Struct FileSeq 

pub struct FileSeq { /* private fields */ }

File-backed sequence counter that survives restarts, including power loss.

Each write goes to a sibling temp file that is fsync’d, atomically renamed over the target, and (on Unix) followed by an fsync of the parent directory so the rename itself is durable. This matters because the counter is a fiscal anti-replay guard — a value that silently reverted after a crash would re-issue a sequence number the device already saw (rejected as BadSequenceNumber).

The file’s content is a single decimal integer (UTF-8, optionally followed by whitespace). On open, missing files initialise to 0; corrupted contents are surfaced as io::ErrorKind::InvalidData rather than silently reset.

This is not safe to share between processes. The crate does not take an OS-level file lock. Consumers running multiple processes against the same counter file must coordinate externally.

Implementations

impl FileSeq

pub fn open_or_create(path: impl AsRef<Path>) -> Result<Self>

Open or create a counter file. If the file exists, its contents are parsed as the last- returned value; otherwise the counter starts at zero.

Errors

Surfaces filesystem failures and parsing failures (corrupted file contents).

pub const fn current(&self) -> i64

Most-recently-issued value (without advancing the counter).

Trait Implementations

impl Debug for FileSeq

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

Formats the value using the given formatter.

impl SequenceProvider for FileSeq

fn next(&mut self) -> Result<i64>

Advance and return the next sequence number.