utxopsbt: let caller specify locktime, add tests and python binding.

Changelog-Added: JSON-RPC: `utxopsbt` takes a new `locktime` parameter
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

tests/test_wallet.py

@@ -559,6 +559,92 @@ def test_fundpsbt(node_factory, bitcoind, chainparams):
         l1.rpc.fundpsbt(amount // 2, feerate, 0)
 
 
+def test_utxopsbt(node_factory, bitcoind):
+    amount = 1000000
+    l1 = node_factory.get_node()
+
+    outputs = []
+    # Add a medley of funds to withdraw later, bech32 + p2sh-p2wpkh
+    txid = bitcoind.rpc.sendtoaddress(l1.rpc.newaddr()['bech32'],
+                                      amount / 10**8)
+    outputs.append((txid, bitcoind.rpc.gettransaction(txid)['details'][0]['vout']))
+    txid = bitcoind.rpc.sendtoaddress(l1.rpc.newaddr('p2sh-segwit')['p2sh-segwit'],
+                                      amount / 10**8)
+    outputs.append((txid, bitcoind.rpc.gettransaction(txid)['details'][0]['vout']))
+
+    bitcoind.generate_block(1)
+    wait_for(lambda: len(l1.rpc.listfunds()['outputs']) == len(outputs))
+
+    feerate = '7500perkw'
+
+    # Explicitly spend the first output above.
+    funding = l1.rpc.utxopsbt(amount // 2, feerate, 0,
+                              ['{}:{}'.format(outputs[0][0], outputs[0][1])],
+                              reserve=False)
+    psbt = bitcoind.rpc.decodepsbt(funding['psbt'])
+    # We can fuzz this up to 99 blocks back.
+    assert psbt['tx']['locktime'] > bitcoind.rpc.getblockcount() - 100
+    assert psbt['tx']['locktime'] <= bitcoind.rpc.getblockcount()
+    assert len(psbt['tx']['vin']) == 1
+    assert funding['excess_msat'] > Millisatoshi(0)
+    assert funding['excess_msat'] < Millisatoshi(amount // 2 * 1000)
+    assert funding['feerate_per_kw'] == 7500
+    assert 'estimated_final_weight' in funding
+    assert 'reservations' not in funding
+
+    # This should add 99 to the weight, but otherwise be identical except for locktime.
+    funding2 = l1.rpc.utxopsbt(amount // 2, feerate, 99,
+                               ['{}:{}'.format(outputs[0][0], outputs[0][1])],
+                               reserve=False, locktime=bitcoind.rpc.getblockcount() + 1)
+    psbt2 = bitcoind.rpc.decodepsbt(funding2['psbt'])
+    assert psbt2['tx']['locktime'] == bitcoind.rpc.getblockcount() + 1
+    assert psbt2['tx']['vin'] == psbt['tx']['vin']
+    assert psbt2['tx']['vout'] == psbt['tx']['vout']
+    assert funding2['excess_msat'] < funding['excess_msat']
+    assert funding2['feerate_per_kw'] == 7500
+    assert funding2['estimated_final_weight'] == funding['estimated_final_weight'] + 99
+    assert 'reservations' not in funding2
+
+    # Cannot afford this one (too much)
+    with pytest.raises(RpcError, match=r"not afford"):
+        l1.rpc.utxopsbt(amount, feerate, 0,
+                        ['{}:{}'.format(outputs[0][0], outputs[0][1])])
+
+    # Nor this (even with both)
+    with pytest.raises(RpcError, match=r"not afford"):
+        l1.rpc.utxopsbt(amount * 2, feerate, 0,
+                        ['{}:{}'.format(outputs[0][0], outputs[0][1]),
+                         '{}:{}'.format(outputs[1][0], outputs[1][1])])
+
+    # Should get two inputs (and reserve!)
+    funding = l1.rpc.utxopsbt(amount, feerate, 0,
+                              ['{}:{}'.format(outputs[0][0], outputs[0][1]),
+                               '{}:{}'.format(outputs[1][0], outputs[1][1])])
+    psbt = bitcoind.rpc.decodepsbt(funding['psbt'])
+    assert len(psbt['tx']['vin']) == 2
+    assert len(funding['reservations']) == 2
+    assert funding['reservations'][0]['txid'] == outputs[0][0]
+    assert funding['reservations'][0]['vout'] == outputs[0][1]
+    assert funding['reservations'][0]['was_reserved'] is False
+    assert funding['reservations'][0]['reserved'] is True
+    assert funding['reservations'][1]['txid'] == outputs[1][0]
+    assert funding['reservations'][1]['vout'] == outputs[1][1]
+    assert funding['reservations'][1]['was_reserved'] is False
+    assert funding['reservations'][1]['reserved'] is True
+
+    # Should refuse to use reserved outputs.
+    with pytest.raises(RpcError, match=r"already reserved"):
+        l1.rpc.utxopsbt(amount, feerate, 0,
+                        ['{}:{}'.format(outputs[0][0], outputs[0][1]),
+                         '{}:{}'.format(outputs[1][0], outputs[1][1])])
+
+    # Unless we tell it that's ok.
+    l1.rpc.utxopsbt(amount, feerate, 0,
+                    ['{}:{}'.format(outputs[0][0], outputs[0][1]),
+                     '{}:{}'.format(outputs[1][0], outputs[1][1])],
+                    reservedok=True)
+
+
 def test_sign_and_send_psbt(node_factory, bitcoind, chainparams):
     """
     Tests for the sign + send psbt RPCs