File Permissions

std::fs::Permissions represents the access-control permissions of a file or directory. To stay portable across all operating systems, the core Permissions struct exposes a universal .readonly() / .set_readonly(bool) interface, while full POSIX 9-bit octal mode permissions (rwxr-xr-x, 0o755, 0o600) are unlocked through std::os::unix::fs::PermissionsExt.

Reading and Modifying Permissions

Note that modifying a Permissions value in memory (perms.set_readonly(true) or perms.set_mode(0o600)) does not change the file on disk until you apply it using fs::set_permissions(path, perms) or file.set_permissions(perms):

Two-Step Permission Update Flow:

  1. Obtain or construct `Permissions`:
       `let mut perms = file.metadata()?.permissions();`
       (or on Unix: `let perms = Permissions::from_mode(0o600);`)

  2. Mutate & apply to the filesystem:
       `perms.set_readonly(true);`
       `file.set_permissions(perms)?;`  (or `fs::set_permissions(path, perms)?;`)

Cross-Platform and Unix Octal Permission Example

use std::fs::{self, File};
use std::io;

fn main() -> io::Result<()> {
    let path = std::env::temp_dir().join("rust_ch50_perms_demo.key");
    let file = File::create(&path)?;

    // 1. Cross-platform `.readonly()` and `.set_readonly(true)`:
    let mut perms = file.metadata()?.permissions();
    println!("initial readonly: {}", perms.readonly());

    perms.set_readonly(true);
    file.set_permissions(perms)?;
    println!(
        "after set_readonly(true): {}",
        fs::metadata(&path)?.permissions().readonly()
    );

    // 2. On Unix, set exact octal mode `0o600` (owner read/write only):
    #[cfg(unix)]
    {
        use std::os::unix::fs::PermissionsExt;
        file.set_permissions(fs::Permissions::from_mode(0o600))?;
        let mode = file.metadata()?.permissions().mode() & 0o777;
        println!("unix octal mode: {:04o}", mode);
    }

    // Ensure writable on Windows before removing:
    #[cfg(windows)]
    {
        let mut p = file.metadata()?.permissions();
        p.set_readonly(false);
        file.set_permissions(p)?;
    }

    drop(file);
    fs::remove_file(&path)?;
    Ok(())
}

initial readonly: false
after set_readonly(true): true
unix octal mode: 0600