Struct tokio::fs::File [−][src]
pub struct File { /* fields omitted */ }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
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