Implement accepting dual-funded channels without contributing

Cargo.toml

@@ -63,7 +63,6 @@ check-cfg = [
     "cfg(taproot)",
     "cfg(async_signing)",
     "cfg(require_route_graph_test)",
-    "cfg(dual_funding)",
     "cfg(splicing)",
     "cfg(async_payments)",
 ]

ci/ci-tests.sh

@@ -166,8 +166,6 @@ RUSTFLAGS="--cfg=taproot" cargo test --verbose --color always -p lightning
 [ "$CI_MINIMIZE_DISK_USAGE" != "" ] && cargo clean
 RUSTFLAGS="--cfg=async_signing" cargo test --verbose --color always -p lightning
 [ "$CI_MINIMIZE_DISK_USAGE" != "" ] && cargo clean
-RUSTFLAGS="--cfg=dual_funding" cargo test --verbose --color always -p lightning
-[ "$CI_MINIMIZE_DISK_USAGE" != "" ] && cargo clean
 RUSTFLAGS="--cfg=splicing" cargo test --verbose --color always -p lightning
 [ "$CI_MINIMIZE_DISK_USAGE" != "" ] && cargo clean
 RUSTFLAGS="--cfg=async_payments" cargo test --verbose --color always -p lightning

lightning-types/src/features.rs

@@ -49,6 +49,8 @@
 //!     (see [BOLT-4](https://github.com/lightning/bolts/blob/master/04-onion-routing.md#route-blinding) for more information).
 //! - `ShutdownAnySegwit` - requires/supports that future segwit versions are allowed in `shutdown`
 //!     (see [BOLT-2](https://github.com/lightning/bolts/blob/master/02-peer-protocol.md) for more information).
+//! - `DualFund` - requires/supports V2 channel establishment
+//!     (see [BOLT-2](https://github.com/lightning/bolts/blob/master/02-peer-protocol.md#channel-establishment-v2) for more information).
 //! - `OnionMessages` - requires/supports forwarding onion messages
 //!     (see [BOLT-7](https://github.com/lightning/bolts/pull/759/files) for more information).
 //     TODO: update link
@@ -146,7 +148,7 @@ mod sealed {
 			// Byte 2
 			BasicMPP | Wumbo | AnchorsNonzeroFeeHtlcTx | AnchorsZeroFeeHtlcTx,
 			// Byte 3
-			RouteBlinding | ShutdownAnySegwit | Taproot,
+			RouteBlinding | ShutdownAnySegwit | DualFund | Taproot,
 			// Byte 4
 			OnionMessages,
 			// Byte 5
@@ -167,7 +169,7 @@ mod sealed {
 			// Byte 2
 			BasicMPP | Wumbo | AnchorsNonzeroFeeHtlcTx | AnchorsZeroFeeHtlcTx,
 			// Byte 3
-			RouteBlinding | ShutdownAnySegwit | Taproot,
+			RouteBlinding | ShutdownAnySegwit | DualFund | Taproot,
 			// Byte 4
 			OnionMessages,
 			// Byte 5
@@ -502,6 +504,16 @@ mod sealed {
 		supports_shutdown_anysegwit,
 		requires_shutdown_anysegwit
 	);
+	define_feature!(
+		29,
+		DualFund,
+		[InitContext, NodeContext],
+		"Feature flags for `option_dual_fund`.",
+		set_dual_fund_optional,
+		set_dual_fund_required,
+		supports_dual_fund,
+		requires_dual_fund
+	);
 	define_feature!(
 		31,
 		Taproot,

lightning/src/events/mod.rs

@@ -606,6 +606,20 @@ impl_writeable_tlv_based_enum_upgradable!(PaymentFailureReason,
 	(10, UnexpectedError) => {},
 );
 
+/// Used to indicate the kind of funding for this channel by the channel acceptor (us).
+///
+/// Allows the differentiation between a request for a dual-funded and non-dual-funded channel.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum InboundChannelFunds {
+	/// For a non-dual-funded channel, the `push_msat` value from the channel initiator to us.
+	PushMsat(u64),
+	/// Indicates the open request is for a dual funded channel.
+	///
+	/// Note that these channels do not support starting with initial funds pushed from the counterparty,
+	/// who is the channel opener in this case.
+	DualFunded,
+}
+
 /// An Event which you should probably take some action in response to.
 ///
 /// Note that while Writeable and Readable are implemented for Event, you probably shouldn't use
@@ -1337,16 +1351,17 @@ pub enum Event {
 	},
 	/// Indicates a request to open a new channel by a peer.
 	///
-	/// To accept the request, call [`ChannelManager::accept_inbound_channel`]. To reject the request,
-	/// call [`ChannelManager::force_close_without_broadcasting_txn`]. Note that a ['ChannelClosed`]
-	/// event will _not_ be triggered if the channel is rejected.
+	/// To accept the request (and in the case of a dual-funded channel, not contribute funds),
+	/// call [`ChannelManager::accept_inbound_channel`].
+	/// To reject the request, call [`ChannelManager::force_close_without_broadcasting_txn`].
+	/// Note that a ['ChannelClosed`] event will _not_ be triggered if the channel is rejected.
 	///
 	/// The event is only triggered when a new open channel request is received and the
 	/// [`UserConfig::manually_accept_inbound_channels`] config flag is set to true.
 	///
 	/// # Failure Behavior and Persistence
 	/// This event will eventually be replayed after failures-to-handle (i.e., the event handler
-	/// returning `Err(ReplayEvent ())`) and will be persisted across restarts.
+	/// returning `Err(ReplayEvent ())`) and won't be persisted across restarts.
 	///
 	/// [`ChannelManager::accept_inbound_channel`]: crate::ln::channelmanager::ChannelManager::accept_inbound_channel
 	/// [`ChannelManager::force_close_without_broadcasting_txn`]: crate::ln::channelmanager::ChannelManager::force_close_without_broadcasting_txn
@@ -1373,8 +1388,10 @@ pub enum Event {
 		counterparty_node_id: PublicKey,
 		/// The channel value of the requested channel.
 		funding_satoshis: u64,
-		/// Our starting balance in the channel if the request is accepted, in milli-satoshi.
-		push_msat: u64,
+		/// If `channel_negotiation_type` is `InboundChannelFunds::DualFunded`, this indicates that the peer wishes to
+		/// open a dual-funded channel. Otherwise, this field will be `InboundChannelFunds::PushMsats`,
+		/// indicating the `push_msats` value our peer is pushing to us for a non-dual-funded channel.
+		channel_negotiation_type: InboundChannelFunds,
 		/// The features that this channel will operate with. If you reject the channel, a
 		/// well-behaved counterparty may automatically re-attempt the channel with a new set of
 		/// feature flags.