Struct File

pub struct File<F> { /* private fields */ }

Wraps file-like objects for asynchronous I/O.

Normally, you should use File::new_nb rather than File::raw_new unless the underlying file descriptor has already been set to nonblocking mode. Using a file descriptor that is not in nonblocking mode for asynchronous I/O will lead to subtle and confusing bugs.

Wrapping regular files has no effect because they do not support nonblocking mode.

The most common instantiation of this type is File<std::fs::File>, which indirectly provides the following trait implementation:

impl AsyncRead + AsyncWrite for PollEvented<File<std::fs::File>>;

Example: read standard input line by line

use tokio::stream::StreamExt;
use tokio_util::codec::FramedRead;
use tokio_util::codec::LinesCodec;

#[tokio::main]
async fn main() -> std::io::Result<()> {
    // convert stdin into a nonblocking file;
    // this is the only part that makes use of tokio_file_unix
    let file = tokio_file_unix::raw_stdin()?;
    let file = tokio_file_unix::File::new_nb(file)?;

    let mut framed = FramedRead::new(file, LinesCodec::new());

    while let Some(got) = framed.next().await {
        println!("Got this: {:?}", got);
    }

    println!("Received None, lol");
    Ok(())
}

Example: unsafe creation from raw file descriptor

To unsafely create File<F> from a raw file descriptor fd, you can do something like:

use std::os::unix::io::FromRawFd;

let file = tokio_file_unix::File::new_nb(F::from_raw_fd(fd))?;

which will enable nonblocking mode upon creation. The choice of F is critical: it determines the ownership semantics of the file descriptor. For example, if you choose F = std::fs::File, the file descriptor will be closed when the File is dropped.

Implementations

impl<F: AsRawFd> File<F>

pub fn new_nb(file: F) -> Result<PollEvented<Self>>

Wraps a file-like object into a pollable object that supports tokio::io::AsyncRead and tokio::io::AsyncWrite, and also enables nonblocking mode on the underlying file descriptor.

pub fn raw_new(file: F) -> Result<PollEvented<Self>>

Raw constructor that does not enable nonblocking mode on the underlying file descriptor. This constructor should only be used if you are certain that the underlying file descriptor is already in nonblocking mode.

Trait Implementations

impl<F: AsRawFd> AsRawFd for File<F>

fn as_raw_fd(&self) -> RawFd

Extracts the raw file descriptor.

impl<F: Debug> Debug for File<F>

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

Formats the value using the given formatter.

impl<F: AsRawFd> Evented for File<F>

fn register( &self, poll: &Poll, token: Token, interest: Ready, opts: PollOpt, ) -> Result<()>

Register self with the given Poll instance.

fn reregister( &self, poll: &Poll, token: Token, interest: Ready, opts: PollOpt, ) -> Result<()>

Re-register self with the given Poll instance.

fn deregister(&self, poll: &Poll) -> Result<()>

Deregister self from the given Poll instance

impl<F: Read> Read for File<F>

fn read(&mut self, buf: &mut [u8]) -> Result<usize>

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

fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize, Error>

Like read, except that it reads into a slice of buffers.

fn is_read_vectored(&self) -> bool

🔬This is a nightly-only experimental API. (can_vector)

Determines if this Reader has an efficient read_vectored implementation.

fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize, Error>

Reads all bytes until EOF in this source, placing them into buf.

fn read_to_string(&mut self, buf: &mut String) -> Result<usize, Error>

Reads all bytes until EOF in this source, appending them to buf.

fn read_exact(&mut self, buf: &mut [u8]) -> Result<(), Error>

Reads the exact number of bytes required to fill buf.

fn read_buf(&mut self, buf: BorrowedCursor<'_>) -> Result<(), Error>

🔬This is a nightly-only experimental API. (read_buf)

Pull some bytes from this source into the specified buffer.

fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<(), Error>

🔬This is a nightly-only experimental API. (read_buf)

Reads the exact number of bytes required to fill cursor.

fn by_ref(&mut self) -> &mut Self

where Self: Sized,

Creates a “by reference” adaptor for this instance of Read.

fn bytes(self) -> Bytes<Self>

where Self: Sized,

Transforms this Read instance to an Iterator over its bytes.

fn chain<R>(self, next: R) -> Chain<Self, R>

where R: Read, Self: Sized,

Creates an adapter which will chain this stream with another.

fn take(self, limit: u64) -> Take<Self>

where Self: Sized,

Creates an adapter which will read at most limit bytes from it.

impl<F: Seek> Seek for File<F>

fn seek(&mut self, pos: SeekFrom) -> Result<u64>

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

fn rewind(&mut self) -> Result<(), Error>

Rewind to the beginning of a stream.

fn stream_len(&mut self) -> Result<u64, Error>

🔬This is a nightly-only experimental API. (seek_stream_len)

Returns the length of this stream (in bytes).

fn stream_position(&mut self) -> Result<u64, Error>

Returns the current seek position from the start of the stream.

fn seek_relative(&mut self, offset: i64) -> Result<(), Error>

Seeks relative to the current position.

impl<F: Write> Write for File<F>

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

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

fn flush(&mut self) -> Result<()>

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

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

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

fn is_write_vectored(&self) -> bool

🔬This is a nightly-only experimental API. (can_vector)

Determines if this Writer has an efficient write_vectored implementation.

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

Attempts to write an entire buffer into this writer.

fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<(), Error>

🔬This is a nightly-only experimental API. (write_all_vectored)

Attempts to write multiple buffers into this writer.

fn write_fmt(&mut self, args: Arguments<'_>) -> Result<(), Error>

Writes a formatted string into this writer, returning any error encountered.

fn by_ref(&mut self) -> &mut Self

where Self: Sized,

Creates a “by reference” adapter for this instance of Write.