X-Git-Url: http://nitlanguage.org

diff --git a/lib/privileges.nit b/lib/privileges.nit
index e3e1220..7a5503f 100644
--- a/lib/privileges.nit
+++ b/lib/privileges.nit
@@ -22,6 +22,22 @@ module privileges
 
 import opts
 
+redef class Text
+	# Does the operating system know the user named `self`?
+	fun user_exists: Bool
+	do
+		var passwd = new Passwd.from_name(to_s)
+		return not passwd.address_is_null
+	end
+
+	# Does the operating system know the group named `self`?
+	fun group_exists: Bool
+	do
+		var passwd = new Group.from_name(to_s)
+		return not passwd.address_is_null
+	end
+end
+
 # Class to manage user groups
 class UserGroup
 
@@ -31,16 +47,20 @@ class UserGroup
 	# Group name
 	var group: nullable String
 
-	# Drop privileges of a user and set his privileges back to default (program privileges)
+	# Drop privileges of the running program to those of `self`
+	#
+	# require: `user.user_exists and (group == null or group.group_exists)`
 	fun drop_privileges
 	do
 		var passwd = new Passwd.from_name(user)
+		assert not passwd.address_is_null
 		var uid = passwd.uid
 
 		var group = group
 		var gid
 		if group != null then
 			var gpasswd = new Group.from_name(group)
+			assert not gpasswd.address_is_null
 			gid = gpasswd.gid
 		else gid = passwd.gid