Struct OpenOptions

pub struct OpenOptions(/* private fields */);

Options and flags which can be used to configure how a file is opened.

This builder exposes the ability to configure how a File is opened and what operations are permitted on the open file. The File::open and File::create methods are aliases for commonly used options using this builder.

Generally speaking, when using OpenOptions, you’ll first call OpenOptions::new, then chain calls to methods to set each option, then call OpenOptions::open, passing the path of the file you’re trying to open. This will give you a std::io::Result with a File inside that you can further operate on.

Examples

Opening a file to read:

use compio_fs::OpenOptions;

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

Opening a file for both reading and writing, as well as creating it if it doesn’t exist:

use compio_fs::OpenOptions;

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

Implementations

impl OpenOptions

pub fn new() -> Self

Creates a blank new set of options ready for configuration.

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

Sets the option for read access.

This option, when true, will indicate that the file should be read-able if opened.

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

Sets the option for write access.

This option, when true, will indicate that the file should be write-able if opened.

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

Sets the option for truncating a previous file.

If a file is successfully opened with this option set it will truncate the file to 0 length if it already exists.

The file must be opened with write access for truncate to work.

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

Sets the option to create a new file, or open it if it already exists.

In order for the file to be created, OpenOptions::write access must be used.

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

Sets the option to create a new file, failing if it already exists.

No file is allowed to exist at the target location, also no (dangling) symlink. In 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).

If .create_new(true) is set, .create() and .truncate() are ignored.

The file must be opened with write or append access in order to create a new file.

pub async fn open(&self, path: impl AsRef<Path>) -> Result<File>

Opens a file at path with the options specified by self.

impl OpenOptions

pub fn custom_flags(&mut self, flags: u32) -> &mut Self

Available on Windows only.

Combines it with attributes and security_qos_flags to set the dwFlagsAndAttributes for CreateFile.

Custom flags can only set flags, not remove flags set by Rust’s options. This option overwrites any previously set custom flags.

pub fn access_mode(&mut self, access_mode: u32) -> &mut Self

Available on Windows only.

Overrides the dwDesiredAccess argument to the call to CreateFile with the specified value.

This will override the read, write, and append flags on the OpenOptions structure. This method provides fine-grained control over the permissions to read, write and append data, attributes (like hidden and system), and extended attributes.

pub fn share_mode(&mut self, share_mode: u32) -> &mut Self

Available on Windows only.

Overrides the dwShareMode argument to the call to CreateFile with the specified value.

By default share_mode is set to FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE. This allows other processes to read, write, and delete/rename the same file while it is open. Removing any of the flags will prevent other processes from performing the corresponding operation until the file handle is closed.

pub fn attributes(&mut self, attrs: u32) -> &mut Self

Available on Windows only.

Combines it with custom_flags and security_qos_flags to set the dwFlagsAndAttributes for CreateFile.

If a new file is created because it does not yet exist and .create(true) or .create_new(true) are specified, the new file is given the attributes declared with .attributes().

If an existing file is opened with .create(true).truncate(true), its existing attributes are preserved and combined with the ones declared with .attributes().

In all other cases the attributes get ignored.

pub fn security_qos_flags(&mut self, flags: u32) -> &mut Self

Available on Windows only.

Combines it with custom_flags and attributes to set the dwFlagsAndAttributes for CreateFile.

By default security_qos_flags is not set. It should be specified when opening a named pipe, to control to which degree a server process can act on behalf of a client process (security impersonation level).

When security_qos_flags is not set, a malicious program can gain the elevated privileges of a privileged Rust process when it allows opening user-specified paths, by tricking it into opening a named pipe. So arguably security_qos_flags should also be set when opening arbitrary paths. However the bits can then conflict with other flags, specifically FILE_FLAG_OPEN_NO_RECALL.

For information about possible values, see Impersonation Levels on the Windows Dev Center site. The SECURITY_SQOS_PRESENT flag is set automatically when using this method.

Trait Implementations

impl Clone for OpenOptions

fn clone(&self) -> OpenOptions

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for OpenOptions

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

Formats the value using the given formatter.