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macro_rules! file_ext {
($file:ty, $file_name:literal) => {
use std::io::Result;
#[doc = concat!("Extension trait for `", $file_name, "` which provides allocation and locking methods.")]
///
/// ## Notes on File Locks
///
/// This library provides whole-file locks in both shared (read) and exclusive
/// (read-write) varieties.
///
/// File locks are a cross-platform hazard since the file lock APIs exposed by
/// operating system kernels vary in subtle and not-so-subtle ways.
///
/// The API exposed by this library can be safely used across platforms as long
/// as the following rules are followed:
///
/// * Multiple locks should not be created on an individual `File` instance
/// concurrently.
/// * Duplicated files should not be locked without great care.
/// * Files to be locked should be opened with at least read or write
/// permissions.
/// * File locks may only be relied upon to be advisory.
///
/// File locks are released automatically when the file handle is closed (for
/// example when the owning `File` is dropped), so calling [`FileExt::unlock`]
/// explicitly is optional.
///
/// File locks are implemented with
/// [`flock(2)`](http://man7.org/linux/man-pages/man2/flock.2.html) on Unix and
/// [`LockFileEx`](https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-lockfileex)
/// on Windows.
pub trait FileExt {
/// Returns the amount of physical space allocated for a file.
fn allocated_size(&self) -> Result<u64>;
/// Ensures that at least `len` bytes of disk space are allocated for the
/// file. After a successful call to `allocate`, subsequent writes to the
/// file within the specified length are guaranteed not to fail because of
/// lack of disk space.
///
/// On most platforms the file's logical size is also extended to `len`
/// bytes. On Windows, if the file's existing cluster-aligned allocation
/// already covers `len`, the logical size is left unchanged to work around
/// buffered-I/O quirks observed when the end-of-file pointer is moved
/// inside an already-allocated cluster.
fn allocate(&self, len: u64) -> Result<()>;
/// Acquires a shared lock on the file, blocking until the lock can be
/// acquired.
fn lock_shared(&self) -> Result<()>;
/// Acquires an exclusive lock on the file, blocking until the lock can be
/// acquired.
///
/// This is the blocking counterpart of [`FileExt::try_lock`]. It mirrors
/// [`std::fs::File::lock`].
fn lock(&self) -> Result<()>;
/// Attempts to acquire a shared lock on the file, without blocking.
///
/// Returns `Ok(())` if the lock was acquired, or
/// `Err(`[`TryLockError::WouldBlock`](crate::TryLockError::WouldBlock)`)`
/// if the file is currently locked. Mirrors
/// [`std::fs::File::try_lock_shared`].
fn try_lock_shared(&self) -> std::result::Result<(), crate::TryLockError>;
/// Attempts to acquire an exclusive lock on the file, without blocking.
///
/// Returns `Ok(())` if the lock was acquired, or
/// `Err(`[`TryLockError::WouldBlock`](crate::TryLockError::WouldBlock)`)`
/// if the file is currently locked. Mirrors [`std::fs::File::try_lock`].
fn try_lock(&self) -> std::result::Result<(), crate::TryLockError>;
/// Releases any lock held on the file. The lock is also released
/// automatically when the file handle is closed.
fn unlock(&self) -> Result<()>;
}
impl FileExt for $file {
fn allocated_size(&self) -> Result<u64> {
sys::allocated_size(self)
}
fn allocate(&self, len: u64) -> Result<()> {
sys::allocate(self, len)
}
fn lock_shared(&self) -> Result<()> {
sys::lock_shared(self)
}
fn lock(&self) -> Result<()> {
sys::lock(self)
}
fn try_lock_shared(&self) -> std::result::Result<(), crate::TryLockError> {
sys::try_lock_shared(self)
}
fn try_lock(&self) -> std::result::Result<(), crate::TryLockError> {
sys::try_lock(self)
}
fn unlock(&self) -> Result<()> {
sys::unlock(self)
}
}
}
}
macro_rules! test_mod {
($($use_stmt:item)*) => {
#[cfg(test)]
mod test {
extern crate tempfile;
use super::*;
use crate::{allocation_granularity, statvfs, FsStats, TryLockError};
$(
$use_stmt
)*
/// Tests shared file lock operations.
#[test]
fn lock_shared() {
let tempdir = tempfile::TempDir::with_prefix("fs4").unwrap();
let path = tempdir.path().join("fs4");
let file1 = fs::OpenOptions::new()
.read(true)
.write(true)
.create(true)
.truncate(true)
.open(&path)
.unwrap();
let file2 = fs::OpenOptions::new()
.read(true)
.write(true)
.create(true)
.truncate(true)
.open(&path)
.unwrap();
let file3 = fs::OpenOptions::new()
.read(true)
.write(true)
.create(true)
.truncate(true)
.open(&path)
.unwrap();
// Concurrent shared access is OK, but not shared and exclusive.
FileExt::lock_shared(&file1).unwrap();
FileExt::lock_shared(&file2).unwrap();
assert!(matches!(
FileExt::try_lock(&file3),
Err(TryLockError::WouldBlock),
));
FileExt::unlock(&file1).unwrap();
assert!(matches!(
FileExt::try_lock(&file3),
Err(TryLockError::WouldBlock),
));
// Once all shared file locks are dropped, an exclusive lock may be created;
FileExt::unlock(&file2).unwrap();
FileExt::lock(&file3).unwrap();
}
/// Tests exclusive file lock operations.
