reserve/unreserve input: new RPC commands for reserving inputs/outputs

Reserve and unreserve wallet UTXOs using a PSBT which includes those
inputs.

Note that currently we unreserve inputs everytime the node restarts.
This will be addressed in a future commit.

Changelog-Added: JSON-RPC: Adds two new rpc methods, `reserveinputs` and `unreserveinputs`, which allow for reserving or unreserving wallet UTXOs

tests/test_wallet.py

@@ -436,6 +436,131 @@ def test_txprepare(node_factory, bitcoind, chainparams):
     assert decode['vout'][changenum]['scriptPubKey']['type'] == 'witness_v0_keyhash'
 
 
+def test_reserveinputs(node_factory, bitcoind, chainparams):
+    """
+    Reserve inputs is basically the same as txprepare, with the
+    slight exception that 'reserveinputs' doesn't keep the
+    unsent transaction around
+    """
+    amount = 1000000
+    total_outs = 12
+    l1 = node_factory.get_node(feerates=(7500, 7500, 7500, 7500))
+    addr = chainparams['example_addr']
+
+    # Add a medley of funds to withdraw later, bech32 + p2sh-p2wpkh
+    for i in range(total_outs // 2):
+        bitcoind.rpc.sendtoaddress(l1.rpc.newaddr()['bech32'],
+                                   amount / 10**8)
+        bitcoind.rpc.sendtoaddress(l1.rpc.newaddr('p2sh-segwit')['p2sh-segwit'],
+                                   amount / 10**8)
+
+    bitcoind.generate_block(1)
+    wait_for(lambda: len(l1.rpc.listfunds()['outputs']) == total_outs)
+
+    utxo_count = 8
+    sent = Decimal('0.01') * (utxo_count - 1)
+    reserved = l1.rpc.reserveinputs(outputs=[{addr: Millisatoshi(amount * (utxo_count - 1) * 1000)}])
+    assert reserved['feerate_per_kw'] == 7500
+    psbt = bitcoind.rpc.decodepsbt(reserved['psbt'])
+    out_found = False
+
+    assert len(psbt['inputs']) == utxo_count
+    outputs = l1.rpc.listfunds()['outputs']
+    assert len([x for x in outputs if not x['reserved']]) == total_outs - utxo_count
+    assert len([x for x in outputs if x['reserved']]) == utxo_count
+    total_outs -= utxo_count
+    saved_input = psbt['tx']['vin'][0]
+
+    # We should have two outputs
+    for vout in psbt['tx']['vout']:
+        if vout['scriptPubKey']['addresses'][0] == addr:
+            assert vout['value'] == sent
+            out_found = True
+    assert out_found
+
+    # Do it again, but for too many inputs
+    utxo_count = 12 - utxo_count + 1
+    sent = Decimal('0.01') * (utxo_count - 1)
+    with pytest.raises(RpcError, match=r"Cannot afford transaction"):
+        reserved = l1.rpc.reserveinputs(outputs=[{addr: Millisatoshi(amount * (utxo_count - 1) * 1000)}])
+
+    utxo_count -= 1
+    sent = Decimal('0.01') * (utxo_count - 1)
+    reserved = l1.rpc.reserveinputs(outputs=[{addr: Millisatoshi(amount * (utxo_count - 1) * 1000)}], feerate='10000perkw')
+
+    assert reserved['feerate_per_kw'] == 10000
+    psbt = bitcoind.rpc.decodepsbt(reserved['psbt'])
+
+    assert len(psbt['inputs']) == utxo_count
+    outputs = l1.rpc.listfunds()['outputs']
+    assert len([x for x in outputs if not x['reserved']]) == total_outs - utxo_count == 0
+    assert len([x for x in outputs if x['reserved']]) == 12
+
+    # No more available
+    with pytest.raises(RpcError, match=r"Cannot afford transaction"):
+        reserved = l1.rpc.reserveinputs(outputs=[{addr: Millisatoshi(amount * 1)}], feerate='253perkw')
+
+    # Unreserve three, from different psbts
+    unreserve_utxos = [
+        {
+            'txid': saved_input['txid'],
+            'vout': saved_input['vout'],
+            'sequence': saved_input['sequence']
+        }, {
+            'txid': psbt['tx']['vin'][0]['txid'],
+            'vout': psbt['tx']['vin'][0]['vout'],
+            'sequence': psbt['tx']['vin'][0]['sequence']
+        }, {
+            'txid': psbt['tx']['vin'][1]['txid'],
+            'vout': psbt['tx']['vin'][1]['vout'],
+            'sequence': psbt['tx']['vin'][1]['sequence']
+        }]
+    unreserve_psbt = bitcoind.rpc.createpsbt(unreserve_utxos, [])
+
+    unreserved = l1.rpc.unreserveinputs(unreserve_psbt)
+    assert unreserved['all_unreserved']
+    outputs = l1.rpc.listfunds()['outputs']
+    assert len([x for x in outputs if not x['reserved']]) == len(unreserved['outputs'])
+    for i in range(len(unreserved['outputs'])):
+        un = unreserved['outputs'][i]
+        u_utxo = unreserve_utxos[i]
+        assert un['txid'] == u_utxo['txid'] and un['vout'] == u_utxo['vout'] and un['unreserved']
+
+    # Try unreserving the same utxos again, plus one that's not included
+    # We expect this to be a no-op.
+    unreserve_utxos.append({'txid': 'b' * 64, 'vout': 0, 'sequence': 0})
+    unreserve_psbt = bitcoind.rpc.createpsbt(unreserve_utxos, [])
+    unreserved = l1.rpc.unreserveinputs(unreserve_psbt)
+    assert not unreserved['all_unreserved']
+    for un in unreserved['outputs']:
+        assert not un['unreserved']
+    assert len([x for x in l1.rpc.listfunds()['outputs'] if not x['reserved']]) == 3
+
+    # passing in an empty string should fail
+    with pytest.raises(RpcError, match=r"should be a PSBT, not "):
+        l1.rpc.unreserveinputs('')
+
+    # reserve one of the utxos that we just unreserved
+    utxos = []
+    utxos.append(saved_input['txid'] + ":" + str(saved_input['vout']))
+    reserved = l1.rpc.reserveinputs([{addr: Millisatoshi(amount * 0.5 * 1000)}], feerate='253perkw', utxos=utxos)
+    assert len([x for x in l1.rpc.listfunds()['outputs'] if not x['reserved']]) == 2
+    psbt = bitcoind.rpc.decodepsbt(reserved['psbt'])
+    assert len(psbt['inputs']) == 1
+    vin = psbt['tx']['vin'][0]
+    assert vin['txid'] == saved_input['txid'] and vin['vout'] == saved_input['vout']
+
+    # reserve them all!
+    reserved = l1.rpc.reserveinputs([{addr: 'all'}])
+    outputs = l1.rpc.listfunds()['outputs']
+    assert len([x for x in outputs if not x['reserved']]) == 0
+    assert len([x for x in outputs if x['reserved']]) == 12
+
+    # FIXME: restart the node, nothing will remain reserved
+    l1.restart()
+    assert len(l1.rpc.listfunds()['outputs']) == 12
+
+
 def test_txsend(node_factory, bitcoind, chainparams):
     amount = 1000000
     l1 = node_factory.get_node(random_hsm=True)