rpc: include_unsafe option for fundrawtransaction

Allow RPC users to opt-in to unsafe inputs when funding a raw transaction.

Applications that need to manage a complex RBF flow (such as lightning
nodes using anchor outputs) are very limited if they can only use safe inputs.

Fixes #21299

src/wallet/coincontrol.cpp

@@ -11,6 +11,7 @@ void CCoinControl::SetNull()
     destChange = CNoDestination();
     m_change_type.reset();
     m_add_inputs = true;
+    m_include_unsafe_inputs = false;
     fAllowOtherInputs = false;
     fAllowWatchOnly = false;
     m_avoid_partial_spends = gArgs.GetBoolArg("-avoidpartialspends", DEFAULT_AVOIDPARTIALSPENDS);

src/wallet/coincontrol.h

@@ -29,6 +29,8 @@ class CCoinControl
     std::optional<OutputType> m_change_type;
     //! If false, only selected inputs are used
     bool m_add_inputs;
+    //! If false, only safe inputs will be used
+    bool m_include_unsafe_inputs;
     //! If false, allows unselected inputs, but requires all selected inputs be used
     bool fAllowOtherInputs;
     //! Includes watch only addresses which are solvable

src/wallet/rpcwallet.cpp

@@ -3073,6 +3073,7 @@ void FundTransaction(CWallet& wallet, CMutableTransaction& tx, CAmount& fee_out,
         RPCTypeCheckObj(options,
             {
                 {"add_inputs", UniValueType(UniValue::VBOOL)},
+                {"include_unsafe", UniValueType(UniValue::VBOOL)},
                 {"add_to_wallet", UniValueType(UniValue::VBOOL)},
                 {"changeAddress", UniValueType(UniValue::VSTR)},
                 {"change_address", UniValueType(UniValue::VSTR)},
@@ -3133,6 +3134,10 @@ void FundTransaction(CWallet& wallet, CMutableTransaction& tx, CAmount& fee_out,
             lockUnspents = (options.exists("lock_unspents") ? options["lock_unspents"] : options["lockUnspents"]).get_bool();
         }
 
+        if (options.exists("include_unsafe")) {
+            coinControl.m_include_unsafe_inputs = options["include_unsafe"].get_bool();
+        }
+
         if (options.exists("feeRate")) {
             if (options.exists("fee_rate")) {
                 throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot specify both fee_rate (" + CURRENCY_ATOM + "/vB) and feeRate (" + CURRENCY_UNIT + "/kvB)");
@@ -3203,6 +3208,9 @@ static RPCHelpMan fundrawtransaction()
                     {"options", RPCArg::Type::OBJ, RPCArg::Optional::OMITTED_NAMED_ARG, "for backward compatibility: passing in a true instead of an object will result in {\"includeWatching\":true}",
                         {
                             {"add_inputs", RPCArg::Type::BOOL, /* default */ "true", "For a transaction with existing inputs, automatically include more if they are not enough."},
+                            {"include_unsafe", RPCArg::Type::BOOL, /* default */ "false", "Include inputs that are not safe to spend.\n"
+                                                          "Beware that the resulting transaction may become invalid if one of the unsafe inputs disappears.\n"
+                                                          "If that happens, you will need to fund the transaction with different inputs and republish it."},
                             {"changeAddress", RPCArg::Type::STR, /* default */ "pool address", "The bitcoin address to receive the change"},
                             {"changePosition", RPCArg::Type::NUM, /* default */ "random", "The index of the change output"},
                             {"change_type", RPCArg::Type::STR, /* default */ "set by -changetype", "The output type to use. Only valid if changeAddress is not specified. Options are \"legacy\", \"p2sh-segwit\", and \"bech32\"."},

