Struct tokio::fs::File

pub struct File { /* fields omitted */ }

A reference to an open file on the filesystem.

This is a specialized version of std::fs::File for usage from the Tokio runtime.

An instance of a File can be read and/or written depending on what options it was opened with. Files also implement Seek to alter the logical cursor that the file contains internally.

Files are automatically closed when they go out of scope.

Examples

Create a new file and asynchronously write bytes to it:

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

let mut file = File::create("foo.txt").await?;
file.write_all(b"hello, world!").await?;

Read the contents of a file into a buffer

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

let mut file = File::open("foo.txt").await?;

let mut contents = vec![];
file.read_to_end(&mut contents).await?;

println!("len = {}", contents.len());

Methods

impl File

pub fn open<P>(path: P) -> impl Future<Output = Result<File, Error>> where
    P: AsRef<Path>, 

Attempts to open a file in read-only mode.

See OpenOptions for more details.

Errors

This function will return an error if called from outside of the Tokio runtime or if path does not already exist. Other errors may also be returned according to OpenOptions::open.

Examples

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

let mut file = File::open("foo.txt").await?;

let mut contents = vec![];
file.read_to_end(&mut contents).await?;

println!("len = {}", contents.len());

pub fn create<P>(path: P) -> impl Future<Output = Result<File, Error>> where
    P: AsRef<Path>, 

Opens a file in write-only mode.

This function will create a file if it does not exist, and will truncate it if it does.

See OpenOptions for more details.

Errors

Results in an error if called from outside of the Tokio runtime or if the underlying create call results in an error.

Examples

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

let mut file = File::create("foo.txt").await?;
file.write_all(b"hello, world!").await?;

pub fn from_std(std: File) -> File

Convert a std::fs::File to a tokio_fs::File.

Examples

// This line could block. It is not recommended to do this on the Tokio
// runtime.
let std_file = std::fs::File::open("foo.txt").unwrap();
let file = tokio::fs::File::from_std(std_file);

pub fn seek(
    &'_ mut self,
    __arg1: SeekFrom
) -> impl Future<Output = Result<u64, Error>>

Seek to an offset, in bytes, in a stream.

Examples

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

use std::io::SeekFrom;

let mut file = File::open("foo.txt").await?;
file.seek(SeekFrom::Start(6)).await?;

let mut contents = vec![0u8; 10];
file.read_exact(&mut contents).await?;

pub fn sync_all(&'_ mut self) -> impl Future<Output = Result<(), Error>>

Attempts to sync all OS-internal metadata to disk.

This function will attempt to ensure that all in-core data reaches the filesystem before returning.

Examples

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

let mut file = File::create("foo.txt").await?;
file.write_all(b"hello, world!").await?;
file.sync_all().await?;

pub fn sync_data(&'_ mut self) -> impl Future<Output = Result<(), Error>>

This function is similar to poll_sync_all, except that it may not synchronize file metadata to the filesystem.

This is intended for use cases that must synchronize content, but don't need the metadata on disk. The goal of this method is to reduce disk operations.

Note that some platforms may simply implement this in terms of poll_sync_all.

Examples

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

let mut file = File::create("foo.txt").await?;
file.write_all(b"hello, world!").await?;
file.sync_data().await?;

pub fn set_len(
    &'_ mut self,
    size: u64
) -> impl Future<Output = Result<(), Error>>

Truncates or extends the underlying file, updating the size of this file to become size.

If the size is less than the current file's size, then the file will be shrunk. If it is greater than the current file's size, then the file will be extended to size and have all of the intermediate data filled in with 0s.

Errors

This function will return an error if the file is not opened for writing.

Examples

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

let mut file = File::create("foo.txt").await?;
file.write_all(b"hello, world!").await?;
file.set_len(10).await?;

pub fn metadata(&'_ self) -> impl Future<Output = Result<Metadata, Error>>

Queries metadata about the underlying file.

Examples

use tokio::fs::File;

let file = File::open("foo.txt").await?;
let metadata = file.metadata().await?;

println!("{:?}", metadata);

pub fn try_clone(&'_ self) -> impl Future<Output = Result<File, Error>>

Create a new File instance that shares the same underlying file handle as the existing File instance. Reads, writes, and seeks will affect both File instances simultaneously.

Examples

use tokio::fs::File;

let file = File::open("foo.txt").await?;
let file_clone = file.try_clone().await?;

pub fn set_permissions(
    &'_ self,
    perm: Permissions
) -> impl Future<Output = Result<(), Error>>

Changes the permissions on the underlying file.

Platform-specific behavior

This function currently corresponds to the fchmod function on Unix and the SetFileInformationByHandle function on Windows. Note that, this may change in the future.

Errors

This function will return an error if the user lacks permission change attributes on the underlying file. It may also return an error in other os-specific unspecified cases.

Examples

use tokio::fs::File;

let file = File::open("foo.txt").await?;
let mut perms = file.metadata().await?.permissions();
perms.set_readonly(true);
file.set_permissions(perms).await?;

Trait Implementations

impl Debug for File

fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error>

Formats the value using the given formatter.

impl AsyncRead for File

fn poll_read(
    self: Pin<&mut File>,
    cx: &mut Context,
    dst: &mut [u8]
) -> Poll<Result<usize, Error>>

Attempt to read from the AsyncRead into buf.

unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [u8]) -> bool

Prepares an uninitialized buffer to be safe to pass to read. Returns true if the supplied buffer was zeroed out.

fn poll_read_buf<B>(
    self: Pin<&mut Self>,
    cx: &mut Context,
    buf: &mut B
) -> Poll<Result<usize, Error>> where
    B: BufMut, 

Pull some bytes from this source into the specified BufMut, returning how many bytes were read.

impl From<File> for File

fn from(std: File) -> File

Performs the conversion.

impl AsyncWrite for File

fn poll_write(
    self: Pin<&mut File>,
    cx: &mut Context,
    src: &[u8]
) -> Poll<Result<usize, Error>>

Attempt to write bytes from buf into the object.

fn poll_flush(self: Pin<&mut File>, cx: &mut Context) -> Poll<Result<(), Error>>

Attempt to flush the object, ensuring that any buffered data reach their destination.

fn poll_shutdown(
    self: Pin<&mut File>,
    _cx: &mut Context
) -> Poll<Result<(), Error>>

Initiates or attempts to shut down this writer, returning success when the I/O connection has completely shut down.

fn poll_write_buf<B>(
    self: Pin<&mut Self>,
    cx: &mut Context,
    buf: &mut B
) -> Poll<Result<usize, Error>> where
    B: Buf, 

Write a Buf into this value, returning how many bytes were written.