splice: Add easy spliceout command

contrib/msggen/msggen/schema.json

@@ -33917,6 +33917,91 @@
         }
       ]
     },
+    "spliceout.json": {
+      "$schema": "../rpc-schema-draft.json",
+      "type": "object",
+      "additionalProperties": false,
+      "added": "v26.04",
+      "rpc": "spliceout",
+      "title": "Command to splice funds out of a channel",
+      "warning": "experimental-splicing only",
+      "description": [
+        "`spliceout` is the command to move funds into a channel."
+      ],
+      "request": {
+        "required": [
+          "channel",
+          "amount"
+        ],
+        "properties": {
+          "channel": {
+            "type": "string",
+            "description": [
+              "channel identifier or channel query. Format is the same as is used in `dev-splice`."
+            ]
+          },
+          "amount": {
+            "type": "string",
+            "description": [
+              "Amount in satoshis taken from the channel. Format is the same as is used in `dev-splice`."
+            ]
+          },
+          "destination": {
+            "type": "string",
+            "description": [
+              "Where to send the funds to. Defaults to `wallet` which sends the funds to your onchain wallet. Specify a bitcoin address to send funds to that address or specify a channel identifier to send funds to another channel. Format is the same as is used in `dev-splice`."
+            ]
+          },
+          "force_feerate": {
+            "type": "boolean",
+            "description": [
+              "By default splices will fail if the fee provided looks too high. This is to protect against accidentally setting your fee higher than intended. Set `force_feerate` to true to skip this saftey check"
+            ]
+          }
+        }
+      },
+      "response": {
+        "required": [],
+        "properties": {
+          "psbt": {
+            "type": "string",
+            "description": [
+              "The final psbt"
+            ]
+          },
+          "tx": {
+            "type": "string",
+            "description": [
+              "The final transaction in hex"
+            ]
+          },
+          "txid": {
+            "type": "string",
+            "description": [
+              "The txid of the final transaction"
+            ]
+          }
+        }
+      },
+      "usage": [
+        "`spliceout` is the command take funds from a channel. It takes `amount` funds from the specified `channel` and puts them somewhere.",
+        "",
+        "The default destination is your onchain wallet.",
+        "By specifying the `destination` as a bitcoin address, the funds will be sent to the specified address",
+        "By specifying the `destination` as a channel identifier, the funds will be sent to the specified channel. This accomplishes a simple \"cross-splice\".",
+        "",
+        "The fee for the transaction will be taken from channel funds."
+      ],
+      "author": [
+        "Dusty [@dusty_daemon](mailto:@dustydaemon) is mainly responsible."
+      ],
+      "see_also": [
+        "lightning-dev-splice(7)"
+      ],
+      "resources": [
+        "Main web site: [https://github.com/ElementsProject/lightning](https://github.com/ElementsProject/lightning)"
+      ]
+    },
     "sql-template.json": {
       "$schema": "../rpc-schema-draft.json",
       "type": "object",

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

@@ -1226,6 +1226,16 @@ def splice(self, script_or_json, dryrun=None, force_feerate=None, debug_log=None
         }
         return self.call("dev-splice", payload)
 
+    def spliceout(self, channel, amount, destination=None, force_feerate=None):
+        """ Execute a splice out """
+        payload = {
+            "channel": channel,
+            "amount": amount,
+            "destination": destination,
+            "force_feerate": force_feerate,
+        }
+        return self.call("spliceout", payload)
+
     def stfu_channels(self, channel_ids):
         """ STFU multiple channels """
         payload = {

doc/Makefile

@@ -138,6 +138,7 @@ MARKDOWNPAGES := doc/addgossip.7 \
 	doc/splice_init.7 \
 	doc/splice_signed.7 \
 	doc/splice_update.7 \
+	doc/spliceout.7 \
 	doc/staticbackup.7 \
 	doc/stop.7 \
 	doc/txdiscard.7 \

doc/index.rst

@@ -154,6 +154,7 @@ Core Lightning Documentation
    splice_init <splice_init.7.md>
    splice_signed <splice_signed.7.md>
    splice_update <splice_update.7.md>
+   spliceout <spliceout.7.md>
    sql <sql.7.md>
    staticbackup <staticbackup.7.md>
    stop <stop.7.md>

