Renamore

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 that renameat2 exists.
• always-fallback. Assume that renameat2 doesn't exist.

Hopefully using these features shouldn't be necessary. If they do become necessary, then there might be a bug.

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.