feat: add get_display function

src/login.rs

@@ -92,6 +92,17 @@ pub fn get_session(pid: Option<pid_t>) -> Result<String> {
     Ok(ss)
 }
 
+/// Determines the session identifier of a .user
+///
+/// Specific user can be optionally targeted via their UID.
+/// This method can be used to retrieve a session identifier.
+pub fn get_display(uid: uid_t) -> Result<String> {
+    let mut c_session: *mut c_char = ptr::null_mut();
+    ffi_result(unsafe { libsystemd_sys::login::sd_uid_get_display(uid, &mut c_session) })?;
+    let ss = unsafe { free_cstring(c_session).unwrap() };
+    Ok(ss)
+}
+
 /// Determines the seat identifier of the seat the session identified
 /// by the specified session identifier belongs to.
 ///

tests/login.rs

@@ -103,6 +103,36 @@ fn test_get_owner_uid() {
     }
 }
 
+#[test]
+fn test_get_display() {
+    let ou = login::get_owner_uid(None);
+    let has_systemd = booted();
+    assert!(has_systemd.is_ok());
+    if has_systemd.unwrap() {
+        // Running under systemd, inside a slice somewhere
+        // even in this case, we might get a "no data available" (github actions runners return
+        // this)
+        if let Err(e) = ou {
+            match e.raw_os_error() {
+                Some(libc::ENODATA) => { /* ok */ }
+                _ => panic!("{}", e),
+            }
+            return;
+        }
+        let ou = ou.unwrap();
+        let display = login::get_display(ou);
+        if let Err(e) = display {
+            match e.raw_os_error() {
+                Some(libc::ENODATA) => { /* ok */ }
+                _ => panic!("{}", e),
+            }
+            return;
+        }
+    } else {
+        // Nothing meaningful to check here
+    }
+}
+
 #[test]
 fn test_get_sessions() {
     let sessions = login::get_sessions();