Handle re-establishment next_funding_txid

Author: dunxen

lightning/src/ln/channel.rs

@@ -1494,6 +1494,21 @@ pub(super) struct ChannelContext<SP: Deref> where SP::Target: SignerProvider {
 	/// If we can't release a [`ChannelMonitorUpdate`] until some external action completes, we
 	/// store it here and only release it to the `ChannelManager` once it asks for it.
 	blocked_monitor_updates: Vec<PendingChannelMonitorUpdate>,
+	// The `next_funding_txid` field allows peers to finalize the signing steps of an interactive
+	// transaction construction, or safely abort that transaction if it was not signed by one of the
+	// peers, who has thus already removed it from its state.
+	// 
+	// If we've sent `commtiment_signed` for an interactive an interactively constructed transaction
+	// during a signing session, but have not received `tx_signatures` we MUST set `next_funding_txid`
+	// to the txid of that interactive transaction, else we MUST NOT set it.
+	//
+	// See the spec for further details on this:
+	//   * `channel_reestablish`-sending node: https://github.com/lightning/bolts/blob/247e83d/02-peer-protocol.md?plain=1#L2466-L2470
+	//   * `channel_reestablish`-receiving node: https://github.com/lightning/bolts/blob/247e83d/02-peer-protocol.md?plain=1#L2520-L2531
+	//
+	// TODO(dual_funding): Persist this when we actually contribute funding inputs. For now we always
+	// send an empty witnesses array in `tx_signatures` as a V2 channel acceptor
+	next_funding_txid: Option<Txid>,
 }
 
 /// A channel struct implementing this trait can receive an initial counterparty commitment
@@ -2159,6 +2174,8 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
 			blocked_monitor_updates: Vec::new(),
 
 			is_manual_broadcast: false,
+
+			next_funding_txid: None,
 		};
 
 		Ok(channel_context)
@@ -2390,6 +2407,7 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
 			blocked_monitor_updates: Vec::new(),
 			local_initiated_shutdown: None,
 			is_manual_broadcast: false,
+			next_funding_txid: None,
 		})
 	}
 
@@ -4601,6 +4619,14 @@ impl<SP: Deref> Channel<SP> where
 		self.context.channel_state.clear_waiting_for_batch();
 	}
 
+	pub fn set_next_funding_txid(&mut self, txid: &Txid) {
+		self.context.next_funding_txid = Some(*txid);
+	}
+
+	pub fn clear_next_funding_txid(&mut self) {
+		self.context.next_funding_txid = None;
+	}
+
 	/// Unsets the existing funding information.
 	///
 	/// This must only be used if the channel has not yet completed funding and has not been used.
@@ -7680,10 +7706,7 @@ impl<SP: Deref> Channel<SP> where
 			next_remote_commitment_number: INITIAL_COMMITMENT_NUMBER - self.context.cur_counterparty_commitment_transaction_number - 1,
 			your_last_per_commitment_secret: remote_last_secret,
 			my_current_per_commitment_point: dummy_pubkey,
-			// TODO(dual_funding): If we've sent `commtiment_signed` for an interactive transaction
-			// construction but have not received `tx_signatures` we MUST set `next_funding_txid` to the
-			// txid of that interactive transaction, else we MUST NOT set it.
-			next_funding_txid: None,
+			next_funding_txid: self.context.next_funding_txid,
 		}
 	}
 
@@ -9439,7 +9462,8 @@ impl<SP: Deref> Writeable for Channel<SP> where SP::Target: SignerProvider {
 			(47, next_holder_commitment_point, option),
 			(49, self.context.local_initiated_shutdown, option), // Added in 0.0.122
 			(51, is_manual_broadcast, option), // Added in 0.0.124
-			(53, funding_tx_broadcast_safe_event_emitted, option) // Added in 0.0.124
+			(53, funding_tx_broadcast_safe_event_emitted, option), // Added in 0.0.124
+			(55, self.context.next_funding_txid, option) // Added in 0.0.125
 		});
 
