feat: Let the coordinator open single-funded channels

With the `TradeAction::OpenSingleFundedChannel`, the coordinator can
choose to open a DLC channel with a trader, without using any trader
UTXOs. This is useful if the coordinator wants to onboard trading
through alternate means, such as Lightning.

`rust-dlc` now allows to configure the TX fee split between the offer
party and the accept party.

The feature has been tested locally, but is currently disabled as we
need a different flow to trigger the creation of a single-funded DLC
channel.

Also, the DLC channel is now 0-conf: the trader can keep trading as
soon as the fund transaction is found in mempool.

Cargo.toml

@@ -19,11 +19,11 @@ resolver = "2"
 # We are using our own fork of `rust-dlc` at least until we can drop all the LN-DLC features. Also,
 # `p2pderivatives/rust-dlc#master` is missing certain patches that can only be found in the LN-DLC
 # branch.
-dlc-manager = { git = "https://github.com/get10101/rust-dlc", rev = "8d9920d" }
-dlc-messages = { git = "https://github.com/get10101/rust-dlc", rev = "8d9920d" }
-dlc = { git = "https://github.com/get10101/rust-dlc", rev = "8d9920d" }
-p2pd-oracle-client = { git = "https://github.com/get10101/rust-dlc", rev = "8d9920d" }
-dlc-trie = { git = "https://github.com/get10101/rust-dlc", rev = "8d9920d" }
+dlc-manager = { git = "https://github.com/get10101/rust-dlc", rev = "2545d6e" }
+dlc-messages = { git = "https://github.com/get10101/rust-dlc", rev = "2545d6e" }
+dlc = { git = "https://github.com/get10101/rust-dlc", rev = "2545d6e" }
+p2pd-oracle-client = { git = "https://github.com/get10101/rust-dlc", rev = "2545d6e" }
+dlc-trie = { git = "https://github.com/get10101/rust-dlc", rev = "2545d6e" }
 
 # We should usually track the `p2pderivatives/split-tx-experiment[-10101]` branch. For now we depend
 # on a special fork which removes a panic in `rust-lightning`.

coordinator/src/trade/mod.rs

@@ -58,6 +58,8 @@ pub mod websocket;
 
 enum TradeAction {
     OpenDlcChannel,
+    #[allow(dead_code)]
+    OpenSingleFundedChannel,
     OpenPosition {
         channel_id: DlcChannelId,
         own_payout: u64,
@@ -98,6 +100,18 @@ pub struct TradeExecutor {
     notifier: mpsc::Sender<OrderbookMessage>,
 }
 
+/// The funds the trader will need to provide to open a DLC channel with the coordinator.
+///
+/// We can extend this enum with a `ForTradeCost` variant to denote that the trader has to pay for
+/// everything except for transaction fees.
+enum TraderRequiredLiquidity {
+    /// Pay for margin, collateral reserve, order-matching fees and transaction fees.
+    ForTradeCostAndTxFees,
+    /// Do not pay for anything. The trader has probably paid in a different way e.g. using
+    /// Lightning.
+    None,
+}
+
 impl TradeExecutor {
     pub fn new(node: Node, notifier: mpsc::Sender<OrderbookMessage>) -> Self {
         Self { node, notifier }
@@ -212,6 +226,26 @@ impl TradeExecutor {
                     collateral_reserve_coordinator,
                     collateral_reserve_trader,
                     is_stable_order,
+                    TraderRequiredLiquidity::ForTradeCostAndTxFees,
+                )
+                .await
+                .context("Failed to open DLC channel")?;
+            }
+            TradeAction::OpenSingleFundedChannel => {
+                let collateral_reserve_coordinator = params
+                    .coordinator_reserve
+                    .context("Missing coordinator collateral reserve")?;
+                let collateral_reserve_trader = params
+                    .trader_reserve
+                    .context("Missing trader collateral reserve")?;
+
+                self.open_dlc_channel(
+                    &mut connection,
+                    &params.trade_params,
+                    collateral_reserve_coordinator,
+                    collateral_reserve_trader,
+                    is_stable_order,
+                    TraderRequiredLiquidity::None,
                 )
                 .await
                 .context("Failed to open DLC channel")?;
@@ -270,6 +304,7 @@ impl TradeExecutor {
         collateral_reserve_coordinator: Amount,
         collateral_reserve_trader: Amount,
         stable: bool,
+        trader_required_utxos: TraderRequiredLiquidity,
     ) -> Result<()> {
         let peer_id = trade_params.pubkey;
 
