impl Permissions

fn readonly(&self) -> bool

Returns true if these permissions describe a readonly (unwritable) file.

Note

This function does not take Access Control Lists (ACLs), Unix group membership and other nuances into account. Therefore the return value of this function cannot be relied upon to predict whether attempts to read or write the file will actually succeed.

Windows

On Windows this returns FILE_ATTRIBUTE_READONLY. If FILE_ATTRIBUTE_READONLY is set then writes to the file will fail but the user may still have permission to change this flag. If FILE_ATTRIBUTE_READONLY is not set then writes may still fail due to lack of write permission. The behavior of this attribute for directories depends on the Windows version.

Unix (including macOS)

On Unix-based platforms this checks if any of the owner, group or others write permission bits are set. It does not consider anything else, including:

• Whether the current user is in the file's assigned group.
• Permissions granted by ACL.
• That root user can write to files that do not have any write bits set.
• Writable files on a filesystem that is mounted read-only.

The PermissionsExt trait gives direct access to the permission bits but also does not read ACLs.

Examples

use std::fs::File;

fn main() -> std::io::Result<()> {
    let mut f = File::create("foo.txt")?;
    let metadata = f.metadata()?;

    assert_eq!(false, metadata.permissions().readonly());
    Ok(())
}

fn set_readonly(&mut self, readonly: bool)

Modifies the readonly flag for this set of permissions. If the readonly argument is true, using the resulting Permission will update file permissions to forbid writing. Conversely, if it's false, using the resulting Permission will update file permissions to allow writing.

This operation does not modify the files attributes. This only changes the in-memory value of these attributes for this Permissions instance. To modify the files attributes use the set_permissions function which commits these attribute changes to the file.

Note

set_readonly(false) makes the file world-writable on Unix. You can use the PermissionsExt trait on Unix to avoid this issue.

It also does not take Access Control Lists (ACLs) or Unix group membership into account.

Windows

On Windows this sets or clears FILE_ATTRIBUTE_READONLY. If FILE_ATTRIBUTE_READONLY is set then writes to the file will fail but the user may still have permission to change this flag. If FILE_ATTRIBUTE_READONLY is not set then the write may still fail if the user does not have permission to write to the file.

In Windows 7 and earlier this attribute prevents deleting empty directories. It does not prevent modifying the directory contents. On later versions of Windows this attribute is ignored for directories.

Unix (including macOS)

On Unix-based platforms this sets or clears the write access bit for the owner, group and others, equivalent to chmod a+w <file> or chmod a-w <file> respectively. The latter will grant write access to all users! You can use the PermissionsExt trait on Unix to avoid this issue.

Examples

use std::fs::File;

fn main() -> std::io::Result<()> {
    let f = File::create("foo.txt")?;
    let metadata = f.metadata()?;
    let mut permissions = metadata.permissions();

    permissions.set_readonly(true);

    // filesystem doesn't change, only the in memory state of the
    // readonly permission
    assert_eq!(false, metadata.permissions().readonly());

    // just this particular `permissions`.
    assert_eq!(true, permissions.readonly());
    Ok(())
}