allow setting 0 tickets to disable sending tickets in TLS 1.3

scripts/tls.py

@@ -493,7 +493,8 @@ def serverCmd(argv):
     settings = HandshakeSettings()
     settings.useExperimentalTackExtension=True
     settings.dhParams = dhparam
-    settings.ticket_count = tickets or settings.ticket_count
+    if tickets is not None:
+        settings.ticket_count = tickets
     if psk:
         settings.pskConfigs = [(psk_ident, psk, psk_hash)]
     settings.ticketKeys = [getRandomBytes(32)]

tlslite/handshakesettings.py

@@ -483,7 +483,7 @@ def _sanityCheckTicketSettings(other):
         if not 0 < other.max_early_data <= 2**64:
             raise ValueError("max_early_data must be between 0 and 2GiB")
 
-        if not 0 < other.ticket_count < 2**16:
+        if not 0 <= other.ticket_count < 2**16:
             raise ValueError("Incorrect amount for number of new session "
                              "tickets to send")
 

unit_tests/test_tlslite_handshakesettings.py

@@ -436,6 +436,31 @@ def test_none_as_record_size_limit(self):
 
         self.assertIsNone(hs.record_size_limit)
 
+    def test_ticket_count_zero(self):
+        hs = HandshakeSettings()
+        hs.ticket_count = 0
+
+        hs = hs.validate()
+
+        self.assertIsNotNone(hs.ticket_count, 0)
+
+    def test_ticket_count_200(self):
+        hs = HandshakeSettings()
+        hs.ticket_count = 200
+
+        hs = hs.validate()
+
+        self.assertIsNotNone(hs.ticket_count, 200)
+
+    def test_ticket_count_negative(self):
+        hs = HandshakeSettings()
+        hs.ticket_count = -1
+
+        with self.assertRaises(ValueError) as e:
+            hs.validate()
+
+        self.assertIn("new session tickets", str(e.exception))
+
 
 if __name__ == '__main__':
     unittest.main()