base: NULL-terminate getarg_strings

lib/roken/getarg.c

@@ -334,7 +334,16 @@ add_string(getarg_strings *s, char *value)
 {
     char **strings;
 
-    strings = realloc(s->strings, (s->num_strings + 1) * sizeof(*s->strings));
+    /*
+     * O(N^2) here.  Fortunately counts will generally be low here.
+     *
+     * Either break the ABI by adding an allocated count field to
+     * `getarg_strings`, or use a specific set of counts like 1, 4, 8, 12, 18,
+     * etc., i.e., powers of two for a while then switch to increasing by half.
+     * After some unrealistic number of string arguments switch to incrementing
+     * by 1.
+     */
+    strings = realloc(s->strings, (s->num_strings + 2) * sizeof(*s->strings));
     if (strings == NULL) {
 	free(s->strings);
 	s->strings = NULL;
@@ -343,6 +352,7 @@ add_string(getarg_strings *s, char *value)
     }
     s->strings = strings;
     s->strings[s->num_strings] = value;
+    s->strings[s->num_strings + 1] = NULL; /* NULL-terminator is handy */
     s->num_strings++;
     return 0;
 }