Merge bitcoin#13988: Add checks for settxfee reasonableness

317f2cb test: Check RPC settxfee errors (João Barbosa)
48618da Add checks for settxfee reasonableness (Anthony Towns)

Pull request description:

  When using the `settxfee` RPC, the value is silently ignored if it is less than either than minrelaytxfee or the wallet's mintxfee. This adds an error response if that's going to happen, but still allows "settxfee 0" to deliberately default to the minimum value.

Tree-SHA512: ce685584cf8d6b9ca2cc97196d494220e3892b6a804a458086e04b3a23df281da432ad0a3053106a064c90c541ddb6f6b96a27cf8376d45af1e44449baf88456

src/wallet/rpcwallet.cpp

@@ -2982,8 +2982,16 @@ static UniValue settxfee(const JSONRPCRequest& request)
     LOCK2(cs_main, pwallet->cs_wallet);
 
     CAmount nAmount = AmountFromValue(request.params[0]);
+    CFeeRate tx_fee_rate(nAmount, 1000);
+    if (tx_fee_rate == 0) {
+        // automatic selection
+    } else if (tx_fee_rate < ::minRelayTxFee) {
+        throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("txfee cannot be less than min relay tx fee (%s)", ::minRelayTxFee.ToString()));
+    } else if (tx_fee_rate < pwallet->m_min_fee) {
+        throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("txfee cannot be less than wallet min fee (%s)", pwallet->m_min_fee.ToString()));
+    }
 
-    pwallet->m_pay_tx_fee = CFeeRate(nAmount, 1000);
+    pwallet->m_pay_tx_fee = tx_fee_rate;
     return true;
 }
 

test/functional/wallet_bumpfee.py

@@ -31,7 +31,7 @@ class BumpFeeTest(BitcoinTestFramework):
     def set_test_params(self):
         self.num_nodes = 2
         self.setup_clean_chain = True
-        self.extra_args = [["-deprecatedrpc=addwitnessaddress", "-walletrbf={}".format(i)]
+        self.extra_args = [["-deprecatedrpc=addwitnessaddress", "-walletrbf={}".format(i), "-mintxfee=0.00002"]
                            for i in range(self.num_nodes)]
 
     def run_test(self):
@@ -190,6 +190,8 @@ def test_dust_to_fee(rbf_node, dest_address):
 
 
 def test_settxfee(rbf_node, dest_address):
+    assert_raises_rpc_error(-8, "txfee cannot be less than min relay tx fee", rbf_node.settxfee, Decimal('0.000005'))
+    assert_raises_rpc_error(-8, "txfee cannot be less than wallet min fee", rbf_node.settxfee, Decimal('0.000015'))
     # check that bumpfee reacts correctly to the use of settxfee (paytxfee)
     rbfid = spend_one_input(rbf_node, dest_address)
     requested_feerate = Decimal("0.00025000")