Struct OpenOptions

pub struct OpenOptions<Permissions> { /* 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.

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

Implementations

impl<Permissions: Default> OpenOptions<Permissions>

pub fn new() -> Self

Creates a blank new set of options ready for configuration.

All options are initially set to false.

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.

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

pub fn append(&mut self, append: bool) -> &mut 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(0)), and restore it before the next read.

Note

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

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 for creating a new file.

This option indicates whether a new file will be created if the file does not yet already exist.

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

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

Sets the option to always create a new file.

This option indicates whether a new file will be created. No file is allowed to exist at the target location, also no (dangling) symlink.

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 fn mode(&mut self, mode: Permissions) -> &mut Self

Sets the mode bits that a new file will be created with.

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

Pass custom flags to the flags argument of open.

Trait Implementations

impl<Permissions: Clone> Clone for OpenOptions<Permissions>

fn clone(&self) -> OpenOptions<Permissions>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<Permissions: Debug> Debug for OpenOptions<Permissions>

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

Formats the value using the given formatter.

impl<Permissions: Default> Default for OpenOptions<Permissions>

fn default() -> OpenOptions<Permissions>

Returns the “default value” for a type.

impl<Permissions: Hash> Hash for OpenOptions<Permissions>

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl<Permissions: PartialEq> PartialEq for OpenOptions<Permissions>

fn eq(&self, other: &OpenOptions<Permissions>) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<Permissions: Eq> Eq for OpenOptions<Permissions>

impl<Permissions> StructuralPartialEq for OpenOptions<Permissions>