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|
//! The files this node reads and writes for itself, and how much it did (`/admin/stats`,
//! `disk`): the state file (`swarm::state_file`) and a backup to recover from
//! (`swarm::bootstrap`). Not the Mycelium daemon's files, configuration or logs.
//!
//! Writes replace a file atomically: a temporary file next to it, flushed to disk, then
//! renamed over it, so a crash leaves the old content or the new one.
use std::io::Write;
use std::path::{Path, PathBuf};
use std::sync::{Mutex, MutexGuard};
/// What a file is, for the counts.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub(crate) enum FileKind {
State,
Backup,
}
impl FileKind {
pub(crate) const ALL: [FileKind; 2] = [FileKind::State, FileKind::Backup];
pub(crate) fn as_str(self) -> &'static str {
match self {
FileKind::State => "state",
FileKind::Backup => "backup",
}
}
fn index(self) -> usize {
self as usize
}
}
/// Counts for one kind of file, since the node started.
#[derive(Clone, Copy, Debug, Default)]
pub(crate) struct Counts {
pub(crate) reads: u64,
pub(crate) read_bytes: u64,
pub(crate) writes: u64,
pub(crate) written_bytes: u64,
/// Reads or writes that failed (a missing file read is no failure).
pub(crate) errors: u64,
}
/// Reads and writes this node's files, counting per kind.
#[derive(Default)]
pub(crate) struct Files {
// A std mutex: every access is short and never spans an await.
counts: Mutex<[Counts; FileKind::ALL.len()]>,
}
impl Files {
fn lock(&self) -> MutexGuard<'_, [Counts; FileKind::ALL.len()]> {
self.counts
.lock()
.unwrap_or_else(|poisoned| poisoned.into_inner())
}
fn count(&self, kind: FileKind, f: impl FnOnce(&mut Counts)) {
f(&mut self.lock()[kind.index()]);
}
/// The file's content; None if it doesn't exist.
pub(crate) fn read(&self, kind: FileKind, path: &Path) -> std::io::Result<Option<Vec<u8>>> {
match std::fs::read(path) {
Ok(bytes) => {
self.count(kind, |counts| {
counts.reads += 1;
counts.read_bytes += bytes.len() as u64;
});
Ok(Some(bytes))
}
Err(error) if error.kind() == std::io::ErrorKind::NotFound => Ok(None),
Err(error) => {
self.count(kind, |counts| counts.errors += 1);
Err(error)
}
}
}
/// Replaces the file's content atomically (see the module docs).
pub(crate) fn write_atomic(
&self,
kind: FileKind,
path: &Path,
bytes: &[u8],
) -> std::io::Result<()> {
let result = write_atomic(path, bytes);
self.count(kind, |counts| match &result {
Ok(()) => {
counts.writes += 1;
counts.written_bytes += bytes.len() as u64;
}
Err(_) => counts.errors += 1,
});
result
}
/// Moves an unusable file aside (`<path><suffix>`), returning where to.
pub(crate) fn move_aside(&self, path: &Path, suffix: &str) -> std::io::Result<PathBuf> {
let aside = with_suffix(path, suffix);
std::fs::rename(path, &aside)?;
Ok(aside)
}
/// The counts per kind.
pub(crate) fn counts(&self) -> Vec<(FileKind, Counts)> {
let counts = *self.lock();
FileKind::ALL
.into_iter()
.map(|kind| (kind, counts[kind.index()]))
.collect()
}
}
fn write_atomic(path: &Path, bytes: &[u8]) -> std::io::Result<()> {
let temporary = with_suffix(path, ".tmp");
{
let mut file = std::fs::File::create(&temporary)?;
file.write_all(bytes)?;
file.sync_all()?;
}
std::fs::rename(&temporary, path)?;
sync_parent(path);
Ok(())
}
/// Makes a rename in `path`'s directory durable (best effort: not every platform syncs
/// directories).
fn sync_parent(path: &Path) {
if let Some(dir) = path.parent().filter(|dir| !dir.as_os_str().is_empty()) {
if let Ok(dir) = std::fs::File::open(dir) {
let _ = dir.sync_all();
}
}
}
fn with_suffix(path: &Path, suffix: &str) -> PathBuf {
let mut name = path.as_os_str().to_owned();
name.push(suffix);
PathBuf::from(name)
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn writes_reads_and_counts() {
let dir = std::env::temp_dir().join(format!("continuum-files-{}", std::process::id()));
std::fs::create_dir_all(&dir).unwrap();
let path = dir.join("state.json");
let files = Files::default();
assert_eq!(files.read(FileKind::State, &path).unwrap(), None);
files.write_atomic(FileKind::State, &path, b"one").unwrap();
files
.write_atomic(FileKind::State, &path, b"three")
.unwrap();
assert_eq!(
files.read(FileKind::State, &path).unwrap().as_deref(),
Some(&b"three"[..])
);
assert!(!with_suffix(&path, ".tmp").exists());
let (kind, state) = files.counts()[0];
assert_eq!(kind, FileKind::State);
assert_eq!((state.writes, state.written_bytes), (2, 8));
assert_eq!((state.reads, state.read_bytes, state.errors), (1, 5, 0));
assert_eq!(files.counts()[1].1.reads, 0);
std::fs::remove_dir_all(&dir).unwrap();
}
}
|
