xenomorph1096/faccess

Cross-platform file access checks in Rust

faccess

Basic cross-platform file accessibility checks for Rust.

Synopsis

pub trait PathExt {
    fn access(&self, mode: AccessMode) -> std::io::Result<()>;
    fn readable(&self) -> bool;
    fn writable(&self) -> bool;
    fn executable(&self) -> bool;
}

impl PathExt for std::path::Path;

Description

faccess provides an extension trait for std::path::Path which adds an access method for checking the accessibility of a path for the given access permissions — a bitwise-inclusive OR of one or more AccessMode flags (EXISTS, READ, WRITE, EXECUTE).

It also provides convenience methods readable, writable, and executable if only a single permission needs to be checked in a simple boolean fashion.

Example

use std::path::Path;
use faccess::{AccessMode, PathExt};

let path = Path::new("/bin/ls");

assert!(path.access(AccessMode::READ | AccessMode::EXECUTE).is_ok());
assert!(path.readable());
assert!(!path.writable());
assert!(path.executable());

Platform-specific Behaviour

On Unix platforms, access directly maps to faccessat(2), with the AT_EACCESS flag used where available to test against the effective user and group ID's.

On Windows, a complex custom implementation is used to approximate these semantics in a best-effort fashion, using a mixture of file extension checks, simply attempting to open a file, GetNamedSecurityInfoW, and AccessCheck, depending on the permissions being checked. This is similar to implementations found in other languages.

On other platforms it simply proxies to exists() and readonly() as appropriate.

Caveats

There is a history of time-of-check to time-of-use (TOCTOU) bugs with this class of function, particularly with set-user-ID programs relying on them to validate effective user/group permissions prior to accessing files on behalf of other users. They should not be relied upon in a security context.