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§
Source§impl File
impl File
Sourcepub async fn open(path: impl AsRef<Path>) -> Result<File>
pub async fn open(path: impl AsRef<Path>) -> Result<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.
Sourcepub async fn create(path: impl AsRef<Path>) -> Result<File>
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 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.
Sourcepub async fn create_new<P: AsRef<Path>>(path: P) -> Result<File>
pub async fn create_new<P: AsRef<Path>>(path: P) -> Result<File>
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.
Sourcepub fn options() -> OpenOptions
pub fn options() -> OpenOptions
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?;
Sourcepub fn from_std(std: StdFile) -> File
pub fn from_std(std: StdFile) -> File
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);
Sourcepub async fn sync_all(&self) -> Result<()>
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-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.
Sourcepub async fn sync_data(&self) -> Result<()>
pub async fn sync_data(&self) -> Result<()>
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.
Sourcepub async fn set_len(&self, size: u64) -> Result<()>
pub async fn set_len(&self, size: u64) -> Result<()>
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.
Sourcepub async fn metadata(&self) -> Result<Metadata>
pub async fn metadata(&self) -> Result<Metadata>
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);
Sourcepub async fn try_clone(&self) -> Result<File>
pub async fn try_clone(&self) -> Result<File>
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?;
Sourcepub async fn into_std(self) -> StdFile
pub async fn into_std(self) -> StdFile
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;
Sourcepub fn try_into_std(self) -> Result<StdFile, Self>
pub fn try_into_std(self) -> Result<StdFile, Self>
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();
Sourcepub async fn set_permissions(&self, perm: Permissions) -> Result<()>
pub async fn set_permissions(&self, perm: Permissions) -> Result<()>
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?;
Sourcepub fn set_max_buf_size(&mut self, max_buf_size: usize)
pub fn set_max_buf_size(&mut self, max_buf_size: usize)
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?;
Trait Implementations§
Source§impl AsFd for File
impl AsFd for File
Source§fn as_fd(&self) -> BorrowedFd<'_>
fn as_fd(&self) -> BorrowedFd<'_>
Source§impl AsyncWrite for File
impl AsyncWrite for File
Source§fn poll_write(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
src: &[u8],
) -> Poll<Result<usize>>
fn poll_write( self: Pin<&mut Self>, cx: &mut Context<'_>, src: &[u8], ) -> Poll<Result<usize>>
buf
into the object. Read moreSource§fn poll_write_vectored(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
bufs: &[IoSlice<'_>],
) -> Poll<Result<usize, Error>>
fn poll_write_vectored( self: Pin<&mut Self>, cx: &mut Context<'_>, bufs: &[IoSlice<'_>], ) -> Poll<Result<usize, Error>>
poll_write
, except that it writes from a slice of buffers. Read moreSource§fn is_write_vectored(&self) -> bool
fn is_write_vectored(&self) -> bool
poll_write_vectored
implementation. Read moreAuto Trait Implementations§
impl !Freeze for File
impl !RefUnwindSafe for File
impl Send for File
impl Sync for File
impl Unpin for File
impl UnwindSafe for File
Blanket Implementations§
Source§impl<R> AsyncReadExt for R
impl<R> AsyncReadExt for R
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