Struct FileStorage 

pub struct FileStorage { /* private fields */ }

A Storage backed by one file per key, under the OS’s per-app data directory (data_dir).

The folder holds <key>.ron, the value, and <key>.ron.bak, the value before it (ticket 3045). A <key>.ron.tmp is there only between a crash and the next write, which removes it. A sync of the folder (Steam Auto-Cloud) must carry the .bak files with the .ron files: a key whose .ron is gone reads its good .bak, so a save deleted on one machine would come back from its backup on another.

A write puts the new value in <key>.ron.tmp and flushes it to the disk, copies the old <key>.ron (when it is a good copy: not empty, not all zero bytes, UTF-8) to <key>.ron.bak and flushes that, renames the .tmp onto the .ron, and syncs the folder. A read of a .ron that is missing, empty, all zero bytes or not UTF-8 beside a good .bak reads the .bak, and logs a warning. What that promises:

• a crash of the game, on every OS: the key reads the old value or the new one;
• a power cut or a crash of the system, on Linux (the Steam Deck) and macOS: the key reads the old value or the new one, and a write that returned Ok reads the new one, since the file and the folder are flushed before it returns (F_FULLFSYNC on macOS). A file system that can’t sync a folder (it answers Unsupported) keeps the rename only as well as it journals it;
• a power cut on Windows: std opens no folder for a sync, so the folder isn’t flushed. NTFS journals the rename, so the key reads the old value or the new one, never damage; a write that returned in the moments before the cut may read the old one.

A key written "" or only \0 characters keeps no backup, so it reads back as written and not as damage.

Implementations

impl FileStorage

pub fn new(name: &str) -> Result<Self, StorageError>

Locates (but does not create) the data directory of the game whose storage is called name (data_dir). Fails only if the OS has no usable home directory.

Trait Implementations

impl Debug for FileStorage

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

Formats the value using the given formatter.

impl Storage for FileStorage

fn read(&self, key: &str) -> Result<Option<String>, StorageError>

The value stored at key, or None if nothing has been written there (or it was deleted).

fn write(&mut self, key: &str, value: &str) -> Result<(), StorageError>

Stores value at key, replacing whatever was there.

fn delete(&mut self, key: &str) -> Result<(), StorageError>

Removes key. Not an error if it didn’t exist.

fn list(&self) -> Result<Vec<String>, StorageError>

Every key currently stored, in no particular order.