src/wallet/wallet.cpp

@@ -2509,6 +2509,7 @@ bool CWallet::SelectCoins(const std::vector<COutput>& vAvailableCoins, const CAm
         (m_spend_zero_conf_change && SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, std::min((size_t)4, max_ancestors/3), std::min((size_t)4, max_descendants/3)), vCoins, setCoinsRet, nValueRet, coin_selection_params, bnb_used)) ||
         (m_spend_zero_conf_change && SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, max_ancestors/2, max_descendants/2), vCoins, setCoinsRet, nValueRet, coin_selection_params, bnb_used)) ||
         (m_spend_zero_conf_change && SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, max_ancestors-1, max_descendants-1, true /* include_partial_groups */), vCoins, setCoinsRet, nValueRet, coin_selection_params, bnb_used)) ||
+        (m_spend_zero_conf_change && coin_control.m_include_unsafe_inputs && SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 0, max_ancestors-1, max_descendants-1, true /* include_partial_groups */), vCoins, setCoinsRet, nValueRet, coin_selection_params, bnb_used)) ||
         (m_spend_zero_conf_change && !fRejectLongChains && SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, std::numeric_limits<uint64_t>::max(), std::numeric_limits<uint64_t>::max(), true /* include_partial_groups */), vCoins, setCoinsRet, nValueRet, coin_selection_params, bnb_used));
 
     // because SelectCoinsMinConf clears the setCoinsRet, we now add the possible inputs to the coinset
@@ -2799,7 +2800,7 @@ bool CWallet::CreateTransactionInternal(
         txNew.nLockTime = GetLocktimeForNewTransaction(chain(), GetLastBlockHash(), GetLastBlockHeight());
         {
             std::vector<COutput> vAvailableCoins;
-            AvailableCoins(vAvailableCoins, true, &coin_control, 1, MAX_MONEY, MAX_MONEY, 0);
+            AvailableCoins(vAvailableCoins, !coin_control.m_include_unsafe_inputs, &coin_control, 1, MAX_MONEY, MAX_MONEY, 0);
             CoinSelectionParams coin_selection_params; // Parameters for coin selection, init with dummy
             coin_selection_params.m_avoid_partial_spends = coin_control.m_avoid_partial_spends;
 

test/functional/rpc_fundrawtransaction.py

@@ -96,6 +96,7 @@ def run_test(self):
         self.test_option_subtract_fee_from_outputs()
         self.test_subtract_fee_with_presets()
         self.test_transaction_too_large()
+        self.test_include_unsafe()
 
     def test_change_position(self):
         """Ensure setting changePosition in fundraw with an exact match is handled properly."""
@@ -928,6 +929,29 @@ def test_transaction_too_large(self):
         self.nodes[0].generate(10)
         assert_raises_rpc_error(-4, "Transaction too large", recipient.fundrawtransaction, rawtx)
 
+    def test_include_unsafe(self):
+        self.log.info("Test fundrawtxn with unsafe inputs")
+
+        self.nodes[0].createwallet("unsafe")
+        wallet = self.nodes[0].get_wallet_rpc("unsafe")
+
+        # We receive unconfirmed funds from external keys (unsafe output).
+        addr = wallet.getnewaddress()
+        txid = self.nodes[2].sendtoaddress(addr, 10)
+        self.sync_all()
+        vout = find_vout_for_address(wallet, txid, addr)
+
+        # Unsafe inputs are ignored by default.
+        rawtx = wallet.createrawtransaction([], [{wallet.getnewaddress(): 5}])
+        assert_raises_rpc_error(-4, "Insufficient funds", wallet.fundrawtransaction, rawtx)
+
+        # But we can opt-in to use them for funding.
+        fundedtx = wallet.fundrawtransaction(rawtx, {"include_unsafe": True})
+        tx_dec = wallet.decoderawtransaction(fundedtx['hex'])
+        assert any([txin['txid'] == txid and txin['vout'] == vout for txin in tx_dec['vin']])
+        signedtx = wallet.signrawtransactionwithwallet(fundedtx['hex'])
+        wallet.sendrawtransaction(signedtx['hex'])
+
 
 if __name__ == '__main__':
     RawTransactionsTest().main()