Merge #19800: test: Mockwallet

fa188c9c59 test: Use MiniWalet in p2p_feefilter (MarcoFalke)
fa39c62eb7 test: inline hashToHex (MarcoFalke)

Pull request description:

  This introduces a minimalistic test wallet, which can be used as a drop in replacement for the Bitcoin Core wallet to create dummy transactions with a given fee rate.

ACKs for top commit:
  jnewbery:
    utACK fa188c9c59

Tree-SHA512: 0aad9cb14eea4f0055bd6a47cc8c8f82a16941b152598c3bf1e083aae84cca4ffa23f0b854a362a68be1b917deba1b5ec7c0207b63b0805d747ba9a7d1d82efe

test/functional/test_framework/wallet.py

@@ -0,0 +1,64 @@
+#!/usr/bin/env python3
+# Copyright (c) 2020 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+"""A limited-functionality wallet, which may replace a real wallet in tests"""
+
+from decimal import Decimal
+from test_framework.address import ADDRESS_BCRT1_P2WSH_OP_TRUE
+from test_framework.messages import (
+    COIN,
+    COutPoint,
+    CTransaction,
+    CTxIn,
+    CTxInWitness,
+    CTxOut,
+)
+from test_framework.script import (
+    CScript,
+    OP_TRUE,
+)
+from test_framework.util import (
+    assert_equal,
+    hex_str_to_bytes,
+    satoshi_round,
+)
+
+
+class MiniWallet:
+    def __init__(self, test_node):
+        self._test_node = test_node
+        self._utxos = []
+        self._address = ADDRESS_BCRT1_P2WSH_OP_TRUE
+        self._scriptPubKey = hex_str_to_bytes(self._test_node.validateaddress(self._address)['scriptPubKey'])
+
+    def generate(self, num_blocks):
+        """Generate blocks with coinbase outputs to the internal address, and append the outputs to the internal list"""
+        blocks = self._test_node.generatetoaddress(num_blocks, self._address)
+        for b in blocks:
+            cb_tx = self._test_node.getblock(blockhash=b, verbosity=2)['tx'][0]
+            self._utxos.append({'txid': cb_tx['txid'], 'vout': 0, 'value': cb_tx['vout'][0]['value']})
+        return blocks
+
+    def send_self_transfer(self, *, fee_rate, from_node):
+        """Create and send a tx with the specified fee_rate. Fee may be exact or at most one satoshi higher than needed."""
+        self._utxos = sorted(self._utxos, key=lambda k: -k['value'])
+        largest_utxo = self._utxos.pop()  # Pick the largest utxo and hope it covers the fee
+        vsize = Decimal(96)
+        send_value = satoshi_round(largest_utxo['value'] - fee_rate * (vsize / 1000))
+        fee = largest_utxo['value'] - send_value
+        assert (send_value > 0)
+
+        tx = CTransaction()
+        tx.vin = [CTxIn(COutPoint(int(largest_utxo['txid'], 16), largest_utxo['vout']))]
+        tx.vout = [CTxOut(int(send_value * COIN), self._scriptPubKey)]
+        tx.wit.vtxinwit = [CTxInWitness()]
+        tx.wit.vtxinwit[0].scriptWitness.stack = [CScript([OP_TRUE])]
+        tx_hex = tx.serialize().hex()
+
+        txid = from_node.sendrawtransaction(tx_hex)
+        self._utxos.append({'txid': txid, 'vout': 0, 'value': send_value})
+        tx_info = from_node.getmempoolentry(txid)
+        assert_equal(tx_info['vsize'], vsize)
+        assert_equal(tx_info['fee'], fee)
+        return {'txid': txid, 'wtxid': tx_info['wtxid'], 'hex': tx_hex}