[Early Draft][Splicing] Partial, perform interactive transaction negotiation for new funding

lightning/src/events/mod.rs

@@ -1463,6 +1463,58 @@ pub enum Event {
 	///
 	/// [`ChannelHandshakeConfig::negotiate_anchors_zero_fee_htlc_tx`]: crate::util::config::ChannelHandshakeConfig::negotiate_anchors_zero_fee_htlc_tx
 	BumpTransaction(BumpTransactionEvent),
+
+	/// Indicates that a transaction constructed via interactive transaction construction for a
+	/// dual-funded (V2) channel is ready to be signed by the client. This event will only be triggered
+	/// if at least one input was contributed by the holder.
+	///
+	/// The transaction contains all inputs provided by both parties when the channel was
+	/// created/accepted along with the channel's funding output and a change output if applicable.
+	///
+	/// No part of the transaction should be changed before signing as the content of the transaction
+	/// has already been negotiated with the counterparty.
+	///
+	/// Each signature MUST use the SIGHASH_ALL flag to avoid invalidation of initial commitment and
+	/// hence possible loss of funds.
+	///
+	/// After signing, call [`ChannelManager::funding_transaction_signed`] with the (partially) signed
+	/// funding transaction.
+	///
+	/// Generated in [`ChannelManager`] message handling.
+	///
+	/// [`ChannelManager`]: crate::ln::channelmanager::ChannelManager
+	/// [`ChannelManager::funding_transaction_signed`]: crate::ln::channelmanager::ChannelManager::funding_transaction_signed
+	FundingTransactionReadyForSigning {
+		/// The channel_id of the V2 channel which you'll need to pass back into
+		/// [`ChannelManager::funding_transaction_signed`].
+		///
+		/// [`ChannelManager::funding_transaction_signed`]: crate::ln::channelmanager::ChannelManager::funding_transaction_signed
+		channel_id: ChannelId,
+		/// The counterparty's node_id, which you'll need to pass back into
+		/// [`ChannelManager::funding_transaction_signed`].
+		///
+		/// [`ChannelManager::funding_transaction_signed`]: crate::ln::channelmanager::ChannelManager::funding_transaction_signed
+		counterparty_node_id: PublicKey,
+		/*
+		/// The `user_channel_id` value passed in to [`ChannelManager::create_dual_funded_channel`] for outbound
+		/// channels, or to [`ChannelManager::accept_inbound_channel`] or [`ChannelManager::accept_inbound_channel_with_contribution`]
+		/// for inbound channels if [`UserConfig::manually_accept_inbound_channels`] config flag is set to true.
+		/// Otherwise `user_channel_id` will be randomized for an inbound channel.
+		/// This may be zero for objects serialized with LDK versions prior to 0.0.113.
+		///
+		/// [`ChannelManager::create_dual_funded_channel`]: crate::ln::channelmanager::ChannelManager::create_dual_funded_channel
+		/// [`ChannelManager::accept_inbound_channel`]: crate::ln::channelmanager::ChannelManager::accept_inbound_channel
+		/// [`ChannelManager::accept_inbound_channel_with_contribution`]: crate::ln::channelmanager::ChannelManager::accept_inbound_channel_with_contribution
+		/// [`UserConfig::manually_accept_inbound_channels`]: crate::util::config::UserConfig::manually_accept_inbound_channels
+		user_channel_id: u128,
+		*/
+		/// The unsigned transaction to be signed and passed back to
+		/// [`ChannelManager::funding_transaction_signed`].
+		///
+		/// [`ChannelManager::funding_transaction_signed`]: crate::ln::channelmanager::ChannelManager::funding_transaction_signed
+		unsigned_transaction: Transaction,
+	},
+
 	/// We received an onion message that is intended to be forwarded to a peer
 	/// that is currently offline. This event will only be generated if the
 	/// `OnionMessenger` was initialized with
@@ -1768,7 +1820,7 @@ impl Writeable for Event {
 					BumpTransactionEvent::HTLCResolution { .. } => {}
 				}
 				write_tlv_fields!(writer, {}); // Write a length field for forwards compat
-			}
+			},
 			&Event::ChannelReady { ref channel_id, ref user_channel_id, ref counterparty_node_id, ref channel_type } => {
 				29u8.write(writer)?;
 				write_tlv_fields!(writer, {
@@ -1828,6 +1880,13 @@ impl Writeable for Event {
 					(8, former_temporary_channel_id, required),
 				});
 			},
+			&Event::FundingTransactionReadyForSigning { .. } => {
+				45u8.write(writer)?;
+				// We never write out FundingTransactionReadyForSigning events as, upon disconnection, peers
+				// drop any V2-established channels which have not yet exchanged the initial `commitment_signed`.
+				// We only exhange the initial `commitment_signed` after the client calls
+				// `ChannelManager::funding_transaction_signed` and ALWAYS before we send a `tx_signatures`
+			},
 			// Note that, going forward, all new events must only write data inside of
 			// `write_tlv_fields`. Versions 0.0.101+ will ignore odd-numbered events that write
 			// data via `write_tlv_fields`.