util: expose urlsafe_base64char()

src/basic/hexdecoct.c

@@ -526,6 +526,16 @@ char base64char(int x) {
         return table[x & 63];
 }
 
+/* This is almost base64char(), but not entirely, as it uses the "url and filename safe" alphabet,
+ * since we don't want "/" appear in interface names (since interfaces appear in sysfs as filenames).
+ * See section #5 of RFC 4648. */
+char urlsafe_base64char(int x) {
+        static const char table[64] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+                                      "abcdefghijklmnopqrstuvwxyz"
+                                      "0123456789-_";
+        return table[x & 63];
+}
+
 int unbase64char(char c) {
         unsigned offset;
 

src/basic/hexdecoct.h

@@ -27,6 +27,7 @@ char base32hexchar(int x) _const_;
 int unbase32hexchar(char c) _const_;
 
 char base64char(int x) _const_;
+char urlsafe_base64char(int x) _const_;
 int unbase64char(char c) _const_;
 
 char *base32hexmem(const void *p, size_t l, bool padding);