Struct rarena_allocator::OpenOptions

pub struct OpenOptions { /* private fields */ }

Available on crate feature memmap and non-target_family="wasm" only.

Options for opening a file for memory mapping.

Implementations

impl OpenOptions

pub fn new() -> Self

Creates a blank new set of options ready for configuration.

All options are initially set to false.

Examples

use rarena_allocator::OpenOptions;

let mut options = OpenOptions::new();

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

Sets the option for read access.

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

Examples

use rarena_allocator::OpenOptions;

let opts = OpenOptions::new().read(true);

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

Sets the option for write access.

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

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

Examples

use rarena_allocator::OpenOptions;

let opts = OpenOptions::new().write(true);

pub fn append(self, append: bool) -> Self

Sets the option for the append mode.

This option, when true, means that writes will append to a file instead of overwriting previous contents. Note that setting .write(true).append(true) has the same effect as setting only .append(true).

For most filesystems, the operating system guarantees that all writes are atomic: no writes get mangled because another process writes at the same time.

One maybe obvious note when using append-mode: make sure that all data that belongs together is written to the file in one operation. This can be done by concatenating strings before passing them to write(), or using a buffered writer (with a buffer of adequate size), and calling flush() when the message is complete.

If a file is opened with both read and append access, beware that after opening, and after every write, the position for reading may be set at the end of the file. So, before writing, save the current position (using seek(SeekFrom::Current(opts))), and restore it before the next read.

Note

This function doesn’t create the file if it doesn’t exist. Use the OpenOptions::create method to do so.

Examples

use rarena_allocator::OpenOptions;

let opts = OpenOptions::new().append(true);

pub fn truncate(self, truncate: bool) -> 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 opts length if it already exists.

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

Examples

use rarena_allocator::OpenOptions;

let opts = OpenOptions::new().write(true).truncate(true);

pub fn create(self, size: Option<u32>) -> Self

Sets the option to create a new file, or open it if it already exists. If the file does not exist, it is created and set the lenght of the file to the given size.

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

See also std::fs::write() for a simple function to create a file with some given data.

Examples

use rarena_allocator::OpenOptions;

let opts = OpenOptions::new().write(true).create(Some(1000));

use rarena_allocator::OpenOptions;

let opts = OpenOptions::new().write(true).create(None);

pub fn create_new(self, size: Option<u32>) -> Self

Sets the option to create a new file and set the file length to the given value, 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.

Examples

use rarena_allocator::OpenOptions;

let file = OpenOptions::new()
  .write(true)
  .create_new(Some(1000));

use rarena_allocator::OpenOptions;

let opts = OpenOptions::new()
  .write(true)
  .create_new(None);

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.

impl Default for OpenOptions

fn default() -> Self

Creates a blank new set of options ready for configuration.

All options are initially set to false.

Examples

use rarena_allocator::OpenOptions;

let options = OpenOptions::default();

impl From<OpenOptions> for OpenOptions

fn from(opts: StdOpenOptions) -> Self

Converts to this type from the input type.