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/*!
# Write Atomic
[![docs.rs](https://img.shields.io/docsrs/write_atomic.svg?style=flat-square&label=docs.rs)](https://docs.rs/write_atomic/)
[![changelog](https://img.shields.io/crates/v/write_atomic.svg?style=flat-square&label=changelog&color=9b59b6)](https://github.com/Blobfolio/write_atomic/blob/master/CHANGELOG.md)<br>
[![crates.io](https://img.shields.io/crates/v/write_atomic.svg?style=flat-square&label=crates.io)](https://crates.io/crates/write_atomic)
[![ci](https://img.shields.io/github/actions/workflow/status/Blobfolio/write_atomic/ci.yaml?style=flat-square&label=ci)](https://github.com/Blobfolio/write_atomic/actions)
[![deps.rs](https://deps.rs/repo/github/blobfolio/write_atomic/status.svg?style=flat-square&label=deps.rs)](https://deps.rs/repo/github/blobfolio/write_atomic)<br>
[![license](https://img.shields.io/badge/license-wtfpl-ff1493?style=flat-square)](https://en.wikipedia.org/wiki/WTFPL)
[![contributions welcome](https://img.shields.io/badge/PRs-welcome-brightgreen.svg?style=flat-square&label=contributions)](https://github.com/Blobfolio/write_atomic/issues)
Write Atomic was originally a stripped-down remake of [`tempfile-fast`](https://crates.io/crates/tempfile-fast), but with the `3.4.0` release of [`tempfile`](https://crates.io/crates/tempfile), it has largely been mooted.
(`tempfile` now supports Linux optimizations like `O_TMPFILE` natively.)
That said, one might still enjoy the ergonomic single-shot nature of Write Atomic's [`write_file`] and [`copy_file`] methods, as well as their permission/ownership-syncing behaviors, and so it lives on!
## Examples
```no_run
// One line is all it takes:
write_atomic::write_file("/path/to/my-file.txt", b"Some data!").unwrap();
```
*/
#![forbid(unsafe_code)]
#![warn(
clippy::filetype_is_file,
clippy::integer_division,
clippy::needless_borrow,
clippy::nursery,
clippy::pedantic,
clippy::perf,
clippy::suboptimal_flops,
clippy::unneeded_field_pattern,
macro_use_extern_crate,
missing_copy_implementations,
missing_debug_implementations,
missing_docs,
non_ascii_idents,
trivial_casts,
trivial_numeric_casts,
unreachable_pub,
unused_crate_dependencies,
unused_extern_crates,
unused_import_braces,
)]
use std::{
fs::File,
io::{
Error,
ErrorKind,
Result,
Write,
},
path::{
Path,
PathBuf,
},
};
use tempfile::NamedTempFile;
/// # Atomic File Copy!
///
/// This will copy the contents of one file to another, atomically.
///
/// Under the hood, this uses [`std::fs::copy`] to copy the file to a temporary
/// location. It then syncs the file permissions — and on Unix, the owner/group
/// — before moving it to the final destination.
///
/// See [`write_file`] for more details about atomicity.
///
/// ## Errors
///
/// This will bubble up any filesystem-related errors encountered along the
/// way.
pub fn copy_file<P>(src: P, dst: P) -> Result<()>
where P: AsRef<Path> {
let src = src.as_ref();
let (dst, parent) = check_path(dst)?;
let file = tempfile::Builder::new().tempfile_in(parent)?;
std::fs::copy(src, &file)?;
let touched = touch_if(&dst)?;
if let Err(e) = write_finish(file, &dst) {
// If we created the file earlier, try to remove it.
if touched { let _res = std::fs::remove_file(dst); }
Err(e)
}
else { Ok(()) }
}
/// # Atomic File Write!
///
/// This will write bytes atomically to the specified path, maintaining
/// permissions and ownership if it already exists, or creating it anew using
/// the same default permissions and ownership [`std::fs::File::create`] would.
///
/// ## Examples
///
/// ```no_run
/// // It's just one line:
/// write_atomic::write_file("/path/to/my/file.txt", b"Some data!")