doc/schemas/spliceout.json

@@ -0,0 +1,85 @@
+{
+  "$schema": "../rpc-schema-draft.json",
+  "type": "object",
+  "additionalProperties": false,
+  "added": "v26.04",
+  "rpc": "spliceout",
+  "title": "Command to splice funds out of a channel",
+  "warning": "experimental-splicing only",
+  "description": [
+    "`spliceout` is the command to move funds into a channel."
+  ],
+  "request": {
+    "required": [
+      "channel",
+      "amount"
+    ],
+    "properties": {
+      "channel": {
+        "type": "string",
+        "description": [
+          "channel identifier or channel query. Format is the same as is used in `dev-splice`."
+        ]
+      },
+      "amount": {
+        "type": "string",
+        "description": [
+          "Amount in satoshis taken from the channel. Format is the same as is used in `dev-splice`."
+        ]
+      },
+      "destination": {
+        "type": "string",
+        "description": [
+          "Where to send the funds to. Defaults to `wallet` which sends the funds to your onchain wallet. Specify a bitcoin address to send funds to that address or specify a channel identifier to send funds to another channel. Format is the same as is used in `dev-splice`."
+        ]
+      },
+      "force_feerate": {
+        "type": "boolean",
+        "description": [
+          "By default splices will fail if the fee provided looks too high. This is to protect against accidentally setting your fee higher than intended. Set `force_feerate` to true to skip this saftey check"
+        ]
+      }
+    }
+  },
+  "response": {
+    "required": [],
+    "properties": {
+      "psbt": {
+        "type": "string",
+        "description": [
+          "The final psbt"
+        ]
+      },
+      "tx": {
+        "type": "string",
+        "description": [
+          "The final transaction in hex"
+        ]
+      },
+      "txid": {
+        "type": "string",
+        "description": [
+          "The txid of the final transaction"
+        ]
+      }
+    }
+  },
+  "usage": [
+    "`spliceout` is the command take funds from a channel. It takes `amount` funds from the specified `channel` and puts them somewhere.",
+    "",
+    "The default destination is your onchain wallet.",
+    "By specifying the `destination` as a bitcoin address, the funds will be sent to the specified address",
+    "By specifying the `destination` as a channel identifier, the funds will be sent to the specified channel. This accomplishes a simple \"cross-splice\".",
+    "",
+    "The fee for the transaction will be taken from channel funds."
+  ],
+  "author": [
+    "Dusty [@dusty_daemon](mailto:@dustydaemon) is mainly responsible."
+  ],
+  "see_also": [
+    "lightning-dev-splice(7)"
+  ],
+  "resources": [
+    "Main web site: [https://github.com/ElementsProject/lightning](https://github.com/ElementsProject/lightning)"
+  ]
+}

plugins/spender/splice.c

@@ -1462,10 +1462,63 @@ json_splice(struct command *cmd, const char *buf, const jsmntok_t *params)
 	return send_outreq(req);
 }
 
+static struct command_result *
+json_spliceout(struct command *cmd, const char *buf, const jsmntok_t *params)
+{
+	struct out_req *req;
+	const char *channel, *amount, *destination;
+	struct splice_cmd *splice_cmd;
+	bool *force_feerate;
+	char *script;
+
+	if (!param(cmd, buf, params,
+		   p_req("channel", param_string, &channel),
+		   p_req("amount", param_string, &amount),
+		   p_opt("destination", param_string, &destination),
+		   p_opt_def("force_feerate", param_bool, &force_feerate,
+		   	     false),
+		   NULL))
+		return command_param_failed();
+
+	if (!destination)
+		destination = "wallet";
+
+	script = tal_fmt(NULL,
+			 "%s -> %s + fee; 100%% -> %s",
+			 channel, amount, destination);
+
+	splice_cmd = tal(cmd, struct splice_cmd);
+
+	splice_cmd->cmd = cmd;
+	splice_cmd->script = tal_steal(splice_cmd, script);
+	splice_cmd->psbt = create_psbt(splice_cmd, 0, 0, 0);
+	splice_cmd->dryrun = false;
+	splice_cmd->wetrun = false;
+	splice_cmd->feerate_per_kw = 0;
+	splice_cmd->force_feerate = *force_feerate;
+	splice_cmd->wallet_inputs_to_signed = 0;
+	splice_cmd->fee_calculated = false;
+	splice_cmd->initial_funds = AMOUNT_SAT(0);
+	splice_cmd->emergency_sat = AMOUNT_SAT(0);
+	splice_cmd->debug_log = NULL;
+	splice_cmd->debug_counter = 0;
+	memset(&splice_cmd->final_txid, 0, sizeof(splice_cmd->final_txid));
+
+	req = jsonrpc_request_start(cmd, "listpeerchannels",
+				    listpeerchannels_get_result,
+				    splice_error, splice_cmd);
+
+	return send_outreq(req);
+}
+
 const struct plugin_command splice_commands[] = {
 	{
 		"dev-splice",
 		json_splice
 	},
+	{
+		"spliceout",
+		json_spliceout
+	},
 };
 const size_t num_splice_commands = ARRAY_SIZE(splice_commands);

