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>

contrib/pyln-client/pyln/client/lightning.py

@@ -1140,6 +1140,21 @@ class LightningRpc(UnixDomainSocketRpc):
         }
         return self.call("fundpsbt", payload)
 
+    def utxopsbt(self, satoshi, feerate, startweight, utxos, reserve=True, reservedok=False, locktime=None):
+        """
+        Create a PSBT with given inputs, to give an output of satoshi.
+        """
+        payload = {
+            "satoshi": satoshi,
+            "feerate": feerate,
+            "startweight": startweight,
+            "utxos": utxos,
+            "reserve": reserve,
+            "reservedok": reservedok,
+            "locktime": locktime,
+        }
+        return self.call("utxopsbt", payload)
+
     def signpsbt(self, psbt):
         """
         Add internal wallet's signatures to PSBT

doc/lightning-utxopsbt.7

@@ -3,7 +3,7 @@
 lightning-utxopsbt - Command to populate PSBT inputs from given UTXOs
 .SH SYNOPSIS
 
-\fButxopsbt\fR \fIsatoshi\fR \fIfeerate\fR \fIstartweight\fR \fIutxos\fR [\fIreserve\fR] [\fIreservedok\fR]
+\fButxopsbt\fR \fIsatoshi\fR \fIfeerate\fR \fIstartweight\fR \fIutxos\fR [\fIreserve\fR] [\fIreservedok\fR] [\fIlocktime\fR]
 
 .SH DESCRIPTION
 
@@ -27,6 +27,10 @@ is equivalent to setting it to zero)\.
 Unless \fIreservedok\fR is set to true (default is false) it will also fail
 if any of the \fIutxos\fR are already reserved\.
 
+
+\fIlocktime\fR is an optional locktime: if not set, it is set to a recent
+block height\.
+
 .SH RETURN VALUE
 
 On success, returns the \fIpsbt\fR containing the inputs, \fIfeerate_per_kw\fR

doc/lightning-utxopsbt.7.md

@@ -4,7 +4,7 @@ lightning-utxopsbt -- Command to populate PSBT inputs from given UTXOs
 SYNOPSIS
 --------
 
-**utxopsbt** *satoshi* *feerate* *startweight* *utxos* \[*reserve*\] \[*reservedok*\]
+**utxopsbt** *satoshi* *feerate* *startweight* *utxos* \[*reserve*\] \[*reservedok*\] \[*locktime*\]
 
 DESCRIPTION
 -----------
@@ -26,6 +26,9 @@ is equivalent to setting it to zero).
 Unless *reservedok* is set to true (default is false) it will also fail
 if any of the *utxos* are already reserved.
 
+*locktime* is an optional locktime: if not set, it is set to a recent
+block height.
+
 RETURN VALUE
 ------------
 

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

wallet/reservation.c

@@ -427,7 +427,7 @@ static struct command_result *json_utxopsbt(struct command *cmd,
 	u32 *feerate_per_kw, *weight;
 	bool all, *reserve, *reserved_ok;
 	struct amount_sat *amount, input, excess;
-	u32 current_height;
+	u32 current_height, *locktime;
 
 	if (!param(cmd, buffer, params,
 		   p_req("satoshi", param_sat_or_all, &amount),
@@ -436,6 +436,7 @@ static struct command_result *json_utxopsbt(struct command *cmd,
 		   p_req("utxos", param_txout, &utxos),
 		   p_opt_def("reserve", param_bool, &reserve, true),
 		   p_opt_def("reservedok", param_bool, &reserved_ok, false),
+		   p_opt("locktime", param_number, &locktime),
 		   NULL))
 		return command_param_failed();
 
@@ -479,7 +480,7 @@ static struct command_result *json_utxopsbt(struct command *cmd,
 	}
 
 	return finish_psbt(cmd, utxos, *feerate_per_kw, *weight, excess,
-			   *reserve, NULL);
+			   *reserve, locktime);
 }
 static const struct json_command utxopsbt_command = {
 	"utxopsbt",