'a mut self, n: i128) -> WriteI128<&'a 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]
async fn main() -> io::Result<()> {
    let mut writer = Vec::new();

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

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

fn write_u16_le<'a>(&'a mut self, n: u16) -> WriteU16Le<&'a 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]
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<'a>(&'a mut self, n: i16) -> WriteI16Le<&'a 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]
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<'a>(&'a mut self, n: u32) -> WriteU32Le<&'a 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]
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<'a>(&'a mut self, n: i32) -> WriteI32Le<&'a 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]
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<'a>(&'a mut self, n: u64) -> WriteU64Le<&'a 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]
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<'a>(&'a mut self, n: i64) -> WriteI64Le<&'a 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]
async fn main() -> io::Result<()> {
    let mut writer = Vec::new();

    writer.write_i64_le(i64::min_value()).await?;
    writer.write_i64_le(i64::max_value()).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<'a>(&'a mut self, n: u128) -> WriteU128Le<&'a 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]
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<'a>(&'a mut self, n: i128) -> WriteI128Le<&'a 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]
async fn main() -> io::Result<()> {
    let mut writer = Vec::new();

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

    assert_eq!(writer, vec![
         0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0x80
    ]);
    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.

Examples

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 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

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(())
}

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Implementors

impl<W: AsyncWrite + ?Sized> AsyncWriteExt for W

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