tests/test_splice.py

@@ -195,3 +195,107 @@ def test_script_splice_in(node_factory, bitcoind, chainparams):
     l1.wait_for_channel_onchain(l2.info['id'])
     account_info = only_one([acct for acct in l1.rpc.bkpr_listbalances()['accounts'] if acct['account'] == account_id])
     assert not account_info['account_closed']
+
+
+@pytest.mark.openchannel('v1')
+@pytest.mark.openchannel('v2')
+@unittest.skipIf(TEST_NETWORK != 'regtest', 'elementsd doesnt yet support PSBT features we need')
+def test_easy_splice_out(node_factory, bitcoind, chainparams):
+    fundamt = 1000000
+
+    coin_mvt_plugin = Path(__file__).parent / "plugins" / "coin_movements.py"
+    l1, l2 = node_factory.line_graph(2, fundamount=fundamt, wait_for_announce=True,
+                                     opts={'experimental-splicing': None,
+                                           'plugin': coin_mvt_plugin})
+
+    initial_wallet_balance = Millisatoshi(bkpr_account_balance(l1, 'wallet'))
+
+    # Splice out 100k from first channel, putting result less fees into onchain wallet
+    spliceamt = 100000
+    l1.rpc.spliceout("*:?", f"{spliceamt}", force_feerate=True)
+
+    bitcoind.generate_block(6, wait_for_mempool=1)
+    l2.daemon.wait_for_log(r'lightningd, splice_locked clearing inflights')
+
+    p1 = only_one(l1.rpc.listpeerchannels(peer_id=l2.info['id'])['channels'])
+    p2 = only_one(l2.rpc.listpeerchannels(l1.info['id'])['channels'])
+    assert 'inflight' not in p1
+    assert 'inflight' not in p2
+
+    wait_for(lambda: len(l1.rpc.listfunds()['outputs']) == 2)
+    wait_for(lambda: len(l1.rpc.listfunds()['channels']) == 1)
+
+    end_wallet_balance = Millisatoshi(bkpr_account_balance(l1, 'wallet'))
+    assert initial_wallet_balance + Millisatoshi(spliceamt * 1000) == end_wallet_balance
+
+
+@pytest.mark.xfail(strict=True)
+@pytest.mark.openchannel('v1')
+@pytest.mark.openchannel('v2')
+@unittest.skipIf(TEST_NETWORK != 'regtest', 'elementsd doesnt yet support PSBT features we need')
+def test_easy_splice_out_address(node_factory, bitcoind, chainparams):
+    fundamt = 1000000
+
+    coin_mvt_plugin = Path(__file__).parent / "plugins" / "coin_movements.py"
+    l1, l2 = node_factory.line_graph(2, fundamount=fundamt, wait_for_announce=True,
+                                     opts={'experimental-splicing': None,
+                                           'plugin': coin_mvt_plugin})
+
+    initial_wallet_balance = Millisatoshi(bkpr_account_balance(l1, 'wallet'))
+
+    addr = l1.rpc.newaddr()['p2tr']
+
+    # Splice out 100k from first channel, putting result less fees into onchain wallet via addres
+    spliceamt = 100000
+    l1.rpc.spliceout("*:?", f"{spliceamt}", destination=addr, force_feerate=True)
+
+    bitcoind.generate_block(6, wait_for_mempool=1)
+    l2.daemon.wait_for_log(r'lightningd, splice_locked clearing inflights')
+
+    p1 = only_one(l1.rpc.listpeerchannels(peer_id=l2.info['id'])['channels'])
+    p2 = only_one(l2.rpc.listpeerchannels(l1.info['id'])['channels'])
+    assert 'inflight' not in p1
+    assert 'inflight' not in p2
+
+    wait_for(lambda: len(l1.rpc.listfunds()['outputs']) == 2)
+    wait_for(lambda: len(l1.rpc.listfunds()['channels']) == 1)
+
+    end_wallet_balance = Millisatoshi(bkpr_account_balance(l1, 'wallet'))
+    assert initial_wallet_balance + Millisatoshi(spliceamt * 1000) == end_wallet_balance
+
+
+@pytest.mark.xfail(strict=True)
+@pytest.mark.openchannel('v1')
+@pytest.mark.openchannel('v2')
+@unittest.skipIf(TEST_NETWORK != 'regtest', 'elementsd doesnt yet support PSBT features we need')
+def test_easy_splice_out_into_channel(node_factory, bitcoind, chainparams):
+    fundamt = 1000000
+
+    coin_mvt_plugin = Path(__file__).parent / "plugins" / "coin_movements.py"
+    l1, l2, l3 = node_factory.line_graph(3, fundamount=fundamt, wait_for_announce=True,
+                                         opts={'experimental-splicing': None,
+                                               'plugin': coin_mvt_plugin})
+
+    chan1 = first_channel_id(l1, l2)
+    chan2 = first_channel_id(l2, l3)
+
+    initial_chan1_balance = Millisatoshi(bkpr_account_balance(l2, chan1))
+    assert initial_chan1_balance == 0
+
+    # Splice out 100k from first channel, putting result into channel
+    spliceamt = 100000
+    l2.rpc.spliceout(f"{chan2}", f"{spliceamt}", destination=chan1, force_feerate=True)
+
+    bitcoind.generate_block(6, wait_for_mempool=1)
+    l2.daemon.wait_for_log(r'lightningd, splice_locked clearing inflights')
+
+    p1 = only_one(l1.rpc.listpeerchannels())
+    p2 = only_one(l3.rpc.listpeerchannels())
+    assert 'inflight' not in p1
+    assert 'inflight' not in p2
+
+    wait_for(lambda: len(l2.rpc.listfunds()['outputs']) == 1)
+    wait_for(lambda: len(l2.rpc.listfunds()['channels']) == 2)
+
+    end_chan1_balance = Millisatoshi(bkpr_account_balance(l2, chan1))
+    assert initial_chan1_balance + Millisatoshi(spliceamt * 1000) == end_chan1_balance