swapserver: add config variable SWAPSERVER_FEE_MILLIONTHS

electrum/simple_config.py

@@ -1204,6 +1204,7 @@ Warning: setting this to too low will result in lots of payment failures."""),
     SWAPSERVER_URL = ConfigVar('swapserver_url', default=_default_swapserver_url, type_=str)
     # run submarine swap server locally
     SWAPSERVER_PORT = ConfigVar('swapserver_port', default=5455, type_=int)
+    SWAPSERVER_FEE_MILLIONTHS = ConfigVar('swapserver_fee_millionths', default=5000, type_=int)
     TEST_SWAPSERVER_REFUND = ConfigVar('test_swapserver_refund', default=False, type_=bool)
 
     # zeroconf channels

electrum/submarine_swaps.py

@@ -879,7 +879,7 @@ class SwapManager(Logger):
 
     def init_pairs(self) -> None:
         """ for server """
-        self.percentage = 0.5
+        self.percentage = float(self.config.SWAPSERVER_FEE_MILLIONTHS) / 10000
         self._min_amount = 20000
         self._max_amount = 10000000
         self.normal_fee = self.get_fee(CLAIM_FEE_SIZE)