Expand description
More ways to rename files.
Overview
The Rust standard library offers std::fs::rename
for renaming files.
Sometimes, that’s not enough. Consider the example of renaming a file but
aborting the operation if something already exists at the destination path.
That can be achieved using the Rust standard library but ensuring that the
operation is atomic requires platform-specific APIs. Without using
platform-specific APIs, a TOCTTOU bug can be introduced. This library aims
to provide a cross-platform interface to these APIs.
Examples
Renaming a file without the possibility of accidentally overwriting anything
can be done using rename_exclusive
. It should be noted that this feature
is not supported by all combinations of operating system and file system.
rename_exclusive
will fail if it can’t be done atomically.
use std::io::Result;
fn main() -> Result<()> {
renamore::rename_exclusive("old.txt", "new.txt")
}
Alternatively, rename_exclusive_fallback
can be used. This will try to
perform the operation atomically, and use a non-atomic fallback if that’s
not supported. The return value will indicate what happened.
use std::io::Result;
fn main() -> Result<()> {
if renamore::rename_exclusive_fallback("old.txt", "new.txt")? {
// `new.txt` was definitely not overwritten.
println!("The operation was atomic");
} else {
// `new.txt` was probably not overwritten.
println!("The operation was not atomic");
}
Ok(())
}
Platform-specific behaviour
On Linux, the renameat2
syscall is used. A wrapper around this syscall is
provided by glibc since version 2.28 but not musl (yet?). The existence of
the wrapper is checked at build time and a wrapper is provided if one isn’t
found. In case something goes wrong, there are two features that can be used
to bypass this mechanism.
always-supported
. Assume thatrenameat2
exists.always-fallback
. Assume thatrenameat2
doesn’t exist.
Hopefully using these features shouldn’t be necessary. If they do become necessary, then there might be a bug.
Functions
- Rename a file without overwriting the destination path if it exists.
- Rename a file without overwriting the destination path if it exists, using a non-atomic fallback if necessary.
- Determine whether an atomic
rename_exclusive
is supported.