Fix fund transaction case at 0-value, 0-fee

Author: instagibbs

src/wallet/spend.cpp

@@ -917,6 +917,12 @@ static util::Result<CreatedTransactionResult> CreateTransactionInternal(
     const CAmount not_input_fees = coin_selection_params.m_effective_feerate.GetFee(coin_selection_params.m_subtract_fee_outputs ? 0 : coin_selection_params.tx_noinputs_size);
     CAmount selection_target = recipients_sum + not_input_fees;
 
+    // This can only happen if feerate is 0, and requested destinations are value of 0 (e.g. OP_RETURN)
+    // and no pre-selected inputs. This will result in 0-input transaction, which is consensus-invalid anyways
+    if (selection_target == 0 && !coin_control.HasSelected()) {
+        return util::Error{_("Transaction requires one destination of non-0 value, a non-0 feerate, or a pre-selected input")};
+    }
+
     // Fetch manually selected coins
     PreSelectedInputs preset_inputs;
     if (coin_control.HasSelected()) {

test/functional/rpc_psbt.py

@@ -931,6 +931,9 @@ def test_psbt_input_keys(psbt_input, keys):
         assert_equal(self.nodes[0].finalizepsbt(psbt.to_base64()),
             {'hex': '0200000001dddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd0000000000000000000100000000000000000000000000', 'complete': True})
 
+        self.log.info("Test we don't crash when making a 0-value funded transaction at 0 fee without forcing an input selection")
+        assert_raises_rpc_error(-4, "Transaction requires one destination of non-0 value, a non-0 feerate, or a pre-selected input", self.nodes[0].walletcreatefundedpsbt, [], [{"data": "deadbeef"}], 0, {"fee_rate": "0"})
+
 
 if __name__ == '__main__':
     PSBTTest().main()