split threshold into upper and lower bounds (#816)

tools/keymaster/keymaster.py

@@ -107,13 +107,15 @@ def top_up(ctx):
         for role, address in config["homes"][home]["addresses"].items():
             logging.info(f"Processing {role}-{address} on {home}")    
             # fetch config params 
-            home_threshold = config["networks"][home]["threshold"]
+            home_upper_bound = config["networks"][home]["threshold"]
+            # don't top up until balance has gone beneath lower bound
+            home_lower_bound = home_upper_bound / 3
             home_endpoint = config["networks"][home]["endpoint"]
             home_bank_signer = config["networks"][home]["bank"]["signer"]
             home_bank_address = config["networks"][home]["bank"]["address"]
             
             # check if balance is below threshold at home
-            threshold_difference = is_wallet_below_threshold(address, home_threshold, home_endpoint)
+            threshold_difference = is_wallet_below_threshold(address, home_lower_bound, home_upper_bound, home_endpoint)
             # get nonce
             home_bank_nonce = get_nonce(home_bank_address, home_endpoint)
             
@@ -127,12 +129,14 @@ def top_up(ctx):
 
             for replica in config["homes"][home]["replicas"]:
                  # fetch config params 
-                replica_threshold = config["networks"][replica]["threshold"]
+                replica_upper_bound = config["networks"][replica]["threshold"] 
+                # don't top up until balance has gone beneath lower bound
+                replica_lower_bound = replica_upper_bound / 3
                 replica_endpoint = config["networks"][replica]["endpoint"]
                 replica_bank_signer = config["networks"][replica]["bank"]["signer"]
                 replica_bank_address = config["networks"][replica]["bank"]["address"]
                 # check if balance is below threshold at replica
-                threshold_difference = is_wallet_below_threshold(address, replica_threshold, replica_endpoint)
+                threshold_difference = is_wallet_below_threshold(address, replica_lower_bound, replica_upper_bound, replica_endpoint)
                 # get nonce
                 replica_bank_nonce = get_nonce(replica_bank_address, replica_endpoint)
                 # if so, enqueue top up with (threshold - balance) ether

tools/keymaster/utils.py

@@ -3,14 +3,16 @@ from web3 import Web3
 # Checks if an address is below the threshold
 # returns difference in wei if true
 # returns False if not
-def is_wallet_below_threshold(address:str, threshold:int, endpoint:str):
+def is_wallet_below_threshold(address:str, lower_bound:int, upper_bound:int, endpoint:str):
     w3 = Web3(Web3.HTTPProvider(endpoint))
     address = Web3.toChecksumAddress(address)
     # get balance
     wallet_wei = w3.eth.get_balance(address)
-    # if balance below threshold
+    # if balance below lower bound
-    if wallet_wei < threshold:
+    if wallet_wei < lower_bound:
-        return threshold - wallet_wei
+        # return the amount we have to top up
+        # to reach upper bound 
+        return upper_bound - wallet_wei
     else: 
         return False