Trait OpenOptions 

pub trait OpenOptions: Sized {
    type File: File;

    // Required methods
    fn new() -> Self;
    fn read(&mut self, read: bool) -> &mut Self;
    fn write(&mut self, write: bool) -> &mut Self;
    fn append(&mut self, append: bool) -> &mut Self;
    fn truncate(&mut self, truncate: bool) -> &mut Self;
    fn create(&mut self, create: bool) -> &mut Self;
    fn create_new(&mut self, create_new: bool) -> &mut Self;
    fn open<'life0, 'async_trait, P>(
        &'life0 self,
        path: P,
    ) -> Pin<Box<dyn Future<Output = Result<Self::File>> + Send + 'async_trait>>
       where P: 'async_trait + AsRef<Path> + Send,
             Self: 'async_trait,
             'life0: 'async_trait;
}

An async abstraction over std::fs::OpenOptions.

A builder for opening files with configurable options.

Files can be opened in read and/or write mode.

The append option opens files in a special writing mode that moves the file cursor to the end of file before every write operation.

It is also possible to truncate the file right after opening, to create a file if it doesn’t exist yet, or to always create a new file with create_new.

Examples

Open a file for reading using the tokio runtime:

use tokio::fs::OpenOptions;

let file = OpenOptions::new()
    .read(true)
    .open("a.txt")
    .await?;

Open a file for reading using the async_std runtime:

use async_std::fs::OpenOptions;

let file = OpenOptions::new()
    .read(true)
    .open("a.txt")
    .await?;

Open a file for both reading and writing, and create it if it doesn’t exist yet using the tokio runtime:

use tokio::fs::OpenOptions;

let file = OpenOptions::new()
    .read(true)
    .write(true)
    .create(true)
    .open("a.txt")
    .await?;

Open a file for both reading and writing, and create it if it doesn’t exist yet using the async_std runtime:

use async_std::fs::OpenOptions;

let file = OpenOptions::new()
    .read(true)
    .write(true)
    .create(true)
    .open("a.txt")
    .await?;

Required Associated Types

type File: File

The file object which gets returned by the open method.

Required Methods

fn new() -> Self

Creates a blank set of options.

All options are initially set to false.

fn read(&mut self, read: bool) -> &mut Self

Configures the option for read mode.

When set to true, this option means the file will be readable after opening.

fn write(&mut self, write: bool) -> &mut Self

Configures the option for write mode.

When set to true, this option means the file will be writable after opening.

If the file already exists, write calls on it will overwrite the previous contents without truncating it.

fn append(&mut self, append: bool) -> &mut Self

Configures the option for append mode.

When set to true, this option means the file will be writable after opening and the file cursor will be moved to the end of file before every write operaiton.

fn truncate(&mut self, truncate: bool) -> &mut Self

Configures the option for truncating the previous file.

When set to true, the file will be truncated to the length of 0 bytes.

The file must be opened in write or append mode for truncation to work.

fn create(&mut self, create: bool) -> &mut Self

Configures the option for creating a new file if it doesn’t exist.

When set to true, this option means a new file will be created if it doesn’t exist.

The file must be opened in write or append mode for file creation to work.

fn create_new(&mut self, create_new: bool) -> &mut Self

Configures the option for creating a new file or failing if it already exists.

When set to true, this option means a new file will be created, or the open operation will fail if the file already exists.

The file must be opened in write or append mode for file creation to work.

fn open<'life0, 'async_trait, P>( &'life0 self, path: P, ) -> Pin<Box<dyn Future<Output = Result<Self::File>> + Send + 'async_trait>>

where P: 'async_trait + AsRef<Path> + Send, Self: 'async_trait, 'life0: 'async_trait,

Opens a file with the configured options.

Errors

An error will be returned in the following situations:

• The file does not exist and neither create nor create_new were set.
• The file’s parent directory does not exist.
• The current process lacks permissions to open the file in the configured mode.
• The file already exists and create_new was set.
• Invalid combination of options was used, like truncate was set but write wasn’t, or none of read, write, and append modes was set.
• An OS-level occurred, like too many files are open or the file name is too long.
• Some other I/O error occurred.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementations on Foreign Types

impl OpenOptions for OpenOptions

Available on crate feature async-std-rt only.

type File = File

fn new() -> Self

fn read(&mut self, read: bool) -> &mut Self

fn write(&mut self, write: bool) -> &mut Self

fn append(&mut self, append: bool) -> &mut Self

fn truncate(&mut self, truncate: bool) -> &mut Self

fn create(&mut self, create: bool) -> &mut Self

fn create_new(&mut self, create_new: bool) -> &mut Self

fn open<'life0, 'async_trait, P>( &'life0 self, path: P, ) -> Pin<Box<dyn Future<Output = Result<Self::File>> + Send + 'async_trait>>

where P: 'async_trait + AsRef<Path> + Send, Self: 'async_trait, 'life0: 'async_trait,

impl OpenOptions for OpenOptions

Available on crate feature tokio-rt only.

type File = TokioCompat<File>

fn new() -> Self

fn read(&mut self, read: bool) -> &mut Self

fn write(&mut self, write: bool) -> &mut Self

fn append(&mut self, append: bool) -> &mut Self

fn truncate(&mut self, truncate: bool) -> &mut Self

fn create(&mut self, create: bool) -> &mut Self

fn create_new(&mut self, create_new: bool) -> &mut Self

fn open<'life0, 'async_trait, P>( &'life0 self, path: P, ) -> Pin<Box<dyn Future<Output = Result<Self::File>> + Send + 'async_trait>>

where P: 'async_trait + AsRef<Path> + Send, Self: 'async_trait, 'life0: 'async_trait,

Implementors