fsutil

Helpers for appending to shared log files without following symlinks, and for reading lines that may be torn.

The fsutil module holds the two small helpers behind the Telamon OS history and event logs (history.jsonl, events.jsonl; see telamon-framework-system). Use them for any append-only line file that several programs share.

Example

use telamon_framework_core::fsutil::{append_line, lossy_lines};
use std::path::Path;

let path = Path::new("/tmp/example.log");
append_line(path, r#"{"event":"x"}"#, 0o644)?;
let lines = lossy_lines(&std::fs::read(path)?);

Items

Name	Signature	Description
`append_line`	`pub fn append_line(path: &Path, line: &str, mode: u32) -> io::Result<()>`	Appends `line` and a newline. Refuses to follow a symlink at the final path component (`O_NOFOLLOW`). Starts with a newline if the file does not end in one (a torn earlier write). Creates the file with `mode` and syncs before returning
`read_capped`	`pub fn read_capped(path: &Path, max: u64) -> io::Result<Vec<u8>>`	Reads a regular file of at most `max` bytes. Opens with `O_NONBLOCK` (a FIFO never blocks), requires a regular file, follows a symlink, and fails with `InvalidData` for a non-file or a larger file
`lock_with_deadline`	`pub fn lock_with_deadline(f: &File, wait: Duration) -> io::Result<()>`	An exclusive `flock` polled with `LOCK_NB` for up to `wait`; `ErrorKind::TimedOut` after that. Released when `f` is dropped
`LOCK_WAIT`	`pub const LOCK_WAIT: Duration`	2 seconds: what the settings, events and history locks wait
`lossy_lines`	`pub fn lossy_lines(bytes: &[u8]) -> Vec<String>`	Splits on `\n` and decodes each line lossily, so one torn multibyte character spoils only its own line. Empty lines are dropped