/// .unwrap();
/// ```
///
/// ## Errors
///
/// This will bubble up any filesystem-related errors encountered along the
/// way.
pub fn write_file<P>(src: P, data: &[u8]) -> Result<()>
where P: AsRef<Path> {
let (dst, parent) = check_path(src)?;
let mut file = tempfile::Builder::new().tempfile_in(parent)?;
file.write_all(data)?;
file.flush()?;
let touched = touch_if(&dst)?;
if let Err(e) = write_finish(file, &dst) {
// If we created the file earlier, try to remove it.
if touched { let _res = std::fs::remove_file(dst); }
Err(e)
}
else { Ok(()) }
}
/// # Handle Path.
///
/// This checks the path and returns it and its parent, assuming it is valid,
/// or an error if not.
fn check_path<P>(src: P) -> Result<(PathBuf, PathBuf)>
where P: AsRef<Path> {
let src = src.as_ref();
// The path cannot be a directory.
if src.is_dir() {
return Err(Error::new(ErrorKind::InvalidInput, "Path cannot be a directory."));
}
// We don't need to fully canonicalize the path, but if there's no stub, it
// is assumed to be in the "current directory".
let src: PathBuf =
if src.is_absolute() { src.to_path_buf() }
else {
let mut absolute = std::env::current_dir()?;
absolute.push(src);
absolute
};
// Make sure it has a parent.
let parent: PathBuf = src.parent()
.map(Path::to_path_buf)
.ok_or_else(|| Error::new(ErrorKind::NotFound, "Path must have a parent directory."))?;
// Create the directory chain if necessary.
std::fs::create_dir_all(&parent)?;
// We're good to go!
Ok((src, parent))
}
/// # Copy Metadata.
///
/// Make sure we don't lose details like permissions, ownership, etc., when
/// replacing an existing file.
fn copy_metadata(src: &Path, dst: &File) -> Result<()> {
let metadata = match src.metadata() {
Ok(metadata) => metadata,
Err(ref e) if ErrorKind::NotFound == e.kind() => return Ok(()),
Err(e) => return Err(e),
};
dst.set_permissions(metadata.permissions())?;
#[cfg(unix)]
copy_ownership(&metadata, dst)?;
Ok(())
}
#[cfg(unix)]
/// # Copy Ownership.
///
/// Copy the owner/group details from `src` to `dst`.
fn copy_ownership(src: &std::fs::Metadata, dst: &File) -> Result<()> {
use std::os::unix::fs::MetadataExt;
std::os::unix::fs::fchown(dst, Some(src.uid()), Some(src.gid())).map_err(Into::into)
}
/// # Touch If Needed.
///
/// This creates paths that don't already exist to set the same default
/// permissions and ownerships the standard library would.
fn touch_if(src: &Path) -> Result<bool> {
if src.exists() { Ok(false) }
else {
File::create(src)?;
Ok(true)
}
}
/// # Finish Write.
///
/// This attempts to copy the metadata, then persist the tempfile.
fn write_finish(file: NamedTempFile, dst: &Path) -> Result<()> {
copy_metadata(dst, file.as_file())
.and_then(|()| file.persist(dst).map(|_| ()).map_err(|e| e.error))
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_write() {
// Hopefully sandboxes running this test can write to their own
// temporary directory!
let mut path = std::env::temp_dir();
if ! path.is_dir() { return; }
path.push("write-atomic-test.txt");
// Now that we have a path, let's try to write to it!
assert!(write_file(&path, b"This is the first write!").is_ok());
// Make sure the content is written correctly.
assert_eq!(
std::fs::read(&path).expect("Unable to open file."),
b"This is the first write!",
);
// One more time with different content.
assert!(write_file(&path, b"This is the second write!").is_ok());
// Make sure the content is written correctly.
assert_eq!(
std::fs::read(&path).expect("Unable to open file."),
b"This is the second write!",
);
// Test copy!
let path2 = path.parent()
.expect("Missing parent?!")
.join("copy-atomic-test.txt");
assert!(copy_file(&path, &path2).is_ok());
assert_eq!(
std::fs::read(&path2).expect("Unable to open file."),
b"This is the second write!",
);
// Let's clean up after ourselves.
let _res = std::fs::remove_file(path);
let _res = std::fs::remove_file(path2);
}
}