@@ -337,11 +372,29 @@ impl TradeExecutor {
         // coordinator.
         let event_id = format!("{contract_symbol}{maturity_time}");
 
+        let (offer_collateral, accept_collateral, fee_config) = match trader_required_utxos {
+            TraderRequiredLiquidity::ForTradeCostAndTxFees => (
+                margin_coordinator + collateral_reserve_coordinator.to_sat(),
+                margin_trader + collateral_reserve_trader + order_matching_fee,
+                dlc::FeeConfig::EvenSplit,
+            ),
+            TraderRequiredLiquidity::None => (
+                margin_coordinator
+                    + collateral_reserve_coordinator.to_sat()
+                    + margin_trader
+                    + collateral_reserve_trader
+                    // If the trader doesn't bring their own UTXOs, including the order matching fee
+                    // is not strictly necessary, but it's simpler to do so.
+                    + order_matching_fee,
+                0,
+                dlc::FeeConfig::AllOffer,
+            ),
+        };
+
         let contract_input = ContractInput {
-            offer_collateral: margin_coordinator + collateral_reserve_coordinator.to_sat(),
-            // The accept party has do bring additional collateral to pay for the
-            // `order_matching_fee`.
-            accept_collateral: margin_trader + collateral_reserve_trader + order_matching_fee,
+            offer_collateral,
+
+            accept_collateral,
             fee_rate,
             contract_infos: vec![ContractInputInfo {
                 contract_descriptor,
@@ -370,6 +423,7 @@ impl TradeExecutor {
                 contract_input,
                 trade_params.pubkey,
                 protocol_id,
+                fee_config,
             )
             .await
             .context("Could not propose DLC channel")?;

crates/xxi-node/src/dlc_wallet.rs

@@ -213,6 +213,10 @@ impl<D: BdkStorage, S: TenTenOneStorage, N> dlc_manager::Wallet for DlcWallet<D,
         base_weight_wu: u64,
         lock_utxos: bool,
     ) -> Result<Vec<dlc_manager::Utxo>, dlc_manager::error::Error> {
+        if amount == 0 {
+            return Ok(Vec::new());
+        }
+
         let network = self.on_chain_wallet.network();
 
         let fee_rate = fee_rate.expect("always set by rust-dlc");

crates/xxi-node/src/node/dlc_channel.rs

@@ -47,6 +47,7 @@ impl<D: BdkStorage, S: TenTenOneStorage + 'static, N: LnDlcStorage + Sync + Send
         contract_input: ContractInput,
         counterparty: PublicKey,
         protocol_id: ProtocolId,
+        fee_config: dlc::FeeConfig,
     ) -> Result<(ContractId, DlcChannelId)> {
         tracing::info!(
             trader_id = %counterparty,
@@ -90,6 +91,7 @@ impl<D: BdkStorage, S: TenTenOneStorage + 'static, N: LnDlcStorage + Sync + Send
                 let offer_channel = dlc_manager.offer_channel(
                     &contract_input,
                     to_secp_pk_29(counterparty),
+                    fee_config,
                     Some(protocol_id.into()),
                 )?;
 
@@ -122,8 +124,9 @@ impl<D: BdkStorage, S: TenTenOneStorage + 'static, N: LnDlcStorage + Sync + Send
 
         tracing::info!(channel_id = %channel_id_hex, "Accepting DLC channel offer");
 
-        let (accept_channel, _channel_id, _contract_id, counter_party) =
-            self.dlc_manager.accept_channel(channel_id)?;
+        let (accept_channel, _channel_id, _contract_id, counter_party) = self
+            .dlc_manager
+            .accept_channel(channel_id, dlc::FeeConfig::EvenSplit)?;
 
         self.event_handler.publish(NodeEvent::SendDlcMessage {
             peer: to_secp_pk_30(counter_party),

crates/xxi-node/src/tests/dlc_channel.rs

@@ -465,6 +465,7 @@ async fn open_channel_and_position_and_settle_position(
             contract_input,
             app.info.pubkey,
             ProtocolId::new(),
+            dlc::FeeConfig::EvenSplit,
         )
         .await
         .unwrap();

mobile/native/src/dlc/node.rs

@@ -540,7 +540,14 @@ impl Node {
         match self
             .inner
             .dlc_manager
-            .accept_channel(&channel_id)
+            .accept_channel(
+                &channel_id,
+                offer
+                    .offer_channel
+                    .fee_config
+                    .map(dlc::FeeConfig::from)
+                    .unwrap_or(dlc::FeeConfig::EvenSplit),
+            )
             .map_err(anyhow::Error::new)
         {
             Ok((accept_channel, _, _, node_id)) => {