fcoreutils 0.22.0

/// users -- print the user names of users currently logged in
///
/// Reads utmpx records and prints a sorted, space-separated list of login names
/// for all USER_PROCESS entries.
use std::ffi::CStr;
#[cfg(target_os = "linux")]
use std::ffi::CString;

use crate::who;

// utmpxname is a glibc extension to set the utmpx database file path.
#[cfg(target_os = "linux")]
unsafe extern "C" {
    fn utmpxname(file: *const libc::c_char) -> libc::c_int;
}

/// Retrieve a sorted list of currently logged-in user names from utmpx.
/// If `file` is Some, reads from that file; otherwise uses the default database
/// with systemd fallback.
///
/// # Safety
/// Uses libc's setutxent/getutxent/endutxent which are not thread-safe.
/// This function must not be called concurrently.
pub fn get_users() -> Vec<String> {
    get_users_from(None)
}

pub fn get_users_from(file: Option<&str>) -> Vec<String> {
    if let Some(_path) = file {
        // Reading from a specific file — use direct utmpx API
        let mut users = Vec::new();
        unsafe {
            #[cfg(target_os = "linux")]
            {
                if let Ok(cpath) = CString::new(_path) {
                    utmpxname(cpath.as_ptr());
                }
            }

            libc::setutxent();
            loop {
                let entry = libc::getutxent();
                if entry.is_null() {
                    break;
                }
                let entry = &*entry;
                if entry.ut_type == libc::USER_PROCESS {
                    let name = CStr::from_ptr(entry.ut_user.as_ptr())
                        .to_string_lossy()
                        .to_string();
                    if !name.is_empty() {
                        users.push(name);
                    }
                }
            }
            libc::endutxent();

            // Reset to default database after reading custom file
            #[cfg(target_os = "linux")]
            {
                if let Ok(cpath) = CString::new("/var/run/utmp") {
                    utmpxname(cpath.as_ptr());
                }
            }
        }
        users.sort();
        users
    } else {
        // Default: use shared utmpx reader with systemd fallback
        let entries = who::read_utmpx_with_systemd_fallback();
        let mut users: Vec<String> = entries
            .iter()
            .filter(|e| e.ut_type == 7) // USER_PROCESS
            .map(|e| e.ut_user.clone())
            .filter(|name| !name.is_empty())
            .collect();
        users.sort();
        users
    }
}

/// Format the user list as a single space-separated line (matching GNU users output).
pub fn format_users(users: &[String]) -> String {
    users.join(" ")
}