#[test]
fn lock_exclusive() {
let tempdir = tempfile::TempDir::with_prefix("fs4").unwrap();
let path = tempdir.path().join("fs4");
let file1 = fs::OpenOptions::new()
.read(true)
.write(true)
.create(true)
.truncate(true)
.open(&path)
.unwrap();
let file2 = fs::OpenOptions::new()
.read(true)
.write(true)
.create(true)
.truncate(true)
.open(&path)
.unwrap();
// No other access is possible once an exclusive lock is created.
FileExt::lock(&file1).unwrap();
assert!(matches!(
FileExt::try_lock(&file2),
Err(TryLockError::WouldBlock),
));
assert!(matches!(
FileExt::try_lock_shared(&file2),
Err(TryLockError::WouldBlock),
));
// Once the exclusive lock is dropped, the second file is able to create a lock.
FileExt::unlock(&file1).unwrap();
FileExt::lock(&file2).unwrap();
}
/// Tests that a lock is released after the file that owns it is dropped.
#[test]
fn lock_cleanup() {
let tempdir = tempfile::TempDir::with_prefix("fs4").unwrap();
let path = tempdir.path().join("fs4");
let file1 = fs::OpenOptions::new()
.read(true)
.write(true)
.create(true)
.truncate(true)
.open(&path)
.unwrap();
let file2 = fs::OpenOptions::new()
.read(true)
.write(true)
.create(true)
.truncate(true)
.open(&path)
.unwrap();
FileExt::lock(&file1).unwrap();
assert!(matches!(
FileExt::try_lock_shared(&file2),
Err(TryLockError::WouldBlock),
));
// Drop file1; the lock should be released.
drop(file1);
FileExt::lock_shared(&file2).unwrap();
}
/// Tests file allocation.
#[test]
fn allocate() {
let tempdir = tempfile::TempDir::with_prefix("fs4").unwrap();
let path = tempdir.path().join("fs4");
let file = fs::OpenOptions::new()
.write(true)
.create(true)
.truncate(true)
.open(&path)
.unwrap();
let blksize = allocation_granularity(&path).unwrap();
// New files are created with no allocated size.
assert_eq!(0, FileExt::allocated_size(&file).unwrap());
assert_eq!(0, file.metadata().unwrap().len());
// Allocate space for the file, checking that the allocated size steps
// up by block size, and the file length matches the allocated size.
FileExt::allocate(&file, 2 * blksize - 1).unwrap();
assert_eq!(2 * blksize, FileExt::allocated_size(&file).unwrap());
assert_eq!(2 * blksize - 1, file.metadata().unwrap().len());
// Truncate the file, checking that the allocated size steps down by
// block size.
file.set_len(blksize + 1).unwrap();
assert_eq!(2 * blksize, FileExt::allocated_size(&file).unwrap());
assert_eq!(blksize + 1, file.metadata().unwrap().len());
}
/// Regression for issue #13: on Windows, re-`allocate`-ing inside
/// an already-allocated cluster must not move the EOF pointer
/// (the old behaviour called `set_len`, which triggered Windows
/// buffered-I/O quirks). The trait doc explicitly carves this
/// behaviour out from the general "file size is at least `len`"
/// contract, so this test asserts the strict invariant on
/// Windows and a loose one on Unix.
#[test]
fn allocate_preserves_eof_within_cluster() {
let tempdir = tempfile::TempDir::with_prefix("fs4").unwrap();
let path = tempdir.path().join("fs4");
let file = fs::OpenOptions::new()
.write(true)
.create(true)
.truncate(true)
.open(&path)
.unwrap();
let blksize = allocation_granularity(&path).unwrap();
// Reserve cluster-aligned space but leave EOF below the
// cluster boundary — the precondition reported in #13.
FileExt::allocate(&file, 2 * blksize - 1).unwrap();
assert_eq!(2 * blksize - 1, file.metadata().unwrap().len());
// Request `allocate` up to the cluster boundary. Before
// the fix, Windows would `set_len(2*blksize)`; after, it
// short-circuits since `allocated_size >= len`.
FileExt::allocate(&file, 2 * blksize).unwrap();
#[cfg(windows)]
assert_eq!(
2 * blksize - 1,
file.metadata().unwrap().len(),
"Windows allocate must not extend EOF inside an already-allocated cluster (#13)",
);
#[cfg(unix)]
assert!(file.metadata().unwrap().len() >= 2 * blksize - 1);
}
/// Re-allocating the same length must not fail. Regression for issue #15.
#[test]
fn allocate_idempotent() {
let tempdir = tempfile::TempDir::with_prefix("fs4").unwrap();
let path = tempdir.path().join("fs4");
let file = fs::OpenOptions::new()
.write(true)
.create(true)
.truncate(true)
.open(&path)
.unwrap();
let blksize = allocation_granularity(&path).unwrap();
FileExt::allocate(&file, 2 * blksize).unwrap();
FileExt::allocate(&file, 2 * blksize).unwrap();
FileExt::allocate(&file, blksize).unwrap();
assert!(file.metadata().unwrap().len() >= 2 * blksize);
}
/// Checks filesystem space methods.
///
/// Does not assert `available_space <= free_space`: on
/// macOS APFS the kernel reports `f_bavail > f_bfree`
/// because purgeable space (snapshots, cached data) is
/// counted as available but not as free, so the usual
/// POSIX invariant does not hold.
#[test]
fn filesystem_space() {
let tempdir = tempfile::TempDir::with_prefix("fs4").unwrap();
let FsStats {
free_space,
available_space,
total_space,
..
} = statvfs(tempdir.path()).unwrap();
assert!(total_space >= free_space);
assert!(total_space >= available_space);
}
}
};
}
cfg_sync! {
pub(crate) mod std_impl;
}
cfg_fs_err2! {
pub(crate) mod fs_err2_impl;
}
cfg_fs_err3! {
pub(crate) mod fs_err3_impl;
}