Struct File

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::io::AsyncReadExt;

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

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

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

The read_to_end method is defined on the AsyncReadExt trait.

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::io::AsyncWriteExt;

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

The write_all method is defined on the AsyncWriteExt trait.

Opens a file in read-write mode.

This function will create a file if it does not exist, or return an error if it does. This way, if the call succeeds, the file returned is guaranteed to be new.

This option is useful because it is atomic. Otherwise between checking whether a file exists and creating a new one, the file may have been created by another process (a TOCTOU race condition / attack).

This can also be written using File::options().read(true).write(true).create_new(true).open(...).

See OpenOptions for more details.

Examples

use tokio::fs::File;
use tokio::io::AsyncWriteExt;

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

The write_all method is defined on the AsyncWriteExt trait.

Returns a new OpenOptions object.

This function returns a new OpenOptions object that you can use to open or create a file with specific options if open() or create() are not appropriate.

It is equivalent to OpenOptions::new(), but allows you to write more readable code. Instead of OpenOptions::new().append(true).open("example.log"), you can write File::options().append(true).open("example.log"). This also avoids the need to import OpenOptions.

See the OpenOptions::new function for more details.

Examples

use tokio::fs::File;
use tokio::io::AsyncWriteExt;

let mut f = File::options().append(true).open("example.log").await?;
f.write_all(b"new line\n").await?;

Converts 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);

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::io::AsyncWriteExt;

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

The write_all method is defined on the AsyncWriteExt trait.

This function is similar to 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 sync_all.

Examples

use tokio::fs::File;
use tokio::io::AsyncWriteExt;

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

The write_all method is defined on the AsyncWriteExt trait.

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::io::AsyncWriteExt;

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

The write_all method is defined on the AsyncWriteExt trait.

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);

Creates 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?;

Destructures File into a std::fs::File. This function is async to allow any in-flight operations to complete.

Use File::try_into_std to attempt conversion immediately.

Examples

use tokio::fs::File;

let tokio_file = File::open("foo.txt").await?;
let std_file = tokio_file.into_std().await;

Tries to immediately destructure File into a std::fs::File.

Errors

This function will return an error containing the file if some operation is in-flight.

Examples

use tokio::fs::File;

let tokio_file = File::open("foo.txt").await?;
let std_file = tokio_file.try_into_std().unwrap();

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?;

Set the maximum buffer size for the underlying AsyncRead / AsyncWrite operation.

Although Tokio uses a sensible default value for this buffer size, this function would be useful for changing that default depending on the situation.

Examples

use tokio::fs::File;
use tokio::io::AsyncWriteExt;

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

// Set maximum buffer size to 8 MiB
file.set_max_buf_size(8 * 1024 * 1024);

let mut buf = vec![1; 1024 * 1024 * 1024];

// Write the 1 GiB buffer in chunks up to 8 MiB each.
file.write_all(&mut buf).await?;

Get the maximum buffer size for the underlying AsyncRead / AsyncWrite operation.

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.