use idna python module to check domainpart when available

gajim/common/helpers.py

@@ -59,6 +59,12 @@ try:
 except ImportError:
     HAS_PRECIS_I18N = False
 
+try:
+    import idna
+    HAS_IDNA = True
+except ImportError:
+    HAS_IDNA = False
+
 HAS_SOUND = True
 if sys.platform == 'win32':
     try:
@@ -283,11 +289,16 @@ def prep(user, server, resource):
 
     if not ip_address:
         if server is not None:
+            if server.endswith('.'): # RFC7622, 3.2
+                server = server[:-1]
             if len(server) < 1 or len(server.encode('utf-8')) > 1023:
                 raise InvalidFormat(_('Server must be between 1 and 1023 bytes'))
             try:
-                from nbxmpp.stringprepare import nameprep
-                server = nameprep.prepare(server)
+                if HAS_IDNA:
+                    server = idna.encode(server).decode('utf-8')
+                else:
+                    from nbxmpp.stringprepare import nameprep
+                    server = nameprep.prepare(server)
             except UnicodeError:
                 raise InvalidFormat(_('Invalid character in hostname.'))
         else: