From 4a90f13dee78d00a954f8931ff8be4676fbdd797 Mon Sep 17 00:00:00 2001
From: Markus Triska <triska@metalevel.at>
Date: Thu, 23 Jul 2020 00:27:31 +0200
Subject: [PATCH] better error handling for options

---
 src/lib/charsio.pl | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/lib/charsio.pl b/src/lib/charsio.pl
index dd41a597..71223884 100644
--- a/src/lib/charsio.pl
+++ b/src/lib/charsio.pl
@@ -200,6 +200,8 @@ read_line_to_chars(Stream, Cs0, Cs) :-
    Relation between a list of characters Cs and its Base64 encoding Bs,
    also a list of characters.
 
+   At least one of the arguments must be instantiated.
+
    Options are:
 
       - padding(Boolean)
@@ -226,6 +228,10 @@ chars_base64(Cs, Bs, Options) :-
             )
         ),
         must_be(boolean, Padding),
+        must_be(atom, Charset),
+        (   member(Charset, [standard,url]) -> true
+        ;   domain_error(charset, Charset, chars_base64/3)
+        ),
         (   var(Cs) ->
             must_be(list, Bs),
             maplist(must_be(character), Bs),
-- 
2.54.0