address comments of @kristapsk and @PulpCattel

jmclient/jmclient/blockchaininterface.py

@@ -412,19 +412,24 @@ class BitcoinCoreInterface(BlockchainInterface):
         how this is distinguished).
         In the latter case, it is prevented from falling below the
         minimum allowed feerate for relay on the Bitcoin network.
+        In case of failure to connect, None is returned.
+        In case of failure to source a specific minimum fee relay rate
+        (which is used to sanity check user's chosen fee rate), 1000
+        is used.
+        In case of failure to source a feerate estimate for targeted
+        number of blocks, a default of 10000 is returned.
         """
         if super().fee_per_kb_has_been_manually_set(N):
             # use the local bitcoin core relay fee as floor to avoid relay
             # problems
-            btc_relayfee = -1
             rpc_result = self._rpc('getnetworkinfo', None)
-            btc_relayfee = rpc_result.get('relayfee', btc_relayfee)
+            if not rpc_result:
-            if btc_relayfee > 0:
+                # in case of connection error:
-                relayfee_in_sat = int(Decimal(1e8) * Decimal(btc_relayfee))
+                return None
-            else:   # cannot get valid relayfee: fall back to 1000 sat/kbyte
+            btc_relayfee = rpc_result.get('relayfee', 1000)
-                relayfee_in_sat = 1000
+            relayfee_in_sat = int(Decimal(1e8) * Decimal(btc_relayfee))
-            log.debug("Using this min relay fee as tx feerate per kB floor: " +
+            log.debug("Using this min relay fee as tx feerate floor: " +
-                btc.fee_per_kb_to_str(1000))
+                btc.fee_per_kb_to_str(relayfee_in_sat))
             return int(max(relayfee_in_sat, random.uniform(N * float(0.8),
                                                            N * float(1.2))))
 
@@ -433,19 +438,25 @@ class BitcoinCoreInterface(BlockchainInterface):
         # should be used instead of falling back to hardcoded values
         tries = 2 if N == 1 else 1
 
-        estimate = -1
-        retval = -1
         for i in range(tries):
             rpc_result = self._rpc('estimatesmartfee', [N + i])
-            estimate = rpc_result.get('feerate', estimate)
+            if not rpc_result:
-            if estimate > 0:
+                # in case of connection error:
+                return None
+            estimate = rpc_result.get('feerate')
+            # `estimatesmartfee` will currently return in the format
+            # `{'errors': ['Insufficient data or no feerate found'], 'blocks': N}`
+            # if it is not able to make an estimate. We insist that
+            # the 'feerate' key is found and contains a positive value:
+            if estimate and estimate > 0:
+                retval = int(Decimal(1e8) * Decimal(estimate))
                 break
-        else:  # estimate <= 0
+        else:  # cannot get a valid estimate after `tries` tries:
+            log.warn("Could not source a fee estimate from Core, " +
+                     "falling back to default.")
             retval = 10000
 
-        if retval == -1:
+        log.info("Using bitcoin network feerate: " +\
-            retval = int(Decimal(1e8) * Decimal(estimate))
-        log.info("Using bitcoin network feerate (per kB in sats): " +\
                  btc.fee_per_kb_to_str(retval))
         return retval
 

jmclient/jmclient/wallet.py

@@ -81,6 +81,9 @@ def estimate_tx_fee(ins, outs, txtype='p2pkh', extra_bytes=0):
             "without blockchain source.")
     fee_per_kb = jm_single().bc_interface.estimate_fee_per_kb(
                 jm_single().config.getint("POLICY","tx_fees"))
+    if fee_per_kb is None:
+        raise RuntimeError("Cannot estimate fee per kB, possibly" +
+                           " a failure of connection to the blockchain.")
     absurd_fee = jm_single().config.getint("POLICY", "absurd_fee_per_kb")
     if fee_per_kb > absurd_fee:
         #This error is considered critical; for safety reasons, shut down.

scripts/sendpayment.py

@@ -178,8 +178,8 @@ def main():
     if options.makercount != 0:
         fee_per_cp_guess = estimate_tx_fee(2, 2,
                                            txtype=wallet_service.get_txtype())
-        log.debug("Estimated miner/tx fee for each cj participant: " + str(
+        log.debug("Estimated miner/tx fee for each cj participant: " +
-            fee_per_cp_guess))
+                  btc.amount_to_str(fee_per_cp_guess))
 
     # From the estimated tx fees, check if the expected amount is a
     # significant value compared the the cj amount; currently enabled