Struct kvarn::prelude::fs::File

pub struct File { /* private fields */ }
Expand description

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 AsyncSeek to alter the logical cursor that the file contains internally.

A file will not be closed immediately when it goes out of scope if there are any IO operations that have not yet completed. To ensure that a file is closed immediately when it is dropped, you should call flush before dropping it. Note that this does not ensure that the file has been fully written to disk; the operating system might keep the changes around in an in-memory buffer. See the sync_all method for telling the OS to write the data to disk.

Reading and writing to a File is usually done using the convenience methods found on the AsyncReadExt and AsyncWriteExt traits.

Examples

Create a new file and asynchronously write bytes to it:

use tokio::fs::File;
use tokio::io::AsyncWriteExt; // for write_all()

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::io::AsyncReadExt; // for read_to_end()

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

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

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

Implementations§

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.

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?;

Trait Implementations§

Extracts the raw file descriptor. Read more
Attempts to read from the AsyncRead into buf. Read more
Attempts to seek to an offset, in bytes, in a stream. Read more
Waits for a seek operation to complete. Read more
Attempt to write bytes from buf into the object. Read more
Attempts to flush the object, ensuring that any buffered data reach their destination. Read more
Initiates or attempts to shut down this writer, returning success when the I/O connection has completely shut down. Read more
Like poll_write, except that it writes from a slice of buffers. Read more
Determines if this writer has an efficient poll_write_vectored implementation. Read more
Formats the value using the given formatter. Read more
Converts to this type from the input type.
Constructs a new instance of Self from the given raw file descriptor. Read more

Auto Trait Implementations§

Blanket Implementations§

Gets the TypeId of self. Read more
Creates a new AsyncRead instance that chains this stream with next. Read more
Pulls some bytes from this source into the specified buffer, returning how many bytes were read. Read more
Pulls some bytes from this source into the specified buffer, advancing the buffer’s internal cursor. Read more
Reads the exact number of bytes required to fill buf. Read more
Reads an unsigned 8 bit integer from the underlying reader. Read more
Reads a signed 8 bit integer from the underlying reader. Read more
Reads an unsigned 16-bit integer in big-endian order from the underlying reader. Read more
Reads a signed 16-bit integer in big-endian order from the underlying reader. Read more
Reads an unsigned 32-bit integer in big-endian order from the underlying reader. Read more
Reads a signed 32-bit integer in big-endian order from the underlying reader. Read more
Reads an unsigned 64-bit integer in big-endian order from the underlying reader. Read more
Reads an signed 64-bit integer in big-endian order from the underlying reader. Read more
Reads an unsigned 128-bit integer in big-endian order from the underlying reader. Read more
Reads an signed 128-bit integer in big-endian order from the underlying reader. Read more
Reads an 32-bit floating point type in big-endian order from the underlying reader. Read more
Reads an 64-bit floating point type in big-endian order from the underlying reader. Read more
Reads an unsigned 16-bit integer in little-endian order from the underlying reader. Read more
Reads a signed 16-bit integer in little-endian order from the underlying reader. Read more
Reads an unsigned 32-bit integer in little-endian order from the underlying reader. Read more
Reads a signed 32-bit integer in little-endian order from the underlying reader. Read more
Reads an unsigned 64-bit integer in little-endian order from the underlying reader. Read more
Reads an signed 64-bit integer in little-endian order from the underlying reader. Read more
Reads an unsigned 128-bit integer in little-endian order from the underlying reader. Read more
Reads an signed 128-bit integer in little-endian order from the underlying reader. Read more
Reads an 32-bit floating point type in little-endian order from the underlying reader. Read more
Reads an 64-bit floating point type in little-endian order from the underlying reader. Read more
Reads all bytes until EOF in this source, placing them into buf. Read more
Reads all bytes until EOF in this source, appending them to buf. Read more
Creates an adaptor which reads at most limit bytes from it. Read more
Creates a future which will seek an IO object, and then yield the new position in the object and the object itself. Read more
Creates a future which will rewind to the beginning of the stream. Read more
Creates a future which will return the current seek position from the start of the stream. Read more
Writes a buffer into this writer, returning how many bytes were written. Read more
Like write, except that it writes from a slice of buffers. Read more
Writes a buffer into this writer, advancing the buffer’s internal cursor. Read more
Attempts to write an entire buffer into this writer. Read more
Attempts to write an entire buffer into this writer. Read more
Writes an unsigned 8-bit integer to the underlying writer. Read more
Writes a signed 8-bit integer to the underlying writer. Read more
Writes an unsigned 16-bit integer in big-endian order to the underlying writer. Read more
Writes a signed 16-bit integer in big-endian order to the underlying writer. Read more
Writes an unsigned 32-bit integer in big-endian order to the underlying writer. Read more
Writes a signed 32-bit integer in big-endian order to the underlying writer. Read more
Writes an unsigned 64-bit integer in big-endian order to the underlying writer. Read more
Writes an signed 64-bit integer in big-endian order to the underlying writer. Read more
Writes an unsigned 128-bit integer in big-endian order to the underlying writer. Read more
Writes an signed 128-bit integer in big-endian order to the underlying writer. Read more
Writes an 32-bit floating point type in big-endian order to the underlying writer. Read more
Writes an 64-bit floating point type in big-endian order to the underlying writer. Read more
Writes an unsigned 16-bit integer in little-endian order to the underlying writer. Read more
Writes a signed 16-bit integer in little-endian order to the underlying writer. Read more
Writes an unsigned 32-bit integer in little-endian order to the underlying writer. Read more
Writes a signed 32-bit integer in little-endian order to the underlying writer. Read more
Writes an unsigned 64-bit integer in little-endian order to the underlying writer. Read more
Writes an signed 64-bit integer in little-endian order to the underlying writer. Read more
Writes an unsigned 128-bit integer in little-endian order to the underlying writer. Read more
Writes an signed 128-bit integer in little-endian order to the underlying writer. Read more
Writes an 32-bit floating point type in little-endian order to the underlying writer. Read more
Writes an 64-bit floating point type in little-endian order to the underlying writer. Read more
Flushes this output stream, ensuring that all intermediately buffered contents reach their destination. Read more
Shuts down the output stream, ensuring that the value can be dropped cleanly. Read more
Immutably borrows from an owned value. Read more
Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Instruments this type with the provided Span, returning an Instrumented wrapper. Read more
Instruments this type with the current Span, returning an Instrumented wrapper. Read more

Calls U::from(self).

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

Should always be Self
The type returned in the event of a conversion error.
Performs the conversion.
The type returned in the event of a conversion error.
Performs the conversion.
Attaches the provided Subscriber to this type, returning a WithDispatch wrapper. Read more
Attaches the current default Subscriber to this type, returning a WithDispatch wrapper. Read more