Struct tokio_uring::fs::File

pub struct File { /* private fields */ }

A reference to an open file on the filesystem.

An instance of a File can be read and/or written depending on what options it was opened with. The File type provides positional read and write operations. The file does not maintain an internal cursor. The caller is required to specify an offset when issuing an operation.

While files are automatically closed when they go out of scope, the operation happens asynchronously in the background. It is recommended to call the close() function in order to guarantee that the file successfully closed before exiting the scope. Closing a file does not guarantee writes have persisted to disk. Use sync_all to ensure all writes have reached the filesystem.

Examples

Creates a new file and write data to it:

use tokio_uring::fs::File;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    tokio_uring::start(async {
        // Open a file
        let file = File::create("hello.txt").await?;

        // Write some data
        let (res, buf) = file.write_at(&b"hello world"[..], 0).await;
        let n = res?;

        println!("wrote {} bytes", n);

        // Sync data to the file system.
        file.sync_all().await?;

        // Close the file
        file.close().await?;

        Ok(())
    })
}

Implementations

impl File

pub async fn open(path: impl AsRef<Path>) -> Result<File>

Attempts to open a file in read-only mode.

See the OpenOptions::open method for more details.

Errors

This function will return an error if path does not already exist. Other errors may also be returned according to OpenOptions::open.

Examples

use tokio_uring::fs::File;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    tokio_uring::start(async {
        let f = File::open("foo.txt").await?;

        // Close the file
        f.close().await?;
        Ok(())
    })
}

pub async fn create(path: impl AsRef<Path>) -> Result<File>

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 the OpenOptions::open function for more details.

Examples

use tokio_uring::fs::File;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    tokio_uring::start(async {
        let f = File::create("foo.txt").await?;

        // Close the file
        f.close().await?;
        Ok(())
    })
}

pub fn from_std(file: File) -> File

Converts a std::fs::File to a tokio_uring::fs::File.

pub async fn read_at<T: IoBufMut>(&self, buf: T, pos: u64) -> BufResult<usize, T>

Read some bytes at the specified offset from the file into the specified buffer, returning how many bytes were read.

Return

The method returns the operation result and the same buffer value passed as an argument.

If the method returns [Ok(n)], then the read was successful. A nonzero n value indicates that the buffer has been filled with n bytes of data from the file. If n is 0, then one of the following happened:

1. The specified offset is the end of the file.
2. The buffer specified was 0 bytes in length.

It is not an error if the returned value n is smaller than the buffer size, even when the file contains enough data to fill the buffer.

Errors

If this function encounters any form of I/O or other error, an error variant will be returned. The buffer is returned on error.

Examples

use tokio_uring::fs::File;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    tokio_uring::start(async {
        let f = File::open("foo.txt").await?;
        let buffer = vec![0; 10];

        // Read up to 10 bytes
        let (res, buffer) = f.read_at(buffer, 0).await;
        let n = res?;

        println!("The bytes: {:?}", &buffer[..n]);

        // Close the file
        f.close().await?;
        Ok(())
    })
}

pub async fn readv_at<T: IoBufMut>( &self, bufs: Vec<T>, pos: u64 ) -> BufResult<usize, Vec<T>>

Read some bytes at the specified offset from the file into the specified array of buffers, returning how many bytes were read.

Return

The method returns the operation result and the same array of buffers passed as an argument.

If the method returns [Ok(n)], then the read was successful. A nonzero n value indicates that the buffers have been filled with n bytes of data from the file. If n is 0, then one of the following happened:

1. The specified offset is the end of the file.
2. The buffers specified were 0 bytes in length.

It is not an error if the returned value n is smaller than the buffer size, even when the file contains enough data to fill the buffer.

Errors

If this function encounters any form of I/O or other error, an error variant will be returned. The buffer is returned on error.

Examples

use tokio_uring::fs::File;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    tokio_uring::start(async {
        let f = File::open("foo.txt").await?;
        let buffers = vec![Vec::<u8>::with_capacity(10), Vec::<u8>::with_capacity(10)];

        // Read up to 20 bytes
        let (res, buffer) = f.readv_at(buffers, 0).await;
        let n = res?;

        println!("Read {} bytes", n);

        // Close the file
        f.close().await?;
        Ok(())
    })
}

pub async fn writev_at<T: IoBuf>( &self, buf: Vec<T>, pos: u64 ) -> BufResult<usize, Vec<T>>

Write data from buffers into this file at the specified offset, returning how many bytes were written.

This function will attempt to write the entire contents of bufs, but the entire write may not succeed, or the write may also generate an error. The bytes will be written starting at the specified offset.

Return

The method returns the operation result and the same array of buffers passed in as an argument. A return value of 0 typically means that the underlying file 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_uring::fs::File;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    tokio_uring::start(async {
        let file = File::create("foo.txt").await?;

        // Writes some prefix of the byte string, not necessarily all of it.
        let bufs = vec!["some".to_owned().into_bytes(), " bytes".to_owned().into_bytes()];
        let (res, _) = file.writev_at(bufs, 0).await;
        let n = res?;

        println!("wrote {} bytes", n);

        // Close the file
        file.close().await?;
        Ok(())
    })
}

pub async fn write_at<T: IoBuf>(&self, buf: T, pos: u64) -> BufResult<usize, T>

Write a buffer into this file at the specified offset, returning how many bytes were written.

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. The bytes will be written starting at the specified offset.

Return

The method returns the operation result and the same buffer value passed in as an argument. A return value of 0 typically means that the underlying file 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_uring::fs::File;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    tokio_uring::start(async {
        let file = File::create("foo.txt").await?;

        // Writes some prefix of the byte string, not necessarily all of it.
        let (res, _) = file.write_at(&b"some bytes"[..], 0).await;
        let n = res?;

        println!("wrote {} bytes", n);

        // Close the file
        file.close().await?;
        Ok(())
    })
}

pub async fn sync_all(&self) -> Result<()>

Attempts to sync all OS-internal metadata to disk.

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

This can be used to handle errors that would otherwise only be caught when the File is closed. Dropping a file will ignore errors in synchronizing this in-memory data.

Examples

use tokio_uring::fs::File;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    tokio_uring::start(async {
        let f = File::create("foo.txt").await?;
        let (res, buf) = f.write_at(&b"Hello, world!"[..], 0).await;
        let n = res?;

        f.sync_all().await?;

        // Close the file
        f.close().await?;
        Ok(())
    })
}

pub async fn sync_data(&self) -> Result<()>

Attempts to sync file data to disk.

This method 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_uring::fs::File;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    tokio_uring::start(async {
        let f = File::create("foo.txt").await?;
        let (res, buf) = f.write_at(&b"Hello, world!"[..], 0).await;
        let n = res?;

        f.sync_data().await?;

        // Close the file
        f.close().await?;
        Ok(())
    })
}

pub async fn close(self) -> Result<()>

Closes the file.

The method completes once the close operation has completed, guaranteeing that resources associated with the file have been released.

If close is not called before dropping the file, the file is closed in the background, but there is no guarantee as to when the close operation will complete.

Examples

use tokio_uring::fs::File;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    tokio_uring::start(async {
        // Open the file
        let f = File::open("foo.txt").await?;
        // Close the file
        f.close().await?;

        Ok(())
    })
}

Trait Implementations

impl AsRawFd for File

fn as_raw_fd(&self) -> RawFd

Extracts the raw file descriptor.

impl Debug for File

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl FromRawFd for File

unsafe fn from_raw_fd(fd: RawFd) -> Self

Constructs a new instance of Self from the given raw file descriptor.