Add is system user

src/passwd.rs

@@ -96,6 +96,14 @@ impl TryFrom<&str> for Uid {
     }
 }
 
+impl Uid {
+    #[must_use]
+    pub const fn is_system_uid(&self) -> bool {
+        // since it is a u32  it cannot be smaller than 0
+        self.uid < 1000
+    }
+}
+
 #[derive(Debug, PartialEq, Eq)]
 pub struct Gid {
     gid: u32,
@@ -116,6 +124,14 @@ impl TryFrom<&str> for Gid {
     }
 }
 
+impl Gid {
+    #[must_use]
+    pub const fn is_system_gid(&self) -> bool {
+        // since it is a u32  it cannot be smaller than 0
+        self.gid < 1000
+    }
+}
+
 /// The gecos field of a user.
 ///
 /// In the `/etc/passwd` file this field is a `,` sepparated list of items.
@@ -455,6 +471,16 @@ fn test_default_user() {
     assert_eq!(pwd.uid.uid, 1001);
 }
 
+#[test]
+fn test_guid_system_user() {
+    // Check uids of system users.
+    let values = vec![("999", true), ("0", true), ("1000", false)];
+    for val in values {
+        assert_eq!(Uid::try_from(val.0).unwrap().is_system_uid(), val.1);
+        assert_eq!(Gid::try_from(val.0).unwrap().is_system_gid(), val.1);
+    }
+}
+
 #[test]
 fn test_parse_gecos() {
     // test if the Gecos field can be parsed and the resulting struct is populated correctly.