lib LibC
	struct Passwd
		pw_name    : Char*
		pw_passwd  : Char*
		pw_uid     : UInt
		pw_gid     : UInt
		pw_gecos   : Char*
		pw_dir     : UInt
		pw_shell   : Char*
	end

	fun setuid(Int32) : Int32
	fun setgid(Int32) : Int32
	fun getpwnam(Char*) : Passwd*

	fun initgroups(Char*, Int32) : Int32
end

module System
	def self.become_user(user_name : String)
		pointer = LibC.getpwnam user_name.to_unsafe

		if pointer.null?
			return nil
		end

		passwd = pointer.value

		uid = passwd.pw_uid
		gid = passwd.pw_gid

		r = LibC.initgroups user_name, passwd.pw_gid
		# raise Errno.new "initgroups" if r != 0
		raise Exception.new "initgroups" if r != 0

		r = LibC.setgid gid
		# raise Errno.new "setgid" if r != 0
		raise Exception.new "setgid" if r != 0

		r = LibC.setuid uid
		# raise Errno.new "setuid" if r != 0
		raise Exception.new "setuid" if r != 0
	end
end