Crate users

This is a library for getting information on Unix users and groups. It supports getting the system users, and creating your own mock tables.

In Unix, each user has an individual user ID, and each process has an effective user ID that says which user’s permissions it is using. Furthermore, users can be the members of groups, which also have names and IDs. This functionality is exposed in libc, the C standard library, but as an unsafe Rust interface. This wrapper library provides a safe interface, using User and Group types and functions such as get_user_by_uid instead of low-level pointers and strings. It also offers basic caching functionality.

It does not (yet) offer editing functionality; the values returned are read-only.

Users

The function get_current_uid returns a uid_t value representing the user currently running the program, and the get_user_by_uid function scans the users database and returns a User with the user’s information. This function returns None when there is no user for that ID. The uid_t type is re-exported from the libc crate.

A User value has the following accessors:

• uid: The user’s ID
• name: The user’s name
• primary_group: The ID of this user’s primary group

Here is a complete example that prints out the current user’s name:

use users::{get_user_by_uid, get_current_uid};

let user = get_user_by_uid(get_current_uid()).unwrap();
println!("Hello, {}!", user.name().to_string_lossy());

This code assumes (with unwrap()) that the user hasn’t been deleted after the program has started running. For arbitrary user IDs, this is not a safe assumption: it’s possible to delete a user while it’s running a program, or is the owner of files, or for that user to have never existed. So always check the return values!

There is also a get_current_username function, as it’s such a common operation that it deserves special treatment.

Caching

Despite the above warning, the users and groups database rarely changes. While a short program may only need to get user information once, a long-running one may need to re-query the database many times, and a medium-length one may get away with caching the values to save on redundant system calls.

For this reason, this crate offers a caching interface to the database, which offers the same functionality while holding on to every result, caching the information so it can be re-used.

To introduce a cache, create a new UsersCache. It has functions with the same names as the ones from earlier. For example:

use users::{Users, Groups, UsersCache};

let mut cache = UsersCache::new();
let uid = cache.get_current_uid();
let user = cache.get_user_by_uid(uid).unwrap();
println!("Hello again, {}!", user.name().to_string_lossy());

This cache is only additive: it’s not possible to drop it, or erase selected entries, as when the database may have been modified, it’s best to start entirely afresh. So to accomplish this, just start using a new UsersCache.

Groups

Finally, it’s possible to get groups in a similar manner. A Group has the following accessors:

• gid: The group’s ID
• name: The group’s name

And again, a complete example:

use users::{Users, Groups, UsersCache};

let mut cache = UsersCache::new();
let group = cache.get_group_by_name("admin").expect("No such group 'admin'!");
println!("The '{}' group has the ID {}", group.name().to_string_lossy(), group.gid());

Caveats

You should be prepared for the users and groups tables to be completely broken: IDs shouldn’t be assumed to map to actual users and groups, and usernames and group names aren’t guaranteed to map either!

Use the mocking module to create custom tables to test your code for these edge cases.

Re-exports

pub use cache::UsersCache;

Modules

cache	A cache for users and groups provided by the OS.
mock	Mockable users and groups.
os	OS-specific extensions to users and groups.
switch	Functions for switching the running process’s user or group.

Structs

Group	Information about a particular group.
User	Information about a particular user.

Traits

Groups	Trait for producers of groups.
Users	Trait for producers of users.

Functions

all_users⚠	Creates a new iterator over every user present on the system.
get_current_gid	Returns the group ID for the user running the process.
get_current_groupname	Returns the groupname of the user running the process.
get_current_uid	Returns the user ID for the user running the process.
get_current_username	Returns the username of the user running the process.
get_effective_gid	Returns the group ID for the effective user running the process.
get_effective_groupname	Returns the groupname of the effective user running the process.
get_effective_uid	Returns the user ID for the effective user running the process.
get_effective_username	Returns the username of the effective user running the process.
get_group_by_gid	Searches for a Group with the given ID in the system’s group database. Returns it if one is found, otherwise returns None.
get_group_by_name	Searches for a Group with the given group name in the system’s group database. Returns it if one is found, otherwise returns None.
get_user_by_name	Searches for a User with the given username in the system’s user database. Returns it if one is found, otherwise returns None.
get_user_by_uid	Searches for a User with the given ID in the system’s user database. Returns it if one is found, otherwise returns None.
get_user_groups	Returns groups for a provided user name and primary group id.
group_access_list	Returns the group access list for the current process.

Type Definitions

gid_t
uid_t