 		Ok(())
@@ -9729,6 +9753,7 @@ impl<'a, 'b, 'c, ES: Deref, SP: Deref> ReadableArgs<(&'a ES, &'b SP, u32, &'c Ch
 		let mut channel_pending_event_emitted = None;
 		let mut channel_ready_event_emitted = None;
 		let mut funding_tx_broadcast_safe_event_emitted = None;
+		let mut next_funding_txid = None;
 
 		let mut user_id_high_opt: Option<u64> = None;
 		let mut channel_keys_id: Option<[u8; 32]> = None;
@@ -9789,6 +9814,7 @@ impl<'a, 'b, 'c, ES: Deref, SP: Deref> ReadableArgs<(&'a ES, &'b SP, u32, &'c Ch
 			(49, local_initiated_shutdown, option),
 			(51, is_manual_broadcast, option),
 			(53, funding_tx_broadcast_safe_event_emitted, option),
+			(55, next_funding_txid, option) // Added in 0.0.125
 		});
 
 		let (channel_keys_id, holder_signer) = if let Some(channel_keys_id) = channel_keys_id {
@@ -10048,6 +10074,10 @@ impl<'a, 'b, 'c, ES: Deref, SP: Deref> ReadableArgs<(&'a ES, &'b SP, u32, &'c Ch
 
 				blocked_monitor_updates: blocked_monitor_updates.unwrap(),
 				is_manual_broadcast: is_manual_broadcast.unwrap_or(false),
+				// If we've sent `commtiment_signed` for an interactive transaction construction,
+				// but have not received `tx_signatures` we MUST set `next_funding_txid` to the
+				// txid of that interactive transaction, else we MUST NOT set it.
+				next_funding_txid,
 			},
 			interactive_tx_signing_session: None,
 		})

lightning/src/ln/channelmanager.rs

@@ -8279,6 +8279,7 @@ where
 					peer_state.pending_msg_events.push(msg_send_event);
 				};
 				if let Some(mut signing_session) = signing_session_opt {
+					let funding_txid = signing_session.unsigned_tx.txid();
 					let (commitment_signed, funding_ready_for_sig_event_opt) = match chan_phase_entry.get_mut() {
 						ChannelPhase::UnfundedOutboundV2(chan) => {
 							chan.funding_tx_constructed(&mut signing_session, &self.logger)
@@ -8291,7 +8292,7 @@ where
 							.into())),
 					}.map_err(|err| MsgHandleErrInternal::send_err_msg_no_close(format!("{}", err), msg.channel_id))?;
 					let (channel_id, channel_phase) = chan_phase_entry.remove_entry();
-							let channel = match channel_phase {
+							let mut channel = match channel_phase {
 								ChannelPhase::UnfundedOutboundV2(chan) => chan.into_channel(signing_session),
 								ChannelPhase::UnfundedInboundV2(chan) => chan.into_channel(signing_session),
 								_ => {
@@ -8301,6 +8302,7 @@ where
 											.into()))
 								},
 							}.map_err(|err| MsgHandleErrInternal::send_err_msg_no_close(format!("{}", err), msg.channel_id))?;
+							channel.set_next_funding_txid(&funding_txid);
 							peer_state.channel_by_id.insert(channel_id, ChannelPhase::Funded(channel));
 							if let Some(funding_ready_for_sig_event) = funding_ready_for_sig_event_opt {
 								let mut pending_events = self.pending_events.lock().unwrap();
@@ -8344,6 +8346,7 @@ where
 				match channel_phase {
 					ChannelPhase::Funded(chan) => {
 						let (tx_signatures_opt, funding_tx_opt) = try_chan_phase_entry!(self, chan.tx_signatures(msg), chan_phase_entry);
+						chan.clear_next_funding_txid();
 						if let Some(tx_signatures) = tx_signatures_opt {
 							peer_state.pending_msg_events.push(events::MessageSendEvent::SendTxSignatures {
 								node_id: *counterparty_node_id,