Allow absurd fee override when setting tx fee manually

scripts/sendpayment.py

@@ -157,6 +157,27 @@ def main():
 
     # If tx_fees are set manually by CLI argument, override joinmarket.cfg:
     if int(options.txfee) > 0:
+        if jm_single().bc_interface.fee_per_kb_has_been_manually_set(
+                options.txfee):
+            absurd_fee = jm_single().config.getint("POLICY",
+                                                   "absurd_fee_per_kb")
+            tx_fees_factor = jm_single().config.getfloat("POLICY",
+                                                         "tx_fees_factor")
+            max_potential_txfee = int(max(options.txfee,
+                options.txfee * float(1 + tx_fees_factor)))
+            if max_potential_txfee > absurd_fee:
+                jmprint(
+                    "WARNING: Manually specified Bitcoin transaction fee "
+                    f"{btc.fee_per_kb_to_str(options.txfee)} can be "
+                    "randomized up to "
+                    f"{btc.fee_per_kb_to_str(max_potential_txfee)}, "
+                    "above absurd value "
+                    f"{btc.fee_per_kb_to_str(absurd_fee)}.",
+                    "warning")
+                if input("Still continue? (y/n):")[0] != "y":
+                    sys.exit("Aborted by user.")
+            jm_single().config.set("POLICY", "absurd_fee_per_kb",
+                                   str(max_potential_txfee))
         jm_single().config.set("POLICY", "tx_fees", str(options.txfee))
 
     maxcjfee = (1, float('inf'))

src/jmclient/blockchaininterface.py

@@ -233,7 +233,7 @@ class BlockchainInterface(ABC):
         # and return the indices of the others:
         return [i for i, val in enumerate(res) if val]
 
-    def _fee_per_kb_has_been_manually_set(self, tx_fees: int) -> bool:
+    def fee_per_kb_has_been_manually_set(self, tx_fees: int) -> bool:
         """If the block target (tx_fees) is higher than 1000, interpret it
         as manually set fee sats/kvB.
         """
@@ -242,7 +242,7 @@ class BlockchainInterface(ABC):
     def estimate_fee_per_kb(self, tx_fees: int) -> int:
         """ The argument tx_fees may be either a number of blocks target,
         for estimation of feerate by Core, or a number of satoshis
-        per kilo-vbyte (see `_fee_per_kb_has_been_manually_set` for
+        per kilo-vbyte (see `fee_per_kb_has_been_manually_set` for
         how this is distinguished).
         In both cases it is prevented from falling below the current
         minimum feerate for tx to be accepted into node's mempool.
@@ -264,7 +264,7 @@ class BlockchainInterface(ABC):
         mempoolminfee_in_sat_randomized = random.uniform(
             mempoolminfee_in_sat, mempoolminfee_in_sat * float(1 + tx_fees_factor))
 
-        if self._fee_per_kb_has_been_manually_set(tx_fees):
+        if self.fee_per_kb_has_been_manually_set(tx_fees):
             N_res = random.uniform(tx_fees, tx_fees * float(1 + tx_fees_factor))
             if N_res < mempoolminfee_in_sat:
                 msg = "Using this mempool min fee as tx feerate"