Merge #16257: [wallet] abort when attempting to fund a transaction above -maxtxfee

806b0052c3b45415862f74f20ba5f389e5b673de [wallet] abort when attempting to fund a transaction above maxtxfee (Sjors Provoost)

Pull request description:

  `FundTransaction` calls `GetMinimumFee` which, when the fee rate is absurdly high, quietly reduces the fee to `-maxtxfee`.

  Becaue an absurdly high fee rate is usually the result of a fat finger, aborting seems safer behavior.

  Before:
  ```
  bitcoin-cli walletcreatefundedpsbt '[]' '[{"tb1q...": 0.01}]' 0 '{"feeRate": 10}' true
  {
    "psbt": "cHNidP8...gAA=",
    "fee": 0.10000000,
    "changepos": 1
  }

  ```

  After:
  ```
  bitcoin-cli walletcreatefundedpsbt '[]' '[{"tb1q...": 0.01}]' 0 '{"feeRate": 10}' true
  error code: -25
  error message:
  Fee exceeds maximum configured by -maxtxfee
  ```

  QT still checks the max fee rate as expected:
  <img width="566" alt="Schermafbeelding 2019-06-20 om 19 52 00" src="https://user-images.githubusercontent.com/10217/59888424-a2aa7100-9395-11e9-8ae6-8a3c1f7de585.png">

ACKs for top commit:
  laanwj:
    Code review ACK 806b0052c3b45415862f74f20ba5f389e5b673de

Tree-SHA512: bee95811711cdab100b614d2347921407af3b400aea613ca156953ed3f60b924ad29a1d335bd0e240c0b7c0fbb360226bab03294d226a5560cdf2a3f21e6d406

2 files changed, 11 insertions, 0 deletions

diff --git a/test/functional/rpc_fundrawtransaction.py b/test/functional/rpc_fundrawtransaction.py
index d89fd6461f..cdf636e200 100755
--- a/test/functional/rpc_fundrawtransaction.py
+++ b/test/functional/rpc_fundrawtransaction.py
@@ -662,6 +662,7 @@ class RawTransactionsTest(BitcoinTestFramework):
         result = self.nodes[3].fundrawtransaction(rawtx) # uses min_relay_tx_fee (set by settxfee)
         result2 = self.nodes[3].fundrawtransaction(rawtx, {"feeRate": 2*min_relay_tx_fee})
         result3 = self.nodes[3].fundrawtransaction(rawtx, {"feeRate": 10*min_relay_tx_fee})
+        assert_raises_rpc_error(-4, "Fee exceeds maximum configured by -maxtxfee", self.nodes[3].fundrawtransaction, rawtx, {"feeRate": 1})
         result_fee_rate = result['fee'] * 1000 / count_bytes(result['hex'])
         assert_fee_amount(result2['fee'], count_bytes(result2['hex']), 2 * result_fee_rate)
         assert_fee_amount(result3['fee'], count_bytes(result3['hex']), 10 * result_fee_rate)
diff --git a/test/functional/rpc_psbt.py b/test/functional/rpc_psbt.py
index 430be6dd37..8bfa7a0238 100755
--- a/test/functional/rpc_psbt.py
+++ b/test/functional/rpc_psbt.py
@@ -9,6 +9,7 @@ from decimal import Decimal
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
     assert_equal,
+    assert_greater_than,
     assert_raises_rpc_error,
     connect_nodes_bi,
     disconnect_nodes,
@@ -129,6 +130,15 @@ class PSBTTest(BitcoinTestFramework):
         assert_equal(walletprocesspsbt_out['complete'], True)
         self.nodes[1].sendrawtransaction(self.nodes[1].finalizepsbt(walletprocesspsbt_out['psbt'])['hex'])
 
+        # feeRate of 0.1 BTC / KB produces a total fee slightly below -maxtxfee (~0.05280000):
+        res = self.nodes[1].walletcreatefundedpsbt([{"txid":txid,"vout":p2wpkh_pos},{"txid":txid,"vout":p2sh_p2wpkh_pos},{"txid":txid,"vout":p2pkh_pos}], {self.nodes[1].getnewaddress():29.99}, 0, {"feeRate": 0.1})
+        assert_greater_than(res["fee"], 0.05)
+        assert_greater_than(0.06, res["fee"])
+
+        # feeRate of 10 BTC / KB produces a total fee well above -maxtxfee
+        # previously this was silenty capped at -maxtxfee
+        assert_raises_rpc_error(-4, "Fee exceeds maximum configured by -maxtxfee", self.nodes[1].walletcreatefundedpsbt, [{"txid":txid,"vout":p2wpkh_pos},{"txid":txid,"vout":p2sh_p2wpkh_pos},{"txid":txid,"vout":p2pkh_pos}], {self.nodes[1].getnewaddress():29.99}, 0, {"feeRate": 10})
+
         # partially sign multisig things with node 1
         psbtx = self.nodes[1].walletcreatefundedpsbt([{"txid":txid,"vout":p2wsh_pos},{"txid":txid,"vout":p2sh_pos},{"txid":txid,"vout":p2sh_p2wsh_pos}], {self.nodes[1].getnewaddress():29.99})['psbt']
         walletprocesspsbt_out = self.nodes[1].walletprocesspsbt(psbtx)